Tetramethyl Ammonium Hydroxide Etchant Improvement for Aluminum Passivation and Smooth of Silicon Surface

This paper purpose to the structural design and improvement of etchant solution for U-shaped MetalSemiconductor-Metal (UMSM) photodetector fabrication on Al/n-Si/Al with anisotropic wet etching technique, the etchant solutions include tetramethylammonium hydroxide (TMAH), ammonium persulfate (AP) and silicic acid with different concentrations. Experimental design of photodetector structure to optimize the photodetector and improvement conditions of the etching solution by adding AP and silicic acid into the TMAH solution to increase the silicon surface roughness and reduce the rate of etching aluminum as electrodes. For structural design experiments, increasing the exposure area on the U-shaped groove up to 1.73 times. The results from the addition of AP to TMAH solution showed that the silicon surface is smoothness. It has a highest silicon etching rate and the addition of silicic acid to TMAH solution can reduce aluminum and silicon dioxide etching rate. Therefore, this research has the effective condition is 5 wt% TMAH with 7 g/l AP and 34 g/l silicic acid added. The results show the silicon surface has smooth about 5 nm and high silicon etch rate including etching aluminum equal to 0.26 μm/hr that suitable for design photodetector in further research.