JP3391470B2 - Projection exposure apparatus and projection exposure method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for projecting and exposing an image such as a circuit pattern on a photosensitive substrate, and more particularly to a projection exposure apparatus having a focus detection device for focusing the photosensitive substrate.

[0002]

2. Description of the Related Art In a conventional projection exposure apparatus, a reticle (mask) pattern is exposed to a photosensitive substrate (a wafer or a glass plate coated with a resist layer) through a projection optical system having a high resolution.
When the projection exposure is performed on the surface, the work of accurately matching the surface of the photosensitive substrate with the image plane of the reticle pattern, that is, focusing is essential. In recent years, the depth of focus of the projection optical system has become narrower, while the exposure illumination light has a wavelength
Even with the 5 nm i-line, only a depth of about ± 0.7 μm can be obtained at present. Furthermore, the projection field of view of the projection optical system tends to increase year by year, and it is becoming difficult to design and manufacture a projection optical system that secures a maximum depth of focus over the entire wide exposure field (for example, 22 mm square). . For this reason, several methods have been proposed for increasing the depth of focus.

However, in order to achieve good focusing over the entire wide exposure field, the flatness of the partial area on the photosensitive substrate within the field of exposure and the flatness of the image plane, the so-called image, are in any case. It is required that both the surface curvature and the image plane inclination are good. Of these, the curvature of field and the inclination of the field often depend on the optical performance of the projection optical system itself, but in addition, the flatness and parallelism of the reticle may be a factor. On the other hand, the flatness for each partial area on the photosensitive substrate, that is, for each projection exposure area (shot area) is
Although there is a difference in the degree depending on the photosensitive substrate, it is possible to set the surface of the shot area on the photosensitive substrate and the image plane in parallel by inclining the holder holding the photosensitive substrate by a minute amount.

As a method for focusing in consideration of the inclination of the surface of one shot area on the photosensitive substrate as described above, Japanese Patent Laid-Open Nos. 58-113706 and 55-1 are available.
The technique disclosed in Japanese Patent No. 34812 is known.
Particularly, in JP-A-55-134812, spots of a light beam are projected onto four points on a photosensitive substrate through a projection optical system, and a spot image resulting from the reflected light is photoelectrically detected to focus the photosensitive substrate and correct the inclination ( Leveling) is disclosed.

However, in the above-mentioned two conventional techniques, it is determined how much the surface of the photosensitive substrate deviates in the direction of the projection optical axis from a reference plane (which coincides with the image plane as much as possible) which is virtually set in advance. Only the detection is performed, and the method of directly detecting the deviation between the image forming surface and the surface of the photosensitive substrate is not used. Therefore, if a virtual reference plane that serves as a reference for measuring the positional deviation of the photosensitive substrate in the optical axis direction deviates from the image plane of the projection optical system due to drift or the like, the deviation is caused when the pattern is projected and exposed on the photosensitive substrate. Was the residual focus offset.

Therefore, a method for reducing such residual focus offset is disclosed in Japanese Patent Application Laid-Open No. 60-168112 or Japanese Patent Application Laid-Open No. 59-94032. Among them, in Japanese Patent Laid-Open No. 60-168112,
A reference pattern is provided on the stage (holder) on which the photosensitive substrate is placed, and the reference pattern is back-projected onto a specific pattern on the reticle via a projection optical system, and an image of the reference pattern formed on the specific pattern is displayed. After adjusting the height position of the stage to maximize the contrast, the surface on which the reference pattern is formed is the best focus surface (the best focus surface) due to the focus detection system (oblique incidence light type) for focusing the photosensitive substrate. The focus detection system is calibrated so that it is detected as the image plane). Further, in Japanese Patent Laid-Open No. 59-94032, a best focus plane is obtained by using a slit-shaped light receiving sensor as a reference pattern on a stage and detecting the contrast of a pattern image when a slit pattern on a reticle is projected by a projection optical system. Has been identified.

Another method is disclosed in Japanese Patent Laid-Open No. 1-2626.
As disclosed in Japanese Patent No. 24, a slit-shaped light emitting mark is provided on the stage, and the image of the light emitting mark is back-projected onto a specific mark on the reticle, and the stage is moved to X-axis.
A method is also known in which the best focus plane is detected by photoelectrically detecting the light transmitted above the reticle when the reticle mark is moved in the Y direction and scanned with the light emission mark image.

The above-mentioned Japanese Patent Laid-Open No. 58-11370.
As a development of the oblique incidence focus detection system disclosed in Japanese Patent No. 6, a pinhole image is formed on each of a plurality of points (for example, 5 points) in a shot area on a photosensitive substrate without passing through a projection optical system. A multi-point grazing incidence optical focus detection system of a type in which a two-dimensional position detecting element (CCD) receives all the reflected images by the grazing incidence system is also known from JP-A-2-102518. There is. The method disclosed in this conventional example is generally called an oblique incidence type multipoint AF system, and can perform focus detection and tilt detection with high accuracy. However, in this conventional example,
There is no disclosure or suggestion of calibration of the focus offset with respect to the best focus plane during projection exposure.

[0009]

In each of the above-mentioned conventional techniques, the system for detecting the positional deviation (focal point deviation) of the surface of the photosensitive substrate in the projection optical axis direction during the actual pattern exposure is not limited to the reticle pattern and the photosensitive substrate. Instead of directly detecting the in-focus state, the positional deviation in the optical axis direction of only the photosensitive substrate is detected. Therefore, it is ideal to calibrate from time to time considering the drift on the device. Further, considering the flatness and parallelism of the photosensitive substrate, the multi-point AF system method, in which a plurality of points in the shot area are individually and substantially simultaneously focus-detected, is superior.

Therefore, when a multi-point AF system is adopted and it is necessary to calibrate the AF system, it is difficult to apply the conventional calibration method as it is. That is, in the above-mentioned conventional calibration method, since it was necessary to detect a specific pattern on the reticle by some detection system, the specific pattern was always engraved in the peripheral portion of the circuit pattern area of the reticle or in the street line area. It was necessary to do so. For this reason, the positions of a plurality of measurement points within the projection field determined by the multipoint AF system and the position of the specific pattern on the reticle to be detected during calibration are completely different, and the difference in the positions is taken into consideration. Even if it is calibrated as it is, there is a problem in that accurate calibration cannot be performed due to the influence of the aberration of the projection optical system, the deflection of the reticle, and the like.

Further, even if it is not a multi-point AF system, it is a fixed-point AF system in which the focus measurement point on the oblique incident light type photosensitive substrate is set only in the center of the projection visual field, that is, in the center of the shot area. Had the same problem. The present invention has been made in view of these problems, and even if a measurement point of the AF system is set at an arbitrary position within the projection visual field, accurate calibration at that measurement point (focus calibration)
It is possible to improve the accuracy, reproducibility, stability and the like of a multipoint AF system.

