JPH04217260A - Projection aligner - Google Patents

Abstract

PURPOSE:To extend a life of gas in a light source by preventing throughput from decreasing as a device total unit so that high accurate position alignment of a mask can be performed with a small quantity only required of also a light emitting circuit spent for measurement. CONSTITUTION:In a position detecting optical system as a mark detecting means, a mark of a mask is imaged spread on an image sensor 25 of one- dimensional array sensor or the like. Here, a specific picture element(reference picture element)position of the image sensor 25 is predetermined, and by picture- processing a mark waveform of a picture signal, output from the image sensor 25, by arithmetic operation, a mask mark position on the image sensor 25 is obtained as a deviation from the reference picture element. Further, a position(coordinate value) on a substrate stage 5 of the reference picture element on this image sensor 25 is given correspondence by previously taking a picture of a reference mark 10 on the substrate stage 5 on the image sensor 25 through a projecting optical system.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to a projection exposure apparatus used in the manufacture of high-density integrated circuit chips such as semiconductor memories and large substrates for liquid crystals, and in particular, the present invention relates to a projection exposure apparatus used for manufacturing high-density integrated circuit chips such as semiconductor memories and large substrates for liquid crystals. This relates to a device for

0002

Conventionally, in this type of projection exposure apparatus, a mask (also called a reticle) having an original image pattern and a photosensitive substrate to which the pattern is exposed are precisely positioned relative to each other in a predetermined positional relationship with a projection optical system in between. ing. Relative positioning in this case means, for example, in the batch projection method, aligning the center of the mask with the center of the photosensitive substrate (wafer, plate, etc.), and in the step-and-repeat method, aligning the center of the mask with the center of the photosensitive substrate (wafer, plate, etc.). This is to precisely define (correspond to) the relative positional relationship with the center of each of the plurality of chip pattern regions formed.

That is, in a projection exposure apparatus, it is an extremely important problem how to precisely overlap the original pattern image formed by the projection optical system and the pattern formed on the substrate. At the same time, how quickly the superimposition work can be completed is also a big issue. In view of these requirements for the apparatus, the first thing that must be considered is highly accurate alignment of the mask (reticle) with respect to the apparatus.

[0004] For example, the following method is known as a conventional mask alignment method. ■ Unexamined Japanese Patent Publication No. 56-134737 ■ Unexamined Japanese Patent Publication No. 56-134737
Publication No. 9-74625■ JP-A-61-121437-A■ JP-A-61-121437■
Publication No. 3-81818 In the conventional example of item (2) above, a reference mark is provided on a step-and-repeat wafer stage, and the reference mark and the mark on the mask are simultaneously detected through a projection optical system. This is to correct the positional deviation with respect to.

[0005] In the conventional example (2) above, a micro slit type photoelectric sensor is provided on the wafer stage, and the wafer stage is moved so that the projected image of the mask mark is scanned by this photoelectric sensor. The mask is aligned by controlling the wafer stage position at the time of detection. In addition, in the conventional example (2) above, dedicated alignment marks for the mask are provided at three locations on the mask, and these marks are enlarged and imaged onto a fixed slit that serves as a reference through three alignment microscopes (objective lenses). A vibrating mirror installed in the optical path causes the enlarged mark image to vibrate slightly relative to a fixed slit, and the amount of light transmitted through the fixed slit is photoelectrically detected and synchronously detected. This is for alignment.

Furthermore, in the conventional example (2) above, a minute slit-shaped light-emitting mark is provided on the wafer stage, and this light-emitting mark is imaged onto the mask side via a projection optical system, and the mark on the mask is scanned by the wafer stage. is photoelectrically detected. Furthermore, although projection exposure apparatuses using excimer lasers have been put into practical use in recent years, the oscillation frequency of excimer laser light sources is currently relatively low at 100 to 500 Hz. As an example of mask alignment in such an excimer laser exposure device,
A method such as that disclosed in Japanese Patent Publication No. In this conventional example, a slit-shaped mark emitted by an excimer laser is provided on the wafer stage, and the mask mark is detected using the same configuration as the conventional example (2) above. However, the light emission of the luminescent mark is a measurement pulse (up-down pulse) from a laser interferometer for position measurement of the wafer stage.
is applied as a trigger pulse to an excimer laser light source.

[0007]

[Problems to be Solved by the Invention] Among the above-mentioned conventional mask positioning methods, in the synchronous detection method (2), the range in which the S-curve signal, which is the detection output, is linear is extremely narrow. Therefore, the mask stage must be moved at a slow speed until the mark is placed within the linear region of the S-curve signal.

That is, simply placing the mask on the mask stage after mechanical prealignment does not guarantee that the mark will always be located in the linear region of the S-curve signal of synchronous detection, and the mask (mask stage) Search operation is required. Further, in both of the above conventional methods (1) and (2), scanning of the wafer stage is required to detect mask marks.

