JPH113853A - Method and device for detecting position - Google Patents

Abstract

PROBLEM TO BE SOLVED: To detect the three-dimensional shape of an alignment mark on a wafer with high accuracy without deteriorating the contract, by arranging a diffraction grating-like and slit-like pinhole near an image surface which is in an imagery relation with the object to be observed, and detecting the shape of the object while the object is irradiated with illuminating light through the pinhole. SOLUTION: Light reflected by a beam splitter PBS is introduced to a projection optical system 13 by means of a mirror, after passing through a diffraction grating-like and slit-like pinhole provided on a prism WGP arranged at a position which is conjugate with the vicinity of the formed image of a wafer 1, a relay 10, and an objective lens 11 and irradiates an alignment mark 2 on the wafer 1. The reflected light from the irradiated mark 2 once forms the image of the mark 2 near the pinhole after reversely passing through the optical system 13, and the formed image is detected in a confocal state through the pinhole. Therefore, the three-dimensional shape of the alignment mark 2 on the wafer 1 can be detected with high accuracy without deteriorating the contrast.

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 a position detecting apparatus, and more particularly to an exposure apparatus (projection exposure apparatus) of a step-and-repeat method or a step-and-scan method for manufacturing a semiconductor device. When detecting positional information of a wafer mounted for performing relative positioning (alignment) of a fine electronic circuit pattern such as an IC, LSI, or VLSI formed on a reticle surface with a wafer of a second object. It is suitable.

[0002]

2. Description of the Related Art In a projection exposure apparatus for manufacturing semiconductor devices, high precision of relative positioning between a reticle and a wafer has become an important factor for achieving high integration of semiconductor devices. With the miniaturization of semiconductor devices, alignment accuracy of submicron or less is required.

Accordingly, a projection exposure apparatus for manufacturing a semiconductor device is provided with a position detecting device, and a reticle and a wafer position detecting method (alignment method) in the position detecting device.
Various methods are known. One of the methods is a TTL method for detecting a detection target object via a projection lens. In the TTL method, a luminous flux having a wavelength different from that of exposure light used to print a pattern on a reticle surface onto a wafer surface, and a relative position between a reference position (reference mark) on a predetermined surface and an alignment mark provided on the wafer surface. There have been proposed position detecting devices having various configurations with a method of performing position detection.

[0004] The present applicant also filed Japanese Patent Application No. 1-198261,
There has been proposed a position detecting device for observing an alignment mark image formed on a predetermined surface, for example, an imaging means surface by using an imaging means such as a CCD camera.

In such a position detecting device, if the wavelength width of the light beam used is narrow, when observing an alignment mark on a wafer surface coated with a resist, interference fringes due to reflected light from the resist surface and the substrate surface are large. And may cause a detection error. In order to reduce this interference fringe, there is also a projection exposure apparatus for manufacturing a semiconductor device equipped with a position detection apparatus for observing an alignment mark using a light source that emits a polychromatic light beam having a wide half-width of about several tens of nanometers. Proposed.

The conventional position detecting device has a problem that it is difficult to distinguish which position of the alignment mark on the wafer surface is being detected due to the relationship between the optical depth of the detecting optical system and the process. This is a position cause that deteriorates the position detection accuracy. This problem can be solved by applying Confocal detection which has already been proposed and implemented by the present applicant in Japanese Patent Application Laid-Open No. 6-302499. Confocal detection enables three-dimensional detection of a wafer mark, for example, detection in which the lower surface and the upper surface of the mark are distinguished.

FIG. 9 and FIG. 10 are diagrams showing the principle of performing stereoscopic measurement by conventional confocal detection. FIG. 9 shows a state in which the upper part of the alignment mark is observed, and FIG. 10 shows a state in which the lower part of the alignment mark is observed. In FIG. 9, the drivable pinhole P is reflected light TL from above the alignment mark.
, But most of the reflected light BL from below is blocked by the pinhole P. For this reason, the depth in the detection becomes shallow, and the observation image of only the section to be observed can be received by the CCD camera 14, so that three-dimensional measurement is possible. In this embodiment, to change the observation cross section, for example, to change the observation from the upper part of the alignment mark to the lower part,
It is necessary to move the wafer 1 in the optical axis direction of the detection system as shown in FIG. At this time, the pinhole P transmits the reflected light BL from below the alignment mark, and blocks most of the reflected light TL from above.

