JPH09152309A - Method and device for position detection - Google Patents

Abstract

PROBLEM TO BE SOLVED: To raise precision of position detection by detecting a position of a mark based an intensity of diffracted light modulated according to structure of a diffraction grating mark. SOLUTION: A diffraction grating mark consisting of the first area, acting as a light shielding area, and the second area, acting as transmission area, which are formed alternately with a specified pitch along a specified direction, is made into a position detecting mark WM. The light flux from a laser light source 1 is frequency-modulated at acousto-optic elements 3a and 3b, and the resulting things are crossed on the mark WM on a to-be-detected material 9. Two reflection diffracted lights generated on the mark WM work as interference light for introduced to a photodetecting optical system, and, a signal process system 11 detects the position of the mark WM based on the detection signal of a photoelectric conversion element 10. When the center of mark WM and the intersecting point of two irradiating flux correspond to each other, that is, when intensity of primary diffracted light from the mark WM to irradiation of two flux comes to the maximum, the central position of mark WM is detected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a position detecting apparatus and method, and more particularly to an apparatus for detecting the position of a photosensitive substrate or a mask in an exposure apparatus for manufacturing semiconductor elements, liquid crystal display elements and the like.

[0002]

2. Description of the Related Art As a conventional device of this type, for example, Japanese Patent Application Laid-Open No. 2-272305 discloses a position detecting device utilizing two-beam interference. In this position detecting device, the position of the object to be inspected can be detected with high accuracy. However, if the amount of positional deviation of the object to be inspected becomes more than half the pitch of the position detection marks (diffraction grating pattern), the phase of the detection signal will exceed 2π, and whether or not the object to be inspected is in the correct position. It becomes impossible to determine whether or not.

Therefore, for example, Japanese Patent Laid-Open No. 60-1307
With another suitable alignment mechanism such as the LSA (laser step alignment) system disclosed in Japanese Patent Laid-Open No. 42-42, coarse alignment of the object to be inspected is performed in advance with an accuracy of half the pitch of the position detection marks or less. Pre-alignment)
There is a need to. For example, if the final position detection accuracy is 6
When the phase detection accuracy is about 1/1000, the required pitch of the position detection marks is 6 μm. That is, it is necessary to roughly position the position detection mark in advance with an accuracy of 3 μm or less before detection by the position detection device using the two-beam interference.

[0004]

However, the accuracy of the alignment mechanism of another method such as the LSA system is remarkably deteriorated with respect to the object to be inspected such as a wafer having a small mark step or an aluminum wafer having a rough surface. Sometimes. In this case, it becomes difficult to roughly align the position detection marks with an accuracy of half the pitch of the position detection marks prior to high-precision detection by the position detection device using the two-beam interference.

The present invention has been made in view of the above-mentioned problems, and it is possible to perform position detection with high accuracy without rough alignment of the position detection marks by another type of alignment mechanism. It is an object to provide an apparatus and method.

[0006]

In order to solve the above problems, in the present invention, the predetermined direction is changed so that the ratio of the lengths of the first region and the second region along the predetermined direction changes. An irradiation optical system for irradiating a coherent light beam to an object to be inspected having diffraction grating marks in which first regions and second regions are alternately arranged along a predetermined pitch, Scanning means for relatively scanning the interference fringes formed on the diffraction grating mark by the light beam and the diffraction grating mark, and diffracted light generated from the diffraction grating mark by irradiation of the coherent light beam is detected. A photoelectric detector for photoelectrically converting into a signal, and the intensity of the diffracted light modulated by the structure of the diffraction grating mark in which the length ratio of the first region and the second region along the predetermined direction changes. Is detected when the Based on the output of the signal and provides a position detecting apparatus characterized by comprising a detecting means for detecting the position of said diffraction grating mark.

[0007] According to a preferred aspect of the present invention, the detecting means outputs the detection signal based on the output of the detection signal when the intensity of the diffracted light modulated by the structure of the diffraction grating mark becomes maximum or minimum. The position of the diffraction grating mark is detected.

