Browse Prior Art Database

Two and Three Layer Photoresist Technique

IP.com Disclosure Number: IPCOM000078405D
Original Publication Date: 1972-Dec-01
Included in the Prior Art Database: 2005-Feb-25
Document File: 2 page(s) / 13K

Publishing Venue

IBM

Related People

Kaplan, LH: AUTHOR [+2]

Abstract

The monochromatic exposure of photoresist films over reflecting substrates establishes a standing-wave pattern of the light within the film. This results in a significant variation of the intensity of the light along the thickness direction of the film resulting in varying exposure of the photoresist. This condition becomes deleterious, when using projection exposures for the production of patterns within the micron and submicron range, in that excessive exposures are required to fully bring out the smaller patterns.

This text was extracted from a PDF file.
This is the abbreviated version, containing approximately 52% of the total text.

Page 1 of 2

Two and Three Layer Photoresist Technique

The monochromatic exposure of photoresist films over reflecting substrates establishes a standing-wave pattern of the light within the film. This results in a significant variation of the intensity of the light along the thickness direction of the film resulting in varying exposure of the photoresist. This condition becomes deleterious, when using projection exposures for the production of patterns within the micron and submicron range, in that excessive exposures are required to fully bring out the smaller patterns.

The variation of exposure in the thickness direction can be related to the square of the well-known standing-wave ratio (SWR), values for which range up to the order of 25 for bare or oxidized silicon substrates and higher for highly reflective substrates such as aluminum films. The least favorable situation occurs for those reflective surfaces (i.e., aluminum, other metals, bare silicon, and oxidized silicon with specific oxide thicknesses) that produce an optical node or minimum intensity at the photoresist-substrate interface, thereby requiring aggressive development or special procedures such as post development ozone etching to remove the photoresist residues within the micron sized images. Dimensional control of micron sized images is therefore difficult to maintain, especially for densely packed image arrays.

It can be shown, analytically, that, with the use of a double-layer photoresist film, whereby the top layer only is photosensitive, a significant reduction of the SWR occurs within the top layer, and improved dimensional control of th...