[0008] The applicant of the present invention is disclosed in Japanese Patent Application Laid-open No. Hei 6-307814.
As shown in FIG.
A position detection device that enables cal detection has been proposed.
In FIG. 2, a pinhole GP on a slit in the form of a diffraction grating is arranged in the vicinity of an image plane having an image forming relationship with the wafer 1 in the detection optical system AS, and is driven obliquely with respect to the optical axis of the detection optical system. . By this driving, it is possible to detect the focal point without driving the wafer 1 as the observation object in the focus direction, and the position is determined from the detection of the three-dimensional shape of the alignment mark of the wafer. This method is superior in accuracy and throughput to any method considered so far.

[0009]

In the above-mentioned three-dimensional shape detection of the alignment mark, the measurement range is a diffraction grating-like and slit-like pinhole (slit-like pinhole) in the detection optical system and an image sensor. It is limited within the depth of the detection optical system determined by a certain CCD camera, and measuring outside the depth lowers the contrast.

This will be described with reference to FIGS. 2, 3 and 4. FIG. 2 shows a TTL exposure apparatus for manufacturing semiconductor devices.
In a detection method called -Offaxis detection method, a slit-shaped pinhole GP is arranged at a position conjugate with the image forming plane of the wafer 2, and this is driven obliquely with respect to the optical axis of the detection optical system AS to perform confocal detection. It shows the method.

FIGS. 3 and 4 illustrate the principle of the system of FIG. 2 with illustration omitted. FIG. 3 shows a case where a signal with high contrast is obtained by moving in the depth, and FIG. Shows a case where only a signal with low contrast can be obtained.

When the slit pinhole GP moves,
The observation position on one surface of the wafer changes by the square of the imaging magnification. For example, from the slit pinhole GP to the wafer 1
Assuming that the magnification up to 1/100 times, the change in the optical axis direction of the observation position of the wafer 1 corresponding to the movement of the pinhole GP by 1 mm is 1 / (100 × 100) = 1/10000 mm = 0.1
μm.

In the range where the movement amount of the slit pinhole GP is within the depth, the position of the image BP of the wafer 1 formed by the erector 15 as shown in FIG.
No decrease in contrast occurs with the photoelectric conversion surface 14 of No. 6.

On the other hand, if the amount of movement of the slit pinhole GP is large, the position of the image BP of the wafer 1 formed by the erector 15 defocuses from the photoelectric conversion surface 14 of the CCD camera 16 as shown in FIG. Out of depth, contrast is reduced.

As shown in FIG. 12, a method of resolving a decrease in contrast is to replace a plurality of drivable parallel plane plate groups MP with different thicknesses according to the amount of movement of the slit pinhole GP, as shown in FIG. As shown in (2), there is a method of adjusting the optical path length by moving the movable mirror MM by half of the moving amount of the slit pinhole GP. Both of these methods require two types of actuators, and it is necessary to control the two types of actuators with high accuracy.

[0016]

SUMMARY OF THE INVENTION An object of the position detecting method and the position detecting device of the present invention is to expand the measurable range which is the above-mentioned problem. For this reason, according to the present invention, even if the position of the diffraction grating-shaped and slit-shaped pinhole in the detection optical system moves beyond the depth that can be detected by the CCD camera of the imaging device placed on the detection surface, the pinhole and the CCD are not moved. A position detection method and a position detection device which can detect the three-dimensional shape of the alignment mark on the wafer with high accuracy without reducing the contrast by performing correction so as to maintain the imaging relationship of the present invention.

