JP2006114836A - Projection aligner and method for manufacturing semiconductor device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a step-and-scan system projection aligner for improving the deterioration of pattern precision due to the deviation of an in-shot scan reduction rate and a lens reduction rate. <P>SOLUTION: This projection aligner is configured to independently control the correction of the magnification of the scanning direction of a lens configuring the projection optical system of a step-and-scan system projection aligner and a direction orthogonal to the scan direction, and newly provided with a means for measuring and correcting the difference of an in-shot scan reduction rate due to the deviation of the scan relative speeds of a mask and a wafer and the lens reduction rate of the scan direction. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a projection exposure apparatus and a method of manufacturing a semiconductor device, and more particularly to a step-and-scan type scanning exposure type projection exposure apparatus and a semiconductor device that perform exposure by synchronously scanning a mask and a wafer with respect to a projection optical system. It relates to a manufacturing method.

Conventionally, when a semiconductor device is manufactured using a photolithography technique, a stepper is used that collectively exposes and transfers a pattern on a mask to a wafer coated with a photoresist or the like via a projection optical system.
In recent years, as semiconductor technology has been highly integrated, it has been required to transfer a large area pattern on a mask to each shot region on a wafer. For this reason, in order to satisfy these requirements, various step-and-scan type scanning exposure apparatuses have been proposed.

FIG. 6 is a schematic diagram showing an outline of a step-and-scan type scanning exposure apparatus. FIG. 6 shows only necessary components for explaining the state of exposure, and other portions are omitted.
The exposure light 601 processed into a slit shape passes through the mask M, is adjusted to an arbitrary size by the reduction lens 602, and forms an image at a predetermined position on the wafer W. The mask M and the wafer W are synchronously scanned in the scanning direction indicated by the arrow in the drawing in accordance with the reduction ratio of the reduction lens 602, and the pattern on the mask is exposed to each shot on the wafer W (one shot is exposed at a time). Areas that represent possible areas on the wafer) are successively exposed.

  In a step-and-scan type scanning exposure apparatus, there is a great demand for forming a fine pattern with high dimensional accuracy, and further, there is a requirement for alignment accuracy when superposed and transferred on the pattern formed in the previous step. . For this reason, in order to improve the pattern alignment accuracy, adjustment of the reduction ratio of the mask pattern printed image in the shot is also an important issue.

  The step-and-scan projection exposure apparatus has a function of adjusting the reduction ratio of the mask pattern printing image in the shot to match the size of the base pattern in order to improve the base pattern alignment accuracy.

FIG. 7 is a schematic diagram showing a state of exposure in a shot. 7 shows an area corresponding to one shot on the mask M shown in FIG. 6 and an area on the wafer W corresponding to this. Since the mask stage and wafer stage (not shown) are synchronously scanned in the direction indicated by the arrow in the figure, the slit-shaped exposure light 701 sequentially scans the inside of the shot. In FIG. 6, for the sake of convenience, coordinate grids are written in the mask area and the wafer area.
FIG. 7 shows a case where the on-mask coordinate grid 702 represented by a solid line is larger than the on-wafer coordinate grid 703 represented by a dotted line, and this is adjusted by the reduction ratio correction function. This reduction ratio correction function can be adjusted independently in two directions, ie, a scanning direction 704 and a direction 705 orthogonal thereto.
The reduction ratio correction in the scan direction 704 is adjusted by the ratio between the scan speed of the mask and the scan speed of the wafer. For example, when the mask scanning speed is lower than the wafer scanning speed, a pattern reduced in the scanning direction from the pattern on the mask is exposed on the wafer. On the other hand, when the mask scanning speed is higher than the wafer scanning speed, a pattern enlarged in the scanning direction from the pattern on the mask is exposed on the wafer. This is called intra-shot scan reduction rate adjustment.
Correction of the reduction ratio in the direction 705 perpendicular to the scan direction is adjusted by the reduction ratio of the reduction lens 602 shown in FIG. This is called lens reduction rate correction.
Thus, by performing correction in two directions, the reduction ratio can be finely adjusted, and the pattern alignment accuracy is improved.

  However, if a reduction ratio is corrected using a conventional step-and-scan projection exposure apparatus, a difference between the in-shot scan reduction ratio and the lens reduction ratio in the scan direction occurs, and the contrast of the projected image decreases. It turns out that the problem of doing it occurs.

