JP3381258B2 - Projection exposure apparatus, projection exposure method, and device manufacturing method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a projection exposure method and apparatus suitable for application to, for example, an autofocus mechanism or an autoleveling mechanism of a slit scan exposure type projection exposure apparatus.

[0002]

2. Description of the Related Art A substrate on which a photosensitive material is applied with a pattern of a photomask or reticle (hereinafter referred to as "reticle") when manufacturing a semiconductor device, a liquid crystal display device, a thin film magnetic head, or the like by a photolithography process. A projection exposure apparatus for transferring onto a (wafer, glass plate, etc.) is used. As a conventional projection exposure apparatus, a step-and-repeat type reduction projection type in which each shot area of a wafer is sequentially moved into the exposure field of a projection optical system to sequentially expose a pattern image of a reticle on each shot area. The exposure device (stepper) was often used.

FIG. 20 shows a main part of a conventional stepper,
In FIG. 20, under the exposure light EL from the illumination optical system (not shown), each shot area on the wafer 53 on which the image of the pattern on the reticle 51 is coated with the photoresist via the projection optical system 52. Is projected and exposed. The wafer 53 is held on a Z leveling stage 54, and the Z leveling stage 54 is placed on a wafer side XY stage 55. The wafer side XY stage 55 positions the wafer 53 within a plane (XY plane) perpendicular to the optical axis AX1 of the projection optical system 52, and the Z leveling stage 5
Reference numeral 4 denotes a focus position on the exposure surface of the wafer 53 (optical axis AX
The position in the direction parallel to 1) and the tilt angle of the exposure surface are set to the designated state.

A movable mirror 56 is fixed on the Z leveling stage 54. The laser beam from the external laser interferometer 57 is reflected by the moving mirror 56, and the X coordinate and Y coordinate of the wafer side XY stage 55 are constantly detected by the laser interferometer 57, and these X coordinate and Y coordinate are main control system. 58. The main control system 58 controls the operations of the wafer-side XY stage 55 and the Z-leveling stage 54 via the drive unit 59, so that the pattern of the reticle 51 is sequentially formed on each shot area on the wafer 53 by the step-and-repeat method. Expose the image.

At this time, the pattern forming surface (reticle surface) on the reticle 51 and the exposure surface of the wafer 53 are the projection optical system 5.
Although it must be conjugate with respect to 2, the reticle surface does not change much because the projection magnification is high and the depth of focus is large. Therefore, conventionally, whether or not the exposure surface of the wafer 53 is generally aligned with the image plane of the projection optical system 52 within the range of the depth of focus by an oblique incidence type multi-point focus position detection system (whether or not it is in focus). ) Is detected and the wafer 5
The focus position and the tilt angle of the exposure surface of No. 3 were controlled.

In the conventional multi-point focus position detection system, illumination light that does not expose the photoresist on the wafer 53 to the exposure light EL is guided from an illumination light source (not shown) through the optical fiber bundle 60. There is. The illumination light emitted from the optical fiber bundle 60 illuminates the pattern forming plate 62 via the condenser lens 61. The illumination light transmitted through the pattern forming plate 62 is projected onto the exposure surface of the wafer 53 through the lens 63, the mirror 64 and the irradiation objective lens 65, and the image of the pattern on the pattern forming plate 62 is projected onto the exposure surface of the wafer 53. The projection image is formed obliquely with respect to the axis AX1. The illumination light reflected by the wafer 53 passes through a condenser objective lens 66, a rotation direction vibrating plate 67, and an imaging lens 68, and a light receiver 69.
The image of the pattern on the pattern forming plate 62 is re-imaged on the light receiving surface of the light receiver 69. In this case, the main control system 58 applies vibrations to the rotational direction vibration plate 67 via the vibration exciting device 70 as described later, and the detection signals from the large number of light receiving elements of the light receiver 69 are supplied to the signal processing device 71. The signal processing device 71 supplies to the main control system 58 a large number of focus signals obtained by synchronously detecting each detection signal with the drive signal of the vibration device 70.

FIG. 21B shows an opening pattern formed on the pattern forming plate 62. As shown in FIG. 21B, the pattern forming plate 62 has nine slits in a cross shape. The opening patterns 72-1 to 72-9 are provided. The opening patterns 72-1 to 72-9 are 45 ° with respect to the exposure surface of the wafer 53 with respect to the X axis and the Y axis.
Since the irradiation is performed from the direction intersecting with each other, the projection images AF1 to A of the aperture patterns 72-1 to 72-9 in the exposure field of the projection optical system 52 on the exposure surface of the wafer 53 are formed.
F9 is arranged as shown in FIG. Figure 21
In (a), the maximum exposure field 74 is formed inscribed in the circular illumination field of the projection optical system 52, and the central portion of the maximum exposure field 74 and two diagonal measurement points A are measured.
Projected images of slit-shaped opening patterns are projected on F1 to AF9, respectively.

FIG. 21C shows the state of the light receiving surface of the light receiver 69. As shown in FIG. 21C, the light receiver 69 is shown.
9 light receiving elements 75-1 to 75-in a cross shape on the light receiving surface of
9 is disposed, and a light shielding plate (not shown) having a slit-shaped opening is disposed on each of the light receiving elements 75-1 to 75-9. Then, the measurement points AF1 to A in FIG.
The image on F9 is the light receiving element 75-1 of the light receiver 69.
Reimaged on ~ 75-9. In this case, FIG.
The illumination light reflected on the exposure surface (wafer surface) of the wafer 53 of FIG.
Since the light is reflected by the rotation direction vibration plate 67 that vibrates (rotationally vibrates) about an axis substantially perpendicular to the paper plane of 0, as shown in FIG. 7
The position of the projected image re-formed on 5-9 oscillates in the RD direction which is the width direction of the slit-shaped opening.

Further, the measurement points AF1 to A shown in FIG.
Since the image of the slit-shaped aperture on F9 is projected obliquely with respect to the optical axis of the projection optical system 52, when the focus position of the exposure surface of the wafer 53 changes, those projected images are received on the light receiver 69. The re-imaging position of is changed in the RD direction. Therefore, in the signal processing device 71, each of the light receiving elements 75-1 to 75-1
By synchronously detecting the detection signal of -9 with the vibration signal of the rotation direction vibration plate 67, nine focus signals corresponding to the focus positions of the measurement points AF1 to AF9 are obtained. Then, from the nine focus positions, the tilt angle of the average surface of the exposure field 74 and the focus position of the average surface are obtained and supplied to the main control system 58, and the main control system 58 is driven by the drive device 59. Then, the focus position and the tilt angle (leveling angle) of the shot area of the wafer 53 are set to predetermined values via the Z leveling stage 54. In this manner, in the stepper, the pattern image of the reticle 51 is exposed in each shot area of the wafer 53 in a state where the focus position and the tilt angle are matched with the image plane of the projection optical system 52.

[0010]

In recent years, patterns are becoming finer in semiconductor elements and the like, so that it is required to increase the resolution of the projection optical system. Methods for increasing the resolution include methods such as shortening the wavelength of exposure light or increasing the numerical aperture of the projection optical system. However, it is becoming difficult to maintain the imaging performance (distortion, curvature of field, etc.) at a predetermined accuracy over the entire exposure field. Therefore, what is currently being reviewed is a so-called slit scan exposure type projection exposure apparatus.

In this slit scan exposure type projection exposure apparatus, a reticle and a wafer are scanned relatively synchronously with respect to a rectangular or arcuate illumination area (hereinafter referred to as "slit illumination area"). Meanwhile, the pattern of the reticle is exposed on the wafer. Therefore, there is an advantage that the images are averaged in the area conjugate with the slit-shaped illumination area, and the distortion accuracy is improved.

The conventional mainstream reticle size is 6
Inch size, and the mainstream projection magnification of projection optical system is 1
However, the size of the reticle under the magnification of 1/5 is not enough for the 6-inch size due to the increase in the area of the circuit pattern of the semiconductor element or the like. Therefore, it is necessary to design a projection exposure apparatus in which the projection magnification of the projection optical system is changed to, for example, 1/4. Further, the slit scan exposure method, which can reduce the exposure field diameter of the projection optical system against such an increase in the area of the transferred pattern, is also advantageous in terms of cost.

In such a slit scan exposure type projection exposure apparatus, the multipoint focus position detection system used in the conventional stepper is directly applied to measure the focus position and tilt angle of the exposure surface on the wafer. Even so, there is a problem in that it is difficult to align the actual exposure surface with the image plane of the projection optical system because the wafer is scanned in the predetermined direction. That is, conventionally, in the slit scan exposure type projection exposure apparatus, a method for adjusting the focus position and tilt angle of the wafer to the image plane of the projection optical system has not been established.

In view of the above-mentioned problems, the present invention provides a slit-scan exposure type projection exposure apparatus that enables the exposure surface of a photosensitive substrate to be accurately aligned with the image plane of a projection optical system. To aim.

[0015]

A projection exposure apparatus according to the present invention is an exposure apparatus which passes through a projection optical system (8) in synchronization with scanning movement of a mask (12) in a first direction with respect to an exposure beam. Measuring means (62A, 69A) for measuring focus position information regarding a partial area on the substrate in a projection exposure apparatus for scanning and exposing the substrate by scanningly moving the substrate (5) with respect to the beam. And surface setting means (22, 28) for setting the surface position of the substrate based on the focus position information measured by the measuring means, wherein the surface setting means projects the partial area on the substrate by the projection. Based on the measured focus position information before the partial area reaches the irradiation area, the exposure is performed in a focused state when reaching the irradiation area of the exposure beam that has passed through the optical system. The surface position of the plate were to move gradually.

