Study of the relationship between metal-assisted chemical etching and direction of the applied electric field

摘要： Metal-assisted chemical etching (MACE) has been proposed as a promising alternative for the fabrication of micro/nano-structures on silicon with simple process and low cost. Electric field can be applied during the reaction to control the motion of charged particles so as to accelerate the reaction and form uniform vertical trenches with high aspect ratio. In this paper, boron doped p-type (100) silicon wafers with resistivity of 20～30 Ω·cm was used as substrates. After coated with layers of 5 nm Ti and 10 nm Au, the silicon substrate was immersed into the etchant containing hydrofluoric acid (HF) and hydrogen peroxide (H2O2) with high HF-to-H2O2 concentration ratio (ρ) and an applied voltage of 40 volts. It was found that the direction of the applied electric field had a great influence on morphologies of the trenches. Deeper trenches with vertical sidewalls and relatively smoother bottom were observed when silicon substrate was connected to cathode of the power supply. Possible interpretation to these phenomena was proposed, and the effect of the electric field intensity and doping concentration was further studied.