Radiation imagery chemistry: process – composition – or product th – Imaging affecting physical property of radiation sensitive... – Making electrical device
Reexamination Certificate
1998-05-19
2002-05-07
Duda, Kathleen (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Imaging affecting physical property of radiation sensitive...
Making electrical device
C430S394000, C430S396000
Reexamination Certificate
active
06383719
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to techniques for fine feature lithography. More particularly, it relates to a method of enhancing resolution. Even more particularly, it relates to a method of compensating for mechanisms that degrade printed image quality. Finally it relates to a method of providing improved fidelity in providing patterns used in integrated circuits.
BACKGROUND OF THE INVENTION
There is a continuing trend in the field of integrated circuits to reduce the size of the circuitry. As a result, there is an increased demand to improve the resolution of projection printers and other devices used in lithography during the manufacture of integrated circuits.
FIG. 14
illustrates a mask pattern
10
to be formed on a substrate
12
.
FIG. 15
is an illustration of a printed image
14
formed in a photoresist using the mask pattern
10
shown in FIG.
14
. As is shown in
FIG. 15
, the long axis LA
2
of the printed image
14
shortens as compared to the long axis LA
1
of mask pattern
10
. This will henceforth be referred to as foreshortening.
FIG. 16
illustrates square mask image
190
to be formed on a substrate
12
.
FIG. 17
is an illustration of the printed image
190
′ using the mask image
190
shown in FIG.
16
. As shown in
FIG. 17
, the comers of the image
190
′ become round during printing and developing compared to the mask image
190
, because of optical (e.g., diffraction) and resist processing effects. This process is referred to here as “corner rounding.”
FIG. 18
illustrates another mask pattern
40
containing both nested features
42
a
,
42
b
and an isolated feature
44
.
FIG. 19
is an illustration of printed image
40
′ using mask pattern
40
shown in FIG.
18
. As demonstrated in
FIG. 19
, isolated feature
44
′ prints differently than nested features
42
a
′ and
42
b
′. (Depending on effects such as diffraction, lens aberrations, and resist characteristics, isolated feature
44
′ can print either larger or smaller than nested feature
42
a
′ and
42
b
′.) Also, the width of outside images
42
b
′ in a group of nested images print differently than inside images
42
a
′. These two effects are referred to here as “nested-to-isolated print bias.” Outside images
42
b
′ are nested only on one side; consequently they experience less of a proximity effect than fully nested images
42
a′.
FIG. 20
illustrates a mask which includes bar
50
and contact
52
.
FIG. 21
shows printed bar image
50
′ associated with mask bar image
50
and printed contact image
52
′ associated with mask image
52
. When the bar image
50
′ is printed optimally, contact image
52
′ is poorly imaged, as shown in FIG.
21
. If contact image
52
′ is printed optimally, bar image
50
′ is printed too wide. This effect is referenced to here as “feature size dependent bias.”
Adjustments of the mask image to compensate for the foreshortening may be difficult when small images are to be formed in the photoresist. There is limited space between the images in arrays of high-density small images to apply compensation at the mask level (i.e., to grow the image in the direction that it will foreshorten) without introducing undesirable proximity effects such as image bridging.
One prior art technique to improve resolution is to use contrast enhanced layers (CEL) with projection printers. A photo-bleachable layer is spun onto a photoresist-coated wafer to a thickness of approximately 1,000-3,000 Å. Upon exposure of the CEL by the aerial image produced by the mask and projection printer, the regions of the photo-bleachable layer that are exposed to the highest intensities bleach through first, while those areas of the photo-bleachable layer that receive the lowest intensity bleach through at a later time. Therefore, windows in the CEL are formed which allow the imaging light to pass through and expose the underlying photoresist. The net effect is to increase the effective contrast of the CEL and photoresist stack over that of the photoresist alone. Contrast enhanced imaging or multilayer resists alone may be inadequate, however, for significant improvement of image foreshortening in advanced lithography.
To overcome the shortcomings of the prior art, a new process is provided. An object of the present invention is to provide an improved process to reduce image foreshortening, corner rounding, nested to isolated print bias, and other print biases.
SUMMARY OF THE INVENTION
To achieve this and other objects, and in view of its purposes, the present invention provides a process of forming a first device pattern having a first end, a second end, and a center area. The process comprises the steps of providing a substrate having a photosensitive coating, forming the center area of the first device pattern on the photosensitive coating, and forming one of the first end and the second end of the first device pattern on the photosensitive coating.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, but are not restrictive, of the invention.
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patent: 3422442 (1969-01-01), Glendinning et al.
patent: 4021239 (1977-05-01), Ogawa
patent: 4264711 (1981-04-01), Greeneich
patent: 4426584 (1984-01-01), Bohlen et al.
patent: 4935334 (1990-06-01), Boettiger et al.
patent: 5082762 (1992-01-01), Takahashi
patent: 5308741 (1994-05-01), Kemp
patent: 5340700 (1994-08-01), Chen et al.
patent: 5405733 (1995-04-01), Sirkin et al.
patent: 5413898 (1995-05-01), Kim et al.
patent: 5532114 (1996-07-01), Bae
patent: 5635285 (1997-06-01), Bakeman, Jr. et al.
patent: 7181668 (1995-07-01), None
English Abstract of JP62-19860 (Jan. 28, 1987).
Bula Orest
Cole Daniel
Conrad Edward W.
Knight Stephen E.
Leidy Robert K.
Chadurjian Mark F.
Duda Kathleen
International Business Machines - Corporation
Leas James M.
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