[0012]

Projection exposure apparatus of the present invention
Forms an image of the mask (R) pattern on a predetermined image plane.
The projection optical system (PL) for projecting an image and its image plane are almost flat
Hold the photosensitive substrate (W) in a row and in the plane parallel to the image plane
XY stage (21) that moves two-dimensionally with
Z stage that moves the plate in the optical axis direction of the projection optical system
(20) and the projection within the projection visual field (If) of the projection optical system.
Measurement points at a plurality of predetermined positions,
The position of each point on the surface of the photosensitive substrate in the direction of its optical axis.
And a first focus detecting means (1 to 17) for detecting information
A projection exposure apparatus that is located at any point within the projection field of view.
Second focus detection capable of detecting the image plane of the projection optical system
Means (40-45) and its first focus detection means
Humidity of positions of multiple measurement points or positions in their immediate vicinity
In order to detect the image plane of the projection optical system,
Specifying means (3 for specifying the detection point of the second focus detecting means)
10) and the second focus detection hand at each of the designated positions.
The signal detected by operating the stage and the signal obtained at that time
At each measurement point at or near its position
1 of the focus detection means and the first
The detection error by the focus detection means at each of the plurality of measurement points
Calibration means for calibrating the differences individually or on average (3
0) and are provided. Also,
The projection exposure method of the present invention projects an image of a mask pattern.
By projecting onto the substrate through the optical system,
In the projection exposure method of exposing, the projection of the projection optical system
Having measurement points at a plurality of predetermined positions in the visual field,
At each of the multiple measurement points, the surface of the substrate
First focus detecting means for detecting position information, and the first focus detecting means
Multiple measurement points by the focus detection means, or very close to them
Detects the image plane of the projection optical system at each nearby position
A second focus detecting means, and a second focus detecting means
The signal detected by operating the stage at each position and at that time
Measurement of each of its positions or its immediate vicinity
Based on the detection signal of the first focus detection means at the point
And the plurality of measurement points by the first focus detection means.
Calibrate the detection error for each of the
It is characterized by that.

According to the present invention, when a multi-point AF system having a large number of measurement points in the projection field of the projection optical system is used as the first focus detecting means, the best image forming plane is used as a reference for each measurement point. It is possible to perform the calibration. When such a calibration is performed, if the offset (error) at the time of calibration is corrected for the position deviation amount obtained from each measurement point of the multipoint AF system, the surface of the photosensitive substrate is always the best image plane. Focusing that is consistent with can be achieved.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a TT for detecting the best focus plane of a projection optical system in a projection exposure apparatus according to an embodiment of the present invention.
It is a figure which shows the focus detection system of L type. In FIG. 1, a reticle R having a circuit pattern area PA for manufacturing an actual device formed on its lower surface is held by a reticle holder (not shown). The optical axis AX of the projection lens PL, which is schematically shown by dividing the diaphragm surface (pupil surface) EP into a front group and a rear group, has the center of the reticle R, that is, the center of the pattern area PA, with respect to the reticle pattern surface. Pass vertically. Below the projection lens PL, a Z stage 20 on which the wafer W is placed and which moves in the optical axis AX direction by a very small amount (for example, within ± 100 μm) is provided on an XY stage 21. This X
The Y stage 21 moves the wafer W two-dimensionally in the XY plane perpendicular to the optical axis AX. Further, a reference plate FM is fixed to a part of the Z stage 20 at a height position substantially equal to the surface of the wafer W. This reference plate FM has
As shown in FIG. 2, a plurality of transmissive slits extending in the X direction are arranged in the Y direction at a constant pitch, and a mark ISy,
A mark ISx in which a plurality of transmissive slits extending in the Y direction are arranged at a constant pitch in the X direction, and an oblique slit ISa having 45 ° in each of the X and Y directions are formed. These slit marks ISx, IS
In y and ISa, a chromium layer (light-shielding layer) is vapor-deposited on the entire surface of the quartz reference plate FM, and a transparent portion is engraved therein.

Now, in FIG. 1, below the reference plate FM (Z
Inside the stage 20), a mirror M1, an illumination objective lens 40, and an optical fiber 41 are provided, and the illumination light from the exit end of the optical fiber 41 is condensed by the objective lens 40 to form a slit mark ISx on the reference plate FM. , I
Both Sy and ISa are irradiated from the back side. A beam splitter 42 is provided on the incident end side of the optical fiber 41,
The exposure illumination light IE is introduced into the optical fiber 41 via the lens system 43. The illumination light IE is preferably obtained from a light source for reticle R illumination (a mercury lamp, an excimer laser, etc.), but a dedicated light source may be prepared separately. However, when using a different light source, it is necessary to use illumination light having the same wavelength as the exposure illumination light or a wavelength very similar thereto.

The illumination condition of the reference plate FM by the objective lens 40 is matched as much as possible with the illumination condition of the projection lens PL at the time of pattern projection. That is, the numerical aperture (NA) of the illumination light on the image side of the projection lens PL and the numerical aperture (NA) of the illumination light from the objective lens 40 to the reference plate FM are substantially matched. Now, with such a configuration, the illumination light I
When E is introduced into the optical fiber 41, the image light fluxes propagating to the projection lens PL are generated from the marks ISx, ISy, ISa on the reference plate FM. In FIG. 1, the Z stage 2
0 is the best image plane (reticle conjugate plane) F of the projection lens PL
It is assumed that the reference plate FM is set slightly downward from o. At this time, the image light flux L1 generated from one point on the reference plate FM passes through the center of the pupil plane EP of the projection lens PL, is condensed within a plane Fr slightly displaced downward from the pattern surface of the reticle R, and then diverges. After being reflected by the pattern surface of the reticle R, the original optical path is returned. Where surface Fr
Are in a common position with the reference plate FM with respect to the projection lens PL. If the projection lens PL is a telecentric system on both sides, the emission marks ISx, ISy, ISa on the reference plate FM
The image light flux from is normally reflected on the lower surface (pattern surface) of the reticle R and returns so as to be superimposed on the marks ISx, ISy, ISa again. However, as shown in FIG. 1, the reference plate FM
Is deviated from the image plane Fo, a blurred reflection image of each mark ISx, ISy, ISa is formed on the reference plane FM, and when the reference plate FM is coincident with the image plane Fo, Fr also matches the pattern surface of the reticle R,
On the reference plate FM, sharp reflection images of the marks ISx, ISy, ISa are formed so as to be superimposed on the respective marks. FIG. 3 schematically shows the relationship between the emission mark ISx and the reflected image IMx when the reference plate FM is defocused. In the projection lens PL that is telecentric on both sides, the reflected image IMx is thus projected on the light emission mark ISx that is its own source. When the reference plate FM is defocused, the reflected image IMx is
The size is larger than the shape size of the mark ISx, and the illuminance per unit area is also reduced.

Then, of the reflected image formed on the reference plate FM, the light flux of the image portion which is not shielded by the original marks ISx, ISy, ISa is received by the optical fiber 41 via the mirror M ₁ and the objective lens 40, and the beam Splitter 42,
The photoelectric sensor 45 receives light through the lens system 44. The light receiving surface of the photoelectric sensor 45 is arranged substantially conjugate with the pupil surface (Fourier transform surface) EP of the projection lens PL.

In the various known examples described above in the prior art,
A light emitting type mark, a light receiving type mark, or a simple reflection type reference mark is arranged on the image plane side of the projection lens, and an electrical signal for contrast detection is generated by optically or electrically scanning the reticle mark in the XY plane. I was getting. However,
In the configuration of FIG. 1, it is not necessary to scan the reference plate FM in the XY plane to obtain an electric signal indicating a contrast change as in the conventional case, and the contrast signal can be obtained only by moving the Z stage 20 in the vertical direction (Z direction). Can be obtained.

