Study on the impact of Fe₃O₄@Au magnetic nanoparticles in metal-assisted chemical etching

Metal-assisted chemical etch (MACE) has received more and more attention due to its low cost and simple process. Ag, Au, Pt and other noble metals can be used as catalyst in the MACE of silicon. In this paper, MACE on silicon in a hydrofluoric acid (HF) and hydrogen peroxide (H 2 O 2 ) mixture with different HF-to-H 2 O 2 molar ratio R (R = [HF]/([HF] + [H 2 O 2 ])) with Fe 3 O 4 @Au core–shell magnetic nanoparticles (MNPs) as catalyst under an external magnetic field was investigated. Boron doped p-type (100) silicon wafers with resistivity of 20∼30 Ω · cm and 0.01∼0.03 Ω · cm were used as substrates, respectively. We observed that an average etching rate of 5.17 μ m min −1 under an applied magnetic field while the average etching rate was 4 μ m min −1 without magnetic field. The factors were investigated that affect the average etched depth in silicon substrate under magnetic field by using MACE. The relationship between the average etching depth and etching time, resistivity of silicon substrate, ratio R, and the concentration of Fe 3 O 4 @Au magnetic nanoparticles was also studied. This result can be applied to increase the etching rate of silicon to fabricate a variety of devices, where high aspect ratio silicon structure is demanded.