A comparative study and optimal choice of the method of determination of interstitial oxygen-in-silicon concentration from optical transmission spectra

摘要

Currently, the commonly used method for determination of interstitial O-in-Si concentration, N_(ox), which is responsible for defect formation in very different types of semiconductor devices, is measuring optical transmission spectra of silicon wafers in the 8 to 11 μm band. The N_(ox) value is extracted from the experimental data by use of standardized algorithms assuming quasi-continuous sequence of spectral transmission samples are available. According to USA standard (ASTM F951-96) such a procedure is assumed to be applied to the separate wafer's area regions with the diameter of about 7 mm. However, the very much better spatial resolution (up to 30-50μm) is desired under the condition of progressive decreasing of basic element's characteristic size. To do this, one cannot use the standard algorithms assuming quasi-continuous sequence of spectral samples being available in relatively wide (～3μm) spectral band, because of unrealistic times the measurements requires for. For to choose more economical algorithm of extracting the N_o value we have compared several proposed calculation methods, which are based upon moderate numbers of spectral samples. As the input test data set for the calculations, the series of experimental samples were taken with the step in wavelength of 0.05μm obtained on the silicon wafers of different thickness (0.4-2 mm) and of various N_(ox). The results show that the algorithms using small number of samples(one or two), being optimized properly, do not yields to the standard time-consuming procedure.