FIG. 4 shows the signal level characteristic of the output signal KS of the photoelectric sensor 45, and the horizontal axis shows the position of the Z stage 20 in the Z direction, that is, the height position of the reference plate FM in the optical axis AX direction. In FIG. 4, FIG. 4A shows the emission mark ISx,
FIG. 4B shows the signal levels when ISy and ISa are back projected onto the chrome portion in the pattern surface of the reticle R.
Indicates the signal level when back projected onto the glass portion (transparent portion) in the pattern surface. Usually, the chrome portion of the reticle is vapor-deposited on a glass (quartz) plate with a thickness of about 0.3 to 0.5 μm, and the reflectance of the chrome portion is naturally much higher than that of the glass portion. However, since the reflectance at the glass portion is not completely zero, the level is considerably small as shown in FIG. 4B, but detection is possible. Generally, since the reticle for manufacturing an actual device has a high pattern density, it is considered that the probability that all the back projected images of the emission marks ISx, ISy, ISa are simultaneously applied to the glass part (transparent part) in the reticle pattern is extremely small. To be

In any case, when the surface of the reference plate FM is moved in the optical axis direction so as to traverse the best image plane Fo, the signal level becomes the maximum value at the position Zo in the Z direction. Therefore, by measuring the Z direction position of the Z stage 20 and the output signal KS at the same time and detecting the Z direction position when the signal level becomes maximum, the position of the best imaging plane Fo can be obtained, and this detection is performed. In the method, the image plane Fo can be detected at any position in the reticle R. That is, it is not necessary to use a pattern (mark) formed at a specific position in the reticle R as in the conventional technique, and as long as the reticle R is set on the object side of the projection lens PL, it is always possible to select an arbitrary position in the projection field of view. The absolute focus position (best imaging plane Fo) can be measured at the position. Also, as mentioned above, the reticle R
Has a thickness of 0.3 to 0.5 μm, and the detection error of the best imaging plane Fo caused by this thickness is caused by the projection lens PL.
If the projection magnification of is reduced to 1/5, (0.3 to 0.5) ×
(1/5) ² = 0.012 to 0.02 μm, which is almost negligible.

Next, an oblique incident light type AF system will be described with reference to FIG. 5, but here, multipoint AF is adopted. The multi-point AF is one in which measurement points for measuring the positional deviation of the wafer W in the optical axis direction (so-called focal point deviation) are provided at a plurality of positions within the projection visual field of the projection lens PL. In FIG. 5, the illumination light I, which is non-photosensitive to the resist on the wafer W, is used.
L illuminates the slit plate 1. The light that has passed through the slits of the slit plate 1 has a lens system 2, a mirror 3, a diaphragm 4,
The wafer W is obliquely irradiated via the projection objective lens 6 and the mirror 6. At this time, when the surface of the wafer W is on the best imaging plane Fo, the image of the slit of the slit plate 1 is imaged on the surface of the wafer W by the lens system 2 and the objective lens 5. The angle between the optical axis of the objective lens 5 and the wafer surface is 5
It is set to about -12 degrees, and the center of the slit image of the slit plate 1 is located at the point where the optical axis AX of the projection lens PL intersects the wafer W.

The slit image light flux reflected by the wafer W is reflected by the mirror 7, the objective lens 8 for receiving light, the lens system 9, the vibrating mirror 10, and the plane parallel plate 12.
An image is re-formed on the light-receiving slit plate 14 via. The vibrating mirror 10 microvibrates the slit image formed on the light-receiving slit plate 14 in the direction orthogonal to the longitudinal direction thereof, and the plane parallel 12 forms the slit on the slit plate 14 and the reflected slit image from the wafer W. The relative relationship with the vibration center is shifted in the direction orthogonal to the slit longitudinal direction. The vibrating mirror 10 is vibrated by a mirror drive unit (M-DRV) 11 driven by a drive signal from an oscillator (OSC.) 16.

When the slit image vibrates on the light-receiving slit plate 14 in this manner, the light flux transmitted through the slit of the slit plate 14 is received by the array sensor 15. The array sensor 15 is one in which the longitudinal direction of the slit of the slit plate 14 is divided into a plurality of minute regions, and individual photocells are arranged in each of the minute regions. Here, an array sensor of a silicon photodiode or a phototransistor is used. Shall be used. The signals from the respective light receiving cells of the array sensor 15 are selected via the selector circuit 13,
Alternatively, they are grouped and input to the synchronous detection circuit (PSD) 17. This PSD 17 has an OSC. An AC signal having the same phase as the drive signal from 16 is input, and synchronous rectification is performed with the phase of this AC signal as a reference. At this time PSD
Reference numeral 17 includes a plurality of detection circuits for individually synchronously detecting the respective output signals of the plurality of light receiving cells selected from the array sensor 15, and the respective detection output signals FS are provided in the main control unit (MCU) 30. Is output to. Detection output signal FS
Is a so-called S-curve signal, and becomes zero level when the slit center of the light-receiving slit plate 14 and the vibration center of the reflection slit image from the wafer W coincide with each other.
Is a positive level when is displaced upwards from that state,
It is at a negative level when the wafer W is displaced downward. Therefore, the wafer W whose output signal FS becomes zero level
The height position of is detected as the focal point. However, in such an oblique incident light method, there is no guarantee that the height position of the wafer W at the focused point (the output signal FS is at the zero level) always matches the best image plane Fo. That is, in the oblique incident light system, the system has a virtual reference plane determined by the system itself, and when the wafer surface matches the reference plane, PS
Since the D output signal FS becomes zero level, the reference surface and the best image forming surface Fo are set so as to match as much as possible at the time of manufacturing the device, but they match each other for a long period of time. There is no guarantee. Therefore, by tilting the plane parallel 12 in FIG. 5 to displace the virtual reference plane in the optical axis AX direction, the reference plane and the best image formation plane Fo can be matched (or the positional relationship can be defined). it can.

In FIG. 5, the MCU 30 inputs the output signal KS from the photoelectric sensor 45 to calibrate the oblique incident light type multipoint AF system, the function to set the inclination of the plane parallel 12, and the multipoint AF. Based on each output signal FS of the system, the motor 19 for driving the Z stage 20
Signal DS to the circuit (Z-DRV) 18 that drives the
And a function of outputting a command to a drive unit (including a motor and its control circuit) 22 that drives the XY stage 21.

FIG. 6 shows the projection visual field If of the projection lens PL,
It is the figure which looked at the positional relationship with the projection slit image ST of AF system on the wafer surface. The projection field If is generally circular, and the pattern area PA of the reticle R is rectangular included in the circle. The slit image ST is formed on the wafer with an inclination of about 45 ° with respect to each of the moving coordinate axes X and Y of the XY stage 21. Therefore, both optical axes AFx of the light projecting objective lens 5 and the light receiving objective lens 8 extend in the direction orthogonal to the slit image ST on the wafer surface. Further, the center of the slit image ST is set so as to substantially coincide with the optical axis AX. With such a configuration, the slit image ST is set to extend as long as possible within the projection area of the pattern area PA. Generally, on the surface of the wafer onto which the pattern area PA is projected, a shot area to be superposed thereon is already formed. Within the shot region, the variation of the uneven portion increases every time the device manufacturing process progresses, and a large uneven change may exist also in the longitudinal direction of the slit image ST. Especially when a plurality of chips are arranged in one shot area, a scribe line for separating each chip is formed in the shot area so as to extend in the X direction or the Y direction. In the extreme case, a step difference of 2 μm or more may occur between the point on the chip and the point on the chip. Since which part in the slit image ST the scribe line is located in is known in advance from the design shot arrangement, the chip size in the shot, etc., the slit image S
It is naturally understood from which part of the longitudinal direction of T the reflected light should be selected on the array sensor 15.

FIG. 7 shows an example of a concrete structure of the light-receiving slit plate 14 and the array sensor 15.
4 is a chrome layer (light shielding) deposited on the entire surface of the glass substrate,
A transparent slit is formed in a part of it by etching. The slit plate 14 is fixed to a holding metal piece 14A, and the metal piece 14A is fixed to a printed circuit board 15A such as ceramics holding the array sensor 15. As a result, the slits of the slit plate 14 are parallel to the one-dimensional array of the light receiving cells of the array sensor 15 and are in close contact therewith. Thus, the slit plate 14 and the array sensor 15
It is better to contact with or as close as possible to the slit plate 1
An imaging lens system is provided between 4 and the array sensor 15,
The slit plate 14 and the array sensor 15 may be optically conjugated. Although the length of the slit image ST shown in FIG. 6 on the wafer varies depending on the diameter of the projection visual field If, the diameter of the visual field If is 32 with the 1/5 reduction projection lens.
When it is around mm, it is desirable to make it about 1 to 1/3 times the diameter.

