JPH10270300A - Scanning exposure method and equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable scanning exposure wherein, when unevenness change in the surface of a region of an exposure object is sharp, throughput is not decreased, and the surface of the region is made to accurately match with an image surface. SOLUTION: Measurement regions 15F, 15R of a focus position are set, by isolating sections 16F, 16R having a specified width in the scanning direction, from a slit-type irradiation field 3. When scanning exposure is performed to the shot region of a wafer, the shot region is covered with, e.g. the measurement region 15F, at the approach start point of the wafer. At detection points P11 -P53 in the measurement region 15F, the focus position of the surface in the short region is measured. On the basis of the measured result, the controlled variable of surface position of the wafer for making the wafer surface in the irradiation field 3 matches with an image surface at the time of scanning exposure by using an autofocus system and an auto-leveling system is determined.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used for transferring a mask pattern onto a substrate in a lithography process for manufacturing, for example, a semiconductor device, an image pickup device (such as a CCD), a liquid crystal display device, or a thin film magnetic head. More specifically, a scanning exposure method such as a so-called step-and-scan method of transferring a mask pattern onto a substrate by synchronously moving a mask and a substrate with respect to a projection optical system, and an exposure method and apparatus. Related to the device.

[0002]

2. Description of the Related Art When manufacturing a semiconductor device or the like, a reticle as a mask and a wafer coated with a resist are synchronized with a projection optical system together with a batch exposure type projection exposure apparatus such as a conventional stepper. A step-and-scan projection exposure apparatus capable of exposing a shot area wider than the effective field of the projection optical system by moving the projection optical system is being used. Similar to the batch exposure type projection exposure apparatus, in a scanning exposure type projection exposure apparatus such as a step-and-scan method, in order to transfer a fine circuit pattern at a high resolution, the wafer is subjected to an auto focus method. It is necessary to adjust the surface to the image plane of the projection optical system.

However, in a scanning exposure type, the surface of a wafer is continuously scanned relative to, for example, a slit-shaped projection area (hereinafter, referred to as an “illumination field”) of a reticle pattern. Therefore, in addition to the method of measuring the focus position (the position in the optical axis direction of the projection optical system) at a predetermined detection point in the illuminated field, the detection point on the near side in the scanning direction with respect to the illuminated field is also used. There has also been proposed a method of pre-reading the focus position and adjusting the surface of the wafer in the illumination field to the image plane based on the focus position information.

FIG. 11 is a view for explaining exposure on a wafer by a conventional step-and-scan type projection exposure apparatus. In FIG. 11, at the start of exposure, a slit-shaped illumination field 52 is provided. Is at the approach start position on the near side with respect to the shot area 51 to be exposed on the wafer. Thereafter, the approaching of the illuminated field 52 is started along the trajectory indicated by the arrow 53, and the reticle pattern image is transferred to the shot area 51 by relatively scanning the shot area 51 with the illuminated field 52. Although the wafer side actually moves via the wafer stage with respect to the fixed illumination field field 52, the illumination field field 52 is shown to move with respect to the wafer for convenience of explanation. The exposure light is emitted after the illumination field 52 has hit the shot area 51.

In the method of performing pre-reading during the scanning exposure,
Using a predetermined autofocus sensor, the focus position is continuously measured at the detection points 54A to 54E in the illuminated field 52, and the detection in the pre-reading area on the near side in the scanning direction with respect to the illuminated field 52 is performed. Points 55A-55
Also at C, the focus position is continuously measured. Then, based on the measurement results of these focus positions, the auto-focusing is performed such that the surface of the wafer in the illuminated field 52 is adjusted to the image plane in a form including the predictive control continuously from the approach start position. The operation is performed in a servo manner.

At this time, when the shot area 51 is located, for example, near the edge of the wafer, the detection point of the focus position is located outside the wafer at the start position of the approach, or the shot area 51 is located on a region with significant unevenness near the edge of the wafer. May be. In this case, for example, the wafer stage is driven to return the focus position detection point to a flat area on the wafer, and the run-up is performed with the wafer surface position locked based on the measured focus position. I was

[0007]

In the conventional scanning exposure type projection exposure apparatus as described above, at the time of starting the exposure,
The Teruno field is not on the shot area to be exposed but at the approach start position just before the shot area. Therefore, in the method in which the focus position is measured only at the detection point in the illuminated field and the autofocus is performed, if the shot area has a step, the focusing operation cannot follow up. May occur.

Also, in the method of performing the autofocus operation while performing the prediction control using the prefetching together, if the surface irregularities of the shot area to be exposed change rapidly,
In some cases, it is impossible to follow the servo system due to, for example, a mechanical response speed. In particular, in the case of performing exposure by relatively scanning the illumination field from the outside of the wafer with respect to the chipped shot area near the edge of the wafer, accurate follow-up control is performed because the unevenness near the edge is drastic. It is difficult, and it is easy to cause exposure in a defocused state.

To avoid these problems, it is conceivable to measure the distribution of focus positions in the shot area to be exposed prior to scanning exposure. However, since the detection range of the conventional autofocus sensor is within the illuminated field or within a region of a predetermined width in the scanning direction centered on the illuminated field, it is necessary to measure the distribution of the focus position in the shot region. For this, it is necessary to move the position of the wafer stage from the approach start point to a position where the focus position can be measured in the shot area. Therefore,
A series of operations such as pre-measurement of the focus position by moving the wafer stage for each shot area, start of approach, and scanning exposure must be repeated, resulting in a disadvantage that the throughput (productivity) of the exposure process is reduced. .

