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MindMap Gallery Semiconductor MaterialsSEMICONDUCTOR
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Semiconductor MaterialsSEMICONDUCTOR
Semiconductors are still very difficult, especially some basic theories, which are very nerve-wracking. What I summarized is some knowledge about the application of semiconductors. Today’s electronic world is built on semiconductors It is considered a promising industry in the materials category.
Edited at 2020-04-27 19:58:30
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Semiconductor MaterialsSEMICONDUCTOR
- Calendrier Annuel
Ce calendrier annuel, créé avec EdrawMax, présente une disposition claire et organisée des mois de janvier à décembre. Chaque mois est affiché dans un cadre distinct, montrant les jours de la semaine et les dates correspondantes. Les weekends (samedis et dimanches) sont mis en évidence pour une meilleure visibilité. Ce format est idéal pour la planification et l'organisation des activités tout au long de l'année, offrant une vue d'ensemble rapide et facile à consulter.
- 2026 Quarterly Calendar Overview
This quarterly calendar overview for 2026, created with EdrawMax, presents a structured and colorful layout of the entire year divided into four quarters. Each quarter is displayed in a separate column, showcasing the months within that quarter in a clear grid format. The days of the week are labeled, and each date is marked within its respective cell, allowing for easy identification of dates across the year. This calendar is an excellent tool for long-term planning, providing a comprehensive view of the year at a glance.
- Weekly Calendar 2026
This weekly calendar for 2026 is designed using EdrawMax to provide a detailed and organized view of each week, starting from January. The left side features a mini monthly calendar for quick reference, highlighting the current week in yellow. Below it, there's a section for weekly goals to help prioritize tasks. The main area is a time-grid from 6:00 AM to 12:00 AM, divided into half-hour slots, allowing for precise scheduling of daily activities throughout the week. This layout is ideal for managing a busy schedule efficiently.
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- Outline
SEMICONDUCTOR
Review
Characters
Conductivity: 10-3-10-9 S/cm
Between conductor and insulator
The temperature coefficient of conductivity is positive with high purity
Two types of carriers, electrons and holes, participate in conduction
Classification
According to performance
High temperature semiconductor
Magnetic Semiconductor
Thermoelectric Semiconductor
According to crystal structure
Diamond type
sphalerite type
Wurtzite type
Chalcopyrite type
According to the degree of crystallization
crystal
Amorphous
Microcrystalline
Classified according to the width of the forbidden band
wide bandgap semiconductor
Eg>2-6 ev; also known as the third generation semiconductor material
SiC, GaN, ZnO and diamond
Features
Wide bandgap semiconductor materials have large bandgap width, high breakdown electric field strength, high saturated electron drift velocity, large thermal conductivity, small dielectric constant, strong radiation resistance and good chemical stability.
application
Produce radiation-resistant, high-frequency, high-power and high-density integrated electronic devices
Using its unique bandgap width, blue, green and ultraviolet light devices and photodetection devices can also be made
narrow bandgap semiconductor
Eg＜2ev
Lead selenide (PbSe, 0.165 eV), lead telluride (PbTe, 0.19 eV), lead sulfide (PbS)
Features
Narrow bandgap semiconductor materials have excellent properties of absorbing energy in the visible band of sunlight, catalytically degrading organic matter with visible light, and producing hydrogen by splitting water with visible light.
application
The first is to move the band gap to the visible light band by doping and modifying traditional semiconductor materials represented by TiO2; the second is to develop new compositions of narrow band gap semiconductor materials
Composed by chemical elements
element
Si
Ge
Se
Rectifiers, photoconductive devices
compound
Binary
gallium arsenide
batch
Cadmium sulfide
A small amount
o
silicon carbide
lead telluride
Bismuth telluride
Gallium Telluride
Cuprous oxide
three yuan
CuInSe2
Solar battery
CdSnAs2
CuFeS2
Cu2SeSnSe4
solid solution
SiG
application
AHr
InGaAsP
InAs-CdSnAs2
Fundamental of semiconductor fabrication
Basic fabrication steps
Oxidation
Photolithography and etching
Diffusion and implantation
Metalization
Crystal growth
Starting material
Polycrystalline semiconductor
Single crystal
Wafer
Wafer shaping
Crystal characterization
Silicon oxidation
The thermal oxidation process used to form silicon oxidation
Impurity redistribution during oxidation
Masking properties of silicon oxidation
Oxidation quality
Material properties and thickness measurement techniques for SiO2 films
Simulation
Photolithography
Optical lithography
The clean room
Exposure tools
Masks
Photoresist
Pattern transfer
Resolution enhancement techniques
Next generation lithography methods
Electron beam lithography
Electron resist
Extreme ultraviolet lithography
X-RAY lithography
Ion beam lithography
Photolithography simulation
Etching
Wet chemical Etching
Silicon Etching
Silicon oxidation Etching
Silicon nitride and polysilicon Etching
Aluminum Etching
Gallium arsenide Etching
Dry Etching
Plasma fundamental
Etch mechanism, plasma diagnostics, and end point control
Reactive plasma etching techniques and equipments
Reactive plasma etching applications
Etch simulation
Diffusion
Diffusion equation
Diffusion profiles
Evaluation of Diffusion layers
Extrinsic Diffusion
Lateral Diffusion
ion implantation
Ion distribution
Ion stopping
ion channeling
Implant damage
Annealing
Film deposition
CVD
Molecular beam epitaxy
Dielectric deposition
Polysilicon deposition
Metallization
Process integration
The integrated circuit resistor
The integrated circuit capacitor
The integrated circuit inductor
The basic fabrication process
Dielectric isolation
Self aligned double polysilicon bipolar structures
Mosfet techniques
Memory devices
COMS technology
BiCOMS technology
MEMS
Bulk micromachining
Surface micromachining
LIGA process
IC manufacturing
Electronic testing
Test structures
Final test
Packaging
Die separation
types
Statistics process control
Statistics experimental design
Comparing distribution
Analysis variance
Factorial designs
Yield
Functional yield
Parametric yield
Computer integrated manufacturing
Future trends and challenges
Integration
Ultrashallow junction formation
Ultrathin oxidation
Silicide formation
New material for interconnection
Power limitations
SOI integration
System on a chip
Brief History
1833 Faraday
When a-Ag2S is heated, its resistivity drops sharply, which is completely opposite to the properties of metals.
1873 Smith
Selenium photoconductivity
1874 Brown
Lead sulfide and iron sulfide have rectifying phenomena
1906 Dunwoody
Silicon carbide detector
December 1947
transistor
1950
Germanium single crystal
1956
Reduce the content of harmful impurities in silicon to level 10-9 or lower, and achieve industrial production
1958
integrated circuit
Current situation
Semiconductor crystal materials that are used industrially and can be supplied in batches include silicon, germanium, gallium arsenide, gallium phosphide, indium antimonide, indium phosphide, gallium antimonide and cadmium telluride.
In addition to homogeneous epitaxial wafers of silicon, gallium arsenide and gallium phosphide, the epitaxial wafers supplied in batches also include some III-V solid solutions (such as GaAsP), II-VI solid solutions (such as HgCdTe), etc.
There are III-V and II-VI quantum well superlattice materials, as well as some difficult-to-prepare thin-film materials such as diamond, silicon carbide, and zinc selenide.
