Effect of process parameters on sidewall damage in deep silicon etch

Sidewall damage caused in deep reactive ion silicon etch was investigated by varying etch cycle time, bias power, etch pressure and SF 6 flow rate using the Bosch process in a uniquely designed, inductively coupled plasma reactor. The effects of these process parameters on the etch profile and sidewall angle were also studied for high density metal–insulator–metal capacitor structure. By choosing the proper etch cycle time of 2 s, it was observed that the sidewall damage was very sensitive to these etch process parameters. As bias power increased, the sidewall damage increased gradually. Especially, at the bias power of 500 W, a dual bowing shape with severe sidewall damage was seen, which might be due to a combination of two mechanisms: the formation of a redeposition region and a secondary ion etch effect. With increasing pressure, the sidewall damage was not always located in a specific depth range but distributed along almost the whole trench sidewall. An etch pressure below 80 mTorr was favorably recommended for reducing the extent of the sidewall damage. In addition, we found that an appropriate SF 6 flow rate was also very beneficial to the realization of a smooth trench sidewall when it was controlled within an appropriate range. Based on these investigations, an acceptable etch condition could be selected to achieve a nearly vertical etch profile as well as a smooth sidewall surface.