Effects of Plasma Molding on Feature Profile of Silicon Micro-Electro-Mechanical Systems through Flux Ion Velocity Distributions in Two-Frequency Capacitively Coupled Plasma in SF6/O2

Abstract

We numerically investigated large-scale Si etching of several hundreds of micrometers such as that used in micro-electro-mechanical systems (MEMS) fabrication. This was carried out in SF6 (83%)/O2 at 300 mTorr in two-frequency capacitively coupled plasma using an extended VicAddress. We estimated the plasma molding's local characteristics including potential distribution and flux ion velocity distribution adjacent to an artificial microscale hole pattern. The sheath thickness is comparable to or even smaller than the size of the hole, and the sheath tends to wrap around the hole on a Si wafer. The distorted sheath field caused by the plasma molding directly affects the incident ion flux velocity distribution. The incident angle of SF5+ ions with a low energy strongly deviates from the normal surface at the hole's edge. The ion flux becomes radially nonuniform in the vicinity of the hole pattern, suppressing anisotropy of the etch profile. The feature profile of the Si hole indicates that the etching is enhanced particularly at the bottom corner and sidewall.