Erik M. Freer

Silicon-Wafer Cleaning with Aqueous Surfactant-Stabilized Gas/Solids Suspensions

bLam Research Corporation, Fremont, California 94538, USA As feature sizes in the microelectronics industry diminish, cleanliness becomes an ever more important requirement. In response to these challenges, a novel wet-cleaning technology was developed at Lam Research Corporation to remove strongly adhered contaminants. An alkaline, foamed aqueous dispersion of insoluble platelet solids flows in linear shear past a particle-contaminated surface. Contaminant removal increases with solids concentration, foam quality, process time, and shear rate and can approach 100%. Particle-removal experiments indicate that dispersed solids are necessary for contaminant removal. Exponential decline of adhered particles with number of immersion/withdrawal events and a linear increase in the rate of particle removal with solids concentration indicate that the removal mechanism is binary collision between the insoluble fatty-acid platelets and Si3N4 contaminant particles. Foam or surfactant solution alone is not effective in particle removal. A binary-collision rate model is derived to relate particle detachment to contact time. The binary-collision rate law agrees well with experimental removal data and provides a powerful design tool to assess the role of cleaning parameters, including process time, shear rate, dispensing flow rate, system geometry, solids concentration, and foam quality.