JPH0620923A - Exposing method - Google Patents

Abstract

(57) [Summary] [Purpose] To measure the fluctuation of the best focus position due to the process of photosensitive substrate processing, and not to reprocess the measured photosensitive substrate. [Structure] An image of a focus measurement mark of a measurement reticle is exposed on a region 27-i of a series of shot regions 26-i of the first wafer 16-1 of one lot while changing the focus position. Then, a series of shot areas 28-i is exposed with a reticle pattern for actual element exposure at a predetermined focus position. The best focus position is obtained from the image of the focus measurement mark in the area 27-i, and if the best focus position is within the predetermined range from the predetermined focus position, the wafer 16-1 proceeds to the next process.

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 for exposing a pattern image of a reticle onto a photosensitive substrate via a projection optical system, for example, so that the exposure surface of the photosensitive substrate becomes the best focus surface of the projection optical system. The present invention relates to an exposure method for performing matching exposure within a predetermined tolerance range.

[0002]

2. Description of the Related Art For example, when manufacturing a semiconductor device or a liquid crystal display device by using a photolithography technique, a photomask, a reticle or the like (hereinafter collectively referred to as a "reticle").
There is used a projection exposure apparatus that exposes an image of the pattern of (1) to each shot area on a photosensitive substrate coated with a photosensitive material such as photoresist via a projection optical system. The projection optical system used in such a projection exposure apparatus has a numerical aperture N.V. A. Is set large and the depth of focus is relatively shallow. Therefore, in the conventional projection exposure apparatus, exposure is performed with the exposure surface of each shot area of the photosensitive substrate aligned with the best focus surface (best image formation surface) of the projection optical system within a predetermined allowable range. To do this, an autofocus mechanism is provided.

This auto-focusing mechanism is, for example, a light transmitting system that projects a detection pattern such as a slit pattern onto each shot area of a photosensitive substrate obliquely with respect to the optical axis of the projection optical system, and a reflected light from the shot area. And a light receiving system that forms an image of the detection pattern. In this case, when the reticle pattern image is formed on the exposed surface of the photosensitive substrate most clearly in advance, that is, when the exposed surface matches the best focus surface of the projection optical system, The best focus position which is the position of the exposure surface in the optical axis direction of the projection optical system is obtained. Then, when the exposed surface matches the best focus position, the position of the image of the detection pattern formed by the light receiving system is adjusted so as to match a predetermined reference position.
After that, at the time of exposure, by vertically positioning the stage on which the photosensitive substrate is placed so that the position of the image of the detection pattern becomes the reference position, each shot area of the photosensitive substrate is set to the projection optical system. It matches the best focus surface within a predetermined allowable range.

That is, such an autofocus mechanism does not directly detect the best focus surface itself of the photosensitive substrate, but exposes the photosensitive substrate at a preset best focus position in the optical axis direction of the projection optical system. The position of the surface is adjusted. Therefore, how to obtain the best focus position becomes a problem. Furthermore, when the best focus position is obtained by, for example, the method described later, there is no problem if the best focus surface of the projection optical system is unchanged or its change amount is small. However, when the position of the best focus surface changes greatly beyond a predetermined amount, there is a risk that exposure is performed with the exposure surface of the photosensitive substrate largely deviated from the actual best focus surface of the projection optical system. Further, when a circuit pattern or the like is already formed in each shot area of the photosensitive substrate, the image forming position of the detection pattern in the autofocus mechanism changes depending on the unevenness of the shot area. The same inconvenience may occur as when the position of the best focus surface actually changes.

The cause of such a substantial change in the position of the best focus surface is divided into a factor based on the change of the state of the projection exposure apparatus and a factor based on the process of pattern formation on the photosensitive substrate. Therefore, in the autofocus mechanism of the projection exposure apparatus, it is necessary to calibrate the actual average exposure surface of the photosensitive substrate with the actual best focus surface of the projection optical system as needed or periodically. However, conventionally, the calibration has been performed by the following two methods.

