Image analysis – Applications – Manufacturing or product inspection
Reexamination Certificate
1998-12-17
2001-06-19
Couso, Jose L. (Department: 2621)
Image analysis
Applications
Manufacturing or product inspection
C382S145000, C382S151000
Reexamination Certificate
active
06249597
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of correcting a mask pattern which causes a mask pattern of a photomask used when producing a semiconductor device etc. to deform so as to give a transfer image close to a desired design pattern, a correction apparatus working this method of correction, a photomask obtained by this method of correction, an exposure method for performing exposure using a photomask having such a corrected mask pattern, a semiconductor device produced by photolithography using a photomask having such a corrected mask pattern, and an apparatus for production of a photomask and an apparatus for production of a semiconductor device using this method of correction.
2. Description of the Related Art
In the production of a semiconductor device etc., the process for transferring a mask pattern to a resist material on a semiconductor wafer is referred to as the photolithographic process.
In recent years, along with the increasing miniaturization of the semiconductor devices produced, the design rule has become smaller and lithography is being performed near the theoretical limit of resolution. This fact is leading to the disadvantages of a deterioration of the performance of the semiconductor device due to deformation of the transfer pattern and reduction of yield due to bridging (error connection) and disconnection of the patterns. Accordingly, the mask patterns have been optimized by trial and error so as to obtain the desired resist pattern. The practice has been to prepare mask patterns to which have been added a plurality of modification patterns for a design pattern, find the transfer patterns by simulation in transfer experiments, and add the modification pattern giving the transfer pattern closest to the design pattern to the mask pattern.
In recent years, light proximity effect correction techniques by which mask patterns have been automatically optimized by computer, have been developed. In the light proximity effect correction, the mask pattern deformed so as to improve the transfer image to match with the input design pattern has been sought by computations.
However, it suffers from the following disadvantages in the related art. In the trial and error method, it takes tremendous time and work to find the optimal mask pattern. Therefore, this can only be used for limited patterns. Accordingly, it cannot be used for irregular patterns such as ASICs(Applied Specific Integrated Circuits). Further, in the trial and error method, the number of mask patterns which can be evaluated is limited. Therefore, there is the possibility of overlooking a better mask pattern and the precision of correction of the mask pattern is limited.
Therefore, in recent years, technologies for automatically correcting mask patterns have been developed. These have had the following disadvantages, however.
First, the corrected mask pattern would sometimes cause a deterioration in the processing margin, that is, the exposure margin and the focal depth. Therefore, the correction might conversely cause a deterioration in the yield, making use for actual processes impossible.
Further, one method of correction is to find the distribution of light intensity using simulation of the light intensity, use the contour lines obtained by slicing by the threshold value of the same as the transfer image, and correct this to the optimal mask pattern. In this method, however, no consideration is given to the resist process, so the contour lines obtained by slicing the distribution of light intensity do not match the resist image obtained by the actual process and thus the resist image is not sufficiently corrected.
Further, depending on the method of correction, due to the excessive correction of the corners of the pattern or the ends of the line patterns etc., distortion would occur at other portions, bridging (miss-connection) of the resist pattern would occur when the amount of exposure or focal position fluctuated, or mask patterns difficult to fabricate would be produced.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a means and method for enabling calculation of a mask pattern so as to give a resist pattern close to the design pattern and thereby produce a high performance device with a high yield.
According to one aspect of the present invention, there is provided a method of correcting a mask pattern wherein the mask pattern of a photomask used in a photolithography step is made to deform so as to give a transfer image close to a desired design pattern, the method of correcting a mask pattern comprises: an evaluation point arranging step for arranging a plurality of evaluation points along the outer periphery of the desired design pattern; a simulation step for simulating a transfer image obtained at exposure under predetermined transfer conditions using a photomask of a design pattern with evaluation points; a comparison step for comparing for each evaluation point the difference between the simulated transfer image and the design pattern; and a deformation step for deforming the design pattern in accordance with the differences compared for each evaluation point so that the differences become smaller.
The evaluation point arranging step arranges the evaluation points at the corners of the desired design pattern and arranges the evaluation points at predetermined intervals at the sides of the pattern.
Or, the evaluation point arranging steps arranges the evaluation points at the corners of the desired design pattern, adds a predetermined number of evaluation points at predetermined narrow intervals from the corners at the sides of the pattern, and arranges the evaluation points at predetermined wide intervals at remaining portions of the sides away from the corners.
Or, the evaluation point arranging step does not add evaluation points at the small sides of the design pattern of less than predetermined lengths, does not add evaluation points at the corners near the small sides, and arranges the evaluation points at predetermined intervals at the other corners and sides.
Or, the evaluation point arranging step arranges the evaluation points at the corners of the design pattern not at the boundaries of predetermined repeating regions and arranging the evaluation points at predetermined intervals at the sides of the pattern not at the boundaries of predetermined repeating regions.
Or, the evaluation point arranging step arranges the evaluation points at the corners of the design pattern not at the boundaries of predetermined repeating regions and arranging the evaluation points at predetermined intervals at the sides of the pattern not at the boundaries of predetermined repeating regions.
Or, the evaluation point arranging step arranges the evaluation points at the corners of the design pattern, adds evaluation points at the substantially midpoints of short sides of the pattern smaller than a predetermined width, and arranges the evaluation points at predetermined intervals at the other sides of the pattern.
Or, the evaluation point arranging step arranges the evaluation points at the corners of the design pattern except corners of the pattern adjoining sides shorter than a predetermined length, adds evaluation points at relatively large intervals at the ends adjoining the sides shorter than a predetermined length at sides of the pattern longer than a predetermined length and arranges evaluation points at predetermined intervals at the sides of the pattern longer than the predetermined length.
Preferably, a design pattern deformed in the deformation step is used to repeat at least once the process from the simulation step to deformation step.
Preferably, the simulation step simulates transfer images under a plurality of transfer conditions based on combinations of a plurality of amounts of exposure of preset exposure margins and a plurality of focal positions within a preset range of focal depths to obtain a plurality of transfer images, the comparison step compares for each evaluation point the difference with
Couso Jose L.
Dang Duy M.
Kananen Ronald P.
Rader Fishman & Grauer
Sony Corporation
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