JPH10106937A - Position detecting method, its equipment and projection aligner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable to detect the position of a position detection mark with high precision when rotation error is generated between the fixing position of a two-dimensional image sensing element and the position detection mark. SOLUTION: Two-dimensional image sensing signals of a wafer mark WM and index marks 52a, 52b which are imaged on an image surface 70 of a CCD are devided into (n) (=5), in the direction (an arrow VS) perpendicular to the raster scan direction (an arrow HS) of a CCD, and integrated in the arrow VS direction in each divided region. Positions of the wafer marks WM and the index marks 52a, 52b in each divided region are measured on the basis of the integrated signal, and measured values of the respective mark positions are statistically processed. Thereby the final mark position can be detected with high precision.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a position detecting method and apparatus, and a projection exposure apparatus, and more particularly, to a position detecting mark formed on a surface of a substrate such as a semiconductor wafer or a stage for holding the substrate. The present invention relates to a position detection method and apparatus for detecting the position, and a projection exposure apparatus having the position detection apparatus. The position detecting method and the position detecting apparatus according to the present invention are particularly applicable to a method in which a mask pattern is formed on a photosensitive substrate in a photolithography process in a manufacturing process of a semiconductor device, an imaging device (such as a CCD), a liquid crystal display device, or a thin film magnetic head. It is suitable for use as an alignment sensor for detecting a position detection mark formed on a substrate or the like at the time of exposure.

[0002]

2. Description of the Related Art Conventionally, in a photolithography process (a process of forming a resist image of a mask pattern on a substrate) for manufacturing a semiconductor device or the like, a reticle pattern as a mask is exposed to a photoresist through a projection optical system. There is used a projection exposure apparatus (stepper or the like) for exposing a wafer (or a glass plate or the like) coated with, or an exposure apparatus by a proximity method for directly transferring a reticle pattern onto the wafer.

For example, in order to manufacture a semiconductor device, it is necessary to form a multi-layer circuit pattern on a wafer in a predetermined positional relationship by stacking the circuit patterns. When exposing a pattern on a wafer, it is necessary to perform high-precision alignment (alignment) of a reticle and a circuit pattern in each shot area of the wafer prior to exposure. To do this alignment,
An alignment mark (wafer mark) is formed on the wafer as a position detection mark during the previous process, and the position of the alignment mark is detected by an alignment sensor mounted on the projection exposure apparatus. By doing so, an accurate position of the circuit pattern in each shot area on the wafer can be detected.

As a conventional alignment sensor, there is provided a laser beam scanning type sensor which irradiates and scans (scans) a laser beam near an alignment mark and detects a mark position based on a change in intensity of scattered / diffracted light; There are two main types of imaging sensors that irradiate monochromatic light or broadband light (broadband light) in the vicinity of the alignment mark, take an image of the image through a detection optical system, and detect the mark position based on the image signal. It is.

However, in the above-described laser beam scanning type sensor, since the detection light beam used is a monochromatic laser beam, a multiplexing occurs between the surface of the wafer and the surface of the photoresist applied thereon. Interference occurs,
Since a large error may occur in the mark detection position, it is expected that an imaging sensor using broadband light as a detection light beam will become mainstream in the future.

[0006]

In such a conventional imaging sensor, a CCD is generally used as an image pickup device.
(Charge Coupled Device: solid-state imaging device) and an imaging tube are used. In these imaging devices, a two-dimensional image is captured by a raster scan method in which vertical scanning is sequentially performed while repeating horizontal scanning. Therefore, position detection based on the imaging signal is preferably performed in a raster scanning direction (horizontal scanning direction). It is preferred and the detection direction is generally set as such. For this reason, the position detection of the alignment mark is performed in such a manner that the detection direction of the mark position (hereinafter, referred to as “measurement direction”) coincides with the raster scan direction to capture an image signal, and the direction perpendicular to the measurement direction (hereinafter, “ In this case, the imaging signal is integrated, that is, the two-dimensional signal is integrated into the one-dimensional signal, and the position of the mark is detected based on the one-dimensional signal.

As described above, when integrating a two-dimensional image pickup signal into a one-dimensional signal, there is an advantage that the S / N ratio of the signal can be improved and the signal processing time can be shortened. When the measurement direction and the raster scan direction deviate from each other, there is a disadvantage that an alignment mark position detection error occurs.

That is, when the measurement direction and the raster scan direction are shifted (for example, when the mounting position of the image sensor is shifted by an angle θ with respect to the alignment mark).
When an image signal captured by a raster scan of an image sensor is integrated in a direction orthogonal to the image to form a one-dimensional signal, an image signal having substantially the same waveform slightly shifted in phase (for example, a sinusoidal wave) Signals) are added, and the contrast of the integrated signal is reduced, so that a mark position detection error easily occurs.

Therefore, the raster scan direction may be strictly aligned with the measurement direction. However, it is not actually possible to attach the image pickup device to the apparatus such that the rotation direction of the image pickup device has no error in the direction of the alignment mark. However, it is unavoidable that a certain degree of rotation error occurs in manufacturing.

