Applied Science and Convergence Technology 1997; 6(3): 275-281
Published online August 1, 1997
Copyright © The Korean Vacuum Society.
Cha-Keun Yoon,Hyun-Ho Doh,Ki-Woong Whang
Planar type inductively coupled plasma(ICP) etching system, where substrate can be cooled down to -150℃ with liquid nitrogen, has been applied to the gate polysilicon cryogenic dry etching using SF_6 gas. When SF_6 is used in conventional inductively coupled system, the electronegative characteristic of SF_6 gas makes the discharge unstable. In our experiments, an axial weak magnetic field (20 gauss) was applied to solve that problem. We examined the etch rate of the gate polysilicon and selectivity to the thermal oxide as a function of main RF power, gas pressure, and substrate temperature. The dependence of etching characteristics on the main RF power and gas pressure can be explained by the analysis of the inductively coupled SF_6 plasma parameters obtained by Langmuir probe. Cryogenic etching characteristics also can be explained by the difference of etching mechanism between polysilicon and thermal oxide. At the temperature of -100℃ and high gas pressure of 20 mTorr, we could obtain good etch rate and selectivity, but not the desired anisotropic etch Profile. We could obtain a perfect anisotropic etch profile of gate polysilicon with etch rate over 2000 Å/min and selectivity about 10:1 at the gas pressure of 5 mTorr, using only SF_6 gas and no bias to the substrate.