JPH09320947A - Aligner and correction method of imaging characteristics - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize the high precision correction of the imaging characteristics of a projection lens. SOLUTION: The imaging characteristics of a projection lens PL is adjusted while the position of an imaging characteristics correction plate 70 is adjusted. When the required imaging characteristics are obtained, the position discrepancy of the imaging characteristics correction plate 70 from a reference position in a plane perpendicular to a light axis is detected by a position discrepancy detecting means 80 and the detected position discrepancy is memorized. With this constitution, even if the imaging characteristics correction plate 70 has to be removed from an aligner 10 and reloaded onto it by some reason or the position discrepancy of the imaging characteristics correction plate 70 is produced by a vibration, etc., the imaging characteristics correction plate 70 can be restored easily to the original position and hence the high precision correction of the imaging characteristics of the projection lens PL can be realized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exposure apparatus and a method for correcting imaging characteristics, and more particularly, to an exposure apparatus used in a photolithography process in manufacturing semiconductor devices, liquid crystal display substrates and the like, and a projection lens used therefor. The present invention relates to a method for correcting the image forming characteristic.

[0002]

2. Description of the Related Art For example, in a photolithography process in manufacturing a semiconductor integrated circuit, various exposure apparatuses are used. In recent years, a mask (reticle) pattern is a wafer coated with a photoresist through a reduction projection lens. A reduction projection exposure apparatus that transfers images onto the top has become the mainstream.

By the way, the demand for miniaturization of the pattern line width of semiconductor circuits has been increasing year by year, and in particular, in recent years, the demand for miniaturization of the pattern line width has rapidly increased, and the reduction in the reduction projection exposure apparatus has been reduced. There is an urgent need to reduce the imaging characteristics of the projection lens, that is, lens aberration. Although this lens aberration can be suppressed to an extremely small amount by design, it is not possible to manufacture a projection lens according to the design value, and the tolerances that occur during the manufacturing process will eventually be obtained. The imaging performance of the lens. It has a slight error with respect to the design value.

Under these circumstances, reduction of lens aberration has been realized by some methods in the past, but
Still, since the error cannot be completely removed, research is still ongoing to reduce the error. As one of the methods to effectively reduce the lens aberration, a lens aberration correction plate is intentionally processed to cancel the lens aberration between the reticle and the projection lens or between the wafer and the projection lens. It is known how to place it. In other words, for aberrations that cannot be completely compensated for when the final adjustment of the projection lens has been reached, the aberration correction plate is used to intentionally generate aberrations that cancel this aberration, and as a result, let the lens aberrations approach zero as much as possible. And

[0005]

When the above-mentioned lens aberration correction plate is mounted in the exposure apparatus, it is usually mounted in a place different from the lens barrel, and therefore the mounting accuracy is determined by the mechanical tolerance of the mounting apparatus. Determined by For this reason, the mounting accuracy cannot be sufficiently secured, the mounting position of the aberration correction plate deviates from the original position, and the correction value of the aberration correction plate cannot be faithfully applied to the lens, so that the imaging characteristic There was the inconvenience that it could not always be corrected sufficiently.

Further, although the image forming characteristic can be corrected with higher accuracy as the number of decomposition points at the time of measuring the image forming characteristic when manufacturing the aberration correction plate is increased, this is intentionally corrected. As the number of decomposition points increases, the accuracy of alignment of the aberration correction plate in the plane orthogonal to the optical axis of the projection lens becomes stricter. This is because when a lens aberration correction plate is mounted, one point on the wafer surface is formed by gathering many points on this aberration correction plate, and therefore the positional deviation of the lens aberration correction plate in the plane orthogonal to the optical axis is simply This is because the aberration correction plate must be positioned with higher accuracy in the plane orthogonal to the optical axis as the number of measurement resolution points increases, not limited to the positional deviation at one point.

The present invention has been made in view of the above disadvantages of the prior art, and an object thereof is to provide an exposure apparatus which can realize highly accurate correction of the image forming characteristics of the projection lens. .

Another object of the present invention is to provide a method of correcting an image forming characteristic capable of correcting the image forming characteristic of a projection lens with high accuracy.

[0009]

According to a first aspect of the present invention, there is provided an exposure apparatus for transferring an image of a pattern formed on a mask onto a photosensitive substrate via a projection lens, the mask and the projection lens. An image formation characteristic correction plate that is arranged between the photosensitive substrate and the projection lens so that the position in the plane orthogonal to the optical axis of the projection lens can be adjusted, and corrects the image formation characteristic of the projection lens. And a position deviation detecting means for detecting a position deviation of the imaging characteristic correction plate from a reference position in a plane orthogonal to the optical axis.

