JPH065490A - Projection aligner - Google Patents

Abstract

PURPOSE:To measure imagery characteristics such as focal position and magnification error of a projection aligner system concerning a pattern of arbitrary line width. CONSTITUTION:Two reference marks WM1 and WM2 different in line width are formed on a stage substrate 13 on a wafer stage 12. The image of one of the reference marks is projected on the lower surface of a reticle R via a projection optical system PL. The light out of the lights from the projection image on the lower surface which light has passed a reticle mark RM1 or a reticle mark RM2 is received by photoelectric transducers 31 and 33, via a condenser lens 10 and a beam splitter 9. The imagery characteristics of a projection aligner system PL concerning arbitrary line width is calculated from characteristics of two kinds of line widths.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a projection exposure apparatus provided with, for example, a mechanism for measuring image forming characteristics of a projection optical system.

[0002]

2. Description of the Related Art When manufacturing a semiconductor integrated circuit, a liquid crystal display device or the like by using a photolithography technique, a projection exposure apparatus is used which transfers a reticle pattern onto a wafer through a projection optical system. In order to manufacture high-quality semiconductor integrated circuits that are becoming more and more miniaturized these days,
It is necessary to maintain the imaging characteristics of such a projection optical system in a predetermined state. However, in a projection exposure apparatus, when performing long-time exposure, the projection optical system causes thermal deformation or the like due to irradiation of exposure light, and as a result, projection of focal position, field curvature, magnification error or distortion aberration, etc. It is known that the imaging characteristics of the optical system change gradually. Furthermore,
The imaging characteristics of the projection optical system also change due to changes in atmospheric pressure, temperature, or the reflectance of the wafer around the projection optical system.

Therefore, in the conventional projection exposure apparatus, the atmospheric pressure around the projection optical system, the temperature, the amount of change of the exposure light irradiation amount, the amount of light reflected from the wafer, and the like are measured, and a predetermined value is determined according to the measurement result. There is a device provided with a mechanism for obtaining a change in the image forming characteristic of the projection optical system based on the predictive calculation formula and adjusting the change to some extent. As a result, the reticle pattern is always transferred onto the wafer with high contrast and at a predetermined magnification. Examples of the mechanism for controlling the imaging characteristics of the projection optical system include a mechanism that adjusts the temperature of the projection optical system, a mechanism that adjusts the pressure of gas in a predetermined lens chamber of the projection optical system, and a lens that configures the projection optical system. A mechanism for adjusting the distance, a mechanism for slightly tilting the reticle, a mechanism for vertically moving a stage on which a wafer is placed, and the like are known.

The above-described projection exposure apparatus indirectly predicts and controls fluctuations in the reticle pattern image by measuring external factors (such as atmospheric pressure) that deteriorate the projection image of the projection optical system. However, a method of directly measuring the variation of the reticle pattern image has also been developed. In this method, a measuring device that directly measures the focus position, astigmatism, field curvature, magnification error, etc. of the pattern image of the reticle by the projection optical system is used to control the arithmetic device from the measurement result. Thus, the above-mentioned image forming characteristic control mechanism is driven so that the focus position of the pattern image of the reticle, the magnification error, etc. are within a predetermined allowable range.

In a direct measuring device of a reticle pattern image, for example, Japanese Patent Laid-Open Nos. 64-10105, 1-273318, and 1-26262 are known.
As disclosed in Japanese Patent Publication No. 4, a predetermined mark (for example, a cross pattern having a constant line width) is formed on a substrate placed on a wafer stage, and the mark is used as exposure light from inside the wafer stage. The mark image is transferred to the lower surface of the reticle through a projection optical system by transmitting and illuminating with light of the same wavelength. The light of the mark image passes through a predetermined reticle mark arranged in the exposure area on the lower surface of the reticle, and the light receiving surface of the photoelectric conversion element arranged at a position conjugate with the pupil plane of the projection optical system in the illumination optical system. To enter. With the horizontal movement of the wafer stage, the amount of light received by the photoelectric conversion element changes, and when the image of the mark on the wafer stage and the reticle mark match, the amount of light received becomes minimum (or maximum). Conversely, if the coordinates of the wafer stage when the output signal of the photoelectric conversion element becomes the minimum (or maximum) are obtained, this coordinate value indicates the position on the wafer stage of the image of the reticle mark formed via the projection optical system. Will be represented.

The reticle marks are formed at a plurality of predetermined positions in the exposure area on the lower surface of the reticle, and the coordinate position of each reticle mark image on the wafer stage is measured in the same manner. It is possible to measure the magnification error and the distortion of the transferred reticle pattern image. Further, if the light receiving surface of the photoelectric conversion element is divided into two parts so that the respective light receiving amounts can be detected separately, by combining with the vertical and horizontal movement of the wafer stage, the focus position of the pattern image of the reticle, It can also measure point aberrations and field curvature.

With respect to changes in magnification error, distortion aberration, focus position, astigmatism, and field curvature of the reticle pattern image obtained from these measurement results, the above-mentioned image formation is performed under the control of the arithmetic unit. By driving the characteristic control mechanism, the change of the pattern image of the reticle is kept within a predetermined range.

[0008]

However, in the conventional apparatus for directly measuring the pattern image of the reticle,
Since a mark with a specific line width is used as the mark on the wafer stage, all the measured results are the focus position, magnification error, etc. related to the line width. Further, when the projection optical system has an aberration, the focus position, astigmatism, field curvature, magnification error, distortion and the like of the projection optical system differ due to the difference in the line width of the transferred pattern. Therefore, if the line width of the reticle pattern actually transferred is different from the line width of the measurement mark, there is a disadvantage in that the imaging characteristics of the reticle pattern cannot be accurately measured.

In particular, as the irradiation energy of the exposure light is accumulated inside the projection optical system, the aberration of the projection optical system, particularly the spherical aberration and the coma aberration, change. When the irradiation energy of the exposure light is accumulated in such a manner, the temperature of the optical material forming the projection optical system locally rises, for example, near the center, and as a result, the refractive index of the portion where the temperature rises increases. Change occurs. Further, the curvature of the optical member is initially spherical, but gradually changes to aspheric. In this way, spherical aberration and further coma occur in the projection optical system.

For example, when the shape of the spherical aberration tends to be overcorrected, if the line width of the reticle pattern is thin, the diffraction angle of the diffracted light forming the image is large, so that the wafer of the reticle pattern image is large. The focus position at the top shows a tendency to go downward when viewed from the paraxial image plane. Conversely, if the line width of the reticle pattern is thick, the diffraction angle of the diffracted light that forms the image can be small, so the focus position of the reticle pattern image on the wafer remains near the paraxial image plane. .

In the exposure apparatus in actual use, exposure light irradiation is intermittent for step and repeat of the wafer stage, wafer alignment, reticle exchange, etc., and heat is generated by the irradiation energy of the exposure light in the projection optical system each time. Accumulation and dissipation are repeated. Further, since the transmittance and the reflectance of the reticle and the wafer are different depending on the type of the reticle and the wafer, the irradiation energy of the exposure light to the projection optical system changes, and the heat dissipation speed in the projection optical system also changes due to the temperature difference with the outside. .

Under such a complicated thermal non-equilibrium state, the spherical aberration described above changes every moment, so that the focus position using a mark with a specific line width as in the conventional case is used. Alternatively, if a measuring device for measuring a magnification error or the like is used, it is difficult to obtain an accurate focus position or a magnification error for a pattern image of various line widths of a reticle transferred via the projection optical system. . The present invention has been made in view of the above problems, and an object of the present invention is to provide a projection exposure apparatus capable of measuring imaging characteristics such as a focus position and a magnification error of a projection optical system regarding a pattern having an arbitrary line width.

[0013]

A first projection exposure apparatus according to the present invention illuminates a mask R by exposing a light source (1) for generating exposure light and condensing the exposure light as shown in FIG. 1, for example. The illumination optical system (5, 10) and the pattern of the mask R on the photosensitive substrate W on the stage (12) under the exposure light.
Projection optical system PL for projecting onto the stage and its stage (12)
A plurality of measurement marks (WM1, WM2) each having a different line width formed above, and measurement mark illumination for illuminating any one of the plurality of measurement marks with light having the same wavelength as the exposure light. Optical system (21,23,24,2
5, 27) and photoelectric conversion means (31, 33) for receiving light from any one measurement mark illuminated by this measurement mark illumination optical system via the projection optical system PL.
Based on a plurality of output signals obtained by the photoelectric conversion means by illuminating each of the plurality of measurement marks, a connection of the projection optical system PL regarding a mark having a line width different from the line width of the plurality of measurement marks. And an arithmetic means (8) for calculating the image characteristic.

The second projection exposure apparatus according to the present invention is, for example, as shown in FIG. 6, a light source (1) for generating exposure light, and an illumination optical system for converging the exposure light and illuminating the mask R. (5, 10), a projection optical system PL for projecting the pattern of the mask R on the photosensitive substrate W on the stage (12) under the exposure light, and measurement formed on the stage (12). The mark WM1, the measurement mark illumination optical system (21, 45) that illuminates the measurement mark WM1 with light having the same wavelength as the exposure light, and the incident angle of the illumination light from the measurement mark illumination optical system with respect to the measurement mark WM1. And an photoelectric conversion means (31, 33) for receiving the light from the measurement mark WM1 illuminated by the measurement mark illumination optical system via the projection optical system PL. Illumination angle varying means (46)
By illuminating the measurement mark WM1 under an arbitrary illumination angle, the photoelectric conversion means (3
1, 33), and an arithmetic means (8) for calculating the image forming characteristic of the projection optical system PL for a mark having a line width different from the line width of the measurement mark WM1 based on the plurality of output signals. It is a thing.

