Explores the production methods for Silicon Carbide, including Acheson Process, Lely Process, Seeded Sublimation, Liquid Phase Epitaxy, and Chemical Vapor Deposition.

1. Silicon Carbide
Production
Magel Su

2. Silicon Carbide (SiC)
▪ Ceramic crystal with approximately 250 polymorphs
▪ 2 Major Polymorphs
▪ α-SiC (Hexagonal Crystal Structure)
▪ Forms at >1700°C
▪ β-SiC (Cubic Crystal Structure)
▪ Forms at <1700°C
α-SiC (6H)
β-SiC (3C)

3. Properties (6H-SiC)
▪ Colorless
▪ Brown/Black caused by iron impurities
▪ Colorful sheen caused by SiO2
▪ Chemically Inert
▪ High Thermal Conductivity - 4.9 W/(cm*K) at 300K
▪ Low Coefficient of Thermal Expansion (4.3 x 10-6 °C-1)
▪ High Maximum Current Density, High Electric Field Breakdown Strength
▪ High Melting Temperature (3103 ± 40 K)

4. Phase Diagram
http://www.ioffe.ru/SVA/NSM/Semicond/SiC/thermal.html

5. Uses
▪ Semiconductor
▪ n-type with Nitrogen, Phosphorus
▪ p-type with beryllium, boron, aluminum, gallium
▪ Superconductivity at 1.5 K (3C-SiC:Al, 3C-SiC:B, 6H-SiC:B)
▪ Lightning Arresters
▪ Diodes, transistors, LEDs (Replaced by GaN)
▪ Yellow LED (3C-SiC). Blue LED (6H-SiC)

6. Uses
▪ Abrasive sandpaper, Cutting disks
▪ Harder than corundum (AI2O3), Softer than diamond
▪ Ceramic brake discs
▪ Catalyst support
▪ Steel and Graphene Production
▪ Jewelry (Diamond substitute)
Moissanite Engagement Ring
Carbon-Ceramic Discs
Abrasive Sandpaper

7. Natural Sources of SiC
▪ Moissanite-naturally occurring SiC
▪ Found in meteorites and as inclusions in diamonds, kimberlite, lamproite
▪ Extremely rare, only synthetic SiC is used
LamproiteKimberlite

8. Acheson Process (1896)
▪ 50% Silica (quartz sand), 40% carbon (petroleum coke), 7%
sawdust, 3% NaCl heated in Acheson furnace to 2700°C, then
cooled gradually
▪ Acheson furnace
▪ Heated by resistivity-current passes through a graphite core
surrounded by reactants
▪ SiC layer forms around graphite core
Cross Section of Acheson Furnace
C + SiO2 → SiO + CO
SiO2 + CO → SiO + CO2
C + CO2 → 2CO
2C + SiO → SiC + CO

9. Acheson Process (1896)
▪ No control over purity of crystals
▪ No polymorph/polytype control
▪ Sawdust and salt used to increase purity
▪ Sawdust increases mixture porosity
▪ NaCl reacts with volatile metal impurities

10. Lely Process (1955)
▪ SiC lumps packed between two concentric graphite tubes
▪ Inner tube removed, leaving porous SiC layer contained within larger graphite
tube (Crucible)
▪ Crucible placed in furnace with SiC , heated to 2500°C under Argon at 1 Atm
▪ SiC powder near crucible wall sublimes and decomposes due to higher
temperature
▪ SiC crystals nucleate on inner SiC surface due to lower temperatures

11. Lely Process (1955)

12. Lely Process (1955)
▪ Forms high quality crystals compared to Acheson Process
▪ Low product yield
▪ Irregular crystal sizes
▪ No polytype control (Usually forms hexagonal crystals)

13. Seeded Sublimation Method (1978)
▪ Modified Lely Process
▪ Uses same crucible setup from Lely Process, except with inner tube left in
▪ Inner graphite tube is thin and porous
▪ Crucible heated to 2200°C in Argon with <1 Atm
▪ Temperature gradient (20-40°C/cm) applied over length of crucible
▪ SiC powder temperature at bottom of crucible is greater than seed temperature

14. Seeded Sublimation Method (1978)

15. Seeded Sublimation Method (1978)
▪ Growth rate controlled by:
▪ Temperature (1800-2600°C)
▪ Temperature Gradient
▪ Pressure (10-4 – 760 mmHg)
▪ Seed Crystal Quality
▪ High yield, definite size

16. Seeded Sublimation Method (Modern)
▪ Source placed at bottom, seed at top
▪ Used to produce bulk SiC
▪ 90% yield

17. Liquid Phase Epitaxy (LPE)
▪ Used to produce thin films of SiC
▪ SiC substrate attached to graphite holder dipped
into liquid Si with dissolved C
▪ Holder rotated continuously to promote radial
growth
▪ Slow cooling is driving force for crystal formation
▪ Performed at 1650 – 1800°C
▪ Growth rate: 2 – 7 µm/hour

18. Liquid Phase Epitaxy (LPE)
▪ Low solubility of C in Si (15% at 2800°C)
▪ Scandium, Terbium, Praseodymium added to increase solubility to 50%
▪ Argon increases atmospheric pressure, reducing Si vapor pressure effect

19. Chemical Vapor Deposition (CVD)
▪ Seed crystal placed in vertical reactor made of
graphite
▪ Silane (SiH4) and propane (C3H8) diluted in helium
(carrier gas) enter reactor through cracking zone
▪ Cracking zone-heated walls which produce
reactive radicals from gas
▪ Reactor walls covered with SiC to prevent
graphite evaporation
▪ Growth rate: 0.5 – 0.8 mm/hr at 200-800 mbar,
2000 - 2300°C

20. Summary
Seeded
Sublimation
LPE CVD
Growth Rate High Low Low
Crystal Quality Medium Medium High
Defect Quality Medium High Medium
Cost Low Medium High

21. References
▪ Byrappa, K., and T. Ohachi. Crystal Growth Technology. Norwich, NY: William
Andrew Pub., 2003. Print.
▪ Majumdar, Arka. "BULK GROWTH OF SILICON-CARBIDE CRYSTALS." (n.d.): n.
pag. 7 Mar. 2006. Web. 22 Jan. 2016.
▪ "NSM Archive - Silicon Carbide (SiC) - Thermal Properties." NSM Archive -
Silicon Carbide (SiC) - Thermal Properties. N.p., n.d. Web. 20 Jan. 2016.
▪ Saddow, Stephen E., and Anant Agarwal. Advances in Silicon Carbide
Processing and Applications. Boston: Artech House, 2004. Print.