Effect of cations on silicon anisotropic etching process in solutions containing TMAH and TMAH with tensioactive compounds

Abstract

Almost everything has been written on silicon anisotropic etching in alkaline solutions, however, the difference between etching in pure KOH and TMAH as well as in these solutions containing tensioactive compounds has not been completely elucidated yet. This paper present the results of anisotropic etching of Si(100) and Si(110) in the solutions containing two etching agents, KOH and TMAH. Due to this it is possible to control the effect of concentration of each agent on the course of etching and clarify the effect of cation type (inorganic and organic) on the course of the process. The effect of TMA+ ions on etch rate of Si(100) has already been proven both during etching in pure TMAH as well as after addition of tensioactive compounds to this solution. It results in a change in anisotropy ratio (R(110)/R(100)) in TMAH containing solutions in comparison to solutions based on KOH. As the commonly used KOH concentrations (5–10 M) are larger than those of TMAH 25 % (2.7 M), the concentration range of the studied TMAH solution has been extended to 50 %. The paper describes the properties of those concentrated TMAH solutions, both pure and containing surfactants.