In this case, the photoelectric conversion means (31, 3)
3) is illuminated by the measurement mark illumination optical system (38, 23, 25) like the photoelectric conversion means (39) shown in FIG. 4, and is inverted on the mask R via the projection optical system PL. The reflected light from the projected image of the measurement mark WM3 is reflected by the projection optical system PL and the measurement mark WM3.
It may be one that receives light via.

[0016]

The principle of the first projection exposure apparatus of the present invention will be described. For the sake of simplicity, the focus position (best focus plane) will be taken up as the imaging characteristic of the projection optical system PL below. First, since a constant functional relationship is established between the amount of irradiation energy of the exposure light to the projection optical system PL and the amount of spherical aberration generated thereby, the amount of accumulated irradiation energy and the line width of the mask R are A certain relationship is established for the focus positions related to the pattern.

FIG. 13A shows a state in which the focus position Z _f of the image of the pattern of the mask R having different line widths gradually changes with the irradiation time t in the projection exposure apparatus during continuous irradiation. In FIG. 13 (a), the curves CA to CC are focal positions Z of the images of the patterns having different line widths A to C, respectively.
Represents the change in _f . At the start of irradiation, the difference in the focal position due to the difference in the line width of the pattern was almost inconspicuous, but the difference in the focal position becomes larger as the irradiation time advances. This corresponds to the fact that the spherical aberration of the projection optical system PL is increasing with the increase in the accumulated amount of irradiation energy. Then, as the irradiation time further advances, the difference in the focal position becomes constant, but this is because the amount of irradiation energy and the amount of heat dissipation compete with each other, and the projection optical system PL is in a thermal equilibrium state. It is showing that it is going. Therefore, the increase of spherical aberration also disappears.

In the projection exposure apparatus at the time of actual use, as described above, the irradiation of the exposure light is repeated intermittently as the shutter is opened and closed. Further, there is heat dissipation due to interruption of irradiation of exposure light during alignment time for each photosensitive substrate W or during replacement of the mask R, and the accumulated amount of irradiation energy of the projection optical system PL in such a use state is shown in FIG.
It is considered that the difference in the focal position in (a) is within the increasing range. When the accumulated amount of irradiation energy can be accurately measured, the focus position of the pattern image having an arbitrary line width can be calculated according to FIG. However, it is difficult to directly measure the actual accumulated amount of irradiation energy with high accuracy, and the amount of change in atmospheric pressure, temperature, irradiation amount of exposure light, reflected light amount from the wafer, etc., as in the past. Is measured and the irradiation energy accumulated in the projection optical system PL is indirectly calculated, resulting in a large error.

Therefore, as shown in FIG. 13B, the horizontal axis is the difference Z _AB between the focal position for the line width A and the focal position for the line width B in FIG. 13A, and the vertical axis is the measurement target. Take a focal position Z _C for an arbitrary line width C. As the arbitrary line width C to be measured, for example, the minimum line width assumed by the projection optical system PL can be considered. As can be seen from FIG. 13B, the difference Z _AB between the focal position relating to the line width A and the focal position relating to the line width B corresponds to the focal position Z _C relating to an arbitrary line width C in a predetermined relationship. ing. Therefore, for the required line width, a graph or a relational expression showing the functional relation as shown in FIG. 13B is stored in advance in the calculating means (8). Then, for example, when the difference Z _AB between the focal positions of the measurement marks WM1 and WM2 having different line widths shown in FIG. 1 is obtained, the focal position for an arbitrary line width required by the calculating means (8) can be obtained. it can.

Further, when the image forming characteristic control means is provided, the photosensitive substrate W is placed at the focal position thus obtained.
By moving the exposure surface of the mask R, the pattern of the mask R having an arbitrary line width can be accurately and accurately contrasted to the photosensitive substrate W.
Can be projected on. Further, regarding not only the focus position but also the astigmatism, the field curvature, the magnification error, the distortion aberration, etc., the graph or the relational expression of the functional relation as shown in FIG. Then, it is obvious that a better image of the mask R can be projected on the photosensitive substrate W.

Next, the principle of the second projection exposure apparatus of the present invention will be described. For simplicity, the projection optical system PL will be described below.
The focus position (best focus plane) is taken as the imaging property of. First, since a constant functional relationship is established between the amount of irradiation energy of the exposure light to the projection optical system PL and the amount of spherical aberration generated thereby, the amount of accumulated irradiation energy and the line width of the mask R are A certain relationship is established for the focus positions related to the pattern. When the line widths are different, the diffraction angles of the diffracted light are different and the incident angles of the diffracted light with respect to the projection optical system PL are different. Therefore, by changing the illumination angle with respect to the measurement mark WM1, it is possible to measure the imaging characteristics of the projection optical system PL with respect to substantially different line widths.

FIG. 13 (a) also shows a state in which the focal position Z _f of the image of the pattern of the mask R having different irradiation angles gradually changes with the irradiation time t in the projection exposure apparatus during continuous irradiation. In FIG. 13A, the curve CA to
CC represents the change in the focal position Z _f of the image of the pattern having different irradiation angles A to C. At the start of irradiation, the difference in the focal position due to the difference in the irradiation angle of the pattern was hardly noticeable, but the difference in the focal position becomes larger as the irradiation time advances. This corresponds to the fact that the spherical aberration of the projection optical system PL is increasing with the increase in the accumulated amount of irradiation energy. Then, as the irradiation time further advances, the difference in the focal position becomes constant, but this is because the amount of irradiation energy and the amount of heat dissipation compete with each other, and the projection optical system PL is in a thermal equilibrium state. It is showing that it is going. Therefore, the increase of spherical aberration also disappears.

In the projection exposure apparatus at the time of actual use, as described above, the irradiation of the exposure light is repeated intermittently as the shutter is opened and closed. Further, there is heat dissipation due to interruption of irradiation of exposure light during alignment time for each photosensitive substrate W or during replacement of the mask R, and the accumulated amount of irradiation energy of the projection optical system PL in such a use state is shown in FIG.
It is considered that the difference in the focal position in (a) is within the increasing range. When the accumulated amount of irradiation energy can be accurately measured, the focus position of the pattern image having an arbitrary line width can be calculated according to FIG. However, it is difficult to measure the actual amount of accumulated irradiation energy with high accuracy.

Therefore, as shown in FIG. 13B, the horizontal axis is the difference Z _AB between the focal position relating to the irradiation angle A and the focal position relating to the irradiation angle B in FIG. 13A, and the vertical axis is the object of measurement. Take a focal position Z _C for an arbitrary line width C. As the arbitrary line width C to be measured, for example, the minimum line width assumed by the projection optical system PL can be considered. As can be seen from FIG. 13B, for a difference Z _AB between the focal position regarding the irradiation angle A and the focal position regarding the irradiation angle B, an arbitrary line width C
The focus positions Z _C with respect to each other correspond to each other in a predetermined relationship. Therefore, regarding the required line width, FIG.
A graph or a relational expression showing the functional relation as shown in (b) is stored in the calculating means (8). Then, for example, with respect to the measurement mark WM1 of FIG. 6, the focal position is obtained at each of two different irradiation angles, and the difference Z _AB between the focal positions is obtained. For the arbitrary line width required by the calculating means (8). The focus position can be obtained.

Further, those photoelectric conversion means (31, 33)
Is, for example, as in the photoelectric conversion means (39) shown in FIG.
The reflected light from the image of the measurement mark WM3 that is illuminated by the measurement mark illumination optical system (38, 23, 25) and is back-projected onto the mask R via the projection optical system PL is the projection optical system. When the light is received through the PL and the measurement mark WM3 thereof, it is not necessary to form the measurement mark on the reticle R, and the illumination optical system (5, 5) is not required.
It is not necessary to arrange an optical system for measurement in 10). Therefore, the configuration is simplified.

[0026]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Various embodiments of the projection exposure apparatus according to the present invention will be described below with reference to the drawings. [First Embodiment] A first embodiment of the present invention will be described with reference to FIGS. FIG. 1 shows a projection exposure apparatus of this example,
In FIG. 1, reference numeral 1 is a light source such as a mercury lamp. The exposure light from the light source 1 is focused by the elliptical mirror 2, reflected by the mirror 3, and then converted into a substantially parallel light flux by the input lens 4. A shutter 6 is arranged between the ellipsoidal mirror 2 and the mirror 3, and the shutter 6 is closed by a drive motor 7, whereby the supply of exposure light to the input lens 4 can be stopped. Reference numeral 8 denotes a main control system that controls the operation of the entire apparatus, and the main control system 8 controls the operation of the drive motor 7. In addition to the mercury lamp, a pulsed laser light source such as a KrF excimer laser or another light source can be used as the light source 1.

When the shutter 6 is in the open state, the exposure light emitted from the input lens 4 enters the fly-eye lens 5 as an optical integrator and is focused on the exit side (reticle R side) of the fly-eye lens 5. A large number of secondary light sources are formed on the plane. At the time of exposure on the wafer W, the exposure light emitted from the secondary light source formation surface of the fly-eye lens 5 enters a beam splitter 9, and the exposure light transmitted through this beam splitter 9 passes through a condenser lens 10 and a mirror 11 to a suitable degree. Then, the reticle R is illuminated with a substantially uniform illuminance.