According to the present invention, in a position detecting method and a position detecting apparatus for detecting a three-dimensional shape of an observation object by a detection optical system, a diffraction grating is provided in the vicinity of an image plane having an image forming relationship with the observation object in the detection optical system. In addition, a slit-shaped pinhole is arranged, illumination light for illuminating the observation object is illuminated through the pinhole, and detection is also performed through the pinhole. At this time, according to the present invention, the pinhole is driven obliquely with respect to the optical axis of the detection optical system, and the pinhole is formed on a wedge-shaped prism to correct defocus on the imaging surface. In addition, it is possible to perform simple and stable detection.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a schematic view of a main part of a first embodiment of the present invention, which best illustrates the features of the present invention.
FIG. 1 shows a position detection device mounted on a step-and-repeat or step-and-scan projection exposure apparatus for manufacturing a semiconductor element. The position detecting device is H
Wavelength 633n, which is oscillation light from e-Ne laser 40
m, the light applied to the photoresist applied on the wafer is not exposed to light (non-exposure light) 41. After passing through each element, the alignment mark 2 on the wafer 1 is passed through the projection optical system 13.
Observe the three-dimensional shape and detect its position. This system is a TTL position detection device because it is via the projection optical system 13.

In FIG. 1, reference numeral 4 denotes an illumination system of the projection exposure apparatus, which is light from a light source (not shown), for example, g-line or i-line emitted from an extra-high pressure mercury lamp or exposure light having an oscillation wavelength from an excimer laser. Illuminate the reticle 12 on which is formed. The projection optical system 13 projects the circuit pattern on the reticle 12 on the wafer 1 in a reduced size, for example, by ５. Reference numeral 2 denotes an alignment mark on the wafer 1 surface.

An optical system for causing light to enter the projection optical system 13 from between the reticle 12 and the projection optical system 13 is an alignment scope (detection optical system) AS according to the position detecting apparatus of the present invention.
It is. He- which is the light source of the alignment scope AS
The oscillation light 41 emitted from the Ne laser 40 is guided by the fiber 42, enters the illumination system 8, is reflected by the beam splitter PBS, and is guided to the inside of the alignment scope AS.

The light reflected by the beam splitter PBS passes through a diffraction grating-like and slit-like pinhole provided on a drivable wedge-shaped prism WGP disposed at a position conjugate with the vicinity of the image forming surface of the wafer 1. After passing through the relay 10 and the objective lens 11, the light is guided to the projection optical system 13 by the mirror M1. The light transmitted through the projection optical system 13 illuminates the alignment mark 2 on the wafer 1.

The illuminated image of the alignment mark 2 passes through the projection optical system 13, the mirror M1, the objective lens 11, and the relay 10 as reflected light, and then on the drivable wedge-shaped prism WGP. It is formed once near a diffraction-grating, slit-shaped pinhole. The formed image is transmitted through the pinhole to perform a focal detection. The light that has passed through the wedge-shaped prism WGP passes through the beam splitter PBS and becomes an erected image by the erector 15, and is formed as an optical image 14 on the CCD camera 16. The optical image 14 is photoelectrically converted by the CCD camera 16, taken into a computer 51 including a light beam image processing electronic circuit, subjected to image processing, and the position of the alignment mark 2 is detected.

The wedge of the wedge-shaped prism WGP in which a slit-like pinhole is formed in the form of a diffraction grating generates coma aberration. In FIG. 1, in order to correct the coma aberration, a wedge-shaped prism CP having an inclination opposite to that of the wedge-shaped prism WGP having an effect of forming a parallel plate when combined with the wedge-shaped prism WGP is arranged. The wedge-shaped prism CP is a wedge-shaped prism WG
Coma is generated in such an amount as to cancel the coma generated in P, and the aberration is corrected as a whole.

If the generation of astigmatism due to the wedge of the wedge-shaped prism WGP cannot be ignored, correction such as insertion of an element generating reverse astigmatism, for example, two parallel flat plates at an angle, is performed. Do.

If the accuracy of the attitude of the wedge-shaped prism WGP during driving is a problem, the reference mark SM is arranged in the alignment scope AS. Reference mark SM is dedicated illumination system 3
The image is illuminated by the optical system 2 and is imaged on the same photoelectric conversion surface on the CCD camera 16 as the image of the wafer 1 by the optical system 31 and the reference mark projection optical system. Since the optical path of the reference mark SM is combined with the optical path from the alignment mark 2 of the wafer 1 before entering the wedge-shaped prism WGP, the attitude of the wedge-shaped prism WGP has the same effect as the reference mark SM and the wafer 1. Therefore, if the alignment mark of the wafer 1 is measured based on the reference mark SM, the attitude accuracy of the wedge-shaped prism WGP is automatically canceled.