The present invention has been made in view of the above-described circumstances, and when exposing a wafer while performing a focusing operation, even if the unevenness of the surface of the area to be exposed is abruptly changed, the area can be reduced without lowering the throughput. It is an object of the present invention to provide a scanning exposure method capable of accurately adjusting the surface of the image to the image plane. Another object of the present invention is to provide a scanning exposure apparatus capable of performing the scanning exposure method.

[0011]

According to the scanning exposure method of the present invention, a mask (R) and a substrate (W) are synchronously moved to form an image of a pattern of the mask on a projection optical system (PL). in the scanning exposure method for exposing to the substrate via at run-up start position of the substrate, the future position of the optical axis of the projection optical system at a plurality of positions of the substrate surface to be exposed (P ₁₁ ~P ₅₃₎ During the scanning exposure of the substrate, the surface position of the substrate surface is set based on the measured position in the optical axis direction.

According to the present invention, the distribution of the position (focus position) in the optical axis direction on the surface of the region to be exposed can be measured without moving the substrate from the scanning start start position. From the result, surface shape information such as an average focus position and an inclination angle of each part of the area can be obtained. Therefore, before starting the scanning exposure, it is determined how much the surface position of the substrate should be controlled in accordance with the position of the substrate during the scanning exposure so that the surface of the exposure target area can be adjusted to the image plane. Therefore, even when the surface irregularities change rapidly, the surface can be accurately adjusted to the image plane at a high following speed. The operation of adjusting the surface to the image plane may be an autofocus operation in a narrow sense in which only the average focus position of each part of the surface is adjusted to the image plane. Further, it may involve a so-called auto-leveling operation for adjusting not only the focus position of each part of the surface but also the inclination angle of each part of the surface to the image plane.

In this case, after the approach of the substrate is started, the position of the surface of the substrate in the direction of the optical axis of the projection optical system is measured again, and the position of the substrate in the direction of the optical axis is measured based on the re-measured position in the direction of the optical axis. It is desirable to correct the control amount of the substrate when setting the surface position of the front surface. In this case, assuming that a projection area of an image of a part of the mask pattern on the substrate is a slit-shaped exposure area (illumination field), for example, scanning is performed within the slit-shaped exposure area or with respect to this exposure area. The focus position is measured at a predetermined detection point in the pre-reading area on the near side in the direction, and the surface shape information measured in advance is corrected based on the actual focus position measurement result. Therefore, since slight unevenness information on the substrate surface is also reflected, focusing can be performed more accurately. Also, the focus position in the approaching section from the approaching start point to the exposure target area may be detected, and correction may be performed based on the detection result, whereby focusing can be performed more smoothly.

Further, at the approach start position of the substrate, a plurality of shot areas (SA1 to SAN) on the substrate at a plurality of locations on the surface of the shot area to be exposed next in the optical axis direction of the projection optical system. The position may be measured. From this measurement result, it is possible to accurately focus on almost the entire shot area. At this time, it is desirable to change the distribution of detection points for position measurement in the optical axis direction at the approach start position of the substrate in accordance with the shape of the shot area to be exposed next. If the shot area is, for example, near the edge of the substrate and a detection point of the focus position is set outside the substrate, by ignoring information of the focus position at the detection point outside the substrate,
Even a shot area or the like in which a part is missing can be accurately adjusted to the image plane.

In the scanning exposure apparatus according to the present invention, the mask (R) and the substrate (W) are moved in synchronization with each other, so that the image of the pattern of the mask is projected through the projection optical system (PL). In the scanning exposure apparatus that exposes each of the above shot areas, the position of the projection optical system in the optical axis direction at a plurality of positions on the surface of the shot area to be exposed next within the shot area on the substrate is determined by the approach of the substrate. A measurement system (14F, 14R) for measuring at the start position, a stage (10) for mounting the substrate and setting a surface position on the surface of the substrate, and a measurement system for measuring the surface during the scanning exposure of the substrate. A control system for controlling the stage based on the position in the optical axis direction (7)
And According to the present invention, the scanning exposure method of the present invention can be performed.

In this case, the measurement area (15
F, 15R) is determined based on, for example, the acceleration of the substrate during the run and the speed of the substrate during the scanning exposure. For example, as shown in FIG. 5, the measurement area (15F, 1F) is located forward of the slit-shaped exposure area (3) in the scanning direction.
5R) is set. The maximum scanning speed of the substrate stage for moving the substrate is V _Wmax , and the acceleration is a
Then, the maximum value L _{pre, max} of the approach distance of the substrate is V _Wmax
Represented by ² / a ^2, the exposure area (3) from the measurement area (15F, 15R) the interval to L _pre, may be about _max. Further, the moving stroke of the substrate during the scanning exposure is L
_WST , assuming that the width of the slit-shaped exposure area in the scanning direction is H and the length of the deceleration section is substantially the same as the length of the approaching section, the length in the scanning direction of the maximum exposure field that can be exposed by this scanning exposure apparatus. L _EF is as follows.

