M.Sc Thesis

M.Sc StudentSidorov Elena
SubjectControlled Plasma Etching of Silicon
DepartmentDepartment of Chemistry
Supervisors PROFESSOR EMERITUS Chaim Yarnitzky (Deceased)


This thesis summarizes results obtained during experimental studies of reactive ion halogen plasma etch processes of silicon, which find applications in the fabrication of micro mechanical devices. In systematic studies the influence of various parameters (etching mask material, active halogen particles precursors, pressure, gas additives, gas flow, electrode power, and different processes combinations including cycling) on etch result were examined. Their influence on etch rate, etch profiles, aspect ratio, and surface morphology was determined.

The final aim of this work is the process of dry silicon etching development to obtain near vertical sidewalls for deep structures. Silicon etching t has been performed in a PlasmaTherm 790 RIE system. Micro-machining process - deep anisotropic etching with high aspect ratio has never been reported in this system. There are several mechanisms of dry etching running in together during one process: absorption of plasma particles on the substrate surface, chemical reactions of substrate with free radicals (chemical etching), desorption of volatile products, nonvolatile products film growth (passivation) and mechanical sputtering of substrate by direct ions bombardment (physical etching).  In order to obtain acceptable etch rate and anisotropy an optimal combination of different plasma processes was determined.

An efficient plasma chemistry, operating pressure, and gas flow rate for obtaining maximal etch rates and maximal anisotropy were determined for this system. In order to achieve highest anisotropy compositional process was developed. This process includes repetitions of SF6 etching - oxygen passivation cycles. The optimized parameters result 0.98 anisotropy.