JPH08124849A - Projection aligner - Google Patents

Abstract

PURPOSE: To make the image plane of a projection optical system exactly coincident with the surface of a wafer by a method wherein the focal point of the projection optical system is detected by an automatic focusing system, and the surface of the substrate is positioned at the position of an image plane on the basis of the detected focal point. CONSTITUTION: In an automatic focal point detection optical system, an illuminating system is made to illuminate a focusing mark 30 on a reticule 1 and its vicinity with light which is of the same wavelength with exposure light and extracted from a light exposure illuminating system 7 through a light guiding fiber 13. A reflected light returning from a reference plane mirror 6 through the intermediary of the reticule 1 is detected in volume by a photodetection 22 of a photodetective system. The focal point of a projection lens detected by the output signal of the photodetector 22 is made to serve as the reference point of an off-axis automatic focus detection system. The printing optimal position of a wafer is determined on the basis of the above reference point taking offsets such as the thickness of a coating on the wafer, a level difference and the like into consideration. By this setup, the image plane of a projection optical system is made exactly coincident with the plane of a wafer.

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, and more particularly, in the field of semiconductor device manufacturing, it has an automatic focus adjusting function, that is, an autofocus function when repeatedly reducing and projecting a reticle circuit pattern onto a semiconductor wafer surface. The present invention relates to a projection exposure apparatus called a stepper.

[0002]

2. Description of the Related Art In recent years, semiconductor elements, LIS elements, VLSIs
Due to the demand for finer patterning of elements and higher integration, an imaging (projection) optical system having a high resolving power has been required in a projection exposure apparatus. The depth of focus of the imaging optical system is becoming shallower.

Further, from the viewpoint of flat surface processing technology, the wafer is
Some variation in thickness and bending must be allowed. Usually, in order to correct the bending of the wafer, the wafer is placed on a wafer chuck that is processed so as to guarantee the flatness in the order of submicron, and the back surface of the wafer is vacuum-sucked to correct the flatness. However, variations in the thickness of one wafer and the suction method,
Further, the deformation of the wafer caused by the progress of the process cannot be corrected no matter how much the plane of the wafer is corrected.

For this reason, since the wafer has irregularities in the screen area where the reticle pattern is reduced and projected and exposed, the effective depth of focus of the optical system is further reduced.

Therefore, in the reduction projection exposure apparatus, an effective automatic focusing method for matching the wafer surface with the focal plane (the image plane of the projection optical system) is an important theme.

As a wafer surface position detecting method of a conventional reduction projection exposure apparatus, a method using an air microsensor,
There is known a method (optical method) in which a light flux is incident on a wafer surface from an oblique direction without passing through a projection exposure optical system and a positional deviation amount of the reflected light is detected.

On the other hand, in this type of projection exposure apparatus, a change in the ambient temperature of the projection optical system, a change in the atmospheric pressure, a temperature rise due to a light beam applied to the projection optical system, or a temperature rise due to heat generation in an apparatus including the projection optical system. Causes the focus position (image plane position) to move, which must be corrected. Therefore, the focus position of the projection optical system can be determined by measuring the ambient temperature change and atmospheric pressure change with a detector, or measuring the temperature change and atmospheric pressure change in a part of the projection optical system with a detector. It was calculated and corrected.

[0008]

However, in this method, since the focus position of the projection optical system is not directly measured, the detection error of the detector for measuring the temperature and the atmospheric pressure, or the temperature change amount and the atmospheric pressure change. There is a drawback in that it is impossible to detect the focus position of the projection optical system with high accuracy due to an error included in a calculation formula which is an approximate formula when the focus position of the projection optical system is calculated and corrected by the amount.

It is an object of the present invention to detect a focus position (image plane position) of a projection optical system with high accuracy and to accurately match an image plane of the projection optical system with a wafer surface. To provide.

[0010]

An embodiment of a projection exposure apparatus of the present invention for achieving the above object is to provide an exposure illumination optical system for illuminating a mask having a circuit pattern with exposure light, and the circuit pattern. A projection exposure apparatus having a projection optical system for projection exposure on a wafer, wherein a detection illumination optical system for illuminating a focusing pattern located in a screen area of the projection optical system with the same wavelength as the exposure light. A light receiving means for receiving light from the focusing pattern on a reflecting surface via the projection optical system and receiving reflected light from the reflecting surface via the projection optical system and the pattern; Image plane position detection means for detecting the image plane position of the projection optical system based on the amount of light, and the light intensity distribution of the effective light source defined by the detection illumination optical system is on the optical axis of the projection optical system. The optical axis compared to the light intensity of It is characterized in that it is large.