FIG. 8 is a flowchart showing the process of correcting the reduction ratio in the conventional projection exposure apparatus.
First, intra-shot scan reduction rate correction is performed (S801).
Next, the alignment mark provided on the wafer is measured using the wafer alignment unit (S802).
From this measurement result, the correction amount of the reduction ratio of the lens is calculated (S803).
Based on the calculation result, the reduction ratio of the lens is corrected (S804).
Exposure is started (S805).

FIG. 9 is an exposure image diagram illustrating the adjustment of the reduction ratio by the correction process shown in FIG. Only the width portion of the slit-shaped exposure light 601 shown in FIG. 6 is enlarged, and for convenience, a coordinate grid is shown in the mask area and the wafer area.
FIG. 9A shows a case in which the on-wafer coordinate grid 901 represented by a dotted line is larger than the on-mask coordinate grid 902 represented by a solid line, and this is shown in FIG. 9B by the reduction ratio correction function. Adjust as much as possible. The scanning direction is indicated by an arrow in the figure. The reduction ratio is corrected in two steps: a scan direction and a direction orthogonal to the scan direction.
First, as shown in FIG. 9C, the correction in the scan direction is performed by the intra-shot scan reduction rate correction described above. Since the direction perpendicular to the scanning direction (the horizontal direction in the drawing) is not affected by the ratio of the scanning speeds, the reduction ratio does not change.
Next, as shown in FIG. 9D, correction in the direction orthogonal to the scan direction is performed by the lens reduction rate correction described above. By correcting the reduction ratio of the lens, the reduction ratio in the scanning direction is also corrected, so that a difference from the in-shot scan reduction ratio correction performed in FIG. 9C occurs. For this reason, the projected image after the reduction ratio correction has a shape different from the ideal shape as shown in FIG.

  FIG. 9 is a chart showing the relationship between the reduction ratio correction and the contrast of the projected image. If the contrast image when the in-shot scan reduction rate matches the lens reduction rate is shown in FIG. 9 (a), the contrast image when these are shifted is as shown in FIG. 9 (b). The projected image is exposed while shifting.

  FIG. 10 is a chart showing the relationship between the difference between the in-shot scan reduction ratio, the lens reduction ratio in the scanning direction, and the contrast of the projected image. Specifically, the contrast when the difference is zero is plotted as 100, and the change in contrast when the difference is changed is plotted. As the difference between the in-shot scan reduction rate and the lens reduction rate in the scan direction increases, the contrast of the projected image decreases. This causes a variation in the dimension of the pattern and causes a deterioration of the pattern shape and dimensional accuracy.

  Conventionally, techniques relating to lens magnification correction in a projection optical system of a projection exposure apparatus have been proposed. For example, Japanese Patent Laid-Open No. 11-3856 discloses correction of lens magnification and skew components in a step-and-repeat type or step-and-scan type projection exposure apparatus. However, there is no description about the magnification difference caused by the deviation of the relative scanning speed between the mask and the wafer, and even if these techniques are adopted, the above-mentioned problems that are regarded as a problem in the present invention cannot be sufficiently solved. .

The present invention has been made on the basis of recognition of such a problem, and an object of the present invention is to maintain a good contrast of the projected pattern on the wafer by combining the in-shot scan reduction ratio and the lens reduction ratio. It is an object of the present invention to provide a projection exposure apparatus and a semiconductor device manufacturing method that stabilize dimensional accuracy.
Japanese Patent Laid-Open No. 11-3856 JP 2001-230192 A

According to a first aspect of the present invention, there is provided a projection exposure apparatus that projects a pattern on a mask illuminated by slit-shaped exposure light onto a wafer by a projection optical system,
A mask stage mounted with the mask and scanning in a predetermined scanning direction;
A wafer stage on which the wafer is mounted and which scans in the scan direction in synchronization with the mask stage;
A scan direction lens reduction ratio correction unit that corrects the scan direction lens reduction ratio of the lens constituting the projection optical system;
An orthogonal direction lens reduction ratio correction unit that corrects a lens reduction ratio in a direction orthogonal to the scan direction of the lens constituting the projection optical system;
The scanning direction lens reduction ratio correction means provides a projection exposure apparatus that corrects the reduction ratio of the lens in consideration of a reduction ratio component generated by a scanning speed ratio between the mask stage and the wafer stage.