According to another aspect of the present invention, in the position detecting method for detecting the position of the object to be inspected on which the position detecting mark is formed, the position detecting mark is a first region along a predetermined direction. The position detection marks are composed of diffraction grating marks in which the second regions are alternately arranged at a predetermined pitch, and the length ratio of the first regions to the second regions along the predetermined direction changes. A first step of forming interference fringes on the diffraction grating mark by irradiating a coherent light beam with the diffracted light generated by relatively scanning the interference fringe and the diffraction mark. The second step of photoelectrically converting into a detection signal, and the intensity of the diffracted light modulated by the structure of the diffraction grating mark in which the length ratio of the first region and the second region along the predetermined direction changes The detection when a predetermined state is reached Based on the output of the items, to provide a position detecting method comprising that a third step of detecting the position of the mark for the position detection.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, as position detection marks, first regions and second regions are alternately arranged along a predetermined direction at a predetermined pitch, and first regions along a predetermined direction. A diffraction grating mark whose length ratio to the second region changes is used. Therefore, the detection signal is obtained by photoelectrically converting the diffracted light generated by irradiating the position detecting mark with the coherent light beam. In this way, the position of the position detection mark can be detected based on the output of the detection signal when the intensity of the diffracted light modulated by the structure of the diffraction grating mark reaches the predetermined state.

Specifically, for example, a diffraction grating mark having a constant pitch is used in which the duty is 0.5 at the center of the mark and the duty changes almost monotonously toward the end of the mark. Therefore, for example, when the position of the mark center is detected by using the interference of two light beams, when the intersection (center point) of the two light beams coincides with the center of the mark, the first-order diffracted light from the position detection mark for the two light beams is detected. Maximum strength. That is, when the intensity of the diffracted light from the position detection mark becomes maximum, the center position of the position detection mark can be detected. As described above, according to the present invention, even if there is a displacement of more than half the pitch of the position detection marks, it is possible to detect the position with high accuracy and high precision by utilizing, for example, the two-beam interference.

The present invention utilizes the principle that the intensity of diffracted light changes when the duty of the diffraction grating mark is changed. Therefore, even when the position detection light beam completely irradiates the position detection mark, the influence of the intensity distribution of the irradiation light beam and the shape of the irradiation area is determined based on the data on the intensity change of the diffracted light due to scanning. It is possible to detect the position with high accuracy that is hard to receive. Further, rough alignment is performed by the position detection according to the present invention, and final alignment (fine alignment) is performed based on phase information of a detection signal from another position detection mark composed of a normal diffraction grating mark having a constant pitch and duty. Can be performed with higher accuracy.

Embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a diagram schematically showing a configuration of a position detection device according to an embodiment of the present invention. The present embodiment is an example in which the present invention is applied to a position detection device of a two-beam heterodyne interference system. The position detection device of the two-beam heterodyne interference method of FIG. 1 includes a laser light source 1 that supplies position detection light. The light beam from the laser light source 1 is emitted from the beam splitter 2
After being divided into two via the, the light enters the different acousto-optic elements 3a and 3b.

Acousto-optical elements 3a and 3b different from each other
A predetermined frequency difference is imparted to the two light beams that have been frequency-modulated by, and they are converged by the condenser lens 4 so as to intersect on the field stop 5. The two light beams that have passed through the field stop 5 enter the light-transmitting / receiving-light separating prism 7 through the second objective lens 6. The two light beams that have passed through the light-transmitting / receiving-light separating prism 7 cross again via the first objective lens 8 on the position detection mark WM formed on the object 9 to be inspected. As will be described later, the position detection mark WM is a diffraction grating mark composed of first regions as light-shielding regions and second regions as transmissive regions that are alternately formed at a predetermined pitch along a predetermined direction. . The pitch P of the diffraction grating marks referred to here is the distance between the centers of the two second regions that are adjacent to each other with the first region interposed, or the two pitches that are adjacent to each other with the second region interposed. It means the distance between the centers of one region.

