Radiation imagery chemistry: process – composition – or product th – Radiation modifying product or process of making – Radiation mask
Reexamination Certificate
1999-12-28
2001-08-14
Rosasco, S. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Radiation modifying product or process of making
Radiation mask
C430S394000
Reexamination Certificate
active
06274281
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
This invention relates to the use of different transmittance light absorbing material for different duty ratio contact hole patterns and line/space patterns in attenuating phase shifting masks.
(2) Description of the Related Art
Attenuating phase shifting masks are often used to form patterns on integrated circuit wafers. As pattern dimensions become very small critical dimension proximity effect can become a significant problem and methods to correct for the proximity effect problems must be used.
U.S. Pat. No. 5,869,212 to Hashimoto describes an attenuating phase shifting mask using regions of increased light transmissivity adjacent to the defined circuit features.
U.S. Pat. No. 5,786,114 to Hashimoto describes an attenuating phase shifting mask where boundary regions are formed form the same halftone layer used to form circuit regions. The halftone layer in the boundary regions are not subjected to the stabilization step and thus have lower transmittance than the stabilized halftone layer. This lower transmittance halftone material in the boundary regions helps avoid light leakage to adjacent chip areas.
U.S. Pat. No. 5,766,806 to Spence describes a phase shift mask using different phase shift amounts in different regions of the pattern.
U.S. Pat. No. 5,783,337 to Tzu et al. describes an attenuating phase shifting mask using an opaque border.
U.S. Pat. No. 5,618,643 to Dao et al. describes an embedded phase shifting mask with a roughened surface to change the transmission.
SUMMARY OF THE INVENTION
Attenuating phase shifting masks are often used to form patterns on integrated circuit wafers. As pattern dimensions become very small optical proximity effects can become a significant problem in critical dimension regions of a mask pattern. Correction methods such as Optical Proximity Correction are often used to correct for these types of problems, but these methods can be complicated and consume a large amount of computer design resource. In masks having both dense and more isolated line/space patterns and contact hole patterns the problems of pattern correction become even more complicated.
It is a principal objective of this invention to provide a mask which can be used for both dense and more isolated line/space or contact hole patterns without using correction methods such as Optical Proximity Correction.
It is another principal objective of this invention to provide a method of forming a mask which can be used for both dense and more isolated line/space or contact hole patterns without using correction methods such as Optical Proximity Correction.
These objectives are achieved by using attenuating phase shifting masks with different light transmission in different regions of the mask. In the more isolated regions of a contact hole mask the contact holes have 0° phase shift and 100% light transmission while the region around the contact holes have 180° phase shift and relatively high light absorption. In the dense regions of a contact hole mask the contact holes have 0° phase shift and relatively low light absorption while the region around the contact holes have 180° phase shift and relatively high light absorption. In the more isolated regions of a line/space mask the lines have a 180° phase shift and relatively high light absorption while the spaces between the lines have 0° phase shift and 100% light transmission. In the dense regions of a line/space mask the lines have a 180° phase shift and relatively high light absorption while the spaces between the lines have 0° phase shift and relatively low light absorption.
The masks are formed by using a mask blank having a transparent mask substrate, a layer of light absorbing material formed on the transparent mask substrate, and a layer of transparent phase shifting material formed on the layer of light absorbing material. A layer of resist is formed on the layer of phase shifting material and exposed using variable exposure doses with a method such as an electron beam. In the contact hole mask a first exposure dose is used for the isolated contact holes and a second exposure dose, smaller than the first exposure dose, is used for the dense contact holes. In the line/space mask a first exposure dose is used for the spaces between the isolated lines a second exposure dose, smaller than the first exposure dose, is used for spaces between the dense lines.
The layer of resist is then developed to form a resist mask having no resist material in the isolated contact holes and spaces between isolated lines, a reduced thickness of resist material in the dense contact holes and spaces between the dense lines, and the full resist thickness in other regions of the mask. Dry anisotropic etching is then used to remove all of the phase shifting material and all of the light absorbing material from the isolated contact holes and the spaces between the isolated lines. The dry anisotropic etching also removes all of the phase shifting material and part of the light absorbing material from the isolated contact holes and the spaces between the isolated lines. The mask has a residue of resist material which is then removed to complete the mask. The dense and isolated parts of the mask are separated by performing logic operations on a pattern data file.
REFERENCES:
patent: 5618643 (1997-04-01), Dao et al.
patent: 5766806 (1998-06-01), Spence
patent: 5783337 (1998-07-01), Tzu et al.
patent: 5786114 (1998-07-01), Hashimoto
patent: 5869212 (1999-02-01), Hashimoto
patent: 6183915 (2001-02-01), Rolfson
patent: 6190809 (2001-02-01), Tzu et al.
Ackerman Stephen B.
Prescott Larry J.
Rosasco S.
Saile George O.
Taiwan Semiconductor Manufacturing Company
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