JP3606410B2 - Vertical illumination setting device for epi-illumination optical system - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a vertical illumination setting device in an epi-illumination optical system, and more particularly, to a misalignment measuring device for measuring misregistration amounts between various patterns formed on a wafer, so-called registration. The present invention relates to a vertical illumination setting device capable of detecting a vertical degree of irradiation light of a measurement optical system and adjusting the detection light to be vertical.
[0002]
[Prior art]
In the manufacture of semiconductor ICs, various patterns are formed on a wafer having a smooth surface. The positions of these patterns must be accurately formed, and the amount of misalignment between them, the so-called registration, is precisely measured between the pre-formed pattern and the next pattern to be formed. Has been.
For example, in a certain semiconductor manufacturing process, the amount of misalignment between a resist pattern formed by exposure through a mask or the like and an etched pattern already formed in the previous process is registered. By measuring with high accuracy by a measuring device (position displacement measuring device).
[0003]
In recent years, with a dramatic increase in the storage capacity of DRAM from 16M to 64M, 256M, measurement and inspection of this misregistration amount has become increasingly important. In order to manufacture a DRAM having a high storage capacity, it is necessary to adjust the detection optical system of the exposure apparatus and position the center of the detection optical system and the center of each chip on the wafer with high accuracy. In this conventional positioning, the center of the wafer surface and the center of the objective lens of the optical system of the exposure apparatus, the relay lens, and the center of a detector such as a CCD for detecting the alignment mark are aligned by laser light. By aligning with.
[0004]
[Problems to be solved by the invention]
Since the measurement optical system of the registration measuring apparatus is normally irradiated to a sample such as a wafer through an objective lens by epi-illumination, the center alignment and various alignments are performed through the epi-illumination optical system. Is called. Since this epi-illumination optical system also serves as a detection optical system at the same time, alignment and detection with high accuracy cannot be performed unless the vertical illumination of the epi-illumination optical system is accurately set vertically.
The position adjustment for aligning the epi-illumination optical system perpendicularly to the sample has been conventionally performed. This is because the sample is measured several times, and the perpendicularity of the illumination light is determined empirically from the tendency of the measured values. The current situation is adjusting. For example, 10 or more samples are measured first, adjustments are made according to the results, and this is repeated. Therefore, the vertical adjustment will take several hours or more. Moreover, it is unclear whether it is perfectly adjusted vertically. In other words, adjustment of the verticality of the epi-illumination light requires skill and takes time.
An object of the present invention is to solve such a problem of the prior art, and an epi-illumination optical system capable of detecting the vertical degree quantitatively and setting the state of the epi-illumination to be substantially vertical. A vertical illumination setting device is provided.
[0005]
[Means for Solving the Problems]
In order to achieve such an object, the vertical illumination setting device in the epi-illumination optical system of the present invention is characterized by an aperture having an aperture that transmits light to the position of the optical path of the illumination optical system that is conjugate with the focal point of the objective lens. The aperture has a pattern in a direction perpendicular to the pixel array direction and the aperture is moved to perform epi-illumination on the pattern at first and second epi-illumination positions on the sample surface. The focus position is moved by a predetermined amount in the vicinity of the pattern in the direction perpendicular to the pattern, and this detection signal is handled based on the detection signal of the optical sensor reflected from the edge of the pattern obtained at each of the multiple focus positions. The pixel position to be calculated is calculated, and the change amount of the pixel position according to the movement of the predetermined amount at each of the first epi-illumination position and the second epi-illumination position, the first epi-illumination position and the second Substantially determine the epi-illumination position on the specimen surface where the pixel position is not changed by the epi-illumination position is for setting the aperture stop so as to correspond to this position.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
The principle of the vertical illumination setting according to the present invention will be described first with reference to FIG. 7. It is assumed that the image of the pattern 9 a in the inspection area is directly imaged on the one-dimensional optical sensor via the objective lens 1 and the pattern image is collected. . In such a case, when the illumination light is substantially perpendicular to the wafer 9, as shown in FIG. Even if it is moved, the position of the image of the pattern 9a formed on the wafer 9 does not shift so much. Therefore, the light receiving position of the edge on the one-dimensional optical sensor (position indicated by ●) hardly changes.