In this case, the measuring means has a detection point for detecting the focus position information on an area apart from the irradiation area. Further, in this case, the measuring unit has the detection point on an area distant from the irradiation area in the scanning direction. Also in this case,
The measuring unit has the detection points on a plurality of areas that are apart from the irradiation area in the scanning direction. Further, in this case, the detection points are arranged at a plurality of points separated in a direction intersecting the scanning direction. Further, in this case, the detection points are also provided in the irradiation area. Further, in this case, the detection points are arranged two-dimensionally.

In the projection exposure method of the present invention, the exposure beam that has passed through the projection optical system (8) is synchronized with the scanning movement of the mask (12) in the first direction with respect to the exposure beam. In a projection exposure method of scanning and exposing the substrate by scanningly moving the substrate (5) in a second direction, focus position information regarding a partial region on the substrate is measured, and the partial region on the substrate is the projection optical system. Before the partial area reaches the irradiation area, the focused area is exposed when the irradiation area of the exposure beam that has passed through the system is reached.
The surface position of the substrate is gradually moved based on the measured focus position information.

In this case, the focus position information is detected at a detection point on an area apart from the irradiation area. Further, in this case, the detection point is provided on an area distant from the irradiation area in the scanning direction. Further, in this case, the detection points are provided on a plurality of areas that are apart from the irradiation area in the scanning direction. Further, in this case, the detection points are arranged at a plurality of points separated in a direction intersecting the scanning direction.

[0019]

According to the present invention, in the projection exposure apparatus of the slit scan exposure system, the exposure surface of the photosensitive substrate can be accurately aligned with the image plane of the projection optical system.

Next, in this embodiment, when performing leveling, the response speed of leveling in the scanning direction and the response speed of leveling in the non-scanning direction are different. In order to explain the effect of this, the error factors of focusing and leveling during slit scan exposure will be described. The following errors can be considered in the slit scan exposure type exposure apparatus. Focus offset error and vibration error The focus offset error is the difference in focus position between the average surface of the exposure surface and the image plane of the projection optical system, and the vibration error is the focus direction of the substrate side stage during scanning exposure. This is an error caused by the vibration of. This will be described in more detail by dividing into a case of performing a batch exposure like a stepper and a case of performing an exposure by a slit scan exposure method, in which only autofocus control is performed.

FIG. 14A shows the case of FIG.
(B) shows the case of performing exposure by the slit scan exposure method. In FIG. 14A, the average surface 34 of the exposed surface 5a of the photosensitive substrate matches the image plane of the projection optical system,
The focus positions of the positions Ya, Yb, and Yc are −ΔZ1, 0 and ΔZ2 with respect to the constant average surface 34, respectively.
Only different. Therefore, the focus offset errors at the positions Ya and Yb are −ΔZ1 and ΔZ, respectively.
It is 2.

On the other hand, in the case of FIG. 14B, a series of partial average surfaces 35 on the exposure surface 5a with respect to the scanning direction.
A, 35B, 35C, ... Are sequentially aligned with the image plane of the projection optical system. Therefore, the focus offset error at each position Ya, Yb, and Yc becomes 0 due to the averaging effect. However, since the focus position moves between the heights ΔZB from the average surface 35B to the average surface 35D to form the image on the position Yb, the image on the position Yb has a variation in the focus direction by ΔZB. It becomes an image. Similarly, the images on the positions Ya and Yc are images having variations in the focusing direction by ΔZA and ΔZB, respectively.

That is, in the slit scan exposure method, the focus offset error is almost zero for the unevenness of the photosensitive substrate surface having a certain frequency or less, but the rolling, pitching, and the focus direction (Z-axis direction) of the substrate-side stage. A new error (vibration error) is caused by an error component caused by the autofocus mechanism and the auto-leveling mechanism following vibration and low-frequency air fluctuation error, short-term wavelength fluctuation of exposure light (KrF excimer laser light, etc.), etc. Occurs.

Focus following error, air fluctuation error,
It is a typical example of the vibration errors mentioned in the stage vibration error, and these are dependent on the response frequency of the autofocus mechanism and the autoleveling mechanism, but can be further classified into the following errors. (1) High-frequency stage vibration error that cannot be controlled by the control system, short-term wavelength fluctuation error of exposure light (KrF excimer laser light, etc.), etc. (2) Air fluctuation error (3) Frequency air fluctuation error, etc. (3) Measurement error of focus position detection system or tilt angle detection system, but it does not become a focus error because the substrate side stage does not follow.

Error due to unevenness of the exposed surface of the photosensitive substrate This error is because the exposure field by the projection optical system is a two-dimensional surface unit, and the measurement of the focus position on the exposed surface of the photosensitive substrate is performed at a finite number of measurement points. Moreover, it is an error caused by performing the slit scan exposure, and can be classified into the following two errors. (1) For example, as shown in FIGS. 15A and 15B, the focus position is measured at multiple points on the exposure surface 5a of the photosensitive substrate, and the alignment target surface (focus surface) 36
The error of the deviation between the focus surface 36A and the ideal focus surface due to the calculation method for the position of the measurement point when obtaining A and 36B, Error due to difference, response speed of focus position detection system, etc.

In this case, the response speed (focus response) when the focus position is adjusted to the image plane of the projection optical system is
The time delay error as shown in FIG.
It is determined by the servo gain as shown in (d).
That is, in FIG. 15C, a curve 37A shows a drive signal for the focus direction (target focus position signal) for sequentially aligning a series of partial areas of the exposure surface 5a of the photosensitive substrate with the image plane of the projection optical system. , The curve 38A indicates the exposed surface 5a.
Signal obtained by converting the amount of movement of the series of partial areas in the focus direction into the drive signal (following focus position signal)
Indicates. The curve 38A lags the curve 37A by a certain time. Similarly, in FIG. 15D, the curve 3
7B is a target focus position signal of a series of partial areas of the exposure surface 5a of the photosensitive substrate, a curve 38B is a follow-up focus position signal of a series of partial areas of the exposure surface 5a, and a curve 37B.
The amplitude (servo gain) of the curve 38B is smaller than B by a certain amount.

In the present embodiment, in order to remove these errors, the response of the leveling mechanism in the scanning direction and the response in the non-scanning direction are changed. The multipoint measuring means for the auto-leveling mechanism in this embodiment is premised on an oblique incidence type multipoint focus position detection system. Further, instead of considering the average surface of the exposure surface of the photosensitive substrate in a predetermined area in the exposure field of the projection optical system, each point of the exposure surface in the predetermined area and the image surface of the projection optical system The goal is to minimize the maximum value of the deviation from. In this way, in a predetermined area within the exposure field of the projection optical system, the exposure field in the case where the maximum value of the deviation between almost all the points on the exposure surface of the photosensitive substrate and the image plane of the projection optical system is minimum is We call it "Good Field".

First, as shown in FIG. 16, it is assumed that there are many measurement points (not shown) of the focus position in the slit-shaped exposure field 24 which is conjugate with the slit-shaped illumination area and the projection optical system. In FIG. 16, assuming that one shot area SAij on the photosensitive substrate is scanned at a speed V / β in the Y direction with respect to the slit-shaped exposure field 24, the width of the shot area SAij in the scanning direction is WY,
The width in the non-scanning direction is WX, and the width in the scanning direction of the exposure field 24 is D. Further, by averaging the focus positions at a large number of measurement points in the central region 24a in the exposure field 24, the average focus position of the surface at the center point of the exposure field 24 is obtained, and the scan of the exposure field 24 is performed. Measurement regions 24b and 24c at both ends in the direction
The average tilt angle θY in the scan direction of the surface is obtained from the focus position at the measurement point within the range based on the least square approximation, and the measurement area 2 at both ends of the exposure field 24 in the non-scan direction is obtained.
It is assumed that the average inclination angle θX of the surface in the non-scanning direction is obtained from the focus positions at the measurement points within 4b and 24c based on the least square approximation. The leveling response frequency in the scan direction is fm [Hz], and the leveling response frequency in the non-scan direction is fn [Hz], and the values of fm and fn are set independently.

Then, the shot area SAij on the photosensitive substrate
The period of the periodic bending in the scan direction is represented by the bending parameter F as a value of the ratio with the width WY in the scanning direction (the same bending period is set in the non-scan direction), and when there is the periodic bending. The focus error at each measurement point within the exposure field 24 is represented by the sum of the absolute value of the average value of the focus error when scanned and 1/3 of the amplitude of the focus error when scanned. In addition, the amplitude of the periodic bending of the bending parameter F is standardized to 1, and when the bending parameter is F, the error parameter S indicating the maximum value of the focus errors at those measurement points is set to the bending parameter F. It is expressed as a ratio to.
That is, the following equation is established. F = Bending cycle / WY (1) S = Maximum focus error value / F (2)

FIG. 17A shows the error parameter S with respect to the bending parameter F when the leveling response frequency fm in the scanning direction and the leveling response frequency fn in the non-scanning direction are equal and large, and the curve A1 represents the non-scanning. The error parameter S in the direction, the curve B1 is the absolute value of the average value of the normal focus error in the error parameter S in the non-scan direction, the curve A2 is the error parameter S in the scan direction, and the curve B2 is the error parameter S in the scan direction. The average value of the normal focus error is shown. Curve A
1 and the curve A2 respectively represent more realistic focus errors. When the value of the parameter F is small and the cycle of the unevenness of the exposed surface is small, the followability of the leveling control in the scan direction is poor (curve A2), and the leveling control in the scan direction follows the curve as the cycle of the unevenness increases. It turns out that Further, since the focus position does not change successively in the non-scanning direction as in the scanning direction, even if the bending cycle becomes large, the followability in the scanning direction is worse (curve A1). As described above, it is desirable that the focus error be such that the parameter S is 0.5 or less, but the focus error is large as a whole in both the scanning direction and the non-scanning direction.

