Publication: Optimization of silicon-on-insulator (soi) wafer wet etching process by Using potassium hydroxide(koh) and tetramethylammonium hydroxide (TMAH)
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Date
2025-09-01
Authors
Sun Jiajing
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Abstract
Wet chemical etching of silicon-on-insulator (SOI) wafers in alkaline solutions such as potassium hydroxide (KOH) and tetramethylammonium hydroxide (TMAH) is widely used in microfabrication. While etch rate has often been emphasized, the effect of etching parameters on surface roughness and wettability is equally important. This work systematically investigated the influence of concentration(KOH25to65wt%, TMAH5to25wt%),temperature(40to90℃),and time(5to25mim) on SOI wafers etched in KOH and TMAH.For KOH etching, the optimum condition was identified at 35 wt%, 60 °C, and 25 min, producing the smoothest surface with AFM Ra = 1.144 nm, the lowest contact angle (36.34 °), with a remaining top silicon thickness of 35.4389 nm. For TMAH etching, the best result was obtained at 15 wt%, 70 °C, and 10 min, yielding Atomic Force Microscope Ra = 1.060 nm, profilometer Ra = 1.930nm, and a
favorable contact angle (28.28 ° ) while preserving 36.6643nm of top
silicon.Characterization by AFM, SEM, EDX, ellipsometry, and contact angle
measurements confirmed that smoother surfaces consistently correlate with lower contact angles. A comparative evaluation showed that KOH induced stronger surface modifications, whereas TMAH offered smoother and more uniform surfaces within its optimal window, making
it more compatible with Complementary Metal-Oxide-Semiconductor fabrication