In the first method, exposure is performed while changing the position (focus position) in the optical axis direction of the projection optical system of the exposure surface of the reference photosensitive substrate such as a bare silicon wafer having no actual element structure. The reticle pattern in which the best focus measurement marks are formed is sequentially exposed in a series of shot areas on the surface. After developing the photosensitive substrate, the shape of the image of the best focus measurement mark exposed at each of the above focus positions is measured to determine the best focus position of the reference photosensitive substrate as the best focus of the apparatus. Find as a position. After that, the best focus position is obtained by adding a process offset value, which is obtained in advance, in consideration of the influence of the element structure and the like, to the best focus position of the photosensitive substrate having the element structure. .

In the second method, after the exposure and development of the photosensitive substrate at the beginning of the lot, the image of the actual element pattern or the like is observed or measured to obtain the image of the element pattern or the like at the preset focus position. It is determined whether the shape of is within the allowable range. If not, the best focus position is obtained again by the first method.

[0008]

When the first method described above is used, the best focus position of the apparatus is obtained by test printing using a reference photosensitive substrate, and the offset due to the process is The best focus position of the photosensitive substrate having the actual element structure is estimated as being constant. Therefore, when the best focus position changes due to instability of the process such as the thickness of the resist and the thickness of the base, there is a disadvantage that the change of the best focus position based on such a factor cannot be found.

Further, when the second method is used, the pattern shape changes regardless of which of the exposure amount and the focus position changes. Therefore, it is best only from the set exposure condition (exposure amount and focus position). The focus position cannot be determined. Therefore, if the pattern shape under the initially set exposure conditions is a shape that cannot be advanced to the next process, it is necessary to re-measure the reference photosensitive substrate, or There is an inconvenience that it is necessary to obtain the best focus position by performing exposure while changing the focus position using a photosensitive substrate having an element structure.

In this case, when the focus position is changed to expose the pattern on the photosensitive substrate in order to obtain the best focus position, there is always a defocused and exposed portion on the photosensitive substrate, and the exposed portion is always The photosensitive substrate had to be reprocessed. Further, when a focus measurement mark is provided in the pattern area of the reticle and only that focus measurement mark is exposed by changing the focus position, the projection position of the focus measurement mark is the autofocus mechanism of the projection exposure apparatus. Since it does not match the projection position (focus detection position) of the detection pattern of
There is a disadvantage that an accurate best focus position cannot be obtained due to the flatness of the photosensitive substrate.

In view of the above problems, the present invention has an object of providing an exposure method capable of measuring the fluctuation of the best focus position due to the process of processing a photosensitive substrate and not necessarily reprocessing the measured photosensitive substrate. And Also,
In addition to these objects, an object of the present invention is to provide an exposure method capable of measuring the best focus position without being affected by the flatness of the photosensitive substrate.

[0012]

An exposure method according to the present invention comprises an illumination optical system (1, 6 to 11) for illuminating a transfer mask (12) with exposure light, as shown in FIGS. 1 to 3, for example.
The exposure surface of the photosensitive substrate (16) of an exposure apparatus having a projection optical system (14) for projecting the image of the pattern of the transfer mask (12) onto the photosensitive substrate (16) is directed to the projection optical system (14). In the method of performing exposure by setting the best focus position within a predetermined allowable range, the first mask (12A) on which the best focus measurement mark (23) is formed is arranged as the transfer mask, and the exposure is performed. While varying the position of the exposure surface of the substrate (16) in the direction of the optical axis of the projection optical system (14), the images of the best focus measurement marks (23) are respectively formed on a plurality of shot areas of the photosensitive substrate (16). It has the 1st process (steps 101-105) of exposing.

Furthermore, the present invention provides a transfer pattern (24).
The second mask (12B) on which is formed is arranged as the transfer mask, and the exposure surface of the photosensitive substrate (16) is set at a predetermined position in the optical axis direction of the projection optical system (14). Then, a second step (steps 106 to 109) of exposing the plurality of shot areas of the photosensitive substrate (16) with images of the pattern of the second mask (12B), respectively.
The third step (step 110) of developing the photosensitive substrate (16) and the state of the image of the best focus measurement mark (23) exposed in the first step are measured and the projection optical system ( 14) the fourth step (step 111) of obtaining the best focus position, the position of the exposure surface of the photosensitive substrate (16) set in the second step, and the best focus position obtained in the fourth step. If the difference is within the allowable range, it is determined that the photosensitive substrate (16) is advanced to the next step, and if the difference is outside the allowable range, it is determined that the photosensitive substrate (16) is reprocessed. Fifth step (step 112) and its photosensitive substrate (16)
The sixth step (step of setting the exposure surface of the photosensitive substrate of the same lot as that in the best focus position obtained in the fourth step and exposing the pattern of the second mask (12B) or another transfer mask (step) 115) and.