L _EF = L _WST −2 · L _{pre, max} −H Therefore, to measure the distribution of the focus position over the entire shot area to be exposed next at the approach start point, the measurement area (15F, 15R) may be set to be substantially equal to or longer than the length L _EF of the maximum exposure field.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. In this example, the present invention is applied to the case where exposure is performed by a step-and-scan type projection exposure apparatus. FIG. 1 shows a projection exposure apparatus of this embodiment. In FIG. 1, at the time of exposure, an i-line of a mercury lamp or an excimer laser beam from an illumination optical system 1 including a light source, a fly-eye lens, a field stop, a condenser lens, and the like. Exposure light IL illuminates the rectangular illumination area 2 on the pattern surface (lower surface) of the reticle R. Exposure light IL
, The image of the pattern in the illumination area 2 of the reticle R is projected at a predetermined projection magnification β (β is 1 /
(4, 1/5, etc.), projection exposure is performed in the rectangular illumination field 3 on the wafer W coated with the photoresist. Hereinafter, the Z axis is taken in parallel with the optical axis AX of the projection optical system PL, the X axis is taken in a plane perpendicular to the optical axis, the X axis is taken perpendicular to the plane of FIG. 1, and the Y axis is taken in parallel with the plane of FIG. explain.

First, the reticle R is held on the reticle stage 4, and the reticle stage 4 continuously moves in the Y direction (scanning direction) on the reticle base 5, and finely adjusts the position of the reticle R in the XY plane. . The position of the reticle stage 4 (reticle R) is measured by the movable mirror 6m on the reticle stage 4 and the external laser interferometer 6.
The measurement result is supplied to a main control system 7 that controls the operation of the entire apparatus. The main control system 7 controls the position and the moving speed of the reticle stage 4 via a reticle stage drive system 8.

On the other hand, the wafer W is mounted on a wafer holder (not shown).
Is held by vacuum suction, and its wafer holder is Z
Z tilt stage 1 fixed on tilt stage 10
0 is placed on the XY stage 11. Z tiltos
Stage 10 and wafer stage from XY stage 11
9 is configured, and the Z tilt stage 10 is arranged in the Z direction of the wafer W.
Direction (focus position) control and tilt angle control
(Leveling). The XY stage 11
Move the tilt stage 10 (wafer W) continuously in the Y direction
At the same time, stepping in the X and Y directions is performed.
Moving mirror 12 fixed to the upper end of Z tilt stage 10
m and the external laser interferometer 12
The position of the page 10 (wafer W) is constantly measured and the main control system
, And based on the measurement result, the main control system 7
Of the XY stage 11 via the wafer stage drive system 13
Controls scanning and positioning operations. Reticle during scanning exposure
Stage 4 and wafer stage 9 synchronized
Then, through the reticle stage 4 using the projection magnification β,
The reticle R is in the + Y direction (or -Y
Direction V)_RThe XY stage is synchronized with the
The wafer W moves to the Teruno field 3 via the page 11
Speed V in -Y direction (or + Y direction)_W(= Β · V _RRun with
Will be examined.

Next, the autofocus sensor of this embodiment will be described. On the side surface in the + Y direction below the projection optical system PL of this example, a first multi-point autofocus sensor (hereinafter, referred to as a “multi-point AF sensor”) of a wide area detection type and an oblique incidence type.
14F, and a second multi-point AF sensor 14R of a wide area detection type and an oblique incidence type is installed on a side surface in the −Y direction below the projection optical system PL. Multipoint AF sensor 14F,
14R have the same configuration, and the configuration of one multipoint AF sensor 14F will be described below.

FIG. 2 is a side view of FIG. 1 viewed from the + Y direction. In FIG. 2, the multipoint AF sensor 14F includes an irradiation optical system 14Fa and a light receiving optical system 14Fb. In the irradiation optical system 14Fa, the non-photosensitive detection light AL is applied to the photoresist emitted from the light source 26.
Is the light transmitting slit plate 2 through the condenser lens 27.
8, a large number of slits are illuminated, and the images of the slits are oblique to the optical axis AX of the projection optical system PL via the objective lens 29, and the first measurement area 15F on the wafer W (FIG.
It is projected to the detection point P ₁₁ to P ₅₃ of 5 rows × 3 columns in the reference).

FIG. 5 shows their focus on the wafer W.
Position detection point P₁₁~ P₅₃FIG.
To the rectangular illumination field 3 which is elongated in the X direction.
Length L in Y direction (F direction)_{pre, max}Across section 16F of
The first measurement area 15F is set. Start point
In, the section 16F is the approach section. Measurement area 1
The width in the X direction (non-scanning direction) of 5F is
Equal to the width, the length of the measurement area 15F in the Y direction (scanning direction)
Say Y_maxIs the maximum that can be scanned and exposed by the projection exposure apparatus of this example.
Exposure field, which is the exposure area (shot area)
Is set equal to the length of
Detection points P in 5 rows in Y direction and 3 columns in X direction ₁₁~ P₅₃Is set
Have been.

A second measurement area 15R having the same size as the measurement area 15F is set in the -Y direction (R direction) with respect to the illumination field 3 with a section 16R having a length _{Lpre, max} therebetween. , detection points Q ₁₁ to Q ₅₃ of three rows in the X direction in five rows in the Y direction to the detection point P ₁₁ to P ₅₃ symmetrical in the measurement region 15R is set. These detection points Q _{11 to} Q ₅₃ are provided in FIG.
A slit image is projected from the second multipoint AF sensor 14R.

Returning to FIG. 2, the reflected light from the detection points P _{11 to} P ₅₃ is collected by the condenser lens 30 in the light receiving optical system 14Fb.
The slit images condensed on the vibrating slit plate 31 via the optical axis are projected on the vibrating slit plate 31 at their detection points again. The vibration slit plate 31 vibrates in a predetermined direction by a vibrator 32 driven by a drive signal DS from the main control system 7. Light that has passed through a number of slits of the vibrating slit plate 31 is photoelectrically converted by a number of photoelectric conversion elements on a photoelectric detector 33, and these photoelectric conversion signals are supplied to a signal processing system 34.