On the other hand, in FIG. 17B, the leveling response frequency fm in the scanning direction is higher than the leveling response frequency fn in the non-scanning direction, and both response frequencies fm.
And fn are small, they represent the error parameter S with respect to the bending parameter F, the curve A3 is the error parameter S in the non-scan direction, the curve B3 is the absolute value of the average value of the normal focus error in the non-scan direction, and the curve A4 is the scan. The error parameter S in the direction and the curve B4 show the absolute value of the average value of the normal focus error in the scanning direction. Figure 1
7 (a) and FIG. 17 (b), the error parameter S is 0 when the response frequency is smaller (FIG. 17 (b)) than when the response is almost perfect (FIG. 17 (a)). It is close to 0.5 and it can be seen that the focus error is small. This is because when the auto-leveling mechanism follows fine irregularities on the photosensitive substrate, the slit-shaped exposure field 24
This is because there is a point where the accuracy deteriorates. However, if the response frequency is made too small, it becomes impossible to follow even the low frequency unevenness, so the response frequency must be set to an appropriate value.

In the example of FIG. 17B, the leveling response frequency fm in the scan direction is set higher than the leveling response frequency fn in the non-scan direction. This is because even if the unevenness has the same bending parameter F, the cycle becomes substantially shorter in the scanning direction depending on the slit width. This is also because it is necessary to increase the height in the scanning direction.

Further, the multi-point measuring means for the auto-leveling mechanism is provided at a plurality of points in the exposure area (24) conjugate with the illumination area of the predetermined shape and the projection optical system (8) and in the conjugate exposure area. On the other hand, when the height of the photosensitive substrate (5) is measured at each of a plurality of measurement points formed in a front region when the photosensitive substrate (5) is scanned, Partial prefetching of the focus position is performed. This is called "division prefetching". Therefore, as compared with the method of performing pre-reading at all measurement points (complete pre-reading), the length (running distance) at the time of reading the focus position by the multi-point measuring means before exposure is shortened.

When the multipoint measuring means sequentially changes the positions of the plurality of measuring points in the process of sequentially exposing the pattern of the mask (12) onto one shot area of the photosensitive substrate (5), For example, division pre-reading is performed at the end of the shot area, complete pre-reading is performed after the center of the shot area, and open control is confirmed by the exposure position detector. This makes it possible to shorten the run-up distance at the end of the shot area and increase the exposure throughput while maintaining the leveling accuracy at a high level.

Next, the autofocus control in this embodiment will be examined. The above good fields (Good
Incorporating the concept of (Field), as shown in FIG.
Accuracy may be deteriorated by performing the averaging process of the focus positions of the measurement points in the central portion 24a of the exposure field 24 and aligning the surface indicated by the average value of the focus positions with the image plane of the projection optical system. There is a nature. That is, FIG.
(A) is a surface 34A corresponding to the average value of the focus positions of the respective measurement points on the exposure surface 5a having a recess of the depth H of the photosensitive substrate.
And the difference Δ in the focus direction between the surface 34A and the concave portion.
Z3 is larger than H / 2.

On the other hand, in the present embodiment, the maximum value and the minimum value of the focus position of each measurement point within the predetermined measurement area on the exposure surface 5a are obtained, and the intermediate value between the maximum value and the minimum value is obtained. The surface corresponding to the focus position is aligned with the image plane of the projection optical system. FIG. 18B shows a surface corresponding to an intermediate focus position between the maximum value Z _max and the minimum value Z _min of the focus positions at each measurement point on the exposure surface 5 a having a recess of the depth H of the photosensitive substrate. 34B and face 34
The B focus position Z _34B can be expressed as follows. Z _34B = (Z _max + Z _min ) / 2 (3)

Thereafter, the surface 34B is aligned with the image plane of the projection optical system. Further, the difference ΔZ4 in the focusing direction between the surface 34B and the surface of the exposure surface 5a and the difference ΔZ5 in the focusing direction between the surface 34B and the concave portion thereof are approximately H / H.
It is 2. That is, the maximum value of the error of the focus position at each point on the exposure surface 5a is smaller on the surface 34B of FIG. 18B than on the surface 34A of FIG. According to the present invention, the exposed surface of the photosensitive substrate can be more accurately aligned with the image plane of the projection optical system in the concept of field).

Further, as shown in FIG. 17A, the leveling response frequency fm in the scanning direction and the leveling response frequency fn in the non-scanning direction are made equal and large to perform auto-leveling control, and at the same time as shown in FIG. Autofocus control based on the averaging process of a) or FIG.
The characteristics of the error parameter S with respect to the bending parameter F in the case of performing the autofocus control based on the average value of the maximum value and the minimum value in (b) are shown in FIGS. 19A and 19B, respectively. That is, FIG. 19A based on the averaging process.
In, the curves A5 and B5 represent the error parameter S in the non-scan direction, and the curves A6 and B6 represent the error parameter S in the scan direction. Further, in FIG. 19B based on the average value of the maximum value and the minimum value, the curve A
7 and B7 represent the error parameter S in the non-scan direction, and the curves A8 and B8 represent the error parameter S in the scan direction.

As is clear from FIG. 19B, when the autofocus control is performed based on the average value of the maximum value and the minimum value, all the bending parameters F, that is, the error parameters in all frequency bands. The value of S is close to 0.5, and the maximum value of the focus error is smaller than that when the autofocus control is performed based on the averaging process.

Returning to FIGS. 15A and 15B, only the autofocus control is performed based on the average value of the maximum value and the minimum value of the focus positions obtained at the measurement points within the predetermined measurement area. In that case, as shown in FIG.
For the exposure surface 5a having a bend with an amplitude of 2 · ΔZa,
The surface 36A whose difference in focus position from the maximum value is ΔZa is aligned with the image plane of the projection optical system. On the other hand, amplitude 2 · ΔZ
With respect to the exposed surface 5a having a curvature of a, autofocus control is performed simply based on the average value of the focus positions obtained at those measurement points, and autoleveling control is performed based on the least square approximation of the obtained focus position. Then, as shown in FIG. 15B, the amplitude ΔZc (> 2 ·
The surface 36B having a difference in focus position from the maximum value of ΔZb (> ΔZa) within the range of ΔZa) may be aligned with the image plane of the projection optical system. Therefore, regardless of whether the auto-leveling mechanism is used or not, the focus error is smaller when the auto-focus control is performed based on the average value of the obtained maximum and minimum focus positions.

In this embodiment, the surface determined by (maximum value Z _{max of} focus position + minimum value Z _{min of} focus position) / 2 is controlled so as to be aligned with the image plane, but depending on the device process. In some cases, the depth of focus of either the convex portion or the concave portion of the exposed surface 5a of the photosensitive substrate is required. Therefore, it is desirable to perform control such that the surface of the focus position Z _MN , which is determined by proportional distribution as shown in the following equation, is aligned with the image surface by using the predetermined coefficients M and N. Z _MN = (M · Z _max + N · Z _min ) / (M + N) (4)

[0042]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. In this embodiment, the present invention is applied to an autofocus mechanism and an autoleveling mechanism of a slit scan exposure type projection exposure apparatus. FIG. 1 shows a projection exposure apparatus of the present embodiment. In FIG. 1, a reticle 12 is formed by a rectangular illumination area (hereinafter, referred to as “slit-shaped illumination area”) by exposure light EL from an illumination optical system (not shown). The upper pattern is illuminated, and the image of the pattern is projected and exposed on the wafer 5 via the projection optical system 8.
At this time, for the slit-shaped illumination area of the exposure light EL,
In synchronism with the reticle 12 being scanned at a constant speed V in the front direction (or the other side) with respect to the paper surface of FIG. 1, the wafer 5 is fixed in the other side (or the front direction) with respect to the paper surface of FIG. The scanning is performed at the speed V / β (1 / β is the reduction magnification of the projection optical system 8).

A drive system for the reticle 12 and the wafer 5 will be described. A reticle Y drive stage 10 that is freely driveable in the Y-axis direction (direction perpendicular to the paper surface of FIG. 1) is placed on the reticle support base 9. A reticle micro-driving stage 11 is placed on the reticle Y driving stage 10, and a reticle 12 is held on the reticle micro-driving stage 11 by a vacuum chuck or the like. Reticle micro drive stage 1
Reference numeral 1 indicates the position control of the reticle 12 with a small amount and with high accuracy in the X direction, the Y direction, and the rotation direction (θ direction) parallel to the paper surface of FIG. 1 in the plane perpendicular to the optical axis of the projection optical system 8. To do. A movable mirror 21 is arranged on the reticle micro-driving stage 11, and an interferometer 14 arranged on the reticle support 9 is provided.
The position of the reticle micro-driving stage 11 in the X direction, Y direction, and θ direction is constantly monitored by. The position information S1 obtained by the interferometer 14 is the main control system 22A.
Is being supplied to.

