A method is disclosed for eliminating under-etchings. In a substrate having a lower silicon dioxide layer thereon, a polysilicon layer on the silicon dioxide layer, and an upper silicon dioxide layer on the polysilicon layer, an etched window provided in the layers has first under-etchings formed at an edge of the lower silicon dioxide layer adjacent the substrate and a second under-etching formed at an edge of the polysilicon layer. A sputtering source is provided with a given target voltage. A grid potential is applied to the substrate wherein the grid potential is between one-tenth and one-third of the target voltage. A layer is then sputter deposited in the etching window for filling in the first under-etching by re-emission from the surface of the substrate and for sloping the edge of the polysilicon layer at the second under-etching. An overhanging portion of the upper silicon dioxide layer is also removed at the second under-etching by re-emission during the sputter deposition.