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Elimination of Light-Scattering Effects in CMOS Metallization Processes

IP.com Disclosure Number: IPCOM000100181D
Original Publication Date: 1990-Mar-01
Included in the Prior Art Database: 2005-Mar-15
Document File: 1 page(s) / 34K

Publishing Venue

IBM

Related People

Artero, R: AUTHOR [+5]

Abstract

A light-scattering effect was noticed in the Metal 2 (or Metal 3) in the manufacturing steps of CMOS products. The underlying topography, Metal 1 (or Metal 2), crossing over polysilicon structures, causes reflections during the first exposure step of the MIRP (Modified Image Reversal Process) when using the UV 4 range of the mercury lamp wavelengths as standard. As a result, the unexposed areas are notched and lead to unwanted lateral exposure. In fact, the interconnecting material, typically aluminum, crossing over the end of polysilicon pattern, acts as a condensing mirror which focuses and reflects light on the edge of exposed areas (see the figure).

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Elimination of Light-Scattering Effects in CMOS Metallization Processes

       A light-scattering effect was noticed in the Metal 2 (or
Metal 3) in the manufacturing steps of CMOS products. The underlying
topography, Metal 1 (or Metal 2), crossing over polysilicon
structures, causes reflections during the first exposure step of the
MIRP (Modified Image Reversal Process) when using the UV 4 range of
the mercury lamp wavelengths as standard. As a result, the unexposed
areas are notched and lead to unwanted lateral exposure.  In fact,
the interconnecting material, typically aluminum, crossing over the
end of polysilicon pattern, acts as a condensing mirror which focuses
and reflects light on the edge of exposed areas (see the figure).

      After the reversal and development steps of the MIRP have been
completed, the unexposed areas reveal resist residues remaining
between lift-off structures. These resist residues will hinder the
metallization process by giving ridging defects that cause inter- or
intra-level shorts and necking defects that could lead to open
conductors.

      All the defects were eliminated by shifting the exposure
wavelengths from UV4 to UV3, by using a UV3 filter.