Further, a projection exposure apparatus that projects a pattern on a mask illuminated by slit-shaped exposure light onto a wafer by a projection optical system,
A mask stage mounted with the mask and scanning in a predetermined scanning direction;
A wafer stage on which the wafer is mounted and which scans in the scan direction in synchronization with the mask stage;
Wafer alignment means for measuring alignment marks formed on the wafer;
A scanning direction lens reduction ratio correction means for correcting the scanning direction lens reduction ratio of the lens constituting the projection optical system based on the measurement value of the wafer alignment means;
Based on the measurement value of the wafer alignment unit, an orthogonal direction lens reduction rate correction unit that corrects a lens reduction rate in a direction orthogonal to the scan direction of the lens constituting the projection optical system;
An in-shot scan reduction ratio correcting means for correcting an in-shot scan reduction ratio caused by a speed ratio when the mask stage and the wafer stage scan an area (one shot) that can be exposed at a time;
A projection exposure apparatus is provided that includes a scan direction reduction rate difference detection unit that measures a difference between an in-shot scan reduction rate determined by the in-shot scan reduction rate correction unit and the scan direction lens reduction rate.

  Here, there is provided a projection exposure apparatus that corrects the difference between the in-shot scan reduction ratio measured by the scan direction reduction ratio difference detection means and the scan direction lens reduction ratio by the scan direction lens reduction ratio correction means.

  Further, the scan direction reduction rate difference detection unit repeatedly scans a test pattern at a scan speed determined by the in-shot scan reduction rate correction unit while varying the scan direction lens reduction rate, and a projected image of the test pattern A projection exposure apparatus that calculates the lens reduction ratio in the scan direction that maximizes the contrast of the image is provided.

  More specifically, the scanning direction reduction rate difference detecting means is provided in a line-and-space pattern mask installed on a mask stage, and in the same shape obtained by multiplying the mask dimension by a design magnification, provided at the imaging position of the wafer stage. And a sensor for measuring the light intensity of the exposure light transmitted through the shield, and a projection exposure apparatus that performs scanning in a direction orthogonal to the length direction of the line and space.

According to another aspect of the present invention, a semiconductor device is manufactured by projecting a pattern on a mask illuminated by slit-shaped exposure light onto a wafer by a projection optical system, and performing exposure by synchronously scanning the mask and the wafer. A method,
Correcting the lens reduction rate in the scan direction and the lens reduction rate in the direction orthogonal to the scan direction of the lens system constituting the projection system based on an alignment mark formed on the wafer;
Correcting the scan reduction ratio generated by the scanning speed ratio of the mask and the wafer in the projection optical system in which the magnification of the lens system is corrected;
A step of detecting a difference between the scan reduction rate and the lens reduction rate in the scan direction under the scanning condition in which the scan reduction rate is corrected,
Provided is a method of manufacturing a semiconductor device in which the difference is corrected by a lens reduction ratio in the scan direction.

Further, in the step of detecting a difference between the scan reduction ratio and the lens reduction ratio in the scan direction, the test pattern is scanned at a scan speed in which the scan reduction ratio is corrected while varying the lens reduction ratio in the scan direction. Repeatedly, the lens reduction ratio in the scan direction that maximizes the contrast of the projected image of the test pattern is calculated,
In the correction of the difference, a method of manufacturing a semiconductor device is provided in which the lens reduction ratio in the scan direction is corrected again so that the lens reduction ratio in the scan direction has the maximum contrast.

  According to the present invention, it is possible to independently control the correction of the magnification in the scanning direction and the direction orthogonal to the scanning direction in the lens constituting the projection optical system of the step-and-scan type projection exposure apparatus. Then, by newly providing a means for measuring and correcting the difference between the in-shot scan reduction ratio and the lens reduction ratio in the scan direction due to the deviation of the scan relative speed between the mask and the wafer, the projection on the wafer is performed. Prevent deterioration of pattern contrast. Thereby, the shape and dimensional accuracy of the pattern are improved.