FIG. 8 shows an example of a concrete processing circuit of the array sensor 15, the selector 13, the PSD 17, and the MCU 30. Here, the light receiving cells in the array sensor 15 are divided into three groups Ga, Gb, Gc, It is assumed that the light receiving cells are selected and integrated in each group. The group Gb is for detecting the central portion of the slit image ST, and the groups Ga and Gc are for detecting both end sides of the slit image ST. First, since a plurality of light receiving cells in the array sensor 15 are included in the group Ga, at least one of the light receiving cells is selected by the selector 13A and its output signal is output to the PSD 17A.
Output to. The selector 13A selects an arbitrary one of the light receiving cells in the group Ga and outputs its output signal to P
In addition to the function of sending to the SD17A, it also has a function of arbitrarily selecting two or three adjacent light receiving cells in the group Ga and sending a signal obtained by adding their output signals to the PSD17A. The output signals from the light receiving cells in the groups Gb and Gc are similarly processed by the selectors 13B and 13C, and the selected signals are sent to the PSDs 17B and 17C. PSD 17A, 17B, 17C are OS respectively
C. Detection output FS by inputting the fundamental wave AC signal from 16
It outputs a, FSb, and FSc. These detection outputs FS
Each of a, FSb, and FSc is converted into a digital signal by an analog-digital converter (ADC) 30A in the MCU 30, and sent to the correction calculation unit 30B. The correction calculator 30B calculates a value corresponding to the target position in the Z direction of the Z stage 20 based on the values of the three detection outputs, that is, the focus shift amounts at the three points, and calculates the value as the deviation. Output to the detection circuit 30C. This detection circuit 30C is an ADC 30A
Z-DR as the command signal DS with the difference from the detection output value from
Output to V18. At this time, the correction calculation unit 30B causes the detection outputs FSa, F stored in advance in the storage unit 30D.
Various calculations are performed by introducing offset values for Sb and FSc, respectively. This offset value is measured and calculated by the calibration value determination unit 30E, and the determination unit 3
0E inputs the three detection outputs FSa, FSb, FSc and the output signal KS of the photoelectric sensor 45, and calculates the deviation between the reference surface of the multipoint AF system itself and the best focus surface Fo from the zero level on the detection output. The deviation voltage is calculated as

Since the deviation detection circuit 30C selects any one of the three detection output values from the ADC 30A and compares it with the target value from the arithmetic unit 30B, the difference becomes zero or a predetermined value. A servo system like this is assembled. The calibration value determination unit 30E also includes an A-D converter, a waveform memory, etc. for simultaneously digitally sampling the respective levels of the three detection outputs and the level of the signal KS (FIG. 4).

Here, referring to FIG. 9, a calibration value determination unit 30E
A specific example of the configuration will be described. First, the output signal KS from the photoelectric sensor 45 of the absolute focus detection system of the TTL (through the lens) system is an analog-digital converter (AD).
C) Input to 300, converted into a digital value corresponding to the signal level, and stored in the memory (RAM) 301. This RAM 301 is addressed by the counter 304
The increment of the counter 304 and the conversion timing of the ADC 300 are both in response to the clock pulse from the clock generator (CLK) 303. Similarly, three detection output signals FSa,
One of FSb and FSc is input to the ADC 305 via the selection switch, and the converted digital value is addressed by the counter 307 RAM 306.
Memorized in. Therefore, the RAMs 301 and 306 respectively capture the temporal changes of the waveforms of the output signal KS and one detection output. The waveforms in the RAMs 301 and 306 are used by the arithmetic processing unit 310 as processing data such as smoothing and maximum value detection. In the arithmetic processing unit 310, a signal for instructing the Z stage 20 to move at a constant speed is output to the Z-DRV 18 in order to capture the signal waveforms in the RAMs 301 and 306, and each measurement of the multipoint AF system is performed. A signal for moving the center of the light emitting mark to the point position is output to the XY-DRV 22.

FIG. 10A shows the time change characteristic of one detection output signal, and RAM 306 when the Z stage 20 is moved at a constant speed within a certain range including the best focus plane.
FIG. 10B shows the waveform inside the RAM 3 at that time.
01 represents the waveform of the signal KS obtained in 01. Since the synchronous detection signal has a waveform that is substantially point-symmetric with respect to the zero point, negative level data smaller than the zero point is AD converted in consideration of the negative level.

Since the maximum value waveform of the signal KS is stored in the RAM 301 with the time axis as an address,
The arithmetic processing unit 310 analyzes the waveform of FIG. 10B to obtain the time T ₁ when the maximum point is obtained. This time T ₁ is RA
It uniquely corresponds to a specific address point in M301. Next, the arithmetic processing unit 310 obtains the corresponding address point in the RAM 306, and obtains the level value ΔFS of the detection output signal stored at that address point. This level value ΔFS is an offset voltage from the zero point on the detection signal, and the detection output is + ΔF at the measurement point of the multipoint AF system that generates the detection output as shown in FIG. 10 (A).
When the wafer surface at the measurement point is moved in the Z direction so as to be S, the wafer surface and the best focus surface Fo coincide with each other.

By the way, when using the circuit of FIG.
The stage 21 is moved so that the center of the light emission mark on the reference plate FM is positioned at any one of the measurement points of the multipoint AF system. The positioning does not have to be so strict, and the measurement point of the multipoint AF system and the center of the light emitting mark group may be deviated by about 100 μm in the X and Y directions. Therefore, when the measurement point of the multi-point AF system, that is, the point in the slit image ST shown in FIG. 6 is determined, the position of the light emission mark group is set to X, within a range of about ± 100 μm around the point.
A coordinate position where the peak of the signal KS becomes large to some extent may be obtained by shifting in the Y direction and shaking in the Z direction. Although this is extremely small in probability, it is a disadvantage that the entire emission mark group coincides with the transparent portion of the reticle R (signal K).
This is to prevent the S / N ratio of S from decreasing as much as possible. However, when the calibration operation is performed at high speed, it is possible to obtain the offset value ΔFS with substantially the same accuracy without searching for the coordinate position where the peak of the signal is particularly large.

FIG. 11 shows three measurement points MP of the multipoint AF system.
a, MPb, MPc and the existing range CAa, CAb, CAc of the center point of the light emission mark group are schematically shown. The optical axis AX of the projection lens PL is located at the intersection of the X axis and the Y axis.
Shall pass. Each measurement point MPa to MPc corresponds to the position of the light receiving cell on the array sensor 15.
Further, PA indicates the range when the pattern area of the reticle R is projected, that is, the range of one shot area on the wafer. In the present embodiment, three points on the slit image ST are set as measurement points, the central measurement point MPb is set near the shot center point, and the other measurement points MPa and MPc are set near both ends of the slit image ST. And Further, in order to simplify the following description, it is assumed that there are no scribe lines on the X axis and the Y axis in FIG. 11 and the range PA is one chip.

Therefore, three measuring points MPa to M shown in FIG.
Aligning the centers of the emission marks with Pc
As shown in FIG. 10, the stage 20 (reference plate FM) is moved from top to bottom (or bottom to top) in the Z direction at a substantially constant speed only once, and the TTL absolute focus detection system and oblique incidence light system are used. The offset amounts ΔFSa, ΔFSb, and ΔFSc at each measurement point are individually obtained by simultaneously using the multipoint AF system of (1) and stored in the storage unit 30D in FIG. During the operation for this calibration, the surface of the reference plate FM is detected by the oblique incident light type multi-point AF system, so that the emission mark groups ISx, ISy, ISa, etc. are exactly on the slit image ST. When it is located and the detection output FS at each measurement point is affected, the position of the light emission mark group is shifted within the existing range CAa to CAc in FIG. 11, and the slit image ST is slightly displaced from the light emission mark group. The light may be projected onto the reflection surface portion of the reference plate FM.