As shown in FIG. 2A, in the pattern area of the reticle R of this example, a cross-shaped reticle mark RM1 having a thick line width and a cross-shaped reticle mark RM2 having a thin line width are provided.
To form the measurement mark RM. A large number of measurement marks RM are formed in a matrix in the pattern area of the reticle R. This measurement mark RM is used to measure the focal position of the projection optical system PL, astigmatism, field curvature, magnification error, distortion, and the like. However, in the measurement mark RM, two reticle marks RM1 and RM2 are used.
One of them may be omitted.

Returning to FIG. 1, during exposure of the wafer W, the exposure light passing through the pattern area of the reticle R is focused on the shot area on the wafer W by the projection optical system PL, whereby the pattern of the reticle R is transferred to the wafer. It is transferred to the shot area of W at a predetermined reduction ratio. Projection optical system PL
The Fourier transform plane (pupil plane) of is conjugate with the secondary light source formation surface of the fly-eye lens 5. The wafer W is held on the wafer stage 12, and the wafer stage 12 two-dimensionally positions the wafer W in a plane (XY plane) perpendicular to the optical axis of the projection optical system PL and the projection optical system. P
The Z stage or the like positions the wafer W in a direction (Z direction) parallel to the optical axis of L.

A light-transmissive stage substrate 13 is attached near the wafer W on the wafer stage 12, and the surface of the stage substrate 13 is set at the same height as the exposure surface of the wafer W. 2B shows a pattern on the stage substrate 13. In FIG. 2B, the reference mark W formed of a cross-shaped opening pattern having a thick line width is formed on the stage substrate 13.
A reference mark WM2 formed of M1 and a cross-shaped opening pattern having a narrow line width is formed. In this example, the reticle marks RM1 and RM2 in the measurement mark RM on the reticle R are used.
The reference marks WM1 and WM2 are set to have substantially the same size with respect to the image projected by the projection optical system PL.

Returning to FIG. 1, a movable mirror 14 for reflecting the laser beam of the laser interferometer 15 is fixed on the wafer stage 12, and the laser interferometer 15 is a two-dimensional structure of the XY stage in the wafer stage 12. Measure the coordinates. The main control system 8 positions the wafer stage 12 via the driving device 16 while monitoring the two-dimensional coordinates measured by the laser interferometer 15.

Reference numeral 19 denotes an irradiation optical system of the focus detection system, and 20 denotes a light reception optical system of the focus detection system. The irradiation optical system 19 obliquely forms an image of, for example, a slit pattern at a predetermined position in the exposure area of the projection optical system PL. Upon projection, the light receiving optical system 20 re-images the image of the slit pattern on, for example, a vibrating slit plate. A light receiving element is arranged on the back surface of the vibrating slit plate, and a detection signal of the light receiving element is synchronously rectified by a drive signal of the vibrating slit plate to produce the projection optical system PL.
When an object in the exposure area of is matched with the focal plane of the projection optical system PL, a focus signal having a predetermined level is obtained. This focus signal is supplied to the main control system 8. The main control system 8 controls the operation of the Z stage in the wafer stage 12 via the driving device 16 so that the focus signal becomes a predetermined level.
As a result, autofocus control is performed.

An aperture stop 17 is provided on the pupil plane of the projection optical system PL. Reference numeral 18 denotes an image forming characteristic control device, and the main control system 8 passes through the image forming characteristic control device 18,
The imaging characteristics of the projection optical system PL are controlled. The imaging characteristic control device 18 adjusts, for example, the pressure of a predetermined air chamber of the projection optical system PL, or adjusts the distance between the lens groups forming the projection optical system PL. Further, by the image forming characteristic control device 18,
The tilt angle of the reticle R with respect to the plane perpendicular to the optical axis of the projection optical system PL may be finely adjusted. This imaging characteristic control device 18
Also, the main control system 8 via the drive unit 16 and the projection optical system P
It is possible to adjust the image forming characteristics such as the focus position of L, astigmatism, field curvature, magnification error, and distortion within a predetermined range.

Reference numeral 21 denotes a light guide. One end 21a of the light guide 21 is arranged in the vicinity of the shutter 6, and the other end of the light guide 21 which is bifurcated is housed in the wafer stage 12. In the state where the shutter 6 is closed, the exposure light reflected by the shutter 6 is focused on the end surface of the one end 21 a of the light guide 21 by the condenser lens 22, and the other two end portions of the light guide 21 in the wafer stage 12 are converged. Exposure light is emitted from the end faces of 21b and 21c. The exposure light emitted from the end surface of the one end 21b is converted into a substantially parallel light flux by the condenser lens 23 to illuminate the reference mark WM1 on the stage substrate 13 from the bottom, and the end surface of the other end 21c. The exposure light emitted from is converted into a substantially parallel light flux by the condenser lens 24 and illuminates the reference mark WM2 on the stage substrate 13 from the bottom.

The one end 21b and the condenser lens 23
A shutter 25 is placed between the
Is opened and closed by the drive motor 26. Similarly, one end 2
A shutter 27 is arranged between 1c and the condenser lens 24, and the shutter 27 is opened and closed by a drive motor 28. At the time of measuring the image forming characteristics of the projection optical system PL, one shutter 25 is opened (the other shutter 27 when measuring the characteristics relating to one of the reference marks WM1).
Is closed), and the other shutter 27 is opened (one shutter 25 is closed) when the characteristic relating to the other reference mark WM2 is measured.

When measuring the image forming characteristics of the projection optical system PL,
The reference mark WM1 or WM2 of the stage substrate 13 is arranged in the exposure area of the projection optical system PL. Then, the shutter 6 is closed and the other end portion 2 of the light guide 21 is closed.
Exposure light is emitted from the end faces of 1b and 21c. Here, assuming that the image forming characteristic of the projection optical system PL for one reference mark WM1 on the stage substrate 13 is measured, one shutter 25 is opened and the other shutter 27 is closed. The end 21 of the light guide 21
The exposure light emitted from the end face of b is irradiated onto one of the reference marks WM1 on the stage substrate 13 via the condenser lens 23, and the image of this reference mark WM1 is formed on the lower surface of the reticle R by the projection optical system PL. To be done.

In this case, by driving the XY stage of the wafer stage 12, one of the reticle marks R on the reticle R becomes the reference mark WM1 on the stage substrate 13.
Scan in the X and Y directions in the vicinity of the position where M1 is projected. In the light from the conjugate image of the lower surface of the reticle R of the reference mark WM1, the reticle mark RM on the reticle R is
The exposure light that has passed through 1 enters the beam splitter 9 via the mirror 11 and the condenser lens 10. The exposure light reflected by the beam splitter 9 is focused on the plane P1 which is conjugate with the pupil plane of the projection optical system PL.

In this example, the knife-edge shaped split mirror 29 is fixed at an angle of about 45 ° with respect to the optical axis so that the edge is in contact with the optical axis of the surface P1. Then, after being reflected by the beam splitter 9, the exposure light that has passed through the surface P1 as it is is applied to the light receiving surface of the photoelectric conversion element 31 formed of a photomultiplier through the condenser lens 30. On the other hand, after being reflected by the beam splitter 9, the split mirror 29
The exposure light reflected by is irradiated onto the light receiving surface of the photoelectric conversion element 33 formed of a photomultiplier through the condenser lens 32. The output signals of the photoelectric conversion elements 31 and 33 are supplied to the main control system 8.

Using the output signals of these two photoelectric conversion elements 31 and 33, the stage substrate 13 is processed as follows.
Projection optical system P for the reference marks WM1 and WM2 above
The characteristics of the focus position of L can be obtained respectively. First, one fiducial mark WM1 on the stage substrate 13 now
Is projected on the lower surface of the reticle R. in this case,
The main control system 8 includes a wafer stage 12 via a drive unit 16.
The inner Z stage is driven to set the height of the reference mark WM1 on the stage substrate 13 in the optical axis direction (Z direction) of the projection optical system PL to the first position Z1. In this state, the reference mark WM1 is scanned in the X direction and the Y direction in a plane perpendicular to the optical axis of the projection optical system PL, so that the reticle mark RM1 on the reticle R is positioned at the conjugate image position of the projection optical system PL. When the reference marks WM1 match, the output signals of the photoelectric conversion elements 31 and 33 become maximum or minimum. Therefore, conversely, the main control system 8 can know the position of the conjugate image of the reticle mark RM1 in the exposure area of the projection optical system PL from the output signals of the photoelectric conversion elements 31 and 33.

However, in this example, since the light from the reference mark WM1 is split by the split mirror 29 at the pupil conjugate position of the projection optical system PL, the reference mark WM1 is the focus position (best focus position) of the projection optical system PL. If it does not match, the position (X1, Y) of the conjugate image of the reticle mark RM1 obtained based on the output signal of the photoelectric conversion element 31.
1) and the position (X2, Y2) of the conjugate image of the reticle mark RM1 obtained based on the output signal of the photoelectric conversion element 33 have different values.

Next, the main control system 8 drives the Z stage in the wafer stage 12 via the drive unit 16 to set the second height of the reference mark WM1 on the stage substrate 13 in the Z direction.
Position Z2. In this state, the reference mark WM1 is scanned in the X direction and the Y direction in the plane perpendicular to the optical axis of the projection optical system PL, and the main control system 8 causes the projection optical system PL to output from the output signals of the photoelectric conversion elements 31 and 33. The position of the conjugate image of the reticle mark RM1 in the exposure area can be known. Even in this case, the reference mark WM1 is the projection optical system PL.
If it does not match the focus position (best focus position) of the reticle mark RM1, the conjugate image position (X1 ′, Y) obtained based on the output signal of the photoelectric conversion element 31 is determined.
1 ') and the position (X2', Y) of the conjugate image of the reticle mark RM1 obtained based on the output signal of the photoelectric conversion element 33.
The value is different from 2 ').

