Radiation imagery chemistry: process – composition – or product th – Radiation modifying product or process of making – Radiation mask
Reexamination Certificate
1999-05-26
2004-05-18
Huff, Mark H. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Radiation modifying product or process of making
Radiation mask
C430S312000
Reexamination Certificate
active
06737198
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a photomask to be used in a fabrication process of semiconductor integrated circuits such as liquid crystal displays, a fabrication method of the photomasks, and a fabrication method for semiconductor integrated circuits.
2. Description of the Related Art
A projection exposure apparatus exposures circuit patterns such as semiconductor circuit elements printed on a photomask to a wafer. In addition, it is required for the projection exposure apparatus to have functions of a higher resolution and a fine-pattern reprinted.
In general, when a numerical aperture NA is greater and the wavelength of exposing light is shorter, the resolution of the projection exposure apparatus can be increased. Because the depth of focus becomes small during a pattern printing process when the numerical aperture NA of the projection exposure apparatus is increased, it is limited to increase the numerical aperture NA. Further, when the wavelength of exposure light is changed to smaller wavelength, it must be required to greatly change the pattern printing process.
In the prior art, an improved method to improve an image formation of a photomask has been disclosed. In this improved method, a phase shifter to be used for reversing a phase is formed in a part of a photomask where an exposure light is passed, and a phase of the exposure light is controlled in addition to the control of an amplitude of the exposure light.
For example, there are conventional methods about the phase shifter described in following patent documents: JP-A-57/62052, JP-A-58/173744, JP-A-62/67514, JP-A-62/67547, JP-A-63/304257, and JP-A-3/263045.
FIG. 1A
to
FIG. 1F
are diagrams showing a conventional fabrication method of a photomask. In
FIG. 1A
to
FIG. 1F
, the reference number
220
designates a transparent substrate such as a transparent glass substrate,
222
denotes a shade film, and
224
indicates a resist film. When the fabrication process for the photomask is completed, shade patterns
111
are formed on the transparent glass substrate
220
at desired intervals shown in FIG.
1
F.
FIG. 2A
to
FIG. 2F
are diagrams showing a conventional fabrication method of a photomask of a low reflection type. In
FIG. 2A
to
FIG. 2F
, the reference numbers
231
and
232
designates reflection preventing film formed under and on the shade film
222
. When the fabrication process for the photomask is completed, the shade patterns
111
are formed at desired intervals on the transparent glass substrate
220
shown in FIG.
2
F. In this configuration, the reflection preventing films
231
and
232
are formed under and on each shade pattern
111
.
FIG. 3A
to
FIG. 3D
are diagrams showing a conventional fabrication method of a phase shift photomask. In
FIG. 3A
to
FIG. 3D
, the reference numbers
226
designates phase shift sections, and
225
denotes a hollow section (or a cavity section).
In the final fabrication process to fabricate a conventional phase shift photomask, as shown in
FIG. 3D
, the shade patterns
111
are formed adjacent to the hollow section
225
formed on the transparent glass substrate
220
. Further, the phase shift section
226
are formed adjacent to each shade pattern
111
.
As described above, a complicated topography or shape is formed on the photomask fabricated by the conventional photomask fabrication methods such as the method to form the shade patterns on the photomask at desired intervals shown in
FIG. 1A
to FIG.
1
F and
FIG. 2A
to
FIG. 2F
, and the method to form the phase shift pattern on the photomask at desired intervals shown in
FIG. 3A
to FIG.
3
D.
Thus, because each conventional photomask fabricated by the conventional methods has a complicated topography, it happens that the shade film is fallen or separated from the transparent glass substrate by a brush to be used during a washing process to eliminate dusts. In other words, the conventional photomask has a lower durability during the photomask fabrication process. This drawback of the conventional photomask causes to decrease a reliability of the photomask and to decrease the yield and quality of semiconductor integrated circuits manufactured by using the conventional photomask.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is, with due consideration to the drawbacks of the conventional technique, to provide photomasks, fabrication methods of the photomasks, and a semiconductor fabrication method of semiconductor integrated circuits such as liquid crystal displays. The photomasks of the present invention have a high mechanical durability during a fabrication process to fabricate the photomask, and has characteristics of a high image formation, a high quality, a high printing precision, and a higher yield in the fabrication process.
In accordance with a preferred embodiment of the present invention, a photomask comprises a transparent substrate, a hollow section formed on a surface of said transparent substrate, a shade pattern including a shade section, said shade section made up of a shade film and formed in said hollow section, and reflection preventing sections, each formed according to one of cases: each reflection preventing section formed on said shade section; each reflection preventing section formed under said shade section; and each reflection preventing section formed on and under said shade section.
In accordance with another preferred embodiment of the present invention, a photomask comprises a transparent substrate, a shade pattern formed on said surface of said transparent substrate, and a phase shift pattern selectively formed on said shade pattern and said transparent substrate. In the photomask, a surface of said phase shift pattern is flat.
In the photomask as another preferred embodiment, an end section of said phase shift pattern that is contacted to said transparent substrate has a sloped shape that is gradually thin.
In the photomask as another preferred embodiment, a difference of a step between said phase shift pattern and said transparent substrate at said end section of said phase shift pattern that is contacted to said transparent substrate is gradually small.
In accordance with a preferred embodiment of the present invention, a photomask comprises a transparent substrate, a hollow section formed on a surface of said transparent substrate, a shade pattern made up of a shade film, said shade film formed in said hollow section, and a phase shift pattern, whose surface is flat, selectively formed on said transparent substrate having said shade pattern formed in said hollow section.
In the photomask as another preferred embodiment, a thickness of an end section of said phase shift pattern contacted to said transparent substrate is gradually thin.
In accordance with a preferred embodiment of the present invention, a photomask comprises a transparent substrate, a hollow section formed on a surface of said transparent substrate, a shade pattern made up of a shade film, said shade film formed in said hollow section, and a phase shift pattern formed on said transparent substrate including said shade pattern formed in said hollow section.
In the photomask as another preferred embodiment, an end section of said phase shift pattern that is contacted to said transparent substrate has a sloped shape that is gradually thin.
In the photomask as another preferred embodiment, said phase shift pattern includes one of or a combination of: a phase shift pattern of a Levenson's type, a phase shift pattern of an auxiliary shifter type; a phase shift pattern of an edge highlighting type; a phase shift pattern of a half tone type; a phase shift pattern of a half tone type with a shade pattern, a phase shift pattern of a shifter shading type with a shade pattern; and a phase shift pattern of an intermediate phase type.
In accordance with a preferred embodiment of the present invention, a photomask fabrication method comprises the steps of forming a resist film on a transparent substrate, forming a desir
Burns Doane Swecker & Mathis L.L.P.
Huff Mark H.
Mohbamedulla Saleha R.
Renesas Technology Corp.
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