Crystalline silicon etching in quiescent concentrated aqueous HF solutions

The behaviour of n- and p-type crystalline silicon wafers in quiescent concentrated aqueous HF solutions has been studied for immersion times up to 205 days. The etch rate, as determined from weighing experiments, decreased with time to values as low as after prolonged etching. The experimental findings are consistent with the view that the oxidation of the hydrogenated Si surface is the rate-limiting step, which is most likely carried out via a hydroxyl ion until the defect-poor surface becomes predominantly oxidized by direct attack of HF molecules. The formation of a new type of etch pit has been observed in weakly doped p-type Czochralski-grown material.