Furthermore, even in the conventional method (2) above, mask marks could not be detected and aligned until after the reference position mark on the wafer stage was positioned within the projection field of the projection optical system. As described above, all conventional mask alignment methods inevitably involve search movement of the mask stage and scanning or movement of the wafer stage.

[0010] Therefore, when setting up an exposure sequence in which a plurality of masks must be replaced one after another to expose one wafer, a problem arises in that time efficiency is reduced. In particular, in the method of scanning or moving the wafer stage for mask alignment,
The original wafer stage operations, ie, movements for wafer alignment, wafer loading, etc., cannot be performed during mask alignment, leading to a reduction in the throughput on the apparatus.

[0011] Furthermore, if the light that illuminates the mask mark reaches the wafer stage via the projection optical system, the wafer stage must be temporarily retracted so that the wafer is not exposed to the illumination light. It is clear that this also causes a decrease in throughput. In addition, in the excimer laser exposure system described in (2) above, the moving speed of the wafer stage must be slowed so that the measurement pulse from the laser interferometer is generated at a frequency lower than the oscillation frequency response of the laser light source. , which necessarily means that it takes time to detect the mask mark.

Furthermore, when detecting a mask mark, a trigger of several hundred pulses or more is required for laser oscillation each time a luminescent mark is scanned once, so the gas life of the excimer laser light source (the gas life required for original exposure) is shortened. It will be shortened. The present invention aims to solve the problems of the conventional techniques as described above and to obtain a projection exposure apparatus that can align a mask with high precision without reducing the throughput of the entire apparatus. .

[0013]

[Means for Solving the Problems] In order to solve this problem, the present invention provides a mask stage that holds a mask (1) having a pattern to be exposed (PE) and alignment marks (9). (2) and pattern (PE),
Alternatively, a projection optical system (3) that projects the mark (9) onto a predetermined image plane, a substrate stage (5) that holds a photosensitive substrate (4) near the image plane, and a mark (9) on the mask (1) 9)
A mark detection means detects the deviation of the mark (9) from a predetermined reference position by photoelectrically detecting the mark (9), and a mask stage (2) based on the detection result from the mark detection means.
), the mark detection means includes a light source (30) that emits illumination light for detecting the mark (9), and a drive means (42) for adjusting the position of the mark (9); 9), and an illumination optical system (11, 22, 23) that irradiates a local area on the mask (1), and an image of the mark (9) by inputting reflected light or transmitted light from the mark (9). An imaging optical system (22, 23, 24) to form an image, an image sensor (25) to receive the image of the mark (9), and an image sensor (25) to analyze the imaging signal from the image sensor (25) to form an image of the mark (9). a mark position detection circuit that detects the position on the sensor (25); and a storage circuit (as the mark position detection circuit) that stores a value representing a specific position (PXC) on the image sensor (25) serving as a reference position. 60, step 112), and the position on the image sensor corresponding to the center of the image of the mark (9) based on the waveform on the imaging signal (
A mark center position detection circuit (50,
Step 108) and the center position of the mark image (PXm)
and the specific position (PXC) stored in the memory circuit (60).
The present invention is characterized in that it is provided with an arithmetic circuit (50, step 118) that calculates the amount of positional deviation of the mark by calculating the difference (ΔP) between the mark and the mark.

[0014]

[Function] In the projection exposure apparatus according to the present invention, the position detection optical system serving as the mark detection means enlarges and images the mark on the mask onto an image sensor such as a one-dimensional array sensor. At this time, the position of a specific pixel (reference pixel) on the image sensor is determined in advance, and the position of the mask mark on the image sensor is changed from the reference pixel by performing image processing on the mark waveform of the image signal output from the image sensor. It is determined as the deviation of Furthermore, the position (coordinate values) of the reference pixel on this image sensor on the substrate stage is determined by using the reference mark (10) on the substrate stage in advance.
The correspondence is established by capturing an image on an image sensor via a projection optical system. Therefore, by detecting the position of the mask mark on the image sensor, the mask can be aligned with the coordinate system of the substrate stage, that is, with the apparatus.

Furthermore, when the illumination light of the position detection optical system hits the mark on the mask, a movable light shielding member such as a shutter is provided under the illumination light, so that the photosensitive substrate (wafer) on the substrate stage is
This prevents illumination light for position detection from being applied to the area. This allows alignment of the mask to the device without retracting the wafer. Furthermore, by providing parts with different reflectances on the light irradiation side of the shutter,
The signal contrast from the image sensor can be optimized according to the reflectance of the mask mark.

[0016]

Embodiment FIG. 1 shows the configuration of a projection exposure apparatus which is an embodiment of the present invention. Here, the relative position of the reticle (synonymous with mask) 1 with respect to the apparatus is measured by measuring the relative position with respect to the mark position detection optical system (alignment system) 22 to 24, whose position with respect to the wafer stage 5 has been determined in advance, using a one-dimensional image sensor ( (array sensor) 25.