The two light beams incident on the position detecting mark WM are ± 1 of the position detecting mark WM with respect to the vertically incident light.
It is configured to enter from the directions of the second-order diffracted lights. That is, when the mark pitch of the position detection marks WM is P and the wavelength of the detection light is λ, the incident angles of the two light beams are ± λ / P. Therefore, the two light beams form an interference fringe on the position detection mark WM, and the position detection mark WM is optically scanned by the interference fringe. In this way, the ± first-order reflected diffracted light of the light generated from the position detection mark WM by the irradiation of the two light fluxes is reflected in the direction normal to the surface of the object 9 to be inspected. These two reflected diffracted lights become interference lights, are condensed again by the first objective lens 8, are reflected by the light-transmitting / receiving separation prism 7, and are guided to the light-receiving optical system.

In the light receiving optical system, a photoelectric conversion element 10 such as an SPD (silicon photodiode) converts the amount of interference light into an electric signal, that is, a detection signal. As will be described later, the signal processing system 11 can detect the position of the position detection mark WM based on the output of this detection signal. Further, in the signal processing system 11, the photoelectric conversion element 1
The detection signal from 0 is converted into a position shift signal representing the position shift amount of the position detection mark WM. The position shift signal from the signal processing system 11 is supplied to the control system 12. Control system 1
In 2, in accordance with the position shift signal from the signal processing system 11,
Positioning is performed by appropriately driving a stage (not shown) holding the object 9 to be inspected and correcting the positional deviation of the position detection mark WM.

FIG. 2 is a diagram showing the structure of a normal diffraction grating mark having a pattern in which both pitch and duty are constant. As shown in FIG. 2, in the position detecting mark composed of a normal diffraction grating mark, a pattern (indicated by a shaded portion in the drawing) is formed along a predetermined direction at a constant pitch P and a constant duty d. The pitch P is the distance between the patterns along the predetermined direction, and the duty d is the ratio L / P of the length L of the pattern along the predetermined direction to the pitch P.

For simplicity, let us consider the case of an intensity grating (diffraction grating consisting of a light and dark pattern) mark in which diffracted light is reflected only from the pattern area shown by the hatched portion in FIG.
At this time, the amplitude A (1) of the first-order diffracted light is expressed by the following equation (1).
Is represented by A (1) = sin (πd) / π (1) From the above formula (1), it is understood that the amplitude (intensity) of the first-order diffracted light depends on the duty d of the diffraction grating mark.

FIG. 3 shows the 1 in the diffraction grating mark of FIG.
It is a figure which shows the relationship between the amplitude A (1) of the next-order diffracted light and the duty d of a diffraction grating mark. In FIG. 3, the duty d is plotted on the horizontal axis and the amplitude A (1) of the first-order diffracted light is plotted on the vertical axis. Referring to FIG. 3, when the duty d is 0.5, the amplitude A (1) of the first-order diffracted light is maximum.
Then, as the duty d approaches from 0.5 to 0 or from 0.5 to 1, the amplitude A (1) of the first-order diffracted light monotonically decreases.

FIG. 4 is a diagram showing the structure of a diffraction grating mark having a pattern in which the pitch is constant and the duty monotonously decreases from the center to the end of the mark. FIG.
FIG. 6 is a diagram showing a configuration of a diffraction grating mark having a pattern in which the pitch is constant and the duty monotonously changes from one end to the other end of the mark. In the diffraction grating mark shown in FIG. 4, the duty at the center of the mark is set to 0.5, and the duty linearly decreases from both ends. Also,
In the diffraction grating mark shown in FIG. 5, the duty at the center of the mark is 0.5, and the duty increases linearly from the left end to the right end in the figure.

The amplitude of the first-order diffracted light with respect to the diffraction grating mark whose pitch is constant and whose duty is sequentially changed is the sum of the amplitudes represented by the above equation (1). Therefore, in the present embodiment, by using the diffraction grating mark whose duty is sequentially changed as shown in FIGS. 4 and 5, when the center of the mark and the center (intersection point) of the two irradiation light fluxes coincide with each other, The intensity of breaking light is maximum. In other words, the center position of the position detection mark WM can be detected when the intensity of the first-order diffracted light from the position detection mark WM with respect to the irradiation of the two light fluxes becomes maximum.

