Radiation imagery chemistry: process – composition – or product th – Radiation modifying product or process of making – Radiation mask
Reexamination Certificate
1999-09-13
2001-02-06
Rosasco, S. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Radiation modifying product or process of making
Radiation mask
Reexamination Certificate
active
06183916
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
This invention relates to phase shifting masks used to form photolithographic images on wafers and more particularly to mask corrections to compensate for image distortion.
(2) Description of the Related Art
Photolithography is critical to the fabrication of integrated circuit wafers and utilizes masks to transfer images, such as line/space patterns, to the wafer. As circuit densities increase critical dimensions decrease and line/space patterns become more and more dense.
FIG. 1
shows an example of a part of a dense line/space pattern on a wafer with a number of lines
20
having a first linewidth
22
on a first pitch
24
.
FIG. 2
shows an example of a part of an isolated line/space pattern with lines
21
having a second linewidth
23
, greater than the first linewidth
22
, on a second pitch
25
, greater than the first pitch
24
. Frequently both dense line/space patterns and isolated line/space patterns are part of the same circuit pattern formed on a wafer.
FIG. 3
shows a part of a binary mask, often used in the formation of the patterns on a wafer, having opaque lines
32
formed on a transparent mask wafer
30
.
FIG. 4
shows an alternative phase shifting mask, sometimes referred to as a Levenson phase shifting mask, used as an alternative to a conventional binary mask for forming line/space patterns. The alternative phase shifting mask has lines
34
formed of phase shifting material on a transparent mask substrate
30
.
In forming photolithographic patterns exposure latitude and depth of focus are important parameters. As the line/space patterns become more dense optical distortion becomes a problem in the pattern formation. Optical proximity effect is a form of optical distortion associated with the formation of photolithographic images. Diffraction effects occurring on both sides of a sharp pattern edge become important as the critical dimensions of pattern features decreases. The use of alternative phase shifting masks in place of binary masks improves the exposure latitude and depth of focus but the problem of proximity effect increases.
U.S. Pat. No. 5,858,591 to Lin et al. describes a method of correcting for optical distortion during wafer processing by modification of subfiles used to form the masks. The subfiles are modified to correct for optical proximity effect and to add or subtract a suitable bias to the subfiles.
U.S. Pat. No. 5,682,323 to Pasch et al. describes a system and method of performing optical proximity correction on an integrated circuit by performing optical proximity correction on a library of cells.
SUMMARY OF THE INVENTION
It is a principal objective of this invention to provide a method of forming phase shifting masks which provide correction for optical proximity effect and add critical dimension bias.
It is another principal objective of this invention to provide a method of forming circuit patterns on a wafer using phase shifting masks which provide correction for optical proximity effect and add critical dimension bias.
These objectives are achieved by beginning with a data file used to form a traditional binary mask for a circuit pattern. Optical proximity correction is then added to the file to obtain a first modified data file. The first modified data file is then separated into a second modified data file, for regions of the mask having dense line/space patterns, and a third modified data file, for regions of the mask having isolated line space patterns. Critical dimension bias is then added to the second modified data file forming a fourth modified data file.
The third modified data file and the fourth modified data file are then merged into a single fifth modified data file. The fifth modified data file could be used to form a binary mask having optical proximity correction and critical dimension bias. The fifth modified data file is then converted to an alternative phase shift data file. An alternative phase shift mask is then formed from the alternative phase shift data file. The alternative phase shift mask has been corrected for optical proximity effect and critical dimension bias has been added. This alternative phase shift mask can then be used in forming the circuit pattern on an integrated circuit wafer.
REFERENCES:
patent: 5682323 (1997-10-01), Pasch et al.
patent: 5858591 (1999-01-01), Lin et al.
Kuo Chen-Cheng
Lin Chia-Hui
Lin Hua-Tai
Ackerman Stephen B.
Prescott Larry J.
Rosasco S.
Saile George O.
Taiwan Semiconductor Manufacturing Company
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