[0010] In addition to the above, if the resist on the wafer surface has coating unevenness or the like, the reflectance of the wafer mark formed on the wafer changes depending on the location due to the influence.
If the mark position is detected using the whole-area integration signal for integrating the imaging signal over the entire area as in the related art, there is an inconvenience that a detection error occurs due to being dragged to a portion having a high reflectance.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned disadvantages of the related art, and an object of the present invention is to set a direction in which a two-dimensional image sensor is mounted and a direction in which a position detection mark is measured in a rotation direction. The present invention is to provide a position detection method capable of detecting the position of a position detection mark with high accuracy without being affected even if the position detection mark is shifted or the reflectance of the position detection mark has partial unevenness. .

It is an object of the present invention to provide a position detecting method capable of detecting the position of a position detecting mark with higher accuracy by performing statistical processing according to the situation. is there.

An object of the invention described in claim 4 is to determine the position of the position detection mark without being affected by the rotational direction shift between the two-dimensional image pickup device and the position detection mark and the unevenness of the reflectance of the position detection mark. An object of the present invention is to provide a position detecting device capable of detecting with high accuracy.

An object of the present invention is to provide a position detecting device capable of detecting the position of a position detection mark with high accuracy based on the relative position between the index mark and the position detection mark. .

An object of the invention described in claim 6 is to determine the position of the position detection mark without being affected by the rotational direction shift between the two-dimensional image pickup device and the position detection mark or the unevenness of the reflectance of the position detection mark. An object of the present invention is to provide a projection exposure apparatus capable of improving the superposition accuracy of a mask pattern image and a substrate by detecting with high accuracy.

[0016]

According to a first aspect of the present invention, there is provided a position detecting method for detecting a position of a position detecting mark (WM, 52a, 52b) in a predetermined measurement direction, wherein the position detecting mark (WM, 52a, 52b) is provided. WM, 52a, 52b) to the illumination light (D
L) to irradiate the position detection mark (WM, 52a, 5).
2b) a first step of forming a two-dimensional image; a second step of imaging the two-dimensional image using a two-dimensional image sensor (14); and measuring the image signal (DSA) of the two-dimensional image by the measurement. A plurality of divisions are made in a non-measurement direction that is substantially orthogonal to the direction, and integration is performed in the non-measurement direction for each of the divided areas (A to E), based on the obtained integrated signals of the divided areas (A to E). The position detection mark (W
M, 52a, 52b) for detecting the position of each of the divided areas (A to E) obtained in the third step (WM, 52a, 52b).
And a fourth step of statistically processing the position detection value of (i) to calculate a final mark detection position.

According to this, a two-dimensional image of the position detection mark is formed by irradiating the position detection mark with illumination light, the two-dimensional image is picked up using a two-dimensional image pickup device, and the image pickup signal is measured. Is divided into a plurality of regions in the non-measurement direction substantially orthogonal to the direction, and the position of the mark for each divided region is detected based on an integrated signal obtained by integrating the imaging signal of each divided region in the non-measurement direction. The final position of the position detection mark is calculated by statistically processing a plurality of position detection values.

If the mounting position of the two-dimensional image sensor is shifted and the relative positional relationship with the position detection mark is shifted in the rotation direction, the imaging signal in the measurement direction is integrated over the entire surface in the non-measurement direction as in the related art. When the whole-area integrated signal is used, the detection of the mark position may be inaccurate due to the low contrast, but in the present invention, the image signal is divided into a plurality of parts in the non-measurement direction, and the image signal is divided for each divided region. By performing the integration, it is possible to avoid lowering the contrast of the integrated signal. If the reflectivity of the position detection mark changes depending on the location, using a full integration signal that integrates all the imaging signals in the measurement direction in the non-measurement direction as in the past, the mark is dragged toward the one with the higher reflectance. However, in the present invention, the imaging signal is divided into a plurality of parts in the non-measurement direction, the mark position is detected for each divided region, and the position detection values of the plurality of marks are statistically processed. Thus, the influence of the reflectivity of the mark is dispersed, the detection error of the position detection mark is reduced, and the mark position can be detected with high accuracy.

In this case, the image pickup signal is divided into a plurality of parts in the non-measurement direction, and the position detection value of the position detection mark based on a plurality of image pickup signals obtained by integrating the image pickup signals for each divided area in the non-measurement direction. Various processing methods are conceivable for the statistical processing. For example, as the statistical processing in the fourth step, the position detection values in a plurality of divided areas (A to E) are simply averaged as the statistical processing in the fourth step. You may do.
In this case, multiple position detection values are treated as equivalent,
By simply averaging these, even if the position detection mark and the two-dimensional image sensor are relatively displaced in the rotational direction, the position of the position detection mark can be detected with high contrast and with high accuracy. .

Alternatively, as the statistical processing in the fourth step, each of the divided areas (A to A)
The weighted averaging process of averaging a plurality of position detection values by weighting the corresponding position detection values according to the position in the non-measurement direction in E) may be performed. In general, a position detection mark is likely to cause a measurement error due to the deformation of the mark in the vicinity of both ends. Therefore, for example, by making the weight in the vicinity of both ends smaller than that in the center, the detection error due to the deformation of the position detection mark or the like is generated. Can be prevented. Of course, the example of weighting is not limited to this, and various types of weighting may be performed in accordance with the status of the mark or the like, and then averaging may be performed.