In this exposure apparatus, a reticle 1 having a predetermined circuit pattern to be exposed and a reticle mark 9 for positioning is attached to a reticle stage 2,
It faces the wafer stage 5 via a projection lens 3 that is telecentric on both sides (or may be telecentric on one side). The reticle 1 is mounted on the reticle stage 2 by the drive motor 1.
4 allows two-dimensional movement in the X and Y directions, and the amount of movement is measured by a laser interferometer 15. Movement of the reticle stage 2 is used for positioning the reticle 1, which will be described later. The movement width of the reticle stage 2 is several millimeters or less, and the interferometer 15 detects a change in the distance of the mirror 6 fixed to the reticle stage 2 from a reference mirror (not shown) with a detection resolution of about 0.01 μm.

In reality, three sets of interferometers (laser light wave interferometric length measuring devices) 15 and mirrors 6 are installed in order to independently detect positions in the X direction, Y direction, and rotational θ direction. , some illustrations are omitted here to simplify the explanation. A total of three drive motors 14 are also installed in each direction, but some of them are similarly omitted from the illustration. The wafer stage 5 is freely two-dimensionally movable by a drive motor 17 along the imaging plane of the projection lens 3 of the reticle 1. The positional coordinates of the wafer stage 5 with respect to the main body of the exposure apparatus are calculated as the distance from a predetermined reference point by measuring the amount of movement of the mirror 7 fixed to the wafer stage 5 using a laser interferometer 16. In reality, the interferometer (laser light wave interferometric length measuring device) 16 and mirror 7 are
Although two sets are installed to independently detect the position in the direction, some illustrations are omitted here to simplify the explanation. A total of two sets of drive motors 17 are also installed corresponding to each direction, but some of them are similarly omitted from the illustration. The illumination optical system for exposure includes a light source (mercury lamp or excimer laser) 30, an input lens group 31 (zoom expander in the case of excimer laser), and an optical integrator (
It is composed of a fly eye lens) 32, mirrors 33, 35, a relay lens 34, a main condenser lens 36, a reticle blind 37, etc. Illumination light in the exposure wavelength range emitted from the light source 30 is sent to an input lens group 31, an optical integrator 32, and a main condenser lens 36.
The light is adjusted so as to have a uniform intensity distribution on the irradiation surface of the reticle 1, and is transmitted through the beam splitter 21 to illuminate a predetermined area of the reticle 1. The beam splitter 21 has a transmittance of 90% and a reflectance of 10% for the wavelength of the exposure illumination light.

Illumination light to the optical system for detecting the position of the reticle 1 is transmitted from a light source 30 to a movable total reflection mirror 1.
1 or a partially reflecting mirror 11. The position detection optical system (alignment system) includes a shutter 12,
Beam splitter 23, objective lens 22, imaging optical system 2
4. Consists of a one-dimensional image sensor 25. When performing this position detection, illumination light emitted from the light source 30 is reflected by the mirror 11 and used as measurement light. After opening the shutter 12, this measurement light passes through the beam splitter 23, the objective lens 22, and the beam splitter 21, and illuminates a local area including the reticle mark 9 of the reticle 1. The light reflected from the reticle mark 9 passes through the beam splitter 21 and the objective lens 22 again and forms an enlarged image of the reticle mark 9 on the image sensor 25 by the imaging optical system 24. The mark position detection optical system shown in FIG. 1 can change its position by a drive system 26 such as a motor if the reticle mark 9 is within an appropriate range on the reticle 1, and can form an image on the image sensor 25. In addition, the optical axis (more precisely, the detection center) of the mark position detection optical system is monitored by the position sensor, and the origin of the position sensor is located on the coordinate system predefined by the laser interferometer 16 of the wafer stage 5. It is sought after as a position in

A shutter 13 is provided between the reticle mark 9 and the projection lens 3 to prevent the measurement light that illuminates the reticle mark 9 from exposing the wafer 4 on the wafer stage 5 through the projection lens 3. Preventing. This shutter 13 is closed before the light transmission shutter 12 is opened to prevent the wafer 4 from being exposed to light. This shutter 1
3 only needs to block the measurement light that has passed through the reticle mark 9, so it can be made smaller and can be driven at high speed. This enables high-speed reticle exchange and reticle alignment without retracting the wafer 4 on the wafer stage 5.

