Electrochemical etch-stop characteristics of TMAH:IPA:pyrazine solutions

In this paper, the authors present the electrochemical etch-stop characteristics of single-crystal silicon in tetramethyl ammonium hydroxide (TMAH):isopropyl alcohol (IPA): pyrazine solutions. 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 open circuit potential (OCP) and passivation potential (PP) of n- and p-type silicon were 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 microdiaphragms of 20 mum thickness on a 5-inch silicon wafer. The average thickness of 801 microdiaphragms fabricated on one wafer was 20.03 mum and the standard deviation was +/-0.26 mum. The silicon surface of the etch-stopped microdiaphragm was extremely flat with no noticeable taper or nonuniformity. The benefits of the electrochemical etch-stop method for the etching of silicon in TMAH:IPA:pyrazine solutions become apparent when reproducibility of microdiaphragm thickness for mass production is realized. The results indicate that use of the electrochemical etch-stop method for the etching of silicon in TMAH:IPA:pyrazine solutions provide a powerful and versatile alternative process for fabricating high-yield silicon microdiaphragms.