Amorphous silicon thin film materials have been produced in large quantities
10,000 tons of polycrystalline silicon, more than 4,000 tons of monocrystalline silicon, and about 100 tons of semiconductor germanium materials
information technology subject
Acquisition and transformation of information
sensor
Semiconductor sensor materials are easily connected to signal amplification devices (the main components of these devices are made of semiconductor materials)
Silicon photosensitive device
Selenium and cadmium sulfide photosensitive devices
Magnetic sensitive devices made of gallium arsenide and indium antimonide
transfer of information
Oscillate, amplify, transmit, receive
Crystal diodes, transistors, microwave diodes, laser diodes, phototransistors and various integrated circuits
information processing
computer
Semiconductor integrated circuit
Semiconductor device
storage of information
Semiconductor memory constitutes the internal storage of the computer and directly provides information for computer operations.
display of information
Indicator lights, digital tubes and displays composed of semiconductor light-emitting diodes
Thin film transistor-driven liquid crystal display made of semiconductor materials
Giants in energy technology
Photovoltaic-Solar
Thermoelectricity-thermoelectric power generation
AC-DC-AC Semiconductor devices
Pioneer in materials
Silicon single crystal
Ge with purity of 12 9s
Neutron transmutation technology
Convert one element to another
High precision machining
The flatness requirement of silicon polishing wafers with a diameter of 200mm is less than 3mm
There should be no more than 10 dust particles with a size of no less than 0.2mm on a silicon wafer, and the impurity concentration on the surface should be less than 10-11 g/cm2
Low-dimensional quantum materials
epitaxial technology
Fundamental
Conductive
Conductivity is proportional to carrier concentration and carrier mobility
Semiconductors generally have higher mobility than metals
The main difference between metals and semiconductors is the carrier concentration
Metal 10^22
Semiconductor 10^6-10^20
Semiconductor conductivity can be tuned over a wide range
Hall Effect
If a current flows through a rectangular sample in one direction, and a magnetic field (H) is added in the direction perpendicular to the current, an electromotive force will appear in the third direction of the sample.
When measuring metals using this method, it is proven that most metals conduct electricity by electrons, which are negatively charged carriers.
When measuring semiconductors, it was discovered that a material can conduct electricity by both negatively charged electrons and positively charged carriers.
carrier scattering
Lattice vibration phonons
acoustic wave scattering
Ionized impurity scattering
alloy scattering
excess carriers
band structure
The electrons around the nucleus are quantized, which is the energy level
When electrons transition between energy levels, they absorb or generate a certain amount of energy.
Pauling's rule, there are at most two electrons in one energy level
When many atoms are close to each other to form a crystal, the electrons of each atom interact with each other, and the original energy levels of the atoms in the dispersed state expand into energy bands.
The valence band and conduction band overlap each other, which is a conductor
A type of material because the electrons are not filled in the valence band, and the electrons can flow freely at various energy levels in the band, which requires very little energy.
Although another type of material is filled in the valence band, due to the overlap between energy bands, valence electrons can easily enter from the valence band to the conduction band to become free electrons and conduct electricity.
There is a forbidden band between the valence band and the conduction band, which includes semiconductors and insulators
Semiconductor materials have a filled valence band, and there is a forbidden band between the valence band and the conduction band. The valence electrons must have enough energy to jump over the forbidden band to enter the conduction band and conduct electricity at room temperature or higher. , due to the uneven distribution of energy, some valence electrons can always enter the conduction band, giving it a certain conductivity
For insulators, their bandgaps are so large that their valence electrons cannot enter the conduction band at room temperature or higher temperatures, so they cannot conduct electricity.
Semiconductor original manufacturing process
front section
Wafer handling process
The main job is to produce circuits and electronic components (such as transistors, capacitors, logic gates, etc.) on silicon wafers. It is the most technically complex and capital-intensive process among the above processes.
Microprocessor as an example
The required manufacturing environment is a clean room (Clean-Room) where temperature, humidity and dust (Particles) need to be controlled.
Wafer probing process
A grid of small grids is formed on the wafer, which we call a crystal cube or a grain (Die).
The dies will pass through the Probe instrument one by one to test their electrical characteristics, and the unqualified dies will be marked with an Ink Dot.
back section
Construct
Using plastic or ceramics to package chips and wiring to form integrated circuits
It is to create a protective layer for the circuits produced to prevent the circuits from being mechanically scratched or damaged by high temperatures.
Test process
Semiconductor manufacturing process classification
MOS type
PMOS type
NMOS type
CMOS type
BiMOS
Advantages and Disadvantages
Low static power consumption, wide power supply voltage range, wide output voltage amplitude (no threshold loss), high speed and high density potential; compatible with TTL circuits. Low current drive capability
Integrated circuit technology
Photolithography I---well area photolithography, carving well area injection holes
Well region injection and advancement to form well region
Remove SiO2, grow thin oxygen, grow Si3N4
Photo II---Active area lithography
Photo III---N tube field area photolithography, N tube field area injection to improve field opening, reduce latch-up effect and improve well contact
Photo III---N tube field area photolithography, N tube field area injection hole is carved; N tube field area injection
Photo IV---P tube field area photolithography, p tube field area injection, adjust the turn-on voltage of PMOS tube, and grow polysilicon
Photo V---Polysilicon photolithography to form polysilicon gates and polysilicon resistors
PhotoVII---P area photolithography, P area implantation. Form the source, drain regions and P protection ring of the PMOS tube
Photo VII---N tube field area photolithography, N tube field area injection, forming the source, drain area and N protection ring of NMOS
Long PSG (phosphosilicate glass)
Photolithography VIII---lead hole photolithography
Photolithography IX---Lead hole photolithography (reverse etching AL)
bipolar
saturated type
BiMOS
TTL
Typical PN junction isolation gold-doped TTL circuit process flow
Substrate preparation
primary oxidation
Buried layer lithography
buried layer diffusion
epitaxial deposition
Thermal oxidation
isolation lithography
isolation diffusion
reoxidation
Base area lithography
base diffusion
Redistribution and oxidation
Emissive area lithography
gold doped back
emission zone diffusion
Redistribution and oxidation
Contact hole photolithography
aluminum deposition
Reverse engraved aluminum
Aluminum alloy
Deposit passivation layer
Bond photolithography
Mid-term test
I2L
Unsaturated type
ECL/CML
Advantages and Disadvantages
Medium speed, strong driving ability, high simulation accuracy, relatively large power consumption
Semiconductor manufacturing environment requirements
Main sources of pollution
Examples of light metals such as dust particles, medium metal ions, organic residues and sodium ions
super clean room
The cleanliness level is mainly determined by the number of fine dust particles/m3
Main process introduction
front section
General cleaning technology <General cleaning technology.png>
optical development
After exposure and development procedures on the photosensitive adhesive, the pattern on the photomask is transferred to the thin film layer or silicon crystal under the photosensitive adhesive.
Including photoresist coating, baking, mask alignment, exposure and development procedures
Key technical parameters: Minimum resolvable graphic size Lmin (nm)
Depth of focus DOF
Exposure method
Ultraviolet, X-ray, electron beam, extreme ultraviolet
Etching Technology
Technology that removes materials using chemical reactions and physical impacts
wet etching
Wet etching uses a chemical solution to achieve the purpose of etching after a chemical reaction.
Dry etching
Dry etching uses a type of plasma etching. The effect of etching in plasma etching may be the physical effect caused by the impact of ions in the plasma on the wafer surface, or the chemical reaction between active radicals (Radical) in the plasma and atoms on the wafer surface, or even both of the above. The composite effect<Common wet etching technology.png>
CVD chemical vapor deposition
Physical Vapor Deposition (PVD)
Ion Implant
Implant dopants in ion form into specific areas of a semiconductor component to obtain precise electronic properties
Chemical mechanical grinding technology
It combines the functions of mechanical grinding with abrasive substances and chemical grinding with acid and alkali solutions, which can achieve comprehensive planarization of the wafer surface to facilitate subsequent film deposition.
Process monitoring
Measure the micron pitch of sub-micron circuits within the chip to ensure the accuracy of the manufacturing process. Generally speaking, macro measurement is only performed after the lithography pattern (photolithographic patterning) and the subsequent etching process are performed.
Mask inspection (Retical inspection)
The photomask is a high-precision quartz flat plate used to produce electronic circuit images on the wafer; it must be perfect to present a complete circuit image, otherwise the incomplete image will be copied to the wafer.
