Optical diagnostic instrument for monitoring etch uniformity during plasma etching of polysilicon in a chlorine-helium plasma
Nonuniform etching is a serious problem in plasma processing of semiconductor materials and has important consequences in the quality and yield of microelectronic components. In many plasmas, etching occurs at a faster rate near the periphery of the wafer, resulting in nonuniform removal of specific materials over the wafer surface. This research was to investigate in situ optical diagnostic techniques for monitoring etch uniformity during plasma processing of microelectronic components. We measured 2-D images of atomic chlorine at 726 nm in a chlorine-helium plasma during plasma etching of polysilicon in a parallel-plate plasma etching reactor. The 3-D distribution of atomic chlorine was determined by Abel inversion of the plasma image. The experimental results showed that the chlorine atomic emission intensity is at a maximum near the outer radius of the plasma and decreases toward the center. Likewise, the actual etch rate, as determined by profilometry on the processed wafer, was approximately 20% greater near the edge of the wafer than at its center. There was a direct correlation between the atomic chlorine emission intensity and the etch rate of polysilicon over the wafer surface. Based on these analyses, 3-D imaging would be a useful diagnostic technique for in situ monitoring of etch uniformity on wafers.