According to a fourth aspect of the present invention, a position detection mark (WM, 52a, 52a) formed on at least one of the sample (W) and the stage (18) holding the sample (W).
b) a position detection device for detecting a position in a predetermined measurement direction, wherein the position detection mark (WM, 52a, 52b)
An imaging optical system (12) for irradiating the illumination light (DL) with the light to form a two-dimensional image of the position detection mark; a two-dimensional image sensor (14) for capturing the two-dimensional image; and the two-dimensional image Signal processing means (1) for dividing the imaging signal (DSA) into a plurality of non-measurement directions substantially orthogonal to the measurement direction, and integrating each of the divided areas (A to E) in the non-measurement direction.
6) and the position detection marks (WM, 52a, 52) for each divided area based on the integrated signal of each of the divided areas (A to E) obtained by the signal processing means (16).
detecting means (16) for respectively detecting the position of b); each of the divided areas (A to E) detected by the detecting means (16)
The position detection marks (WM, 52a, 52
(b) statistically processing the position detection value to calculate a final mark detection position.

According to this, when the position detecting mark is irradiated with illumination light by the image forming optical system and a two-dimensional image of the position detecting mark is formed, the two-dimensional image is picked up by the two-dimensional image pickup device and the signal processing is performed. The image signal is divided into a plurality of parts in the non-measurement direction by means, and the image signals for each divided region are integrated in the non-measurement direction. The position of the position detection mark is detected by the detection unit based on the integrated signal for each divided area, the position detection value of the position detection mark is statistically processed by the calculation unit, and the final mark detection position is calculated. .

For this reason, when the relative positional relationship between the two-dimensional image sensor and the position detection mark is shifted in the rotational direction due to a shift in the mounting position of the two-dimensional image sensor, the image signal is divided into a plurality of signals. Thus, since the position of the position detection mark in each area is detected and the position detection value of the mark in each divided area is statistically processed by the calculating means, the contrast of the integrated signal is prevented from lowering. Further, even when the reflectance of the position detection mark partially changes,
Since the imaging signal is divided into a plurality of parts in the non-measurement direction and the mark position is detected using the integrated signal of each divided area, the degree of change in the mark reflectivity within one area can be reduced, and each divided area can be reduced. The exact mark position is detected at
Since the position detection values are statistically processed, the detection error of the mark position is reduced, and the mark position can be detected with high accuracy.

According to a fifth aspect of the present invention, there is provided a position detecting device for detecting a position of a position detection mark (WM, 52a, 52b) formed on a sample (W) in a predetermined measurement direction, wherein (W) irradiating illumination light (DL) on the first imaging optical system (30, 32, 34, 36, 38, 40, 42, 44, 44) for forming a two-dimensional image of the position detection mark.
46, 48); an indicator plate (52) which is arranged on a surface on which a two-dimensional image of the position detection mark (WM) is formed or a surface conjugate to the surface and on which indicator marks (52a, 52b) are formed.
A second imaging optical system (50, 5) for irradiating the index plate (52) with illumination light to form a two-dimensional image of the index mark;
6, 58, 60, 62); and the position detection mark (W
M) and a two-dimensional image sensor (14) for capturing a two-dimensional image of the index mark (52a, 52b); and an imaging signal (DSA) from the two-dimensional image sensor (14).
Divided into a plurality of non-measurement directions substantially orthogonal to the measurement direction,
A signal processing means (16) for outputting an integrated signal integrated in the non-measurement direction for each of the plurality of divided areas; and the index marks (52a, 52b) based on the integrated signal.
, The position detection mark (W
M) detecting means for detecting the position of the position detection mark (WM) for each of the divided areas detected by the detection means (16); And (16) for calculating the position.

According to this, the first imaging optical system irradiates the position detection mark with illumination light to form a two-dimensional image of the position detection mark. At the same time, the second imaging optical system forms a two-dimensional image of the index mark by irradiating the index plate on which the index mark is formed with illumination light. The two-dimensional image sensor simultaneously captures these two-dimensional images. in this way,
Since the two-dimensional images of the position detection mark and the index mark are individually formed using their own optical systems,
It is possible to form an image on the imaging surface of the two-dimensional imaging device so that the marks do not overlap each other, and it is possible to reliably detect the position of each mark. Further, the image signal picked up by the two-dimensional image sensor is divided into a plurality of parts in the non-measurement direction by the signal processing means, and the image signals for each divided area are integrated in the non-measurement direction. , The respective positions of the position detection mark and the index mark in each divided area are detected, and the calculation means statistically processes the position detection values of the position detection marks in each divided area to obtain the final mark position.

For this reason, not only when the mounting position of the two-dimensional image pickup device is displaced or the reflectance of the position detection mark differs depending on the place, but also the position detection mark and an index serving as a reference for baseline measurement used in the off-axis method. Even when the mark is displaced in the rotation direction, the detection error is reduced, and the position of the position detection mark can be detected with high accuracy.

According to a sixth aspect of the present invention, there is provided a projection exposure apparatus for transferring an image (CCr) of a pattern formed on a mask (R) onto a substrate (W) coated with a photosensitive material. A position detection device (10) according to 4 or 5 is provided for detecting a position detection mark formed on the substrate.

According to this, since the position detecting device according to claim 4 is provided in the projection exposure apparatus for detecting the position detecting mark formed on the substrate, the position detecting device and the position detecting device can be used. Even if the detection mark is relatively displaced in the rotational direction or the reflectivity of the position detection mark is partially changed, the mark position can be detected with high accuracy without being affected by the change. In addition, it is possible to improve the overlay accuracy of the mask pattern image and the substrate.

