The Effect of Doping Atoms on the Kinetics of Self‐Limiting Tungsten Film Growth on Silicon by Reduction of Tungsten Hexafluoride

Abstract

The reaction of with a Si substrate plays an important role in the metallization of Si active areas by tungsten chemical vapor deposition (W‐CVD). At typical low pressure W‐CVD conditions, this reaction leads to self‐limiting growth of a W film. The reaction, which takes place at the film surface, is maintained by Si diffusion through the W film, and stops when the (rapid) supply of silicon becomes rate limiting. Although the mechanism controlling the reduction of by intrinsic Si is reasonably understood, little is known about the influence of doping atoms in the Si substrate. In this paper we describe the effect of doping atoms on the growth kinetics of tungsten films deposited by the reaction of with highly doped Si at temperatures ranging from 275 to 360°C. Doping atoms can have a large effect on the self‐limiting time of the reaction, the self‐limiting thickness of the W film, and the rate of the reaction. Similar to undoped Si substrates, depositions on As‐doped n+ Si are controlled by gas‐phase diffusion and the self‐limiting effect occurs earlier than on undoped Si; the W growth rate on N+ Si is linear in pressure and almost independent of temperature. On B doped p+ Si the reaction rate is decreased to such an extent that this surface reaction becomes rate limiting, instead of the gas‐phase diffusion; the W growth rate on p+ Si is thermally activated and independent of the pressure. The results obtained with the doped Si substrates are discussed in the light of a model for self‐limiting W film growth on undoped Si substrates.