Anisotropic etching of silicon in TMAH solutions

• Published in: Sensors and actuators. A, Physical Physical, 1992-07, Vol.34 (1), p.51-57
• Main Authors: Tabata, Osamu, Asahi, Ryouji, Funabashi, Hirofumi, Shimaoka, Keiichi, Sugiyama, Susumu
• Format: Article
• Language: English
• Subjects: Applied sciences; Electronics; Exact sciences and technology; Microelectronic fabrication (materials and surfaces technology); Semiconductor electronics. Microelectronics. Optoelectronics. Solid state devices
• ISSN: 0924-4247; 1873-3069
• DOI: 10.1016/0924-4247(92)80139-T

Detailed characteristics of tetramethyl ammonium hydroxide (TMAH, (CH 3) 4NOH) as silicon anisotropic etching solutions with various concentrations from 5 to 40 wt.% and temperatures from 60 to 90 °C have been studied. The etch rates of (100) and (110) crystal planes decrease with increasing concentration. The etched (100) planes are covered by pyramidal hillocks below 15 wt.%, but very smooth surfaces are obtained above 22 wt.%. Etch rates of 1.0 μ/min for the (100) plane and 1.4 μ/min for the (110) plane at 90 °C are obtained using a 22 wt.% solution. The etch-rate ratio of (111)/(100) varies from 0.02 to 0.08. The etch rate of thermally oxidized SiO 2 is almost four orders of magnitude lower than that for (100) and (110) planes. The etch rates of aluminium are reduced by dissolving silicon in TMAH solution. Etch-stop techniques using a heavily boron-doped layer or p—n junction prove to be applicable to TMAH solutions.