The offset amounts ΔFSa, ΔFSb, and ΔFSc (unit: voltage V) at the respective measurement points thus obtained are all in the optical axis AX in which the three points of the multipoint AF system are the in-focus points (zero points). The height position of is the best focus plane F
a constant distance offset ΔZ with respect to the corresponding point in o
It means that it has a, ΔZb, and ΔZc.
If the slope k (unit V / μm) of the straight line portion including the zero point on the waveform of the detection output signal shown in (A) is known, the offsets ΔZa to ΔZ as the distance in the Z direction are calculated by the following equation.
c is obtained.

ΔZa = ΔFSa / k ₁ , ΔZb = ΔFS
b / k ₂ , ΔZc = ΔFSc / k ₃ Here, k ₁ , k ₂ and k ₃ originally have the same value, but strictly speaking, they are individually different, so it is desirable to obtain them in advance for each measurement point. . FIG. 12 is an example schematically showing how the offset amount ΔFS appears, and FIG. 12 (A) shows 3 points MPa,
Offset amounts ΔFSa and ΔFS of MPb and MPc, respectively
This shows a case where both b and ΔFSc have positive values and there is a substantially constant inclination in the direction in which the slit image ST extends. Various factors can be considered as the factors representing the tendency of the offset, but they are divided into two problems, a problem on the multipoint AF system side and a problem on the reticle R side. First, as a problem on the side of the multi-point AF system, when the slit image ST from the light-projecting slit plate 1 is re-imaged on the light-receiving slit plate 14, the parallelism with the slit of the slit plate 14 is slightly increased. It may be crazy. Further, the problem on the reticle R side is that the reticle pattern surface is inclined at least in the longitudinal direction of the slit image ST, or the image surface inclination of the projection lens PL itself is considered.

In any case, since the problems of both of them are compounded, it is difficult to specify them independently of each other. Further, FIG. 12B shows the offset amount ΔF of the central measurement point MPb.
It shows a case where Sb is a negative value and offset amounts ΔFSa and ΔFSc at the measurement points MPa and MPc at both ends are positive values and have substantially the same magnitude. The main cause of such characteristics is the problem on the reticle R side, and the curvature of the reticle pattern surface and the curvature of field of the projection lens PL itself are considered. However, the curvature of field of the projection lens PL is suppressed sufficiently small by inspection and adjustment during manufacturing of the apparatus, and even if it remains slightly, the degree of curvature of field is quantitatively obtained in advance. Figure 12
If you deduct it from the characteristics of (B), you will get a reticle R exclusively.
It can be seen whether or not the curvature is the main factor.

Further, FIG. 12C shows a case where the inclination tendency and the bending tendency of FIG. 12A are combined. Therefore, a specific example of a series of calibration sequences in consideration of the tendency of offset at each measurement point as shown in FIG. 12 will be described. However, in principle, each measurement point MPa to MPc
Since the offset amounts ΔFSa to ΔFSc obtained in step 1 become calibration values at the measurement points, for example, when the surface of the wafer W is detected at the measurement points MPa, the detection output signal F
If the Z stage 20 is driven so that Sa becomes ΔFSa, the wafer surface and the best focus surface Fo can be matched at the measurement point MPa.

However, the actual focusing is not always performed with only one point, and it may be necessary to determine it in consideration of the surfaces. In addition to this, it is necessary to consider the depth of focus of the projection lens PL. FIG. 13 shows a flowchart of the measurement operation in the calibration sequence, in which multipoint A
The F system measurement points are generalized to n points, the measurement points shown in FIG. 11 are MPi (where i = 1 to n), and the area where the center of the emission mark group is to be positioned is CAi (where i = 1 to 1).
n), the synchronous detection output signal at each measurement point is FSi (i = 1
˜n) and the offset amount is ΔFSi (i = 1 to n).

First, in step 100, i = 1 is set,
In step 101, the XY stage 21 is moved to move to the area C.
The center of the emission mark group is positioned within Ai. Next, at step 102, the Z stage 20 is positioned in the vicinity of the starting point of the signal waveform to be stored in the RAMs 301 and 306 of FIG. 9 based on the detection output signal FSi at the measurement point MPi. In this case, since it is necessary to load the waveforms shown in FIG. 10 into the RAMs 301 and 306, the detection output signal FS
The Z stage 20 is set at a position where i is outside the maximum value or the minimum value as shown in FIG. In order to do this easily, the focus servo system is operated in the straight line portion including the zero point of the detection output FSi, and the servo enable signal that prohibits the feedback to the servo system is made outside the straight line portion, and the servo enable signal is set to the servo enable signal. The Z stage 20 may be positioned based on this.

Next, in step 103, the light emitting mark group is turned on by the light having the same wavelength as the exposure light, and the Z stage 20 is moved in one direction at a substantially constant speed, while the RAM 30 in the circuit of FIG.
Waveforms of the detection output signal FSi and the signal KS are digitally sampled for each of 1 and 306. When the waveform acquisition is completed, the offset amount ΔFSi is calculated in step 104 and stored in the storage unit 30D. Then step 1
In 05, it is determined whether or not i = n. If i has not reached the n-th value, i is incremented by 1 in step 106, the process returns to step 101, and the same sequence is repeated for other measurement points. If i = n is determined to be true in step 105, the sequence of FIG. 14 is executed. Note that in the sequence of FIG. 13, step 102 does not necessarily have to be executed for all measurement points. For example, just before step 101, only measurement points near the center in the visual field If of the multipoint AF system are measured. Alternatively, the waveform acquisition start point (the height position of the Z stage 20) stored at that time may be applied at the time of measurement at another measurement point.

Now, FIG. 14 shows a unique calibration method in the multipoint AF system, and shows an example of performing the calibration in consideration of various factors described in FIG. 12 above. First, in step 110, it is determined whether or not the averaging calibration considering all the plurality of measurement points of the multipoint AF system is performed. In this case, the offset amount Δ at each measurement point
When only FSi needs to be obtained (for example, when it is assumed that the pinpoint AF is to focus independently at each measurement point), the series of calibration processes ends. When performing averaging calibration, the following step 11
At 1, the range of each offset amount ΔFSi is checked.
The algorithm for the check is whether the difference between the offset amounts at two measurement points adjacent to each other is extremely large, or the absolute value of the offset amount at each measurement point is the upper limit or the lower limit of the linear range of the detection signal FS. It is possible to adopt whether or not you are close to.

In the next step 112, as a result of the check in step 111, it is judged whether or not there is an offset amount that has become an abnormal value. If an abnormal value exists, the process proceeds to step 113. At this time, the number of measurement points that become an abnormal value and how far to allow the positions are determined by the reticle R that is mounted.
Pattern is determined due to the surface structure in the shot area on the wafer W on which the pattern of FIG.

Now, in step 113, it is judged whether or not the measurement operation of FIG. 13 is to be performed again. Whether or not to perform the remeasurement is set in advance by the operator when setting the parameters of the device operating conditions. And step 11
When it is determined in 3 that re-measurement is to be performed (retry), it is determined in the next step 114 whether or not the number of re-measurements has been performed a preset number of times. If it is determined in step 114 that the number of times is not exceeded, the sequence from step 100 in FIG. 13 is repeatedly executed. If it is set in step 113 that the remeasurement is not executed even once, the process proceeds to step 118, an error display and warning indicating that an abnormal value exists is generated, and the series of sequences is ended. .

When the number of times is further exceeded in step 114, the process proceeds to the next step 115, and it is determined whether or not the setting for realigning the reticle is set.
As described above, when there is a large variation for each offset amount ΔFSi, there is a problem with the reticle R as one factor. For example, when the reticle R is sucked onto the holder, a relatively large foreign substance or the like may be sandwiched between the suction surface and the reticle R. Alternatively, the adsorption may cause the reticle R to bend. Therefore, once the reticle R is removed from the holder and realigned, the inclination of the pattern surface of the reticle R
The deflection is changed to the desired one.

