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Dual Density Mask for Photoresist

IP.com Disclosure Number: IPCOM000088206D
Original Publication Date: 1977-May-01
Included in the Prior Art Database: 2005-Mar-04
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Abolafia, OR: AUTHOR [+2]

Abstract

It is conventional to expose photoresist through a mask which has opaque and transparent areas therein. Under certain conditions it is desirable to have a tri-level mask which has partially transparent areas in addition to the completely opaque and completely transparent areas. The purpose of the partially transparent areas is to partially expose some of the photoresist. When such masks are used, the photoresist is removed in two stages. First, the fully exposed photoresist is removed and the areas thus exposed are etched. Next, the partially exposed photoresist is removed by a more concentrated developer, and different areas can then be etched.

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Dual Density Mask for Photoresist

It is conventional to expose photoresist through a mask which has opaque and transparent areas therein. Under certain conditions it is desirable to have a tri-level mask which has partially transparent areas in addition to the completely opaque and completely transparent areas. The purpose of the partially transparent areas is to partially expose some of the photoresist. When such masks are used, the photoresist is removed in two stages. First, the fully exposed photoresist is removed and the areas thus exposed are etched. Next, the partially exposed photoresist is removed by a more concentrated developer, and different areas can then be etched.

A dual-density, or tri-level, photoresist mask can be fabricated in the following manner. The fully opaque and fully transparent areas of the mask are fabricated in the conventional manner. Where one desires a partially transparent area, one places a grid of very fine opaque lines. The fineness of the grid can be near the limit of the resolution of the photolithographic process used to make the mask. The ratio of the width of the lines in the mesh to the width of the spacing between these lines can be selected to produce the desired degree of transparency. A ratio of one-to-one results in 25% of the light being transmitted.

A second mask which has partially transparent areas can be made from the first mask by exposing a layer of emulsion on the second mask using the first mask. In order t...