FIG. 2 is a block diagram specifically showing the configuration of the control system 47 shown in FIG. 1. As shown in FIG. The one-dimensional image sensor 25 has a predetermined size for each pixel,
The controller 40 serially reads out the photoelectric signal for each pixel. This image sensor 25 is composed of, for example, 1024 pixels, and a photoelectric signal read out for each pixel is input to an analog-digital converter (ADC) 42 via an AGC circuit 41. The ADC 42 converts the magnitude of the photoelectric signal for each pixel into a digital value and stores it in the RAM 43.
stores converted digital values in pixel order. The controller 40 outputs a control pulse of one pulse per pixel to the ADC 42 and the counter (CNT) 44 in synchronization with the readout of the image sensor 25. The ADC 42 converts the signal level into a digital value for each pixel in response to this control pulse, and the CNT 44 counts this control pulse to generate an address value for the RAM 43.

A CPU (central processing unit) 50 analyzes the digital waveform information in the RAM 43 and detects the position of the reticle mark 9, reference mark 10, alignment mark, etc. on the wafer 4. Further, the CPU 50 outputs a control signal to the drive system 26 and inputs information from a position sensor 52 such as an encoder that detects the position of the objective lens 22 of the mark position detection optical system that is moved by the drive system 26. . The CPU 50 also controls the drive of the motor 54 of the shutter 13 via the drive system 53. Here, the shutter 13 is a rotary shutter with four blades.

Now, the memory 60 is the image sensor 25
In order to detect the position of the reticle mark 9 detected in the image sensor 25, a value (including a decimal number) representing which pixel position on the image sensor 25 is used as a reference is stored. This reference value is updated when the reference mark 10 is used to calibrate the mark position detection optical system. The memory 61 is
When calibrating the mark position detection optical system using the reference mark 10, the position of the wafer stage 5 and the position of the reticle stage 2 are read from the interferometers 15 and 16 and stored. This stored value is used to associate the reference pixel position (including decimal numbers) of the image sensor 25 with the coordinate system of the wafer stage 5. By the way, as shown in FIG. 3(a), the shutter 13 has a surface facing the reticle 1 with a
Two of the blades 13A have a low reflectance, and the other two blades 13B have a high reflectance. in this way,
By changing the reflectance of the blades 13A and 13B, the detection contrast of the mark 9 can be made the best by switching in accordance with the change in the reflectance of the reticle mark 9 (50% to 10%). Further, the shutter 13 is provided with cutout portions (transmission portions) 13C alternately with blades so that the measurement light transmitted through the reticle mark 9 can be guided to the wafer stage 5 via the projection lens 3. Note that the same effect can be obtained even if the shutter 13 is of a slide shutter type as shown in FIG. 3(b).

Next, position measurement of the reticle 1 and alignment of the reticle 1 using the projection exposure apparatus of this embodiment will be explained. FIG. 4(a) shows the arrangement of reticle marks 9 set at three locations in the transparent portion around the transfer area (circuit pattern area) PE of the reticle 1. Reticle mark 9
is a reflective cross mark that is a combination of bar marks extending in the X and Y directions, and is set at three locations, 9A, 9B, and 9C. Therefore, the mark position detection optical system in FIG. 1 is also arranged at three locations corresponding to each mark.

Now, after the reticle 1 is pre-aligned and placed on the reticle stage 2, the reticle mark 9 is placed on the reticle stage 2.
Position detection of A, 9B, and 9C and reticle alignment are started. At this time, the magnification of the mark position detection optical system (
As shown in FIG. 4(b), all of the reticle marks 9A, 9B, and 9C are placed on the image sensor of each mark position detection optical system at the pre-aligned position Let it form an image.

Here, assuming that the image sensors 25 of the three mark position detection optical systems are 25A, 25B, and 25C, the image sensor 25A detects X of the reticle marks 9A.
The image sensor 25B is arranged to measure the bar mark part extending in the Y direction of the reticle mark 9B in the X direction, and the image sensor 25C is arranged so as to measure the bar mark part extending in the Y direction of the reticle mark 9B. is arranged so that a bar mark portion of the reticle mark 9C extending in the X direction is measured in the Y direction. That is, image sensor 2
The pixel arrays of 5A and 25C are determined in the Y direction, and the pixel array of the image sensor 25B is determined in the X direction.

Next, after the shutter 12 is opened from the closed state of the shutter 13, each of the reticle marks 9A, 9B, and 9C is illuminated with the shutter 13 as a background. At this time, when the reflectance of the chrome layer of the reticle mark is low, the blade 13B with high reflectance is selected for the shutter 13, and when the reflectance of the chrome layer of the reticle mark is high, the blade 13A with low reflectance is selected. Controlled so that it is below the reticle mark. FIG. 5(a) shows a case where a reticle mark 9 with a low reflectance is formed in a transparent part of the reticle 1, and at this time, a blade 13B with a high reflectance is located below the peripheral area of the reticle mark 9. Therefore, the serial pixel signal output from the image sensor 25 is shown in FIG.
), the waveform bottoms out at mark 9. FIG. 5(b) shows a case where a reticle mark 9 with a high reflectance is formed in a transparent part of the reticle 1, and at this time, a blade 13A with a low reflectance is located below the peripheral area of the reticle mark 9. Therefore, the serial pixel signal output from the image sensor 25 has a waveform that peaks at the mark 9 as shown in FIG. 5(d). In the following description, only the processing of the waveform in FIG. 5(c) will be considered, but the waveform in FIG. 5(d) may be processed in exactly the same way.

