1. K.N.T University of technology Electronic Department
Crystal Growth
Instructor:
Prof. F. Hossein-Babaei
Presented by:
M. H. Jalalpour
P. Talebnia
Fall 2014

2. Outline History Examples Crystal Growth Theories
Crystal Growth Classes
ZnSe
Quartz
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img.directindustry.com

3. Example single crystals
Semiconductors:
Electronic grade Ge and Si, doped and undoped.
II-VI semiconductors (CdTe, CdS, CdSe, ZnS, ZnSe, ZnTe, etc.)
III-V semiconductors (GaAs, GaP, GaSb, InAs, InP, InSb, etc.)
IV-VI semiconductors (PbS, PbSe, PbTe, SnTe, etc.)
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4. Art crystals and jewelry : Amethyst
Optical crystals:
AgBr, AgCl, BaF2, CaF2, CdTe,
CsI, Ge, KBr, KCl, KRS-5,
LiF, MgF2, NaCl, sapphire,
ruby, Si, ZnSe.
Art crystals and jewelry :
Amethyst
A selection of both rough and cut Kashmir sapphires.
Amethyst crystal
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5. Crystal growth classes
Growth from solid
Growth from vapor
Growth from solution
Growth from melt
Bridgman method
Czochralski method
Floating zone
Verneuil method
Vapor
Si ingot from melt
Solution
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Al from solid

6. History
Industrial crystal production started with Verneuil 1902 who with the flame-fusion growth process named after him, for the first time achieved growth of single ruby and sapphire crystals with melting points above 2000oC.
Czochralski process is named after Polish scientist Jan Czochralski, who invented the method in 1916.
Bridgman, in 1940’s, used temperature gradients to grow single crystals by directional solidification.
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7. Growth from melt Heating methods Chamber pressure Growth from melt
Bridgman method
Czochralski method
Floating Zone method
Verneuil method
Heating methods
RF heating
Hydrogen torch
Resistance heating
Optical heating
Chamber pressure
High pressure
Atmospheric pressure
Vacuum
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8. Bridgman Method
The method involves heating polycrystalline material in a container above its melting point and slowly cooling it from one end where a seed crystal is located. Single crystal material is progressively formed along the length of the container. The process can be carried out in a horizontal or vertical geometry.
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9. Vertical Bridgman Method
Vertical Bridgman Tube Furnace
Temperature Profile
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10. Vertical Bridgman Method
Obtaining cadmium zinc telluride (CZT) crystals
Obtaining zinc selenide (ZnSe) crystals
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National Academy of Sciences of Ukraine

11. Horizontal Bridgman-Stockbarger Method
Temperature ºC
Schematics of the furnace and crucible used for GaAs growth.
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12. The growth from a single crystal seed
With the necking technique shown, the grown crystal is in contact with a single grain of the polycrystalline material used as the seed.
The growth will follow the structure of the grain that is in contact with.
The selected crystal orientation is almost random.
Melt
Single crystal
Polycrystal
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Copyright
تصویر کشیده شده توسط محمد حسین جلال پور تحت نظر استاد

13. An example of industrial horizontal Bridgman system
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14. Photograph of a Cd(1-x)MnxTe single crystal ingot 30 mm in diameter and 120 mm in length
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15. Czochralski method
A highly developed method of crystal growth, widely used in semiconductor industry.
High-purity, semiconductor-grade silicon (only with a few ppm of impurities) is melted down in a crucible, which is usually made of SiO2-lined graphite. A seed crystal, mounted on a rod, is dipped into the molten silicon. The seed crystal is pulled upwards and rotated at the same time.
By precisely controlling the temperature gradients, rate of pulling and speed of rotation, it is possible to extract a large, single-crystal, cylindrical ingot from the melt.
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16. Czochralski method FHB

17. Czochralski Method
In order to prevent the oxidation of the melt and the crystal, the whole process must be performed in oxygen- and moisture-free atmosphere.
While the largest silicon ingots produced today are 400 mm in diameter and 1 to 2 meters in length, 200 mm and 300 mm diameter crystals are standard in industrial processes.
The pulling rate (usually a few mm/min) and the temperature profile determine the crystal diameter.
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18. Czochralski (CZ) crystal growth
2. Start of necking. Seed is dipped to > 1415 °C melt.
4. Start of body.
6. Conical tail growth after completion of body.
1. Polysilicon charge in silica crucible placed in a graphite holder.
3. Shoulder growth, after neck is complete.
5. Body growth.
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19. Crystal growth
The raw material contains only < 1 ppb impurities. Pulled crystals contain oxygen≈ 1018 cm-3, and C ≈ 1016 cm-3, plus any added dopants.
• Essentially all Si wafers used for ICs today come from Czochralski grown crystals.
• Polysilicon material is melted, held at close to 1417 ˚C, and a single crystal seed is used to start the growth.
• Pull rate, melt temperature and rotation rate are all important control parameters.
→ Introduces O ≈ cm-3
→ C ≈ cm-3
Ar +H2 atmosphere
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20. Crystal growth some problems and solutions
Crucible dissolving =>
Introduce noble gas plus hydrogen
Seed dislocation
Seed/melt contact shock
Solution : Necking
Temperature and density gradients => convection
Solution : Seed rotation and magnetic Field
Dopant segregation coefficient
Solution : Growth Rate Control
Generating gas
Generating gas; introducing impurity
Using graphite crucible
=> Crystal dislocation
=> in homogeneity