Patterned wafer inspection systems illuminate the wafer surface with white light or laser light. One or more sets of detectors then receive the light diffracted from the wafer surface, and pass the image to high-function software to eliminate underlying patterns to identify and find defects.
Copper process technology
Because copper has a smaller resistance than aluminum, it can carry a larger current in a smaller area.
back section
Die Saw
Cutting and separating the dies one by one on the wafer that has been processed in the previous process
Die Bond
Place the dies one by one on the lead frame and adhere them with silver glue (epoxy)
Wire Bond
In order to create a protective layer for the circuits produced, to prevent the circuits from being mechanically scratched or damaged by high temperatures. Finally, the pins will be pulled out around the entire integrated circuit, which is called wiring, and is used to connect to the external circuit board.
Sealing glue (Mold)
Prevent moisture from intruding from the outside, mechanically support wires, remove internal heat, and provide a shape that can be held in hand
Trim/Form
Separate the assembled dies on the lead frame independently, and cut off unnecessary connection materials and partially protruding resin (dejunk)
Mark
The purpose of printing fonts on the assembled colloid is to indicate the specifications and manufacturer of the product.
Inspection
The purpose of inspecting the wafers processed in the previous process one by one is to determine whether the assembled products are suitable for use. The items include appearance inspection such as: the flatness of the outer pins, coplanarity, pitch, whether the printing is clear, and whether the colloid is damaged, etc.
Encapsulation
The last step of the manufacturing process usually includes the wiring process. Use gold wire to connect the chip and the lead frame, then encapsulate it in an insulating plastic or ceramic casing, and test whether the integrated circuit functions normally.
Silicon device failure mechanism
1 Oxide layer failure: pinhole, hot electron effect
2 Interlayer separation: The thermal expansion coefficient of AL-Si, Cu-Si alloy and substrate does not match.
3 Metal interconnections and stress voids
4 Mechanical stress
5 Electrical overstress/static electricity accumulation
6 LATCH-UP
7 Ionic pollution
Typical testing and inspection procedures
1. Chip test (wafer sort)
2. Chip visual inspection (die visual)
3. Chip attach test (die attach)
4. Lead bond strength test
5. stabilization bake
6. Temperature cycle test (temperature cycle)
8. Centrifugal test (constant acceleration)
9. Leak test
10. High and low temperature electrical testing
11. High temperature aging (burn-in)
12. Post-burn-in electrical test
Chip packaging
DIP dual in-line package
QFP plastic quad flat package and PFP plastic flat component package
BGA ball grid array package
PGA pin grid array package
CSP chip size package
MCM multi-chip module
Properties and Characteristics
intrinsic conductivity
At a certain temperature, due to the uneven distribution of electron energy, the electrons in some atoms or molecules rise from the valence band to the energy level in the conduction band.
Impurities conduct electricity
Carriers formed by electrically active impurities conduct electricity
Impurities that mainly conduct electricity and can contribute electrons to the conductive band are called donor impurities. For Group IV element semiconductors, Group V elements are donor impurities.
Impurities that capture electrons from the valence band and form holes in the valence band are called acceptor impurities. For group IV element semiconductors, group III elements are acceptor impurities.
Ionization energy: The energy required for a donor or acceptor to release electrons or holes to the conduction band or valence band respectively is called ionization energy.
carrier mobility
size
It is an important parameter that characterizes the inherent characteristics of semiconductor materials. It is also related to the impurity content of the crystal, crystal integrity, temperature and other factors.
scattering
From lattice vibration, ionized impurities, neutral impurities, crystal defects, and also from the interaction between carriers
Relationship with temperature
In the low temperature range, scattering by ionized impurities is dominant. Due to the interaction between carrier motion and the electrostatic field of ionized impurities, the mobility increases with temperature.
In the high temperature region, lattice scattering plays a dominant role. As the temperature increases, the amplitude of lattice vibration increases, and the scattering effect on the movement of carriers increases, so the mobility becomes lower.
Tunnel Penetration Barrier-Tunnel Current
PN junction
P type
holes as carriers
N type
electrons as carriers
diffusion potential
When the P/N type is combined into a whole, the ions that lose electrons in the n-type semiconductor form a positive potential; a negative potential is formed in the p-type region, and a potential difference is formed near the boundary, which is called the built-in potential field (electric field), or diffusion potential
barrier layer
In the area connected in the middle, it can be considered that the holes in the p-type area and the electrons in the n-type area no longer diffuse toward each other, which is equivalent to acting as a barrier. Therefore, this area of the pn junction is also called a barrier layer.
forward bias
The positive electrode is connected to the p-type area, and the negative electrode is connected to the n-type area, see (c) in Figure 3.6. Because the semiconductor material has a certain conductivity, the main part of the voltage drop falls on the barrier layer. At this time, the external electric field and The built-in electric field is opposite, thus reducing the built-in electric field and reducing the thickness of the barrier layer, allowing the current to pass smoothly
reverse bias
When the direction of the electric field is opposite, the built-in electric field and the external electric field are superimposed, as shown in (d) in Figure 3.6, which increases the thickness of the barrier layer and prevents current from passing through. This is the rectifying effect of the knot
metal semiconductor contact
Depositing a layer of metal on a semiconductor chip to form a close contact is called metal-semiconductor contact
Classification
Semiconductor doping concentration is low (such as less than 5×1017/cm3, then it shows unidirectional conductivity similar to PN junction)
One type is that the semiconductor doping concentration is very high (such as higher than 1020/cm3). At this time, no matter forward or reverse voltage is applied, the current increases quickly with the voltage, which is equivalent to a small resistance.
Schottky Barrier Diode SBD
Metal-semiconductor contact with unidirectional conductivity
If an n-type semiconductor is in contact with a metal, the work function of the semiconductor is generally smaller than that of the metal, so the electrons in the semiconductor flow into the metal, and after reaching equilibrium, a potential barrier is formed, which is called Schottky barrier
Ohmic contact
Very low resistance metal-semiconductor contact
In order to overcome the above-mentioned potential barrier between metal and semiconductor, a high concentration of impurities is doped into the semiconductor material in contact with the metal. In this case, a tunnel effect will occur and an ohmic contact will be formed.
efficacious work
The energy required for electrons to move from a material into a vacuum
Heterojunction
The structure composed of two different semiconductor materials is a heterojunction
Abrupt junction. The transition zone between the two materials is only a few atomic distances thick.
Used to make semiconductor lasers, heterojunction bipolar transistors, and high electron mobility transistors
Quantum wells and superlattice
quantum well
If semiconductor materials A and B form a multi-layer heterojunction, and A is sandwiched between B, when the thickness of layer A is small enough to be equivalent to the de Broglie wavelength (~10nm) of electrons in quantum mechanics, a quantum state is formed. trap
superlattice
In multiple quantum wells, if the thickness of the B layer is also reduced, so that the thickness of each single layer reaches 1~10nm, which is less than the mean free path of electrons, then the wave functions of adjacent electrons can couple to each other, Rather than being isolated from each other, this multi-barrier structure is dominated by quantum effects in the vertical direction (z-axis). This structure is called a superlattice.
Lasers, photodiodes, optical bistable devices
low dimensional structure
The above are all situations where the movement of carriers is restricted in one-dimensional space but can move freely in two dimensions. Using the same principle, carriers can be restricted in two dimensions and move freely in one dimension, which is called a quantum wire. The movement of carriers can also be restricted in three dimensions (zero dimension), which is called a quantum box or quantum dot. Zero-dimensional, one-dimensional and two-dimensional materials are collectively called low-dimensional materials
thermoelectric effect
Seebeck effect
Electrical effects caused by temperature differences
The thermoelectric conversion efficiency obtained by using metal materials is very low, with a maximum of no more than 0.6%.
