Anisotropic etching and electrochemical etch-stop properties of silicon in TMAH:IPA:pyrazine solutions

Abstract

Anisotropic etching and electrochemical etch-stop properties of single-crystal silicon in tetramethylammonium hydroxide (TMAH): isopropyl alcohol (IPA) solutions containing pyrazine were investigated. With the addition of IPA to TMAH solution, an improvement in flatness on the etching front and a reduction in undercutting were observed, but the etch rate on (100) silicon decreased. However, the (100) silicon etch rate is improved by the addition of pyrazine. An etch rate of 0.8 μm/min on (100) silicon, which is faster by 13% than a 20 wt.% solution of pure TMAH, is obtained using 20 wt.% TMAH:0.005g/ml pyrazine solutions, but the etch rate on (100) silicon is decreased if there is an increase in the amount of pyrazine in the solution. With the addition of pyrazine to a 25 wt.% TMAH solution, no significant variations in flatness on the etching front were observed and the undercutting ratio was reduced by 30∼50%. The addition of pyrazine to TMAH:IPA solutions increased the etch rate of (100) silicon, thus the time required by the etch-stop process was shortened. The current-voltage (I–V) characteristics of n- and p-type silicon in TMAH:IPA:pyrazine solutions were obtained. The passivation potential (PP) of n- and p-type silicon was obtained and the applied potential was selected between n- and p-type silicon PPs. The electrochemical etch-stop method was applied to the fabrication of 801 silicon microdiaphragms of 20 μm thickness on a 5-inch silicon wafer. The average thickness of fabricated 801 microdiaphragms on one wafer was 20.03 μm and the standard deviation was ±0.26 μm. The silicon surface of the etch-stopped microdiaphragms was extremely flat with no noticeable taper or non-uniformity. The benefits of the electrochemical etch-stop method for the anisotropic etching of silicon in TMAH:IPA:pyrazine solutions become apparent when reproducibility of silicon microdiaphragm thickness for mass production is realized. The results indicate that use of the electrochemical etch-stop method for the anisotropic etching of silicon in TMAH:IPA:pyrazine solutions provides a powerful and versatile alternative process for fabricating high-yield silicon microdiaphragms.