Growth Verification
The silicon carbide (SiC) seed crystals were prepared following the outlined process and validated through SiC crystal growth. The growth platform used was a self-developed SiC induction growth furnace with a growth temperature of 2200℃, a growth pressure of 200 Pa, and a growth duration of 100 hours.
Preparation involved a 6-inch SiC wafer with both the carbon and silicon faces polished, a wafer thickness uniformity of ≤10 µm, and a silicon face roughness of ≤0.3 nm. A 200 mm diameter, 500 µm thick graphite paper, along with glue, alcohol, and lint-free cloth were also prepared.
The SiC wafer was spin-coated with adhesive on the bonding surface for 15 seconds at 1500 r/min.
The adhesive on the bonding surface of the SiC wafer was dried on a hot plate.
The graphite paper and SiC wafer (bonding surface facing down) were stacked from bottom to top and placed in the seed crystal hot press furnace. The hot pressing was carried out according to the preset hot press process. Figure 6 shows the seed crystal surface after the growth process. It can be seen that the seed crystal surface is smooth with no signs of delamination, indicating that the SiC seed crystals prepared in this study have good quality and a dense bonding layer.
Conclusion
Considering the current bonding and hanging methods for seed crystal fixation, a combined bonding and hanging method was proposed. This study focused on the carbon film preparation and wafer/graphite paper bonding process required for this method, leading to the following conclusions:
The viscosity of the adhesive required for the carbon film on the wafer should be 100 mPa·s, with a carbonization temperature of ≥600℃. The optimal carbonization environment is an argon-protected atmosphere. If done under vacuum conditions, the vacuum degree should be ≤1 Pa.
Both the carbonization and bonding processes require low-temperature curing of the carbonization and bonding adhesives on the wafer surface to expel gases from the adhesive, preventing peeling and void defects in the bonding layer during carbonization.
The bonding adhesive for the wafer/graphite paper should have a viscosity of 25 mPa·s, with a bonding pressure of ≥15 kN. During the bonding process, the temperature should be raised slowly in the low-temperature range (<120℃) over approximately 1.5 hours. The SiC crystal growth verification confirmed that the prepared SiC seed crystals meet the requirements for high-quality SiC crystal growth, with smooth seed crystal surfaces and no precipitates.
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