THE PATTERN DEPENDENCE OF SELECTIVITY IN LOW-PRESSURE SELECTIVE EPITAXIAL SILICON GROWTH

The dependence of selectivity on HCl flow and operating pressure for an 850-degrees-C SiH2Cl2/2HCl 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 > 10(6) nuclei/cm2, (b) a pattern dependent regime with < 10(6) 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.