Impurity contact diffusion in semiconductor

Abstract

This work introduces an approach to solve the problems encountered in semiconductor device fabrisation, difficulties of low concentration control, complexity and toxicity of traditional impurity diffusion processes. Doped silicon dioxide film as a diffusion source was formed through heat-treatment of mixture of dimethylpolysiloxane which was dissolved in $CCl_4$ and phosphorus pentoxide which was dissolved in ethanol, coated on the surface of a semiconductor wafer with a spinner. The heat-treatment temperature and time were 700$^\circ$C and 7 minutes, respectively. And the diffusions were performed at the temperature of 1000$^\circ$C, 1050$^\circ$C, 1100$^\circ$C, 1150$^\circ$C, and 1200$^\circ$C. As results, the spinning speed of 4000 RPM and the gas composition of 10\% $O_2$ - 90\% $N_2$ in the heat-treatment atmosphere were the best conditions to obtain the phosphorus-doped silicon dioxide film of about 2000$\mbox{\AA}$ - thick as a diffusion source. And the total gas flow rate was at 1000 CC/min. The doped oxide gave constant surface concentration of $2\times10^{18}/cm^3$ for 10 hour diffusion time in the range of diffusion temperature of 1000$^\circ$C to 1200$^\circ$C in $N_2$ diffusion atmosphere. The diffusivities for surface concentration of $2\times10^{18}/cm^3$ were $$(6.75\pm1.75)\times10^{-15}cm^2/sec\;\;at\;\;1000^\circ{C},$ $$(3.26\pm0.39)\times10^{-14}cm^2/sec\;\;at\;\;1050^\circ{C},$ $$(7.35\pm0.88)\times10^{-14}cm^2/sec\;\;at\;\;1100^\circ{C},$ $$(3.05\pm0.36)\times10^{-13}cm^2/sec\;\;at\;\;1150^\circ{C},$$ and $$(8.14\pm0.65)\times10^{-13}cm^2/sec\;\;at\;\;1200^\circ{C},$$ The most powerful advantages over the present method over traditional diffusion method are 1. the fact that it is easy to control very low surface concentration (down to $5\times10^{15}/cm^3$) and 2. uniformity of the impurity distribution The diffusivity for surface concentration of $5\times10^{15}/cm^3$ was $(1.35\pm0.27)\times10^{-13}cm^2$/sec at 1150$^\circ$C in $N_2$ di...