THE DEPENDENCE OF ETCH RATE OF PHOTO-CVD SILICON-NITRIDE FILMS ON NH4F CONTENT IN BUFFERED HF

The influence was studied of the concentration of ammonium fluoride (NH4F) on the etch rates of silicon nitride films deposited by the mercury-sensitized photochemical vapour deposition method. The composition of the buffered HF was varied between 0 and 40 weight percent (wt%) NH4F with 2 to 12 wt% hydrofluoric acid (HF). The etch rates as a function of buffered HF composition were measured for films deposited under various process parameters, viz. reactant gas ratio, substrate temperature and chamber pressure. The results of etch rates as a function of process parameters were correlated to variations in material density and silicon content (Si/N ratio) in the films.