According to this, for example, while adjusting the position of the image formation characteristic correction plate, the image formation characteristic of the projection lens is adjusted, and when the desired image formation characteristic is obtained, the image is formed by the positional deviation detecting means. By detecting the displacement of the characteristic correction plate from the reference position in the plane orthogonal to the optical axis, and storing this amount of displacement, the imaging characteristic correction plate can be removed from the device and mounted again for some reason. Also, when the image forming characteristic correction plate is displaced due to vibration or the like, it is possible to easily reset the image forming characteristic correction plate to the original position based on the stored positional displacement amount. It is possible to realize highly accurate correction of the imaging characteristics of the projection lens.

According to a second aspect of the present invention, in the exposure apparatus according to the first aspect, the positional deviation detecting means is preliminarily provided at a position where the alignment mark formed in advance on the image-forming characteristic correction plate and a fixed portion of the apparatus. It is characterized in that it includes simultaneously capturing the formed index mark. According to this, the alignment mark previously formed on the imaging characteristic correction plate and the index mark previously formed on the fixed portion of the apparatus are simultaneously imaged by the image processing type mark detecting means.

According to a third aspect of the present invention, there is provided a method for correcting an image-forming characteristic, wherein an alignment mark including at least three position information is provided at a predetermined position between the mask and the projection lens or between the photosensitive substrate and the projection lens. A first step of arranging a plane-parallel plate on which is formed; and after adjusting the projection lens in the state where the plane-parallel plate is arranged, the imaging characteristics of the projection lens are measured and the alignment mark A second step of measuring a displacement from a reference position in a plane orthogonal to the optical axis; a third step of removing the plane-parallel plate from the optical path of the projection lens; and a measurement result of the imaging characteristic of the second step. An image formation characteristic correction plate processed based on the above is arranged on the optical path of the projection lens, and image formation is performed in advance corresponding to the alignment mark on the parallel plane plate based on the position displacement measurement result of the second step. Formed on the characteristic correction plate The position of the alignment mark, and a fourth step of adjusting to coincide with the alignment mark position of the parallel flat plate in the installation position in the first step.

According to this, the plane parallel plate on which the alignment mark including at least three pieces of position information is formed at a predetermined position is provided between the mask and the projection lens or between the photosensitive substrate and the projection lens, The projection lens is adjusted with the plane-parallel plate arranged. After that, the image forming characteristics of the projection lens are measured, and the positional deviation of the alignment mark from the reference position in the plane orthogonal to the optical axis is measured. After that, the plane-parallel plate is removed from the optical path of the projection lens,
An image forming characteristic correction plate processed based on the previous image forming characteristic measurement result is arranged on the optical path of the projection lens, and based on the position displacement measurement result of the parallel plane plate, it is used as an alignment mark on the parallel plane plate. Correspondingly, the position of the alignment mark previously formed on the imaging characteristic correction plate is adjusted so as to coincide with the alignment mark position of the parallel plane plate at the previous arrangement position. As a result, the imaging characteristic correction plate is accurately positioned at the position where the correction value most faithfully acts on the projection lens,
The image forming characteristic of the projection lens is corrected with high accuracy.

[0014]

DETAILED DESCRIPTION OF THE INVENTION An embodiment of the present invention will be described below with reference to FIGS.

FIG. 1 shows an exposure apparatus 10 according to one embodiment.
Is schematically shown. This exposure apparatus 10
A reduction projection type exposure apparatus (so-called wafer stepper) that projects a pattern image formed on a reticle R as a mask onto a shot area of a wafer W as a photosensitive substrate by a step-and-repeat method via a projection lens PL.

The exposure apparatus 10 includes an illumination system including a light source 12, a projection lens PL that projects a pattern image formed on a reticle R onto a wafer W, a stage device that constitutes a moving mechanism of the wafer W, a magnification and a distortion. The image forming characteristic correcting means, the focus correcting means, the control system, and the like are provided.

