Globally planarized binary optical mask using buried absorbers
First Claim
1. A binary optical photolithography mask for use in projecting an image pattern onto a target comprising:
- a mask substrate formed from a substantially transparent material for permitting light transmission therethrough;
an absorber pattern formed from a light absorbing material, buried a set distance d below a surface of said substrate proximal to said target but not adjacent to said surface for absorbing at least a significant portion of light transmission therethrough to form a substantially opaque image pattern on said target;
wherein having said absorber pattern buried below said surface of said substrate, but not adjacent to said surface, allows for light scattered from surface areas of said absorber pattern to be reflected back into said substrate at a surface interface of said substrate, in order to improve image feature definition at said target; and
wherein having said absorber pattern buried below said surface at said set distance d is of sufficient depth in order to provide for a maximum depth of focus of an exposure system being utilized to reside within said substrate, such that surface defects and contaminants at said surface interface are not imaged onto said target.
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Accused Products
Abstract
A globally planarized binary optical mask has absorbers embedded (buried) in the mask substrate, instead of on the surface of the mask. Light scattering at rough vertical edges of absorbers of prior art masks are reduced or eliminated. Also, due to the buried nature of the absorbers, a triple singularity point encountered in prior art masks at the interface of three environments of quartz, absorber and air, no longer exists. The buried absorbers have an offset distance from the surface of the substrate so that with a minimum effective offset distance, defects and contaminants at the surface of the mask are no longer in the image plane, wherein alleviating a need for a pellicle to protect the mask surface. By reducing light scattering and distortion, the mask of the present invention allows for conventional optical lithography to be extended to ranges of shorter wavelength.
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Citations
20 Claims
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1. A binary optical photolithography mask for use in projecting an image pattern onto a target comprising:
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a mask substrate formed from a substantially transparent material for permitting light transmission therethrough; an absorber pattern formed from a light absorbing material, buried a set distance d below a surface of said substrate proximal to said target but not adjacent to said surface for absorbing at least a significant portion of light transmission therethrough to form a substantially opaque image pattern on said target; wherein having said absorber pattern buried below said surface of said substrate, but not adjacent to said surface, allows for light scattered from surface areas of said absorber pattern to be reflected back into said substrate at a surface interface of said substrate, in order to improve image feature definition at said target; and wherein having said absorber pattern buried below said surface at said set distance d is of sufficient depth in order to provide for a maximum depth of focus of an exposure system being utilized to reside within said substrate, such that surface defects and contaminants at said surface interface are not imaged onto said target. - View Dependent Claims (2, 3, 4)
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5. The mask of claim 5 wherein said set distance d for said absorber pattern is determined by a relationship d=w/(2 tan ν
- c), where θ
c is a critical angle for total internal reflection for said mask substrate and w is a width of a feature of said absorber pattern.
- c), where θ
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6. The mask of claim 6 wherein said mask substrate is made from quartz.
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7. A method of fabricating a binary optical photolithography mask for use in projecting an image onto a target, comprising the steps of:
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forming a photoresistive layer over a mask substrate; patterning said photoresistive layer to expose portions of said substrate underlying said photoresistive layer; etching said exposed portions of said substrate to a predefined depth to form trenches in said substrate; removing remaining portions of said photoresistive layer; depositing a layer of light absorbing material over said substrate and filling said trenches; selectively etching back said layer of light absorbing material until only said trenches are filled with said light absorbing material; forming a dielectric layer of a predefined thickness over said substrate and said trenches to form an upper boundary region of said mask in order to bury said light absorbing material below a surface of said mask now formed by exposed surface of said dielectric layer; wherein said absorbing material forms an absorber pattern below said surface of said substrate but not adjacent to said surface, such that light scattered from surface areas of said absorber pattern are reflected back into said substrate at a surface interface of said substrate, in order to improve image feature definition at said target; and wherein having said absorber pattern buried below said surface at a depth d, determined by said predefined thickness of said dielectric layer, is of sufficient depth in order to provide for a maximum depth of focus of an exposure system being utilized to reside within said substrate, such that surface defects and contaminants at said surface interface are not imaged. - View Dependent Claims (8, 9, 10, 11, 12, 13, 14)
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15. A method of fabricating a binary optical photolithography mask for use in projecting an image onto a target, comprising the steps of:
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forming an oxide layer over a mask substrate; forming a photoresistive layer over said oxide layer; patterning said photoresistive layer to expose portions of said oxide layer underlying said photoresistive layer; etching said exposed portions of said oxide layer to expose portions of said underlying substrate; removing remaining portions of said photoresistive layer, but leaving patterned portions of said oxide layer; implanting doped ions into exposed portions of said substrate to a set depth d below exposed surface of said substrate to form patterned light absorbing regions in said substrate but not adjacent to said surface; removing remaining portion of said oxide layer such that said substrate has a substantially planar surface with buried light absorbing regions below surface of said substrate; wherein said buried absorbing regions allow for light scattered from surface areas of said absorbing regions to be reflected back into said substrate at a surface interface of said substrate, in order to improve image feature definition at said target; and wherein having said patterned absorbing regions buried below said surface at said depth d is of sufficient depth in order to provide for a maximum depth of focus of an exposure system being utilized to reside within said substrate, such that surface defects and contaminants at said surface interface are not imaged. - View Dependent Claims (16, 17, 18, 19, 20)
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Specification