Studies of the effects of NF3 on the growth of polysilicon films by low-pressure CVD. Part 3.—Effect on composition

Abstract

A range of analytical techniques (FTIR, SIMS, AES, SNMS, XPS) has been used to study the effect of adding NF₃ to an LPCVD gas mixture of SiH₄–He on the composition of the resulting as-deposited and annealed polysilicon. Comparisons have been made with CVD silicon nitride and with polysilicon deposited in the absence of NF₃. It has been shown by all the techniques used that for LPCVD in the presence of NF₃, nitrogen is incorporated into the layer, but quantitative analysis with SNMS and XPS shows that such films are very similar to polysilicon and contain less than ca. 5 atom% of nitrogen. FTIR and SIMS also have revealed the presence of fluorine in as-deposited layers from LPCVD with NF₃, but results from SIMS suggest that its concentration is very low and decreases by a factor of about two on annealing. It is concluded that while polysilicon deposited in the presence of NF₃ does contain small quantities of N and F, nevertheless the material may have interesting properties, with the use of NF₃ improving the surface quality.