1. Chapter 1
Crystal Growth
Wafer Preparation

2. Polycrystalline semiconductor
Process Flow Overview
Starting Material
Polycrystalline semiconductor
Single crystal
Wafer
Distillation
and
Reduction
Synthesis
Crystal growth
Crystal growth
Grind, saw , polish
Grind, saw , polish

3. Overview
Material preparation is the beginning of the process in making an IC chip .
The goal for this part of the process is to grow the ingot that will be sliced up into wafers.
The wafer is a round solid silicon disc that will have all of the processing performed on it.

4. CRYSTAL GROWTH 6. Edge Rounding 1. Crystal Growth 7. Lapping
2. Single Crystal Ingot
3. Crystal Trimming and Diameter Grind
4. Flat Grinding
5. Wafer Slicing
6. Edge Rounding
7. Lapping
8. Wafer Etching
9. Polishing
10. Wafer Inspection
Slurry
Polishing table
Polishing head
Polysilicon
Seed crystal
Heater
Crucible

5. Starting Material Preparation
The starting material for silicon is relatively pure form of sand (SiO2) called quartzite.
This is placed in a furnace with various forms of Carbon.
The Silicon treated with HCL at 300° to form tricholosilane.

6. Starting Material Preparation
Fractional Distillation of the liquid removes the unwanted impurities. The purified SiHCL3 is then used in a hydrogen reduction reaction to prepare the electronic-grade silicon ( EGS) .
EGS ,a polycrystalline material of high purity is the raw material of single-crystal silicon.

7. Silicon Crystal Growth from the Melt
The Basic Technique , Which is material in liquid form, is Czochralski Technique.
The Float –Zone Process also can be used to grow silicon that has lower contamination than normally obtained from CZ Technique.
Most popular technique is CZ.

8. Czochralski Technique
Czochralski Process is a Technique in Making Single-Crystal Silicon
A Solid Seed Crystal is Rotated and Slowly Extracted from a Pool of Molten Si
Requires Careful Control to Give Crystals Desired Purity and Dimensions

9. CYLINDER OF MONOCRYSTALLINE
The Silicon Cylinder is Known as an Ingot
Typical Ingot is About 1 or 2 Meters in Length
Can be Sliced into Hundreds of Smaller Circular Pieces Called Wafers
Each Wafer Yields Hundreds or Thousands of Integrated Circuits

10. Czochralski Technique
Graphite susceptor
Sio2 crucible
Heating element
Crystal Puller
Furnace
Power supply
Rotation mechanism
Seed Holder
Crystal-pulling mechanism
Rotation mechanism
Gas Source
Ambient control
Flow control
Exhaust system
Control system
Control process parameters: Crystal Diameter, pull rate and rotation speed.

11. Distribution of Dopant
In crystal-growth a known amount of Dopant is added to the melt to obtain the desired doping concentration in the growth crystal.
At interface, The doping concentration incorporated into the crystal ( solid) is usually different from the doping concentration of the melt ( liquid).
The ratio of these two concentration is defined as the equilibrium segregation coefficient:
Equilibrium concentration of the dopant in the Solid
Equilibrium concentration of the dopant in the Liquid

12. Distribution of Dopant
Note the most values are below 1.
As the crystal grows , the melt becomes enriched.

13. Distribution of Dopant
Find the doping concentration in the crystal in CZ technique?
The doping concentration in the crystal
The initial doping concentration in the crystal
The doping concentration in Melt
Given point of growth
The amount of the dopant remaining in the melt
The reduction of the dopant from the melt

14. Distribution of Dopant

16. Example

17. Effective Segregation Coefficient
There is a concentration gradient developed at the interface, when

18. Effective Segregation Coefficient

19. Silicon Float-Zone ProcessRF
Gas inlet (inert)
Molten zone
Traveling RF coil
Polycrystalline rod (silicon)
Seed crystal
Inert gas out
Chuck

20. Silicon Float-Zone Process

21. Silicon Float-Zone Process

22. Silicon Float-Zone Process

23. Silicon Float-Zone Process

24. Neutron Irradiation

25. Saturated electron velocity
GaAs Advantages
Fabrication Cost
Noise
Breakdown voltage
Operating Power
Cutoff Frequency
Electron mobility
Saturated electron velocity
Substrate Type
High
Low
GaAs Si
These properties make GaAs circuitry ideal for mobile phones, satellite communications, microwave point-to-point links, and radar systems However, high fabrication costs and high power consumption have made GaAs circuits unable to compete with silicon CMOS circuits in most applications. 

26. Ga & As Elemental Gallium Native Gallium With 99.9999% purity
Bayer Process
Zone passes refining
Native Arsenic
Elemental Arsenic
With % purity

27. GaAs Polycrystalline Elemental Gallium With 99.9999% purity
Synthesis Process
Elemental Gallium
With % purity

28. GaAs Crystal-growth
The starting materials for the synthesis of polycrystalline gallium arsenide are the elemental , chemically pure gallium and arsenic.
The behavior of a combination can be described by phase diagram.

29. As boiling point
Ga boiling point
GaAs Crystal-growth

30. Example Find the fraction of melt that will be solidified?
Weight percent scale
Weight of the liquid.
Weight of the solid (GaAs).
Concentration of Dopant in the Liquid.
Concentration of Dopant in the Solid.
Weight of the Arsenic in the Liquid.
Weight of the Arsenic in the solid (GaAs).
Tototal Weight of the Arsenic in Ta and Tb.

31. As boiling point
Ga boiling point
Example ( cont.)

32. GaAs Crystal-growth

33. Bridgman Technique

34. Equilibrium Segregation Coefficient

35. Wafer Coding

36. Packed Wafers

37. Chapter Overview
Raw materials (SiO2) are refined to produce electronic grade silicon with a purity unmatched by any other available material on earth.
CZ crystal growth produces structurally perfect Si single crystals which are cut into wafers and polished.
Dopants can be incorporated during crystal growth
Point, line, and volume (1D, 2D, and 3D) defects can be present in crystals, particularly after high temperature processing.
Point defects are "fundamental" and their concentration depends on temperature (exponentially), on doping level and on other processes like ion implantation which can create non-equilibrium transient concentrations of these defects.