Next, the state of waveform processing by the CPU 50 will be explained with reference to FIGS. 6 and 7. FIG. 6 is a flowchart showing the sequence of reticle mark alignment and calibration using the reference mark 10. First, in step 100 of FIG. 6, the CPU 50 determines whether a calibration operation is to be performed to determine a reference pixel of the image sensor 25. usually,
After the reticle 1 is placed on the reticle stage 2 in a pre-aligned state, the objective lens 22 is moved by the drive system 26.
is set at a position where the reticle mark 9 can be observed. However, when performing the calibration in step 100, the reticle stage 2 is shifted so that the reticle mark 9 is retracted from the detection area (straight line) of the image sensor 25. Next, the CPU 50 performs step 1
02, move the wafer stage 5 and place the reference mark 10.
is positioned within the detection range of the objective lens 22. Then, in step 104, the CPU 50 reads the coordinate values of the wafer stage 5 at that time from the interferometer 16 and stores them in the memory 61. At this time, the coordinate values and rotation amount values of the reticle stage 2 are simultaneously read from the interferometer 15 and stored in the memory 61.

Next, in step 106, the CPU 50 controls the RAM 43 to read the waveform data of the one-dimensional pixel signal from the image sensor 25. in this case,
Waveform data corresponding to the reference mark 10 is stored in the RAM 43. Then, in step 108, the CPU 50
The waveform data in the RAM 43 is analyzed and the reference mark 10 is
The pixel position on the waveform data representing the center of is determined as a real value (including decimal numbers). There are several algorithms that can be used for this waveform analysis, but the simplest and most accurate method is to binarize the bottom (or peak) waveform part at a predetermined slice level. This is a method of finding the midpoint of the pixel position between . Furthermore, when the symmetry of the bottom (peak) waveform portion with respect to the scanning direction is good, methods such as finding the zero-crossing point determined by the differential method or finding the center of gravity of the waveform using the integral method can also be applied.

Now, in step 110, the CPU 50 determines that the mark processed in step 108 is the reference mark 10.
Determine whether or not. Here, since the reference mark 10 has been detected, the CPU 50 executes step 112 and stores the pixel position of the center of the mark obtained in step 108 in the memory 60 as the reference pixel position (real value) PXC. C
During the above calibration operation, the PU 50 detects each image sensor 2 of the other two mark position detection optical systems.
5, steps 102 to 112 are repeatedly executed, and the reference pixel position PXC of each of the three image sensors 25, the coordinate values of the wafer stage 5, etc. are stored in the memories 60 and 61, respectively. Note that the position of each objective lens 22 of the three mark position detection optical systems is determined by the position sensor 52.
The value is also stored in the memory 60. This value serves as a reference when moving the mark position detection optical system.

Although the calibration operation is completed by the above operation, there is no need to repeat this operation in principle unless another reticle with a different arrangement of reticle marks 9 is attached. Therefore, while exposing multiple wafers throughout the day while exchanging multiple reticles whose reticle mark placement does not change, it is sufficient to calibrate only when the first reticle is attached. Calibration is not required during subsequent reticle alignment.

Next, the actual reticle mark 9 is detected, but for the reticle during the calibration operation,
The reticle mark 9 is returned to its original position and placed within the detection range of each image sensor 25. At this time,
Memory 61 determines how far to return reticle stage 2.
This can be easily determined from the coordinate values of the reticle stage stored in the reticle stage. The CPU 50 executes the sequence shown in FIG. 6 again, but this time it is not a calibration operation, so steps 100, 106, and 108 are executed in this order. In step 106, waveform data as shown in FIG. 7, for example, is stored in the RAM 43. In FIG. 7, the horizontal axis represents the pixel positions (PX1 to PXn) of the image sensor 25, and the vertical axis represents the signal level of each pixel. The bottom waveform corresponding to reticle mark 9 appears at pixel position PXm, and the CPU 50
In step 108, the pixel position PXm is accurately determined as a real value.

Next, the CPU 50 moves the execution from step 110 to step 114, reads out the stored contents of the memories 60 and 61 (reference pixel position PXc, coordinate values of the wafer stage at the time of calibration, etc.), and executes the next step 1.
At step 16, the detected value of the position sensor 52 is read. If the detected value of the position sensor 52 matches the value stored at the time of calibration, that detected value will not be used in subsequent calculations.

