Volatile Cr Contamination Reduction in Atmospheric Pressure Chemical Vapor Deposition Systems by Selective Alloy Oxidation

Abstract

The dominant mode of transition metal contamination in atmospheric pressure chemical vapor deposition reactors constructed from a Cr-containing Ni alloy was found to be the generation of volatile Cr-containing species that condense on processed wafers. These compounds are generated in detectable amounts from hot Cr2O3 surfaces in a test apparatus at temperatures as low as 400 degrees C. Tests indicate that the predominant volatile species generated in an oxidizing ambient containing oxygen and water vapor is CrO2(OH)(2), in accordance with published literature. Controlled oxidation of reactor components made from an Al-containing Ni-based alloy has been found to produce a pure Al2O3 surface oxide, reducing the generation rate of volatile Cr-containing species by at least three orders of magnitude at temperatures up to 575 degrees C. Installation of a wafer conveyor belt made from an alumina-forming Ni alloy in a working atmospheric pressure chemical vapor deposition reactor in place of a belt made from a chromia-forming alloy reduced volatile Cr contamination levels on processed silicon wafers by as much as three orders of magnitude to about 10(10) atom/cm(2). This result demonstrates the compatibility of semiconductor processing equipment fabricated from alumina-forming Ni-based alloys with metal contamination levels acceptable for sub-0.25 mu m device geometries.