21. An example industrial Czochralski growth system.
Czochralski method
An example industrial Czochralski growth system.
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22. Output of a Czochrolski system; single crystal Si ingot.
Czochralski method
Output of a Czochrolski system; single crystal Si ingot.
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23. Floating zone method
The basic idea in float zone (FZ) crystal growth is to move a liquid zone through the material. If properly seeded, a single crystal may result in.
The melt never comes into contact with anything but the inert atmosphere of the furnace.
The maximum diameter of the FZ-grown crystals is about 20 mm.
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24. Floating zone method Advantages:
Optical heating
RF heating
Advantages:
No crucible; no impurity is introduced; can produce high resistivity Si;
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25. Optical floating zone method
Optical heating of the zone.
Photograph of an optical FZ growth system.
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people.seas.harvard.edu

26. Floating zone method
Lab floating zone puller with resistance heater (left part = transformer / right part = control system)
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27. Verneuil Method
Verneuil process, also called flame fusion, was the first commercially successful method of manufacturing synthetic gemstones developed in 1902 by the French chemist Auguste Verneuil.
For higher crystal quality, the produced ingots are annealed for hours at elevated temperatures close to the melting point.
Auguste Verneui
A sketch of an early furnace used by Verneuil to synthesise rubies using the Verneuil process
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28. Verneuil Method O2 + Al2O3 + Cr2O3 inlet
O2 + H2 mix and ignite, T > 2000K
Molten drops fall onto “pedestal”
Xtal forms and grows
Example of Al2O3 xtal (right end)
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29. Verneuil Method
It is primarily used to produce ruby and sapphire varieties of corundum, as well as the diamond simulants rutile and strontium titanate. The method is still the least expensive way to make sapphire and ruby adequate for many applications.
In principle, the process involves melting powdered substance using an oxyhydrogen flame. The melt droplets crystallize on a single crystal seed which grows to produce the crystal ingot. The process is considered to be the founding step of the modern industrial crystal growth technology. The technique remains in wide use to this day.
A crucial factor in growth of good quality artificial gemstones is using highly pure starting material, with at least % purity. The presence of sodium impurities is especially undesirable, as it makes the crystal opaque.
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30. Verneuil Method
The starting material (alumina) is finely powdered and placed in a container above the Verneuil furnace.
Oxygen is supplied into the furnace, which carries the powder particles down a narrow tube.
Combustion occurs at the point where the narrow tube opens into a larger one. The flame, at least 2000 °C hot at its core, melts the powder into small droplets, which fall onto an earthen support rod placed underneath.
The seed crystal eventually forms. As more droplets fall onto the seed tip, a single crystal, called a boule, starts to form.
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31. Industrial Verneuil Method
Ruby production line according to the Verneuil technique in the Chemiekombinat Bitterfeld (around 1970)
Industrial Verneuil Method
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32. Kyropoulos method
Kyropoulos method (1926) is somewhat similar to Czochralski technique. It also starts from the contact of a seed crystal mounted in the holder with a molten alumina. However the crystallization front in a crystal pulled by Czochralski method is a meniscus located in the column connecting the surface of the molten alumina with the growing crystal. In Kyropoulos technique the growing crystal is surrounded by the melt. The crystal growth occurs within the crucible with the molten alumina. The crystal grows until its surface reaches the crucible walls. Then the crystal is pulled out (lifted) and the growing cycle repeats. There is also a version of the process with continuous pulling the crystal from the crucible.
The diameter of the crystal grown by Kyropoulos method is limited by the diameter of the crucible.

33. Kyropoulos method
The main advantage of Kyropoulos method is the crystallization at low temperature gradients – below 10ºC/cm , which results in low thermal stresses in the crystal. High optical quality large crystals (boules) with diameter exceeding 350 mm may be produced by Kyropoulos method.
Kyropoulos method is widely used for growing sapphire crystals of a very high optical quality. Kyropulos sapphire is suitable for manufacturing ingots and substrates for LED and RF applications.

34. Crystal Growth from Gas Phase
The gas coats the crystal, inhibiting growth. The ordered crystal phase has grown around a gas bubble impinging on its surface.
Slow
Examples:
Snowflakes

36. Crystal Growth from Solution
Dissolving the material in the solvent→ saturation
Cooling saturated solution slowly → Crystal growth
Methods:
Growth from Aqueous Solution: Solvent is water. Examples NaCl, Rock candy
Growth from Non-aqueous solution: Solvent is not water, e.g. alcohol
Flux Growth: Solvent is solid. First, solvent is melted. Then, material is dissolved.

37. Crystal Growth from Solution
Advantages:
-Grow congruently and incongruently melting materials
- Need relatively simple equipment
- Has short growth-time scales
Need small amounts of materials
Disadvantages:
- Results not too large a crystal (mm to cm)

38. Sources
Lecture notes on “semiconductor device fabrication technology” by Prof. F. Hossein-Babaei, 2013
2.Microchip Fabrication, peter van zant
3.crystal Growth Technology ,Hans.J.Scheel 4.
5. Single crystal growth employing Czochralski method, adam pikul 6. 7. 8. 9.
10.
11. Flux Method for Preparing Crystals: Athena S. Sefat
12.
13.
14.
15.

39. Thank you for your attention

40. Crystal Growth Theories
اسلاید حذف شده
Crystal Growth Theories
Surface Energy Theory
Surface Nucleation Theory
Diffusion Theory
Pierre Curie
J. Willard Gibbs
Arthur Amos Noyes
Ivan Stranski
Max Volmer
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41. Crystal growth اسلاید حذف شده