Etching Rate Profile of C-Face 4H-SiC Wafer Depending on Total Gas Flow Rate of Chlorine Trifluoride and Nitrogen

Abstract

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.

Chlorine Trifluoride Gas Etching Design for Quickly and Uniformly Removing a Thick C-Face 4H-Silicon Carbide Layer

“…4b2. As reported in a previous study, 9 the high gas flow rate could make the wavy etching rate profile flat. However, because the high gas flow rate simultaneously influences the global etching rate profile, it should be limited to a fine adjustment.…”

“…For the gas distributor design, the etching was assumed to locally occur at the wafer position beneath the pinhole of the gas distributor, through which the chlorine trifluoride gas flowed downward. The etching rate at various distances from the center of the rotating wafer was assumed as the average value along the concentric circle, similar to the previous study, 9 as shown in Fig. 3.…”

“…Following Eq. 2, the etching rate profile was calculated for Distributors A and B, 9 which had the orthogonal and the slanted pinhole arrangements, as shown in Figs. 4a1 and 4b1, respectively.…”

“…The etching rate profile was significantly uniform in contrast to those reported in previous studies. 9,12 In this study, the wafer rotation rate was fixed at 10 rpm. Because the wafer rotation at around 10 rpm takes the average of the etching rate along the concentric circle, 10,15 the window of the allowable and effective wafer rotation rate is very wide, probably those between 1 and several tens rpm.…”

“…In previous studies [9][10][11][12] for developing the dry etcher using the chlorine trifluoride gas, the local etching rate was shown to depend on the local chlorine trifluoride gas supply, similar to the chemical vapor deposition rate. 13 The gas distributor design [9][10][11][12] have been studied based on the theoretical calculations and experiments, in order to show the concept that the etching rate profile might be the average between different wavy etching rate profiles.…”