In this case, a focus position detecting device (18a, 18a, 18a, 18a) for measuring the position of a predetermined measurement point in the exposure region of the projection optical system (14) in the optical axis direction of the projection optical system (14) in the exposure device. 18b) is provided, and the best focus measurement mark (2) of the first mask (12A) is provided.
It is desirable to provide 3) near the position conjugate with the predetermined measurement point. Furthermore, it is desirable to make the region on the second mask (12B) corresponding to the best focus measurement mark (23) of the first mask (12A) on the light shielding part (25).

[0015]

According to the present invention, the best focus measurement mark (23) and the transfer pattern (24) such as the actual element pattern are formed on different masks (12A, 12B). Then, regarding the best focus measurement mark (23), the photosensitive substrate (1
Exposure is performed while changing the focus position in each shot area of 6). On the other hand, in the second step, even if the photosensitive substrate (16) is the head of the same lot, the transfer pattern (24) is preliminarily considered to be the best focus position in all the shot areas of the photosensitive substrate (16). Exposure is performed only at the focus position of. Then, in the fourth step, the best focus position with respect to the projection optical system (14) is detected by measuring the state of the image of the best focus measurement mark (23) exposed at each focus position.

Next, if the focus position at the time of exposure of the transfer pattern (24) is within an allowable range preset with respect to the best focus position measured in the fourth step, the photosensitive substrate ( Since the image of the transfer pattern (24) exposed in each shot area on 16) is exposed within the allowable focus range, the photosensitive substrate (16) proceeds to the next step such as exposure to the next layer. Can be made. On the contrary, if it is outside the allowable range, the photosensitive substrate (16) may be subjected to reprocessing such as resist stripping and re-exposure. In addition, regarding the photosensitive substrate in the same lot to be processed thereafter,
By performing exposure at the best focus position measured in the fourth step, exposure is performed under the best conditions. Therefore, for example, the best focus position can be obtained without wasting the first photosensitive substrate (16) of one lot, and the best focus position can be corrected for the second and subsequent photosensitive substrates, for example.

Next, the projection optical system (1
4) The projection optical system (1
4) is provided with a focus position detection device (18a, 18b) for measuring the position in the optical axis direction, and the first mask (12)
The mark (23) for best focus measurement of A) is
A case will be described where it is provided near a position conjugate with the predetermined measurement point. First, in the present invention, another mask (12A, 12
Since it is divided into B), the best focus measurement mark (23) can be provided at an arbitrary position on the first mask (12A) regardless of the structure of the transfer pattern (24). Therefore, the focus position detecting device (1
8a, 18b), the best focus measurement mark (23) can be provided in the area on the first mask (12A) near the position conjugate with the measurement point by the focus position detection device (18a, 18b). And the detection area of the focus position by the best focus measurement mark (23) are substantially the same area.

Therefore, even when the flatness of the photosensitive substrate (16) is poor, after the best focus position is obtained based on the best focus measurement mark (23), the focus position detection device (18a, 18b) detects it. If the photosensitive substrate is focused based on the result, accurate focusing can be performed.

Further, in the case where the region on the second mask (12B) corresponding to the best focus measurement mark (23) of the first mask (12A) is used as the light shielding part (25),
The pattern of the first mask (12A) and the second mask (1
Even if the pattern of 2B) is overlapped and exposed on the photosensitive substrate (16), double exposure is performed on the image of the best focus measurement mark (23) in each shot area on the photosensitive substrate (16). Not done Therefore, the state of the image of the best focus measurement mark (23) can be accurately measured, and the measurement accuracy is improved.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. In this example, the present invention is applied when a reticle pattern is exposed on a wafer as a photosensitive substrate by a step-and-repeat type reduction projection type exposure apparatus (stepper).