On the other hand, a wafer Y-axis drive stage 2 which can be driven in the Y-axis direction is mounted on the wafer support base 1, and a wafer X-axis drive stage 3 which can be driven in the X-axis direction is mounted thereon. The Z leveling stage 4 is provided on the Z leveling stage 4, and the wafer 5 is held on the Z leveling stage 4 by vacuum suction. The movable mirror 7 is also fixed on the Z leveling stage 4, and the interferometer 13 is arranged outside.
The position of the Z leveling stage 4 in the X direction, the Y direction, and the θ direction is monitored, and the position information obtained by the interferometer 13 is also supplied to the main control system 22A. The main control system 22A uses the wafer drive device 22B and the like to move the wafer Y.
While controlling the positioning operation of the axis drive stage 2, the wafer X-axis drive stage 3 and the Z leveling stage 4,
Controls the operation of the entire device.

In order to correspond the wafer coordinate system defined by the coordinates measured by the wafer-side interferometer 13 and the reticle coordinate system defined by the coordinates measured by the reticle-side interferometer 14, A reference mark plate 6 is fixed near the wafer 5 on the Z leveling stage 4. Various reference marks are formed on the reference mark plate 6. Among these reference marks, a reference mark illuminated from the back side by the illumination light guided to the Z leveling stage 4 side, that is, a luminescent reference mark is also provided.

Above the reticle 12 of this example, reticle alignment microscopes 19 and 20 for simultaneously observing the reference mark on the reference mark plate 6 and the mark on the reticle 12 are provided. In this case, the deflection mirrors 15 and 16 for guiding the detection light from the reticle 12 to the reticle alignment microscopes 19 and 20, respectively, are movably arranged, and when the exposure sequence is started, a command from the main control system 22A is also issued. And the mirror drive devices 17 and 1
The deflecting mirrors 15 and 16 are retracted by 8 respectively.

The slit scan type projection exposure apparatus of FIG. 1 is equipped with the conventional oblique incidence type multi-point focus position detection system described with reference to FIGS. 20 and 21. However, in the multipoint focus position detection system of this example, the number of measurement points is larger than in the conventional example, and the arrangement of the measurement points is devised. FIG. 2B shows a pattern forming plate 62A of this example corresponding to the conventional pattern forming plate 62 of FIG. 21B, and as shown in FIG. 2B, the first row of the pattern forming plate 62A. 9 slit-shaped opening patterns 72-1
1 to 72-19 are formed, and nine opening patterns 72-12 to 72-59 are also formed in the second to fifth columns, respectively. That is, a total of 45 slit-shaped opening patterns are formed on the pattern forming plate 62A, and images of these slit-shaped opening patterns are formed on the exposure surface of the wafer 5 in FIG. Is projected diagonally to.

FIG. 2A shows the exposure surface of the wafer 5 below the projection optical system 8 of this example, and in FIG.
The reticle 12 of FIG. 1 is placed in a rectangular exposure field 24 that is long in the X direction and that is inscribed in the circular illumination field 23 of the projection optical system 8.
Pattern is exposed, and the wafer 5 is scanned in the Y direction with respect to the exposure field 24. With the multi-point focus position detection system of this example, the exposure field 24
Measurement points AF11 to AF19 in the first row and measurement points AF21 to AF2 in the second row extending in the X direction on the upper side in the Y direction of
9, the measurement points AF31 to AF31 of the third column in the exposure field 24
AF39, measurement points AF41 to AF49 in the fourth row and measurement points AF5 in the fifth row on the lower side of the exposure field 24 in the Y direction.
Images of slit-shaped opening patterns are projected on the first to the AF 59, respectively.

FIG. 2C shows a photodetector 69A of the multi-point focus position detection system of this example. Nine photodetectors 75-11 to 75-19 are arranged on the photodetector 69A in the first column. , And nine light receiving elements 75-12 to 75-59 are also arranged in the second to fifth columns, respectively. That is, a total of 45 light receiving elements are arranged in the light receiver 69A, and a slit-shaped diaphragm (not shown) is provided on each light receiving element.
Are arranged. Also, the light receiving elements 75-11 to 75-11
75-59 on the measuring points AF11 to AF11 of FIG.
The image of the slit-shaped opening pattern projected on the AF 59 is re-formed. Then, the light reflected on the exposed surface of the wafer 5 is rotationally vibrated by a vibration plate corresponding to the rotation direction vibration plate 67 of FIG. 20, so that the position of each image re-formed on the light receiver 69A is stopped. It vibrates in the RD direction which is the width direction of the.

The detection signals of the light receiving elements 75-11 to 75-59 are supplied to the signal processing device 71A, and the signal processing device 7 is operated.
In 1A, the respective detection signals are synchronously detected by the signals of the rotational vibration frequency, so that each measurement point AF11 on the wafer is detected.
~ 45 focus signals corresponding to the focus position of AF 59 are generated, and the tilt angle (leveling angle) and average of the exposure surface of the wafer are averaged from the predetermined focus signal of these 45 focus signals as described later. Calculate the focus position. These measured leveling angle and focus position are supplied to the main control system 22A of FIG. 1, and the main control system 22A passes the drive device 22B and the Z leveling stage 4 based on the supplied leveling angle and focus position. The leveling angle and the focus position of the wafer 5 are set.

Therefore, in this example, the focus positions of all 45 measurement points AF11 to AF59 shown in FIG. 2A can be measured. However, in this example, as shown in FIG. 3, the point at which the focus position is actually measured among these 45 measurement points according to the scanning direction of the wafer (hereinafter,
The position of "sample point" is changed. As an example, as shown in FIG. 3A, in the case where the wafer is scanned in the Y direction with respect to the exposure field 24, and when the division pre-reading as described later is performed, the measurement points in the second row 25B are measured. Of odd-numbered measurement points AF21, AF23, ..., A
F29 and even measurement point A in the exposure field 24
The sampling points are F32, AF34, ..., AF38. In addition, as shown in FIG.
4 when the wafer is scanned in the -Y direction with respect to No. 4 and division pre-reading as described later is performed.
The odd-numbered measurement points AF41, AF43, among the measurement points of D,
, AF49 and even-numbered measurement points AF32, AF34, ..., AF38 in the exposure field 24 are sample points.

Further, since the measurement result of the focus position during slit scan exposure changes sequentially according to the moving coordinate of the stage on the wafer side, the measurement result of the focus position shows the coordinate in the scanning direction of the stage and the non-coordinate. It is stored in the storage device in the main control system 22A of FIG. 1 as a two-dimensional map including the coordinates of the measurement points in the scanning direction. The focus position and the leveling angle of the wafer at the time of exposure are calculated using the measurement results stored in this way. When the Z leveling stage 4 of FIG. 1 is actually driven to set the focus position and the leveling angle of the exposure surface of the wafer, the operation of the Z leveling stage 4 is controlled by open loop control according to the measurement result. In this case, the exposure field 24
In-house exposure is performed. That is, as shown in FIG. 4A, for example, the focus position of the region 26 on the wafer is measured at a predetermined sampling point of the measurement points in the second row 25B, and then as shown in FIG. Area 26 on wafer
When reaches the exposure field 24, focusing and leveling control of the region 26 on the wafer is performed based on the measurement result in FIG.

FIG. 5 shows the Z-leveling stage 4 of this embodiment and its control system. In FIG. 5, the upper surface member of the Z-leveling stage 4 has three fulcrums 28A ...
28C, and each fulcrum 28A-28C.
Each can be expanded and contracted in the focus direction. By adjusting the expansion and contraction amount of each fulcrum 28A to 28C, the focus position of the exposure surface of the wafer 5 on the Z leveling stage 4, the tilt angle θ _{Y in the} scan direction and the tilt angle θ _X in the non-scan direction are set to desired values. Can be set. Height sensors 29A to 29C that can measure the displacement amount of each fulcrum in the focus direction with a resolution of, for example, about 0.01 μm are attached near the fulcrums 28A to 28C. A high-precision mechanism having a longer stroke may be separately provided as a positioning mechanism in the focus direction (Z direction).

In order to control the leveling operation of the Z leveling stage 4, the main control system 22A includes a filter section 30A.
And 30B are supplied with a tilt angle θ _X to be set in the non-scan direction and a tilt angle θ _Y to be set in the scan direction, which are changing every moment. The filter units 30A and 30B supply the inclination angles obtained by filtering with different filter characteristics to the arithmetic unit 31, and the main control system 22A informs the arithmetic unit 31 of the coordinates W of the area to be exposed on the wafer 5.
Supply (X, Y). The calculation unit 31 calculates the coordinates W (X,
Y) and the drive units 32A to 32C based on the two tilt angles.
The information of the displacement amount to be set to is supplied. Each drive unit 32A
.. to 32C are also supplied with information on the current heights of the fulcrums 29A to 29C from the height sensors 29A to 29C, respectively, and the driving units 32A to 32C set the heights of the fulcrums 29A to 29C in the computing unit 31. Set to height.