When conducting research on semiconductor materials, it was found that its thermoelectric conversion efficiency can reach more than 3.5%.
principle
If one end of a semiconductor is heated and the other end is cooled, then the number of carriers at the hot end increases, the kinetic energy increases, and they diffuse to the cold end, and the cold end naturally diffuses to the hot end, and finally reaches equilibrium. The result is that the number of carriers leaving the hot end is greater than the number of carriers entering the hot end from the cold end.
If this was an n-type semiconductor rod, the hot end would be positively charged due to lack of electrons, and the cold end would be negatively charged.
If it is a p-type semiconductor, its hot end is negatively charged and its cold end is positively charged.
Widely used thermoelectric materials
Bi2Te3 materials suitable for cold temperature zone refrigeration
Preparation can use zone melting method and Bridgman method. Strictly controlling growth conditions can produce single crystals, generally polycrystalline materials.
Undoped Bi2Te3 materials are always P-type; impurities such as Pb, Cd, Sn, etc. can be used as acceptor dopants to form P-type Bi2Te3. Excess Te, or doping with elements such as I, Br, A1, Se, Li, and halides such as AgI, CuI, CuBr, BiI3, SbI3, etc. can make the material N-type.
advantage
(1) The relative molecular mass is the largest among compounds with good chemical stability;
(2) The melting point is lower and the Debye temperature is lower;
(3) Although chemical bonds contain dissociative components, they are mainly covalent bonds;
(4) The energy band structure is a multi-energy valley with a forbidden band width of 0.13~0.16eV;
(5) In the area with the largest merit value, the carrier scattering mechanism is dominated by phonon scattering;
(6) The optimal Seebeck coefficient is near 200mV;
(7) The thermoelectric figure of merit can be further improved by forming a solid solution alloy. The main reason is that the thermal conductivity is significantly reduced.
PbTe materials suitable for thermoelectric power generation in medium temperature zones
300 to 900K
SiGe alloy suitable for thermoelectric power generation in high temperature areas
Peltier effect
Reversible heating effect caused by electric current
When current passes through the contact of two metals, the contact will release heat in one direction, and in the opposite direction, the contact will absorb heat.
principle
When the current enters the p region from the n region, the carriers at the pn junction continue to flow away, so new carriers need to be generated accordingly, and energy is consumed for this, as shown in the figure, which reduces the temperature
When carriers flow toward the pn junction, the two carriers move toward each other, which produces the recombination of electrons and holes, thereby releasing energy, as shown in Figure (b), causing the temperature to rise.
Thomson effect
When a current flows through a uniform conductor with a temperature gradient, in addition to generating Joule heat equivalent to the conductor resistance, the conductor also absorbs or releases heat.
thermomagnetic effect
In a vertical magnetic field, the longitudinal temperature difference causes a transverse voltage effect
Phonon drag effect
When there is a temperature difference in the sample, there is a flow of phonons in the direction of decreasing temperature.
Optical properties
Except for a few materials such as diamond, gallium phosphide, etc., most materials are opaque to visible light. However, semiconductor materials are transparent to infrared light of certain wavelengths.
intrinsic light absorption
According to the concept of quantum mechanics, light with a certain wavelength has energy hn, where h is Planck's constant and n is the frequency of the light wave. When hn ≥Eg, this photon can excite electrons in the valence band to the conduction band to form electron-hole pairs. In this way, the energy hn of the photon is consumed in this excitation process, so hn0 =Eg, n0 becomes the boundary of light absorption. This absorption is called intrinsic absorption
Metals are opaque both in the visible and infrared regions
intrinsic photoconductivity
Photoconductivity is formed by directly exciting electrons from the valence band to the conduction band by the energy of photons.
When the photon energy is greater than the critical value, the photoconductivity reaches a maximum value, and then the photoconductivity decreases as the energy increases. This is because the high energy is quickly absorbed by the surface, and the recombination speed on the surface is faster than in the body.
Excitons and exciton absorption
Luminous phenomenon
autonomous launch
stimulated emission
Piezoelectric effect
Stress can change a material’s resistivity
Under the action of stress, the energy level structure changes
Acoustoelectric effect
The interaction of carriers through coherent acoustic waves propagating in them
Strong magnetic field transport and magneto-optical phenomena
amorphous semiconductor
Thin film materials and their applications
Wear-resistant and surface protective coatings
hard coating
Classification
ceramics
intermetallic compounds
Features
1. They all have high hardness, melting point and elastic modulus;
Why use hard coating
2. Low linear expansion coefficient;
Residual thermal stress and its closely related adhesion between coating and substrate
3. Fracture toughness is lower than commonly used metal materials
Fatigue and impact resistance of coatings
Another indicator that measures the resistance of a coating to stress caused by temperature changes is the thermal shock resistance ST <Coating Resistance to Thermal Shock Resistance.png>
The heat flux density caused by the temperature difference ΔT is related to the ratio of the thermal stress σ caused by the linear expansion coefficient mismatch and temperature change.
The larger the value of ST, the smaller the stress generated when the coating is subjected to a certain thermal shock, and the lower the tendency of fracture.
The thermal conductivity κ of oxide ceramics is much lower than that of other materials, so its ST is low and it is most likely to break when the temperature changes.
thermal protective coating
Increase the service temperature of high-temperature alloys to prevent performance degradation in high-temperature oxidizing environments
It is usually a composite coating consisting of a metal coating and an oxide thermal protective layer.
The general composition of metal coatings is (Ni,Co,Fe)CrAlY
Provides a transition layer between the base metal and the oxide coating, thereby improving the overall
Adhesion of thermal protective layer to base material
The rare earth element Y in the metal coating also protects the base material and coating interface from oxygen
the important role of
The main component of the oxide thermal protection layer is ZrO2
With low thermal conductivity, it can effectively reduce the temperature of high-temperature working parts in key parts, thereby achieving the purpose of increasing the use temperature of the material.
The above-mentioned thermal protective composite coating is prepared by plasma spraying, and the thickness of the coating is several hundred microns. The service temperature of coated parts can usually reach around 1300°C
Anti-corrosion coating
Anode protective coating
Zn, Al, Zn-Al, and Al-Mg-Re alloy coatings can rely on their own relatively negative electrode potential to improve the ability of the coated steel material to resist corrosion under various atmospheric and seawater conditions.
Stainless steel and various nickel-chromium alloy coatings
The surface of stainless steel will naturally form a dense Cr2O3 protective film, which has good corrosion resistance and appropriate strength, toughness, wear resistance and processability. It has good adhesion to the steel material base, so it is often sprayed on various on mechanical parts to improve their corrosion resistance
ceramic material coating
Ceramic materials generally have good corrosion resistance, heat resistance and wear resistance, so they can also be used to make corrosion-resistant coatings.
Polymer material coating
Polymer materials generally have good chemical stability, and have appropriate toughness and wear resistance, so they can also be used to prepare protective coatings for metal parts.
diamond film
Preparation technology
The CVD method for synthesizing diamond films generally uses substrate temperatures below 1000°C and pressure conditions below 0.1MPa. Within this temperature and pressure range, graphite is a stable phase of carbon, while diamond is unstable.
application
Mechanics
High hardness and high wear resistance
Thermal
At room temperature, diamond has five times the thermal conductivity of copper
At the same time, diamond itself is an excellent insulating material, which makes diamond an excellent heat dissipation device material for high-power optoelectronic components.
Optics
Diamond has high spectral transmission properties over a wide wavelength range from ultraviolet to far infrared
Extremely high hardness, strength, thermal conductivity, extremely low linear expansion coefficient and good chemical stability. The combination of these excellent properties makes diamond films an excellent optical window material for use in harsh environments.
acoustics
Extremely high elastic modulus, which determines the extremely high propagation speed of sound waves in diamond
Electricity
Diamond has a wide bandgap and high carrier mobility
and saturation motion speed, high breakdown field strength and high thermal conductivity
Integrated circuits and energy band engineering
Manufacturing Technology
Light emitting diodes and heterojunction lasers
Conditions for semiconductor p-n junction to generate laser light
(1) The electro-optical conversion efficiency of carriers must be high, that is, there must be a sufficiently high proportion of carrier recombination processes leading to the generation of photons.