The light intensity distribution of the effective light source is ring-shaped.

Another embodiment of the projection exposure apparatus of the present invention is an exposure illumination optical system for illuminating a mask on which a circuit pattern is formed with exposure light, and a projection optical system for projecting and exposing the circuit pattern on a wafer. A projection exposure apparatus having a detection illumination optical system for illuminating a focusing pattern located in a screen area of the projection optical system with the same wavelength as the exposure light, and light from the focusing pattern. Is incident on a reflecting surface via the projection optical system, and light receiving means for receiving reflected light from the reflecting surface via the projection optical system and the pattern, and of the projection optical system based on the received light quantity. Image plane position detecting means for detecting the image plane position is provided, and the light intensity distribution of the effective light source defined by the detection illumination optical system is decentered with respect to the optical axis of the projection optical system.

[0013]

1 is a conceptual diagram showing the configuration of a reduction projection exposure apparatus having an automatic focus control apparatus according to an embodiment of the present invention.

In FIG. 1, a reticle (photomask) 1 is held on a reticle stage 2. The circuit pattern on the reticle 1 is reduced by ⅕ onto the wafer 5 on the XYZ stage 4 by the reduction projection lens 3 to form an image, and exposure is performed. In FIG. 1, at a position adjacent to the wafer 5, a reference plane mirror 6 in which the heights of the upper surface of the wafer 5 and its mirror surface are substantially the same is arranged.
The mirror surface of the reference plane mirror 6 is formed of a metal film such as Cr or Al. The reason why the reference plane mirror 6 is used instead of using the wafer coated with the actual resist is as described above.

Further, the XYZ stage 4 includes a reduction projection lens 3
In the optical axis direction (Z direction) and in the plane orthogonal to this direction (x
It can be moved in the (-y plane) and can of course be rotated around the optical axis.

When the wafer circuit pattern is transferred, the reticle 1 is illuminated by the illumination optical system 7 within the screen area where the circuit pattern is transferred.

Reference numerals 8 and 9 in FIG. 1 indicate elements constituting an off-axis surface position detecting optical system. A light projecting optical system 8 projects a plurality of light beams. Projection optical system 8
Each of the light beams projected by the light is composed of non-exposure light and does not expose the photoresist on the wafer 5 to light. Then, the plurality of light beams are respectively condensed and reflected on the reference plane mirror 6 (or the upper surface of the wafer 5).

The light beam reflected by the reference plane mirror 6 enters the detection optical system 9. Although not shown, a plurality of light receiving elements for position detection are arranged in the detection optical system 9 in correspondence with the respective reflected light beams, and the light receiving surfaces of the light receiving elements for position detection and the reference plane mirror 6 are arranged. The reflection points of the respective light beams at are substantially conjugate by the imaging optical system. The positional deviation of the reference plane mirror 6 in the optical axis direction of the reduction projection lens 3 is measured as the positional deviation of the incident light beam on the position detection light receiving element in the detection optical system 9.

The position deviation of the reference plane mirror 6 measured from the detection optical system 9 from a predetermined reference plane is determined based on the output signal from the position detecting light receiving element.
0 is calculated as a surface position, and a signal corresponding to this is input to the autofocus control system 11 via a signal line.

The autofocus control system 11 gives a command signal via a signal line to a stage driving device 12 for driving the XYZ stage 4 on which the reference plane mirror 6 is fixed. When the focus position of the projection lens 3 is detected by TTL, a command is given to the stage drive device 12 by the autofocus control system 11 so that the reference plane mirror 6 moves in the optical axis direction of the projection lens 3 in the vicinity of a predetermined reference position. The XYZ stage is driven so as to be vertically displaced in the Z direction).
In this embodiment, the position control of the wafer 5 in the xy plane at the time of exposure is also performed by the autofocus control system 11 and the stage driving device 12.

Next, the reduction projection lens 3 according to the present invention.
The focus position detection optical system will be described.