If, for example, the horizontal axis is the Z-direction position and the vertical axis is the X-direction conjugate position, a straight line connecting the coordinates X1 and X1 'obtained from the output signal of one photoelectric conversion element 31 is obtained. The Z coordinate Z0 at the intersection with the straight line connecting the coordinates X2 and X2 ′ obtained from the output signal of the other photoelectric conversion element 33 is the obtained focus position. The line width of the reference mark WM1 is w
1. If the projection magnification from the reticle R of the projection optical system PL to the wafer W is β, the focal position Z0 thus obtained is a pattern of the line width w1 / β on the reticle R at the conjugate position of the reticle mark RM1. Is the focus position of the projection optical system PL. Further, the difference between the coordinate on the XY plane of the conjugate image of the reticle mark RM1 at the focal position Z0 and the theoretical coordinate of the conjugate image of the reticle mark RM1 is the pattern of the line width w1 / β on the reticle R. Is based on the magnification error and the distortion of the projection optical system PL.

Then, for each of the reticle marks RM1 formed in a matrix on the lower surface of the reticle R, the focus position and the XY coordinates of the conjugate image of the reticle mark RM1 are obtained using the reference mark WM1 of the stage substrate 13. The main control system 8 can obtain the focus position, astigmatism, field curvature, magnification error, and distortion of the projection optical system PL regarding the pattern of the line width w1 / β on the reticle R.

Next, the main control system 8 for measuring the image forming characteristic of the projection optical system PL with respect to the other reference mark WM2 on the stage substrate 13 closes one shutter 25 and opens the other shutter 27. . Then, the mark to be measured on the reticle R is changed to the other reticle mark R.
As M2, a projection optical system P for this reticle mark RM2
Near the conjugate image of L, the other reference mark WM2 on the stage substrate 13 is scanned in the X direction and the Y direction. In this case, the exposure light emitted from the end surface of the end portion 21c of the light guide 21 passes through the condenser lens 24 and the stage substrate 1
The reference mark WM2 on the other side of the reference mark 3 is irradiated, and the image of the reference mark WM2 is formed on the lower surface of the reticle R by the projection optical system PL.

Of the light from the conjugate image of the lower surface of the reticle R of the reference mark WM2, the exposure light transmitted through the reticle mark RM2 on the reticle R is incident on the beam splitter 9 via the mirror 11 and the condenser lens 10.
Of the exposure light reflected by this beam splitter 9,
The exposure light that has passed through the surface P1 as it is is incident on the light receiving surface of the photoelectric conversion element 31 via the condenser lens 30, and the split mirror 2
The exposure light reflected by 9 enters the light receiving surface of the photoelectric conversion element 33 through the condenser lens 32.

The main control system 8 uses the output signals of the two photoelectric conversion elements 31 and 33 to determine the focus position of the projection optical system PL with respect to the reference mark WM2 and the reticle mark RM2.
The difference between the actual position and the theoretical position of the conjugate image of can be obtained. Then, the line width of the reference mark WM2 is set to w2.
Then, for each of the reticle marks RM2 formed in a matrix on the lower surface of the reticle R, the focal point and the XY coordinates of the conjugate image of the reticle mark RM2 are obtained by using the reference mark WM2 of the stage substrate 13. The control system 8 has a line width w2 / β on the reticle R.
The focus position of the projection optical system PL, the astigmatism, the field curvature, the magnification error, and the distortion aberration relating to the pattern can be obtained.

In this case, it is assumed that the line width w1 of the reference mark WM1 is thicker than the line width w2 of the reference mark WM2 (w
1> w2), assuming that the exposure light emitted from the reference mark WM1 is distributed in the shaded area 34 in FIG. 3A on the pupil plane of the projection optical system PL, the exposure light emitted from the reference mark WM2. The light is distributed in the shaded area 35 in FIG. 3C on the pupil plane of the projection optical system PL. Further, the light amount distributions along the X axis in FIGS. 3A and 3C are shown in FIGS. 3B and 3D, respectively. On the contrary, the exposure light applied to the pattern of the line width w1 / β on the reticle R and the exposure light applied to the pattern of the line width w2 / β on the reticle R are respectively shown in the pupil plane of the projection optical system PL. Passes through areas (a) and (c). Therefore, when the exposure of the pattern of the reticle R is continued, the heated portion of the projection optical system PL is different due to the difference in the line width of the pattern, so that the change in the imaging characteristics also tends to be different depending on the line width of the pattern. it is conceivable that.

However, the line width of the pattern on the reticle R to be actually transferred is different from w1 / β and w2 / β, and the minimum line width of the pattern on the reticle R is w1 / β. And smaller than w2 / β. Therefore, the main control system 8 of the present example uses the image forming characteristic of the projection optical system PL regarding the line width w1 / β and the image forming characteristic of the projection optical system PL regarding the line width w2 / β to actually transfer the reticle. The image forming characteristics of the R pattern, for example, the pattern having the minimum line width are obtained by calculation or the like. Specifically, for example, when obtaining the focus position of the projection optical system PL regarding the pattern of the line width w3 / β on the reticle R, the main control system 8 controls the projection optical system PL regarding the line widths w1 / β and w2 / β. The focus position difference Z _AB is determined. In this case, the focus position Z _C of the projection optical system PL for different line widths w3 / β is
It is represented by a characteristic curve as shown in FIG.

Therefore, the result of the measurement or calculation shown in FIG.
By obtaining the characteristic curve of (b), the main control system 8
Can determine the focus position Z _C of the projection optical system PL with respect to the line width w3 / β from the difference Z _AB between the focus positions.
After that, in FIG. 1, the main control system 8 moves to the wafer stage 12
By driving the Z stage inside and adding the focus position Z _C to the focus position obtained by the light receiving optical system 20 as an offset, the wafer W can be always aligned with the focus position of the projection optical system PL.

Similarly, the main control system 8 determines the astigmatism and the image plane of the projection optical system PL regarding the line width w3 / β from the imaging characteristics of the projection optical system PL regarding the line widths w1 / β and w2 / β. Curvature, magnification error, distortion, etc. can also be calculated. Then, the main control system 8 can maintain those imaging characteristics of the projection optical system PL in a predetermined state via the imaging characteristics control device 18.

[Second Embodiment] A second embodiment of the present invention will be described with reference to FIGS. 4, parts corresponding to those in FIG. 1 are designated by the same reference numerals, and detailed description thereof will be omitted. FIG. 4 shows the projection exposure apparatus of this example.
In, fly eye lens 5 and condenser lens 1
No beam splitter is placed between 0 and 0. Also,
No mark for imaging characteristic measurement is formed on the lower surface of the reticle R. Also in this example, the optically transparent stage substrate 13 is arranged in the vicinity of the wafer W on the wafer stage 12.

FIG. 5 (a) shows the pattern on the stage substrate 13, and as shown in FIG. 5 (a), a part of the stage substrate 13 has a thick line width in various directions of phase type or amplitude. Forming a reference mark WM3 made of a diffraction grating of
A reference mark WM made of a phase-type or amplitude-type diffraction grating with a narrow line width in various directions is formed on another portion of the stage substrate 13.
4 is formed. The reference marks WM3 and WM4 are formed of diffraction gratings in various directions in order to reduce the influence of the pattern of the reticle R.

Returning to FIG. 4, reference numeral 36 denotes a light guide,
With the shutter 6 closed, the exposure light emitted from the light source 1 from the shutter 6 is focused on the end surface of the one end 36a of the light guide 36 by the condenser lens 22. The exposure light emitted from the end surface of the other first end portion 36b of the light guide 36 is passed through a condenser lens 37 to a light guide 38.
It is focused on the end face of one of the first end portions 38a. The other end portion 38b of the light guide 38 is housed inside the wafer stage 12, and the exposure light emitted from the end surface of this end portion 38b is passed through the condenser lens 23 to the one reference mark WM3 of the stage substrate 13 at the bottom portion. Irradiate from. Further, the light incident on the end portion 38b from the stage substrate 13 side is irradiated from the end surface of the one second end portion 38c of the light guide 38 to the light receiving surface of the photoelectric conversion element 39 including the photomultiplier.

Similarly, the exposure light emitted from the other end surface of the second end portion 36c of the light guide 36 is condensed by the condenser lens 4
One of the first end portions 41a of the light guide 41
Focus on the end face of. The other end 41 of the light guide 41
b inside the wafer stage 12, and the end portion 41
The exposure light emitted from the end surface of b is applied to the other reference mark WM4 of the stage substrate 13 from the bottom through the condenser lens 24. In addition, the stage substrate 13 is attached to the end portion 41b.
The light incident from the side is irradiated from the end surface of the one second end portion 41c of the light guide 41 to the light receiving surface of the photoelectric conversion element 42 including a photomultiplier. The main control system 8 outputs the output signals S1 and S2 of the photoelectric conversion elements 39 and 42, respectively.
Supply to.

