Diode Circuit-based Glass Plasma-Chemical Etching Capabilities

Abstract

The paper discusses technological capabilities to improve a plasma-chemical etching (PCE) rate of the silicate glasses through a chromium mask in the equipment with a planar inductor located outside, which forms a high-frequency diode system. Suggests a case when the inductor in the form of a planar spiral antenna is above the work-piece.The PCE process stages were analytically studied and the limiting effects of each step that affect the etching rate and the quality of the treated surface were determined. The paper shows that for the type of equipment under consideration the stage of removing etch products from the work-piece is a quality-limiting factor for the PCE-exposed surface while the limiting factor for the etching rate is the stage of formation of chemically active particles (CAP) in plasma.The comparison of analytical results with the experimental data shows that in the considered case plasma of low density and high pressure is formed. The experimentation was aimed at studying the impact of the surface position under treatment and the working pressure in the chamber on the etching rate and the peculiarities of the etched surface formation. As a treated material, the blanks of the photomasks for integrated circuits made from Cr-covered silicate glass were considered. The electron beam lithography method was used to create a mask for the PCE process.It was experimentally found that when a treating surface of the work-piece in plasma is “downward” the etching depth is by 5-10% more than the etching depth of the “upward” surface. Another finding was that with raising gas flow the etching depth was twice increased as well.Optical-microscopic examinations of the etched surfaces of work-pieces have shown that there are areas with green or brown coating. Supposedly, this is due to the effect of the reverse deposition of the mask material as in the form of CrF3, CrF4 compounds that reinforce the need to look for a replacement of the chrome mask.The etching rates of 45-90 nm/min are obtained for the silicate glass, which is close in composition to the optical glass of K8 grade. This allows using the PCE in the equipment with a planar inductor located outside the chamber and realizing a high-frequency diode circuit to produce diffraction and hologram optical elements with a depth of the surface relief up to 400-500 nm.