FIG. 2 shows a schematic structure of the projection exposure apparatus of this embodiment. In FIG. 2, reference numeral 1 is a light source for exposure light such as a mercury lamp. The exposure light emitted from the light source 1 is condensed by the elliptical mirror 2, then reflected by the reflecting mirror 5 toward the input lens system 4, is converted into a substantially parallel light flux by the input lens system 4, and is converted by the fly-eye lens 6. Incident. A shutter 3a is arranged near the second focal point of the ellipsoidal mirror 2, and the shutter 3a is provided when the exposure light is supplied to the fly-eye lens 6.
Is opened by the drive motor 3b, and when the supply of exposure light to the fly-eye lens 6 is stopped, the shutter 3a is closed by the drive motor 3b.

Rear side of the fly-eye lens 6 (reticle side)
A large number of secondary light sources are formed on the focal plane, and the exposure light from these secondary light sources is transmitted from the first relay lens 7, the projection type variable reticle blind 8, the second relay lens 9, the reflecting mirror 10 and the main condenser lens 11. The reticle 12 is illuminated with a uniform illuminance through the illumination optical system. The arrangement surface of the projection-type variable reticle blind 8 is conjugate with the pattern formation surface of the reticle 12, and the projection-type variable reticle blind 8 arbitrarily sets the illumination visual field of the pattern area of the reticle 12. Reference numeral 17 denotes a reticle alignment system. The reticle alignment system 17 detects the alignment mark on the reticle 12 to align the reticle 12.

Under the exposure light, the reticle pattern 13 formed on the reticle 12 is transferred onto the resist-coated wafer 16 through the projection optical system 14. The wafer 16 is placed on the wafer stage 15. The optical axis of the projection optical system 14 (this is taken as the Z axis) is the focus direction, and the wafer stage 15 has the focus direction and the Z direction.
The wafer 16 is positioned in a plane perpendicular to the axes (this orthogonal coordinate system is the X axis and the Y axis). The wafer stage 15 incorporates a measurement sensor for measuring the positioning coordinate in the Z-axis direction, and the laser interferometer (not shown) constantly measures the positioning coordinate of the wafer stage 15 in the XY plane.

Reference numeral 18a denotes a light transmitting system of the autofocus detection system, and 18b denotes a light receiving system of the autofocus detection system.
The light sending system 18a projects an image of a detection pattern such as a slit pattern on a predetermined detection area on the wafer 16 obliquely with respect to the optical axis of the projection optical system 14. For example, an area on the optical axis of the projection optical system 14 is selected as the predetermined detection area on the wafer 16. In the light receiving system 18b, the reflected light from the image of the detection pattern on the wafer 16 is re-imaged on the vibrating slit, and the output signal of the light receiving element on the back surface of the vibrating slit is synchronously rectified by the drive signal of the vibrating slit. Then, a focus detection signal is obtained. In this case, when the exposure surface of the wafer 16 matches the best focus surface of the projection optical system 14 in advance, that is, when the exposure surface of the wafer 16 is at the best focus position in the Z-axis direction, the vibration center of the vibration slit thereof. The image of the detection pattern is re-imaged. As a result, the focus detection signal becomes 0 when the exposure surface of the wafer 16 is at the best focus position, and when the exposure surface deviates vertically from that position, the focus detection signal changes substantially linearly within a predetermined range. Detection signal is 0
The exposure surface of the wafer 16 is automatically focused by driving the wafer stage 15 so that

The best focus position of the exposure surface of the wafer 16 is the clearest when the pattern of the reticle 12 is exposed on a series of shot areas of the wafer 16 while changing the position (focus position) in the Z direction little by little. It can be obtained as the focus position when a different image is exposed. Further, in the light receiving system 18b, in order to set the position where the image of the detection pattern is re-imaged at the vibration center of the vibration slit, for example, a parallel flat glass plate is arranged in front of the vibration slit and the parallel flat glass is arranged. The angle of the flat glass may be adjusted. Further, even when a change in the best focus position is detected by calibration as described later, the angle of the parallel flat plate glass may be adjusted.