The shutter 25 is arranged between the end portion 38b of the light guide 38 and the condenser lens 23, and the shutter 27 is arranged between the end portion 41b of the light guide 41 and the condenser lens 24. When measuring the imaging characteristics of the projection optical system PL with respect to the reference mark WM3, the main control system 8
Opens the shutter 25 and closes the shutter 27, and when measuring the imaging characteristics of the projection optical system PL with respect to the reference mark WM4, the main control system 8 opens the shutter 27 and closes the shutter 25. Other configurations are the same as those in FIG.

An example of the operation of measuring the image forming characteristics of the projection optical system PL of this example will be described. First, assuming that the imaging characteristics of the projection optical system PL with respect to one of the reference marks WM3 on the stage substrate 13 is measured, one shutter 25 is opened and the other shutter 27 is opened with the shutter 6 closed. To be closed. The end 3 of the light guide 38
The exposure light emitted from the end face of 8b is applied to one of the reference marks WM3 on the stage substrate 13 via the condenser lens 23, and the image of the reference mark WM3 is formed on the lower surface of the reticle R by the projection optical system PL. To be done.

The reflected light from the conjugate image of the lower surface of the reticle R of the reference mark WM3 is irradiated again onto the reference mark WM3 via the projection optical system PL, and the reference mark WM3.
The light that has passed through 3 enters the photoelectric conversion element 39 via the condenser lens 23, the other end 38b of the light guide 38, and the one second end 38c. In this case, the main control system 8 moves the Z stage of the wafer stage 12 to the Z stage via the drive unit 16.
When scanning in the direction, the reference mark WM on the stage substrate 13
Since the output signal of the photoelectric conversion element 39 is maximized or minimized when 3 is aligned with the focus position of the projection optical system PL, the main control system 8 controls the focus of the projection optical system PL with respect to the reference mark WM3 having a thick line width. The position can be measured. Further, by moving the reference mark WM1 in the X direction and the Y direction within the exposure area of the projection optical system PL to obtain the respective focus positions, it is possible to obtain the field curvature of the projection optical system PL and the like.

Next, assuming that the image forming characteristic of the projection optical system PL with respect to the other reference mark WM4 on the stage substrate 13 is measured, one shutter 25 is closed and the other shutter 25 is closed while the shutter 6 is closed. Shutter 27
Can be opened. The exposure light emitted from the end surface of the end portion 41b of the light guide 41 is applied to the other reference mark WM4 on the stage substrate 13 via the condenser lens 24,
The image of the reference mark WM4 is formed on the lower surface of the reticle R by the projection optical system PL.

The reflected light from the conjugate image of the lower surface of the reticle R of the reference mark WM4 is again irradiated onto the reference mark WM4 via the projection optical system PL, and the reference mark WM4.
The light having passed through 4 enters the photoelectric conversion element 42 via the condenser lens 24, the other end 41b of the light guide 41, and the one second end 41c. In this case, the main control system 8 moves the Z stage of the wafer stage 12 to the Z stage via the drive unit 16.
When scanning in the direction, the reference mark WM on the stage substrate 13
4 becomes the maximum or minimum output signal of the photoelectric conversion element 42 when the focal point of the projection optical system PL is matched, the main control system 8 controls the focus of the projection optical system PL with respect to the reference mark WM4 having a thin line width. Position and field curvature can be measured.

In this case, it is assumed that the line width w3 of the reference mark WM3 is thicker than the line width w4 of the reference mark WM4 (w
3> w4), assuming that the exposure light emitted from the reference mark WM3 is distributed in the shaded area 43 in FIG. 5B on the pupil plane of the projection optical system PL, the exposure light emitted from the reference mark WM4. The light is distributed in the shaded area 44 in FIG. 5C on the pupil plane of the projection optical system PL. Conversely, with the projection magnification of the projection optical system PL from the reticle R onto the wafer W being β, the exposure light irradiated on the pattern having the line width w3 / β on the reticle R and the line width w4 / β on the reticle R are shown.
The exposure light applied to the pattern of (1) passes through the regions of FIGS. 5B and 5C on the pupil plane of the projection optical system PL. Therefore, when the exposure of the pattern of the reticle R is continued, the heated portion of the projection optical system PL is different due to the difference in the line width of the pattern, so that the change in the imaging characteristics also tends to be different depending on the line width of the pattern. it is conceivable that.

However, the line width of the pattern on the reticle R to be actually transferred is different from w3 / β and w4 / β, and the minimum line width of the pattern on the reticle R is w3 / β. And w4 / β. Therefore, the main control system 8 of this example uses the image forming characteristics of the projection optical system PL regarding the line width w3 / β and the image forming characteristics of the projection optical system PL regarding the line width w4 / β, and the reticle to be actually transferred. For example, the characteristics of the focus position and the field curvature regarding the pattern of R, for example, the pattern of the minimum line width are calculated. Then, the main control system 8 uses the imaging characteristic control device 18
The image forming characteristics of the projection optical system PL can be maintained in a predetermined state via the.

[Third Embodiment] A third embodiment of the present invention will be described with reference to FIGS. 6 and 7, parts corresponding to those in FIG. 1 are designated by the same reference numerals, and detailed description thereof will be omitted. FIG. 6 is a front view of the projection exposure apparatus of this example,
FIG. 7 is a right side view of FIG. 6 (however, a part thereof is shown in a sectional view). In FIG. 6, a stage substrate having a light transmitting property also in the vicinity of the wafer W on the wafer stage 12 of this example. 13 is arranged, and a reference mark WM1 formed of a cross-shaped opening pattern having a line width w1 is formed on the stage substrate 13 (this is the same mark as the reference mark WM1 in FIG. 2B). A condenser lens 45 is arranged inside the wafer stage 12 at the bottom of the stage substrate 13, a disk-shaped spatial filter plate 46 is arranged below the condenser lens 45, and the main control system 8 drives a drive motor 47. The rotation angle of the spatial filter plate 46 is positioned via the.

FIG. 8A shows an opening pattern of the spatial filter plate 46. As shown in FIG. 8A, a circular opening pattern 48 is formed in a part of the spatial filter plate 46 to form a spatial filter plate. An inclined illumination opening pattern 49 composed of four circular opening patterns 49a to 49d is formed on the other portion of 46. By rotating the spatial filter plate 46 about the central axis 46a, the center of the circular opening pattern 48 or the inclined illumination opening pattern 4 is formed.
The center of 9 is arranged on the optical axis of the condenser lens 45 of FIG.

Returning to FIG. 6, the other end 21b of the light guide 21 of this example is not branched. Also, the end 21
b inside the wafer stage 12 and its end 21
The beam expander 50 is attached to the end face of b. Further, a large number of predetermined reticle marks RM3 are formed in a matrix on the lower surface of the reticle R of this example. FIG. 9A shows a reticle mark RM formed on the lower surface of the reticle R.
9A, the reticle mark RM3 is formed by overlapping a diffraction grating having a pitch P in the X direction and a diffraction grating having a pitch P in the Y direction in a cross shape.

Returning to FIG. 6, the other structure is similar to that of FIG. The operation of measuring the image forming characteristics of the projection optical system PL with the projection exposure apparatus of FIG. 6 will be described. First, the case where the center of the circular opening pattern 48 of the spatial filter plate 46 is arranged on the optical axis of the condenser lens 45 will be described. In this case, the reference mark WM1 on the stage substrate 13 is moved to the vicinity of a position conjugate with the reticle mark RM3 in the exposure area of the projection optical system PL. Then, the shutter 6 is closed and the exposure light from the light source 1 reflected by the shutter 6 is focused on the end face of the one end 21 a of the light guide 21 via the condenser lens 22. The exposure light emitted from the end surface of the other end 21b of the light guide 21 housed in the wafer stage 12 has its beam diameter expanded by the beam expander 50, and then the circular opening pattern 4 of the spatial filter plate 46.
The reference mark WM1 on the stage substrate 13 is irradiated with the light through the lens 8 and the condenser lens 45.

The exposure light transmitted through the reference mark WM1 forms an image of the reference mark WM1 near the reticle mark RM3 on the lower surface of the reticle R via the projection optical system PL. The reticle mark RM3 is a diffraction grating as shown in FIG. 9A, and in this example, the 0th-order light from the reticle mark RM3 enters the beam splitter 9 via the mirror 11 and the condenser lens 10. The exposure light reflected by the beam splitter 9 is focused on the plane P1 which is conjugate with the pupil plane of the projection optical system PL.

The exposure light that has passed through the surface P1 as it is after being reflected by the beam splitter 9 is collected by the condenser lens 30.
The light receiving surface of the photoelectric conversion element 31 is irradiated through the photoelectric conversion element 31 and is reflected by the beam splitter 9, and then the exposure light reflected by the split mirror 29 is condensed by the photoelectric conversion element 3 through the condenser lens 32.
Irradiate the light receiving surface of No. 3. These photoelectric conversion elements 31 and 3
The output signal of 3 is supplied to the main control system 8.

When the output signals of these two photoelectric conversion elements 31 and 33 are used, the stage substrate 13 is as follows.
The characteristic of the focus position of the projection optical system PL under the circular opening pattern 48 with respect to the upper reference mark WM1 can be obtained. In this case, the main control system 8 drives the Z stage in the wafer stage 12 via the drive unit 16 to set the height of the reference mark WM1 on the stage substrate 13 in the optical axis direction (Z direction) of the projection optical system PL. Is set to the first position Z1. In this state, the reference mark WM1 is scanned in the X direction and the Y direction in a plane perpendicular to the optical axis of the projection optical system PL, so that the reticle mark RM3 on the reticle R is positioned at the position of the conjugate image of the projection optical system PL. When the reference marks WM3 match, the output signals of the photoelectric conversion elements 31 and 33 become maximum or minimum. Therefore, conversely, the main control system 8 can know the position of the conjugate image of the reticle mark RM3 in the exposure area of the projection optical system PL from the output signals of the photoelectric conversion elements 31 and 33.