FIG. 1 is a schematic diagram showing an outline of a projection exposure apparatus according to an embodiment of the present invention. In the figure, only the configuration necessary for explaining the present invention is shown.
Mask M and wafer W are mounted on mask stage 101 and wafer stage 102. The mask stage 101 and the wafer stage 102 perform a synchronous scanning motion, and the circuit pattern formed on the mask M is sequentially exposed on the wafer W at an arbitrary reduction ratio.
The reduction ratio is determined by the reduction lens 104 constituting the projection optical system 103. The wafer alignment unit 105 measures the alignment mark 106 provided on the wafer W, and calculates the position correction and the reduction rate correction amount of the reduction lens 104. The lens reduction ratio correction unit 107 adjusts the magnification of the magnification correction lens 108 based on the calculated reduction ratio correction amount. The magnification correction lens 108 can independently adjust the magnification in the scanning direction and the direction orthogonal thereto.

The synchronous scanning movement of the mask stage 101 and the wafer stage 102 is controlled by the scan control mechanism 109. The in-shot scan reduction rate is determined by the speed ratio of the scanning speed of the mask stage 101 and the wafer stage 102.
The scan direction reduction rate difference detection unit 110 measures the difference between the in-shot scan reduction rate and the reduction rate in the scan direction determined by the projection optical system. Here, the calculated difference in the reduction ratio in the scan direction is sent to the lens reduction ratio correction means 107, and this difference is corrected by the lens reduction ratio in the scan direction of the magnification correction lens 108.

Next, a reduction rate correction process using the projection exposure apparatus shown in FIG. 1 will be described.
FIG. 2 is a flowchart showing a reduction rate correction process in the projection exposure apparatus according to the embodiment of the present invention.
First, in-shot scan reduction rate correction is performed using the scan control mechanism 109 (S201).
Next, the alignment mark 106 provided on the wafer W is measured using the wafer alignment unit 105 (S202).
From this measurement result, the correction amount of the reduction ratio of the reduction lens 104 is calculated (S203).
From this calculation result, the reduction ratio of the magnification correction lens 108 is corrected (S204).
Next, the difference between the in-shot scan reduction rate and the reduction rate in the scan direction of the projection optical system 103 corrected in the previous step (S204) is measured using the scan direction reduction rate difference detection unit 110 (S205). .
From this measurement result, the correction amount of the scanning direction of the reduction lens 104 is calculated (S206).
Based on the calculation result, the reduction ratio in the scanning direction of the magnification correction lens 108 is corrected (S207). At this time, the magnification correction is performed only in the scanning direction and not in the direction orthogonal to the scanning direction. This is because the direction orthogonal to the scan direction is not affected by the in-shot scan reduction rate.
Exposure is started (S208).

As described above, the projection exposure apparatus according to the embodiment of the present invention has a function capable of independently correcting the reduction lens in the scan direction and the lens reduction rate in the direction orthogonal thereto, the in-shot scan reduction rate, and the lens in the scan direction. Because it has a function to detect the difference in reduction ratio, after correcting the lens reduction ratio of the projection optical system in a stationary state, the lens reduction ratio in the scan direction of the projection optical system is again matched to this in-shot scan reduction ratio. Can be corrected.
With the conventional projection exposure apparatus, it is possible to correct the deviation between the in-shot scan reduction ratio and the lens reduction ratio as shown in FIG. 8D, and an ideal projection as shown in FIG. An image can be obtained.

Next, the configuration of the scanning direction reduction rate difference detection unit 110 shown in FIG. 1 and the reduction rate difference calculation method will be described.
FIG. 3 is an image diagram showing how the scan direction reduction rate is detected in the projection exposure apparatus shown in FIG. The same components as those in FIG. 1 are denoted by the same reference numerals.
The scan direction reduction rate difference detection means 110 includes a test pattern 301 installed on the mask stage, a light shielding object 302 installed at the imaging position on the wafer stage, and a sensor 303 installed under the light shielding object 302. Consists of.

FIG. 4 is a schematic diagram showing the shape of the test pattern 301.
The line and space shape is a shape in which the width of the line 401 and the space 402 is obtained by multiplying the limit resolution size of the exposure apparatus by the exposure magnification. A test pattern 301 is placed on the mask stage 101 and irradiated with exposure light 304. A light shielding object 302 having the same shape as the test pattern 301 is placed on the wafer stage 102 on which the exposure light transmitted through this pattern forms an image via the projection optical system 103. The size of the light shield 302 is a value obtained by multiplying the mask dimension by the reduction ratio of the projection optical system. A sensor 303 is installed below the light shield 302 and measures the light intensity of the exposure light transmitted through the light shield.

