Kinetics of Phosphorus Predeposition in Silicon Using POCl3

Abstract

Phosphorus predeposition in silicon using a POC13 source and oxidizingconditions has been studied over a wide range of temperature (850~176and doping gas compositions, by determining the total and electricallyactivedopant and the thickness of the surface oxide. The dependence of thefractionof electrically inactive phosphorus on temperature, time, and dopinggascomposition was studied; and it is reported that phosphide precipitationtakesplace in the course of the predeposition. These observations leadto the conclusionthat the flux of phosphorus is not limited by the solubility of thiselement in silicon, and this is confirmed by the results of the studyof thekinetics, which are reported. They show that the rate-determiningprocess ofphosphorus predeposition and the associated oxide growth is the diffusionacross the oxide layer. The amount Q of dopant predeposited in anisothermalprocess increases with a parabolic time lawQ -- ~/Ko exp ( -EK/ kT) 9tand a simil~ar behavior is observed for the oxide thicknessXo : ~/Bo exp ( - -EB/kT) 9tIt is shown that EK and EB are constants in a wide range of experimentalconditions, and the dependence of Ko and Bo on gas composition isreported.A method, based on surface resistivity measurements after drive-in,whichprovides quantitative determinations of the predeposited phosphorusin satisfactoryagreement with activation analysis, is reported in the Appendix.