In the ongoing enhancement of MEMS applications, the STS Advanced Silicon Etch, ASE(TM), process satisfies the demanding requirements of the industry. Typically, highly anisotropic, high aspect ratios profiles with fine CD control are required. Selectivities to photoresist of 150:1 with Si etch rates of up to 7 mu m/min are achievable. Applications range from shallow etched optical devices to through wafer membrane etches. This paper details some of the fundamental trends of the ASE(TM) process and goes on to discuss how the process has been enhanced to meet product specifications. Parameter ramping is a powerful technique used to achieve the often conflicting requirements of high etch rate with good profile/CD control. The results are presented in this paper. (C) 1999 Elsevier Science S.A. All rights reserved.