The detection of the scan direction reduction rate difference is performed in the following steps.
First, adjustment is performed so that the projected image of the test pattern 301 overlaps the light shielding object 302 in a stationary state where no scanning operation is performed. The length direction of the line and space is set to a direction orthogonal to the scanning direction of the exposure apparatus indicated by an arrow in FIG.
Next, the scanning operation is repeated with the set scan direction reduction ratio, and the light intensity of the exposure light transmitted through the light shielding object 302 is measured by the sensor 303. At this time, the reduction ratio in the scanning direction of the magnification correction lens 108 is gradually changed by the lens reduction ratio correction means 107 shown in FIG.
From this measurement result, the value of the reduction ratio in the scanning direction of the magnification correction lens 108 that maximizes the light intensity is determined.

  In the scanning direction reduction difference detection process described here, the value of the sensor 303 becomes the highest value when scanning is performed in a state where the test pattern 301 and the pattern on the light shielding object 302 match. This state means that the intra-shot scan reduction rate and the lens reduction rate of the projection optical system coincide. The difference between the reduction ratio of the magnification correction lens adjusted in the stationary state and the reduction ratio of the magnification correction lens adjusted through the scanning direction reduction ratio difference detection process is the difference between the in-shot scan reduction ratio and the scan direction lens reduction ratio. It becomes a difference. Therefore, the difference between the in-shot scan reduction ratio and the scan direction lens reduction ratio is corrected by the magnification correction lens by adjusting the reduction ratio in the scan direction of the magnification correction lens so that the value of the sensor 303 becomes the maximum value. Become.

FIG. 5 is a chart showing the relationship between the light intensity measured by the scanning direction reduction rate difference detecting means and the lens reduction rate in the scanning direction. The vertical axis represents the light intensity, and the horizontal axis represents the reduction ratio in the scanning direction of the magnification correction lens.
From FIG. 5, it can be seen that when the reduction ratio of the magnification correction lens reaches a certain value, the light intensity reaches the maximum value. At this time, the contrast of the projected image becomes the maximum value.
The effect of the present invention can be confirmed by looking at an enlarged view of an actual pattern at each of the points (1) to (3) shown in the chart.

Thus, according to the embodiment of the present invention, the contrast of the projection pattern on the wafer can be kept good by adjusting the reduction ratio. As a result, the pattern shape and dimensions on the wafer can be stabilized with high accuracy.
In addition, it is not necessary to actually expose and observe the resist, thereby shortening the adjustment time and reducing the cost.
Furthermore, the throughput is remarkably improved by automatically performing a series of steps for correcting the reduction ratio.

It is a schematic diagram showing the outline | summary of the projection exposure apparatus concerning embodiment of this invention. It is a flowchart showing the correction process of the reduction ratio in the projection exposure apparatus concerning embodiment of this invention. It is an image figure showing the mode of the scanning direction reduction rate detection in the projection exposure apparatus shown in FIG. It is a schematic diagram showing the shape of a test pattern. It is a graph showing the relationship between the light intensity measured by the scanning direction reduction rate difference detection means and the lens reduction rate in the scanning direction. Schematic diagram showing the outline of a conventional step-and-scan type scanning exposure apparatus It is a schematic diagram showing the mode of exposure in a shot. It is a flowchart showing the process of the correction | amendment of the reduction ratio in the conventional projection exposure apparatus. It is an exposure image figure explaining adjustment of the reduction rate by the correction process shown in FIG. It is a chart showing the relationship between the difference between the in-shot scan reduction ratio and the lens reduction ratio in the scanning direction and the contrast of the projected image.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 Mask stage 102 Wafer stage 103 Projection optical system 104,602 Reduction lens 105 Wafer alignment unit 106 Alignment mark 107 Lens reduction rate correction means 108 Magnification correction lens 109 Scan control mechanism 110 Scan direction reduction rate difference detection means 301 Test pattern 302 Light shielding object 303 Sensors 304, 601 and 701 Exposure light 401 Line 402 Spaces 702 and 902 On-mask coordinate grid 703 and 901 On-wafer coordinate grid 704 Scan direction 705 Direction perpendicular to the scan direction M Mask W Wafer

