Study on the impact of silicon doping level on the trench profile using metal-assisted chemical etching

Abstract

Metal-assisted chemical etching (MACE) has been used as a promising alternative method to fabricate micro/nano-structures on silicon substrates inexpensively. In this paper, profiles of deep trenches on silicon substrates, with different doping levels, fabricated by MACE were studied. A layer of interconnected gold islands was first deposited onto the silicon substrate as catalyst. Electrochemical etching was then performed in a hydrofluoric acid (HF) and hydrogen peroxide (H₂O₂) mixture solution with different HF-to-H₂O₂ ratio ρ (ρ = [HF]/([HF] + [H₂O₂])). Vertical deep trenches were fabricated successfully by using this method. It was observed that even under identical experimental condition, sidewalls with various tilting angles and different morphology could still form on silicon substrates with different resistivity. This possibly because with different resistivity silicon substrate, the gradient of holes in it greatly changed, and so did the final morphology. As a result, the tilting angle of etched trench sidewall can be tuned from 6° to 96° using silicon substrates with different resistivity and etchants with different ρ. By applying the angle-tuning technique revealed in this study, high aspect ratio patterns with vertical sidewalls could be fabricated and three-dimensional complex structures could be designed and realized in the future.