Nonuniformities in chemical oxides on silicon surfaces formed during wet chemical cleaning

We studied the uniformity of chemical oxides formed on Si surfaces during wet chemical cleaning. The uniformity was determined by the surface morphology during the initial stage of photoexcited F-2 etching. Since photoexcited F-2 etches silicon 40 times faster than it etches silicon oxide, it highlights chemical oxides on silicon surfaces making them observable by scanning tunnel microscopy or atomic force microscopy. We found that the chemical oxides were not uniform, whereas oxides formed in gas phase were uniform. Boiling in HCl-H2O2-H2O (1:1:4 volume) or NH4OH-H2O2-H2O (1:1.4:4 cm(-2). Boiling In a HNO3 volume) solutions formed 30 to 70 nm oxide islands. The island density was in the order of 10(10) cm solution also resulted in a chemical oxide which was composed of 25 nm diam dense islands and had pinholes at a den; sity of 5 x 10(9) cm(-2). The island density was between 1 x 10(11) acid 3 x 10(11) cm(-2). The chemical oxide nonuniformities were independent of both crystallographic orientation and substrate resistivity for the most part. It is possible that the nonuniformities may negatively influence subsequent processing.