[0029]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIG.
A description will be given with reference to FIG.

FIG. 1 shows a position detecting device according to the present invention.
A projection exposure apparatus 100 according to one embodiment provided as an off-axis type alignment sensor is shown.
The projection exposure apparatus 100 is a step-and-repeat type reduction projection exposure apparatus (a so-called stepper).

The projection exposure apparatus 100 includes an illumination system IOP for illuminating a reticle R as a mask with illumination light for exposure.
A reticle stage RST for holding a reticle R;
A projection optical system PL for projecting an image of the pattern formed on the reticle R onto a wafer W as a sample, a sample stage 18 as a stage for holding the wafer W via a wafer holder (not shown), and a sample stage 18 are mounted. The XY stage 20 is movable in the X-axis direction (left-right direction in FIG. 1) and in the Y-axis direction (perpendicular direction in FIG. 1) perpendicular to the XY two-dimensional plane, and a position detected on the wafer W is detected. Off-axis type alignment sensor OF for detecting alignment mark (wafer mark) as mark
A, a signal processing system 16 for processing an imaging signal from the alignment sensor OFA, a moving mirror 24 mounted on a sample stage 18, and irradiating the moving mirror 24 with a laser beam.
A laser interferometer 26 for receiving the reflected light and measuring the position of the sample table 18 in the XY plane, a drive system 22 for driving the XY stage 20, a CPU (Central Processing Unit), and a ROM
(Read Only Memory), RAM (Random Access Memor)
y), etc., and a main controller 28 for controlling the entire apparatus as a whole.

The illumination system IOP includes a light source (such as a mercury lamp or an excimer laser), a fly-eye lens, a relay lens,
And an illumination optical system including a condenser lens and the like. The illumination system IOP illuminates the pattern CCr on the lower surface (pattern formation surface) of the reticle R with uniform illumination distribution by the illumination light IL for exposure from the light source. here,
As the illumination light for exposure IL, a bright line such as an i-line of a mercury lamp, or an excimer laser beam such as KrF or ArF is used.

The reticle R is fixed on a reticle stage RST by fixing means (not shown). The reticle stage RST is driven by a driving system (not shown) in the X-axis direction, the Y-axis direction, and the θ-direction (two-dimensional plane). Direction of rotation)
Can be finely driven. Thereby, reticle stage RST can position reticle R (reticle alignment) in a state where the center (reticle center) of pattern CCr of reticle R substantially coincides with the optical axis of projection optical system PL. FIG. 1 shows a state in which this reticle alignment has been performed.

The projection optical system PL has its optical axis AX in the Z-axis direction orthogonal to the moving surface of the reticle stage RST.
Here, both sides are telecentric and a predetermined reduction magnification β
(Β is, for example, １ ／) is used.
For this reason, if the reticle R is illuminated with uniform illuminance by the illumination light IL in a state where the reticle pattern CCr and the shot area on the wafer W are aligned (aligned), the pattern CCr on the pattern forming surface is obtained. Is reduced by the projection optical system PL at the reduction magnification β, projected onto the wafer W coated with the photoresist, and a reduced image of the pattern is formed in each shot area on the wafer W.

The XY stage 20 is actually a Y stage that moves on a base (not shown) in the Y axis direction.
And an X stage that moves on the stage in the X axis direction. The sample stage 18 is mounted on an X stage and minutely drives a wafer holder that holds the wafer W in the Z-axis direction, and is also called a Z stage.

The wafer W is fixed on the sample table 18 via a wafer holder (not shown). Also,
A movable mirror 24 is provided on the upper surface of one end of the sample table 18, and the position of the sample table 18 in the XY plane is projected by projecting a laser beam onto the movable mirror 24 and receiving the reflected light. The laser interferometer 26 to be measured is
Are provided so as to face the reflection surfaces of the first and second mirrors. The movable mirror 24
Is actually provided with an X moving mirror having a reflecting surface orthogonal to the X axis and a Y moving mirror having a reflecting surface orthogonal to the Y axis. Correspondingly, the laser interferometer is also used for measuring the position in the X direction. An X laser interferometer and a Y laser interferometer for position measurement in the Y direction are provided, but these are shown as a movable mirror 24 and a laser interferometer 26 in FIG. Therefore, in the following description, it is assumed that the XY coordinates of the sample stage 18 are measured by the laser interferometer 26.

The measured values of the laser interferometer 26 are stored in the main controller 2
The main controller 28 controls the laser interferometer 2
The sample stage 18 is positioned by driving the XY stage via the drive system 22 while monitoring the measurement value of No. 6. In addition, the output of a focus sensor (not shown) is also supplied to the main controller 28. The main controller 28 controls the drive system 22 based on the output of the focus sensor.
The sample stage 18 is driven in the Z-axis direction (focus direction) via the. That is, the wafer W is positioned in the three axes of X, Y, and Z via the sample table 18 in this manner.

A reference plate FP is fixed on the sample table 18 so that its surface is at the same height as the surface of the wafer W. On the surface of the reference plate FP, various reference marks including a reference mark used for baseline measurement (measurement of the distance between the optical axis AX of the projection optical system PL and the detection center Rf4 of the alignment sensor OFA) are formed. ing.

