Effect of mechanical agitation and additives on the anisotropic etching of silicon by using a TMAH based solution

The anisotropic etching properties of single crystal silicon with the Tetramethyl ammonium hydroxide (TMAH) solution were investigated. The variations in Si etching rate and surface morphology at different etching temperatures and TMAH concentrations were evaluated. The effects of different additives and solution agitation were also discussed. As the THAM concentration (1025 wt%) decreased, the etching rate increased from 10 μm/h to 70 μm/h in the range of 7090 °C. However, the etched surface roughness was degraded as the hillock density and corner undercut ratio increased. To solve these problems, the agitation and wafer holder direction were changed and two additives (Pyrazine and Ammonium Persulfate (AP)) dissolved in the TMAH solution. Experimental results showed that additives played an important role to increase the etching rate significantly up to 20% and the change of agitation led to smooth etched surface. Hillock formation was also suppressed by adding these additives and changing agitation direction.