(2) The forward injected current must exceed a certain threshold, that is, there must be a sufficient concentration of carrier density to be forward injected into the p-n junction.
(3) There must be a resonant cavity to maintain laser emission. This is why heterojunctions are used to create semiconductor lasers.
Integrated optics
Magnetic recording films and optical storage films
magnetic recording
At the same time that the read-write head and the magnetic recording medium are in relative motion, or the magnetic head continuously changes the magnetization state to change the magnetization direction of the magnetic recording medium, that is, writing data, or the relative motion generates an induced electric potential in the head coil, that is, reading data
optical storage media
CD-ROM
It detects changes in the intensity of the light reflected back by the laser on the uneven surface of the medium to read out the information.
write-once disc
erasable rewritable optical disc
direct rewritable disc
Magneto-optical storage
Depends on two properties of magnetic materials
When the temperature changes, the magnetization state of the material produces corresponding changes in the thermomagnetic effect.
The Kerr magneto-optical effect in which the magnetization state of a material changes the polarization direction of the polarized light reflected back from its surface
Phase change optical storage
Under higher power laser irradiation, the film material will melt. After irradiation with the laser beam, the temperature of the film will drop below the melting point at an extremely high rate, which will cause the irradiated area to solidify into an amorphous structure. If the laser irradiation power is not enough to melt the film area, but is enough to heat it above the crystallization temperature, the laser irradiation area will undergo a crystallization process and transform into a crystalline structure. Since the optical properties of the crystalline and amorphous regions are different, the crystalline region has stronger light reflection ability and poor light transmittance. Therefore, the record can be read by relying on the changes in the reflection or transmission ability of the laser beam in different regions. Information
Polymeric chalcogen films with good stability such as Te-As-Ge, Te-Se-S, Te-Se-Sb, In-Sb-Te and Te-Ge-Sn are used as phase change memory materials
application
Organic electroluminescent thin film OLED: flat panel display
Oxide semiconductor sensitive films SnO2, TiO2, Fe3O4: Highly sensitive gas sensors
Force-sensitive and magnetic-sensitive metal film FeSiB: micro-pressure, vibration, torque, speed, acceleration sensors
Photocatalytic thin film TiO2: environmentally friendly material
Optical film: smart building materials, decorative lighting
Wide bandgap semiconductor thin films GaN, ZnO, SiC: short wavelength devices, high power CMOS devices
Superconducting film YBCO, MgB
In magneto-optical disks, the direction of the magnetization vector is perpendicular to the film plane, either upward along the normal direction, or opposite to it downward. During the writing process as shown in the figure, the laser beam locally heats the magnetic medium to a temperature where the ferromagnetism disappears. When the temperature drops and ferromagnetism reappears, the writing head applies a certain magnetic field, which causes the magnetization vectors in this area to be arranged according to the information to be recorded, thus completing the writing process.
When polarized light is vertically incident, areas with different magnetization directions will cause small but completely different changes in the polarization direction of the reflected light. This is the Kerr magneto-optical effect. Therefore, during the reading process as shown in the figure, the polarization direction of the reflected laser beam will correspond to the information to be read, that is, the information can be read out by detecting changes in the polarization plane of the laser.
New photoelectric emission film Ag-BaO
Technical requirements for semiconductor materials
Device requirements for materials
Select materials that can meet the performance of the device based on its function, including the material's energy band structure, crystal structure, mobility, optical properties, etc.
The material must have corresponding physical parameters and chemical purity to ensure good function of the device. At the same time, in order to ensure the implementation of the device process, the material is also required to have corresponding geometric dimensions.
High background purity, few crystal defects, large crystal size, and high processing accuracy
chemical components
Types and behavior of impurities
electroactive impurities
Since the number of valence electrons of the impurity atoms is different from that of the bulk material, a donor or acceptor is formed.
Impurities can affect the material's resistivity, mobility, etc. Therefore, their concentrations should be kept as low as possible. However, in the preparation process of semiconductor materials or devices, some shallow donor or shallow acceptor impurities are often used to form n-type or p-type semiconductors.
These impurities are distributed in groups adjacent to the bulk material in the periodic table. Since the energy levels they form are very close to the conduction band or valence band, their dissociation energy is very small and they can be completely dissociated at room temperature.
Another type of electroactive impurities has a large ionization energy, and their energy level is close to the middle of the forbidden band. This type of impurities is called deep energy level impurities. They often have several energy levels and are not fully ionized at room temperature, but they are Carriers act as recombination centers or traps, so such impurities are generally harmful to materials. They are mainly Group IB in the periodic table of elements, such as copper, gold and Group VIII, such as iron, nickel, etc.
electrically neutral impurities
Most neutral impurities are in the same group of the periodic table as the bulk material or a constituent element of the bulk material. These impurities have the same number of valence electrons as an element in the bulk material
Although such isoelectronic impurities cannot release electrons and holes, their number of electron layers is different from that of the bulk elements. For example, nitrogen in gallium phosphide and phosphorus both have 5 valence electrons, but their valence electrons are in the L layer, while phosphorus has filled the L layer, and their valence electrons are in the M layer. Therefore, nitrogen is more likely to capture electrons and become an isoelectron trap. Similarly, if the gravitational force of impurities on holes is relatively large, it will become a hole trap. Devices can be made using these traps
Some electrically neutral impurities can also be used to improve the mechanical properties of materials
chemical ratio deviation
Some valence electrons cannot bond and form carriers or point defects.
background purity
First, the semiconductor material is purified, and all impurities in it are reduced to a certain level, so that the material can obtain a higher background purity, and then the required impurities are added.
Uniformity of impurity distribution
Devices are generally made on wafers, so macroscopic longitudinal unevenness, that is, the difference in impurity concentration from the head to the tail of the crystal, mainly affects the size of the available part of the crystal; while radial unevenness affects the quality and quality of the device. Yield
Microscopic unevenness manifests as impurity streaks, which also have a significant impact on the performance of some devices
crystal defects
The atoms in the crystal are periodically arranged according to certain principles, and this arrangement is destroyed
Any impurities will destroy the regular lattice of the crystal
However, defects close to the active area of the device can absorb impurities and defects in the active area. This principle is often used to improve device performance.
Geometric dimensions and accuracy
Generally, the larger the diameter and cross-sectional area of a semiconductor single crystal, the better.
One is technical, such as rectifiers or thyristors. If the current they are required to pass is large, the size of the device must be large, so the required chip diameter must also be large.
The other type is economic. The larger the wafer, the more devices can be made at one time, and the cost of a single device will also be reduced.