As a result, the tilt angle in the scan direction and the tilt angle in the non-scan direction of the exposure surface of the wafer 5 are set to desired values, respectively. The level leveling response frequency fm [Hz] is set to be higher than the leveling response speed fn [Hz] in the non-scanning direction. As an example, the leveling response frequency fm in the scan direction is 10 Hz, and the leveling response speed fn in the non-scan direction is 2 Hz.

When the positions where the fulcrums 28A, 28B and 28C are arranged are called driving points TL1, TL2 and TL3 respectively, the driving points TL1 and TL2 are arranged on one straight line parallel to the Y axis, and the driving points TL3 is located on the vertical bisector of the driving points TL1 and TL2. Assuming that the slit-shaped exposure field 24 of the projection optical system is located on the shot area SA _ij on the wafer 5, in this example, the leveling control of the wafer 5 is performed via the fulcrums 28A to 28C. When the shot area SA
The focus position of _ij does not change. Therefore, the leveling control and the focus control are performed separately. The focus position of the exposure surface of the wafer 5 is set by displacing the three fulcrums 28A to 28C by the same amount.

Next, the leveling operation and focusing operation of this example will be described in detail. First, a method of calculating the tilt angle for leveling and the focus position for focusing will be described. (A) Calculation method of tilt angle As shown in FIG. 4, the X coordinate of the m-th sample point in the non-scanning direction is X _m , and the Y-coordinate of the n-th sample point in the scanning direction is Y, at the measurement points in each column. _n is the X coordinate X
The value of the focus position measured at the sample points of the _m and Y coordinates Y _n is represented by AF (X _m , Y _n ). Further, the following calculation is performed with the number of samples in the non-scanning direction as M and the number of samplings in the scanning direction as N. However, the sum operation Σ _m represents the sum of 1 to M regarding the subscript m.

SX = Σ _m X _m , SX2 = Σ _m X _m ² , SMZ = Σ _m AF (X _m , Y _n ), SXZ = Σ _m (AF (X _m , Y _n ) · X _m ) (5 Similarly, the following calculation is performed _assuming that the sum calculation Σ _n represents the sum of 1 to N regarding the subscript n. SY = Σ _n Y _n , SY2 = Σ _n Y _n ² , SNZ = Σ _n AF (X _m , Y _n ), SYZ = Σ _n (AF (X _m , Y _n ) · Y _n ) (6)

Then, the following calculation is performed using the equations (5) and (6). An = (SX · SMZ-M · SXZ) / (SX 2 -M · SX2) (7) Am = (SY · SNZ-N · SYZ) / (SY 2 -N · SY2) (8) Next, each From An, the non-scanning direction (X direction) at the nth sample point in the scanning direction by least square approximation
The tilt angle determine the AL (Y _n), from each Am, obtains the scan direction in the m-th sample point in the non-scanning direction inclination angle (Y-direction) AL (X _m) by least squares approximation. Then, the inclination angle θ _{X in the} non-scan direction and the inclination angle θ _Y in the scan direction are obtained by the following averaging process. θ _X = (Σ _n AL (Y _n )) / N (9) θ _Y = (Σ _m AL (X _m )) (10)

(B) Focus Position Calculation Method The focus position calculation method includes an averaging processing method and a maximum / minimum detection method. In this example, the focus position is calculated by the maximum / minimum detection method. For reference, in the averaging processing method, the focus position <AF> of the entire exposure surface of the wafer 5 is calculated from the following equation using the above-mentioned focus position value AF (X _m , Y _n ). <AF> = (Σ _n Σ _m AF (X _m , Y _n )) / (M · N) (11)

Next, in the maximum / minimum detection method, the focus position AF ′ of the entire exposure surface of the wafer 5 is calculated from the following equation, using the functions representing the maximum value and the minimum value as Max () and Min (), respectively. . AF ′ = (Max (AF (X _m , Y _n )) + Min (AF (X _m , Y _n )) / 2 (12) Then, as shown in FIG.
Reaches the exposure field 24, equation (9),
The detection results θ _X , θ _Y and A of the equations (10) and (12)
Based on F ′, the three fulcrums 28A to 28C in FIG. 5 are driven in an open loop with reference to the measurement results of the height sensors 29A to 29C, respectively. Specifically, the autofocus control is executed by driving the three fulcrums 28A to 28C at the same time, and the autoleveling control is performed by
This is performed so that the focus position in the exposure field 24 shown in FIG. 5 does not change.

That is, in FIG. 5, the exposure field 24
The distance between the center point of X and the fulcrum 28A, 28B in the X direction is X ₁ ,
X ₂ apart in the X direction of the center point and the fulcrum 28C of the exposure field 24, Y ₁ a distance in the Y direction of the center point and the fulcrum 28A of the exposure field 24, Y direction between the center point and the fulcrum 28B of the exposure field 24 _Let Y ₂ be Y ₂ , and based on the result of the inclination angle θ _{X in} the non-scanning direction, the fulcrums 28A, 28B and the fulcrum 28C are respectively displaced in the opposite directions at the ratio of X ₁ : X ₂ to obtain the inclination angle in the scanning direction. Based on the result of θ _Y , displacements in opposite directions are given to the fulcrums 28A and 28B at the ratio of Y ₁ : Y ₂ .

Further, in the above processing method, since the focus position and the tilt angle change every moment according to the exposure apparatus, it is necessary to correct the actual measured value of the focus position. Figure 6
6A shows a state in which the focus position and tilt angle of the entire region 26 on the exposure surface 5a of the wafer are measured at a measurement point (AF point) at a certain focus position, and FIG.
In the state of (a), the driving amounts <TL1>, <TL in the focus direction of the fulcrums at the driving points TL1 to TL3 in FIG.
2> and <TL3> are 0 (reference position). Then, when the area 26 reaches the exposure point in the exposure field as shown in FIG. 6B, the drive amounts for the exposure are <TL1> = a,
<TL2> = b and <TL3> = c are set. In this case, the focus position of the area 26A measured at the focus position measurement point (AF point) changes by ΔF as compared with the case of FIG. 6A, but the amount of change in ΔF is Since the influence of the driving amount at the driving points TL1 to TL3 is included, when the area 26A is exposed next,
It is necessary to perform leveling and focusing in such a manner that the drive amounts of the drive points TL1 to TL3 in the state of FIG. 6B are corrected.

That is, the focus position measured in the area 26, the tilt angle in the X direction and the tilt angle in the Y direction are set as F ₁ , θ _1X and θ _1Y , respectively, and the focus position measured in the area 26A and the tilt in the X direction. The angle and the inclination angle in the Y direction are F _n ′, θ _nX ′, and θ _nY ′, respectively. In addition, X between the focus point measurement point (AF point) and the exposure point
If the distances in the Y direction and the Y direction are ΔX and ΔY, respectively, the correction amount ΔF1 of the focus position is as follows. ΔF1 = −F ₁ −θ _1X · ΔX−θ _1Y · ΔY (13)

Using the correction amount ΔF1, the area 26A
Measured focus position, tilt angle in X direction
And the corrected value F of the tilt angle in the Y direction_n, Θ_nXOver
And θ _nYIs as follows. F_n= F_n′ + ΔF1 (14) θ_nX= Θ_nX′ −θ_1X    (15) θ_nY= Θ_nY′ −θ_1Y    (16) In addition, for the high-frequency uneven surface of the exposed surface of the wafer 5,
It is necessary to manage responsiveness so as not to comply. That is,
Corresponds to the stage position even if the scanning speed of c
The measured focus position
And the tilt angle for the fast Fourier transform (FFT)
It is managed by Luther or three fulcrums 28A to 28C in FIG.
A mechanism that can change the servo gain of the drive unit according to the speed
To However, the numerical filter for FFT is a spare scan.
This is because the servo gain has a phase delay.
A mechanism that takes these into consideration is required.

(C) Variable Servo Gain Method Here, an example of a method of varying the servo gain of the drive unit of the three fulcrums 28A to 28C in FIG. 5 according to the speed will be described. When the response frequency when the wafer scanning speed is V / β is ν, the transfer function G (s) is expressed as follows. G (s) = 1 / (1 + Ts) (17) However, T = 1 / (2πν) and s = 2πfi.

From the analysis result, the scanning speed V / β is 80 mm.
In the case of / s, it was found that the optimum response frequency ν in the non-scan direction is 2 Hz, and the optimum response frequency ν in the scan direction is 10 Hz. However, if the unevenness of the exposure surface of the wafer is represented by a sine wave with a pitch p and the length of each shot area on the wafer in the scanning direction is L ₀ , the frequency f in equation (17) is as follows. f = (V / β) / L ₀ · (L ₀ / p) = (V / β) / p (18) Therefore, when the scanning speed V / β changes, the frequency f also changes, so the optimum response frequency ν Needs to be newly requested. The servo gain is determined from the response frequency ν thus obtained.

(D) Numerical filtering method Since the pitch p of the irregularities on the exposure surface of the wafer is a function depending on the stage position, if the sampling of the focus position is performed in synchronization with the stage position on the basis of the position, the scanning speed is Control that does not depend on V / β becomes possible. That is, in order to give the position function a filtering effect equivalent to that of the transfer function G (s), the transfer function G (s) is subjected to inverse Fourier transform to obtain the position function F (x), and this position function F (x ) Is used to perform numerical filtering. Specifically, FIG. 7A shows an example of the transfer function G (s) of the response frequency ν, and FIG. 7B shows the corresponding position function F (x). However, it is necessary to keep the run-up scan distance at the time of numerical filtering, and if this is not done, a phase delay occurs.