However, in this example, since the light from the reference mark WM1 is split by the split mirror 29 at the pupil conjugate position of the projection optical system PL, the reference mark WM1 is the focus position (best focus position) of the projection optical system PL. If it does not match, the position (X1, Y) of the conjugate image of the reticle mark RM3 obtained based on the output signal of the photoelectric conversion element 31.
1) and the position (X2, Y2) of the conjugate image of the reticle mark RM3 obtained based on the output signal of the photoelectric conversion element 33 have different values.

Next, the main control system 8 drives the Z stage in the wafer stage 12 via the drive unit 16 to adjust the height of the reference mark WM1 on the stage substrate 13 in the Z direction to the second level.
Position Z2. In this state, the reference mark WM1 is scanned in the X direction and the Y direction in the plane perpendicular to the optical axis of the projection optical system PL, and the main control system 8 causes the projection optical system PL to output from the output signals of the photoelectric conversion elements 31 and 33. It is possible to know the position of the conjugate image of the reticle mark RM3 in the exposure area of. Even in this case, the reference mark WM1 is the projection optical system PL.
If it does not match the focus position (best focus position) of the reticle mark RM3, the position (X1 ', Y) of the conjugate image of the reticle mark RM3 obtained based on the output signal of the photoelectric conversion element 31.
1 ') and the position (X2', Y) of the conjugate image of the reticle mark RM3 obtained based on the output signal of the photoelectric conversion element 33.
The value is different from 2 ').

If, for example, the horizontal axis is the Z-direction position and the vertical axis is the X-direction conjugate position, a straight line connecting the coordinates X1 and X1 'obtained from the output signal of one photoelectric conversion element 31 is obtained. The Z coordinate Z0 at the intersection with the straight line connecting the coordinates X2 and X2 ′ obtained from the output signal of the other photoelectric conversion element 33 is the obtained focus position. The line width of the reference mark WM1 is w
1. Assuming that the projection magnification of the projection optical system PL from the reticle R to the wafer W is β, the focus position Z0 thus obtained is a pattern of the line width w1 / β on the reticle R at the conjugate position of the reticle mark RM3. Is the focus position of the projection optical system PL. Further, the difference between the coordinate on the XY plane of the conjugate image of the reticle mark RM3 at the focal position Z0 and the theoretical coordinate of the conjugate image of the reticle mark RM3 is the pattern of the line width w1 / β on the reticle R. Is based on the magnification error and the distortion of the projection optical system PL.

Then, for each of the reticle marks RM3 formed in a matrix on the lower surface of the reticle R, the focus position and the XY coordinates of the conjugate image of the reticle mark RM3 are obtained using the reference mark WM1 of the stage substrate 13. The main control system 8 controls the focus position, astigmatism, field curvature, magnification error and distortion of the projection optical system PL under the circular aperture pattern 48 related to the pattern of the line width w1 / β on the reticle R. You can ask.

Next, the case where the center of the inclined illumination opening pattern 49 of the spatial filter plate 46 is arranged on the optical axis of the condenser lens 45 will be described. Also in this case, the reference mark WM1 on the stage substrate 13 is moved to the vicinity of a position conjugate with the reticle mark RM3 in the exposure area of the projection optical system PL. Then, the shutter 6 is closed and the exposure light from the light source 1 reflected by the shutter 6 is focused on the end face of the one end 21 a of the light guide 21 via the condenser lens 22. The exposure light emitted from the end surface of the other end 21b of the light guide 21 housed in the wafer stage 12 has its beam diameter expanded by the beam expander 50, and then the tilted illumination opening pattern 49 of the spatial filter plate 46 and Reference mark WM on the stage substrate 13 through the condenser lens 45
1 is irradiated.

The exposure light transmitted through the reference mark WM1 forms an image of the reference mark WM1 near the reticle mark RM3 on the lower surface of the reticle R via the projection optical system PL. The reticle mark RM3 is a diffraction grating as shown in FIG. 9A, and in this example, the ± first-order light (diffracted light emitted from the reticle R substantially vertically upward) from the reticle mark RM3 is reflected by the mirror 11 and the mirror 11. The light enters the beam splitter 9 through the condenser lens 10. The exposure light reflected by the beam splitter 9 is focused on the plane P1 which is conjugate with the pupil plane of the projection optical system PL.

The exposure light that has passed through the surface P1 as it is after being reflected by the beam splitter 9 is collected by the condenser lens 30.
The light receiving surface of the photoelectric conversion element 31 is irradiated through the photoelectric conversion element 31 and is reflected by the beam splitter 9, and then the exposure light reflected by the split mirror 29 is condensed by the photoelectric conversion element 3 through the condenser lens 32.
Irradiate the light receiving surface of No. 3. These photoelectric conversion elements 31 and 3
The output signal of 3 is supplied to the main control system 8. When the output signals of these two photoelectric conversion elements 31 and 33 are used, the focus position of the projection optical system PL under the inclined illumination opening pattern 49 with respect to the reference mark WM1 on the stage substrate 13 can be determined by the above-described procedure. The imaging characteristics can be obtained.

Then, for each of the reticle marks RM3 formed in a matrix on the lower surface of the reticle R, the focus position and the XY coordinates of the conjugate image of the reticle mark RM3 are obtained using the reference mark WM1 of the stage substrate 13. The main control system 8 controls the focus position, astigmatism, and astigmatism of the projection optical system PL under the inclined illumination aperture pattern 49 regarding the pattern of the line width w1 / β on the reticle R.
The field curvature, the magnification error, and the distortion aberration can be obtained.

In this case, it is assumed that the exposure light emitted from the reference mark WM1 illuminated through the circular opening pattern 48 is distributed in the area 51 of FIG. 8C on the pupil plane of the projection optical system PL. , Inclined illumination opening pattern 49
The exposure light emitted from the reference mark WM1 illuminated through is distributed in regions 52 to 55 decentered from the optical axis of FIG. 8B on the pupil plane of the projection optical system PL. That is, when the illumination is performed through the inclined illumination opening pattern 49, the light is distributed in a region away from the optical axis on the pupil plane of the projection optical system PL, so that the line width of the reference mark WM1 becomes thin. The reference mark W is formed on the lower surface of the reticle R under the influence of the aberration of the projection optical system PL, which is almost equivalent to the above.
An image of M1 will be formed. Therefore, when the line width of the reference mark WM1 when illuminated through the circular opening pattern 48 is w1, the line width of the reference mark WM1 when illuminated through the inclined illumination opening pattern 49 is w2.
The image forming characteristics of the projection optical system PL can be considered by regarding (w1> w2).

The reticle mark RM on the reticle R
When the diffraction grating pattern as shown in FIG. 9A is used as 3, the area 52a in the light quantity distribution shown in FIG.
The image of the reference mark WM1 formed on the lower surface of the reticle R by the exposure light from 55a to 55a is used for measurement. In this case, when the projection magnification from the reticle R of the projection optical system PL to the wafer W is β, the reticle R is substantially
The exposure light applied to the pattern with the upper line width w1 / β and the exposure light applied to the pattern with the upper line width w2 / β on the reticle are shown in FIGS. 8C and 8B, respectively, on the pupil plane of the projection optical system PL. ) Is equivalent to passing through the area. Therefore, when the exposure of the pattern of the reticle R is continued, the heated portion of the projection optical system PL is different due to the substantial difference in the line width, so that the change in the imaging characteristic also tends to be different depending on the line width of the pattern. It is considered to be a thing.

However, the line width of the pattern on the reticle R to be actually transferred is different from w1 / β and w2 / β, and the minimum line width of the pattern on the reticle R is w1 / β. And smaller than w2 / β. Therefore, the main control system 8 of the present embodiment actually uses the image forming characteristics of the projection optical system PL through the opening pattern 48 and the image forming characteristics of the projection optical system PL through the tilt illumination opening pattern 49. In addition, the image forming characteristics of the pattern of the reticle R to be transferred, for example, the pattern of the minimum line width is obtained by calculation or the like. Specifically, for example, reticle R
When obtaining the focus position of the projection optical system PL for the pattern with the above line width w3 / β, the main control system 8 performs projection regarding the case of using the circular aperture pattern 48 and the case of using the inclined illumination aperture pattern 49. Difference in focal position Z of optical system PL
_Ask for _AB . In this case, the focus position Z _C of the projection optical system PL for different line widths w3 / β is represented by a characteristic curve as shown in FIG. 13 (b).

Therefore, FIG. 13 is obtained by actual measurement or calculation in advance.
By obtaining the characteristic curve of (b), the main control system 8
Can determine the focus position Z _C of the projection optical system PL with respect to the line width w3 / β from the difference Z _AB between the focus positions.
After that, in FIG. 6, the main control system 8 moves to the wafer stage 12
By driving the Z stage inside and adding the focus position Z _C to the focus position obtained by the light receiving optical system 20 as an offset, the wafer W can be always aligned with the focus position of the projection optical system PL.

Similarly, the main control system 8 determines the astigmatism of the projection optical system PL with respect to the line width w3 / β from the imaging characteristics of the projection optical system PL with respect to the circular aperture pattern 48 and the tilted illumination aperture pattern 49. Field curvature, magnification error, distortion, etc. can also be calculated. Then, the main control system 8 can maintain those imaging characteristics of the projection optical system PL in a predetermined state via the imaging characteristics control device 18.