FIG. 3A shows the light transmitting slit plate 2 shown in FIG.
FIG. 3A shows the light transmitting slit plate 2.
Slit 28 _{11-28 53} at positions corresponding to the detection point P ₁₁ to P ₅₃ on the wafer of Figure 5 is formed on the 8. In addition, the vibration slit plate 31 shown in FIG.
Detection points P ₁₁ to P ₅₃ at positions slit 31 _{11-31 53} corresponding to FIG. 5, as shown in (b) is formed, perpendicular to the longitudinal direction of each slit by the vibration slit plate 31 vibrator 32 Vibrating in the measuring direction.

Next, FIG. 4 shows the photoelectric detector 33 in FIG.
And shows a signal processing system 34, in FIG. 4, the photoelectric conversion element 33 _{11-33 53} on the photoelectric detector 33 is reflected from the detection point P ₁₁ to P ₁₃ of FIG. 5, respectively, and the vibrating slit plate The light passing through the corresponding slit in 31 enters. Then, the detection signal from the photoelectric conversion element 33 _{11-33 53} synchronously via the amplifier 46 _{11-46 53} Rectifier 47
It is supplied to the ₁₁ to 47 _53. Each of the synchronous rectifiers 47 _{11 to} 47 ₅₃ synchronously rectifies the input detection signal by using the drive signal DS for the vibrator 32, and changes substantially in proportion to a focus position of a corresponding detection point within a predetermined range. Generate a focus signal. In this example, the synchronous rectifier 47 ₁₁
Focus signal output from to 47 _53, in FIG. 1, respectively so as to be 0 when the corresponding detection point meets the extended plane of the image plane of the projection optical system PL (best focus position) Calibration Session is taking place.

The synchronous rectifier 47 _11-47 focus signal output from the ₅₃ is supplied to the multiplexer 48 in parallel, the multiplexer 48 in synchronization with the switching signal from the main control system 7, the order from the focus signal to be supplied Analog / digital (A /
D) The digital focus signal supplied to the converter 49 and output from the A / D converter 49 is sequentially stored in a memory in the main control system 7. The main control system 7 can recognize the focus position (more precisely, the amount of deviation from the best focus position) at the corresponding detection point from the focus signals. In addition, the detection point Q ₁₁ in the second measurement region 15R in FIG.
Light reflected from the to Q ₅₃ is first shown in FIG. 1 2 multipoint AF sensor 14
Incident on R, detection point from the multipoint AF sensor 14R Q ₁₁
Focus signal corresponding to the focus position in the to Q ₅₃ is output and stored in the memory in the main control system 7.

In FIG. 5, the main control system 7 scans the illumination field 3 relative to the wafer in the + Y direction (actually, the wafer is scanned in the −Y direction).
From the information of the focus position at the detection point P ₁₁ to P ₅₃ in the direction of the measurement region 15F, it obtains a surface shape of the shot area subject to exposure, Z during scanning exposure based on the surface shape
By driving the tilt stage 10, the surface of the wafer in the illumination field 3 is adjusted to the image plane of the projection optical system PL by the autofocus method and the autoleveling method. On the other hand, Teruno field 3 is moved to -Y
When relative scanning in a direction (in practice is scanned wafer + Y direction), information of the focus position at the detection point Q ₁₁ to Q ₅₃ in the -Y direction of the measurement region 15R is used. As a result, even when the scanning direction is reversed, the focus position can be measured at the approach start point of the wafer stage 9 as described later, thereby improving the throughput of the exposure step.

Here, the multipoint AF sensor 14 shown in FIG.
Measurement area 15F, 1 of focus position by F, 14R
The arrangement and shape of 5R will be described in detail. In FIG. 5, the length L _{pre, max} of the sections 16F, 16R is set to be the length of the approach distance when the wafer stage 9 of FIG. 1 is moved in the Y direction at the maximum scanning speed V _Wmax . .
That is, in FIG. 1, the projection magnification β of the projection optical system PL is, for example, ４ ，, ５, etc., and the scanning speed of the reticle stage 4 is considerably higher than the scanning speed of the wafer stage 9. The maximum scanning speed V _Wmax of the wafer stage 9 is also determined according to the maximum scanning speed of the stage 4. Assuming that the acceleration of the wafer stage 9 in the Y direction during the scanning exposure is a, the length L _{pre, max} may be approximately the next length.

L _{pre, max} = V _Wmax ² / (2a) (1) Specifically, if the maximum scanning speed V _Wmax is 100 mm / s and the acceleration a is 1000 mm / s ² , the sections 16F, The length L _{pre, max} of the 16R is 5 mm. Also, since the reticle stage 4 is configured to move left and right alternately each time the scanning direction is reversed, it is assumed that the reticle stage 4 and the wafer stage 9 also move at substantially the speed ratio of the projection magnification β even in the approaching section. movement stroke L _{WS T} in the Y direction of the wafer W during the scanning exposure by the movement stroke in the Y direction of the reticle stage 4 is substantially determined. Therefore, in FIG. 5, assuming that the width of the illumination field 3 in the Y direction is H, the length L in the Y direction of the maximum exposure field that can be exposed by the scanning exposure method by the projection exposure apparatus of this embodiment.
_{EF looks} like this:

L _EF = L _WST −2 · L _{pre, max} −H (2) The width Y _max of the measurement areas 15F and 15R in the Y direction in this example is set equal to the length L _EF of the maximum exposure field. is there. This makes it possible to measure the distribution of the focus position in any shot area by one measurement at a standstill. With the width Y _{ma x,} multipoint AF sensor 14F of the present embodiment, 14R of the measurement region 15F, 15R, in FIG. 5, the scanning from the center of the illumination field field 3 (optical axis AX of the projection optical system PL) Direction _Is set to cover the area from the interval (H / 2 + L _{pre, max} ) to the interval (H / 2 + L _{pre, max} + Y _max ).

