THE CHARACTERISTICS OF REACTIVE ION ETCHING OF POLYSILICON USING SF6/O2 AND THEIR INTERDEPENDENCE

An experimental study of the influence of individual process parameters on the characteristics of etched patterns has been made. Three crucial characteristics, viz. etch rate, selectivity and profile observed in the reactive ion etching of polysilicon patterns are analysed over the regions of stability of five process parameters. The etch rate is found to go through a maximum with (a) increasing rf power, (b) increasing oxygen content of the SF6 reactive gas, and (c) increasing interelectrode distance. A maximum followed by a minimum is observed in the etch rate with increasing pressure whereas the former shows a linear increase with total flow rate. Direct current bias, the unique feature of RIE, undergoes an independent variation with four of the five process parameters analysed. It is observed that the etching of polysilicon by atomic species [F0] in SF6 is governed only indirectly by the dc bias and the variations in etch rate map those in dc bias for only one parameter, viz. the etch pressure. Selectivity is found to attain its peak at medium values of rf power as well as etch pressure and at about 40% of oxygen in the etch chemistry. The etch profile undergoes a loss in anisotropy with increasing etch pressure and a loss in line width with increasing oxygen content.