On the other hand, when the illumination light is obliquely applied to the wafer, an image of the pattern 9a formed on the wafer 9 when the focal point is moved before and after the focusing position as shown in FIG. Since the light receiving position moves according to the movement of the focal position, the light receiving position (●) of the edge on the one-dimensional optical sensor changes according to the movement of the focal position.
[0007]
Therefore, as described above, the position of the aperture stop (pinhole) of the illumination optical system arranged in a conjugate relationship with the focal position of the objective lens is set as the first epi-illumination position on the wafer, so that The incident light is tilted to move the focal point before and after the in-focus position with respect to the pattern, the amount of change in the light receiving position of the edge detection signal is sampled, and the second epi-illumination on the wafer in the direction opposite to the tilt. An aperture stop is set at the position, and the amount of change in the edge position is sampled in the same manner, and the aperture stop in which the irradiation light is vertical due to the relationship between the change amount of these two edge positions and the first and second incident illumination positions. By calculating the epi-illumination position on the wafer and setting the aperture stop at a position corresponding to that position, the irradiation light can be made perpendicular to the sample.
[0008]
【Example】
FIG. 1 is an explanatory diagram of a registration measuring apparatus according to an embodiment to which a vertical illumination setting apparatus in an epi-illumination optical system according to the present invention is applied. FIG. 2 shows a pattern detection signal on a wafer and a CCD at each focus position. FIG. 3 is an explanatory view of the relationship with the pixel position of the sensor, FIG. 3 is an explanatory view of the position change for detecting the reflected light receiving position from the edge of the pattern in inclined illumination, and FIG. FIG. 5 is a flowchart of the vertical illumination setting process, and FIG. 6 is each focus position in inclined illumination. FIG. It is explanatory drawing of the relationship with a pixel number.
[0009]
Reference numeral 100 denotes a registration measuring apparatus. Reference numeral 1 denotes an objective lens that performs epi-illumination and sends reflected light from the wafer 9 to the CCD linear sensor 10 and the CCD linear sensor 11. A relay lens 2a, a cylindrical lens 2b (X-axis direction), a relay lens 3a, and a cylindrical lens 3b (Y-axis direction) are provided in alignment with the center of the objective lens 1. The CCD linear sensor 10 and the CCD linear sensor 11 are provided for detecting the amount of positional deviation in registration measurement, and detect the reflected light via the optical system in the X-axis direction and the Y-axis direction. It is a vessel.
[0010]
A half mirror 4 separates reflected light from the wafer 9 into a detection system for the X direction and the Y direction. Reference numeral 5 denotes an illumination optical system, which corresponds to the light source 50, the fiber 52 provided in the middle of the optical path, the diaphragm mechanism 53 that narrows the illumination light, the field diaphragm 54, and the half mirror 55. And a lens system for generating condensed light or parallel light. 7 is a wafer chuck, 8 is an XYZ moving stage for moving the wafer chuck 7 in the XYZ directions, and 9 is a wafer for vertical inspection chucked by the wafer chuck 7.
[0011]
In this embodiment, an opening position moving mechanism for moving the position of the aperture (pinhole) of the aperture mechanism 53 of the illumination optical system 5 in the X and Y directions in the XY coordinate system taken on the surface of the wafer 9 for vertical inspection. 60 is provided. This is driven by the control device 20 via the drive circuit 14 such as a moving mechanism. As a result, the center position of the irradiation light is two-dimensionally moved in the X and Y directions on the wafer 9 to measure and adjust the verticality.
The vertical inspection wafer 9 is arranged so as to be perpendicular to the axis of the objective lens 1, and a strip-like pattern edged with a predetermined width parallel to the surface is formed on the surface. The diameter of the aperture of the diaphragm mechanism 53 is a pinhole (aperture stop) of about 1.0 mmφ.
[0012]
First, in addition to the vertical illumination setting process described later, the control device 20 controls the A / D conversion circuit (A / D) 15 to digitize the detection signals of the CCD linear sensors 10 and 11 under the control of the control device 20. It is sent to the control device 20.
[0013]
The control device 20 includes an image memory 16, a digital signal processor (DSP) 17, a focus controller 18, an MPU 19, and a memory 21. The MPU 19 and the image memory 16, the DSP 17, the focus controller 18, and the memory 21 are connected via a bus 22. Etc. are connected to each other.
