Determination of low concentrations of N and C in CZ-Si by precise FT-IR spectroscopy

Abstract Adding of relatively small amounts of N and C, on the order of 1 × 10 14  cm −3 in the growing crystals of Czochralski Si (CZ-Si) is considered now as a tool for the control of the internal gettering processes based on the precipitation of oxygen. The sensitivity of the conventional procedure of measurements by Fourier transform infrared (FT-IR) spectroscopy measurements is not sufficient to determine, in a reliable manner, such concentrations of N and C. This report contains results of the implementation of the modified method of FT-IR measurements, which allows one to improve the sensitivity for more than one order of magnitude. The new method is based mainly on (1) the modified FT-IR system with enhanced photometric accuracy achieved by a suppression of the influence of the instabilities, and (2) using Brewster geometry to suppress the interference effects. The method contains built-in checking of the achieved accuracy of the recorded spectrum. The examples of the determination of [N] and [C] on the 10 14  cm −3 -level in 2 mm thick samples as well as in industrial wafers are presented.