FIG. 11 shows an embodiment of a pattern configuration of a drivable wedge-shaped prism WGP having a diffraction grating-shaped slit-shaped pinhole. The transparent portions SMW1 and SMW2 that transmit the image of the reference mark SM are patterned above and below the diffraction grating-shaped slit-shaped pinhole portion GWA. By adopting the configuration as shown in FIG. 11, even when the alignment mark on the wafer 1 is detected in a confocal manner, the image forming light flux of the reference mark SM can be transmitted through the transparent portions SMW1, SMW.
W2 is transmitted not as a focal detection but as a normal imaging light flux.

As described above, depending on the object, a wedge-shaped prism WG
By spatially separating the pattern formed on the P, the position measurement of the reference mark SM can be performed with high accuracy without being affected by the pinhole GWA for detecting the focal.

Next, a method of driving the wafer 1 in FIG. 1 will be described. The wafer 1 is placed on a wafer chuck 21. The wafer chuck 21 is formed on a θ-Z stage 22 as a driving means, and sucks the wafer 1 on the chuck surface so that the position of the wafer 1 is not shifted by various vibrations. The θ-Z stage 22 is configured on a tilt stage 23,
Is moved up and down in the focus direction which is the optical axis direction of the projection optical system 13.

The tilt stage 23 is formed on an XY stage 18 controlled by a laser interference system 26, and
Of the projection optical system 13 is minimized with respect to the image plane. Further, the tilt stage 23 can be independently driven in the focus direction. XY
The driving amount of the stage 18 is monitored by a bar mirror 25 and a laser interference system 26 formed on the tilt stage 23. Note that the laser interferometer 26 transfers a measured value relating to the driving amount of the XY stage 18 to the computer 51 via a line. The focus detection systems 29 and 30 also detect the tilt of each shot surface of the wafer with respect to the image plane of the projection optical system 13 in addition to the focus, and corrects the tilt of the tilt stage 23 using the detection results. After measuring the focus of the wafer 1, the focus detection system 30 transfers the measured value to the computer 51 through the line.

FIGS. 5, 6, 7 and 8 are diagrams illustrating the principle of position detection according to the present invention. FIG. 5 shows an initial state of a wedge-shaped prism WGP having a slit-shaped pinhole which can be driven by a diffraction grating, and FIG. 6 shows an optical path length and a physical state of the prism WGP after Δ movement in the optical axis direction of the alignment scope AS. Indicates the length. At this time, the wedge-shaped prism WGP is characterized by being driven obliquely with respect to the optical axis direction of the alignment scope.

In FIG. 5, the confoca of the wafer 1 is shown.
The image of the surface to be detected coincides with the slit-shaped pinhole mark portion GWA in the form of a diffraction grating on the wedge-shaped prism WGP. In FIG. 6, the wedge-shaped prism WGP with a slit-like pinhole in the form of a diffraction grating is moved by Δ in the optical axis direction of the alignment scope AS.
The surface to be subjected to on-focal detection is different from that in FIG. 5 by an amount obtained by multiplying Δ by the square of the imaging magnification from the diffraction grating-shaped slit-shaped pinhole GWA on the wedge-shaped prism WGP to the wafer. Since the image of the detection surface of the wafer 1 is formed at the position of the grid-shaped mark portion GWA, the wedge-shaped prism G
The object of the present invention is achieved by making the optical path length from the WA to the CCD camera the same in FIG. 5 and FIG.

In FIG. 5, the thickness on the optical axis of the alignment scope AS of the wedge-shaped prism WGP having the diffraction grating-shaped slit-shaped pinhole GWA is d0, and the thickness on the optical axis of the wedge-shaped prism WGP in FIG. Let d0 + d. Therefore, the arrangement of the wedge-shaped prism WGP in FIG. At this time, in order to make the optical path length the same, it is necessary to satisfy the following expression: d0 / N = (d + d0) / N + Δ0 (1) Where N is a wedge-shaped prism W
The refractive index of the material of the GP, Δ0, is the opposite surface RG of the lattice mark portion GWA of the wedge-shaped prism WGP on the optical axis before and after the movement.
The amount of movement of the WA, Δ, is the amount of movement of the lattice mark portion GWA.