The A / D 15 receives detection signals from the CCD linear sensors 10 and 11, and sends the A / D converted data to the image memory 16 at a predetermined sampling period. The image memory 16 sequentially stores data from the A / D 15.
[0014]
The DSP 17 is controlled by the MPU 19 to receive the digital data of the image memory 16, calculates the shift amount ΔX (ΔY) at a high speed therefrom, and sends the calculation result to the MPU 19. This is a processor dedicated to calculating a deviation amount. The focus controller 18 is controlled by the MPU 19 to control the CCD linear sensors 10, 11, A / D 15 and image memory 16, receives data from the image memory 16, and moves the XYZ moving stage 8 in the Z direction for focusing. I do. Note that the calculation process of the deviation amount ΔX (ΔY) is not directly related to the invention, and thus will be omitted.
The memory 21 includes an edge pixel position detection program 21a, an aperture stop position adjustment program 21b, a vertical illumination setting program 21c, a mark deviation amount measurement program 21d, and the like.
A stage drive circuit 23 sends a drive signal to the XYZ moving stage 8 for moving the XYZ moving stage 8 in the X, Y, and Z directions according to a control signal from the control device 20.
[0015]
The edge pixel position detection program 21a executes the reflection process from the A / D-converted pattern stored in the image memory 16 after the MPU 19 executes this process to capture the detection signal from the CCD sensor. Detection data (voltage value of the detection signal) about the light is read and taken, and a differential process is performed on this data, and a signal at the edge portion of the pattern formed on the inspection wafer 9 (in this case, reflection from one edge) This program is obtained by differentiating a peak corresponding to a light receiving signal) and detecting a pixel number (pixel position) corresponding to the peak position. Note that the pixel position here may be a relative position from the relationship for obtaining the displacement amount of the pixel position, and is simply a count that is counted in the entire received light signal in the field of view focused at that time stored in the image memory 16. A value may be set as a detection position. Therefore, this position can be easily obtained from the position of the data on the image memory 16 from which the peak value is obtained.
The aperture stop position adjustment program 21b, when executed by the MPU 19, drives the aperture position moving mechanism 60 to move the position of the aperture (pinhole) of the aperture mechanism 53 in the X and Y directions on the surface of the wafer 9. It is a program.
[0016]
When the MPU 19 executes this, the vertical illumination setting program 21c calls the aperture stop position adjustment program 21b to set the aperture position to a predetermined XY coordinate, and the focus position with respect to the pattern is set as the center. The edge pixel position detection program 21a is called to detect the pixel number of the edge light receiving position at each focus moving position, and the coordinates of the opening position and the displacement amount of the edge light receiving position are obtained. Based on the above, the position of the epi-illumination on the wafer 9 is calculated, and the position of the opening (pinhole) is set so as to be the position.
[0017]
FIG. 2 shows the relationship between the pattern detection signal on the wafer and the pixel position of the CCD sensor at each focus position. 9a is a cross-sectional view of one of the patterns formed on the wafer 9 for inspection. Represents. If the cross section of the pattern 9a is a cross section in the X direction, the detection signal of the pattern 9a received by the CCD linear sensor 10 is 10a. Of course, this is a signal from the CCD linear sensor 11 when the cross section is in the Y direction. In the following description, the detection signal from the CCD linear sensor 10 in the X direction will be described as an example. However, since the movement in the X direction and the movement in the Y direction can be performed independently, the following description is applied as it is in the Y direction. can do.
[0018]
2 (a) to 2 (g) show focal positions (dotted lines) when the position of the objective lens 1 is lowered to the wafer 9 side when the incident illumination is performed in the vertical state, respectively. The state of the detection signal of the pattern 9a at that time shown corresponding to the right side. If the position indicated by the dotted line with respect to the pattern 9a is the focal position of the objective lens 1, each detection signal 10a changes sequentially as shown. Here, the position indicated by the arrow on the right side of each detection signal corresponds to the central portion of the right edge of the pattern 9a. Focusing on this position and looking at the relationship with the movement of the focal position of the objective lens 1, the waveform of the detection signal changes, but an arrow indicates that the illumination light is substantially perpendicular to the pattern 9a. There is little substantial change in the position of the edge. Therefore, in the case of the CCD linear sensor 10, the pixel position of the signal (edge detection signal) corresponding to the edge position indicated by the arrow does not change much.
