SELECTIVITY MECHANISMS IN LOW-PRESSURE SELECTIVE EPITAXIAL SILICON GROWTH

Selective silicon processing at 775 and 850-degrees-C using an SiH2Cl2 /HCl/H-2 based chemistry was studied. The selectivity of each experime ntal condition was quantified by measuring the silicon nuclei density/ cm2 on large blanket areas of SiO2. The morphology of the selective si licon films was examined for texture and hillocks. The roles of water vapor and atomic hydrogen on the microchemistry of an SiO2 surface was investigated. Thermodynamic modeling of the effect of different atmos pheric leak rates on the water vapor and atomic hydrogen concentration s was carried out with the aid of the SOLGAS program. A new understand ing of selectivity is proposed. An SiO2 surface is an interruption of the bulk continuous random network structure and, as such, has a chara cteristic density of def ect sites. The degree of selectivity observed is determined by the type of species which terminate these defect sit es, i.e., by the number of defect sites which are not chemically passi vated against the adsorption of silicon species. A universal selective silicon processing regime is predicted and good agreement with a wide range of published selective silicon processes is shown.