STUDIES OF THE EFFECTS OF NF3 ON THE GROWTH OF POLYSILICON FILMS BY LOW-PRESSURE CVD .3. EFFECT ON COMPOSITION

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.