Anisotropic Etching of SiO2 with a 38.2 Weight Percent Hydrofluoric Acid Aerosol

A novel etching system termed aerosol jet etching (AJE) is described and used to etch silicon dioxide films. The method combines the directionality of dry etching with the selectivity of wet etching. Contrary to most etching processes, in AJE the etch rate decreases with increasing substrate temperature, indicating that the residence time of etchant on the substrate can be a rate determining factor. The anisotropy of the etching process is improved by decreasing the nozzle exit to substrate distance, . For a given nozzle diameter, , no undercutting of the mask is apparent so long as the ratio .