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Novel Technique for Improving Contact Window Slopes Using Bi-Focusing

IP.com Disclosure Number: IPCOM000036091D
Original Publication Date: 1989-Sep-01
Included in the Prior Art Database: 2005-Jan-28
Document File: 2 page(s) / 68K

Publishing Venue

IBM

Related People

Conway, JF: AUTHOR [+5]

Abstract

Positively sloped contact windows or vias are typically used in semiconductor metallurgy to allow subsequent layers of metal to make contact to the underlying circuitry through a passivation layer of dielectric material. The positively sloped sidewalls are necessary to prevent metal cracking over abrupt steps, as shown in Figs. 1 and 2.

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Novel Technique for Improving Contact Window Slopes Using Bi-Focusing

Positively sloped contact windows or vias are typically used in semiconductor metallurgy to allow subsequent layers of metal to make contact to the underlying circuitry through a passivation layer of dielectric material. The positively sloped sidewalls are necessary to prevent metal cracking over abrupt steps, as shown in Figs. 1 and 2.

Where lithographic approaches 1.0 um or submicron line widths, dry plasma etching is used because of much greater dimensional control than techniques such as wet etching.

A major problem with plasma etching, particularly where only anisotropic etching is permissible due to dimensional control constraints, is that the contact slope of the via is highly dependent on the slope of the resist image. High resolution lenses, which are necessary for defining the 1.2 um or smaller contacts, inherently produce very steep resist slopes.

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This article describes a novel technique for producing positively sloped resist sidewalls (75 - 80 degrees) in 1.4 um or greater thick resist using two foci instead of one. Traditionally, all exposures are done at the 'Best Focus' or 'Working Focus' which is the focus that produces the best resolution uniformly over the largest field. What we propose is to first expose the contacts or vias using the Working Focus (WF) and then expose them again at a substantially defocused condition. Working focus is used to insure dimension...