The illumination system includes a light source 12 composed of a high-pressure mercury lamp or an excimer laser, a shutter 14 for opening and closing an optical path of illumination light, an illumination optical system 16 including an optical integrator (fly-eye lens), an illumination system aperture stop. It includes a plate (revolver) 18 and a variable blind 20 that limits the illumination field of the illumination light. The shutter 14 is driven by the driving unit 22 and the illumination light I emitted from the light source 12 is emitted.
L (i line, g line, excimer laser light (KrF, ArF)
Etc.) are transmitted or shielded. An illumination optical system 16 is arranged on the optical path behind the shutter 14, and the illumination light IL
Of the light flux, reduction of speckle, etc. are performed. An illumination system aperture stop plate 18 made of a disk-shaped member is arranged at the exit of the illumination optical system 16. The illumination system aperture stop plate 18 has, for example, a normal circular aperture at substantially equal angular intervals. Aperture stop consisting of a small circular aperture, an aperture stop for reducing the coherence factor σ value, an annular aperture stop for annular illumination, and multiple apertures eccentrically arranged for the modified light source method. A modified aperture stop (all not shown) is arranged. The illumination system aperture stop plate 18 is rotatably driven by a drive device 24 such as a motor controlled by a main control device 26, whereby any aperture stop is selectively placed on the optical path of the illumination light. Is set to.

A half mirror 28 is arranged on the optical path behind the aperture stop plate 18 for the illumination system.
An integrator sensor 30 that photoelectrically detects the transmitted light that has passed through the half mirror 28 is disposed on the rear side of the rear side of 8 (the upper side in FIG. 1). The integrator sensor 30 is composed of, for example, a PIN photodiode, photoelectrically detects the illumination light IL, and outputs light information (intensity value) I to the main controller 26. The light information I serves as basic data for obtaining the irradiation variation amount of the image forming characteristic of the projection lens PL, for example.

On the optical path of the illumination light IL behind the half mirror 28, a set of relay lenses 34a and 34b is installed with the variable blind 20 interposed. Variable blind 2
The installation surface of 0 has a conjugate relationship with the reticle R, and the drive mechanism 3
The illumination field of the reticle R can be arbitrarily set by opening and closing the movable blade constituting the variable blind 20 by 6 to change the opening position and shape.

The relay lenses 34a, 34b are located on the optical path of the illumination light IL behind the relay lenses 34a, 34b.
A mirror 37 that reflects the illumination light IL that has passed through the pair toward the reticle R is disposed.
A condenser lens 38 is arranged on the optical path of L.

The reticle R is placed on the reticle stage RS and held by a reticle holder (not shown). The reticle stage RS is configured to be finely movable in a two-dimensional direction in a horizontal plane, and after the reticle R is mounted on the reticle stage RS, the center point of the pattern area PA of the reticle R coincides with the optical axis AX. Is positioned. Initial setting of the reticle R is performed by photoelectrically detecting an alignment mark (not shown) around the reticle by a reticle alignment system (not shown), and finely moving the reticle stage RS based on the mark detection signal. The reticle R is used after being appropriately replaced by a reticle exchanger (not shown).

The projection lens PL is held on the main body column 100, and the projection lens PL has a plurality of lens elements 40, 42, ... Having a common optical axis so that the projection lens PL has a telecentric optical arrangement on both sides. It is configured. Reticle stage RS among lens elements
The uppermost lens element 40 closest to is supported by a ring-shaped support member 42, which is
Stretchable drive elements, eg piezo elements 44a, 44
b and 44c (the drive element 44c on the back side of the paper surface is not shown) are supported at three points and are connected to the lens barrel portion 46. By the drive elements 44a, 44b, 44c, the three peripheral points of the lens element 40 can be independently moved in the optical axis AX direction of the projection lens PL. That is, the lens element 40 is moved along the optical axis AX according to the displacement of the driving elements 44a, 44b, 44c.
Along the optical axis A
It can also be arbitrarily tilted with respect to a plane perpendicular to X. Then, these drive elements 44a, 44b, 44c
The voltage applied to the drive circuit is controlled by the controller 48 based on a command from the main controller 26, and the displacement amount of the drive elements 44a, 44b, 44c is controlled by this. In FIG. 1, the optical axis AX of the projection lens PL refers to the optical axes of the lens element 42 and other lens elements (not shown) fixed to the barrel portion 46.

As described above, the lens element 40 closest to the reticle R is movable, but this element 40 has one of the influences on the magnification and distortion characteristics that are much easier to control than other lens elements. If the above condition is selected and the same condition is satisfied, any lens element may be configured to be movable for adjusting the lens interval, instead of this lens element 40.