Next, in step 118, the CPU 50 calculates the amount of deviation ΔP of each center pixel position PXm of the three reticle marks 9 from the reference pixel position PXc, and adjusts the amount of deviation ΔP of the reticle mark 9 in the X direction corresponding to the amount of deviation ΔP. , or find the amount of positional deviation (μm) in the Y direction. The state at this time is shown in FIG. In FIG. 8, PXCY, PXCθ, PXC
X represents a reference pixel position (real value) determined on each of the three image sensors 25. This reference pixel position is determined by precisely positioning the reference mark 10 on the movement coordinate system of the wafer stage 5, so that it is on an axis parallel to each coordinate axis of the coordinate system XY of the wafer stage 5. here,
The straight line passing through the positions PXCY and PXCθ in the Y direction is defined as the X coordinate axis, the straight line passing through the position PXCX in the X direction is defined as the Y coordinate axis, and the optical axis of the projection lens 3 passes near the intersection O1 of both axes.

Now, the bar mark 9Ay extending in the X direction of the reticle mark 9A is detected as a pixel position (real value) PXma on the image sensor 25, and is a reference pixel position PXma.
The amount of deviation ΔPy in the Y direction from XCY is determined by the following equation, where k is the conversion constant. ΔPy=k(PXCY-PXma)
...(1) Similarly, the bar mark 9Cy extending in the X direction of the reticle mark 9C is the pixel position (real value) on the image sensor 25.
detected as PXmc, and Y with reference pixel position PXCθ
The amount of directional deviation ΔPθ is determined by the following equation.

ΔPθ=k(PXCθ−PXmc)
...(2) Furthermore, the bar mark 9Bx extending in the Y direction of the reticle mark 9B is detected as a pixel position (real value) PXmb,
The amount of deviation ΔPx in the X direction is determined by the following equation. ΔPx=k(PXCX-PXmb)
(3) It is assumed that the origin O2 in FIG. 8 coincides with the center of the pattern area of the reticle 1. What the CPU 50 seeks here is the rotation amount Δθ of the reticle 1 with respect to the coordinate system XY.
and the amount of parallel deviation in the X and Y directions. The rotation amount Δθ is determined by the following equation, where Lx is the span of the bar marks 9Ay, 9Cy in the X direction.

Δθ=sin−1 {(ΔPy−ΔPθ)/Lx }
...(4) However, Δθ
is generally a very small amount (1° or less), so equation (4) may be obtained by approximation using the following equation. Δθ≒(ΔPy−ΔPθ)/Lx
...(5) Furthermore, the amount of parallel deviation ΔX between the origin O2 and the intersection O1
, ΔY are determined by the following equations.

ΔY=(ΔPy+ΔPθ)/2
...(6)
ΔX≒ΔPx−Δθ/2
...(7
) Above, equations (5), (6), and (7) are the rotation amount and shift amount of the reticle stage 2 to be corrected, and the CPU 50 controls the drive motor 14 of the reticle stage 2 based on the measured value of the interferometer 15. The position of the reticle stage 2 is corrected at one time by servo control. The rotational drive of the reticle stage 2 is controlled so that the center of rotation is as close to the reticle center O2 as possible.

[0039] It is also possible to adopt a faster sequence. It is the positioning of reticle stage 2 (
Reticle alignment) is limited to correcting only the rotation amount Δθ, and the parallel deviation amount ΔX, ΔY between the origin O1 and the intersection O2.
The correction is made at the stepping position of the wafer stage 5 during wafer exposure. In this case, after correcting the rotation of Δθ of the reticle stage 2, the bar marks 9Ay at three locations are
, 9Bx, 9Cy, step 106,1 in FIG.
08, 114, and 118 to remeasure the parallel deviation amounts ΔX and ΔY in the X and Y directions.

If the resolution of the image sensor 25 is insufficient at this time, rough alignment of the reticle 1 is performed using the above sequence, and then the optical magnification of the position detection optical system is switched to a higher magnification and the image sensor 25 is Fine alignment may be performed in a similar sequence after increasing the detection resolution for the No. 25 mark images.

The above procedure completes the alignment of the reticle 1 with respect to the apparatus. In addition, the positions of the reticle marks 9A, 9B, and 9C after this alignment is completed are detected again, and the projected image of the circuit pattern area PE on the reticle 1 is determined from the position coordinate values of the wafer stage 5 corresponding to the detection results. The position of the center (origin O2) is determined and stored as a value on the X, Y coordinate system of the wafer stage 5. Furthermore, from the coordinate values of reticle marks 9A and 9C, reticle 1
The residual rotation (rotation amount) error is detected. In addition, the mark position detection optical system (11, 22, 23, 24,
25, 30), or based on the distance between the reference mark 10 on the wafer stage 5 and the alignment mark on the wafer 4 measured by an off-axis alignment system (not shown) installed separately around the projection lens 3, The amount of movement of the wafer stage 5 required to overlap the projected image of the circuit pattern area PE with the transferred area (shot area) on the wafer is calculated. The control system 47 in FIG. 1 (or the CPU 50 in FIG. 2) controls the drive motor 17 according to this movement amount.
The position of the wafer stage 5 is adjusted by. As a result, a relative positioning operation (alignment) between the wafer 4 and the reticle 1 is performed.

