A study of various methods for the analysis of the phophosilicate glass layer

Abstract

The understanding and therefore the optimization of n+-emitter formation in crystalline silicon using POCl3-diffusion requires a more detailed knowledge of the dopant source: the PhosphoSilicate Glass (PSG) layer. The growth of PSG during the phosphorus diffusion process depends on several process parameters, such as temperature, duration, POCl3-N2 and O2 gas flows. In this work, we compare the uncertainties in various methods for PSG thickness measurements: by an Atomic Force Microscope (AFM), a profilometer, a Scanning Electron Microscope (SEM) and a spectroscopic ellipsometer. We then quantify how the PSG thickness is influenced by the process parameters. We also measure the total amount of phosphorus (P-dose) in the PSG layer using Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES) and quantify the P dose in dependence of the process parameters as well. Finally, by combining both the measured PSG thickness and the dose, we successfully determine a lower limit for the phosphorus concentration in the PSG layer. It is, depending on the process parameters, between 7x1021 cm-3 and 1.2x1022 cm-3, which is a remarkably narrow range. These results will help to improve the phosphorus diffusion model by considering both the PSG growth behavior and PSG composition, and so will facilitate the development of a predictive model for the POCl3 diffusions process.