When it is determined in step 115 that reticle realignment is to be performed, the next step 116
Then, it is determined whether or not the number of times exceeds the number designated in advance. Here, when the reticle realignment number exceeds the set number (step 116) or when the reticle realignment execution is not set (step 115), both proceeds to step 118 and an error display or warning is generated. To do. And step 11
If it is determined in 6 that the number of times has not exceeded, in step 117, the reticle R is realigned (remove the reticle R from the holder once, and again suck it to the holder to align it), and then proceed to step 100 in FIG. At this time, the counter for the number of remeasurements determined in step 114 is reset to zero.

On the other hand, if it is determined in the previous step 112 that there is no abnormal value, each offset amount ΔF is determined in step 120.
Calculate the average value ΔFA by adding and averaging Si, and
Each offset amount ΔFSi centered on the average value ΔFA at 21
Is checked (the deviation amount of ΔFSi from ΔFA). If the variance is larger than a predetermined value, the process proceeds to step 122. If the variance is small, the process proceeds to step 130.

FIG. 15 shows the average value ΔFA and the variance.
Will be described with reference to. FIG. 15A shows a case where the offset amount ΔFSi at each measurement point (here, 5 points) has a positive value and has a tendency to be uniformly inclined.
The average value ΔFA at this time appears at almost the midpoint of the uniform slope characteristic (broken line). Further, the dispersion increases or decreases on the peripheral side depending on the inclination of the inclination characteristic. Therefore, the small variance means that the multipoint AF
It means that the focusing reference plane of the system itself and the best focus surface Fo have good parallelism, and it can be approximated to the best focus plane Fo by simply shifting the focusing reference plane of the multipoint AF system itself in parallel. become.

FIG. 15B shows the characteristics when the field curvature, reticle deflection, etc., and the relative tilt are combined, and the average value ΔFA may be small, but the dispersion (ΔFSi
The deviation amount from ΔFA) may increase as a whole. Of course, the smaller the degree of bending and the degree of relative inclination, the smaller the dispersion. Therefore, if it is determined in step 121 that the variance is small to some extent, in step 130, the average value Δ
Judge whether FA is large to some extent. If the average value ΔFA is relatively large, it is determined in step 131 whether or not the offset correction by the plane parallel (harbing) 12 shown in FIG. Harving 1
In No. 2, the focusing reference plane (the plane defined by the zero point of the detection output FS) of the multipoint AF system itself can be translated in the Z direction as a whole by adjusting the inclination. Therefore, in step 131, it is selected to perform the harbing correction, and in the next step 132,
When the correction is performed, the offset amount ΔFSi is corrected so that the average value ΔFA shown in FIG. That is, after the harving 12 is tilted by the interval ΔZf in the Z direction corresponding to the average value ΔFA in step 132, the true offset amount ΔFSi at each measurement point is treated as corrected to ΔFSi = ΔFSi−ΔFA. You can

However, the correction amount by the harving 12 is
It is not always necessary to exactly match the average value ΔFA, and the point is that the correction amount by the harving 12 should be accurately obtained. Next, at step 133, it is judged whether or not the offset amount at each measurement point is to be measured again, and when re-measured, the routine proceeds to step 100 in FIG. This step 13
The selection in 3 is performed according to the parameters preset by the operator.

When it is determined in step 133 that re-measurement is not necessary (when the correction amount due to harving is accurately obtained, etc.), each offset amount ΔFSi is calculated by the harving correction amount (denoted as ΔFA ′) in the next step 134. Correct and memorize. That is, ΔFSi = ΔFSi−ΔF
Calculate A '. As described above, the process when the average value ΔFA is large is completed in step 130, and the process proceeds to the next step 122. This step 122 is the same as the previous step 1.
When it is determined that the variance is large in Step 21, or Step 1
It is also a jump destination when it is determined that the average value ΔFA is small in 30.

In step 122, an approximate plane (or an approximate straight line) is specified by the least square method using each offset amount ΔFSi thus obtained. This approximate plane (or straight line)
15A, under the offset amount ΔFSi having the uniform inclination characteristic as shown in FIG. 15A, the inclination characteristic (broken line) becomes an approximate plane, and the curved characteristic (broken line) as shown in FIG. 15B. With an offset amount ΔFSi having
It becomes an approximate plane (or a straight line) like the inclined line Q in the inside.

Next, in step 123, the amount of inclination of the approximate plane, that is, the amount of inclination of the line Q in FIG. 15B with respect to the zero level is obtained, and in the next step 124, it is judged whether or not the amount of inclination is greater than or equal to the allowable value. To be done. The tilt amount is the relative tilt between the approximate plane and the best focus surface Fo that are determined so that the deviation is smallest everywhere with respect to the offset amount ΔFSi at each measurement point of the multipoint AF system. If this inclination is large, there is a possibility that a part of the shot area may be out of focus due to the relationship between the depth of focus of the projection lens PL and the size of the shot area, that is, an intra-shot focus error may occur. Therefore, when the inclination of the approximate plane is extremely large, it is determined that there is some problem at the time of measurement or on the reticle R side, and step 113 described above is used.
~ 118 are executed.

When it is determined in step 124 that the inclination of the approximate plane is within the allowable value, the final step 125 is executed. In this step 125, the offset amount ΔFSi at each measurement point is set to ΔF using the approximation plane as a new reference.
Calculate the correction to Ji. Specifically, for example, FIG. 15 (B)
At the measurement point where the offset amount is ΔFS ₃ ,
The offset amount ΔFJ ₃ of the corresponding point on the approximate plane is replaced. In this way, the Z stage 20 is moved up and down and tilted so that the detection output signal FSi obtained at each measurement point will have the offset amount ΔFJi, so that good focusing is achieved on the entire surface within the shot area. Will be done. For that purpose, it is desirable that the Z stage 20 is provided with a leveling mechanism and the entire wafer W is tilted in the same direction by the tilt of the approximate plane.

Although a series of calibration operations are completed as described above, it is sufficient in principle to execute the sequence of FIGS. 13 and 14 once when reticle conversion is performed and reticle alignment is completed. In the exposure process using the same reticle, the initial offset amount ΔFSi or ΔFJi may be changed due to a slight drift of the multi-point AF system, a temperature change in the apparatus, an error in focus position correction due to pressure control in the projection lens PL, and the like. It can be crazy. Therefore, the sequences of FIGS. 13 and 14 may be executed for each lot (usually 25) during the wafer exposure process.

Further, in the present embodiment, when the tendency like the image plane inclination appears, the reticle realignment is executed in steps 115, 116 and 117. However, as another method, the holder of the reticle R may be inclined. It is possible. In this case, the best focus plane Fo and the focusing reference plane (or approximate plane) of the multi-point AF system can be set parallel to each other, but the image of the pattern area projected on the wafer W is trapezoidal distortion or rhombus distortion. Etc. may occur. Therefore, the distortion can be reduced by inclining some of the optical lenses near the reticle side in the projection lens PL from the plane perpendicular to the optical axis AX by a small amount.

Further, a tendency such as image plane inclination appears also due to the slit parallelism between the reflection slit image ST of the multipoint AF system and the light-receiving slit plate 14, so that, for example, FIG.
When the inclination tendency as shown in (A) is strongly generated and does not change even by realignment of the reticle, the slit plate 1 for light projection or the slit plate 14 for light reception is relatively automatically moved by a slight amount according to the inclination tendency. The slit parallelism may be adjusted by rotating the slit.