If it is difficult to change the magnification of the reticle position detection optical system, the magnification of the reticle position detection optical system is set to the magnification necessary for fine alignment, and the objective lens 22 of the optical system is driven by a motor or the like. The reticle marks 9A, 9B, and 9C are found by simultaneously driving the three axes in the system 26, and the marks on the image sensor 25 are determined by taking into account the change in the position coordinates of the optical system at that time, that is, the detected value of the position sensor 52. The same thing can be done by converting the center pixel position to the coordinate position on the wafer stage 5 side.

Furthermore, with the same configuration as this embodiment, the shape of the reticle mark 9 may be, for example, a transparent window-like mark as shown in FIG. 9(a). In this case, the wafer also has the shape shown in FIG. 9(b).
If a multi-bar mark like the one shown in FIG. is also possible. The waveform from the image sensor at that time is shown in FIG. Image sensor 2 during alignment of reticle to device
10(a) shows a case where the reflectance of the reticle mark 9 is low and FIG. 10(b) shows a case where the reflectance is high with the output of 5. moreover,
In the configuration of this embodiment, if a multibar mark similar to the wafer mark shown in FIG. 9(b) is included in a part of the reference mark 10, the transparent part 13C of the shutter 13 will be The reticle mark 9 is controlled through the projection optical system 3 so that it is located below the mark 9.
By moving the wafer stage 5 so that the multi-bar mark as the reference mark 10 is placed on the imaging plane of
There is an advantage that the relative distance (so-called baseline) between the shot center and the optical axis of the alignment optical system can be measured at the same time as reticle alignment.

Incidentally, the configurations shown in FIGS. 1, 2, and 6 can also be applied to an exposure apparatus using an excimer laser as the light source 30, but since the excimer laser emits pulsed light, image detection by the image sensor 25, It is necessary to synchronize signal readout and pulsed light emission. For this purpose, as shown in FIG. 2, the controller 40 of the image sensor 25 is configured to output a trigger signal (pulse) for pulse emission to the excimer laser, and also adjusts the image accumulation time and The timing of signal readout is controlled. When an accumulation type image sensor is used, an image signal of a mark image obtained by emitting multiple pulses of excimer laser can be read out. Of course, if it is not an accumulation type, the waveform data is stored in the RAM 43 by reading out each time a trigger signal is output. In either case, it is desirable to control the oscillation trigger of the excimer laser from the controller 40 side, and the oscillation trigger and its timing can be controlled as appropriate depending on how many pulses (at least once) are required to emit light when detecting a mark image. be done. Therefore, the mark position can be detected with a significantly smaller number of pulses than in the conventional method. Furthermore, excimer lasers typically use wavelength selection elements such as etalons, gratings, or prisms to narrow the bandwidth and stabilize the absolute wavelength. For this reason, a wavelength monitor is provided inside the excimer laser to detect whether or not the band-narrowed laser falls within a predetermined absolute wavelength value. Therefore, if the wavelength monitor outputs a detection result (disabled state) that the absolute wavelength value is slightly shifted (for example, about 0.003 nm), the image sensor 2 The image signal corresponding to the image of the reference mark 10 detected by the reference mark 10 or the mark on the wafer 4 is not used.

That is, when the absolute wavelength value is out of order, the correcting operation by the wavelength selection element works, but the correcting operation may not be completed with only one pulse of light emission, and therefore, due to chromatic aberration in the projection lens 3. This is because various imaging errors cannot be ignored. Therefore, the controller 40
When issuing a trigger request for mark image detection to the excimer laser, if the wavelength monitor on the excimer laser side outputs disable (wavelength correction in progress), wait until the disable is released. . however,
When only the reticle mark 9 is detected by the image sensor 25, the image is not detected via the projection lens 3, so the trigger oscillation of the excimer laser is immediately triggered regardless of such a slight shift in the absolute value of the center wavelength. can be applied. Further, depending on the excimer laser, partial gas exchange (PGI) is performed in which the internal laser medium (gas such as Freon, He, Kr, etc.) is replaced little by little, or the entire laser medium itself is replaced. In the case of partial gas exchange, trigger oscillation is fully possible, but the wavelength monitor may detect a disabled state. Therefore, even at the timing of partial gas exchange, when a mark image is detected by the image sensor 25 through the projection lens 3, the same sequence as the above-mentioned absolute wavelength control is possible.

By the way, since the movement position of the objective lens 22 of the mark position detection optical system is constantly monitored by the position sensor 52, the reticle mark 9 and the separately provided reticle for TTR alignment are detected via the objective lens 22. The mark (step mark) and the mark for each shot area on the wafer 4 can be moved to any position in order to be detected simultaneously.