Here, the optical axis AX of the lens element 40
The magnification of the projection lens PL can be corrected by the movement in the direction, and the distortion can be corrected by tilting the lens element 40. Therefore, in the exposure apparatus 10 of the present embodiment, the drive elements 44a, 4a are provided.
The image forming characteristics (lens aberration) are corrected by the controllers 4b and 44c and the controller 48 that controls the amount of displacement thereof.

Next, the stage device constituting the wafer moving mechanism will be described. This stage device is arranged below the projection lens PL and is capable of two-dimensionally moving in a horizontal plane (XY plane), and the XY stage 50.
A Z stage 52 mounted on the top and capable of finely moving in the optical axis direction (Z direction) is provided. A wafer W as a photosensitive substrate is placed on the Z stage 52, and the Z stage 5
2 is finely driven in the optical axis direction by the drive system 54. X
The Y stage 50 is driven in a two-dimensional direction by a drive system 54. The two-dimensional position of the XY stage 50 is set to, for example, 0.0 by the laser interferometer 56.
It is constantly detected with a resolution of about 1 μm, and the output of the laser interferometer 56 is given to the main controller 26. Then, a command from main controller 26 is given to stage controller 58, and drive system 54 is controlled by stage controller 58. With such a closed-loop control system, for example, when the transfer exposure of the reticle R onto one shot area on the wafer W is completed, the XY stage 50 is stepped to the next shot position.

On the Z stage 52, the projection lens P
An image forming characteristic measuring mechanism 59 for measuring the image forming characteristic of L is provided. The image formation characteristic measuring mechanism 59 is arranged such that the surface thereof is substantially level with the surface of the wafer W, and a reference plate FM having a cross-shaped slit in the center in the X and Y directions, for example, and below the reference plate FM. And a photoelectric detector (not shown) provided at the output of the photoelectric detector is supplied to the main controller 26. Here, a mechanism of measuring the image forming characteristic by the image forming characteristic measuring mechanism 59 will be briefly described. A test pattern formed on the reticle R (for example, in the X direction and the Y direction corresponding to the slits on the reference plate). When the wafer stage WST is moved in the X-axis direction and the Y-axis direction in the state where the image of the bar-shaped light-shielding pattern) is projected, the output level of the photoelectric detector increases or decreases, and when the slit comes to the projection position of the light-shielding pattern. The output level of the photoelectric detector is the lowest. Therefore, the main controller 26 detects the coordinate position of the light-shielding pattern formed by monitoring the coordinate position of the wafer stage 50 measured by the laser interferometer 56 together with the output P of the photoelectric detector at this time. By comparing this position with the coordinate position where the original test pattern should be imaged, the imaging characteristics such as magnification error and distortion of the projection lens PL can be obtained from the deviation of the imaging position. Of.

The focus correction means is a projection lens P.
An irradiation optical system 60a for supplying an image forming light beam or a parallel light beam for forming an image of a pinhole or a slit toward the image forming surface of L from an oblique direction with respect to the optical axis AX, and the image forming light beam or the parallel light beam. A grazing incidence light type focus detection system including a light receiving optical system 60b that receives a light beam reflected from the surface of the wafer W, and an inclination of a parallel plane plate (not shown) in the light receiving optical system 60b with respect to the optical axis of the reflected light beam A focus correction controller 62 that corrects a focus variation of the projection lens PL by offsetting the focus detection system by controlling according to a command from the control device 26 is provided. The defocus signal (defocus signal) from the light receiving optical system 60b is given to the above-mentioned stage controller 58, and the stage controller 58 adjusts the defocus signal to zero according to the defocus signal, for example, the S curve signal.
By controlling the position of the stage 52 via the drive system 54, autofocusing (automatic focusing) is performed.

A parallel plane plate is provided in the light receiving optical system 60b to give an offset to the focus detection system (60a, 60b) by, for example, moving the lens element 40 up and down to correct the magnification. The focus also changes, and since the projection lens PL absorbs the exposure light to change the image forming performance and the position of the image forming surface changes, in such a case, an offset is given to the focus detecting system to adjust the focus detecting system. This is because it is necessary to match the focal position with the position of the image plane of the projection lens PL.

The control system is mainly constituted by the main controller 26 in FIG. The main controller 26 includes a CPU (Central Processing Unit), a ROM (Read Only Memory),
It is constituted by a so-called microcomputer (or minicomputer) composed of an AM (random access memory) or the like. The reticle R and the wafer W are aligned, the wafer W is stepped, and the shutter 14 is used so that the exposure operation is properly performed. The exposure timing and the like are generally controlled. Further, the main controller 26 obtains information from the integrator sensor 30 during the exposure, calculates the variation amount of the imaging performance of the projection lens PL by calculation, and controls the entire device including the controller 48 as a whole. .