In FIGS. 2 and 3, reference numeral 1 is a reticle, and 31 is a pattern portion formed on the reticle 1 having a light shielding property. Further, reference numeral 32 is a translucent portion sandwiched between the pattern portions 31. The pattern portion 31 and the light transmitting portion 32 form the focusing mark 30. Here, the reduction projection lens 3
When detecting the focus position (image plane position) of, the XYZ stage 4 moves in the optical axis direction of the reduction projection lens 3 as described above. The reference plane mirror 6 is positioned directly below the reduction projection lens 3, and the pattern portion 31 and the light transmitting portion 32 of the reticle 1 are illuminated by an autofocus illumination optical system described later.

First, the case where the reference plane mirror 6 is on the focus surface of the reduction projection lens 8 will be described with reference to FIG. The light passing through the transmission part 32 on the reticle 1 is condensed and reflected on the reference plane mirror 6 via the reduction projection lens 3. The reflected light follows the same optical path as the outward path, is condensed on the reticle 1 via the reduction projection lens 3, and the reticle 1
The light-transmitting portion 32 between the upper pattern portions 31 passes through. At this time, the entire light flux passes through the transmissive portion of the pattern portion 31 without being eclipsed by the pattern portion 31 on the reticle 1.

Next, the case where the reference plane mirror 6 is located at a position displaced from the focus surface of the reduction projection lens 3 will be described with reference to FIG. The light passing through the transmission part of the pattern part 31 on the reticle 1 reaches the reference plane mirror 6 through the reduction projection lens 3, but since the reference plane mirror 6 is not on the focus surface of the reduction projection lens 3, Is reflected by the reference plane mirror 6 as a spread light beam. That is, the reflected light follows an optical path different from the outward path, passes through the reduction projection lens 3, and is not condensed on the reticle, but the reference plane mirror 6
A light beam having a spread corresponding to the amount of deviation from the focus surface of the reduction projection lens 3 reaches the reticle 1. At this time, part of the light flux is eclipsed by the pattern portion 31 on the reticle 1, and the entire light flux cannot pass through the light transmitting portion 32. That is, there is a difference in the amount of light reflected through the reticle when the focus surface is matched and when it is not.

Next, returning to FIG. 1, the illumination system and the light receiving system of the focus position detection optical system will be described. First, the illumination system extracts light having the same wavelength as the exposure light from the exposure illumination system 7 through the light guide fiber 13. Fiber 1
The light emitted from the end portion of 3 is incident on the relay lens 15 intermittently (as pulsed light) by the chopper (shutter) 14. Then, only the light of the S-polarized component is reflected by the change beam splitter 17 through the diaphragm 16,
The vicinity of the focusing mark 30 on the reticle is illuminated through the λ / 4 plate 18, the objective lens 19, and the switching mirror 20. The diaphragm 16 is a pupil of the illumination system and determines an effective light source of the illumination system. The position of the diaphragm 16 is set to a position conjugate with the pupil of the projection lens 3.

Next, the light receiving system will be described. 2 and 3
As described above, the reflected light from the reference plane mirror 6 returning via the reticle 1 enters the λ / 4 plate 18 through the switching mirror 20 and the objective lens 19. This reflected light becomes P-polarized light by passing through the λ / 4 plate 18, and is transmitted through the polarization beam splitter 17. Then, the light passes through the relay lens 21, enters the light receiving element 22 provided at a position conjugate with the pupil of the projection lens 3, and the light amount is detected by the light receiving element 22. Here, the modified beam splitter and the λ / 4 plate function to increase the light utilization efficiency.

At this time, when light other than the reflected light from the reference plane mirror 6 is directly incident on the reflected light receiving element 22 which is not the signal from the reticle 1, the reflected light from the reticle 1 becomes flare light and the S / N of the signal. It may reduce the ratio. In the case where the projection lens 3 of this embodiment is telecentric only on the wafer side and not on the reticle side, and not on the telecentric side, the incident angle of the illumination light on the reticle 1 is not vertical, so that the reticle directly reflected light does not return to the light receiving element 22. Is not incident. If the projection lens 3 is telecentric on both the reticle and wafer sides, the λ / 4 plate 18 may be inserted between the reticle 1 and the XYZ stage 4, for example, into the projection lens 3 instead of at the position currently shown. For example, reticle 1
The light directly reflected by the light is blocked by the polarization beam splitter 17 so as not to enter the light receiving element 22, and only the reflected light from the reference plane mirror 6 is guided to the light receiving element 22 via the projection lens 3 to obtain the signal S / N. The ratio can be improved.

