Why semiconductor equipment cannot do without graphite
There are several extreme conditions in semiconductor technology:
- 1500-1600 ℃ monocrystalline silicon direct pull
- 2200 ℃+Silicon Carbide (SiC) PVT Crystal Growth
- F ⁻/Cl ⁻ bombardment in plasma etching
- Atmosphere of NH ∝, H ₂, TMGa, etc. in MOCVD
- The wafer cannot be contaminated with elements such as Na, K, Fe, Cu, Ni, B, etc
There are not many materials that can simultaneously meet the requirements of "high temperature resistance+good conductivity and thermal conductivity+low thermal expansion+precision machining+purification to ppm level", and graphite is the most mature type.
One sentence of core advantage:
Metals can melt, ceramics can become brittle, and plastics can coke. High purity isostatic pressed graphite can conduct electricity, uniformly heat up, and remain stationary in high temperature and clean environments.
The 'graphite' used in semiconductors is not ordinary graphite
| Type | Typical purity | Characteristic | Semiconductor applicability |
| Natural graphite paper/foil | 99.8–99.99% | Soft and thermally conductive | Thermal management/sealing, without making equipment core components |
| Molded graphite | Ash content ≤ 300 ppm | Significant anisotropy | Ordinary industrial components |
| Squeezed graphite | Ash content ≤ 500 ppm | Long strip electrode | Ordinary EDM/Metallurgy |
| Fine grained isostatic pressed graphite | Ash content ≤ 50 ppm, semiconductor grade ≤ 5-20 ppm | Isotropic, fine-grained, CNC compatible | Mainstream semiconductor equipment |
| Ultra high purity isostatic pressed graphite | 4N / 5N / 99.9995% | B. Fe, Ni, Cu are controlled to ppb level | 300mm wafer SiC, Epitaxy and etching |
Semiconductor grade typically requires:
- Fixed carbon: ≥ 99.99% (4N), high-end 99.999% (5N)
- Ash content: ≤ 20 ppm, advanced nodes ≤ 5 ppm or even ≤ 1 ppm
- Particle size: fine crystals 2-15 μ m, high-end components 2-5 μ m
- Density: 1.80-1.90 g/cm ³
- CTE：3.5–4.6 ×10⁻⁶ /℃
- Surface: Ra ≤ 0.4 μ m, no powder shedding, no micro cracks, no metal contamination
- Standard: Compliant with SEMI cleanliness and pollution control logic
6 major application scenarios of graphite in semiconductor equipment
1. Monocrystalline silicon direct pull furnace (CZ Furnace)
- Graphite crucible holder
- Heater
- Guide tube
- Insulation tube/insulation screen
Function: Maintain a uniform temperature field in a 1500 ℃+argon environment, preventing Na/K from evaporating into the quartz crucible and silicon melt.
2. Silicon carbide (SiC) crystal growth furnace
SiC PVT crystal growth requires temperatures above 2200 ℃, with graphite components directly facing silicon vapor and carbon vapor.
- graphite crucible
- Graphite insulation cover
- Graphite seed crystal holder
- Graphite flow guiding structure
This type of component must be treated with semiconductor grade isostatic pressed graphite and surface purification, and high-end products also require SiC coating or TaC coating.
3. Epitaxial/MOCVD/CVD substrate (Susceptor)
During the epitaxial growth of GaN, SiC, and Si, the wafer is placed on a graphite substrate：
- Require uniform temperature
- Cannot drop particles
- Cannot release metal impurities
- Surface often coated with CVD SiC/pyrolytic carbon coating
Without a high-purity graphite base, the thickness uniformity of MOCVD epitaxial wafers cannot be controlled at all.
4. Plasma etching equipment
There are F and Cl plasmas in the etching chamber, which can penetrate ordinary metals.
Graphite components are used for:
- Focus Ring
- Electrode
- Inner lining of cavity
- Wafer carrier ring
Bare graphite is not resistant to plasma, so it is necessary to:
- Ultra high purity matrix
- CVD SiC coating
- Low exhaust and low particle shedding
5. Diffusion/oxidation/annealing furnace
- Stone Ink Boat
- Graphite gear rack
- Graphite tray
- Annealing vehicle
In a 12 inch wafer production line, once the graphite boat loses powder or contains Na/K, the yield of the entire batch of wafers collapses.
So the tolerance is often within ± 0.005-0.01 mm, and the surface needs to be cleaned with ultrasound, rinsed with high-purity water, and packaged in a clean room.
6. Ion implantation and vacuum furnace tooling
- Injector carrier
- Vacuum sintering fixture
- High temperature annealing sample rack
Graphite relies on:
- High temperature does not deform
- Not releasing gas
- Non polluting beam path
The 'invisible technological barrier' of semiconductor graphite components
Selling semiconductor graphite is not selling a piece of carbon, but selling this set of capabilities:
1. Raw materials: Low sulfur petroleum coke/asphalt coke, cannot use dirty ore
2. Isostatic pressure forming: 200MPa grade liquid medium compression, isotropic
3. High temperature graphitization: 2800-3200 ℃
4. Halogen/vacuum purification: beat Fe, Ni, Cu, B, Na, K to ppb level
5. Five axis CNC machining: thin-walled, deep hole, irregular shape, diamond cutting tools
6. Ultrasonic cleaning+cleanroom packaging: preventing processing dust and anti pollution
7. Coating ability: SiC/TaC/PyC, determining lifespan and plasma resistance
8. Traceability: Mineral source batch number purification curve machining report COA MTC full chain
Common Misconceptions
❌ Graphite is carbon, 99% and 99.99% are similar
→ 100 ppm ash content in semiconductors = wafer killer.
❌ Even isostatic pressed graphite can enter semiconductors
→ Isostatic pressure graphite without purification, clean processing, or coating ability can only be used as EDM electrodes.
❌ Natural graphite paper can also be used to make wafer trays
→ Natural graphite paper is suitable for heat dissipation/sealing and not suitable for direct contact with wafers.
❌ The customer wants a graphite sensor, just send a graphite block
→ What he wants is: isostatic pressing substrate+purity report+particle size+CTE+coating thickness+Ra+SEMI pollution control.
End
Graphite material in semiconductor equipment = Isostatic pressure fine-grained graphite + Ultra high purity purification + Precision machining + Coating protection.
It doesn't emit light, doesn't expose itself, and doesn't make headlines, but it's a single crystal furnace, SiC crystal growth MOCVD, In the etching chamber and diffusion furnace, without it, the chip yield directly returns to zero.