Reference numeral 19 denotes a wafer alignment system. The alignment light from the wafer alignment system 19 is guided onto the wafer 16 via the mirror and the projection optical system 14, and the alignment light reflected from the wafer 6 is projected into the projection optical system 14.
And via the mirror into the wafer alignment system 19. As a result, the alignment mark on the wafer 16 is detected, and the position of the wafer 16 in the XY plane perpendicular to the optical axis of the projection optical system 14 is detected. Further, the projection exposure apparatus of this example is equipped with a reticle loader and a wafer loader (not shown), and the reticle loader and the wafer loader move the reticle 12 and the wafer 16 respectively from the case or the cassette to a predetermined position at the time of exposure, Conversely, return it to the case or cassette.

Reference numeral 20 denotes a computer that controls the operation of the entire apparatus, and a storage device 21 such as a disk device is connected to the computer 20. The computer 20 controls the operations of, for example, the drive motor 3b, the projection type variable reticle blind 8, the reticle alignment system 17, the wafer alignment system 19, the wafer stage 15, and the light transmitting system 18a and the light receiving system 18b of the autofocus detection system.
Further, the computer 20 is supplied with a focus detection signal from the light receiving system 18b. Furthermore, the computer 20 may be connected to an external computer 22 via a communication unit so that the computer 20 operates according to an instruction from the external computer 22.

As described above, in the projection exposure apparatus of this example, the light transmitting system 18a and the light receiving system 18b of the autofocus detection system are used.
Although the position shift (focus shift) from the best focus position of the exposure surface of the wafer 16 is detected by the above, the position of the best focus surface itself of the projection optical system 14 may change due to accumulation of irradiation energy of the exposure light. is there. Furthermore,
Depending on the process type of the wafer 16, the wafer 16
There is a possibility that the offset between the position of the surface of the exposure surface detected by the autofocus detection system and the position of the surface on which the pattern of the reticle 12 is actually projected may change. Therefore, it is necessary to calibrate the best focus position before exposing one lot of wafers, for example. An example of the calibration method will be described below.

FIG. 3A shows a reticle 12A for focus measurement used in the calibration of this embodiment.
In FIG. 3A, the focus measurement mark 23 is formed in the central portion of the reticle 12A, and the reticle alignment marks RM1 to RM3 are formed in the peripheral portion of the reticle 12A. Then, replace the reticle 12A with the reticle 1 shown in FIG.
When the exposure is performed instead of 2, the image of the focus measurement mark 23 is exposed at the position where the image of the detection pattern is projected from the light transmitting system 18a onto the exposure surface of the wafer 16. That is, the position on the wafer 16 where the image of the detection pattern is projected from the light transmitting system 18a and the reticle 12A.
The position of the upper focus measurement mark 23 is conjugate with respect to the projection optical system 14.

A projected image of the focus measurement mark 23 on the wafer 16 is a diffraction grating-shaped image 23J as shown in FIG. 4 (a9. As an example, the image 23J is Y.
A plurality of groups are arranged in the direction, and each group is composed of four elongated diamond-shaped patterns at equal intervals. Further, when the length of the image 23J in the X direction when the exposure surface of the wafer 16 is at the best focus position is L, when the exposure surface deviates from the best focus surface, the length of the image 23J in the X direction. Is longer than L. Therefore,
The best focus position can be obtained by measuring the length of the image 23J in the X direction.

As the focus measurement mark 23, as shown in FIG. 4B, a pattern in which the projected image on the wafer 16 becomes a line-and-space pattern image 23K may be used. . In this case, when the width of one line portion of the image 23K when the exposure surface of the wafer 16 is at the best focus position is P, and when the exposure surface is out of the best focus position, the width of the line portion is P. Since it becomes larger, the best focus position can be obtained.

FIG. 3B shows a reticle 12B for exposure of an actual element pattern. In FIG. 3B, an actual element pattern for transfer is formed in the pattern area 24 of the reticle 12B, and the pattern thereof is formed. Outside the area 24, FIG.
Similar to the reticle 12A in (a), reticle alignment marks RM4 to RM6 are formed. Further, a light shielding area 25 for protecting the focus measurement mark is provided inside the pattern area 24. The light-blocking region 25 may have the same area as the outer shape of the focus measurement mark 23 shown in FIG.
The position of is arbitrary. If the pattern area 24 has a light-shielding portion having a coarse pattern density and an area equal to or larger than the area of the focus measurement mark 23, this light-shielding portion can be used as it is as the light-shielding area 25.