Further, reference numerals 24 and 25 in FIG. 1 denote elements constituting a light amount monitor of the focus position detecting optical system, 24 is a condenser lens, and 25 is a light receiving element.

As described above, the S-polarized component of the light emitted from the light guiding fiber 13 is reflected by the polarization beam splitter 17 to illuminate the focusing mark 30, but the remaining P-polarized component is polarized. It passes through the beam splitter 17. Then, the transmitted light is condensed on the light receiving element 25 by the condenser lens 24. Then, the light receiving element 25 inputs a signal corresponding to the intensity of the received light to the reference light amount detection system 26 via a signal line.

Therefore, assuming that the light from the fiber 13 has a random polarization characteristic, the signal from the light receiving element 25 changes in proportion to the fluctuation of the light amount of the light from the fiber 13.

The focus position (image plane position) of the reduction projection lens 3 will be described below using the signal output from the light receiving element 22.
A method of detecting the will be described.

The XYZ stage 4 on which the reference plane mirror 6 is mounted is moved by the stage driving device 12 to the reduction projection lens 3
In the optical axis direction of, the zero-axis preset by the off-axis surface position detecting device 9 is driven. At this time, the surface position detecting device 10 monitors the positions of the reference plane mirror 6 at a plurality of positions in the optical axis direction. The focusing mark 3 is detected by the focus position detection system among the plurality of locations.
The position of the reference plane mirror 6 is represented by using z as a measurement value near the position where the image of 0 is projected. When the light reflected by the reference plane mirror 6 is received by the light receiving element 22, the relationship between the signal output obtained from the focal plane detection system 23 and this z is shown in FIG.
Shown in

In this embodiment, in order to eliminate the influence of fluctuation (light amount fluctuation) of a light source such as a mercury lamp of the illumination system 7 for exposure, the signal of the focal plane detection system 23 is sent from the reference light amount detection system 26 described above. Standardize with signals. Further, in order to reduce the influence of shot noise of the light receiving element 22, the light from the fiber 13 is shielded by the chopper 14 at a specific cycle to illuminate the focusing mark 30 intermittently, and the focal plane detection system 23. The signal is obtained in synchronization with the cycle. In order to perform this operation, the chopper 14 is connected to the autofocus control system 11 by a signal line (not shown),
The autofocus control system 11 controls the chopper 14 and the focal plane detection system 23 in synchronization. This is a drive device (not shown) for the chopper 14 which supplies a drive clock of a specific frequency from the timing circuit of the autofocus control system 11.
Is input to the focal plane detection system 23.

When the reference plane mirror 6 is located on the focus plane (image plane) of the reduction projection lens 3, the output of the focal plane detection system 23 shows a peak value. The surface position detection system measurement value z ₀ at this time is used as the focus position of the projection optical system when the wafer 5 is exposed using the reduction projection lens 3.

The focus position of the projection lens 3 determined in this way becomes the reference position of the off-axis auto focus detection system. The actual best position for printing the wafer is a value obtained by offsetting the reference position from the reference position by an amount corresponding to the values such as the coating thickness of the wafer and the step amount. For example, when a wafer is exposed using a multi-layer resist process, only the uppermost portion of the multi-layer needs to be baked, so that the resist surface of the wafer and the reference position are substantially coincident with each other. On the other hand, when the exposure light reaches the substrate sufficiently with the single-layer resist, the focus of the wafer matches the substrate surface, not the resist surface. In this case, therefore, there is an offset of 1 μm or more between the resist surface and the reference position. Things are not rare. Such an offset amount is peculiar to the process and is given as an offset different from the projection exposure apparatus. It suffices for the apparatus itself to accurately determine the focus position of the projection lens itself by the method of the present invention, and the offset amount is projected on the autofocus control system 11 and the drive system 12 only when necessary. It may be input in advance via a system controller (not shown) of the exposure apparatus.

The detection of the focus position z ₀ may be determined by the peak of the output of the focal plane detection system 23, but various other methods are possible. For example, in order to further increase the detection sensitivity, a certain slice level 220 is set with respect to the peak output, and this slice level 220
By knowing the autofocus measurement values z ₁ and z ₂ when the output of

[0037]

[Outside 1] Alternatively, a method such as obtaining the peak position using a differential method may be considered.