Exposure apparatus 10 constructed as described above
In, the illumination light IL emitted from the light source 12 travels to the illumination optical system 16 after passing through the shutter 14. The illumination light IL has a uniform luminous flux by passing through the illumination optical system 16, and after the illumination field of the illumination light is limited by the aperture stop of the illumination system aperture stop plate 18, the mirror 28 is illuminated.
Is reflected by and enters the relay lenses 34a and 34b and the variable blind 20. The illumination light IL, after the illumination field of the reticle R is limited there, is reflected vertically downward by the mirror 37 to reach the condenser lens 38, and then,
The pattern area PA of the reticle R is illuminated with a uniform illuminance. Illumination light IL that has passed through the pattern area PA of the reticle
Enters the projection lens PL. The light flux that has passed through the projection lens PL is focused on one shot area on the wafer W to form a circuit pattern image of the reticle R on that area.

By the way, if the above-mentioned image forming characteristic correcting means is used when assembling the apparatus, the image forming characteristic of the projection lens PL can be corrected from the outside, but it can be corrected by this image forming characteristic correcting means. In most of the aberrations, the linear component is removed. That is, the projection lens PL
As the image height increases with respect to the center of the, the change is limited to those that change linearly. For non-linear components other than the linear component, use the above-mentioned image forming characteristic correcting means. Cannot be removed, and thus this nonlinear component becomes the residual aberration of the final lens.

In order to remove the aberration of the non-linear component, mainly the aberration in the plane such as magnification and distortion, in the exposure apparatus 10 of the present embodiment, an image forming characteristic correction plate is provided between the reticle R and the projection lens PL. The aberration correction plate 70 is mounted via a mounting device (not shown). The aberration correction plate 70 measures the image forming characteristic of the projection lens PL using the image forming characteristic measuring mechanism 59 described above, and based on the measurement result, the residual aberration of the projection lens PL (mainly related to magnification and distortion). The surface of the plane-parallel plate is processed by using a processing device outside the device so as to generate an aberration that cancels out. When the imaging characteristics of the projection lens PL are corrected using such an aberration correction plate 70, the alignment is important as described above, and therefore the device 10 of the present embodiment has the following ideas. Has been done.

That is, as shown in FIG. 2, the alignment marks M _x1 , M _{x2 in} the X-axis direction and the Y-axis direction are aligned in the peripheral portion of the exposure light irradiation area of the aberration correction plate 70, for example, in the center of the four sides. Alignment marks M _y1 and M _y2 are formed in advance. These alignment marks M _x1 , M _x2 , M _y1 , M _y2
Is made of a material such as chrome that does not transmit light. These alignment marks M _x1 , M _x2 , M _y1 , M _y2
Are formed in advance through a lithography process using, for example, an electron beam exposure apparatus.

Further, in this embodiment, the positional deviation detecting means 80 of the aberration correction plate is associated with these alignment marks.
Is provided. This positional deviation detecting means 80 is shown in FIG.
, A light source 82, a beam splitter BS,
It is configured to include a folding mirror 83, lenses L1, L2, L3, L4 and a CCD camera 84 as mark detecting means. Here, the operation of each of the above-mentioned components constituting the positional deviation detecting means 80 will be described. Light source 8
A part of the detected light flux from 2 is reflected by the beam splitter BS and the rest is transmitted through the beam splitter BS.
The reflected light flux passes through the lens L1 and is then bent by the bending mirror 8
The alignment mark M _x1 which is bent by 3 and formed on the peripheral portion of the aberration correction plate 70 is irradiated. The reflected light flux from the alignment mark M _x1 is bent by the folding mirror 83.
The image is formed on the image pickup surface of the CCD camera 84 after passing through the lens L1 from the direction opposite to the front and further passing through the beam splitter BS and the lens L2. On the other hand, the light flux emitted from the light source 82 and transmitted through the beam splitter BS sequentially passes through the lenses L3 and L4, and the projection lens PL.
An index mark m formed in advance is radiated on the main body column 100 that holds the light beam, and the reflected light flux from this index mark m passes through the lenses L4 and L3 from the direction opposite to the front and is reflected by the beam splitter BS, and the lens L2. An image is formed on the image pickup surface of the CCD camera 84 via. Therefore, the CCD camera 84
In this case, the alignment mark M _x1 on the aberration correction plate 70 and the index mark m can be imaged at the same time, and the relative position of the alignment mark M _x1 with the index mark m as a reference can be determined based on the imaged image information. Can be detected. From this relative positional relationship, for example, even when the aberration correction plate 70 is once removed and then mounted again, it can be set to the same position as before, and the reproducibility of positioning of the aberration correction plate can be easily ensured. You can Note that FIG. 1 shows a state in which only one position deviation detecting unit 80 is provided corresponding to the mark M _x1 in the X direction, but in reality, it is 2 for detecting the position deviation of the mark in the X direction. One is provided for detecting the positional deviation of the mark in the Y direction (or two for the Y direction and one for the X direction), and three index marks m are provided on the main body column 100 correspondingly. One is provided. This is because if the positional deviation of the mark including a total of three pieces of positional information can be detected in both the X and Y directions, the positional deviation including the rotation of the aberration correction plate 70 itself can be detected. From this point of view, if a two-dimensional mark is used as the alignment mark M and the index mark m, it is sufficient to provide two marks for each mark, and therefore, it is sufficient to provide two position shift detecting means.