Now, an example of the scanning exposure operation of the projection exposure apparatus of the present embodiment having the multi-point AF sensors 14F and 14R of the wide area detection type having such a configuration will be described with reference to FIG.
FIG. 6 shows a wafer W to be exposed according to the present embodiment. In FIG. 6, the shot areas SA1, SA2,..., SAN (N is an integer of 2 or more) are arranged on the surface of the wafer W at predetermined pitches in the X and Y directions. ) Is formed, and each shot area SAi (i = 1)
ＮN) are assumed to be substantially the same as the maximum exposure field. In addition, assuming that the pattern image of the reticle R is exposed by the scanning exposure method in order from the shot area SA1, the illuminated field 3 is moved along the locus 17 in the + Y direction with respect to the shot area SA8 at the center of the wafer W. The operation in the case where exposure to the shot area SA8 is performed by performing relative scanning will be described. Although the wafer W is actually scanned with respect to the fixed illumination field field 3, the illumination field 3 is assumed to be scanned with respect to the wafer W for convenience of explanation.

In this case, at the start of the scanning exposure,
The center of field 3 is located at the starting point 18A
You. The scanning speed of the wafer stage 9 during the scanning exposure is V_Wmax
Then, the shot area S from the tip of Teruno field 3
The interval of the approach section up to A8 is the length L determined by equation (1).
_{pre, max}Is set to Therefore, it is clear from FIG.
As described above, the shot area SA8 has the multi-point AF sensor 14F.
Is almost covered with the measurement area 15F. In this state, the main
The control system 7 controls the measurement area 15 via the multipoint AF sensor 14F.
F, that is, 15 rows × 3 columns in the shot area SA8
Detection point P₁₁~ P ₅₃Measure the focus position at.

FIG. 7 shows an example of the distribution (surface shape) of the focus positions measured at this time. In FIG. 7, the focus positions at the detection points P _{11 to} P _{53 on} the surface of the shot area SA 8 are the image planes. It is expressed as a deviation from 19. The surface of the shot area SA8 has irregularities that change rapidly. Based on this measurement result, the main control system 7 sets the Y coordinate of the wafer W at the time of scanning exposure to
The projection optical system PL projects the surface of the wafer W in the Teruno field 3
The focus position ΔZ of the wafer W and the tilt angle θ _X (pitching in the scanning direction) of the wafer W around the X axis and the tilt angle θ _{Y of the} wafer W around the Y axis (to the Rolling) and determine.

At this time, taking into account the response speed of the Z tilt stage 10 in FIG. 1, the focus position Δ is adjusted so that the surface of the wafer W is continuously and smoothly adjusted to the image plane.
The Z and the inclination angles θ _X and θ _Y are approximated by, for example, a quartic function of the Y coordinate. The method of determining the coefficient of this function may be the least squares method, or a calculation method such as the so-called Max-Min method that minimizes the maximum deviation. The latter is effective in reducing the focus position error (control error) at the step when there is a step due to foreign matter on the front or back surface of the wafer W.

Specifically, FIG. 8A shows the relationship between the Y coordinate and the focus position ΔZ obtained corresponding to FIG.
In FIG. 8A, the focus position ΔZ changes in a polygonal line due to the finite number of focus position detection points. Therefore, in order to make the operation of the drive unit of the Z tilt stage 10 smooth, the focus position Δ
Z is approximated by a higher-order function of the Y coordinate. FIG. 8B shows an example of the focus position ΔZ obtained as a result of this approximation. Then, in FIG. 6, the approach starting point 1 of Teruno field 3
After the approach from 8A is started and the illuminated field 3 starts to cover the shot area SA8, the irradiation of the exposure light is started, and the Z-tilt stage 10 is moved in accordance with the Y coordinate of the wafer W. , The focus position and the tilt angle of the wafer W are set to predetermined values. Thus, scanning exposure is performed in a state where the entire surface of the shot area SA8 is substantially aligned with the image plane of the projection optical system PL.

When scanning exposure to the shot area SA8 is completed and deceleration is performed, the center of the illumination field 3 reaches the scanning exposure end point 18B. Thereafter, the center of the illuminated field 3 is moved to the next shot starting point 18 with respect to the next shot area SA9 by the stepping of the wafer stage 9 in the X direction.
Move to C. Also in this case, the distance between the territory field 3 and the shot area SA9 is the length L determined by the equation (1).
It is set to _{pre, max} . Therefore, as apparent from FIG. 5, the shot area SA9 is substantially
It is covered with a 4R measurement area 15R. In this state, the main control system 7 measures the measurement area 15 via the multipoint AF sensor 14R.
The focus position at 15 detection points Q _{11 to} Q ₅₃ in 5 rows × 3 columns in R, that is, in the shot area SA9, is measured, and the surface of the shot area SA8 is image plane as in the case of the shot area SA8. The focus position ΔZ and the inclination angles θ _X , θ _Y for adjusting to are determined in advance. Then, after the approaching of the illumination field 3 is started, the surface of the wafer W is adjusted to the image plane by an autofocus method and an autoleveling method based on a predetermined focus position ΔZ or the like.

