The pattern dependence of selectivity in low pressure selective epitaxial silicon growth

The dependence of selectivity on HC1 flow and operating pressure for an 850° C SiH₂Cl₂/ HC1 based SEG process has been investigated. The polysilicon nuclei density (#/cm² measured by optical microscope) on large unpatterned areas of deposited SiO₂ was used to quantify the selectivity of different process conditions. Three distinct selectivity regimes were identified: (a) a non-selective regime with >10⁶ nuclei/cm², (b) a pattern dependent regime with <10⁶ nuclei/cm², and (c) an intrinsically selective regime with <1 nuclei/cm². The intermediate, pattern dependent, selectivity regime was characterized by a much lower density of silicon nuclei in and around patterned areas where windows of Si are exposed, thus making a loss of selectivity more difficult to detect. This phenomenon is shown to arise from feature scale (<100 micron) lateral fluxes of gas phase species. An intrinsically selective regime suitable for VLSI manufacturing, which avoids the high nuclei density associated with the pattern dependent regime, is identified.