Next, in the projection exposure apparatus of FIG. 2, the calibration of the best focus position with respect to the projection optical system 14 is performed and the wafers for one lot are sequentially processed.
The operation in the case of exposing the pattern of the reticle 12B for actual element pattern exposure of (b) will be described with reference to the flowchart of FIG.

First, in step 101 of FIG.
A computer 20 is loaded with a data file for exposure of focus measurement marks from the storage device 21 or the computer 22, and the reticle 12A for focus measurement shown in FIG. 3A is replaced with the optical axis of the reticle 12 shown in FIG. Place it in the specified position above. Then, after setting the projection type reticle blind 8 in a predetermined opening,
In step 102, the top wafer 16-1 (first processed) of the lot is placed on the wafer stage 15. Then, assuming that a predetermined best focus position is Fc, in step 103, the focus position of the first shot area of the wafer 16-1 is set to (Fc
The pattern of the reticle 12A is exposed in the first shot area in the state where it is set to −ΔF). Actually, only the image of the focus measurement mark 23 of the reticle 12A is exposed in the central portion of the first shot area.

Next, in steps 104 and 105, the i-th shot area (i = 2, 3, ...
N), the pattern of the reticle 12A is exposed. In this case, the focus position in the center shot area of the N shot areas is the best focus position F until then.
to be c. As a result, as shown in FIG.
27- in the center of a series of shot areas 26-1, 26-2, ..., 26-N surrounded by broken lines on the exposed surface of the first wafer 16-1. At N, the focus position is gradually changed within the width 2ΔF centering on the initial best focus position Fc, and the image of the focus measurement mark 23 of the reticle 12A is exposed.

Next, in step 106, a data file for actual element pattern exposure is loaded into the computer 20 of FIG. 2 from the storage device 21 or the computer 22,
According to the data, the reticle 12A is replaced by the one shown in FIG.
The reticle 12B for actual element pattern exposure of (b) is placed at a predetermined position on the optical axis. Then, after setting the projection type variable reticle blind 8 to a predetermined opening, in step 107, the focus position of the exposure surface of the reticle 12B is set to the initial best focus position Fc. afterwards,
In steps 108 and 109, a series of shot areas 2 of the reticle 12B are held with the focus position fixed.
Reticle 12B for 8-i (i = 1, 2, ..., N)
The image of the actual element pattern in the pattern area 24 is exposed.

As a result, as shown in FIG.
The pattern of the reticle 12B is exposed on each of a series of shot areas 28-i surrounded by a solid line on the exposure surface of 6-1. In this case, the shot area 26-i when exposing the reticle 12A and the shot area 28-i when exposing the reticle 12B are displaced in the XY plane, and the area 27-i of the shot area 26-i. The light-shielding area 25 of FIG. 3B is projected on the screen. Therefore, double exposure is not performed on the image of the focus measurement mark 23 of FIG. 3A projected on the area 27-i.

Next, in step 110, a predetermined developing process is performed on the wafer 16-1 which has been exposed. As a result, a resist pattern corresponding to the exposure amount and the focus position is formed on the surface of the wafer 16-1. afterwards,
In step 111, the wafer 16-1 is placed on the wafer stage 15 of the projection exposure apparatus of FIG. 2 again, and the image of the focus measurement mark 23 formed in each shot area as shown in FIG. Measure the length of the 23J diamond pattern. This measurement is performed by the wafer alignment system 19 shown in FIG. The measuring method is also disclosed in, for example, Japanese Patent Application No. 63-11729. From the measurement result, the computer 20 determines that the best focus position Fm
To calculate.