As the reticle mark on the reticle R, a cross-shaped diffraction grating-shaped reticle mark RM4 as shown in FIG. 9B may be used. By using this reticle mark RM4, an inclined illumination opening pattern 49 is formed.
When the reference mark WM1 is illuminated via the
As shown in (c), the image of the reference mark WM1 formed on the lower surface of the reticle R by the exposure light from the regions 52b to 55b in the light amount distribution on the pupil plane of the projection optical system PL is used for measurement. It will be.

[Fourth Embodiment] A fourth embodiment of the present invention will be described with reference to FIG. This example is a modification of the second embodiment. In FIG. 10, parts corresponding to those in FIG. 4 are designated by the same reference numerals, and detailed description thereof will be omitted. Figure 10
FIG. 10A shows the projection exposure apparatus of this example, and FIG.
In step 1, only one type of reference mark WM3 is formed on the stage substrate 13. The reference mark WM3 is a set of phase type or amplitude type diffraction gratings having a predetermined pitch in various directions (equivalent to the reference mark WM3 in FIG. 5A). A condenser lens 45 is arranged inside the wafer stage 12 at the bottom of the stage substrate 13, a disk-shaped spatial filter plate 46 is arranged below the condenser lens 45, and the main control system 8 drives a drive motor 47. The rotation angle of the spatial filter plate 46 is positioned via the.

As described above with reference to FIG. 8A, a circular opening pattern 48 is formed in a part of the spatial filter plate 46, and four circular opening patterns 49a to 49d are formed in the other part of the spatial filter plate 46. An opening pattern 49 for inclined illumination is formed. The spatial filter plate 4
By rotating about the axis 46a centered on 6,
The center of the circular aperture pattern 48 or the center of the inclined illumination aperture pattern 49 is arranged on the optical axis of the condenser lens 45 of FIG. The spatial filter plate 46 is arranged on a plane conjugate with the pupil plane of the projection optical system PL.

In FIG. 10A, a light guide 38 is used in this example, and the other end 38 b of this light guide 38 is housed inside the wafer stage 12. At the time of measuring the image forming characteristics of the projection optical system PL using the inclined illumination aperture pattern 49, the shutter 6 is closed and the exposure light from the light source 1 reflected by the shutter 6 is passed through the condenser lens 22. One first end 3 of the light guide 38
Focus on the end face of 8a. Then, the exposure light emitted from the end surface of the other end portion 38b of the light guide 38 is converted into the first relay lens 56, the field stop 57, the second relay lens 58,
The opening pattern 49 for tilting illumination of the spatial filter plate 46 is irradiated through the mirror 59. The exposure light emitted from the inclined illumination opening pattern 49 is applied to the reference mark WM3 on the stage substrate 13 via the condenser lens 45, and the image of the reference mark WM3 is formed on the lower surface of the reticle R by the projection optical system PL. To be imaged.

The reflected light from the conjugate image of the lower surface of the reticle R of the reference mark WM3 is again projected onto the reference mark WM3 via the projection optical system PL, and the reference mark WM3.
The light that has passed through 3 passes through the condenser lens 45, the inclined illumination aperture pattern 49, the mirror 59, the second relay lens 58, the field stop 57, and the first relay lens 56, and the light guide 3
8 is incident on the end face of the other end 38b. The light guide 3
The exposure light emitted from the end surface of one of the second end portions 38c of 8 enters the photoelectric conversion element 39. This photoelectric conversion element 3
The output signal S1 of 9 is supplied to the main control system 8.

In this case, when the main control system 8 scans the Z stage of the wafer stage 12 in the Z direction via the drive unit 16, when the reference mark WM3 of the stage substrate 13 matches the focal position of the projection optical system PL. And the photoelectric conversion element 3
Since the output signal of 9 becomes maximum or minimum, the main control system 8 can measure the focus position of the projection optical system PL with respect to the reference mark WM3 when the tilt illumination aperture pattern 49 is used. Further, by moving the reference mark WM3 in the X direction and the Y direction within the exposure area of the projection optical system PL to obtain the respective focal positions, it is possible to obtain the field curvature of the projection optical system PL.

Next, when measuring the imaging characteristics of the projection optical system PL with respect to the circular aperture pattern 48 of the spatial filter plate 46, as shown in FIG.
The center of the circular opening pattern 48 is arranged on the optical axis of 5. In this case, the exposure light emitted from the circular opening pattern 48 is transmitted through the condenser lens 45 to the stage substrate 13
The reference mark WM3 above is irradiated and the reference mark WM
The image 3 is formed on the lower surface of the reticle R by the projection optical system PL. Then, by using the reflected light from the lower surface of the reticle R, it is possible to measure the focus position of the projection optical system PL and the image forming characteristics such as the field curvature when the circular aperture pattern 48 is used.

In this case, as shown in FIG. 10A, when the inclined illumination opening pattern 49 is used, the light from the reference mark WM3 is separated from the optical axis on the pupil plane of the projection optical system PL. Pass through the area. On the other hand, as shown in FIG. 10B, when the circular aperture pattern 48 is used, high-order diffracted light is vignetted by the aperture stop 17, so that the reference mark WM3.
On the pupil plane of the projection optical system PL passes through a region near the optical axis. Therefore, when the circular opening pattern 48 is used, the image forming characteristic of the projection optical system PL with respect to the reference mark WM3 having a thick line width is obtained, and the inclined illumination opening pattern 49 is obtained.
In the case of using, the image forming characteristics of the projection optical system PL regarding the mark having a thin line width having the same outer shape as the reference mark WM3 can be obtained. Therefore, the main control system 8 can calculate the imaging characteristics of the projection optical system PL for the pattern having an arbitrary line width from the imaging characteristics of the projection optical system PL in those two cases.

[Fifth Embodiment] A fifth embodiment of the present invention will be described with reference to FIG. This example is a modification of the third example. In FIG. 11, parts corresponding to those in FIG. 6 are designated by the same reference numerals, and detailed description thereof will be omitted. FIG. 11 (a)
11A shows a projection exposure apparatus of this example. In FIG. 11A, a light-transmissive stage substrate 13 is arranged near the wafer W on the wafer stage 12 of this example, and a line is formed on the stage substrate 13. A reference mark WM1 (which is the same mark as the reference mark WM1 in FIG. 2B) formed of a cross-shaped opening pattern having a width w1 is formed. A condenser lens 45 is arranged inside the wafer stage 12 at the bottom of the stage substrate 13, and a disk-shaped spatial filter plate 64 is arranged below the condenser lens 45.

FIG. 11B shows the spatial filter plate 64.
11B, a circular opening pattern 65 is formed in the central portion of the spatial filter plate 64, and four eccentric circular opening patterns 66a are formed in the peripheral portion of the spatial filter plate 64, as shown in FIG. To form 66d.
The spatial filter plate 64 is fixed so that the center of the circular opening pattern 65 is located on the optical axis of the condenser lens 45 of FIG.

In FIG. 11A, the light guide 21
One end 21 a is arranged near the shutter 6 and the other end 21 b is housed inside the wafer tage 12.
When the shutter 6 is closed, the exposure light reflected by the shutter 6 is passed through the condenser lens 22 to the other end 2
The exposure light focused on the end portion of 1a and emitted from the other end portion 21b is exposed by the first relay lens 56, the field stop 57, the second relay lens 58, the mirror 59, the spatial filter plate 64,
The reference mark WM1 on the stage substrate 13 is irradiated through the condenser lens 45.

Further, a large number of cross-shaped reticle marks RM1 (the same marks as the reticle mark RM1 in FIG. 2A) are formed in a matrix on the lower surface of the reticle R of this example. Furthermore, the first from the beam splitter 9
Relay lens 60, reticle blind 61, second relay lens 62, mirror 11 and main condenser lens 6
Place 3. The reticle blind 61 is conjugate with the pattern forming surface of the reticle R, and during exposure of the wafer W, the exposure light transmitted through the beam splitter 9 among the exposure light emitted from the secondary light source forming surface of the fly-eye lens 5. , The first relay lens 60, the second relay lens 62,
The reticle R is illuminated with a substantially uniform illuminance via the mirror 11 and the main condenser lens 63.

Further, a phase grating 67 is arranged immediately in front of the reticle blind 61 on the side of the first relay lens 60 so that the phase grating 67 can freely move in and out in the direction perpendicular to the optical axis, and is mainly used when measuring the imaging characteristics of the projection optical system PL. The control system 8 moves its phase grating 67 in and out via a drive 68. Other configurations are similar to the example of FIG. To describe the operation of the projection optical system PL of the present example when measuring the imaging characteristics, in this case, the shutter 6 is closed and the reference mark WM1 of the stage substrate 13 is the conjugate of the reticle mark RM1 to be measured by the reticle R. Scanning is performed in the X and Y directions near the position of the image.

Then, the circular opening pattern 65 of the spatial filter plate 64 and the eccentric circular opening patterns 66a to 6a.
The reference mark WM1 on the stage substrate 13 is illuminated by the exposure light emitted from 6d, an image of the reference mark WM1 is formed on the lower surface of the reticle R via the projection optical system PL, and the light from the image of the reference mark WM1 is formed. The light transmitted through the reticle mark RM1 inside the main condenser lens 6
3, the mirror 11, the second relay lens 62, the reticle blind 61, and the first relay lens 60 are incident on the beam splitter 9. Of the light reflected by the beam splitter 9, a plane P1 conjugate with the pupil plane of the projection optical system PL.
The light that has been transmitted through the condenser lens 30 enters the photoelectric conversion element 31 through the condenser lens 30, and the light reflected by the split mirror 29 among the light reflected by the beam splitter 9 is the condenser lens 3
The light then enters the photoelectric conversion element 33 via 2.

