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Browse Prior Art Database

Phase Shift Masks using Planarized Buried Attenuating Structures

IP.com Disclosure Number: IPCOM000107830D
Original Publication Date: 1992-Mar-01
Included in the Prior Art Database: 2005-Mar-22
Document File: 3 page(s) / 117K

Publishing Venue

IBM

Related People

Ghosh, AP: AUTHOR [+2]

Abstract

A new method is described to fabricate phase-shifting masks that uses the concept of buried mask structure. This novel planar structure with the fabrication technique can give sharper corners and edges of the phase-shifting elements as well as make repairing of the phase- shifting elements easier. The desired image on the wafer can be obtained only if the phase amplitude and the phase of the light passing through the mask have the correct values. In one method for producing rim-type phase-shifting masks, the chrome pattern is laid down on a substrate (e.g., quartz or glass) and subsequently the phase-shifting layer is deposited on top of the chrome pattern. In a typical process the second layer (for example, the phase-shifting layer) is deposited on a non-planar surface.

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This is the abbreviated version, containing approximately 51% of the total text.

Phase Shift Masks using Planarized Buried Attenuating Structures

       A new method is described to fabricate phase-shifting
masks that uses the concept of buried mask structure.  This novel
planar structure with the fabrication technique can give sharper
corners and edges of the phase-shifting elements as well as make
repairing of the phase- shifting elements easier.  The desired image
on the wafer can be obtained only if the phase amplitude and the
phase of the light passing through the mask have the correct values.
In one method for producing rim-type phase-shifting masks, the chrome
pattern is laid down on a substrate (e.g., quartz or glass) and
subsequently the phase-shifting layer is deposited on top of the
chrome pattern.  In a typical process the second layer (for example,
the phase-shifting layer) is deposited on a non-planar surface.  This
can give rise to problems involving step coverage, such as rounded
corner, shadow effect, uniformity of the phase-shifting layer around
the step side, and so on (Fig. 1a).  This will give rise to phase
errors and subsequently to erroneous optical image on the wafer.  In
a second method of producing rim-type phase-shifting masks the
phase-shifting elements are laid down first and then the chrome
pattern is deposited.  In this method, however, the choice of
materials is limited, for example, because of stress and temperature
issues; polymers usually cannot be used as phase-shifting elements
under metal patterns (Fig. 1b).  In a third type of rim
phase-shifting mask the chrome layer is deposited on the substrate
followed by the phase shifting layer.  The phase-shifting layer is
then etched back on the sides (under cut) to obtain the desired
result.  However, the control of the side etch rate is extremely
difficult and can produce non-reproducible results (Fig. 1c).  In
addition, repairing of the phase-shifting elements of a phase-shift
mask is a major challenge that is vital to the fabrication process
and, indeed, needs to be addressed.

      The concept of buried masks is shown in Fig. 2.  There are
several advantages of planar buried masks, such as a flat surface for
the deposition of the second layer, no shadow effects on the corner
of the first metal step, and ease of precise control on the film
uniformity across the substrate.  In this disclosure we propose an
advancement of the prior art, by implementing phase-shifting elements
t...