As the alignment sensor OFA, an image processing type imaging alignment sensor is used. As shown in FIG. 2, the alignment sensor OFA is formed on an index plate 52 serving as a reference for determining a wafer mark WM as a position detection mark formed on the surface of the wafer W and a detection center Rf4 of the alignment sensor OFA. The index marks 52a and 52b are respectively illuminated with illumination light, and the wafer mark WM and the index marks 52a and 52b are illuminated.
a detection optical system 12 as an imaging optical system (including a first imaging optical system and a second imaging optical system) for forming a two-dimensional image of b;
C as a two-dimensional imaging device for capturing those two-dimensional images
It is configured to include a CD 14 and the like.

The detection optical system 12 includes a light source 30, a condenser lens 32, a wavelength selection element 34, an illumination field stop 36, a relay lens 38, an illumination aperture stop 40, a beam splitter 42, an objective lens 44, and an imaging aperture stop 46. ,
An imaging lens 48, a beam splitter 50, an index plate 52,
Relay lens 54, light source 56, condenser lens 5
8, an index illumination field stop 60, a lens 62, and the like. Here, each component of the detection optical system 12 will be described together with its operation.

The light source 30 is constituted by a halogen lamp or the like which emits broadband illumination light (broadband light).
This is because, in the case of an alignment sensor of an image processing method, if monochromatic light is used as a light source, it may be impossible to reliably detect a mark image due to the influence of thin film interference of a photoresist applied to the surface of the wafer W. Therefore, a light source that emits incoherent light is used. Therefore, in the case where there is almost no influence of the thin film interference of the resist or the like, a laser light source that emits a laser beam may be used as the light source.

The broadband illumination light (broadband light) emitted from the light source 30 is supplied to a condenser lens 32 and a wavelength selection element (a sharp cut filter or an interference filter) 3.
Then, the light is incident on the illumination field stop 36 through 4.

The wavelength selecting element 34 is formed of a photoresist (for example, 365 nm or 248 nm) applied on the wafer W.
It transmits only a light beam in a wavelength range (for example, a wavelength of 550 nm to 750 nm) that is insensitive to m light. However, when the alignment sensor OFA according to the present embodiment is used for detecting the position of a substrate that is not covered with photoresist, it is not necessary to prevent exposure, so that a light beam having a short wavelength close to the exposure wavelength can be used. . For example, there is a case where the present invention is applied as an apparatus for detecting an overlay error between a circuit pattern formed on a wafer and a resist pattern after transferring and exposing and developing a mask pattern image thereon.

The illumination light DL transmitted through the transmission portion of the illumination field stop 36 is incident on the illumination aperture stop 40 via the relay lens 38 and is reflected vertically downward by the beam splitter 42, and then is reflected by the wafer of the beam splitter 42. The illumination area including the wafer mark WM formed on the wafer W is irradiated via the objective lens 44 arranged on the W side.

Since the illumination field stop 36 is substantially conjugate (imaging relationship) with the surface of the wafer W (wafer mark WM), it depends on the shape and size of the transmitting portion of the illumination field stop 36. Thus, the illumination area on the wafer W can be limited.

The light beam reflected by the illumination area including the wafer mark WM on the wafer W passes through the objective lens 44 and the beam splitter 42 and reaches the image forming aperture stop 46. The light beam transmitted through the image forming aperture stop 46 is condensed by the image forming lens 48, passes through the beam splitter 50, and forms an image of the wafer mark WM on the index plate 52.
The above is the description of the first imaging optical system.

At a predetermined position of the index plate 52, an index mark 5
2a and 52b are formed. This index mark 52
a and 52b are illuminated by an index plate illumination system 13 as a second imaging optical system described below.
The index plate illumination system 13 includes a light source 56 such as a light emitting diode (LED), a condenser lens 58, and an index illumination field stop 6.
0, a lens 62 and the like. The shape of the transmitting part of the index illumination field stop 60 is set so that the illumination light from the index plate illumination system 13 is reflected by the beam splitter 50 and only a partial area including the index marks 52a and 52b is illuminated. I have.

Conversely, the shape of the transmitting portion of the illumination field stop 36 in the first image forming optical system described above is set so as not to illuminate (shield) the partial area including these index marks 52a and 52b. Have been. Therefore, a two-dimensional image of the wafer mark WM and the index marks 52a and 52b is
Since the two marks can be formed separately, the two-dimensional images of the two marks do not overlap with each other, and the position of each mark can be detected reliably and with high accuracy.

The wafer mark W formed on the index plate 52
The two-dimensional images of M and the index marks 52a and 52b are respectively condensed on the CCD 14 by the relay lens 54,
An image is formed on the imaging surface of D14.

As described above, the detection optical system 12 is formed by the light source 30 to the relay lens 54, and the detection optical system 12 and the CCD 14 form the alignment sensor OFA. Then, the CCD 14
Is supplied to an alignment signal processing system 16 at the next stage. The alignment sensor OF described above
A, the alignment signal processing system 16 and the main controller 28 constitute the position detecting device 10 according to the present invention.

Next, the operation of the alignment signal processing system 16 and the main controller 28, which are characteristic components of the present invention, will be described with reference to FIGS.