Thus, even if the center of the mark and the center (intersection) of the two irradiation light fluxes are initially displaced by more than half the pitch, the position can be detected with high accuracy based on the intensity distribution of the first-order diffracted light. You can That is, the position detection can be performed quickly and highly accurately by the position detection method according to the present embodiment without performing the rough position adjustment by another position adjusting mechanism. It should be noted that the rough position alignment is performed by the position detection according to the present embodiment, and the final position detection is further enhanced based on the phase information of the detection signal from another position detection mark composed of a normal diffraction grating mark having a constant pitch and duty. It can also be done with precision.

Incidentally, in the above-mentioned embodiment, FIG. 4 and FIG.
The change in the duty of the diffraction grating mark shown in (4) was linear, but in the present invention, it is an essential requirement that the change in duty is almost monotonous. Therefore, the change in the amplitude of the first-order diffracted light can be made linear by changing the duty according to the arcsine function, for example. The following table (1) numerically shows the change of the duty of the diffraction grating marks of FIGS. 4 and 5 and the change of the duty according to the above arcsine function.

[0023]

[Table 1]

In Table (1), the numbers on the left side are -9 for the pattern area on the left side in the figure, 0 for the central pattern area in the figure, and 4 for the pattern area on the right side in the figure. Is shown numerically. Therefore, FIG.
In the row A corresponding to the diffraction grating mark of
Linearly increases from 0.1 at the left end to 0.5 at the center, and decreases linearly from 0.5 at the center to 0.5 at the right end.
In the row B corresponding to the diffraction grating mark in FIG. 5, the duty d linearly increases from 0.1 at the left end to 0.5 at the center to 0.9 at the right end.

Further, in the column C showing an example in which the duty d changes according to the arcsine function, the duty d increases from 0.0641 at the left end to 0.5 at the center according to the arcsine function and becomes 0. It decreases according to the arcsine function from 5 to 0.0641 at the right end. In column D showing another example in which the duty d changes according to the arcsine function, the duty d is from 0.0641 at the left end to 0.5 at the center to 0.9359 at the right end according to the arcsine function. It has increased.

In the above embodiment, the detection signal by the ± 1st-order diffracted light generated from the diffraction grating mark is maximized at the mark center, that is, when the center of the light beam for detection coincides with the center of the diffraction grating mark. The duty at the center of the mark is 0.5 so that the diffraction intensity is maximized.
The example is set so that However,
In order to maximize the diffracted light generated at the center position of the diffraction grating mark, the light shielding area (first area) in the center area of the mark is used.
The ratio is not limited to the case where the ratio of the area) to the transmissive area (second area) is 1: 1, that is, the duty of the mark central area is 0.5. That is, the duty at the center of the diffraction grating mark may be set to a predetermined value according to the order of the diffracted light to be detected.

Specifically, n of the intensity grid of duty d
The intensity I _n of the next-order diffracted light (detection light) is generally expressed by the following equation (2).
It is represented as. I _n = | sin (πnd) / (πn) | ² (2) Here, the condition when the intensity of the diffracted light has an extreme value is that the value obtained by differentiating the above formula (2) is the following formula (3). It becomes zero as shown in. sin (πnd) × cos (πnd) = 0 (3)

The maximum value of the above equation (2) is
This is the case when cos (πnd) = 0. Also, the duty d
Takes a value in the range of 0 <d <1. Therefore, for example, the condition that the intensity of the diffracted light has a maximum value is that the duty d is 0.5 when n = ± 1, and the duty d is 0.25 or 0.75 when n = ± 2. That is.

