Wet Chemical Etching of GaAs Via Hole Using Phosphoric Acid Mixture

We report the wet chemical etching of GaAs to form a via hole using different ratios of phosphoric acid mixture. The GaAs substrate was cleaned with the RCA method of prior pattern transfers. The via hole pattern transfer onto the substrate uses the electron beam lithography (EBL) technique with PMMA as an electron beam sensitive resist. We used different H2O ratios 1:1:25, 1:1:10 and 1:1:5. The GaAs substrate was etched for 5, 10 and 34 minutes for each phosphoric mixture ratio. The etching rate was calculated from the etching depth using an optical profiler meter. A phosphoric acid mixture with ratio 1:5 at 10 minutes of etching time was found to give the highest etching rate for a GaAs wafer without pattern deformation after the etching. This phosphoric acid mixture with ratio 1:1:5 gives an average etching rate of 0.91 μm/min with a total via hole depth 9.53 μm.