By the way, in the projection method of the slit image ST shown in FIGS. 6 and 11, the angle is 45 ° with respect to the XY coordinate axes.
However, the multi-point AF system lacks the ability to specify a surface. Therefore, another set of multipoint AF systems may be arranged in the 135 ° direction with respect to the X and Y axis directions, and the slit image ST ′ as shown in FIG. 16 may be projected at the same time. In this way, nine measurement points (see FIG. 1) are included in the vicinity of the four corners in the pattern area PA (shot area on the wafer) and the center.
The circles in 6) can be set. For that purpose, 5 points are selected on each of the two sets of array sensors, and a total of 10 (or 9) synchronous detection circuits are required.

Further, the multipoint AF system projects a minute slit image or a spot image obliquely onto a plurality of predetermined measurement points in the projection visual field If, and reflects slits (spots) from the respective measurement points. The same effect as that of the present invention can be obtained by a method in which an image is collectively received by a two-dimensional image pickup device, for example, a CCD, and a focus shift is obtained by a shift amount of a plurality of received images from a reference pixel position on each CCD. can get. Further, as described in the prior art, it can be similarly applied to a multi-point AF system of a system in which spot light is projected onto four points on a wafer through only a projection lens.

Although the sequence for calibration has been mainly described with reference to FIGS. 13 and 14, some methods of operating the multipoint AF system after further calibration will be described. First, when the offset amounts ΔFSi at n measurement points of the multipoint AF system are obtained, the offset amounts ΔFSi are used to execute steps 122 and 123 in FIG. The relative tilt amount and tilt direction between the average reference focus surface and the best focus surface of the AF system are calculated. As described above, the relative tilt obtained here is a relative value with respect to the best focus surface, so the fact that the relative tilt becomes zero means that the measurement points of the multipoint AF system are different. The virtual surface (that is, the reference focusing surface) formed by connecting the reference focusing positions (Z position where the zero point of the detection signal is obtained) in (1) is best with almost constant offset amount at any point in the projection visual field. It means that it became parallel to the focus plane. However, since it is practically difficult to readjust the device so that the offset amount ΔFSi at each measurement point is substantially constant, when the average surface determined by the n offset amounts ΔFSi is inclined, When operating the multi-point AF system, it is preferable to tilt the wafer W so as to entirely match the tilt, that is, deal with the wafer global level.

To this end, for example, when the offset characteristic is as shown in FIG. 15A, the wafer holder is previously tilted in the same direction by the same amount as the tilt (broken line) of the characteristic by the leveling mechanism. . With this arrangement, in the case of the offset characteristic as shown in FIG. 15A, when the wafer W is positioned in the Z direction so that the offset amount is ΔFS ₃ at the central measurement point, the offset amounts at other measurement points are set. Is the values ΔFS ₁ , ΔFS ₂ , ΔF stored in advance.
It is close to S ₄ and ΔFS ₅ , respectively. Therefore, when leveling the wafer holder immediately after (or at the same time), the leveling drive amount is extremely small, so the throughput when exposing the reticle pattern on the wafer by the step-and-repeat method or the step-and-scan method is improved. There are uses such as doing.

Further, even in the case of the offset characteristic accompanied by the curvature as shown in FIG. 15B, it is preferable to find the approximate plane and tilt the wafer holder in advance by the same amount as the inclination (Q) of the approximate plane. With this configuration, when the shot area on the wafer is detected, the offset amount at each measurement value is close to the offset amount ΔFJi stored in advance, and the drive amount of the leveling mechanism is extremely small. Will be enough.

As described above, if the entire wafer holder is pre-leveled based on the inclination of the offset characteristic obtained at the time of calibration, each measurement of the multipoint AF system at the time of exposure for each shot area on the wafer W is performed. The amount to be leveled based on the detection value at the point can be extremely small, and the throughput can be improved. As a second operation method, after performing leveling correction for each shot area, the best focus plane within the shot area is set based on the focus detection signal (detection output) only at a specific measurement point in that shot area. How to match local parts,
There is a so-called pinpoint AF method. FIG. 17 shows a wafer W
An example of the cross-sectional structure of the surface of one shot area above is shown, and the arrows represent the five measurement points MPa to MPe of the multipoint AF system. Generally, relatively large unevenness is generated in the shot area on the wafer where the process is advanced. In FIG. 17, areas AS ₁ and AS ₃ are convex areas, and
Reference numeral ₂ is a recessed area. Here, assuming that the best focus surface is focused on the area AS ₂ to perform exposure, after leveling correction, focusing (Z stage fine movement) is performed based only on the detection output signal FS ₃ obtained at the measurement point MPc. To do. When the offset characteristic of the multipoint AF system is as shown in FIG. 15 (B), the surface of the shot area is parallel to the line Q in FIG. 15 (B) due to the leveling correction. In the previous embodiment, focusing was performed by the offset amounts ΔFJ _{1 to} ΔFJ ₅ representing the straight line Q, but here, the Z stage is finely moved so that the detection output value at the measurement point MPc becomes the offset amount ΔFS _3. Become. Further, when the harving 12 is corrected by an amount corresponding to the offset amount ΔFJ ₃ calculated during the calibration of the measurement point MPc, the detection output value at the measurement point MPc should be equal to (ΔFS ₃ −ΔFJ ₃ ). To Z
The stage 20 may be slightly moved.

In this way, the area AS _{2 in} FIG.
Therefore, the best focus can be obtained, and the resolution of the selected local portion in the shot area can be maximized. By the way, in each of the above embodiments, the pair of emission marks ISx, ISy, etc. were sequentially moved to the vicinity of each measurement point of the multipoint AF system, and then each measurement point was calibrated. As described above, when the large reference plate FM that substantially covers the projection visual field If of the projection lens PL can be arranged on the Z stage 20, the reference plate F
On the M, n sets of light emitting marks may be provided corresponding to the positions of the respective measurement points of the multipoint AF system. However, in this case, the light emitted from the projection lens PL and returning to each slit defining the n sets of light emission marks must be guided to each of the n photoelectric sensors by an optical fiber or the like provided individually for each set. There is.

When a plurality of sets of light emission marks are provided on the reference plate FM in correspondence with the positions of the respective measurement points in this way, the calibration operation is extremely simplified and the reference plate FM is obtained.
The vertical movement of is only required once. Instead, A shown in FIG.
It is necessary to prepare n sets of DC 305, RAM 306, counter 307, etc. The small circle shown by the broken line in FIG. 18 represents a region where the slits of the light emitting marks ISx and ISy are illuminated from the back side. In addition, when the light emitting mark groups are arranged at a plurality of locations (9 locations in FIG. 18) on one large reference plate FM in this way, calibration is performed.
The orthogonality between the surface of the reference plate FM and the optical axis AX of the projection lens PL seems to affect the mounting error of the reference plate FM.
Even if the surface of M and the best focus surface are relatively inclined, it can be said that there is no substantial effect. that's all
According to the present embodiment, the absolute focus detection of the TTL method is performed.
Depending on the system, the mask for the device used for the actual exposure
Through the projection optical system
Absolute at any point in the projection field using
Since the image plane position can be detected, the surface of the photosensitive substrate
Measurement of an oblique incidence type focus detection system that detects the height position of a surface
Focus calibration can be performed at
It can be expected to improve the accuracy of ribulation. Also oblique incidence
Type focus detection system is a multi-point AF system with multiple measurement points.
In this case, highly accurate calibration is possible for each measurement point.
Therefore, there is a step structure on the photosensitive substrate, and
Even if you want to focus on the stepped portion, multiple measurements
From the fixed point, measure according to the position of the specific step
Select a fixed point and use the detection signal obtained from that measurement point
Accurately projected image of the mask pattern only on the specific step
Can be focused. Furthermore, the absolute TTL method
According to the focus detection system, it is best at multiple points in the projected field of view.
Since it is possible to specify the image plane, the image plane of the projection optical system
Curvature, image plane inclination, etc. will also be required accurately. this
Therefore, the vertical movement of the mask, leveling of the mask (chill
G), movement or feeling of a part of the optical element in the projection optical system.
Leveling of the holder (stage) that holds the optical substrate
So that it can handle the above-mentioned field curvature and field tilt
become.