FIG. 3 shows an image pickup surface 7 of the CCD 14 shown in FIG.
A two-dimensional image of the index marks 52a and 52b and the wafer mark WM formed on 0 is shown. CCD at this time
The raster scan direction 14 is exactly the right-left direction of the paper on the imaging surface 70 in FIG. 3 (the direction of the arrow HS in FIG. 3).
It is assumed that

On the other hand, in the measurement direction of the positions of the wafer mark WM and the index marks 52a and 52b, the wafer mark WM is rotated by θ1 and the index marks 52a and 52b are rotated by θ2 from the above-described raster scan direction. That is, the CCD 14 has a rotation error θ1 with respect to the wafer mark WM and a rotation error θ with respect to the index marks 52a and 52b.
It is assumed that the wafer mark WM is attached to the alignment sensor OFA in FIG. 2 (FIGS. 3 and 4 show the case where θ1 = θ2, but the rotation direction and rotation error of the wafer mark WM and the index marks 52a and 52b are different. In this case, θ1 ≠ θ2).

In such a situation, the alignment signal processing system 16 of this embodiment shown in FIG.
The imaging signal DSA supplied from the line 14 is indicated by an arrow HS in FIG.
Is divided into n in the arrow VS direction (almost a non-measurement direction) in FIG. n is an integer of 2 or more), and the imaging signals in each divided area are integrated in the direction of the arrow VS. Specifically, as shown in FIG. 3, the imaging signal on the imaging surface 70 of the CCD 14 is divided into five regions A to E by dividing the imaging signal at broken line positions in the direction of the arrow VS, and the imaging in each region is performed. Signal processing is performed so that the signal is integrated in the direction of the arrow VS.

FIGS. 4A to 4E show integrated signals obtained by integrating the image pickup signals for each of the divided areas A to E shown in FIG. 3 in the direction of the arrow VS. Indicates the position (time) of the CCD 14 in the raster scan direction (the direction of the arrow HS), and the vertical axis indicates the intensity of the integrated signal.

Next, main controller 28 in the present embodiment
Then, based on the integrated signal of FIG. 4 obtained by integrating the imaging signals of each divided area in the direction of the arrow VS, for example, as shown in FIG. 4A, the coordinates of each intersection of the integrated signal with respect to a predetermined slice level SL Find the position. Here, each divided area (A to A) of the index marks 52a and 52b and the wafer mark WM is used.
E) The coordinate position of the intersection with the slice level SL for each integrated signal is determined, and the index mark 52 is determined from the coordinate position.
The respective center positions of a and 52b and the wafer mark WM are obtained, and are set as the positions of the index mark and the wafer mark in each divided area. Here, as shown in FIG. 4, since a mark whose reflectance at the mark position is lower than that of other portions is used, an integrated signal portion having an intensity lower than the slice level SL is used. Index marks 52a,
52b and the position of the wafer mark WM are detected. As described above, in the present embodiment, the slicing method of detecting the positions of the index mark and the wafer mark WM from the integrated signal of each divided area using the predetermined slice level SL is used. Of course, the mark position may be detected using a pattern matching method, a peak detection method, or the like, other than the above-described slice method.

As shown in FIG. 3, the wafer mark WM
If there is a rotation error of θ1 between the measurement direction of the CCD 14 and the raster scan direction of the CCD 14 (the direction of the arrow HS), as shown in FIG. 4, the wafer mark WM in each of the divided areas (A to E) is generated. Are substantially the same in shape, and the phase of the waveform of the integrated signal is slightly shifted in the raster scan direction in accordance with the rotation error θ1. That is, in FIG. 4, an arbitrary center line CL and a center wafer mark 72 (4 from the end of the seven wafer marks WM in FIG. 3).
Center mark).
It can be seen that the phase of the integrated signal of the wafer mark WM is slightly shifted as shown by Δa to Δe.

The index marks are the same as in the case of the wafer mark WM described above, and the index marks 52a, 52b
When there is a rotation error of θ2 between the measurement direction of the index mark and the raster scan direction (the direction of the arrow HS), the index center obtained from is determined according to the rotation error θ2 as shown in FIG. The phases of the integrated signals of the index marks 52a and 52b are slightly shifted in the raster scan direction.

Therefore, as described above, if rotation errors .theta.1 and .theta.2 occur between the raster scan direction of the CCD 14 and the measurement direction of the wafer mark WM or the index mark, the imaging surface 70 of the CCD 14 as in the prior art. When the above imaging signal is totally integrated in the direction of the arrow VS (almost non-measuring direction), the obtained integrated signal becomes the same as the signal obtained by integrating all the signals of (A) to (E) in FIG. A signal such as a sine wave that is shifted little by little is added, and a decrease in the contrast of the integrated signal is inevitable.

In addition, when the resist on the surface of the wafer W has coating unevenness, the reflectance of the wafer mark W corresponding to the divided areas A and B in FIG. Conversely, when the reflectance of the portion corresponding to the regions D and E becomes high, in the conventional position detection based on the total integrated signal, the position is dragged to the divided regions D and E having high reflectance,
The detection center of the wafer mark WM in FIG. 4 is shifted to the left, and a detection error easily occurs.

