Study of the Silicon Etch Rate and Mechanisms When Using Aluminium, Tin and Copper Electrodes

Abstract

Silicon plasma etching is an important technique in the fabrication of integrated circuits and micro-electronic-mechanical systems. The influence of three electrode materials, aluminium, tin and copper, on the silicon etch rate was studied in a capacitively coupled plasma system. When applying SF6 plasmas, the etch rate was, in general, highest when using a tin electrode and lowest with a copper electrode. But with a CF4 plasma, the etch rate was highest for the aluminium electrode and lowest for the tin electrode. Rutherford Backscattering Spectroscopy indicated that for both plasmas, a very thin and stable aluminium fluoride film was formed on the aluminium electrode; for SF6 plasmas, S was adsorbed or absorbed by the tin electrode, liberating more free fluorine, while copper consumed fluorine and for CF4 plasmas, both copper and tin electrodes consumed fluorine. These mechanisms could explain the differences in the silicon etch rates for the three electrode materials.