Focusing mark 30 formed on reticle 1
The smaller the line width of the transmission part 32, the larger the change in the output signal from the light receiving element 22 with respect to the change in the optical axis direction of the reference plane mirror 6, and the better the detection sensitivity of the image plane position. Therefore, in this embodiment, the line width l of the focusing mark 30 is

[0039]

[Outside 2] To increase the detection sensitivity of the image plane position.
Here, λ is the wavelength of light that illuminates the focusing mark, NA is the numerical aperture of the projection lens, and β is the magnification of the projection lens.

As a result of our examination, the line width l of the focusing mark for good detection of the image plane position is

[0041]

[Outside 3] The condition is to satisfy. In order to detect the image plane position with higher accuracy,

[0042]

[Outside 4] It is preferable to determine the line width l so as to satisfy the above condition.

When the line width of the focusing mark 30 is made smaller, the intensity of the light incident on the light receiving element is reduced and the S / N of the signal is reduced.
Although the ratio tends to deteriorate, in order to reduce this tendency, in this embodiment, focusing marks as shown in FIGS. 5A and 5B are used. As shown in FIGS. 5 (A) and 5 (B), the main focusing mark is configured by arranging a plurality of slits having a line width l, which can increase the intensity of light incident on the light receiving element.

In the present embodiment, the illumination system for illuminating the focusing mark 30 on the reticle 1 is also devised in order to increase the sensitivity of image plane position detection. FIG. 6A is a plan view showing the shape of the diaphragm 16 used in this embodiment. Aperture 16
Is for determining the shape of the effective light source when illuminating the reticle 1. In FIG. 6A, the shaded area is the light-shielding portion and the blank area is the light-transmitting portion.

As shown in FIG. 6 (A), the diaphragm 1 of this embodiment
Reference numeral 6 denotes a light transmitting portion, that is, an effective light source is decentered with respect to the optical axis (optical axis of the illumination system). Since the image of the use mark is blurred and the position is displaced in the plane orthogonal to the optical axis, the change in the output signal from the light receiving element becomes large, and the detection sensitivity of the image plane position can be improved.

FIGS. 6B and 6C are plan views showing another form of the diaphragm that can be used in the present projection exposure apparatus.
In (B), since the light transmitting portion is formed in a ring shape, the intensity of light incident on the light receiving element can be increased and the detection accuracy and detection sensitivity can be improved as compared with the case of FIG. 6 (A).

On the other hand, FIG. 6C shows an example of a diaphragm in which the light transmitting portion is not eccentric with respect to the optical axis. The effective light source at the time of illumination of the focusing mark is almost the same as the effective light source at the time of exposure. It was done. Since such a diaphragm can reproduce the defocus characteristic of the projection lens in actual exposure, the image plane detected by the image plane detection system and the image plane at the time of exposure can be exactly matched.

The process of detecting the image plane position of the projection lens 3 described above and exposing the wafer 5 is shown in the flowchart of FIG. Although FIG. 7 shows a flowchart for detecting the image plane position of the reduction projection lens 3 for each wafer, the image plane position may be detected for each shot, several wafers, or lots. Needless to say, it cannot be used.

Therefore, the focus position of the projection lens is directly measured using the reticle used for actual pattern transfer and the light passing through the projection lens as detection light, and the position detection of the wafer to which the pattern is transferred is off-axis. It is possible to always position the wafer to which the pattern is to be transferred on the focus surface of the projection lens by separately measuring using the surface position detection system of No. 2 and making correspondence between them.

Therefore, conventionally, a change in the focus position with time due to a temperature change around the projection exposure optical system, an atmospheric pressure change, or a temperature rise due to an irradiated light beam, or a temperature rise due to heat generation of an apparatus including the projection optical system. It has the advantage that it is not affected in principle.

Further, since the focus position measurement according to the present invention can be inserted at any time of the exposure cycle,
It also has the advantage that the time difference between calculation and exposure can be minimized.

In the above embodiment, the positions of the focus position detection optical system and the focusing mark are fixed, and if the focusing mark can always be set at a predetermined position of the reticle, the detection position by the focus position detection optical system will be It can be fixed. However, the presence of the focusing mark may limit the exposure range. Therefore, when using a dedicated focusing mark, it is desirable that the mark can be set at any position depending on the size of the circuit pattern to be printed. Therefore, depending on the change in the position of the focusing mark on the reticle,
It is preferable that the detection unit including at least the objective lens 19 and the mirror 20 is configured so that its position with respect to the reticle can be changed.

