Surface polishing of rough (110) silicon plane by HNA etching resulting from wet anisotropic KOH etching

Abstract:
This paper reports a novel technique to polish the rough (110) silicon surfaces generated by anisotropic wet chemical etching in KOH solution by chemical polishing in the mixture of HF+HNO3+CH3COOH (HNA) in a ratio of 2:15:5. We smoothen and planarize rough post-etched (110) surface to make it suitable for further photolithography process to etch different height vertical sidewall 3D structures in (110) monocrystalline silicon using anisotropic wet chemical etching in KOH solution. We investigated different concentrations of KOH varying from 23wt%-50wt% at different etching temperatures in the range of 40deg C-122deg C followed by chemical polishing in different combination ratios of HNA. It is found that 47 wt% KOH at 122deg C followed by HNA combination in ratio 2:15:5 results in smooth and planar (110) surface. The etching in 47 wt% KOH at its boiling point temperature of ca. 122deg C, has an average roughness value of 130 nm. However, the chemical polishing step with the mixture of HNA in the ratio of 2:15:5 results in the most planar and smooth (110) surface with an average roughness of only 5 nm. Thereby the wafer is suitable for further photolithography process.