The requirements for wafer dimensional accuracy mainly come from the device process
Diameter tolerance, thickness tolerance, curvature, warpage, flatness, location and size of positioning surface
Quantum well and superlattice materials require atomic-level precision
Commonly used characterization parameters and measurement methods
electricity
Resistivity
four-probe method
two probe method
Extended resistance method
Electron Beam Induced Current (EBIC)
Conductivity type
Thermal probe method
Place a hot probe and a cold probe on the semiconductor material and keep a certain distance. Because the majority carriers at the hot end diffuse faster than the cold end, a potential difference is generated. The sign of the potential difference depends on the majority carrier. Whether the current is positively or negatively charged can determine whether the material is n-type or p-type.
carrier concentration
Hall measurement
Combined with resistivity measurements, carrier concentration and mobility can be derived
mobility
If we know the relationship between mobility and impurity concentration, we can calculate the impurity concentration
Minority carrier lifetime
Can reflect the deep level impurities and defects of semiconductors
photoconductivity decay method
surface photovoltage method
electron beam induced current method
Resistivity uniformity
chemical purity
background purity
neutron activation method
mass spectrometry
Atomic absorption spectrometry
ll
Infrared absorption method
Photofluorescence method
micro area analysis
Ion probe
electron probe
Analytical electron microscopy
surface purity
Auger spectrum
Total reflection X-ray fluorescence analysis
Gas chromatography
Crystallographic parameters
Due to the anisotropy of crystals, device design requires the crystallographic orientation of the material.
light diffraction method
light mapping
Dislocation
Dislocation density directly affects device performance and yield
Corrosion-Optical Microscopy
X-ray topography
Microdefects
Corrosion-Optical Microscopy
Decorated X-ray appearance
Transmission electron microscope
Geometry
Crystal and plate diameters and their tolerances
Wafer thickness, curvature, warpage, and parallelism
Polishing disc flatness
micrometer
Non-contact thickness gauge
laser interferometer
Principles and applications
Semiconducting Devices and Their Working Principles
1. Thermistors: These utilize the temperature dependency effect of semiconductors.
2. Varistors: These utilize the voltage dependency effect of semiconductors.
3. Rectifiers: These utilize the impurity dependency effect of semiconductors.
4. Strain gauges: These utilize the change in resistance effect of semiconductors.
5. Zener diodes: These utilize the electric field effect of semiconductors.
6. Transistors: These utilize the amplification effects of semiconductors.
7. Photoconductive cells: These utilize the light illumination effect of semiconductors.
8. Photovoltaic cells: These utilize the optical characteristics of semiconductors.
9. Hall effect generators: These utilize the carrier drift effect in semiconductors
Choicest Materials for Different Semiconductor Devices
Diodesdiodes
Si, Ge, GaAs
Zener Diodes Zener Diodes
Zener breakdown, occurs at a precisely defined voltage, allowing the diode to be used as a precision voltage reference
Avalanche Diodes Avalanche Diodes
conduct in the reverse direction when the reverse bias voltage exceeds the breakdown voltage
Cat’s Whisker (or Crystal) Diodes
also called crystal diodes and found application in crystal radio receivers
Thermal Diodes
conventional p-n diodes used to monitor temperature due to their varying forward voltage with temperature
Constant Current Diodes
They allow a current through them to rise to a certain value, and then level off at a specific value
Photodiodes
Photodiodes are intended to sense light (photodetector), so they are packaged in materials that allow light to pass
PIN Diodes
used as radio frequency switches and attenuators. also used as large volume ionizing radiation detectors and as photodetectors
Schottky Diodes
Schottky diodes are constructed from a metal to semiconductor contact useful in voltage clamping applications and prevention of transistor saturation
Gold-Doped Diodes
This allows the diode to operate at signal frequencies, at the expense of a higher forward voltage drop
Super Barrier Diodes
Super barrier diodes are rectifier diodes that incorporate the low forward voltage drop of the Schottky diode with the surge-handling capability and low reverse leakage current of a normal p-n junction diode
Varicap (or Varactor) Diodes
These are important in PLL (phase-locked loop) and FLL (frequency-locked loop) circuits, allowing tuning circuits such as those in television receivers, to lock quickly, replacing older designs that took a long time to warm up and lock
Gunn Diodes
exhibit a region of negative differential resistance. With appropriate biasing, the dipole domains are formed and travel across the diode, allowing high frequency microwave oscillators to be built
Esaki (or Tunnel) Diodes
showing negative resistance caused by quantum tunnelling, allowing amplification of signals and very simple bistable circuits
Light-Emitting Diodes (LEDs)
carriers that cross the junction emit photons when they recombine with the majority carrier on the other side
Laser Diodes
When an LED-like structure is contained in a resonant cavity formed by polishing the parallel end faces, a laser can be formed
Transient Voltage Suppression (TVS) Diode
These are avalanche diodes designed specifically to protect other semiconductor devices from high-voltage transients
Snap-Off (or Step Recovery) Diodes (SRD)
After a forward current has been passing in an SRD and the current is interrupted or reversed, the reverse conduction will cease very abruptly
CPU, microprocessor
AlGaAs chips
Transistors
Si, Ge
Bipolar Junction Transistor (BJT)
A bipolar junction transistor is a sandwiched form of construction in which, one type of semiconductor (say n-type) is placed between two layers of other type of semiconductor (i.e. p-types).
Field-Effect Transistor (FET)
It is a unipolar, 3-terminal solid-state device in which the current is controlled by an electric field
Metal-Semiconductor Field-Effect Transistors (MESFET)
It uses a reverse-biased Schottky barrier instead of a p-n junction
Insulated-Gate Field-Effect Transistor (IGFET)
the channel current is controlled by a voltage applied at gate electrode and an insulator is used to isolate this gate from the channel
MOSFET
The main advantage of MOSFEF over JFET is that the input impedance of a MOSFET is much more than that of a JFET, because of very small gate leakage current
p-Channel Enhancement MOSFET (PMOS)
Photocells
Se, CdS, PbS (i.e. Galena or galenite)
Rectifiers
Si, Se, CuO
ICs
Si chip, GaAs and Si hybrid chips
Light detectors
InSb, CdSe, PbTe, HgCdTe
High-frequency devices
Ge
Fluorescent screens such as T.V. screens
ZnS, Phosphor coating of oxides and sulphides of Zn, Cd, Be
Infrared detectors
Si, Ge
Nuclear radiation detectors
Si, Ge
Gunn diode (a microwave device)
GaAs,InP
Semiconductor lasers
GaAs, AlGaAs, GaP, GaSb
Solar cells/batteries
Photovoltaic action materials such as Se
Absorber material
Si Cu2S CdTe Cu2S CuInSe2 GaAs
Collector material
Si CdS CdS ZnCdS CdS AlGaAs
Cinematography
Photocell effect based materials such as Se, CdS, PbSO4
Xerox-type photocopier
Se
Hyper high-speed computers
New generation AlGaAs chips
Sensor elements for guided missiles
Hg-Cd-Te crystals
Automatic door opener
Photoconductivity based materials such as CdSe, CdS, CdTe
Stroboscope disk (flashing light called stobotron)
Opto-electronic polymers
Red phosphor for TV tubes
Yttrium (Y)
Diamond transistors
Phosphorus-doped diamond film n-type semiconductor
Semiconductor lenses and mirrors for high power lenses
Synthetic diamond
Light absorption and optics
single crystal diamond
Light emitting diode (LED)
For visible green color light
Gap, CdS
For visible red color light
GaAsP, CdSe
For visible yellow light
GaP
For visible blue light
SiC
For invisible infrared light
GaAs, InSb
For ultraviolet region of light
Zn
Avalanche photodiode
InAlAs, InGaAs, GaAsSb
Photon detector
InP, InAs, InSb
Photoconductors
in green light
CdS
in red light
cD
in infrared region
cTi
family of optoelectronic devices <The family of optoelectronic devices.png>
Emerging Wide Bandgap Semiconductors
ikB
It is a metal-insulator semiconductor which is suitable for working at low temperature. It may be used as magnetic sensors.
GaMnAs.
It is suitable for high spin-injection. It may be used for infrared LED and lasers.
CoTiO2.
It has high coherent length.
NiGaAs.
It is suitable for efficient carrier injection. It may be used for high speed digital electronic applications.
ZnGeP2.
It is a chalcopyrite material that exhibits unusual nonlinear optical properties. It can be used in optical oscillations.
ZnSnAs2.
This is a chalcopyrite material. It shows promise for frequency converters and IR-generation.
ZnSiN2.
It is a wide bandgap chalcopyrite having lattice parameter close to GaN and SiC. Achievement of ferromagnetism in it will enable its usefulness to make ultraviolet solar-blind detector and microwave power electronic devices.