FIG. 8 is a graph showing the difference between the actual image plane formed by the projection lens 3 and the ideal image plane. Projection lens 3
In order to accurately project the circuit pattern of the reticle 1 onto the wafer 5, the aberration is strictly corrected, but the field curvature cannot be completely corrected. When the focusing depth of the projection lens 3 is deep or when the required resolution line width is large, a certain amount of field curvature can be ignored, but the NA of the projection lens 3 is increased or the image is increased in order to increase the resolution. When the angle is increased, the existence of field curvature cannot be ignored.

Therefore, when the wafer is positioned at the image plane position of the projection lens 3, it is necessary to consider the field curvature data of the projection lens 3.

For example, in the above-described embodiment, the focusing mark 30 is provided off the axis of the projection lens 3, and the focus position detection optical system is only at a certain image plane position (A) off the axis of the projection lens 3. Not detected. In this case, if the actual image plane is curved as shown by the broken line in FIG. 8, the true image plane position at other points in the image plane is not detected.

Therefore, based on the image plane curvature data of the projection lens which has been inspected and prepared in advance, the image plane positions of other points may be obtained from the image plane position of the specific point obtained by the measurement. . The field curvature data may be stored in the memory in the autofocus control system 11 shown in FIG.

In the projection exposure apparatus of FIG. 1, the off-axis surface position detecting device 10 detects the surface positions of a plurality of (exposed areas or shots) of the wafer 5. Then, based on the data on the surface positions at the plurality of locations, the wafer 5
The position and the inclination of the optical axis in the optical axis direction are corrected. This time,
The relationship between the surface position Z of the wafer 5 adjusted by driving the XYZ stage 4 and the true image surface position Z _0i (i = 1, 2, 3, ..., M) of the projection lens 3 corresponding to the plurality of positions is shown. ,

[0058]

[Outside 5] Then, the surface of the wafer 5 and the projection lens 3 can be positioned at the best image plane position.

This means that the best image plane position of the projection lens 3 is
It is determined based on the image plane curvature data and the image plane position obtained by the focal plane detection system 23, and the wafer plane position adjustment is performed with this best image plane position as a target. Here, the best image plane (reference image plane) is determined from the actual position of each image point on the image plane by the method of least squares.

FIG. 9 is a schematic view showing another embodiment of the focus position detecting optical system, and the portions not shown are shown in FIG.
It has the same configuration as.

In this embodiment, the focus position detection optical system of the TTL is not incorporated as an independent system in the projection exposure apparatus, but the alignment mark detection optical system and the optical system for aligning the reticle and the wafer are used together. Is compact. In particular, the switching mirrors indicated by reference numerals 45 and 46 in FIG. 9 are configured so that they can be inserted into or retracted from the optical path during focus position detection and alignment mark detection system. The difference between the apparatus of FIG. 1 and the apparatus of the present embodiment is that the switching mirror 4 can be freely inserted into and removed from the optical path between the diaphragm 16 and the polarization beam splitter 17.
5, the exposure light is guided from the exposure illumination system 7 by the light guide fiber 13 and is coupled with the illumination system of the focus position detection optical system of the TTL via the relay lens 41 and the half mirror 45 to form the reticle. That is, the alignment mark 1 is illuminated. Although not shown, only the alignment is illuminated by the field limiting slit. At this time, the light that illuminates the alignment mark on the reticle 1 also illuminates the alignment mark on the wafer via the projection lens 3. Then, the light from the reticle alignment mark and the light from the wafer alignment mark is switched by the switching mirror 2.
0 and the objective lens 19 to enter the λ / 4 plate 18, and then the polarized beam splitter 17 and the relay lens 21 to be reflected by the switchable mirror 46 which can be freely put in and taken out unlike the system of FIG. CC
An image is formed on D43. Then, the alignment detection system 44 detects the deviation between the wafer alignment mark image and the reticle alignment mark image formed on the CCD 43 to align the reticle and the wafer.
Further, by retracting the switching mirrors 45, 46 from the illustrated optical path, the focus position described above can be detected.

Further, if the TTL focus position detecting optical system and the alignment mark detecting optical system are used by dividing the visual field of the optical system, the light receiving element may be shared, or,
The reticle alignment mark can also be used as a focusing mark.

