Profile control in isotropic plasma etching

The possibility of controlling the lateral-to-vertical etch ratio of undoped dielectric material is tested. The Lam Research Rainbow 4500i, configured with a downstream isotropic plasma etch chamber, was used for the study. The tetra-ethyl-ortho-silicate (TEOS) isotropic etch profile was examined as a function of process parameters in order to establish trends of isotropic etch profile. A fractional-factorial matrix, with parameters of pressure, power, gas flow, and temperature, was performed. A series of tests varying pressure over a large range were run to confirm the results obtained from the matrix. It was observed that the chamber pressure has the most impact on the isotropic etch profile. The lowest lateral:vertical etch ratio was obtained when both the chamber pressure and wafer paddle temperature were lowered. The highest ratio occurred when wafer was etched at high chamber pressure. The lateral:vertical ratio of the isotropic etch profile could be reduced as much as 30% by baking the wafer at 110°C for 30 minutes prior to isotropic etch. The study showed that it is possible to affect the TEOS isotropic etch profile when a downstream plasma etcher is used