[0019]
However, as shown in (i) to (iii) of FIG. 3 below, when the illumination light from the objective lens 1 becomes oblique, the reflected light R as shown by the front focus position, the focus position, and the rear focus position, as shown in FIG. Even if the directions are the same, the reflected light R at the front focus position is generated as the points A and B are generated by moving the reflected light R at the focus position before and after the focus position to the focus position. The reflected light R at the rear focus position enters the valley portion before the edge of the focus position pattern 9a (see point A). (See point B). Accordingly, the pixel position of the CCD linear sensor 10 that receives the reflected light R from the edge at each position differs as shown as detection signals 10b, 10c, and 10d for the edge of (iv) in FIG.
[0020]
These detection signals 10b to 10d can be easily obtained by differentiating the obtained detection signals. That is, it is a detection signal when the edge detection signal indicated by the position of the arrow in FIG. 2 among the detection signals of the CCD linear sensor is subjected to differentiation processing, and the detection level between the detection processing of the detection signal and the focus position is as follows. FIG. 4 is an explanatory diagram. This differentiation process is performed by the edge pixel position detection program 21a, whereby the peak position is obtained and the pixel position (pixel number) is calculated.
The vertical axis in FIG. 4 is dV / dn and is a differential voltage value with respect to the pixel, the horizontal axis is the height of the objective lens 1, and (a) to (g) of each point in the graph are respectively This corresponds to each of the focal positions in FIGS. As shown in the figure, a detection signal (edge detection signal) can be obtained corresponding to the position where the reflected light is received from the edge by performing differentiation even if the focus is shifted.
[0021]
Next, the vertical illumination setting process of illumination light will be described with reference to FIG.
The MPU 19 executes the vertical illumination setting program 21c and enters the vertical illumination setting process. First, the aperture stop position adjustment program 21b is called and the MPU 19 executes this program to drive the aperture position moving mechanism 60 to set the position of the aperture (pinhole) of the aperture mechanism 53 on the surface of the wafer 9. In the Y direction, it is moved to a position corresponding to the epi-illumination position of coordinates (x1, y1) (step 101). Here, the coordinates (x1, y1) may be input from a keyboard, or may be stored in advance in the memory 21 as a parameter. Further, since the pixels of the edge detection signal are actually obtained only from the pixels on the CCD linear sensor 10, that is, in the X direction, it is not necessary to take a special value for the Y coordinate.
As a result, as shown in FIG. 7B, an inclined light beam is irradiated from the objective lens 1 to the wafer 9.
[0022]
Next, the focus controller 18 is controlled to focus on the wafer 9 (step 102), and the objective lens 1 is raised by a predetermined amount and set to the front focus position corresponding to FIG. 3A (step). 103). Then, the movement step variable m is set to m = 1 (initial value) (step 104). Next, the edge pixel position detection program 21a is called and executed by the MPU 19, and the CCD detection signal is captured at the focal position corresponding to the position shown in FIG. The edge pixel number of the CCD linear sensor 10 is calculated for the light receiving position (step 105), and this pixel number is stored in the mth (initially first) position of the predetermined area of the memory 21 (step 106). Next, it is determined whether or not the focal point movement is ended based on whether or not the variable m> = 60 (step 107). If m is 59 or less, NO is determined, m is incremented as m = m + 1 (step 108), the process returns to step 105, the pixel number corresponding to the edge position is calculated again, and the predetermined number in the memory 21 is obtained. Is stored in the m-th area. When m = 60 and pixel numbers for 60 steps are obtained in this way, the determination in step 107 is YES, and whether the coordinate value of the current epi-illumination (aperture stop position) is (x1, y1). It is determined whether or not the detection process is finished depending on whether or not (step 109).
[0023]
Initially, when YES is determined here, the aperture stop position adjustment program 21b is called again, and the MPU 19 executes this program, and the aperture position moving mechanism 60 is driven to set the aperture position of the aperture mechanism 53 to the surface of the wafer 9. It is moved to a position corresponding to the position of the epi-illumination coordinates (x2, y2) in the X and Y directions above (step 110). The coordinates (x2, y2) may also be input from the keyboard, but values stored in advance as parameters in the memory 21 are subtracted and calculated by x2 = x1-k1, y2 = y1-k2. Here, k1 and k2 are values such that the coordinates (x2, y2) are selected such that the inclination is opposite to the inclination of the irradiation light of the objective lens 1 at the coordinates (x1, y1). is there.