Therefore, in order to maximize the detection signal of the ± 2nd order diffracted light generated from the diffraction grating mark at the center of the mark by using the ± 2nd order diffracted light as the detection light, the light shielding region (first region) The ratio between the transparent area and the transparent area (second area) is set to 3: 1, and the light-shielding area (first area) and the transparent area (second area) are monotonically decreased from the center of the mark to the end of the mark. The diffraction grating mark may be configured so that the ratio of the diffraction grating mark and the mark) is not 3: 1. Alternatively, the ratio of the light-shielding region (first region) and the light-transmitting region (second region) is set to 1: 3, and the light-shielding region (first region) is set so that the detection intensity monotonously decreases from the center of the mark to the end of the mark.
The diffraction grating mark may be configured so that the ratio of the area) to the transmission area (second area) deviates from 1: 3.

Therefore, if the duty d when the above equation (2) shows a maximum value is generally shown, it can be expressed as the following equation (4). d = (m + 0.5) / n (0 <d <1) (4) However, m and n are integers and n is a diffraction order.

As described above, in order to maximize the detection signal by the ± n-order diffracted light generated from the diffraction grating mark at the mark center, the duty d determined by the above equation (4) is obtained, and the duty d at that time is calculated. It may be configured so that the duty d becomes the center of the diffraction grating mark.

As yet another example, the detection signal due to the ± n-order diffracted light generated from the diffraction grating mark is minimized at the mark center, and the detection signal due to the ± n-order diffracted light goes from the center of the mark to the end of the mark. The diffraction grating mark may be configured to monotonically increase. in this case,
The above equation (2) shows the minimum value when sin (πnd) = 0. Further, the duty d takes a value in the range of 0 <d <1. Therefore, for example, the condition that the intensity of the diffracted light has a minimum value is that the duty d is 0.5 when n = ± 2. When n = ± 1, the duty d
Should be near 0 or 1.

Therefore, in order to use the ± 2nd-order diffracted light as the detection light and minimize the detection signal by the ± 2nd-order diffracted light generated from the diffraction grating mark at the center of the mark, the light-shielding region (first region) The ratio between the transparent area and the transparent area (second area) is set to 1: 1 and the light-shielding area (first area) and the transparent area (second area) increase monotonically as the detection intensity increases from the center of the mark to the end of the mark. The diffraction grating mark may be configured so that the ratio with the ratio (1) is outside the range of 1: 1.

Therefore, if the duty d when the above equation (2) shows a minimum value is generally shown, it can be expressed as the following equation (5). d = m / n (0 <d <1) (5) However, m and n are integers, and n is a diffraction order of one or more orders, that is, | n |> 1.

As described above, in order to minimize the detection signal due to the ± nth order diffracted light generated from the diffraction grating mark at the mark center, the duty d determined by the above equation (5) is obtained, and the duty d at that time is calculated. It may be configured so that the duty d becomes the center of the diffraction grating mark.

Further, in the above-mentioned embodiment, the intensity lattice mark composed of the bright and dark patterns is used as the position detecting mark for the sake of simplicity. However, it is also possible to use a phase grating mark formed with a constant step as a position detection mark. Further, it goes without saying that the present invention can be applied to a position detection optical system using a plurality of light sources as disclosed in Japanese Patent Laid-Open No. 6-82215.

As described above, by appropriately setting the duty value at the mark center and the duty change over the entire mark, the intensity of the diffracted light becomes a predetermined state when the light beam center and the mark center coincide with each other, for example, Obviously, it can be configured to be maximum or minimum.

Further, in the above-mentioned embodiment, the position detecting device utilizing the two-beam heterodyne interference is shown.
The present invention can also be applied to a position detection device that uses two-beam homodyne interference that does not give a frequency difference to two beams.

[0039]

As described above, in the present invention, since the positional deviation information between the center of the position detection mark and the center of the detection light is included in the amplitude of the detection signal, the position of the position detection mark at a half or more of the pitch is detected. Even if there is a deviation, it is possible to detect the position with high accuracy and speed by utilizing, for example, two-beam interference. Further, rough position alignment is performed by the position detection according to the present invention, and the final position detection is further highly accurate based on the phase information of the detection signal from another position detection mark composed of a normal diffraction grating mark having a constant pitch and duty. You can also do this.

[Brief description of the drawings]

FIG. 1 is a diagram schematically showing a configuration of a position detection device according to an embodiment of the present invention.

