Plural level chip masking

Abstract

A sequence of masking steps reduces the amount of transference of a workpiece among work stations and reduces certain tolerances required for mask alignment in the construction of integrated circuits, and a gray level mask suitable for photolithography. In the integrated circuit, masking layers are developed directly in a wafer for delineating vertical and horizontal portions of an electrically conductive path. The mask is constructed of a transparent glass substrate which supports plural levels of materials having different optical transmissivities. In the case of a mask employing only two of these levels, one level may be constructed of a glass made partially transmissive by substitution of silver ions in place of metal ions of alkali metal silicates employed in the construction of the glass. The second layer may be made opaque by construction of the layer of a metal such as chromium. Both the wafer and the mask are fabricated by a photoresist structure which is etched in specific regions by photolithographic masking to enable selective etching of exposed regions of the level of materials of differing optical transmissivities. Various etches are employed for selective etching of the photoresist and other ones of the layers. The etches include plasma etch with chloride ions to attack the chromium of the opaque layer, compounds of fluorine to attack the glass layer, and reactive ion etching with oxygen to attack the photoresist structure.