When exposing other shot areas, the multipoint AF sensor 14F, 1
By selectively using the 4Rs, the distribution of the focus position of the shot area to be exposed at the approach start point is measured in advance, and based on the measurement result, the control amount (the focus position and the inclination) of the surface position of the wafer W during scanning exposure is determined. Angle) is determined in advance, and based on the result, the Z tilt stage 1
0 is driven. Therefore, the response speed when performing the focusing operation based on the almost real-time measurement result as in the conventional example is the overall response speed of the signal processing system of the AF sensor and the servo system including the stage system. Since the response speed of this embodiment is substantially determined only by the Z tilt stage 10, it is possible to follow a rapid change in the unevenness of the surface of the wafer W at high speed and smoothly, and to reduce poor resolution and the like. Also,
Since it is not necessary to move the wafer stage 9 from the approach start point to measure the distribution of the focus positions in each shot area, the throughput of the exposure process does not decrease.

In this example, when the distribution of the focus position of the shot area to be exposed next at the approach start point is measured, for example, due to the adhesion of foreign matter to the front and back surfaces of the wafer, the Z tilt stage 10 It may be found that there are irregularities that exceed the response speed. In such a case, the control amount of the Z tilt stage 10 may be determined in advance by removing the unevenness information. in this case,
In the shot region, there is a possibility that a resolution defect locally occurs only in the portion having the unevenness, but in other regions, optimum focusing is possible.

Further, in this embodiment, the operation of determining the control amount of the Z tilt stage 10 for the auto focus and the auto leveling in advance is performed by moving the wafer stage 9 from the end of the scanning exposure of the previous shot area to the next shot area. It is desirable to perform the operations in parallel before moving to the start point of the run. That is, when the wafer stage 9 reaches the vicinity of the approach start point of the next shot area, the measurement area 15F or 15R almost covers the entire surface of the next shot area. The capture of the focus position is started, and the capture of the focus position is finished at the same time when the wafer stage 9 reaches the approach start point, and the control amount of the Z tilt stage 10 is calculated to maximize the throughput of the exposure process. can do.

In the case of FIG. 6, the shot area SA1
Since the size of .about.SAN is almost the same size as the maximum exposure field, and the scanning speed of the wafer stage 9 is also the maximum scanning speed, when the illuminated field 3 is scanned in the + Y direction in FIG. Measurement area 1 at starting point
It has been performed to measure the focus position in all of the detection points P ₁₁ to P ₅₃ in the 5F. However, when the size of the shot area is smaller than the maximum exposure field, or when the scanning speed of the wafer stage 9 is lower than the maximum scanning speed and the length of the approaching section may be shorter, the main control is accordingly performed. The position of the approach start point may be changed by a command from the system 7 and the arrangement of the detection points for detecting the focus position may be changed in advance. Alternatively, a desired detection point may be set in advance by an operator of the projection exposure apparatus based on design data of, for example, a semiconductor device to be exposed.
In order to cope with the case where the approaching section is short, in FIG.
An interval of up to 5R L _pre, it may be set shorter than the _{ma x.}

Next, another example of the embodiment of the present invention will be described with reference to FIGS. 1, 9 and 10. FIG. In this example, a step-and-scan type projection exposure apparatus basically having the same configuration as that shown in FIG. 1 is used. However, the projection exposure apparatus of this example comprises a first and a second wide-area detection type multi-point AF sensor 14.
In addition to the F and R, a third multi-point AF sensor 20 is provided between the multi-point AF sensors 14F and 14R as shown by a two-dot chain line in FIG.

FIG. 9 shows three multipoint AF sensors 14 of this embodiment.
9 shows the distribution of the focus position detection points by F, 14R, and 20. In FIG. 9, in the + Y direction and the −Y direction of the illumination field 3 _, a section 16 of length L _{pre, max} is shown.
Wide-area detection type multi-point AF sensor 14 across F, 16R
Measurement areas 15F and 15R of F and 14R are set. Further, the slit images from the multi-point AF sensor 20 at the center in FIG.
21E, three detection points 22FA to 22FC arranged in the X direction in the section 16F, and three detection points 22RA to 22RC arranged in the X direction in the section 16R are projected obliquely. And these detection points 21A ~
Reflected light from 21E, 22FA to 22FC, and 22RA to 22RC is received by multi-point AF sensor 20, and a focus signal corresponding to a focus position at these detection points is supplied to main control system 7 in FIG.

In this case, the sections 16F and 16R are the approach sections when the Teruno field 3 is at the approach start point,
Pre-reading area of focus position during approach run and synchronous scan,
Or it becomes a prefocus area. While the focus positions of the detection points 21A to 21E in the illumination field 3 are always detected, when the illumination field 3 is relatively scanned in the + Y direction, the detection in the section 16F on the + Y direction side is performed. When the focus positions at the points 22FA to 22FC are continuously detected, and the illumination field 3 is relatively scanned in the −Y direction, the detection point 22RA in the section 16R on the −Y direction side.
Focus positions at 22RC are continuously detected.

Next, an example of the scanning exposure operation of this embodiment will be described. In FIG. 9, when performing exposure by relatively scanning the illumination field 3 in the + Y direction with respect to the shot area to be exposed, the detection points P _{11 to} P ₅₃ in the measurement area 15F are determined in advance at the approach start point. Measure the focus position, that is, the distribution of the focus position of the shot area to be exposed,
Similarly to the method described with reference to FIG. 6, the control amount of the Z tilt stage 10 in FIG. 1 for adjusting the surface of the wafer in the illumination field 3 to the image plane is determined in advance according to the Y coordinate of the wafer. . Then, after starting the approach of the wafer, the detection points 21A to 21E in the illumination field 3 and the section 16F
The focus positions of the detection points 22FA to 22FC are continuously measured, and after the detection points 22FA to 22FC in the section 16F (here, the pre-read area) approach the shot area to be exposed, the detection points 22FA to 22FC By feeding back the information of the focus position, a minute correction is added to the predetermined control amount of the Z tilt stage 10. Further, after the illumination field 3 enters the shot area to be exposed, information on the focus positions of the detection points 21A to 21E is also fed back, so that the control amount of the Z tilt stage 10 is finely corrected.
A scanning exposure is performed. The feedback gain at this time is Z
Optimization may be performed in consideration of the responsiveness of the tilt stage 10.

