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Wire Grid Polarizer for Suppression of Unwanted Dark Lines In Phase Shifting Mask Lithography

IP.com Disclosure Number: IPCOM000122304D
Original Publication Date: 1991-Nov-01
Included in the Prior Art Database: 2005-Apr-04
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Levenson, MD: AUTHOR

Abstract

In photolithography with phase-shifting masks, destructive interference produces a dark line at the position of every 180~ phase step. Topology requires that all dark regions printed by such phase steps be multiply connected. However, circuit designs generally will not tolerate this constraint. Polarization is used to selectively eliminate the destructive interference that causes the dark region around the image of a 180~phase step. It is well known in optics that light of orthogonal polarizations cannot interfere. In a phase-shifting mask with a polarizer, the light on opposite sides of a phase step can have orthogonal polarizations when no interference is desired. Alternatively, it can have the same polarization when destructive interference must occur.

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Wire Grid Polarizer for Suppression of Unwanted Dark Lines In Phase Shifting Mask Lithography

In photolithography with phase-shifting masks, destructive interference produces a dark line at the position of every 180~ phase step. Topology requires that all dark regions printed by such phase steps be multiply connected. However, circuit designs generally will not tolerate this constraint. Polarization is used to selectively eliminate the destructive interference that causes the dark region around the image of a 180~phase step. It is well known in optics that light of orthogonal polarizations cannot interfere. In a phase-shifting mask with a polarizer, the light on opposite sides of a phase step can have orthogonal polarizations when no interference is desired. Alternatively, it can have the same polarization when destructive interference must occur.

The necessary polarizing features of the mask are most conveniently fabricated as fine wire grids in the opaque (metal) layer of a two-level phase-shifting mask. Wire grid polarizers are well known in infrared technology, and can be fabricated for ultraviolet by the advanced electron beam lithography used to pattern the circuit features. Alternatively, oriented conducting ellipsoids have the same polarizing effect as do a number of known homogeneous materials. Ideally, the mask would be patterned in two steps: one for the intensity and polarization (metal layer), and one for the phase (transparent layer). When destructi...