A Method for Simulating Spray Pyrolysis Deposition in the Level Set Framework

The ability to deposit a thin tin oxide film on CMOS chip dies has enabled the manufacture of modern smart gas sensor devices. Spray pyrolysis deposition is used to grow the required thin films, as it is an affordable deposition technique which can be integrated into a standard CMOS processing sequence. A model for spray pyrolysis deposition is developed and implemented within the Level Set framework using Monte Carlo techniques. Two models for the topography modification due to spray pyrolysis deposition are presented, with an electric nozzle and a pressure atomizing nozzle. The resulting film growth is described as a layer by layer deposition of the individual droplets which reach the wafer surface and deposit as flat round disks or as a CVD-like process, depending on whether the droplets form a vapor near the interface or they deposit a film only after surface collision. Some additional geometries are simulated in order to analyze how the spray pyrolysis technique coats trench structures, essential for increasing the surface area of the gas sensing layer.