Ga-a masking contamination source to prevent FIB cross-section on Al film

Abstract

Pure Gallium metal is a good adhesive agent which can be used to paste small coupons on full wafer for metal growth in high temperature PVD chamber as Ga has low vapor pressure in high temperature. However, when the process chamber exceeds a certain critical temperature, Gallium at the back of the coupon can contaminate front metal surface in process chamber to form a Ga rich metal surface layer. With such Ga contamination, Ga+ based FIB (Focus Ion Beam) cannot be used to perform cross-section on the metal film has never been reported. We have observed this phenomenon on thick Al film growth on SiO2/Si substrate. In this paper, we described the details of such phenomenon and listed out a possible explanation.