On the other hand, the actual physical length from the opposite surface RGWA of the grid-like mark portion GWA of the wedge-shaped prism WGP of FIG. 5 to the grid-like mark portion GWA of the wedge-shaped prism WGP moved to FIG. From the relationship, d0 + Δ = d + d0 + Δ0 (2) From (1) and (2), d = NΔ / (N−1) (3) is derived as the relationship between d and Δ.

In order to satisfy (3), a wedge-shaped prism WG
By setting P, the optical path length does not change even if the wedge-shaped prism WGP is moved by Δ, and the position of the diffraction-grating slit-shaped pinhole, that is, the detection position in the optical axis direction can be changed.

FIG. 7 is an optical path diagram of the entire detection optical system in the state of FIG. 5, and FIG. 8 is an optical path diagram of the entire detection optical system in the state of FIG. FIG. 7 shows the position of the detection surface.
8 corresponds to the detection state in FIG. 4 in terms of the position of the detection surface. As is clear from FIGS. 7 and 8, although the detection position was changed with respect to the optical axis direction, confoca
1, high-contrast detection is possible.

In the above embodiment of the alignment,
Although the description has been made of the TTL off-axis alignment system via the projection optical system, the present invention is not limited to this. For example, the TTL-on-axis alignment method and the NON-TTL off-axis alignment method can be applied in the same manner, and the object of the present invention can be achieved.

[0037]

As described above, according to the present invention, even when the measurement range is outside the depth statically determined by the detection optical system, the effect of the oblique movement of the wedge-shaped prism makes it possible to form a diffraction grating and a slit. Since the imaging relationship between the pinhole and the CCD camera serving as the image sensor is maintained, the three-dimensional shape of the alignment mark on the wafer can be detected with high accuracy without causing a decrease in contrast. Became possible.

Since the movement of the wedge-shaped prism according to the present invention requires only one actuator, it is not necessary to control the two actuators with high accuracy as in the other systems. Detection can be performed.

[Brief description of the drawings]

FIG. 1 is a schematic view of a main part of a first embodiment of the present invention,

FIG. 2 is a schematic view of a main part of a conventional confocal detection system,

FIG. 3 is a diagram showing a case where an observation surface is within a depth in a conventional detection system;

FIG. 4 is a diagram showing a case where an observation surface is out of depth in a conventional detection system;

FIG. 5 is a cross-sectional view of a wedge-shaped prism WGP having a diffraction-grating slit-shaped pinhole, which is a feature of the present invention.

FIG. 6 is a diagram showing a state in which the WGP has moved by Δ in the principle diagram of the present invention;

FIG. 7 is a diagram showing a state corresponding to FIG. 3 of the present invention;

FIG. 8 is a diagram showing a state corresponding to FIG. 4 of the present invention;

FIG. 9 is a diagram showing a state in which the upper part of an object is detected by Confocal detection;

FIG. 10 is a diagram showing a state in which the lower part of an object is detected by Confocal detection;

FIG. 11 shows an example of patterning a diffraction grating-shaped slit pinhole;

FIG. 12 shows an example of a detection system in which the optical path length is adjusted by switching between parallel plates.

FIG. 13 shows an example of a detection system in which optical path length adjustment is performed by a driving mirror.

[Explanation of symbols]

Reference Signs List 1 wafer, 2 alignment mark, 4 illumination optical system, 5 exposure light source, 8 alignment illumination optical system 10 relay lens, 11 objective lens, 12 reticle, 13 reduction projection optical system, 15 erector, 16 CCD camera, 18 XY stage, 21 Wafer chuck, 22 θ-Z stage, 23 tilt stage, 25 bar mirror, 26 laser interferometer, 29 focus measurement system (light projection system), 30 focus measurement system (detection system), 31 reference mark SM illumination optical system, 32 optics System, 40 He-Ne laser, light from 41 He-Ne laser, 42 fibers, light receiving range of CCDA CCD camera, CP coma aberration correcting prism, GP Parallel plate with slit pinhole like GP that can be driven, GWA Diffraction grating slit slit Hall part, MM Optical path length correction drive mirror, MP Optical path length correction parallel plate group with different thickness, PBS beam splitter, SM reference mark, SMW1, SMW2 Light transmission part from reference mark SM, WGP wedge shape prism.