EuS.
It is a dilute magnetic semiconductor (DMS) material. It can be used as tunneling barrier, which can effectively function as spin filter
Left Handed (LH) Materials
Microwave components
• Miniaturized antennas
•Probes
• Waveguides
• Interconnections between nanodevices and external terminations
• Novel filters in cellular phones
•Micro-lenses
Applications of Semiconductor Materials
Making semiconductor devices
Discrete part
(1) Crystal diode;
A device with a pn junction, or a Schottky barrier similar to that of a pn junction
Mainly used in rectification and detection
(2) Transistor;
Important discrete device and the main component of integrated circuits
Transistor working principle diagram <Introduction to semiconductors/Transistor working principle diagram.png>
junction transistor
Voltage amplification and power amplification
field effect transistor
a voltage controlled device
(3) Light-emitting diodes;
It is a device that uses a pn junction to emit light. When a forward current is passed through its pn junction, it can emit infrared light or visible light.
GaP is the most commonly used crystal material for light-emitting diodes
The main material structure and luminescent properties of light-emitting diodes <Introduction to Semiconductors/The main material structures and luminescent properties of light-emitting diodes.png>
The relationship between light-emitting diodes and visual sensitivity <Introduction to Semiconductors/The relationship between light-emitting diodes and visual sensitivity.png>
(4) Laser tube;
Excitation method
Electric injection laser diode, which is directly excited by electrical energy to emit laser light
The other is excited by optical pumping
(5) Power electronic devices;
Metal-oxide-semiconductor (MOS) type integrated circuit
bipolar integrated circuit
(6) Electron transfer devices;
(7) Energy conversion devices;
solar cell
(1) Monocrystalline silicon solar cells
Monocrystalline silicon solar cells have the highest conversion efficiency, reaching over 20%, but they are also the most expensive.
(2) Polycrystalline silicon solar cells
Amorphous silicon solar cells have the lowest conversion efficiency, but are the cheapest. This type of cell will be the most promising for general power generation in the future. Once the photoelectric conversion efficiency of its large-area components reaches 10%, and the price of power generation equipment drops to 1-2 US dollars per watt, it will be enough to compete with current power generation methods.
(3) Amorphous silicon solar cells
(4) Multi-compound solar cells
The photoelectric conversion efficiency of a solar cell formed by overlapping gallium arsenide semiconductor and gallium antimonide semiconductor can reach 36%, which is almost catching up with the efficiency of coal-fired power generation.
(5) Concentrated solar cells
Photovoltaic Materials <Introduction to Semiconductors/Photovoltaic Materials.png>
(8) Sensitive components
Integrated circuit (IC for short)
(1) Si integrated circuit;
(1) Bipolar circuit;
(2) Metal-oxide-semiconductor (MOS) type circuit;
(3) Bipolar MOS (BiMOS) circuit, etc.
(2)GaAs integrated circuit;
(3) Hybrid integrated circuit
Optical windows, lenses, etc.
Materials used in main semiconductor devices and their working principles <Introduction to Semiconductors/Materials used in main semiconductor devices and their working principles.png>
Outlook
Microelectronics and optoelectronics will continue to develop at a very high speed
The application of semiconductors in military technology is increasingly important
The development of new technologies will depend on semiconductor technology
New materials, new structures, and new phenomena of semiconductors have opened up new directions for future development.
trend
Silicon’s dominance will not change significantly in the foreseeable future
Compound semiconductor materials will be further developed in terms of variety and quality. The focus of development will be III-V compounds such as GaAs, InP, and GaN, and II-VI compounds such as ZnSe, CdTe, HgCdTe, etc.
Large-diameter single crystal preparation technology and ultra-precision wafer processing technology will be further developed
In terms of low-dimensional structural materials, there will be more materials and structures
Detection technology will also be developed, such as analysis technology with atomic-level accuracy, surface and structure detection technology, and online detection technology.
New materials, new phenomena, and new preparation processes will continue to appear
Preparation of semiconductor materials
process
raw material
Purify
High purity substances
synthesis
High purity compound polycrystalline
Single crystal preparation
Single crystal rod
Wafer processing
slice
Grinding disc
polishing disc
epitaxial growth
Epitaxial wafer
Purify
Purpose purity
The content of a specific impurity(s) must be strictly lower than certain values, while the content of other impurities requires a wider range of purity requirements.
overall purity
Control of all or most impurities in materials
How many 9s are generally used to represent
Residual resistivity ratio, RRR=r300/r4.2
Purification method
chemical purification
electrolysis
Purification principle
chemical potential difference
Constraints
Electrolyte purity
Anode mud pollution
Contamination of the cathode
Example
Ga
In
Al
Extraction method
Purification principle
Partition of compounds between two liquid phases
Constraints
Contamination of the extractant
Contamination in the transformation process
Example
GeCl4
GaCl3
compound distillation
Purification principle
Multiple condensation and evaporation using vapor pressure difference
Constraints
Impurities with similar vapor pressures
Interactions between impurities
contamination of container
Example
GeCl4
SiHCl3
SiH4
AsCl3
complex method
Purification principle
Form complexes to change original properties
Constraints
Complexing agent purity
must be separated by other means
Contamination of vacuum systems
Example
SiHCl3
chemical adsorption method
Purification principle
Constraints
Example
Physical purification
Vacuum evaporation method
Purification principle
vapor pressure difference
Constraints
High boiling point impurities
contamination of container
Example
Ga
As
Se
Zone melting method
Purification principle
Multiple solid-liquid phase separations
Constraints
The starting concentration cannot be high
The segregation coefficient is close to 1
Adsorption of impurities by surface film
contamination of container
Example
Ge
Si
Sn
sb
Al
Czochralski single crystal method
Purification principle
The solid and liquid phases are segregated in this way, and impurities between grain boundaries are eliminated.
The Czochralski method is to melt the material in the crucible, and then lower the seed crystal to fuse the seed crystal with the melt. Control the appropriate temperature gradient so that the melt crystallizes and solidifies along the direction of the seed crystal, and the seed crystal rod is pulled upward accordingly. The crucible and the seed crystal generally rotate in opposite directions to obtain good stirring and ensure uniform heating and cooling. The directional crystallization method is to melt the raw materials in a crucible and then gradually solidify from one end.
Constraints
The starting concentration cannot be high
The segregation coefficient is close to 1
contamination of container
heater contamination
Example
Ga
In
Usually several methods are used to complement each other
Segregation and segregation coefficient
segregation
Use phase diagrams
synthesis
Preparation of single crystal
liquid phase growth
Melt growth
Growth in the crucible
Vertically oriented crystallization method
The heating furnace and ampoule are fixed and the temperature changes according to a certain program, which is the vertical gradient solidification method.
advantage
The temperature gradient can be controlled, the atmosphere can be controlled, and the crystal cross-section is circular.
shortcoming
It is difficult to observe the growth and the crystal must be separated from the crucible.
Application examples
CdTe,GaAs
horizontal oriented crystallization method
advantage
The temperature gradient can be controlled, the atmosphere can be controlled, and the synthesis and single crystal preparation can be carried out in the same equipment.
shortcoming
The crystal cross section is non-circular, the boat easily contaminates the melt, and the crystal orientation selectivity is small.
Application examples
CdTe,GaAs
horizontal zone melting method
Relying on the surface tension of the melt to keep the melting zone stable and move it for zone melting purification or preparation of single crystals
advantage
Impurities are evenly distributed along the growth direction and easy to observe
shortcoming
It is difficult to control the temperature gradient, the crystal cross section is non-circular, the boat is easy to contaminate the melt, and the crystal orientation selectivity is small
Application examples
Ge,GaAs
Growth outside the crucible
Czochralski
The single crystal seed crystal is pulled upward from the crucible melt, so that the crystal grows vertically upward according to the crystal direction of the seed crystal into a single crystal of the required diameter.