The index mark m is formed in advance on the main body column 100 in which the projection lens PL is held. That is, the alignment mark M and the index mark m are imaged at the same time, and the images of both marks are simultaneously captured. This is because, in addition to the purpose of facilitating the positioning reproducibility of the aberration correction plate 70, even if the lens itself changes due to temperature, vibration, or the like, the index mark changes at the same time, so that the error can be reduced.

Next, a method of correcting the image forming characteristic of the present invention including the above-described method of aligning the aberration correction plate 70 will be described.

Here, at least two parallel plane plates 72 of the same thickness and size and made of the same transparent material are prepared.
Alignment marks are previously formed on these parallel plane plates in the peripheral portions so as to have the same positional relationship by using the same electron beam exposure apparatus or the like. Here, it is assumed that the alignment marks M _x1 , M _x2 , M _y1 , and M _y2 as shown in FIG. 2 are formed.

As a premise, a test reticle having a large number of test patterns formed thereon is mounted on the reticle stage RS and positioned with respect to the projection lens optical axis AX. Further, in the wafer stage 50, the reference plate FM has a projection lens FM. P
It is assumed to be moving just below L. At this time, the aberration correction plate is not mounted on the exposure apparatus 10.

First, the operator places the plane-parallel plate 72 at the height position where the aberration correction plate 70 in FIG. 1 is placed.
Is mounted via a mounting device (not shown). Here, the reason why the parallel flat plate 72 is mounted will be described in detail later.

When parallel plane plate 72 is mounted, main controller 26 illuminates the reticle with exposure light IL from the illumination system, and projects a test pattern image onto wafer stage 50 with projection lens PL. In this state, main controller 26 scans wafer stage 50 in the X and Y two-dimensional directions, monitors the measurement value of interferometer 56 and the output of imaging characteristic measurement mechanism 59 at this time, and connects projection lens PL. The image characteristics, more specifically, a linear component such as magnification and distortion that can be corrected by the image forming characteristic correcting means is calculated, and the controller 48 is controlled based on the calculated result to configure the image forming characteristic correcting means. Drive 44a, 44b, 44c. As a result, the projection lens PL is adjusted, and the aberration is driven up to the adjustment limit. Since this adjustment is performed by the image forming characteristic correcting means,
Most of the aberration corresponds to the removal of the linear component. Of course, since it is an adjustment, the residual amount of the linear component cannot be completely removed, but since this amount is very small, this amount will be ignored here.

After this adjustment, main controller 26 again measures the imaging characteristics of projection lens PL in the same manner as described above, and stores the measurement result in a memory (not shown) in association with the wafer stage coordinate system. After that, the main controller 26 calculates the final image formation characteristic of the projection lens PL, that is, the lens aberration based on the information in the memory, and sends this information to an external processing device (not shown). Next, in the main controller 26, the light source 82 is turned on to irradiate the detection light flux to the alignment mark M on the plane parallel plate 72 and the index mark m on the main body column 100. As a result, the CCD camera 84 captures the alignment mark M and the index mark m on the same screen, and the image information and numerical information (a specific example of which will be described later) indicating the positional relationship between the marks are not recorded. It is displayed on the display screen shown.