In this case, when the phase grating 67 is arranged just before the reticle blind 61, the exposure light from the circular aperture pattern 65 at the center of the spatial filter plate 64 is so arranged that the zero-order light at the phase grating 67 disappears. The depth of the groove of the phase grating 67 is set. Further, since the ± 1st order light of the exposure light from the circular aperture pattern 65 at the phase grating 67 has a large diffraction angle, most of the photoelectric conversion elements 31 and 3 are formed.
It does not enter 3. On the other hand, when the phase grating 67 is arranged immediately before the reticle blind 61, the spatial filter plate 64
The ± first-order light of the exposure light from the eccentric circular aperture patterns 66a to 66d at the phase grating 67 is emitted almost vertically from the phase grating 67 and enters the photoelectric conversion elements 31 and 32.

On the contrary, when the phase grating 67 is removed from immediately before the reticle blind 61, the exposure light from the circular aperture pattern 65 at the center of the spatial filter plate 64 enters the photoelectric conversion elements 31 and 33 as it is. However, since the exposure light from the eccentric circular opening patterns 66a to 66d is inclined with respect to the optical axis, it does not enter the photoelectric conversion elements 31 and 33. That is, when the phase grating 67 is removed, the exposure from the circular opening pattern 65 at the center of the spatial filter plate 64 is used, and when the phase grating 67 is arranged immediately before the reticle blind 61, the spatial filter plate 64 is exposed. Eccentric circular opening patterns 66a to 66
d is used. This is substantially equivalent to switching and using the spatial filter plate 46 of FIG.

Also in this example, the focal position of the projection optical system PL, distortion, etc. are obtained for two types of irradiation angles with respect to the reference mark WM1. Based on the result, the main control system 8 can calculate the image forming characteristic of the projection optical system PL regarding the pattern having an arbitrary line width. In this case, in this example, it is not necessary to use a special pattern such as a diffraction grating as the reticle mark RM1.

[Sixth Embodiment] A sixth embodiment of the present invention will be described with reference to FIG. This example is a modification of the fifth example. In FIG. 12, parts corresponding to those in FIG. 11 are designated by the same reference numerals, and detailed description thereof will be omitted. 12
FIG. 12A shows the projection exposure apparatus of this example, and FIG.
In, the relay lenses 60 and 62 of this example can be omitted. Further, the reticle blind and the phase grating are unnecessary for measuring the image forming characteristics of the projection optical system PL. In this example, in the direction in which the light from the reticle R is reflected by the beam splitter 9, a photoelectric conversion element 6 including five photomultipliers is formed on a plane conjugate with the pupil of the projection optical system PL.
9, 70a to 70d are arranged. As shown in FIG. 12B, the photoelectric conversion element 69 is arranged on the optical axis, and four photoelectric conversion elements 70a to 70d are arranged around the photoelectric conversion element 69 at intervals of 90 degrees. Output signals of the photoelectric conversion elements 69, 70a to 70d are supplied to the main control system 8.

In this case, the exposure light from the circular opening pattern at the center of the spatial filter plate 64 is converted into the photoelectric conversion element 6 at the center.
The exposure light received at 9 and emitted from the eccentric circular opening pattern of the spatial filter plate 64 is reflected by the four photoelectric conversion elements 7 in the periphery.
The light is received at 0a to 70d. Therefore, the photoelectric conversion element 69
The same operation as that of FIG. 11 is performed while simultaneously capturing the output signal of 1 and the output signals of the photoelectric conversion elements 70a to 70d.

In the above embodiment, the image forming characteristic of the projection optical system PL is measured using the light guided from the light source 1 by the light guide, but the exposure light emitted from the fly-eye lens 5 is measured. The imaging characteristics of the projection optical system PL can be measured in the same manner by using itself.

The present invention is not limited to the above-mentioned embodiments, and it goes without saying that various configurations can be adopted without departing from the gist of the present invention.

[0103]

According to the first projection exposure apparatus of the present invention,
There is an advantage that it is possible to measure the image forming characteristics such as the focus position and the magnification error of the projection optical system regarding the pattern of an arbitrary line width by using the image forming characteristics of the projection optical system regarding the pattern of a plurality of line widths.
Further, according to the second projection exposure apparatus of the present invention, by using the image forming characteristics of the projection optical system with respect to a plurality of irradiation angles, an image of a focus position, a magnification error, etc. of the projection optical system with respect to a pattern having an arbitrary line width is formed. There is an advantage that the characteristics can be measured.

Further, the photoelectric conversion means illuminates the reflected light from the image of the measurement mark, which is illuminated by the measurement mark illumination optical system and is back projected on the mask through the projection optical system, through the projection optical system and the measurement mark. In the case of receiving light by receiving light, the configuration is simplified.

[Brief description of drawings]

FIG. 1 is a configuration diagram including a partial cross-sectional view showing a first embodiment of a projection exposure apparatus according to the present invention.

2A is a plan view showing the pattern of the reticle R of FIG. 1, and FIG. 2B is a plan view showing the pattern of the stage substrate 13 of FIG.

FIG. 3 is a diagram for explaining a light amount distribution on a pupil plane of the projection optical system PL in the first example.

FIG. 4 is a configuration diagram including a partial cross-sectional view showing a second embodiment of the present invention.

5A is a plan view showing the pattern of the stage substrate 13 of FIG. 4, and FIGS. 5B and 5C are lines used to explain the light amount distribution on the pupil plane of the projection optical system PL in the second embodiment. It is a figure.

FIG. 6 is a front view configuration diagram including a partial cross-sectional view showing a third embodiment of the present invention.

FIG. 7 is a configuration view seen from the right side including a partial cross-sectional view showing a third embodiment of the present invention.

FIG. 8A is a plan view showing a spatial filter plate 46 of a third embodiment, and FIGS. 8B and 8C are provided for explaining the light quantity distribution on the pupil plane of the projection optical system PL in the third embodiment. It is a diagram.

9A is a plan view showing a reticle mark RM3 of the third embodiment, FIG. 9B is a plan view showing another example of the reticle mark of the third embodiment, and FIG. 9C is a plan view of the third embodiment. It is a diagram for explaining the light amount distribution on the pupil plane of the projection optical system PL.

10A is a configuration diagram including a partial cross-sectional view showing a fourth embodiment of the present invention, and FIG. 10B is a configuration diagram of a main part used for explaining the operation of the fourth embodiment.

11A is a configuration diagram including a partial cross-sectional view showing a fifth embodiment of the present invention, and FIG. 11B is a plan view showing a spatial filter plate 64 of the fifth embodiment.

12A is a configuration diagram including a partial sectional view showing a sixth embodiment of the present invention, and FIG. 12B is a plan view showing the arrangement of photoelectric conversion elements of the sixth embodiment.

FIG. 13 is a characteristic diagram for explaining the principle of the present invention.

[Explanation of symbols]

 1 Light Source 5 Fly's Eye Lens 8 Main Control System 9 Beam Splitter 10 Condenser Lens R Reticle PL Projection Optical System W Wafer RM1, RM2 Reticle Mark WM1, WM2 Reference Mark 12 Wafer Stage 13 Stage Substrate 18 Imaging Characteristic Control Device 21 Light Guide 31 , 33 Photoelectric conversion element

Claims (3)

[Claims] 1. A light source that generates exposure light, an illumination optical system that collects the exposure light and illuminates a mask, and a pattern of the mask is projected under the exposure light onto a photosensitive substrate on a stage. A projection optical system, a plurality of measurement marks each having a different line width formed on the stage, and an arbitrary one of the plurality of measurement marks is illuminated with light having the same wavelength as the exposure light. A measurement mark illumination optical system, a photoelectric conversion unit that receives light from any one measurement mark illuminated by the measurement mark illumination optical system via the projection optical system, and illuminates each of the plurality of measurement marks. Thus, the calculating means for calculating the image forming characteristic of the projection optical system regarding the mark having a line width different from the line widths of the plurality of measurement marks based on the plurality of output signals obtained by the photoelectric conversion means. A projection exposure apparatus having: 2. A light source that generates exposure light, an illumination optical system that condenses the exposure light and illuminates a mask, and a pattern of the mask is projected under the exposure light onto a photosensitive substrate on a stage. A projection optical system, a measurement mark formed on the stage, a measurement mark illumination optical system that illuminates the measurement mark with light having the same wavelength as the exposure light, and a measurement mark illumination optical system for the measurement mark. Illumination angle changing means for changing the incident angle of the illumination light, photoelectric conversion means for receiving light from the measurement mark illuminated by the measurement mark illumination optical system through the projection optical system, and the illumination angle variable Line width of the measurement mark based on a plurality of output signals obtained by the photoelectric conversion means by illuminating the measurement mark under arbitrary illumination angles by means. Projection exposure apparatus characterized by having a calculating means for calculates the imaging characteristics of the projection optical system relating to marks having different line widths. 3. The reflected light from the image of the measurement mark, which is illuminated by the measurement mark illumination optical system and is back projected onto the mask via the projection optical system, by the photoelectric conversion means. The projection exposure apparatus according to claim 1, wherein light is received through a system and the measurement mark.