Abstract: In an SOI substrate having a base substrate, an insulating film and a semiconductor active layer, a potential difference is given between the base substrate and an etching solution or among the base substrate, the semiconductor active layer and the etching solution to form a uniform depletion layer on the active layer side from the interface between the insulating film and the active layer. The semiconductor active layer is uniformly thinned down by etching using a solution or by the combination of chemical or electro-chemical surface and etching with the resultant reaction product. In this case, the individual electrodes are provided with seal members to prevent the base substrate electrode and the active layer electrode from contacting the etching solution or the reaction solution due to the etching using the etching solution or the chemical reaction using the reaction solution.

Abstract: The present invention is directed to the etching of a material selected from the group consisting of silicon dioxide, silicon nitride, boronphosphorus silicate glass, fluorosilicate glass, siliconoxynitride, tungsten, tungsten silicide and mixtures thereof under plasma etch conditions, particularly for cleaning operations to remove silicon dioxide or silicon nitride from the walls and other surfaces within a reaction chamber of a plasma-enhanced chemical vapor deposition reactor. The etching chemicals used in the etch process are trifluoroacetic acid and it derivatives, such as; trifluoroacetic anhydride, trifluoromethyl ester of trifluoroacetic acid and trifluoroacetic acid amide and mixtures thereof.