Nonlinear two-layer model for photocarrier radiometry of ion-implanted silicon wafers

Xiaoke Lei,Jing Wang,Qiming Sun,Chunming Gao,Bincheng Li

doi:10.1063/1.5092621

Xiaoke Lei, Jing Wang + Show 3 more

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https://doi.org/10.1063/1.5092621

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Abstract

A nonlinear two-layer model was developed to describe and analyze Photocarrier Radiometric (PCR) signals of ion-implanted Si wafers which are intrinsically nonlinear with excitation laser power. The thickness of the implantation layer and the optical/electronic damage threshold for different implantation doses were estimated using the Monte Carlo method and the effective medium approximation theory, respectively, which can provide key parameter values for the model to calculate the nonlinearity coefficient, defined as the slope of PCR amplitude versus excitation power in log-log scale. Experimentally, the nonlinearity coefficients of seven c-Si wafers with implantation doses from 1011 to 1016 cm-2 were measured at two different excitation wavelengths (830 and 405 nm), and good agreement between theory and experiment was found. Results show that the nonlinearity coefficient has a negative correlation with the implantation dose, and the coefficient measured at 405 nm is consistently smaller than that measured at 830 nm for each sample. Compared with the conventional PCR models, the nonlinear two-layer model proposed here is more coincident with experimental facts, thus enabling PCR to provide more accurate quantitative characterization of the carrier recombination and transport properties of ion-implanted semiconductor wafers.

Highlights

Ion implantation is a widely used doping technology in modern semiconductor manufacturing industry
Contactless and nondestructive characterization techniques with high sensitivity are preferred for in-line inspection, such as modulated optical reflectance,2,3 photo-modulated thermo-reflectance,4,5 photothermal radiometry,6,7 photocarrier radiometry (PCR),8,9 and modulated free carrier absorption
Abundant experimental evidence showed that the nonlinearity of PCR amplitude versus excitation power generally exists for Si materials and devices

Summary

INTRODUCTION

Ion implantation is a widely used doping technology in modern semiconductor manufacturing industry. As a result, compared with the aforementioned photothermal-based techniques, PCR signals purely reflect electronic properties of materials, having higher sensitivity in terms of characterizing the carrier recombination and transport properties (carrier lifetimes, diffusivity, surface recombination velocities etc.) of semiconductor materials and devices.. Scitation.org/journal/adv usually between 1 and 2, and has a positive correlation with wafer resistivity. These works improved the theoretical rigor of the PCR methodology in terms of nonlinearity; only the single-layer nonlinearity was considered in these models, not applicable for ion-implanted semiconductor samples. By using the Monte Carlo method and the effective medium approximation theory, the thickness of the implantation layer and the optical damage threshold under different implantation doses were estimated and used as input parameters for the calculation of the nonlinearity coefficients of Si wafers with implantation doses from 1011 to 1016 cm-2. The influence of the optical excitation wavelength on the nonlinearity coefficient was investigated both theoretically and experimentally

THEORY

EXPERIMENTAL

RESULTS AND DISCUSSIONS

CONCLUSIONS