In this case, as is apparent from FIG. 9, detection points P _{11 to} PR of the focus position detected at the approach start point.
_{Numerals 53} are distributed almost uniformly in the shot area to be exposed, but there is an area where the focus position is not measured between the detection points. On the other hand, since the detection points in the illumination field 3 and in the section (pre-reading area) 16F continuously move the surface of the shot area in the Y direction by the scanning exposure, the focus position is maintained without any gap in the Y direction. Will be measured. Therefore, by feeding back the focus positions of the detection points in the illuminated field 3 and in the pre-reading area, it is possible to cope with minute irregularities (undulations) on the surface of the shot area, and to achieve higher accuracy. Focusing can be performed.

On the other hand, in FIG. 9, when exposure is performed by relatively scanning the illuminated field 3 in the -Y direction with respect to the shot area to be exposed, the measurement area 1 is set in advance at the approach start point.
The focus position is measured at the detection point P ₁₁ to P ₅₃ in the 5R, Z tilt stage 1 pre 1 from the measurement result
A control amount of 0 is determined in advance. Then, after starting the approach of the wafer, the detection points 21A to 21A in the Teruno field 3 are detected.
E, and the focus positions of the detection points 22RA to 22RC in the section 16R are continuously measured, and the information of these focus positions is fed back during scanning exposure to finely correct the control amount of the Z tilt stage 10. The focusing accuracy is improved.

Next, in this example, an example of the operation in the case where scanning exposure is performed on a chipped shot area near the edge of a wafer will be described with reference to FIG. FIG. 10 shows an enlarged plan view near the edge of a predetermined wafer W to be exposed,
In FIG. 10, the X direction is set near the edge of the wafer W.
Shot areas SB6 to SB9 are arranged at a predetermined pitch in the Y direction, and a part of the shot area SB7 in the shot areas SB7 to SB9 is missing. In addition, since the irregularities are remarkably changed near the edge of the wafer, the projection exposure apparatus controls not the geometric edge 23 but a virtual edge 23A slightly inside (usually about 3 mm). In many cases, the shot area within the edge 23A is regarded as an effective area. It is also assumed that these shot areas SB6 to SB9 are six shot areas in which the same circuit pattern is formed in three rows in the Y direction and two columns in the X direction. That is, assuming that the width in the X direction of these shot areas is LX and the width in the Y direction is LY, the widths in the X direction are LX / 2 and the widths in the Y direction are in a state where there is no chip in these shot areas. Six circuit patterns 24 having a width of LY / 3 are formed, and the edge 23
For example, two complete circuit patterns can be formed in the shot area SB7 which is missing due to A.

In such a shot arrangement, the illuminated field 3 is relatively scanned from the outside of the wafer in the + Y direction as shown by an arrow 25 with respect to the missing shot area SB7 on the wafer W (actually, Will move outward), and the case of performing scanning exposure will be described. In this case, the main control system 7 can recognize the shape of the effective area of the shot area SB7 to be exposed in advance from the information of the wafer shape and the shot arrangement. Therefore, FIG.
As shown in FIG.
Of the detection points in the measurement area 15F by the first wide-area detection type multi-point AF sensor 14F inside the edge 23A and the shot area S
By using only eight focus position of the detection point P ₁₁ to P ₃₄ in the B7, advance to determine the control amount of the Z tilt stage 10 at the time of scanning exposure, the approach based on this, and the scanning exposure Do.

At this time, the approach starting points are detected points 22FA to 22FA in the pre-reading area on the + Y direction side of the illuminated field 3.
FC and detection points 21A to 21E in Teruno field 3
Is outside the edge 23A of the wafer W. Further, even after the start-up and the scanning exposure are started, the detection points arranged in the direction orthogonal to the scanning direction (for example, the detection points 22FA to 22F).
Since all of C) enter the effective area inside the edge 23A almost immediately before the end of the scanning exposure, unlike the case of FIG. 9, the focus of the detection point in the pre-read area and the illumination field 3 is different. The amount of real-time feedback with respect to the control amount of the Z tilt stage at the position is reduced.
Alternatively, depending on the state of the lack of the shot area to be exposed due to the wafer edge, the feedback of the focus position of the detection point in the pre-read area and in the illumination field 3 is not performed at all, and only the open control based on the predetermined control amount is performed. Focus and auto leveling are performed. This allows accurate focusing to be performed on the missing shot area without moving the wafer stage 9 from the approach start point for measuring the focus position.

In the above-described embodiment, the measurement area 15 by the wide-area detection type multi-point AF sensors 14F and 14R is used.
The detection points in F and 15R are set with a uniform distribution of 5 rows × 3 columns, but the number and arrangement of these detection points are not limited thereto. As described above, the present invention is not limited to the above-described embodiment, and can take various configurations without departing from the gist of the present invention.