After step 110, the process returns to step 102 and the same processing as described above is performed. Here, the focal distance of one step is, for example, 0.1 μm, and the focal point moves in the height direction by about 6 μm by the movement of 60 steps.
As a result of such processing, the relationship between each focus position and the pixel number in the tilted illumination at the first coordinates (x1, y1) is as shown in FIG. The horizontal axis is the pixel number n, and the vertical axis is the step number m of the focal position. Further, the relationship between each focus position and the pixel number in the inclined illumination at the next coordinates (x2, y2) is as shown in FIG. 6B. Similarly, the horizontal axis is the pixel number, and the vertical axis is the step number m of the focal position.
[0024]
If the determination in step 109 is NO, the process proceeds to step 111 where the vertical irradiation position is calculated. First, the displacement number A1 of the pixel number at the coordinates (x1, y1) (see FIG. 6A) is calculated, and then the displacement amount A2 of the pixel number at the coordinates (x2, y2) (see FIG. b)) is calculated (step 111). Next, the set position x in the X direction is calculated from the coordinate values x1 and x2 in the X direction and the above A1 and A2 by the following formula (step 112).
x = (A1x2-A2x1) / (A1-A2)
This is to obtain an X coordinate such that the displacement amount of the pixel becomes “0” as shown in FIG.
[0025]
Based on the set value x thus determined, the aperture stop position adjustment program 21b is called next, and the MPU 19 executes this program to drive the aperture position moving mechanism 60 to open the aperture (pinhole) of the aperture mechanism 53. ) Is moved to a position corresponding to the position of the epi-illumination coordinate (x, y1) in the X and Y directions on the surface of the wafer 9 (step 113).
Thereby, the irradiation light of the objective lens 1 in the X direction can be adjusted so as to be substantially vertical illumination.
Thereafter, in step 113, the aperture is set so that the X coordinate of the epi-illumination position is fixed to the obtained value x. Further, the y coordinate is set to y3, the coordinate (x, y3) is set, and the processing from step 102 to step 113 is similarly performed in the Y direction. At this time, the pattern 9a shown in FIG. 2 is a pattern perpendicular to the Y direction, and in step 105, the edge pixel number m of the CCD linear sensor 11 is calculated for the reflected light from the edge indicated by the arrow. In step 106, the pixel number m in the Y direction is stored at the mth (initially first) position of the predetermined area of the memory 21. By such processing, the epi-illumination position y without inclination in the Y direction is obtained.
[0026]
Finally, in step 112, the set value y in the Y direction is obtained from y = (A3y3-A4y4) / (A3-A4). Y3 and y4 are the epi-illumination coordinate values at two points taken in the Y direction, respectively, and A3 and A4 are the pixel displacement amounts in the Y direction at each of these two points.
Thus, in the previous step 113, the opening position moving mechanism 60 is driven to set the position of the opening (pinhole) of the diaphragm mechanism 53 to the position of the epi-illumination in the X and Y directions on the surface of the wafer 9 (x , Y) to a position corresponding to this position.
This completes the vertical setting of the epi-illumination in the X and Y directions.
[0027]
As described above, in the embodiment, the description is made using the convex pattern on the wafer, but it is needless to say that the edge of the concave pattern may be used. Of course, the sample may be a liquid crystal substrate or the like and is not limited to a wafer.
[0028]
【The invention's effect】
According to the present invention as described above, the position of the aperture stop (pinhole) of the illumination optical system arranged in a conjugate relationship with the focal position of the objective lens is set as the first epi-illumination position on the wafer. By tilting the illumination light toward the pattern, the focal point is moved before and after the focus position with respect to the pattern, and the amount of change in the light receiving position of the edge detection signal is sampled. The aperture stop is set at the epi-illumination position, and the amount of change in the edge position is sampled in the same manner, and the irradiation light becomes vertical due to the relationship between the variation in these two edge positions and the first and second epi-illumination positions. The position of the epi-illumination on the wafer of the aperture stop is calculated, and the aperture stop is set at a position corresponding to the position, so that the illumination light can be made perpendicular to the sample. .