Further, the illumination system (11, 30) of the mark position detection optical system shown in FIG. 1 emits illumination light from above the reticle 1 through the objective lens 22; A similar effect can be obtained by providing the mark 9 below the mark 9 and detecting the transmitted light of the mark 9 with the objective lens 22 above. Furthermore, although the light source 30 is used commonly for pattern exposure and reticle mark detection, separate light sources may be used for each. In that case, if the wavelength of the illumination light from the exposure light source and the wavelength of the illumination light from the mark detection light source are made approximately equal,
TTR alignment and calibration operations can be performed in exactly the same manner as in the above embodiment. However, when aligning only the reticle mark 9, the wavelength of the illumination light from the mark detection light source may be made different from that of the exposure illumination light to make it non-photosensitive to the wafer 4. In that case, there is no need to provide the shutter 13 to prevent unnecessary exposure to the wafer, but a plurality of blades with different reflectances ( 13A, 13B)
It is desirable to provide a member with the same function as the above.

[0048]

[Effects of the Invention] As described above, according to the present invention, a mask,
Alternatively, alignment of the reticle with respect to the apparatus can be performed at high speed and with high accuracy regardless of the substrate stage such as a wafer, so that the exposure preparation time and the like are shortened and the operating efficiency of the apparatus is improved. This is particularly effective when a plurality of reticles are used for exposure of one wafer, such as in an ASIC. Furthermore, by providing a movable light-shielding member with different reflection characteristics between the projection optical system and the mask mark, a high-contrast image can be obtained even for mask marks with different reflectances, and by opening the light-shielding member, It is also possible to align the substrate and mask, or measure the baseline amount of the alignment optical system.

Furthermore, an exposure apparatus using pulsed light such as an excimer laser as a light source is not limited by the light emission frequency of the pulsed light source, and the number of times of light emission required for measurement can be significantly reduced.
This has the effect of extending the gas life of the light source.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing the configuration of a projection exposure apparatus according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a partial configuration of a signal processing circuit and a control circuit of the device in FIG. 1;

FIGS. 3(a) and 3(b) are diagrams showing the configuration of a shutter that prevents exposure of a wafer and optimizes the contrast of a reticle mark image during alignment of a reticle with respect to a device.

FIGS. 4(a) and 4(b) are diagrams showing the arrangement of reticle marks and their relationship with an image sensor during reticle pre-alignment.

5(a), (b), (c), and (d) are diagrams showing reticle mark images and image sensor output waveforms when the reflectance of the reticle mark is high and low; FIG.

FIG. 6 is a flowchart diagram illustrating a sequence in an embodiment of the present invention.

FIG. 7 is a diagram schematically representing an output waveform of an image sensor when detecting a reticle mark.

FIG. 8 is a diagram illustrating the arrangement of reticle marks detected by three mark position detection optical systems (image sensors).

9A and 9B are diagrams showing examples of reticle marks and wafer marks when aligning a reticle and a wafer and measuring a baseline amount in the configuration of FIG. 1;

10(a) and (b) are diagrams showing image sensor output waveforms when the mark of FIG. 9 is used, and illustrating examples when the reflectance of the reticle mark is low and high.

[Explanation of symbols of main parts]

1 Reticle 2 Reticle stage 3 Projection lens 4 Wafer 5 Wafer stage 9 Reticle mark 10 Standard mark 12,13 Shutter 14, 17 Drive motor 22 Objective lens 25 Image sensor 50 CPU 60,61 Memory

Claims (1)

[Claims] 1. A mask stage that holds a mask having a pattern to be exposed and a mark for alignment; a projection optical system that projects the pattern or the mark onto a predetermined imaging plane; a substrate stage that holds a photosensitive substrate near a surface; a mark detection means that detects a deviation of the mark from a predetermined reference position by photoelectrically detecting the mark on the mask; and a detection result from the mark detection means. In the projection exposure apparatus, the mark detection means includes a light source that emits illumination light for detecting the mark, and a drive means that adjusts the position of the mask stage based on the mark detection means. an illumination optical system that illuminates a local area on the mask, an imaging optical system that receives reflected light or transmitted light from the mark to form an image of the mark, and an image sensor that receives the image of the mark. and a mark position detection circuit that analyzes an imaging signal from the image sensor to detect the position of the mark on the image sensor; the mark position detection circuit detects a specific position on the image sensor. a memory circuit that stores a value representing the specific position to be used as the reference position; and a mark center that detects a position on the image sensor corresponding to the center of the image of the mark based on a waveform on the imaging signal. Projection exposure comprising: a position detection circuit; and a calculation circuit that calculates the amount of positional deviation of the mark by calculating the difference between the center position of the mark image and a specific position stored in the storage circuit. Device.