In this respect, according to the present invention, as described above, the imaging signal is divided into five regions (A to E) substantially in the non-measurement direction, and each of the divided regions has a mark position (a wafer mark and an index mark). ), The main controller 28 statistically processes the detected position value of the mark for each divided area, so that the final mark position can be accurately detected. In order to detect the mark position in this way,
For example, even if the reflectance of the wafer mark WM partially changes, the influence of the detection error can be reduced, and the position of the wafer mark WM can always be detected with high accuracy.

As the statistical processing by the main controller 28 described above, the final position of the wafer mark WM is calculated by dividing the sum of the detected position of the mark for each divided area by the number of divisions and averaging them. In addition to the simple averaging process, in view of the possibility that the wafer marks WM near both ends of the divided region are likely to be deformed, the position detection values near the both ends are more likely to be compared to the other divided regions (for example, divided regions near the center). There is a weighted averaging process for averaging by increasing the weight of the position detection value. In the case of this weighted averaging process, the influence of the partial deformation of the wafer mark can be eliminated as much as possible.

As is clear from the above description, in the present embodiment, the signal processing means is constituted by the alignment signal processing system 16, and the detection means and the arithmetic means are constituted by the main controller 28.

Next, the exposure operation of the above-described projection exposure apparatus 100 in which the position detecting device of the present invention is mounted as an off-axis type imaging sensor will be described.

First, in the main control device 28, the reference plate FP
The XY stage 20 is moved via the drive system 22 so that the reference mark for baseline measurement formed on the surface of the projection optical system PL is located below the optical axis AX of the projection optical system PL. Output of laser interferometer 26 at this time (coordinate position of sample stage 18)
Are stored in a memory (not shown) provided in main controller 28.

Next, main controller 28 moves XY stage 20 via drive system 22 so that the reference mark formed on reference plate FP is located below alignment sensor OFA. And the alignment sensor O at this time
The output (two-dimensional image) of the FA and the output of the laser interferometer 14 are stored in a memory in the main controller 28, and are measured in the baseline (the position between the optical axis AX of the projection optical system PL and the detection center of the alignment sensor OFA). Interval measurement).

The reference mark detected by the above-described alignment sensor OFA is the wafer mark WM shown in FIG.
In the same manner as in the case of the wafer mark WM, the position of the reference mark is detected in the same manner as in the case of the wafer mark WM, and the imaging signal of the two-dimensional image of the index mark and the reference mark is converted into the direction of the arrow VS in FIG. ) Is divided into five (A to E), the imaging signals are integrated for each divided area, and the position detection of the index mark and the reference mark in each divided area is performed. 5
The mark position detection value for each of the divided areas is determined by comparing the output value of the laser interferometer 26 at that time with the index / index of each divided area.
The sum of the distance between the reference marks and the distance between the reference marks is stored in the memory of the main control device 28 as a baseline amount for each divided area.

Next, when detecting the wafer mark WM on the wafer W, the alignment sensor OFA
Is divided into five (A to E) in the direction of the arrow VS in FIG. 3 and integrated in the direction of the arrow VS in each divided area, and the position detection of the wafer mark WM in each area is performed by the alignment signal. The processing is performed by the processing system 16. Then, each detected position value of the wafer mark WM is obtained by subtracting the stored baseline amount of each area from the sum of the output value of the laser interference 26 at that time and the distance between the index and the wafer mark. Value. The main controller 28 performs predetermined statistical processing (simple average or weighted average) on the plurality of detected values of the wafer mark WM to calculate the final wafer mark position.

The main controller 28 drives the XY stage 20 by controlling the drive system 22 based on the detection position of the above-described wafer mark WM on the wafer W to drive each exposure area (here, the formation of a semiconductor chip). Area) projection optical system PL
, Overlay exposure on the wafer W can be accurately performed.

As described above, according to the projection exposure apparatus 100 including the position detecting device 10 according to the present embodiment,
Various marks such as a wafer mark WM, an index mark, or a reference mark on a reference plate FP are used for a two-dimensional imaging device (CCD).
14), the mark position can be detected with high accuracy even if the raster scan direction of the two-dimensional image sensor and the measurement direction of the mark are shifted with a rotation error. It is possible to perform an exposure operation without overlay displacement.

In particular, in the baseline measurement, which is a prerequisite for performing the overlay exposure on the wafer W, the two-dimensional imaging signal of the reference mark is divided into a plurality of parts in the direction orthogonal to the raster scan direction, and the reference Since the mark position is detected and the base line amount is set for each area,
Even if a rotation error occurs between various marks, an appropriate mark position can always be detected.

In the above embodiment, the case where the position detecting device according to the present invention is applied to an off-axis type imaging sensor has been described. However, the scope of the present invention is not limited to this. For example, TTL (Through
The present invention can be similarly applied not only to an alignment sensor for a projection exposure apparatus but also to a position detection apparatus for various measuring apparatuses in the same manner.

In the above embodiment, the signal processing means of the present invention is realized by the alignment signal processing system 16, and the detecting means and the calculating means are realized by the main controller 28. However, the present invention is not limited to this. However, the signal processing means and the detection means are realized by the alignment signal processing system 16, and the calculation means is realized by the main controller 28. Also, the signal processing means, the detection means and the calculation means are It may be realized by the alignment signal processing system 16.

[0074]

As described above, according to the first aspect of the present invention, the mounting direction of the two-dimensional image sensor and the measurement direction of the position detection mark are deviated in the rotation direction, or the position detection mark is reflected. Provided is a position detection method capable of detecting the position of a position detection mark with high accuracy without being affected by partial unevenness in the rate.