In the above-described embodiment, the off-axis surface position detecting optical system detects the positions of the reference plane mirror and the wafer surface in a plurality of positions in the optical axis direction. The inclination may be detected, or when the inclination of the surface is small or the same position as the detection position by the focus position detection optical system of TTL is detected, only one position of the surface may be detected. That is, it is sufficient that the position of the mirror surface in the optical axis direction near the detection position of the focus position detection optical system of TTL can be measured by the off-axis surface position detection optical system. Therefore, the measurement by both detection optical systems may be performed simultaneously or sequentially. FIG.
FIG. 0 shows a flowchart regarding image plane position detection when the off-axis surface position detection optical system detects only one position of the reference plane mirror.

[0064]

As described above, according to the present invention, the focus position (that is, the image plane position) of the projection optical system is controlled by the TTL autofocus system.
Is detected and the wafer surface is positioned at the image plane position with reference to this, the focus position of the projection optical system, which changes over time, can be detected accurately, and high-precision focusing becomes possible. This has an excellent effect that a high resolution pattern can be formed on the wafer and a circuit with a higher degree of integration can be created.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a projection exposure apparatus having an automatic focus control device according to an embodiment of the present invention.

FIG. 2 is an explanatory view showing a state of reflected light from the reference plane mirror when the image planes of the reference plane mirror and the reduction projection lens are coincident with each other and are deviated from the image plane.

FIG. 3 is an explanatory diagram showing a state of reflected light from the reference plane mirror when the image planes of the reference plane mirror and the reduction projection lens are coincident with each other and are deviated from the image plane.

FIG. 4 is a diagram showing a relationship of an output signal of the focal plane detection system with respect to a measurement value by the surface position detection device.

FIG. 5 is a plan view showing an example of the shape of a focusing mark.

FIG. 6 is a plan view showing an example of the shape of a diaphragm of an illumination system.

FIG. 7 is a flowchart showing an example of a sequence from focal plane detection to exposure.

FIG. 8 is a graph showing a relationship between an ideal image plane of a projection lens and an actual curved image plane.

FIG. 9 is a schematic view showing another embodiment of the focus position detection optical system.

FIG. 10 is a flowchart showing another sequence of focal plane detection.

[Explanation of symbols]

 1 reticle 2 reticle stage 3 reduction projection lens 4 XYZ stage 5 wafer 6 reference plane mirror 7 exposure illumination system 8 working light optical system 9 detection optical system 10 surface position detection device 11 autofocus control system 12 stage drive device 13 fiber 14 chopper 15 Relay lens 16 Aperture 17 Polarizing beam splitter 18 λ / 4 plate 19 Objective lens 20 Mirror 21 Relay lens 22 Light receiving element 23 Focal plane detection system 24 Relay lens 25 Light receiving element 26 Reference light amount detection system

Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI Technical display location G02B 7/28 G03F 7/207 H

Claims (3)

[Claims] 1. A projection exposure apparatus comprising: an exposure illumination optical system for illuminating a mask having a circuit pattern formed thereon with exposure light; and a projection optical system for projecting and exposing the circuit pattern onto a wafer. Of the focusing pattern located in the screen area of the detection illumination optical system for illuminating the focusing pattern with the same wavelength as the exposure light, and the light from the focusing pattern is incident on the reflecting surface via the projection optical system. A light receiving means for receiving the reflected light from the reflecting surface via the projection optical system and the pattern, and an image plane position detecting means for detecting the image plane position of the projection optical system based on the received light quantity. A projection exposure apparatus, characterized in that the light intensity distribution of an effective light source defined by the detection illumination optical system is larger outside the optical axis than on the optical axis of the projection optical system. 2. The projection exposure apparatus according to claim 1, wherein the light intensity distribution of the light source has a ring shape. 3. A projection exposure apparatus having an exposure illumination optical system for illuminating a mask on which a circuit pattern is formed with exposure light, and a projection optical system for projecting and exposing the circuit pattern onto a wafer. Of the focusing pattern located in the screen area of the detection illumination optical system for illuminating the focusing pattern with the same wavelength as the exposure light, and the light from the focusing pattern is incident on the reflecting surface via the projection optical system. A light receiving means for receiving the reflected light from the reflecting surface via the projection optical system and the pattern, and an image plane position detecting means for detecting the image plane position of the projection optical system based on the received light quantity. A projection exposure apparatus, characterized in that the light intensity distribution of the effective light source defined by the detection illumination optical system is decentered with respect to the optical axis of the projection optical system.