Technical Parameters
Thermal field configuration,
The direction and speed of the seed rod rotation,
The direction and speed of rotation of the crucible,
The pulling speed of the seed rod,
The lifting speed of the crucible,
Maintain gas pressure and flow rate, etc.
advantage
Easy to observe and control crystal growth, with multiple crystal orientation selectivity, and easy to obtain large-diameter single crystals
shortcoming
The crucible and heating system are contaminated, and single crystals with volatile components cannot be grown.
Application examples
Ge, Se, InSb, GaSb
upgrade
Magnetically controlled crystal pulling method
Applying a magnetic field to the crucible area of the Czochralski method causes the conductive melt to interact with the magnetic field to generate a Lorentz force, which suppresses the convection of the melt.
Liquid seal straight drawing method
Cover the melt surface with another layer of inert melt and maintain a corresponding pressure in the furnace chamber (greater than the dissociation pressure of the melt)
advantage
The pressure can be controlled, and single crystals with volatile components can be grown. It is easy to observe, has many crystal orientation selectivities, and can easily obtain large-diameter single crystals.
shortcoming
The temperature gradient of the growth system is difficult to control
Application examples
GaAs, GaP, InP, GaSb, PbTe, InAs
capillary method
advantage
Can be directly made into flake crystals
shortcoming
Contamination of crucible and mold, small width
Application examples
Si (for solar cells only)
Growing without a crucible
floating area method
advantage
The single crystal has high purity and the longitudinal distribution of impurities is relatively uniform.
shortcoming
Difficulty in growing large diameters, uneven radial distribution of impurities
Application examples
Si
pedestal method
Melt growth
Solution precipitation method
solution reaction method
Vapor phase growth method
Sublimation method
chemical reaction method
chemical migration method
advantage
Single crystals with high decomposition pressure and low growth temperature can be obtained
shortcoming
Large single crystals are difficult to obtain, and crystal orientation and defects are difficult to control.
Application examples
CdS,CdSe
solid phase growth method
recrystallization
powder growth method
advantage
Able to obtain single crystals with more complex compositions
shortcoming
Slow growth rate and difficult to control
Application examples
HgTe
Processing of wafers
process
silicon ingot
Clean corrosion
heat treatment
rounded
Grinding the positioning surface
slice
Clean
chamfer
Clean
Grinding disc
Clean corrosion
polishing
Clean
wipe
Package
heat treatment
Eliminate thermal stress and improve crystal quality
slice
Inner circle cutting machine
Wire cutting machine
Grinding and chamfering
The purpose of grinding is to remove the knife marks and damage layer of the slices, and improve the consistency, parallelism and surface flatness of the thickness of the batch of wafers.
Chamfering: rounding the edge of the wafer to prevent edge chipping during subsequent processing or glue accumulation at the edge of the wafer during the glue removal process of the device
polishing
Geometric accuracy, surface quality, surface cleanliness <Introduction to Semiconductors/Comparison of technical requirements (representative values) of large and small diameter silicon wafers.png>
mechanical polishing
The advantage of mechanical polishing is that the geometric precision of the piece is high. However, since polishing relies on mechanical grinding, the hardness of the abrasive must be higher than the hardness of the semiconductor material, so damage to the polished surface is unavoidable.
chemical polishing
Chemical polishing can achieve no damage to the surface, but the chemical corrosion rate is affected by various factors and it is difficult to be completely uniform and it is difficult to obtain good flatness.
chemical mechanical polishing
What is to be ground away is not the material itself, but the product of the reaction between the material and the chemical reagent. Therefore, the hardness of the abrasive can be lower than the material, so that its surface can not be damaged.
epitaxial growth
The process of continuously growing single crystal layers on a single crystal substrate in a certain relationship with the crystal structure of the substrate
type
true homoepitaxy
Pseudo-homoepitaxy
true heteroepitaxy
Pseudo-heteroepitaxy
effect
Since the epitaxial growth temperature is lower than the temperature of single crystal growth from the melt, low temperature can reduce pollution and help obtain a better chemical ratio, and can obtain a high-quality and high-purity epitaxial layer. The active layer of the device is made of epitaxial growth. on layer
On a heavily doped (i.e. very low resistivity) substrate, growing an epitaxial layer with higher resistivity can solve the contradiction between the breakdown voltage of the device (high withstand voltage requires high resistivity) and series resistance. The conflict between frequency and power
Grow ternary or multi-component compounds or solid solutions. It is difficult to grow single crystals of ternary or multi-component compounds using ordinary melts, and their chemical ratios are difficult to accurately achieve and maintain. As for growing solid solutions, since the elements constituting the solid solution will segregate during solidification, it is difficult to obtain a solid solution with uniform composition along the growth direction.
Using epitaxial methods to create junctions for isolation in bipolar circuits
It is the only way to create heterojunctions, quantum wells, and superlattice structures
growing method
chemical vapor phase epitaxy
working principle
Reduction and disproportionation thermal decomposition of inorganic compounds
Applications
Si
GaAs
GaPa
Metal-Organic Chemistry Vapor Phase Epitaxy
working principle
Thermal Decomposition of Metal-Organic Compounds and Alkanes
Applications
Various compound semiconductors
Microstructures of various quantum well superlattices
liquid phase epitaxy
working principle
Precipitation of solutes from supersaturated solutions
Applications
Si GaAs GaP GaAlAs
molecular beam epitaxy
working principle
Physical deposition of atomic or molecular beams
Applications
Various compound semiconductors
Microstructures of various quantum well superlattices
chemical molecular beam epitaxy
working principle
solid phase change
Applications
SOI structure
Ion beam epitaxy
working principle
The physical deposition of ions forming a beam through the action of an electromagnetic field
Applications
Rare earth compounds, etc.
Application of ZnO semiconductor doping materials
Some major semiconductor materials
Some important semiconductor materials <Introduction to Semiconductors/Some Important Semiconductor Materials 2.png>
silicon
Mechanical and Thermal Properties <Introduction to Semiconductors/Mechanical and Thermal Properties of Silicon.png>
Semiconductor Properties <Introduction to Semiconductors/Semiconductor Properties of Silicon.png>
Preparation Process
Application <Introduction to Semiconductors/Applications of Semiconductor Silicon Materials.png>
development trend
Improve crystal integrity
Improving Purity and Controlling Impurities
Larger diameter
Development of silicon epitaxial wafers and silicon-based materials
(1) Increase in integration and complexity of integrated circuits;
(2) Microwaves expand to shorter wavelength regions;
(3) The development of optoelectronic devices and their integration or matching with microelectronic devices;
(4) Improvement in resistance to harsh conditions (rays, high temperature, high power)
The proportion of highly integrated circuits using epitaxy is increasing
Silicon on insulator (SOI) is developing rapidly
Silicon germanium material (SiGe/Si) is approaching maturity
germanium
Mechanical and thermal properties <Introduction to semiconductors/Thermal and mechanical properties of germanium.png>
Semiconductor Properties <Introduction to Semiconductors/Semiconductor Properties of Germanium.png>
Preparation process <Introduction to Semiconductors/Production Principle Flow Chart of Semiconductor Germanium.png>
gallium arsenide
Mechanical and Thermal Properties <Introduction to Semiconductors/Mechanical and Thermal Properties of Gallium Arsenide.png>
Semiconductor properties
Preparation Process
All GaAs single crystals are made by melt growth method
Horizontal directional crystallization method and liquid seal Czochralski method
application
Gallium Phosphide
Main physical properties <Introduction to Semiconductors/Main Physical Properties of Gallium Phosphide.png>
preparation
Liquid seal straight drawing method
The main use is to manufacture light-emitting diodes (LEDs)
Indium Phosphide (InP)
Main physical properties <Introduction to Semiconductors/Main Properties of Indium Phosphide.png>
Cadmium Telluride