In any of the above-mentioned variable servo gain method and numerical filtering method, the responsiveness is managed by the phase delay and the filtering effect. The phase delay (time delay) is between the signal corresponding to the target focus position shown by the curve 37A in FIG. 15C and the signal corresponding to the actually measured focus position shown by the curve 38A. It is a time delay that exists in. The filtering effect is the curves 37B and 38B of FIG.
As shown by, the amplitude of the actual focus position is reduced by a predetermined amount with respect to the target focus position.

As described above, in this example, the preliminary scan, which is a preliminary scan, may be performed when exposing each shot area of the wafer. Therefore, a method of setting the run-up scan distance will be described. FIG. 8A shows a scanning method in the case where after the exposure of the shot area SA ₁₁ on the wafer is completed, the reticle pattern is sequentially exposed to the adjacent shot areas SA ₁₂ and SA ₁₃ . In FIG. 8A, the wafer is scanned in the −Y direction, and after the exposure to the shot area SA ₁₁ on the wafer is completed, the acceleration / deceleration period T
_The wafer is moved obliquely with respect to the X axis and the Y axis during _W1 , and the vicinity of the lower end of the next shot area SA ₁₂ is arranged in the exposure field of the projection optical system. First shot area SA
_After the exposure to ₁₁ is completed, while moving to the vicinity of the lower end of the next shot area SA ₁₂ , the distance ΔL is moved in the Y direction. At the end of the acceleration / deceleration period T _W1 , the movement of the wafer in the Y direction is started.

Subsequent establishment (settlement) period T_W2In between
The scanning speed of the stack reaches almost V / β, and the exposure period that follows
Interval T_W3Shot area SA between₁₂Reticle putter to
Exposure is performed. Acceleration / deceleration on the wafer side in this case
Period T_W1, Enactment period T_W2And exposure period T_W3Figure 8 (c)
Shows the acceleration / deceleration period T on the reticle side._R1, Enactment period T _R2
And exposure period T_R3Is shown in FIG. Note that the reticle
On the side, it moves to the adjacent shot area as shown in FIG.
Since there is no need to move the stage, the stage movement on the reticle side is Y
It is a reciprocating motion along. On the wafer side, as shown in FIG.
As shown in (c), the acceleration / deceleration period T_W1From enactment period T_W2
Time point at which the transition to_sFrom the multi-point focus position detection
Sampling of the focus position by the output system is started
It

In this example, the responsiveness at the time of leveling and focusing is controlled by the phase delay and the filtering effect, so that the starting point when sampling the focus position on the wafer differs depending on the situation. For example, assuming that sampling is synchronized with the stage position and numerical filtering is performed, the sampling start position is determined by the following procedure.

First, as shown in FIG. 7A, the transfer function G
(S) is given, the position function F (x) of FIG. 7 (b) is obtained from the transfer function G (s) by the inverse Fourier transform, and the length from the origin of this position function F (x) to the zero cross point ΔL
Ask for. This length ΔL is, as shown in FIG.
It is equal to the amount of movement ΔL in the Y direction when moving diagonally for exposure to the adjacent shot area SA ₁₂ .

Since the wafer acceleration / deceleration period T _W1 is smaller than the reticle acceleration / deceleration period T _R1 , the time (T _R1
-T _W1 ) is the waiting time on the wafer side. In this case, ΔL
When <(V / β) (T _R1 −T _W1 ), the throughput does not decrease, but ΔL> (V / β) (T _R1 −T _W1 ),
When, the throughput is reduced. Note that ΔY = ΔL
Even if the length ΔY represented by − (V / β) (T _R1 −T _W1 ) is processed as a phase delay, a fixed function may be used as long as a filtering effect similar to that of the transfer function G (s) can be obtained. .
By performing these filterings, an effect of reducing air fluctuations in the multipoint focus position detection system and the influence of control error of the multipoint focus position detection system can be expected.

Next, the arrangement of the sample points in the measurement points of the multipoint focus position detection system in the slit scan exposure type projection exposure apparatus of this example will be examined. First, FIG.
In (a), when using the measurement result of the focus position of the measurement points AF31 to AF39 in the slit-shaped exposure field 24 among the measurement points AF11 to AF59 by the multipoint focus position detection system, that is, the measurement points AF31 to AF.
When 39 is set as the sample point, the control by the "exposure position control method" similar to that of the conventional stepper is performed. Furthermore, since the wafer is scanned in the Y direction or the -Y direction in this example, by placing the sample in the measurement point before the exposure field 24 in the scanning direction, the prefetch control, the time-division leveling measurement, Also, it becomes possible to average measured values.

Pre-reading control means that when the wafer is scanned in the -Y direction with respect to the exposure field 24 as shown in FIG.
This means selecting a sample point from among AF51 to AF59. By performing prefetch control, the transfer function G of the autofocus mechanism and the autoleveling mechanism
For (s), the tracking error with respect to the actual response frequency is | 1-G (s) |. However, since this tracking error includes a phase delay and a filtering error factor, the phase delay can be removed by performing prefetch control.
Since this error is 1- | G (s) |

FIG. 9A shows a curve 39A corresponding to a target focus position and a curve 38B corresponding to an actually set focus position when the exposure position control similar to the conventional one is performed. b) is a curve 40A corresponding to the target focus position and a curve 40 corresponding to the actually set focus position when the prefetch control is performed.
B is shown, and the phase is shifted in the exposure position control. Therefore, in the case of exposure position control, the difference F between the target position and the following position is
a is a difference F between the target position and the follow-up position in the prefetch control.
It is about 4 times b. Therefore, the read-ahead control can provide a transmission capacity about four times.

However, as described above, the response frequency of the auto-leveling is appropriately about 10 Hz in the scanning direction (in the position control method), so if pre-reading control is performed, a filtering response of about 2.5 Hz in the scanning direction will suffice. It will be. If this filtering is performed with a numerical filter or control gain, the wafer scanning speed will be 80 m.
As m, a run-up scan length of about 5 (≈80 / (2π * 2.5)) mm is required before exposure. Below are both control methods,
Indicates focus error.

Therefore, as in the case of FIG. 17, the period of periodic bending of the shot area SA _ij on the wafer in the scanning direction is represented by the bending parameter F as a value of the ratio to the width in the scanning direction, and the period is shown. The focus error at each measurement point when there is a specific bend is represented by the sum of the absolute value of the average value of the errors of the focus position at each measurement point and 1/3 of the amplitude of the error of the focus position. In addition, the amplitude of the periodic bending of the bending parameter F is standardized to 1, and when the bending parameter is F, the error parameter S indicating the maximum value of the focus errors at those measurement points is set to the bending parameter F. It is expressed as a ratio to.

FIG. 10A shows a case where the exposure position control is performed and the leveling response frequency fm in the scanning direction.
Represents the error parameter S with respect to the bending parameter F in the case where the leveling response frequency fn in the non-scan direction is 2 Hz, the curves A9 and B9 are both the error parameter S in the non-scan direction, and the curves A10 and B10 are both the scan direction. The error parameter S at is shown. on the other hand,
FIG. 17B shows a case where the prefetch control is performed and the leveling response frequency fm in the scan direction is 2.5 Hz.
The leveling response frequency fn in the non-scan direction is 0.5.
The error parameter S with respect to the bending parameter F in the case of Hz is shown. The curves A11 and B11 both show the error parameter S in the non-scan direction, and the curves A12 and B12 both show the error parameter S in the scan direction.

As described above, removing the phase delay by the prefetch control is good for improving the response, but not suitable for reducing the response. However, the prefetch control has a high degree of freedom in terms of software, and it is also possible to perform temporal averaging as shown in FIG. 11 and predictive setting of the focus point measurement point at the start of exposure. That is, in FIG. 11A, at a sample point (AF point) in front of a certain region 26B on the exposure surface 5a of the wafer with respect to the scanning direction of the multipoint focus position detection system, the width of the width ΔL. Only the focus position is detected. Then, as shown in FIG. 11B, when the area 26B reaches the exposure point, the information of the focus position detected in the range of the width ΔL is averaged to perform the leveling and focusing with high accuracy.

Further, as shown in FIG. 11C, in the case where the measurement point and the exposure point are the same in the exposure position control method, even if there is a step 26C on the exposure surface 5a of the wafer, FIG. As shown in, the surface to be focused (focus surface)
The AFP only gradually rises, and the stepped portion 26C is exposed in a defocused state. On the other hand, as shown in FIG. 11E, when the measurement point and the exposure point are separated by the look-ahead control method and the step portion 26D is present on the exposure surface 5a of the wafer, the step portion 26D is adjusted to the step in advance. Figure 11
As shown in (f), by gradually raising the focus surface AFP, exposure is performed in a focused state at the step portion 26D.