Claims (7)

A projection exposure apparatus that projects a pattern on a mask illuminated by slit-shaped exposure light onto a wafer by a projection optical system,
A mask stage mounted with the mask and scanning in a predetermined scanning direction;
A wafer stage on which the wafer is mounted and which scans in the scan direction in synchronization with the mask stage;
A scan direction lens reduction ratio correction unit that corrects the scan direction lens reduction ratio of the lens constituting the projection optical system;
Orthogonal direction lens reduction ratio correction means for correcting a lens reduction ratio in a direction orthogonal to the scanning direction of the lenses constituting the projection optical system;
With
The projection exposure apparatus characterized in that the scanning direction lens reduction rate correction means corrects a reduction rate of a lens in consideration of a reduction rate component generated by a scanning speed ratio of the mask stage and the wafer stage. A projection exposure apparatus that projects a pattern on a mask illuminated by slit-shaped exposure light onto a wafer by a projection optical system,
A mask stage mounted with the mask and scanning in a predetermined scanning direction;
A wafer stage on which the wafer is mounted and which scans in the scan direction in synchronization with the mask stage;
Wafer alignment means for measuring alignment marks formed on the wafer;
A scanning direction lens reduction ratio correction means for correcting the scanning direction lens reduction ratio of the lens constituting the projection optical system based on the measurement value of the wafer alignment means;
Based on the measurement value of the wafer alignment unit, an orthogonal direction lens reduction rate correction unit that corrects a lens reduction rate in a direction orthogonal to the scan direction of the lens constituting the projection optical system;
In-shot scan reduction rate correction means for correcting an in-shot scan reduction rate caused by a speed ratio when the mask stage and the wafer stage scan an area that can be exposed at a time;
A scan direction reduction rate difference detection unit that measures a difference between the in-shot scan reduction rate determined by the in-shot scan reduction rate correction unit and the scan direction lens reduction rate;
A projection exposure apparatus comprising:   3. The projection exposure according to claim 2, wherein the difference between the in-shot scan reduction rate measured by the scan direction reduction rate difference detection unit and the scan direction lens reduction rate is corrected by the scan direction lens reduction rate correction unit. apparatus.   The scan direction reduction rate difference detection unit repeatedly scans a test pattern at a scan speed determined by the in-shot scan reduction rate correction unit while varying the scan direction lens reduction rate, and the contrast of the projected image of the test pattern 4. The projection exposure apparatus according to claim 2, wherein the reduction ratio of the lens in the scan direction is calculated so that the maximum is obtained. The scanning direction reduction rate difference detection means includes a line-and-space pattern mask installed on a mask stage, a shielding object having a similar shape provided at an imaging position of the wafer stage, and the mask size multiplied by a design magnification. A sensor for measuring the light intensity of the exposure light transmitted through the shield,
5. The projection exposure apparatus according to claim 4, wherein scanning is performed in a direction orthogonal to the length direction of the line and space. A method of manufacturing a semiconductor device in which a pattern on a mask illuminated by slit-shaped exposure light is projected onto a wafer by a projection optical system, and exposure is performed by synchronously scanning the mask and the wafer,
Correcting the lens reduction rate in the scan direction and the lens reduction rate in the direction orthogonal to the scan direction of the lens system constituting the projection system based on an alignment mark formed on the wafer;
Correcting the scan reduction ratio generated by the scanning speed ratio of the mask and the wafer in the projection optical system in which the magnification of the lens system is corrected;
Detecting a difference between the scan reduction ratio and the lens reduction ratio in the scan direction in the scanning condition in which the scan reduction ratio is corrected;
With
A method of manufacturing a semiconductor device, wherein the difference is corrected by a lens reduction ratio in the scan direction. In the step of detecting the difference between the scan reduction ratio and the lens reduction ratio in the scan direction, the test pattern scan is repeated at a scan speed in which the scan reduction ratio is corrected while varying the lens reduction ratio in the scan direction, Calculate the scan direction lens reduction ratio that maximizes the contrast of the projected image of the test pattern,
7. The method of manufacturing a semiconductor device according to claim 6, wherein in the correction of the difference, the lens reduction ratio in the scan direction is corrected again so as to be the scan direction lens reduction ratio at which the contrast is maximized.