[0053]

According to the scanning exposure method of the present invention, the distribution of the position (focus position) in the optical axis direction of the projection optical system in the region to be exposed at the approaching start position of the substrate is measured, and based on this measurement result. Thus, the surface position of the substrate during the scanning exposure is set. Therefore, there is an advantage that even when the unevenness of the surface of the exposure target area changes rapidly, the surface of the area can be accurately adjusted to the image plane without lowering the throughput. In addition, during the run, the control response of the stage system for setting the surface position of the substrate does not become a problem, so that the probability of occurrence of a retry (retry) of the run operation due to poor control is reduced, and the throughput is further reduced. Is improved.

After the start of the approach of the substrate, the position of the surface of the substrate in the direction of the optical axis of the projection optical system is measured again, and based on the re-measured position in the direction of the optical axis, the surface of the surface of the substrate is measured. When correcting the control amount of the substrate at the time of setting the position, slight indentation information of the region to be exposed is also reflected, so that focusing can be performed with higher accuracy. In addition, when measuring the positions in the optical axis direction of the projection optical system at a plurality of shot areas on the surface of the shot area to be exposed next among the plurality of shot areas on the board at the approach start position of the board, By using the information on the focus position thus set, it is possible to scan and expose almost the entire shot area in a focused state.

In order to change the distribution of detection points for position measurement in the optical axis direction at the approach start position of the substrate according to the shape of the shot area to be exposed next, for example, the edge of the substrate Even when performing exposure by relatively scanning the exposure region from the outside of the substrate with respect to the nearby chipped shot region, accurate focusing is performed by using only the information on the focus position of the detection point inside the substrate. Can be.

Further, according to the scanning exposure apparatus of the present invention, the scanning exposure method of the present invention can be performed, and the measurement area of the measurement system is
When the determination is made based on the acceleration during the running of the substrate and the speed during the scanning exposure of the substrate, there is an advantage that the measurement area is accurately set on the shot area to be exposed at the starting point of the running of the substrate. .

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing a step-and-scan projection exposure apparatus used in an example of an embodiment of the present invention.

FIG. 2 is a side view of a main part when FIG. 1 is viewed from a + Y direction.

3A is a diagram showing a light transmitting slit plate 28 in FIG. 2, and FIG. 3B is a diagram showing a vibration slit plate 31 in FIG.

FIG. 4 is a diagram showing a photoelectric detector 33 and a signal processing system 34 in FIG.

FIG. 5 is a diagram illustrating distribution of detection points of a focus position according to an example of the embodiment;

FIG. 6 is a plan view of a wafer for explaining a scanning exposure operation according to an example of the embodiment;

FIG. 7 is a diagram illustrating an example of a distribution of focus positions measured in one shot area in FIG. 6;

8A is a diagram showing a change in a control amount of a focus position obtained corresponding to a Y coordinate of a wafer from the distribution of the focus position in FIG. 7, and FIG. 8B is a diagram showing a focus position in FIG. FIG. 4 is a diagram obtained by approximating a broken line indicating a curve.

FIG. 9 is a diagram showing a distribution of detection points of a focus position in another example of the embodiment of the present invention.

FIG. 10 is an explanatory diagram in a case where scanning exposure is performed on a shot area near the edge of a wafer in another example of the embodiment.

FIG. 11 is an explanatory diagram of a conventional scanning exposure operation.

[Explanation of symbols]

R reticle PL projection optical system W wafer 3 illumination field field 4 reticle stage 7 main control system 9 wafer stage 14F, 14R wide detection type multipoint AF sensor 15F, 15R measurement region _{P 11 ~P 53, Q 11 ~Q} 53 Focus Position detection points SA1 to SAN Shot area 20 Multipoint AF sensor 21A to 21E Focus position detection points 22FA to 22FC, 22RA to 22RC Focus position detection points

Claims (6)

[Claims] 1. A scanning exposure method for exposing an image of a pattern of the mask on the substrate via a projection optical system by synchronously moving the mask and the substrate, wherein: Measuring the positions of the projection optical system in the optical axis direction at a plurality of locations on the substrate surface to be exposed from now on, based on the measured positions in the optical axis direction during scanning exposure on the substrate, A scanning exposure method characterized by setting a surface position of the scanning exposure. 2. After starting the approach of the substrate, the position of the substrate surface in the optical axis direction of the projection optical system is re-measured, and based on the re-measured position in the optical axis direction, the substrate surface is re-measured. 2. The scanning exposure method according to claim 1, wherein the control amount of the substrate when setting the surface position is corrected. And measuring, in the approach start position of the substrate, a plurality of positions on a surface of a shot area to be exposed next among a plurality of shot areas on the substrate in an optical axis direction of the projection optical system. The scanning exposure method according to claim 1 or 2, wherein: 4. The distribution of detection points for position measurement in the direction of the optical axis at the start position of the approach of the substrate in accordance with the shape of the shot area to be exposed next. 4. The scanning exposure method according to 3. 5. A scanning exposure apparatus for exposing an image of a pattern of the mask to each shot area on the substrate via a projection optical system by synchronously moving the mask and the substrate. A measurement system that measures the position of the projection optical system in the optical axis direction at a plurality of locations on the surface of the shot area to be exposed next in the shot area at a start-up position of the substrate, and mounting the photosensitive substrate A stage for setting a surface position of the substrate surface, a control system for controlling the stage based on a position in the optical axis direction measured by the measurement system during scanning exposure of the substrate,
A scanning exposure apparatus comprising: 6. The scanning exposure apparatus according to claim 5, wherein the measurement area of the measurement system is determined based on acceleration during the approach of the substrate and speed during scanning exposure of the substrate.