Influence of the skin effect on the structure of relief–phase optical elements obtained by plasma–chemical etching

Abstract

This paper discusses features of the phenomena that occur when optical glass is plasma–chemically etched on an apparatus with inductively coupled plasma during the fabrication of relief-phase optical elements, resulting in nonuniform damage of the metallic (chromium) mask. It is shown that, in fabricating such elements, which are characterized by very significant width variations of sections of the metallic mask, it is necessary to allow for the density nonuniformity of the eddy currents induced in the mask (a thin-film conductor) caused by the use of a high-frequency discharge. It is analytically shown that the nonuniformity of the damage of the mask–conductor is caused by the skin effect; as a consequence of heating nonuniformity, this causes the adsorption and desorption processes of chemically active particles to be dissimilar along the contour and in the middle of the mask. Diagrams of the amplitude distribution of the induced electric field transverse to the field vector are obtained that show that, although the consequences of the skin effect do not exceed 2% on relatively narrow sections of the mask (1–2 μm wide), the skin effect on relatively wide sections (10–20 μm wide) causes a difference in the conditions of the chemical reactions on the edge sections of the mask and in their middle by about a factor of 5.