[0064]

According to the present invention, even when the measurement point of the first focus detection means is set to any position within the projection field, throw
Accurate calibration (focus calibration) based on the image plane of the shadow optical system becomes possible, and in particular, accuracy, reproducibility, stability, etc. of the multipoint AF system can be improved.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a projection exposure apparatus having a second focus detection system according to an embodiment of the present invention.

FIG. 2 is a plan view showing a pattern arrangement on a reference plate FM in FIG.

FIG. 3 is a diagram showing a state of a light emission mark and a reflection image superimposed on it.

FIG. 4 is a diagram showing a waveform of a photoelectric signal obtained by a second focus detection system.

FIG. 5 is a diagram showing a configuration of a first focus detection system suitable for an embodiment of the present invention.

FIG. 6 is a diagram showing a positional relationship between a projection visual field and a slit projection image by the first focus detection system.

FIG. 7 is a perspective view showing a configuration of a light receiving system of a first focus detection system.

FIG. 8 is a block diagram showing a configuration of a signal processing circuit of a first focus detection system.

FIG. 9 is a block diagram showing a configuration of a signal processing circuit of a second focus detection system.

FIG. 10 is a waveform diagram showing how the detection signal from the first focus detection system and the detection signal from the second focus detection system are processed.

FIG. 11 is a diagram showing an arrangement example of measurement points in a shot area on a wafer by the first focus detection system.

FIG. 12 is a graph schematically showing the tendency of the offset amount at each measurement point.

FIG. 13 is a flowchart showing a sequence of measurement operation when calibrating each measurement point of the multipoint AF system.

FIG. 14 is a flowchart showing a sequence of calculation processing for calibration of a multipoint AF system.

FIG. 15 is a graph showing the tendency of the offset amount at each measurement point assumed during calibration.

FIG. 16 is a diagram showing a modification of the arrangement of measurement points of a multipoint AF system.

FIG. 17 is a diagram showing a cross-sectional structure of the surface of a shot area on a wafer.

FIG. 18 is a diagram showing a modification of the arrangement of the light emitting marks on the reference plate.

[Explanation of symbols for main parts] R reticle RL projection lens W wafer FM reference plate 20 Z stage 21 XY stage 30E Calibration value determination unit 30D storage 41 optical fiber 45 photoelectric sensor

Continued front page       (56) References JP-A-1-273318 (JP, A)                 JP 63-306626 (JP, A)                 JP-A-63-255917 (JP, A)                 Japanese Patent Laid-Open No. 1-205418 (JP, A)                 JP-A 1-251716 (JP, A)                 JP-A-2-105514 (JP, A)                 Actual Kaihei 3-34233 (JP, U)

Claims (14)

(57) [Claims] 1. A projection optical system for image-forming and projecting an image of a mask pattern on a predetermined image forming plane, and a plane parallel to the image forming plane for holding a photosensitive substrate substantially parallel to the image forming plane. An XY stage that moves two-dimensionally, a Z stage that moves the photosensitive substrate in the optical axis direction of the projection optical system, and measurement points at a plurality of predetermined positions within the projection visual field of the projection optical system. , in a projection exposure apparatus having a first focus detection means for detecting the <br/> positional information of the optical axis direction of the surface of the photosensitive substrate in people each of the plurality of measurement points, an arbitrary in the projection field forming a point of Oite the projection optical system
And second focus detection means which can detect an image plane; positions of a plurality of measurement points by the first focus detection unit, or the image plane of Oite the projection optical system to each of the positions of the close proximity
Specifying means for specifying a detection point of the second focus detecting means so as to detect the signal; and a signal detected by operating the second focus detecting means at each of the specified positions , Then
At each of the above-mentioned positions obtained or at measurement points in the immediate vicinity
Based on the detection signal of the first focus detection means ,
A projection exposure apparatus comprising: a calibration unit that calibrates the detection error of each of the plurality of measurement points by the first focus detection unit individually or on average. 2. The calibrating means includes the second focus detecting hand.
The step detection signal and the detection signal of the first focus detection means.
Based on the plurality of measurement points,
It is characterized in that the offset amount of the focus detection unit 1 is obtained.
The projection exposure apparatus according to claim 1. 3. The first focus detecting means is configured to detect the first focus.
The virtual reference plane of the point detecting means is defined by the projection optical system.
A parallel plane plate for displacing in the optical axis direction,
The calibration means includes a plurality of calibration points obtained corresponding to the plurality of measurement points.
The parallel plane plate is driven based on the offset amount of
The imaginary reference plane is displaced.
2. The projection exposure apparatus according to item 2. 4. The calibration means is provided for the plurality of measurement points.
Whether or not there are abnormal values in the multiple offset values obtained
It is determined whether or not it is according to claim 2 or 3.
Projection exposure device. 5. The second focus detecting means is the mask.
Detecting the image plane of the projection optical science system through the calibration
When the offset amount has an abnormal value, the means is
After removing the mask from the mask holder once,
5. The mask holder holds the mask holder.
The projection exposure apparatus according to. 6. The calibrating means includes the second focus detecting hand.
Approximation of the image plane of the projection optical system based on the step detection signal
A plane is obtained, and the offset amount is based on the approximate plane.
6. The method according to claim 2, wherein
The projection exposure apparatus according to. 7. The XY stage comprises a tilt of the approximate plane.
A leveling mechanism that tilts the photosensitive substrate according to
The projection exposure apparatus according to claim 6, characterized in that
Place 8. A projection exposure method for exposing a substrate by projecting an image of a pattern of a mask onto the substrate via the projection optical system , wherein:
It has measurement points at a plurality of predetermined positions and
Position information in the optical axis direction on the surface of the substrate at each of the measurement points
Focus detecting means for detecting
Multiple measurement points by means, or each position in its immediate vicinity
Second focus for detecting the image plane of the projection optical system at
Point detection means, and the second focus detection means
The signal detected by operating at each position and the signal obtained at that time
At each of the above-mentioned positions or at measurement points in the immediate vicinity
Based on the detection signal of the first focus detecting means,
At each of the plurality of measurement points by the first focus detection means
Special feature is to calibrate the detection error individually or on average.
Projection exposure method. 9. The calibrating step includes the second focus detection.
Detection signal of output means and detection signal of the first focus detection means
Based on and before each of the plurality of measurement points
Note that the offset amount of the first focus detection means is calculated.
The projection exposure method according to claim 8, wherein the projection exposure method is a characteristic. 10. The first focus detection means is adapted to
The virtual reference plane of the focus detection means is the projection optical system.
It is equipped with a plane-parallel plate for displacing in the optical axis direction of
The step of calibrating is obtained corresponding to the plurality of measurement points.
Drives the parallel plane plate based on multiple offset amounts
And, wherein the displacing the virtual reference plane
The projection exposure method according to claim 9. 11. The step of calibrating comprises: measuring the plurality of measurements.
There are outliers in the multiple offset amounts that are obtained corresponding to the points.
11. The method according to claim 9, wherein it is determined whether or not
The projection exposure method according to. 12. The second focus detection means is the mass sensor.
The image plane of the projection optical system is detected via the
The corrective step is when there is an abnormal value in the offset amount.
If the mask is removed from the mask holder once,
It is characterized in that the mask holder is held again.
The projection exposure method according to claim 11. 13. The step of calibrating comprises using the second focus.
The image plane of the projection optical system based on the detection signal of the detection means
Of the above-mentioned offset plane with reference to the approximate plane.
13. The method according to any one of claims 9 to 12, characterized in that the amount of input is obtained.
The projection exposure method according to any one of them. 14. The projection exposure method according to claim 13, wherein the substrate is tilted according to the tilt of the approximate plane.