A 50-mm diameter silicon carbide wafer thinning technique by means of a chemical reaction using a chlorine trifluoride (ClF3) gas was studied accounting for the gas distributor design and the total gas flow rate. The entire etching depth profile could become uniform with the increasing total gas flow rate at the fixed chlorine trifluoride gas concentration. A relationship between the pinhole arrangement of the gas distributor and the local etching rate profile was clarified by comparing the quick calculation and the measurement.
Effective process conditions to utilize a slim vertical silicon chemical vapour deposition reactor were studied. Based on a numerical analysis taking into account the gas flow, heat and species transport, particularly over a wide range of the trichlorosilane gas concentrations from 1% to 40 % in ambient hydrogen, a heavy and cold gas was shown to quickly go downward to the hot wafer surface through the slim vertical gas channel. The gas phase near the wafer was sufficiently cooled to produce a cold wall thermal condition which enabled the trichlorosilane gas consumption only at the wafer surface, even in a non-axisymmetric and non-steady condition. The slow wafer rotation, less than 30 rpm, had a considerable effect, such as that increasing the gas phase temperature gradient for suppressing the gas phase reaction.
For improving the productivity of the semiconductor silicon carbide power devices, a very large diameter wafer process was studied, particularly for the non-plasma wafer etching using the chlorine trifluoride gas. Taking into account the motion of heavy gas, such as the chlorine trifluoride gas having the large molecular weight, the transport phenomena in the etching reactor were evaluated and designed using the computational fluid dynamics. The simple gas distributor design for a 200-mm-diameter wafer was evaluated in detail in order to uniformly spread the etchant gas over the wide wafer surface.
The etching rate profile over the 50-mm diameter single-crystalline C-face 4H-SiC wafer by ClF3 gas was numerically evaluated by means of the numerical calculation accounting for the transport phenomena. The etching rate uniformity is expected to be improved by means of adjusting the pinhole diameter and their arrangement of the gas distributor.
The powder and plate of aluminum nitride were exposed to chlorine trifluoride gas at the concentration of 100% and at atmospheric pressure for 10 min and temperatures up to about 1000 °C. With the increasing temperature, the weight of the aluminum nitride plate increased in the temperature range between 750 °C and 800 °C, while it decreased at temperatures higher than 800 °C. The thickness also increased at temperatures higher than 750 °C. The change in the aluminum nitride plate thickness showed a peak at 800 °C. The surface remained smooth at temperatures lower than 900 °C. However, the surface had small pits at 995 °C, because the aluminum trifluoride, produced by the chlorine trifluoride gas, was considered to slightly sublimate and affect the surface morphology. Overall, the aluminum nitride remained anticorrosive to the chlorine trifluoride gas at temperatures lower than 900 °C. When the aluminum nitride was used in the silicon carbide etching reactor, its surface was rather smooth after repetitive exposures to the chlorine trifluoride gas at 500 °C.
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