Claims (22)

[Claims] 1. A position detecting device for detecting the position of an observation object by a detection optical system, wherein a diffraction grating-like and slit-like pinhole is arranged near the image plane of the observation object in the detection optical system. When illuminating the object through the pinhole and detecting the reflected light from the object again through the pinhole, the imaging relationship between the pinhole and the detection surface is maintained regardless of the position of the pinhole. A position detecting device characterized in that the position detecting device is configured to lean. 2. The position detecting device according to claim 1, wherein said pinhole is formed on a wedge-shaped prism. 3. The position detecting device according to claim 2, wherein the shape of the object is measured by moving the wedge-shaped prism obliquely with respect to an optical axis. 4. The position detecting device according to claim 3, wherein an optical element for correcting aberration generated by the wedge-shaped prism is disposed in the detection optical system. 5. The position detecting device according to claim 3, wherein the optical element is a wedge-shaped prism that corrects coma generated by the wedge-shaped prism. 6. The position detecting device according to claim 3, wherein said optical element is two parallel flat plates for correcting astigmatism generated by said wedge-shaped prism. 7. The position detecting device according to claim 3, wherein a reference mark projecting optical system for projecting a reference mark indicating a reference position of detection is arranged on the detection optical system. 8. The position detecting device according to claim 7, wherein the optical path of the reference mark projection optical system is combined with the optical path of the reflected light from the object before the light enters the wedge-shaped prism. 9. The position detecting device according to claim 8, wherein a light beam from said reference mark passes through said wedge-shaped prism. 10. The position detecting device according to claim 9, wherein a light beam from the reference mark and a light beam from the object are spatially separated on the wedge-shaped prism. 11. The position detecting apparatus according to claim 7, wherein the light beam from the reference mark is detected by normal image formation, and the light beam from the object is detected by focal detection. 12. The position detecting apparatus according to claim 3, wherein the wedge-shaped prism detects a three-dimensional shape of the object by moving in a diagonal direction with respect to the detection optical system. 13. The shape of the wedge-shaped prism is N, the refractive index of the material is N, the amount of movement of the detection optical system in the direction perpendicular to the optical axis before and after the movement is Δ, and the amount of change in thickness at the optical axis is d. 13. The position detecting device according to claim 12, wherein d = NΔ / (N−1) is satisfied. 14. An exposure apparatus equipped with the position detection device according to claim 1. Description: 15. The exposure apparatus according to claim 14, wherein the position detection device is of a TTL off-axis type. 16. The semiconductor exposure apparatus according to claim 14, wherein said position detecting device is of a TTL on-axis type. 17. An exposure apparatus according to claim 14, wherein said position detection device is of a non-TTL off-axis type. 18. A position detecting method for detecting the position of an observation object by a detection optical system, wherein a diffraction grating-like and slit-like pinhole is arranged near the image plane of the observation object in the detection optical system. When illuminating the object through the pinhole and detecting the reflected light from the object again through the pinhole, the imaging relationship between the pinhole and the detection surface is maintained regardless of the position of the pinhole. A position detection method characterized by doing so. 19. The three-dimensional shape of the object is formed by forming the pinhole in a wedge-shaped prism and moving the wedge-shaped prism obliquely with respect to the detection optical system. The position detection method described. 20. The detection of the object, wherein a reference mark provided on the detection optical system is projected on a detection surface via the wedge-shaped prism, and the detection is performed with reference to the projected reference mark. The position detection method according to claim 19. 21. The position detection method according to claim 20, wherein the detection of the reference mark is performed by normal imaging, and the detection of a light beam from the object is detected by focal. 22. The position detecting method according to claim 21, wherein an optical element for correcting an aberration generated by the wedge-shaped prism is arranged in the detection optical system.