Formation of 45◦ silicon (110) surface using Triton X-n surfactants in potassium hydroxide for infrared applications

Abstract

Silicon (Si) micromirrors are an integral feature for many micro-optomechanical systems (MOEMS). Such mirrors are generally wet etched in alkaline solution at elevated temperature. For 90 beam steering applications, 45 slanted Si (110) plane is the prime choice fabricated with the incorporation of tensioactive surfactants. Here, Triton-Si and Triton-hydroxide (OH )/H O interaction using varying hydrophilic chain length Triton (X-45, X-100 and X-405) were investigated. The surfactant concentration was varied from 0 to 1000 ppm in potassium hydroxide (KOH). Triton molecules were shown to adsorb preferentially on (110) than on (100) surface. Longer chain length Triton hampered OH access to Si surface resulting in slower etch rate. In contrast, contact angle measurement suggested that shorter Triton interfaced better with Si surface. Later, Si wafers etched in Triton 10 ppm - KOH were examined. The measured output for (110)X-45, (110)X-100, (110) and polished Si wafer reference (R < 5Å) mirrors were 0.58, 0.76, 0.72 and 1.25 mW, respectively. Subsequently, Si-SiO thin film in [HLHL] -substrate configuration was fabricated. Broadband micromirror for use in 3.0-5.5 μm spectrum range was experimentally realized with reflected efficiency of 73%.