Radiation imagery chemistry: process – composition – or product th – Radiation modifying product or process of making – Radiation mask
Reexamination Certificate
1999-09-07
2001-04-03
Rosasco, S. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Radiation modifying product or process of making
Radiation mask
C430S311000
Reexamination Certificate
active
06210841
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
This invention relates to attenuating phase shifting masks and the use of attenuating phase shifting masks to achieve increased depth of focus for widely spaced line/space patterns on the same mask as dense line/space patterns.
(2) Description of the Related Art
The depth of focus achieved using binary masks to form parallel line/space patterns is adequate when the density of the line/space patterns is high and the lines are closely spaced. For isolated lines or widely spaced line/space patterns the depth of focus achieved with binary masks is not adequate. Scattering bar patterns can be used in regions having isolated lines or widely spaced line/space patterns but this complicates the fabrication and inspection of the mask.
Attenuating phase shifting masks can be used to improve the depth of focus for isolated lines or widely spaced line/space patterns but dense line/space patterns can not be resolved with attenuating phase shifting masks using a bias even with a very high numerical aperture setting because of the transmittance through the attenuating phase shifting material.
U.S. Pat. No. 5,565,286 to Lin describes a structure and fabrication method for a mask using an attenuating phase shifting mask in combination with an alternating element phase shifting mask.
U.S. Pat. No. 5,786,114 to Hashimoto describes attenuating phase shifting masks with a halftone layer used to form boundary regions such as an inter-chip regions or kerf regions.
U.S. Pat. No. 5,795,682 to Garza describes attenuating phase shifting masks using a compensating transmissive region located where side lobe effects are expected to be most severe.
U.S. Pat. No. 5,766,804 to Spence and U.S. Pat. No. 5,766,806 to Spence describes the use of phase shifting masks showing assignment rules for phase assignment for the phase shift masks.
SUMMARY OF THE INVENTION
FIG. 1
shows a top view of a part of an integrated circuit wafer
10
having a region
30
with a dense line/space pattern and a region
32
having a widely spaced line/space pattern. The lines
12
in the dense line/space pattern region have a width
16
of between about 0.12 and 0.18 micrometers and a duty ratio, the ratio of the width
16
of the lines to the spacing between the lines, of between about 1:1 and 1:1.2. The lines
14
in the widely spaced region have a width
22
of between about 0.13 and 0.18 micrometers and have a duty ratio, the ratio of the width
22
of the lines to the spacing between the lines
20
, of 1:X where X is greater than 1.2.
FIG. 2
shows a cross section of a binary mask
110
used to form the pattern shown in
FIG. 1
on a wafer. The mask
110
has a number of closely spaced opaque lines
112
, formed of chrome or the like, formed on a transparent mask substrate
100
and widely spaced opaque lines
114
, also formed of chrome or the like, formed on the transparent mask substrate
100
. The mask
110
shown in
FIG. 2
will provide good definition for the closely spaced lines but will have inadequate depth of focus for the widely spaced lines.
FIG. 3
shows modifications to the mask shown in
FIG. 2
used to provide improved depth of focus when forming the widely spaced lines
14
on the wafer.
FIG. 3
shows a top view of the mask Ill having lines
112
in the dense line/space pattern region and lines
114
in the more widely spaced line/space pattern region. To improve the depth of focus, scattering bars
124
are formed on the mask next to the lines
114
in the widely spaced region of the pattern. Scattering bars
122
are also formed at the outer edges of the dense line/space pattern region. The narrow scattering bars,
122
and
124
, are located near pattern lines,
112
and
114
, and are sufficiently narrow so they will not be printed on the wafer. They are present on the mask and improve the depth of focus for the mask but they are not large enough to form an image on the layer of resist on the wafer corresponding to the scattering bars. The width of the scattering bars projects to between about 0.06 and 0.08 micrometers on the wafer and depends on the critical dimension in the main pattern. The distance between the main pattern and the scattering bars depends on the design rules as well as the parameters of the optical system used to form the image of the mask on a wafer, and is optimized in each case.
FIG. 4
shows a cross section of the mask
111
shown in
FIG. 3
, taken along line
4
-
4
′of FIG.
3
. As can be seen in
FIG. 4
, the lines
112
in the closely spaced part of the pattern, the lines
114
in the widely spaced part of the pattern, and the scattering bars,
122
and
124
, are all formed of opaque material, such as chrome, in the conventional mask. The mask
111
shown in
FIGS. 3 and 4
will provide good definition in both the dense region of the wafer and widely spaced region of the wafer but has the disadvantage of complicating both the fabrication of the mask and the inspection of the mask.
Attenuating phase shifting masks can be used to provide good definition in the widely spaced region. Adding attenuating phase shifting scattering bars in the widely spaced part of the pattern provides good depth of focus in the widely spaced part of the pattern. Attenuating phase shifting masks do not give satisfactory results in the densely spaced region of the pattern, however.
It is a principle objective of this invention to provide a mask which can be easily fabricated and inspected which will provide good depth of focus and image contrast for forming images having both dense line/space patterns and isolated lines or widely spaced line/space patterns.
It is another principle objective of this invention to provide a method for forming images having both dense line/space patterns and isolated lines or widely spaced line/space patterns using a mask which can be easily fabricated and inspected.
These objectives are achieved by combining both a binary mask pattern and an attenuating phase shifting mask pattern on the same mask. The binary mask region of the mask is used to form the dense line/space region of the pattern and the attenuating phase shifting mask region of the mask is used to form the isolated line or widely spaced line/space region of the pattern. Scattering bars are used in both the widely spaced line/space region and the dense line/space region.
REFERENCES:
patent: 5565286 (1996-10-01), Lin
patent: 5766804 (1998-06-01), Spence
patent: 5766806 (1998-06-01), Spence
patent: 5786114 (1998-07-01), Hashimoto
patent: 5795682 (1998-08-01), Garza
patent: 5882827 (1999-03-01), Nakao
Kuo Hung Jui
Lin Chia-Hui
Ackerman Stephen B.
Prescott Larry
Rosasco S.
Saile George O.
Taiwan Semiconductor Manufacturing Company
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