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Novel Technique for Producing Positive Sloped Contact Vias Using Negatively Sloped Resist Walls

IP.com Disclosure Number: IPCOM000036088D
Original Publication Date: 1989-Sep-01
Included in the Prior Art Database: 2005-Jan-28
Document File: 4 page(s) / 88K

Publishing Venue

IBM

Related People

Katz, SM: AUTHOR [+3]

Abstract

Photo imaging using high resolution reduction lenses produces near vertical resist walls. For many applications, this is desirable, but for contact via definition, where sloped via walls are necessary for good metal continuity and step coverage, it severely impacts the dry etching process. Typically, dry etching processes replicate the resist wall profile into the under passivation layer material. Two common techniques used to modify the resist profile for proper slope are thermal reflow of patterned resist and multistep reactive ion etch (RIE) processes that uses anisotropic resist faceting in conjunction with isotropic resist ashing.

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Novel Technique for Producing Positive Sloped Contact Vias Using Negatively Sloped Resist Walls

Photo imaging using high resolution reduction lenses produces near vertical resist walls. For many applications, this is desirable, but for contact via definition, where sloped via walls are necessary for good metal continuity and step coverage, it severely impacts the dry etching process. Typically, dry etching processes replicate the resist wall profile into the under passivation layer material. Two common techniques used to modify the resist profile for proper slope are thermal reflow of patterned resist and multistep reactive ion etch (RIE) processes that uses anisotropic resist faceting in conjunction with isotropic resist ashing.

Thermal reflow of patterned resist produces excellently sloped resist walls but suffers from a number of shortcomings, particularly when applied to 1.5 um and smaller vias. Some of these problems are poor critical dimension control, i.e., large image etch bias, via shifting, via size reduction and complete exaggeration of proximity effects.

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Multistep RIE also produces adequate contact via slopes with good dimensional control but suffers from poor slope control. The RIE process may have as many as 14 individual steps, all of which must be precisely controlled. Another problem with this process is that diffusion contacts are generally marginally sloped to 70 degrees at best, while the polysilicon contacts are sloped to 55-60 degrees. Numerous studies have shown that the minimum slope for metal coverage over contact steps is 70 degrees. This means that at best RIE processes with incoming vertical resist walls have virtually no process window.

This article describes a process the solves the problems of the prior art techniques. It uses negatively sloped patterned resist walls, produced by deep UV flood exposure, in the same manner as thermally reflowed or positively sloped resist walls would be utilized.

A layer of resist is applied over the passivator, and aligned and exposed using normal processing conditions and parameters. The resist is developed to laser endpoint plus 100%, and then subjected to deep UV flood expose for approximately...