Radiation imagery chemistry: process – composition – or product th – Radiation modifying product or process of making – Radiation mask
Reexamination Certificate
2001-09-24
2004-11-23
Rosasco, S. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Radiation modifying product or process of making
Radiation mask
Reexamination Certificate
active
06821683
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the treatment of correction of design pattern data for fabrication of photomask, which is needed following the miniaturization and high density of patterns on a semiconductor wafer, and in particular relates to a method for correcting design pattern data used for forming a pattern of photomask so as to obtain the objective shape of a figure pattern on a wafer and a photomask having patterns corrected by the method for correcting design pattern data.
2. Related Art
Recently, improved integration and functionality have been desired for various LSIs typified by ASIC. Namely, it is desired to decrease chip size as much as possible to realize high functionality.
The above-mentioned LSIs such as ASIC are produced through several steps of making figure data which are called “pattern data” for forming patterns of a photomask through function design, logical design, circuit design and layout design and others, fabricating a photomask using the figure data, and thereafter transferring the patterns of photomask on a wafer by demagnification projection to carry out the fabrication of a semiconductor circuit.
A photomask is produced generally by drawing the above-mentioned figure data (pattern data) on photosensitive resist put on a shielding film of a substrate for photomask (also called “photomask blanks”) using an electron beam exposure system or aligner of photo such as excimer laser, and through the steps of development and etching.
Namely, photosensitive resist is applied on a shielding metallic thin film provided on a glass substrate and dried. A latent image is formed on the photosensitive resist by applying ionizing radiation only to the fixed,areas, and the photosensitive resist is developed to obtain the resist patterns having a desired shape corresponding to the exposure areas of ionizing radiation. Thereafter, the metallic thin film is etched into the shape of the resist pattern by using the resist pattern as etching resistant resist, by which a photomask having a desired metallic thin film is formed.
In the case where patterns of photomask are exposed onto a wafer by demagnification projection to transfer the patterns to the wafer, the photomask is also called “reticle mask”.
In such a way, patterns of photomask are transferred onto a wafer by demagnification projection by which circuit patterns are formed on a wafer. However, there is a case where patterns are not formed onto a wafer with the same size as the patterns of photomask according to the design conditions because together with LSI being more integrated, recently the size of the exposed shape (size of the exposed shape on a wafer) has miniaturized more and more to the extent that the size of the exposed shape approaches the wavelength of an exposed beam or the size of an exposed shape is smaller than the wavelength of the exposed beam so that transformation of the shape of exposed beam called “optical proximity effect” is generated when transferring patterns of photomask on a wafer through demagnification projection. Accordingly, there is a case where even if patterns formed on a photomask have the same size, patterns corresponding to the patterns formed on the photomask are not formed on a semiconductor wafer with the same size as the size of patterns of the photomask according to design conditions.
In such a way, a difference between figure patterns of the photomask and the patterns formed on a wafer corresponding to the figure patterns of the photomask are produced. Therefore, it is necessary to change the shape of the photomask according to the objective shape of the figures formed on the wafer.
Thus it is now necessary to use figure data in which correction is given to original figure data (hereinafter it is called “design pattern data”) for the fabrication of the photomask.
Further, a difference between figure data used and figures on a photomask corresponding to the figure data has started to be problematic.
In such a way, the correction of design pattern data in the formation of fine patterns on a semiconductor wafer and the correction of design pattern data in the fabrication of photomask came to be applied.
First, referring to drawings, the technique of correction of design pattern data in the formation of fine patterns on a semiconductor wafer is explained concretely.
FIG.
3
(
a
) shows design pattern data. FIG.
3
(
b
) shows an example of patterns formed on a semiconductor wafer in case of the size of the design pattern being smaller than the wavelength of a light source of aligner for production of a semiconductor.
This shows that a difference in angles and width of line of design patterns appears according to the phenomenon of optical diffraction.
The technique of lessening the difference has been carried out actively from the latter half of the 1990's.
FIG.
6
(
a
) shows corrected pattern data in which correction is given to design patterns applied until now. The correction shown in FIG.
6
(
a
) is for the design patterns shown in FIG.
3
(
a
) to form a corrected design pattern.
The shapes of patterns formed on a semiconductor wafer become the shape close to a desired shape as design patterns formed on a wafer shown in FIG.
6
(
b
), using the corrected design pattern data.
Further, when forming design patterns on a semiconductor wafer, deviation from the correct shape of patterns arise according to the position of the pattern within an individual chip as a unit of exposure of the semiconductor, due to a process of semiconductor.
FIG.
3
(
b
) shows an example in which
figure 153
becomes thinner by the influence of position.
As for the deviation from the correct shape of a pattern depending on the position of a pattern generated within a chip of a unit of exposure of the semiconductor, the correction of a design pattern is difficult. Therefore, the correction of a design pattern for controlling deviation is not applied according to a general rule.
Then, referring to drawing, the correction of a design pattern in the production of a photomask is explained.
FIG.
4
(
a
) shows design pattern data. FIG.
4
(
b
) shows the shape of figure patterns formed on a photomask corresponding to the design pattern data shown in FIG.
4
(
a
).
Deviation of the roundness of the shape of the pattern formed on a photomask shown in FIG.
4
(
b
) and deviation of the width of line of the pattern depend on arrangement of the design patterns and the steps of producing a photomask.
Accordingly, in order to make patterns formed on the photomask approach to the shape of design pattern, a use of corrected design pattern data corrected as shown in FIG.
7
(
a
) was suggested.
FIG.
7
(
b
) shows the shape of figure patterns formed on a photomask corresponding to the corrected design pattern.
Further, as shown in FIG.
4
(
b
), there is the problem that a difference between pattern data and the shape of figure patterns formed on a photomask arises according to the position of a pattern within the photomask.
As for a difference between the pattern data and the shape of figure patterns depending on the position of the pattern within a photomask generated in the production of photomask, the correction of design pattern is difficult. Therefore, the correction of the design pattern for controlling the difference is not applied in a general rule.
The application of both the technique of correction of design pattern in the fabrication of a photomask and the technique of correction of design pattern in producing a semiconductor wafer is needed for obtaining both the shape of figure patterns of the photomask close to the objective shape of the pattern and the shape of figure patterns formed on a semiconductor wafer close to the objective shape of the pattern. However, heretofore, first, the correction of a design pattern for semiconductor wafer was applied, then, the correction of a design pattern for a photomask was carried out since the amounts of correction in a semiconductor wafer is larger than that for photomask in general.
An origin
Sakata Wakahiko
Shimohakamada Naoki
Toyama Nobuhito
Dainippon Printing Co., Ltd.
Flynn ,Thiel, Boutell & Tanis, P.C.
Rosasco S.
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