It is desirable to provide a normal exposure position control method in addition to the pre-reading control method and to make the system selectable from the two control methods. Since the auto focus and auto leveling mechanism of this example has the functions as described above, in order to actually control the exposure surface of the wafer,
Three types of control methods are conceivable: exposure position control, complete prefetch control, and division prefetch control. Below these 3
The type of control method will be described in detail. (F) Exposure position control method In this method, the focus position and leveling of the exposure surface of the wafer are used by using the value of the focus position obtained by measurement at the time of exposure without considering the response performance of the autofocus and autoleveling mechanism. Control the corners. That is, FIG.
As shown in FIG. 2A, the even-numbered measurement points of the second row 25B on the front side in the scanning direction (Y direction) with respect to the exposure field 24 are set as sample points 41 and the third row 25C in the exposure field 24 is used. The odd-numbered measurement points of are also sample points. Then, the leveling control in the scan direction of the exposure surface of the wafer is performed based on the measured value of the focus position at the sample point of the second row 25B and the measured value of the focus position at the sample point of the third row 25C.

Further, the inclination in the non-scanning direction is obtained from the measured values of the focus positions at the sample points in the second row 25B and the third row 25C by the least square approximation method, and the leveling control in the non-scanning direction is performed. The focus control is also performed using the measurement value of the focus position at the measurement point of the third column in the exposure field 24. Note that FIG.
As shown in (b), when the wafer scanning direction is the -Y direction, the sample points are selected from the measurement points in the third row 25C and the fourth row 25D. This method is the easiest to control, but has the disadvantage that the tracking accuracy changes depending on the wafer scanning speed and the like. Also, the second
It is necessary to calibrate the focus position at each measurement point on the row 25B and the third row 25C.

(G) Complete prefetch control method In this method, as shown in FIG. 12C, all the measurement points in the first row 25A on the front side in the scanning direction with respect to the exposure field 24 are used as sample points. Pre-exposure first row 2
All the values of the focus position at the sample points of 5A are measured. Then, the averaging process and the filtering process are performed, and the autofocus and autoleveling mechanisms are openly controlled at the time of exposure in consideration of the phase delay. That is, the measured value of the focus position at each sample point in the first row 25A is stored, the tilt in the scan direction is calculated from the value of the focus position measured on the time axis, and the leveling control in the scan direction is performed during exposure. With open control.

At the same time, the inclination in the non-scanning direction is obtained from the measurement value of the focus position at each sample point in the first row 25A by the least square approximation method, and the leveling control in the non-scanning direction is performed by the open control. Since it is read ahead, averaging on the time axis is also possible. In addition, the measured value of the focus position at each sample point of the first row 25A is stored, and the focus adjustment is performed by the open control during the exposure. In addition,
As shown in FIG. 12D, when the wafer scanning direction is the −Y direction, all the measurement points in the fifth row 25E are selected as sample points.

In this system, nine sample points can be secured in the first column 25A, so that the amount of information is large and the accuracy can be improved. Further, since the sample point is one line, there is an advantage that calibration is unnecessary and responsiveness can be managed. On the other hand, if the sample points in the first row 25A are properly measured, the distance (running scan length) to be scanned in order to perform the exposure of the end of each shot area becomes long, which causes a problem of reduced throughput. Further, since it is an open control, there is a disadvantage that it cannot be confirmed by the multipoint focus position detection system.

(H) Division prefetch control method In this method, as shown in FIG. 12E, odd-numbered measurement points in the second row 25B on the front side in the scanning direction (Y direction) with respect to the exposure field 24. Is set as a sample point, and even-numbered measurement points in the third column 25C in the exposure field 24 are also set as sample points. And the second row 25B and the third row 2
At the sample point of 5C, all focus position values are measured in advance before exposure. After that, the averaging process and the filtering process are performed, and the control is performed by the open control at the time of exposure in consideration of the phase delay. That is, the second row 25B and the third row
The measured value of the focus position at the sample point of the column 25C is stored, the tilt in the scan direction is calculated from the value of the focus position measured on the time axis, and the leveling in the scan direction is performed by the open control during exposure.

Further, the inclination in the non-scanning direction is obtained from the measurement values of the focus positions at the sample points in the second row 25B and the third row 25C by the least square approximation method, and the leveling in the non-scanning direction is performed by the open control. Since it is read ahead, averaging on the time axis is also possible. Further, the measured values of the focus positions at the sample points of the second row 25B and the third row 25C are stored, and the focus adjustment is performed by the open control during the exposure. As shown in FIG. 12F, when the wafer scanning direction is the −Y direction, the sample points are selected from the measurement points in the third row 25C and the fourth row 25D.

In this method, since the second row 25B (or the fourth row 25D) is close to the exposure field 24, it is possible to reduce the run-up scan distance for exposing the end portion of each shot area of the wafer. The advantage is that responsiveness can be managed. Further, it is possible to confirm the result of controlling the exposure surface by the open control from the measured value of the focus position at the sample point of the third row 25C at the time of exposure. On the other hand, there is an inconvenience that it is necessary to calibrate the focus position at the sample point of the second row 25B and the focus position at the sample point of the third row.

Further, in the complete prefetch control method, as shown in FIG.
As shown in (a) to (d), more accurate autofocus and autoleveling control are performed by changing the sample points of the focus position at the start of exposure, during exposure, and just before the end of exposure. That is, as shown in FIG. 13A, the shot area SA to be exposed is the exposure field 2
4 when the distance D (the same as the width of the exposure field 24 in the scanning direction) is reached.
The measurement of the focus position by the multi-point focus position detection system is started in the sample area 42 at the interval D from 4. An example of the width D, that is, the width of the exposure field 24 in the scanning direction is 8 mm. After that, as shown in FIG.
When the tip of the shot area SA contacts the exposure field 24, the detection area 4 between two sample points on the wafer
The leveling control in the scanning direction is performed based on the measured value of the focus position in No. 4, and the autofocus control is performed based on the measured value of the focus position in the detection area 45 formed of one sample point.

Next, as shown in FIG. 13C, when the tip of the shot area SA enters the exposure field 24, the focus position of the focus area in the detection area 44 between two sample points on the wafer is changed. Leveling control in the scanning direction is performed based on the measured value, and autofocus control is performed based on the measured value of the focus position in the detection area 45 between the two sample points. Further, as shown in FIG. 13D, when the shot area SA covers the exposure field 24, leveling control in the scanning direction is performed based on the measurement value of the focus position in the detection area 44 covering the exposure field 24. Then, the autofocus control is performed based on the measurement value of the focus position in the detection area 45 that covers the exposure field 24.

On the other hand, even in the division prefetch control method, FIG.
As shown in (e) to (h), more accurate autofocus and autoleveling control are performed by changing the sample points of the focus position at the start of exposure, during exposure, and just before the end of exposure. That is, as shown in FIG. 13E, the shot area SA to be exposed is the exposure field 2
4 at a distance D / 2 (1/2 of the width of the exposure field 24 in the scanning direction), the sample area 43A at a distance D / 2 from the exposure field 24 and the inside from the exposure field 24. Then, the measurement of the focus position by the multipoint focus position detection system is started in the sample area 43B at the interval D / 2. Then, as shown in FIG. 13F, when the tip of the shot area SA contacts the exposure field 24, leveling in the scanning direction is performed based on the measurement value of the focus position in the detection area 46 covering the exposure field 24. The control is performed, and the autofocus control is performed based on the measurement value of the focus position in the detection area 47 including one sample point.

Next, as shown in FIG. 13G, when the front end of the shot area SA enters the exposure field 24 by the width D / 2, the detection area 46 that covers the exposure field 24.
The leveling control in the scanning direction is performed on the basis of the measured value of the focus position at, and the autofocus control is performed on the basis of the measured value of the focus position in the detection area 47 having the width D / 2. As shown in FIG. 13 (h), when the shot area SA covers the exposure field 24, leveling control in the scanning direction is performed based on the measurement value of the focus position in the detection area 46 covering the exposure field 24. Detection area 47 covering the exposure field 24
The autofocus control is performed based on the measured value of the focus position in. From FIG. 13, in the split look-ahead method, the run-up scan length (= D / 2) is 1 / th compared to that in the complete look-ahead method.
You can see that it can be 2.

In the above embodiment, in order to measure the focus positions of multiple points on the exposure surface of the wafer, the multi-point focus positions for projecting the two-dimensionally arranged slit-shaped opening pattern images on the wafer. A detection system is used. However, instead, a one-dimensional focus position detection system is used, which projects an image of a slit-like pattern elongated in the non-scan direction onto the wafer and measures the overall focus position in the non-scan direction. Is also good. Further, even when the two-dimensional focus position distribution on the exposure surface of the wafer is measured by using the focus position detection system of the image processing system, by applying the division prefetch similar to the above-described embodiment, Accurate focusing and leveling can be performed. Furthermore, in this example, as shown in FIG.
As can be seen, since the leveling error in the scanning direction is smaller than the leveling error in the non-scanning direction, the leveling operation in the non-scanning direction may be performed without performing the leveling operation in the scanning direction.

The present invention is not limited to the above embodiment,
Of course, various configurations can be adopted without departing from the scope of the present invention.

[0097]

According to the present invention, in the slit scan exposure type projection exposure apparatus, the exposure surface of the photosensitive substrate can be accurately aligned with the image plane of the projection optical system. Further, according to the embodiment, in the slit scan exposure type projection exposure apparatus, the exposure surface of the photosensitive substrate is corrected by correcting the unevenness of the surface of the photosensitive substrate, the measurement accuracy of the multipoint measuring means, the error due to air fluctuation, etc. Has the advantage that it can be aligned in parallel with the image plane of the projection optical system with high accuracy.

