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Phase Shift Mask utilizing Silicon Oxy-Nitride as a Low Reflectivity Phase Shift Layer

IP.com Disclosure Number: IPCOM000107832D
Original Publication Date: 1992-Mar-01
Included in the Prior Art Database: 2005-Mar-22
Document File: 2 page(s) / 74K

Publishing Venue

IBM

Related People

Dove, DB: AUTHOR

Abstract

There is a growing interest in developing phase-shift lithographic mask arrangements that incorporate a transparent layer as well as or in place of the usual opaque metal mask. The transparent layer typically imparts an optical phase shift of 180 degrees to light traversing the layer compared with light traversing adjoining uncoated regions. Interference between the phase-shifted and non-phase-shifted beams gives rise to the possibility of imaging fine line or dots or other shapes below the normal resolution limit of the lithographic optical system. A feature of such a coating is that unwanted reflection of light may occur at the surface of the phase-shift layer, producing stray light that has a degrading effect on the lithography process. The use of multilayer anti-reflection coatings is not feasible for this application.

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Phase Shift Mask utilizing Silicon Oxy-Nitride as a Low Reflectivity Phase Shift Layer

       There is a growing interest in developing phase-shift
lithographic mask arrangements that incorporate a transparent layer
as well as or in place of the usual opaque metal mask.  The
transparent layer typically imparts an optical phase shift of 180
degrees to light  traversing the layer compared with light traversing
adjoining uncoated regions. Interference between the phase-shifted
and non-phase-shifted beams gives rise to the possibility of imaging
fine line or dots  or other shapes below the normal resolution limit
of the lithographic optical system.  A feature of such a coating is
that unwanted reflection of light may occur at the surface of the
phase-shift layer, producing stray light that has a degrading effect
on the lithography process.  The use of multilayer anti-reflection
coatings is not feasible for this application.

      This article deals with a layer design that minimizes
reflections while preserving the desired phase-shift property by
using a layer of very specific refractive index. This index may be
achieved by using a film composed of silicon nitride containing a
desired proportion of silica in intimate mixture as by cosputtering.
Such films have particular interest for phase-shift layers having the
property of low reflectivity for the lithographic light source.

      The thickness d of a transparent layer required to produce a
path of g/2 in transmission, compared with air is given by
          nd -d = g/2
where n is the refractive index of the film at the wavelength g
employed for lithography in the uv or deep uv. Since it is convenient
to emplo...