Behavior of SiNx/SiO2 Double Layer for Surface Passivation of Compensated p-Type Czochralski Silicon Wafers

Abstract

Surface passivation of Czochralski (Cz) p-type compensated silicon using a hydrogenated silicon nitride/silicon oxide (SiNx-H/SiO2) double layer (hereinafter called SiNx/SiO2) has been investigated. The characteristics of the deposited films depended strongly on surface preparation, deposition process, and annealing parameters. Fourier-transform infrared (FTIR) spectroscopy was used to analyze the chemical bonds in the Si–SiNx/SiO2 structure, and quasi-steady-state photoconductance (QSSPC) measurements were used to evaluate the minority-carrier lifetime (τeff), to check the quality of the passivation. The results showed that, after SiNx/SiO2 double-layer deposition, τeff remained rather poor (13.29 μs). This low degree of passivation is principally due to the appearance of an inversion layer after oxidation, inducing switching of the semiconductor type at the surface. This inversion layer is due to the segregation properties of both boron and phosphorus impurities. This phenomenon was highlighted by secondary-ion mass spectrometry (SIMS) characterization, revealing a substantial phosphorus concentration near the Si–SiO2 interface and penetration of boron inside the oxide, with concentration of 1 × 1018 cm−3 and 4 × 1018 cm−3, respectively. Annealing at 400°C under low pressure of 3.34 × 10−3 kPa improved the minority-carrier lifetime to τeff = 15.94 μs, leading to enhanced surface passivation related to the reduced interface state density and improved statistical distribution of different bonding environments.