Next, the operator uses the plane-parallel plate 72.
Is removed from the exposure device 10 and set in a processing device (not shown). As a result, the processing device performs the surface processing of the plane-parallel plate 72 so as to generate an aberration that cancels the lens aberration, based on the lens aberration information sent from the main control device 26 in advance. Aberration correction plate 72
Is produced. Here, the parallel flat plate 72 removed from the exposure apparatus 10 is processed to manufacture the aberration correction plate 70, but this is for the following reason. That is, in a strict sense, the unprocessed parallel plane plate 72 is not exactly a plane, so that another parallel plane plate 72 is not processed.
When manufacturing a high-precision aberration correction plate by processing, the parallelism of the plane-parallel plate 72 must be measured,
Further, the aberration correction plate 70 must be manufactured by processing the distribution of the plane curve of the plane parallel plate 72 in consideration of the amount of the curve, but the plane parallel plate 72 removed from the exposure apparatus 10 is processed. This is because such a problem does not occur in some cases.

However, when the required accuracy is not so high, another parallel plane plate 72 prepared in advance is used.
Is set in the processing device in advance, and when the data of the lens aberration is sent from the main control device 26, the parallel flat plate 72
You may make it surface-process. In this case, the aberration correction plate 70 is processed and the parallel plane plate 7 is processed.
The position measurement of 2 is performed by the parallel processing at the same time, and the throughput can be improved.

Next, the operator mounts the manufactured aberration correction plate 70 on the exposure apparatus 10 via a mounting device (not shown). When the aberration correction plate 70 is mounted, the light source 82 is turned on by the main controller 26, and the alignment mark M, the index, and the mark m formed on the periphery of the aberration correction plate 70 are simultaneously imaged by the CCD camera 84. The image information and numerical information indicating the positional relationship between both marks (a specific example of which will be described later) are displayed on a display screen (not shown). While looking at this screen, the operator controls the position of the aberration correction plate 70 until the display content of the screen matches the image information previously displayed on the display screen in the above process and the numerical information indicating the positional relationship between both marks. adjust. As a result, the position of the aberration correction plate 70 can be easily and accurately positioned to a position where the effect is most exerted, that is, a position where the correction value of the aberration correction plate 70 can be most faithfully applied to the projection lens PL. Therefore, the aberration of the projection lens PL, that is, the imaging characteristic can be corrected with extremely high accuracy.

In the above process, processing of the aberration correction plate 70
The plane-parallel plate 72 is mounted on the exposure apparatus 10 prior to mounting, because the processed aberration correction plate 70 has an optical thickness, and as a result of imaging, there is no such thickness. However, even before the processed aberration correction plate 70 is mounted, the unprocessed plane-parallel plate 72 is mounted even if the aberration of the projection lens PL is being corrected by the imaging characteristic correction means in advance. This is because the work and the calculation can be performed very easily and highly accurately if they are saved.

That is, since the aberration correction plate 70 originally corrects the aberration of the projection lens PL, the projection lens P
It is most important to align with the image plane of L, but if there is a plane-parallel plate 72 that has not been processed originally, the measurement itself on the plane-parallel plate 72 is actually seen on the image plane of the projection lens PL. Therefore, the parallel plane plate 72
On the other hand, if the aberration correction plate 70 is aligned, it will be aligned with the image plane of the projection lens PL.

In this case, the unprocessed plane-parallel plate 7
It goes without saying that it is fundamental that the position of the processed aberration correction plate 70 with respect to the projection lens PL must be accurately adjusted.

Therefore, in this embodiment, the plane-parallel plate 72 is used.
In order to align the position of the aberration correction plate 70 with the position of the aberration correction plate 70, alignment marks having the same positional relationship are provided in advance on the periphery of the parallel plane plate 72 (including the parallel plane plate to be finally processed for the aberration correction plate). Of.

When the plane parallel plate 72 is mounted,
The image of the index mark m formed on the main body column 100 and the image of the alignment mark M on the plane parallel plate 72 are simultaneously captured by the CCD camera 84, the positional relationship between both marks at this time is stored, and aberration correction is further performed. Similarly, when the plate 70 is mounted, the positional relationship between the marks is measured, and the position in the XY plane of the aberration correction plate 70 is adjusted so that this positional relationship is the same as the positional relationship measured when the parallel plane plate 72 is mounted. adjust.