Subsequently, in step 112, the computer 20 sets the negative focus allowable range Fma, the positive focus allowable range Fpa, and the measured best focus position Fm described in the exposure data file of the actual element pattern. In steps 108 and 109, it is determined whether the focus position (the best focus position up to that point) Fc when the exposure is actually performed satisfies the following expression. Fm−Fma ≦ Fc ≦ Fm + Fpa (1)

If the equation (1) is satisfied, the wafer 16
It is assumed that -1 has been exposed within the allowable focus range, and the operation proceeds to step 115. Further, the first wafer 16-1 proceeds to the next step (for example, the step of exposing the next layer) similarly to the second and subsequent wafers. On the other hand, if the expression (1) is not established, it is assumed that the wafer 16-1 has been exposed outside the allowable focus range, and in step 113, the resist peeling and the resist recoating of the wafer 16-1 are performed. Then, in step 114, the focus position is set to the best focus position Fm obtained in step 111, and the pattern of the reticle 12B is exposed on the leading wafer 16-1.

Next, in step 115, only the pattern of the reticle 12B for actual element pattern exposure is exposed in each shot area at the best focus position Fm obtained in step 111 for the remaining wafers in the lot. As a result, all the remaining wafers are exposed with the actual element pattern at the best focus position after calibration.

As described above, according to this example, the image of the focus measuring mark 23 is stably formed in each shot area of the leading wafer 16-1 of the lot, and the focus measuring mark 23 of the focus measuring mark 23 is formed. The focus position is detected by the autofocus detection system at the image projection position. Therefore, even when the flatness of the wafer 16-1 is poor, the best focus position can be detected stably and accurately, and the best focus position can be accurately calibrated. In this case, as described above, when the initial setting value Fc of the best focus position, the measured best focus position Fm, the permissible value Fma and the permissible value Fpa satisfy the expression (1), the lot top wafer 16-1
Did not have to be reprocessed. Therefore, the exposure throughput is improved. The area required for the projected image of the focus measurement mark 23 on each wafer is about 70 μm.
Since it is about m × 70 μm, the actual element pattern region is not pressed.

When the image of the focus measuring mark 23 is the image 23K of the line and space pattern as shown in FIG. 3B, a scanning electron microscope (SEM) or the like is used in step 111 of FIG. The resist line width may be used to measure the best focus position from the result. Further, the present invention is not limited to the above-described embodiment, and for example, as shown in the second example of the conventional exposure method, it is determined whether the leading wafer of one lot is within the focus allowable range. Alternatively, when the focus position of the leading wafer is out of the allowable range, the above-described exposure method may be performed on the second wafer with the estimated best focus position as the initial best focus position Fc. . At this time, the order of the exposure reticle does not necessarily have to be from the focus measurement reticle 12A to the actual element pattern exposure reticle 12B.

Further, in the above embodiment, the light-shielding region 25 for protecting the focus measurement mark is provided only once in the reticle for exposing the actual element pattern, but a plurality of light-shielding regions may be provided. . Even if the focus position when exposing an actual element pattern on one wafer is the best focus position by design, a light-transmissive reference mark formed on the same plane as the wafer is exposed from the inside of the stage. Light that is illuminated by the exposure light and reflected by the pattern surface of the reticle through the projection optical system is photoelectrically detected through the projection optical system and the reference mark.When the stage is moved in the optical axis direction, it is photoelectrically detected. A position where the signal becomes maximum (or minimum) is obtained as the best focus position, and this best focus position may be used. Further, the reticle does not have to be divided into two sheets (12A, 12B). That is, the focus measurement mark 23 and the light shielding area may be formed on the same reticle. However, in this case, when the focus measurement mark 23 is exposed on the wafer, the mark 2
Shield the parts other than 3 with a reticle blind. As described above, the present invention is not limited to the above-described embodiments, and various configurations can be taken without departing from the gist of the present invention.

[0045]

According to the present invention, since the best focus position is measured on the photosensitive substrate on which the actual element pattern is exposed, the variation of the best focus position due to the process of processing the photosensitive substrate can be measured, and the measured best focus is measured. There is an advantage that the measured photosensitive substrate does not need to be reprocessed when the position is within the allowable range with respect to the predetermined position.

Further, the exposure device is provided with a focus position detection device for measuring the position of a predetermined measurement point in the exposure area of the projection optical system in the optical axis direction of the projection optical system, and the best focus measurement of the first mask is performed. When the use mark is provided near the position conjugate with the predetermined measurement point, the best focus position can be measured without being affected by the flatness of the photosensitive substrate.