According to the second and third aspects of the present invention, there is provided a position detecting method capable of detecting the position of a position detecting mark with higher accuracy by performing statistical processing according to the situation.

According to the fourth aspect of the present invention, the position of the position detection mark can be determined without being affected by the rotational direction shift between the two-dimensional image pickup device and the position detection mark and the unevenness of the reflectance of the position detection mark. It is possible to provide a position detecting device capable of detecting with high accuracy.

According to the invention described in claim 5, it is possible to provide a position detecting device capable of detecting the position of the position detection mark with high accuracy based on the relative position between the index mark and the position detection mark. .

According to the sixth aspect of the present invention, the position of the position detection mark can be determined without being affected by the rotational direction shift between the two-dimensional image pickup device and the position detection mark and the unevenness of the reflectance of the position detection mark. By performing the detection with high accuracy, it is possible to provide a projection exposure apparatus capable of improving the overlay accuracy of the mask pattern image and the substrate as a result.

[Brief description of the drawings]

FIG. 1 is a view schematically showing an overall configuration of a projection exposure apparatus according to one embodiment.

FIG. 2 is a diagram illustrating an example of a configuration of a position detection device in FIG. 1;

FIG. 3 is a diagram showing a two-dimensional image of an index mark and a wafer mark formed on an imaging surface of a CCD in FIG. 2;

4A to 4E are diagrams illustrating an example of an integrated signal obtained by integrating the imaging signals of each of the divided regions A to E illustrated in FIG. 3 in the direction of the arrow VS.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Position detection apparatus 12 Detection optical system 14 CCD 16 Alignment signal processing system 30 Light source 32 Condenser lens 34 Wavelength selection element 36 Illumination field stop 38 Relay lens 40 Illumination aperture stop 42 Beam splitter 44 Objective lens 46 Imaging aperture stop 48 Imaging lens 50 Beam splitter 52a, 52b Index mark 56 Light source 58 Condenser lens 60 Index illumination field stop 62 Lens W Wafer WM Wafer mark OFA Alignment sensor

Claims (6)

[Claims] 1. A position detecting method for detecting a position of a position detection mark in a predetermined measurement direction, wherein a first step of irradiating the position detection mark with illumination light to form a two-dimensional image of the position detection mark. A second step of capturing the two-dimensional image using a two-dimensional image sensor; and dividing the imaging signal of the two-dimensional image into a plurality of non-measuring directions substantially orthogonal to the measuring direction, and for each divided region. A third step of respectively integrating the positions in the non-measurement direction and detecting the position of the position detection mark for each divided area based on the obtained integrated signal of each divided area; Statistically processing the position detection values of the position detection marks for each of the divided areas to calculate a final mark detection position. 2. The position detecting method according to claim 1, wherein the statistical processing in the fourth step is a simple averaging processing of the position detection values for the plurality of divided areas. 3. The statistical processing in the fourth step, wherein weighted averaging is performed on the position detection values corresponding to the positions of the respective divided areas in the non-measurement direction to average the plurality of position detection values. The method according to claim 1, wherein the processing is processing. 4. A position detecting device for detecting a position in a predetermined measurement direction of a position detection mark formed on at least one of a sample and a stage for holding the sample, wherein the position detection mark is irradiated with illumination light. An imaging optical system for forming a two-dimensional image of the position detection mark; a two-dimensional image sensor for capturing the two-dimensional image; and a non-measurement signal for capturing the image signal of the two-dimensional image substantially orthogonal to the measurement direction. Signal processing means for dividing into a plurality of directions and integrating in the non-measurement direction for each divided area; and the position of each divided area based on an integrated signal of each divided area obtained by the signal processing means. Detecting means for respectively detecting the positions of the detection marks; and statistically processing the position detection values of the position detection marks for each of the divided areas detected by the detection means to obtain a final mark detection position. Position detecting device and a computing means for computing. 5. A position detection device for detecting a position of a position detection mark formed on a sample in a predetermined measurement direction, wherein the position detection mark is irradiated on the sample by irradiating the sample with illumination light.
A first imaging optical system that forms a two-dimensional image; an index plate that is arranged on a surface on which the two-dimensional image of the position detection mark is formed or a surface conjugate to the formation surface and has an index mark formed thereon; A second imaging optical system that forms a two-dimensional image of the index mark by irradiating illumination light; a two-dimensional image sensor that captures a two-dimensional image of the position detection mark and a two-dimensional image of the index mark; Signal processing means for dividing an image signal from the two-dimensional image sensor into a plurality of non-measurement directions substantially orthogonal to the measurement direction, and outputting an integrated signal integrated in the non-measurement direction for each of the plurality of divided areas; And; based on the integrated signal,
Detecting means for detecting the position of the position detection mark for each of the divided areas with respect to the index mark; performing statistical processing on the position of the position detection mark for each of the divided areas detected by the detection means; A position detecting device comprising: a calculating means for calculating a position of the mark. 6. A projection exposure apparatus for transferring, via a projection optical system, an image of a pattern formed on a mask onto a substrate coated with a photosensitive material, wherein the position detection apparatus according to claim 4 or 5. A projection exposure apparatus for detecting a position detection mark formed on the substrate.