Impact of the doping concentration on the density of pores using metal-assisted chemical etch

Abstract

Metal-assisted chemical etch (MACE) of silicon substrate in an etchant containing HF and H2O2 with different HF–H2O2 molar ratio R (R = [HF]/([HF] + [H2O2]), where [HF] and [H2O2] are the concentration of HF and H2O2 in mol/L respectively) using silver particles as catalyst was studied. Boron doped p-type (100) silicon wafers with resistivity of 0.01 Ω·cm and 10.65 Ω·cm were used as substrates and etched in the etchant with R = 0.7. It was found that the density of pores on the silicon substrate with resistivity of 0.01 Ω·cm was higher than that with resistivity of 10.65 Ω·cm. A p-type (100) silicon substrate, which was heavily and non-uniformly doped with boron, with nominal resistivity of 0.0013 Ω·cm was processed by using MACE in etchant with different R’s. By comparing the densities of etched pores at different doping regions, we came to the conclusion that the density of pores increased with the increase of doping concentration and with the decrease of R. It was especially obvious in the range where the pore size was smaller than the average size of silver particles. The possible reason was proposed. Finally, we used the two-point probe measurement technique to measure the resistance of this silicon substrate and verified the doping non-uniformity in the microscopic scale. This research can be applied on the detection of doping uniformity on one single wafer.