As a result, it is possible to automatically set the illumination in the epi-illumination optical system to be vertical without fail and without requiring skill.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram of a registration measuring apparatus according to an embodiment to which a vertical illumination setting apparatus in an epi-illumination optical system according to the present invention is applied.
FIG. 2 is an explanatory diagram of a relationship between a pattern detection signal on a wafer and a pixel position of a CCD sensor at each focus position.
FIG. 3 is an explanatory diagram of a change in position with respect to detection of a reflected light receiving position from an edge of a pattern in inclined illumination.
FIG. 4 is an explanatory diagram of an in-focus position with respect to a pattern on a wafer and detection levels before and after the edge detection signal when a detection signal of a CCD sensor is differentiated.
FIG. 5 is a flowchart of a vertical illumination setting process.
FIG. 6 is an explanatory diagram of the relationship between each focusing position and pixel number in tilted illumination, where (a) is an explanatory diagram of measured values at the first epi-illumination position, and (b) is The explanatory diagram of the measured value at the next epi-illumination position, (c) is an explanatory diagram on how to obtain the vertical epi-illumination position.
7A and 7B are explanatory diagrams of a measurement principle, in which FIG. 7A is an explanatory diagram of vertical epi-illumination and an edge light receiving position, and FIG. 7B is an explanation of an inclined epi-illumination and an edge light receiving position; FIG.
[Explanation of symbols]
1 ... objective lens, 2a, 3a ... relay lens,
2b, 3b ... cylindrical lens,
4, 55 ... half mirror, 5 ... illumination optical system,
7 ... wafer chuck, 8 ... XYZ moving stage, 9 ... wafer,
10, 11 ... CCD linear sensor, 15 ... A / D conversion circuit (A / D),
16 ... Image memory, 17 ... High-speed numerical processor,
18 ... focus controller, 19 ... MPU,
20 ... Control device, 21 ... Memory, 22 ... Bus,
21a ... Edge pixel position detection program,
21b ... aperture stop position adjustment program,
21c ... Vertical illumination setting program,
21d ... Mark shift amount measurement program,
30 ... Registration pattern,
50 ... Light source, 51 ... Light quantity adjustment filter, 52 ... Fiber,
53 ... Aperture mechanism, 54 ... Field stop,
60: Opening position moving mechanism.

Claims (2)

An optical system that includes a plurality of light receiving elements arranged in a predetermined direction so that reflected light from the sample is incident on the sample via the objective lens of the epi-illumination optical system and reflected from the sample via the objective lens. In the measuring device or inspection device detected by the sensor,
An aperture stop having an aperture that transmits light to the position of the optical path of the illumination optical system in a conjugate relationship with the focal point of the objective lens;
The sample has a pattern in a direction perpendicular to the pixel arrangement direction, the opening is moved, and the epi-illumination is performed at first and second epi-illumination positions on the sample surface with respect to the pattern. Illumination is performed, and the position of the focal point is moved by a predetermined amount in the direction perpendicular to the pattern in the vicinity of the pattern, and the optical sensor detects the reflected light from the edge of the pattern obtained at each of a plurality of focal positions. The pixel position corresponding to the detection signal is calculated based on the signal, and the amount of change in the pixel position according to the predetermined amount movement at each of the first epi-illumination position and the second epi-illumination position and the first An epi-illumination position on the sample surface where the pixel position does not substantially change depending on the epi-illumination position and the second epi-illumination position is obtained, and the aperture stop is set so as to correspond to this position. Setting the vertical illumination setting device in epi-illumination optical system. The sample is a wafer, the measuring device or the inspection device is a registration measuring device, adopts an XY coordinate system in parallel with the wafer surface, and the optical sensor is in the X and Y directions on the wafer surface. CCD linear sensors arranged respectively, and as the first and second epi-illumination positions, one of the coordinates in the X direction and the Y direction on the wafer surface is adopted, and the epi-illumination position of the sample Is obtained as any one of the coordinate positions, and further, any one of the other coordinates is adopted, and the epi-illumination position of the sample is obtained as the other coordinate position, and is determined by any one of these and the other 2. A vertical illumination setting device in an epi-illumination optical system according to claim 1, wherein the aperture stop is set so as to correspond to the XY coordinate position on the wafer surface. .

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