Further, when the multipoint measuring means samples the height of the photosensitive substrate at a plurality of measurement points on the basis of the position of the substrate side stage while the photosensitive substrate is being scanned through the substrate side stage, The tilt angle in the scanning direction can be measured with higher accuracy. In addition, the multi-point measuring means is arranged in a region in front of which the photosensitive substrate is scanned with respect to a plurality of points in an exposure region which is conjugate with respect to the illumination region of a predetermined shape and the projection optical system and the conjugate exposure region. When measuring the height of the photosensitive substrate at each of a plurality of measurement points, there is an advantage that the run-ahead scan distance at the start of exposure can be shortened by the division pre-reading control.

When the multipoint measuring means sequentially changes the positions of a plurality of measuring points in the process of sequentially exposing the pattern of the mask onto one shot area of the photosensitive substrate, for example, division pre-reading and complete pre-reading are performed. By using together, it is possible to improve both the leveling accuracy and the throughput. Further, according to the embodiment, in the slit scan exposure type projection exposure apparatus, the exposure surface of the photosensitive substrate is corrected by correcting the unevenness of the surface of the photosensitive substrate, the measurement accuracy of the multipoint measuring means, the error due to air fluctuation, etc. There is an advantage that the focus position of can be accurately aligned with the image plane of the projection optical system.

[Brief description of drawings]

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

FIG. 2A is a plan view showing a two-dimensional slit-shaped aperture pattern image projected on a region including an exposure field by a projection optical system in the embodiment, and FIG. 2B is a multi-point focus position detection system. FIG. 3 is a diagram showing an opening pattern on a pattern forming plate, and FIG. 3C is a diagram showing an arrangement of light receiving elements on a light receiver.

FIG. 3A is a diagram showing sample points when division prefetch is performed in the embodiment, and FIG. 3B is a diagram showing sample points when scanning in the reverse direction and division prefetch is performed.

FIG. 4A is a diagram showing a case where a focus position is read ahead, and FIG. 4B is a diagram showing a case where exposure is performed using the read focus position.

FIG. 5 is a configuration diagram showing an auto-focus and auto-leveling mechanism and a control unit thereof according to the embodiment.

FIG. 6 is an explanatory diagram of a correction method of a focus position measurement value.

7A is a diagram showing a transfer function when the response frequency ν is 10 Hz, and FIG. 7B is a diagram showing a position function obtained by inverse Fourier transforming the transfer function of FIG. 7A. .

8A is a diagram showing a trajectory of a wafer when exposing adjacent shot areas, FIG. 8B is a timing chart at the time of scanning a reticle, and FIG. 8C is a timing chart at the time of scanning a wafer. .

FIG. 9A is a diagram showing tracking accuracy when performing leveling and focusing by the exposure position control method, and FIG. 9B is a diagram showing tracking accuracy when performing leveling and focusing by the look-ahead control method.

10A is a diagram showing a calculation result of an error parameter S with respect to the bending parameter F when the exposure position control method is used, and FIG. 10B is an error parameter S with respect to the bending parameter F when the prefetch control method is used. It is a figure which shows the calculation result of.

11A and 11B are explanatory diagrams of an averaging effect in the prefetch control method, FIGS. 11C and 11D are diagrams showing a focus surface when exposure position control is performed, and FIGS. 8A is a diagram showing a focus surface in the case of performing prefetch control. FIG.

12A and 12B are plan views showing sample points of a focus position when performing exposure position control, and FIGS. 12C and 12D show sample points of a focus position when performing complete prefetch control. FIGS. 6E and 6F are plan views showing sample points at the focus position when division prefetch control is performed.

13A to 13D are explanatory diagrams of a control method in the case of performing exposure by the complete prefetch control method, and FIGS. 13A to 13H are explanatory views of a control method in the case of performing exposure by the divided prefetch control method. It is a figure.

FIG. 14A is a diagram showing a focus error when performing a batch exposure, and FIG. 14B is a diagram showing a focus error when performing exposure by a slit scan exposure method.

FIG. 15A is a diagram showing a focus error in the case of performing the autofocus control by using the maximum value and the minimum value of the measurement values, and FIG. 15B is a case in which the autofocus is performed by using the average value of the measurement values. Is a diagram showing the focus error of FIG. 6, (c) is a diagram showing a time delay error, and (d) is a diagram showing a change in servo gain.

FIG. 16 is a plan view showing a state in which a shot area on a wafer is exposed in a slit-shaped exposure field.

17A is a diagram showing a calculation result of an error parameter S with respect to a bending parameter F in the case where leveling control is performed by making the response frequency in the scan direction equal to the response frequency in the non-scan direction, FIG. It is a figure which shows the calculation result of the error parameter S with respect to the bending parameter F when leveling control is performed by making the response frequency in the scan direction higher than the response frequency in the non-scan direction.

FIG. 18 (a) is a diagram showing a state in which auto focus control is performed using an average value of focus positions, and FIG. 18 (b) is a state in which auto focus control is performed using an average value of maximum and minimum values of focus positions. FIG.

19A is a diagram showing a calculation result of an error parameter S with respect to a bending parameter F when autofocus control is performed by averaging processing in the state of FIG. 17A, and FIG. It is a figure which shows the calculation result of the error parameter S with respect to the bending parameter F at the time of performing autofocus control using the average value of the maximum value and minimum value of a focus position further in the state of b).

FIG. 20 is a configuration diagram showing a multipoint focus position detection system in a conventional stepper.

21A is a plan view showing a two-dimensional slit-shaped aperture pattern image projected onto an area including an exposure field by the projection optical system in FIG. 20, and FIG. 21B is a multipoint focus position of FIG. FIG. 21 is a diagram showing an opening pattern on the pattern forming plate of the detection system, and FIG. 21C is a diagram showing an arrangement of light receiving elements on the light receiver of FIG. 20.

[Explanation of symbols]

2 Wafer Y-axis drive stage 4 Z leveling stage 5 wafers 8 Projection optical system 10 Reticle Y drive stage 12 reticle 22A Main control system 24 Slit-shaped exposure field 62A pattern forming plate 69A light receiver 71A signal processing device AF11 to AF59 measurement points

Continuation of the front page (56) Reference JP-A-4-277612 (JP, A) JP-A-4-215015 (JP, A) JP-A-63-255917 (JP, A) JP-A-5-275313 (JP , A) JP 4-196513 (JP, A) JP 2-198130 (JP, A) JP 2-102518 (JP, A) JP 1-170022 (JP, A) JP 5-62871 (JP, A) JP-A-4-354320 (JP, A) JP-A-4-350925 (JP, A) JP-A-3-256317 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01L 21/027 G03F 7/20

Claims (13)

(57) [Claims] 1. The substrate is scanned and moved in a second direction with respect to an exposure beam that has passed through a projection optical system in synchronism with scanning and movement of a mask in the first direction with respect to the exposure beam. In a projection exposure apparatus for scanning and exposing a substrate, measuring means for measuring focus position information on a partial area on the substrate, and surface setting means for setting the surface position of the substrate based on the focus position information measured by the measuring means. And the surface setting means is configured such that when the partial area on the substrate reaches the irradiation area of the exposure beam that has passed through the projection optical system, the partial area is exposed in the focused area so that the partial area is exposed. The projection exposure apparatus is characterized in that the surface position of the substrate is gradually moved based on the measured focus position information before reaching. 2. The projection exposure apparatus according to claim 1, wherein the measuring unit has a detection point for detecting the focus position information on an area apart from the irradiation area. 3. The projection exposure apparatus according to claim 2, wherein the measuring unit has the detection point on an area distant from the irradiation area in the scanning direction. 4. The projection exposure apparatus according to claim 3, wherein the measuring unit has the detection points on a plurality of areas that are apart from the irradiation area in the scanning direction. 5. The projection exposure apparatus according to claim 2, wherein a plurality of the detection points are arranged apart from each other in a direction intersecting with the scanning direction. 6. The projection exposure apparatus according to claim 2, wherein the detection point is also provided in the irradiation area. 7. The projection exposure apparatus according to claim 2, wherein the detection points are arranged two-dimensionally. 8. The substrate is scanned and moved in a second direction with respect to the exposure beam that has passed through the projection optical system in synchronization with the scanning and movement of the mask in the first direction with respect to the exposure beam. In the projection exposure method of scanning exposure, the focus position information about the partial area on the substrate is measured, and when the partial area on the substrate reaches the irradiation area of the exposure beam that has passed through the projection optical system, the focus state is achieved. Projection exposure method, wherein the surface position of the substrate is gradually moved based on the measured focus position information before the partial region reaches the irradiation region. 9. The projection exposure method according to claim 8, wherein the focus position information is detected at a detection point on an area away from the irradiation area. 10. The projection exposure method according to claim 9, wherein the detection point is provided on an area distant from the irradiation area in the scanning direction. 11. The projection exposure method according to claim 10, wherein the detection points are provided on a plurality of areas apart from the irradiation area in the scanning direction. 12. The projection exposure method according to claim 9, wherein a plurality of the detection points are arranged apart from each other in a direction intersecting with the scanning direction. 13. A device manufacturing method using the projection exposure method according to claim 8.