Further, when the area on the second mask corresponding to the best focus measurement mark of the first mask is used as a light shielding part, double exposure is performed on the image of the best focus measurement mark. Is not performed, the best focus position can be accurately measured. Also, 1
When it is not necessary to expose the image of the best focus measurement mark to the area on all the shot areas of the photosensitive substrate corresponding to the light shielding portion of the second mask in the second exposure step,
The regions corresponding to the light-shielding portions arranged on the entire photosensitive substrate are divided into several groups, and the best focus measurement marks are exposed to the regions corresponding to the light-shielding portions for one group per one exposure process. The best focus position may be obtained. As a result, when the best focus measurement mark is provided in the second mask,
There is an advantage that the best focus position can be measured with a smaller area occupied by the image of the best focus measurement mark on the photosensitive substrate.

[Brief description of drawings]

FIG. 1 is a flowchart showing an example of an operation when exposing one lot of wafers while calibrating a best focus position in one embodiment of the present invention.

FIG. 2 is a configuration diagram showing an outline of a projection exposure apparatus of the embodiment.

FIG. 3A is a plan view showing a pattern of a focus measurement reticle used in the embodiment, and FIG. 3B is a plan view showing a pattern of a real element exposure reticle used in the embodiment. is there.

FIG. 4A is a diagram showing an example of an image of a focus measurement mark of the focus measurement reticle shown in FIG.
(B) is a diagram showing another example of the image of the focus measurement mark.

FIG. 5 is a plan view showing an exposure pattern of a leading wafer of wafers for one lot exposed in the embodiment.

[Explanation of symbols]

 1 Light Source 2 Elliptical Mirror 3 Shutter 4 Input Lens System 6 Fly-Eye Lens 7 First Relay Lens 8 Projection-type Variable Reticle Blind 9 Second Relay Lens 11 Main Condenser Lens 12 Reticle 12A Focus Measurement Reticle 12B Actual Element Pattern Exposure Reticle 14 Projection optical system 15 Wafer stage 16 Wafer 17 Reticle alignment system 18a Auto-focus detection system light-transmitting system 18b Auto-focus detection system light-receiving system 19 Wafer alignment system 20 Computer 21 Storage device 22 External computer 23 Focus measurement mark 24 Pattern Area 25 Light-shielding area for protecting focus measurement marks

Claims (3)

[Claims] 1. An exposure surface of the photosensitive substrate of an exposure apparatus, comprising an illumination optical system for illuminating a transfer mask with exposure light, and a projection optical system for projecting an image of the pattern of the transfer mask onto a photosensitive substrate. In a method of performing exposure by setting a best focus position with respect to a projection optical system within a predetermined allowable range, a first mask on which a best focus measurement mark is formed is arranged as the transfer mask, A first step of exposing the images of the best focus measurement marks to a plurality of shot areas of the photosensitive substrate while changing the position of the exposure surface in the optical axis direction of the projection optical system; and a transfer pattern is formed. A second mask is arranged as the transfer mask, and the exposure surface of the photosensitive substrate is set at a predetermined position in the optical axis direction of the projection optical system, and A second step of exposing images of the pattern of the second mask to a plurality of shot areas of the plate; a third step of developing the photosensitive substrate; a best focus measurement exposed in the first step A fourth step of measuring the state of the image of the working mark to obtain the best focus position with respect to the projection optical system; the position of the exposure surface of the photosensitive substrate set in the second step, and the step of obtaining the position in the fourth step. If the difference from the best focus position is within the allowable range, it is determined that the photosensitive substrate is advanced to the next step, and if the difference is outside the allowable range, it is determined that the photosensitive substrate is reprocessed. Fifth step; the exposure surface of the photosensitive substrate of the same lot as the photosensitive substrate is set to the best focus position obtained in the fourth step, and the pattern of the second mask or another transfer mask is exposed. And an exposure method comprising the sixth step. 2. The exposure apparatus is provided with a focus position detection device that measures the position of a predetermined measurement point in the exposure area of the projection optical system in the optical axis direction of the projection optical system, and the focus position detection apparatus is provided on the first mask. The exposure method according to claim 1, wherein the best focus measurement mark is provided near a position conjugate with the predetermined measurement point. 3. The exposure method according to claim 1, wherein a region on the second mask corresponding to the best focus measurement mark of the first mask is a light shielding portion.