More specifically, for example, a pair of index marks m ₁ and m ₂ are used as the index mark m, and the images of the pair of index marks m ₁ and m _{2 and} the alignment mark M on the plane parallel plate 72 are used. _{Assuming that} the image of _{x1 is formed on} the image pickup surface of the CCD camera 84 in the positional relationship shown in FIG. 3A, the index marks m1 and m2 and the alignment mark Mx1 on the plane-parallel plate. As the amount of deviation, for example, (ab)
And measure and store. Here, it is easy to set the positional relationship between the marks as shown in FIG. 3A by appropriately adjusting the magnification of the optical system (L1, L2, L3, L4) that constitutes the positional deviation detecting means 80. Is. The mark M _x1 shown in FIG. 3 (A) is a schematic representation of the mark M _{x1 in} FIG. 2 (same in FIG. 3 (B)).

Furthermore, when the aberration correction plate 70 is mounted,
An image of the pair of index marks m ₁ and m _{2 and} an image of the alignment mark Mx1 on the plane parallel plate 72 are formed on the image pickup surface of the CCD camera 84 in the positional relationship shown in FIG. 3B. Assuming that the difference is between the index marks m ₁ and m ₂ and the alignment mark M _x1 on the aberration correction plate 70, for example, an amount (cd) is measured. Half the difference e between the respective shift amounts is the position error of the aberration correction plate 72. Here, the position error e is expressed by the following equation. e = {(cd)-(ab)} / 2 = {(c-a) +
(B−d)} / 2 Therefore, the aberration correction plate 7 is adjusted so that the shift amount e becomes zero.
If the position of 0 is adjusted, the position of the aberration correction plate 70 becomes the position where the aberration of the projection lens PL is most reduced.

However, by fixing this position,
As long as reproducibility can be secured, there is no need to move it.
The position of the aberration correction plate can be adjusted manually by an operator, and automation or a precise adjustment mechanism is unnecessary.

Through the above steps 1 to 5, the projection lens P
The image forming characteristic of L is corrected with high accuracy not only to the linear component of aberration but also to the nonlinear component.

In the description of the above embodiment, the case where the aberration correction plate is arranged between the reticle R and the projection lens PL has been described, but the present invention is not limited to this, and the projection lens is not limited to this. An aberration correction plate may be arranged between the PL and the wafer W.

[0055]

As described above, according to the exposure apparatus and the method for correcting the image forming characteristic according to the present invention, the image forming characteristic of the projection lens can be corrected more reliably and highly accurately. It has an excellent effect not found in.

[Brief description of drawings]

FIG. 1 is a view schematically showing a configuration of an exposure apparatus according to one embodiment.

FIG. 2 is a plan view showing the aberration correction plate of FIG.

FIG. 3 is a diagram for explaining a method of aligning an aberration correction plate.

[Explanation of symbols]

10 Exposure Device 70 Imaging Characteristic Correction Plate 80 Position Deviation Detection Means 84 CCD Camera (Mark Detection Means) R Reticle (Mask) PL Projection Lens W Wafer (Photosensitive Substrate) M _x1 , M _x2 , M _y1 , M _y2 Alignment Mark m index mark

Claims (3)

[Claims] 1. An exposure apparatus for transferring an image of a pattern formed on a mask onto a photosensitive substrate via a projection lens, wherein the exposure apparatus is provided between the mask and the projection lens or between the photosensitive substrate and the projection lens. An image-forming characteristic correction plate that is arranged between the projection-lens and the position of which is adjustable in the plane orthogonal to the optical axis, and corrects the image-forming characteristic of the projection lens; Exposure apparatus having a positional deviation detecting means for detecting a positional deviation from the reference position of. 2. A mark detecting unit of an image processing system, wherein the position shift detecting unit simultaneously picks up an alignment mark formed in advance on the imaging characteristic correction plate and an index mark formed in advance in a fixed portion of the apparatus. The exposure apparatus according to claim 1, further comprising: 3. A first step of disposing a plane-parallel plate having alignment marks including at least three pieces of position information at predetermined locations between the mask and the projection lens or between the photosensitive substrate and the projection lens. After adjusting the projection lens with the plane-parallel plate arranged, measuring the imaging characteristics of the projection lens and measuring the positional deviation of the alignment mark from the reference position in the plane orthogonal to the optical axis. A second step; a third step of removing the plane-parallel plate from the optical path of the projection lens; and an imaging characteristic correction plate processed based on the measurement result of the imaging characteristics of the second step of the projection lens. The position of the alignment mark, which is arranged on the optical path and is formed in advance on the imaging characteristic correction plate in correspondence with the alignment mark on the parallel plane plate, based on the position shift measurement result of the second step, In the first step Fourth adjustment for adjusting so as to match the position of the alignment mark of the parallel plane plate at the disposition position
A method of correcting imaging characteristics, including the steps of: