CARBON AND OXYGEN REMOVAL FROM SILICON (100) SURFACES BY REMOTE PLASMA CLEANING TECHNIQUES

A hydrogen plasma-based technique for carbon removal has been combined with a modest anneal for oxide desorption at 720-degrees-C to produce atomically clean Si(100) 2 X 1 surfaces. Carbon and oxygen contamination can be removed from silicon surfaces by a 30 s hydrogen plasma exposure at 480-degrees-C (for carbon removal) followed by a 5 min anneal in molecular hydrogen at 720-degrees-C (for oxygen removal). Surface hydrocarbon removal is thought to occur by volatilization through hydrogenation. The mechanism for oxygen removal is believed to be more straightforward and consist of thermal desorption of SiO at approximately 700-degrees-C. Hydrogen plasma exposures on the order of 5 min are seen to induce microscopic surface roughness without complete oxygen elimination. Samples which are devoid of oxygen following the 720-degrees-C anneal are found to reoxidize upon re-exposure to the hydrogen plasma. The origin of the oxygenating species is unclear, but likely sources include, SiO or OH from tube wall erosion, or contamination produced by interactions of atomic hydrogen with the chamber walls. A subsequent anneal at 720-degrees-C effectively removes any surface reoxidation. Anneals at 720-degrees-C with carbon present on the surface results in a surface reaction which complexes the carbon and oxygen on the surface, rendering the surface contamination resistant, under nominal conditions, to subsequent plasma processing or annealing.