FIG. 2 is a diagram showing a configuration of a normal diffraction grating mark having a pattern in which both pitch and duty are constant.

3 is a diagram showing the relationship between the amplitude d (1) of the first-order diffracted light in the diffraction grating mark of FIG. 2 and the duty d of the diffraction grating mark.

FIG. 4 is a diagram showing a structure of a diffraction grating mark having a pattern in which the pitch is constant and the duty is monotonically decreased from the center to the end of the mark.

FIG. 5 is a diagram showing a configuration of a diffraction grating mark having a pattern in which the pitch is constant and the duty is monotonously changed from one end to the other end of the mark.

[Explanation of symbols]

 1 Laser Light Source 2 Beam Splitter 3 Acousto-Optical Element 4 Condensing Lens 5 Field Stop 6 Second Objective Lens 7 Transmitting / Receiving Separation Prism 8 First Objective Lens 9 Test Object 10 Photoelectric Conversion Element 11 Signal Processing System 12 Control System WM Position Detection Mark for

Claims (8)

[Claims] 1. The first region and the second region alternate along the predetermined direction at a predetermined pitch so that the length ratio of the first region and the second region along the predetermined direction changes. An irradiation optical system for irradiating a coherent light beam to a test object having diffraction grating marks arranged in a line, an interference fringe formed on the diffraction grating mark by the coherent light beam, and the diffraction grating A scanning means for relatively scanning the mark, a photoelectric detector for photoelectrically converting the diffracted light generated from the diffraction grating mark by irradiation of the coherent light beam into a detection signal, and in the predetermined direction Based on the output of the detection signal when the intensity of the diffracted light modulated by the structure of the diffraction grating mark in which the ratio of the lengths of the first region and the second region along the line changes, becomes a predetermined state, Detects the position of the diffraction grating mark A position detecting device for detecting the position. 2. The detection means detects the position of the diffraction grating mark based on the output of the detection signal when the intensity of the diffracted light modulated by the structure of the diffraction grating mark has a maximum or a minimum. The position detecting device according to claim 1, wherein 3. In the irradiation optical system, a length ratio of a first region and a second region along the predetermined direction is from the center of the diffraction grating mark to the predetermined direction of the diffraction grating mark. Along the predetermined direction of the diffraction grating mark from the center of the diffraction grating mark, the ratio of the lengths of the first region and the second region along the predetermined direction decreases monotonically along one end along the predetermined direction. Irradiating a coherent light beam to the diffraction grating mark having a structure that monotonically decreases toward the other end, and the detection means is configured such that the intensity of the diffracted light modulated by the structure of the diffraction grating mark becomes maximum. The position detecting device according to claim 2, wherein the center position of the diffraction grating mark is detected based on the output of the detection signal. 4. The irradiation optical system has a length ratio of a first region and a second region along the predetermined direction from one end to the other end of the diffraction grating mark along the predetermined direction. Irradiating a coherent light beam on the monotonically changing diffraction grating mark, the detection means detects the detection signal when the intensity of the diffracted light modulated by the structure of the diffraction grating mark is in a predetermined state. The position detecting device according to claim 1, wherein the center position of the diffraction grating mark is detected based on the output of the position detecting device. 5. A position detecting method for detecting a position of an object to be inspected having a position detecting mark, wherein the position detecting mark has a first region and a second region with a predetermined pitch along a predetermined direction. And the diffraction grating marks are arranged alternately and the ratio of the lengths of the first region and the second region along the predetermined direction is changed. A first step of forming interference fringes on the diffraction grating mark by irradiation, and a second step of photoelectrically converting diffracted light generated by relatively scanning the interference fringe and the diffraction mark into a detection signal And the detection when the intensity of the diffracted light modulated by the structure of the diffraction grating mark in which the ratio of the lengths of the first region and the second region along the predetermined direction changes reaches a predetermined state. Based on the output of the signal, Position detecting method, characterized in that it comprises a third step of detecting the position of the position detecting mark. 6. The third step is based on the output of the detection signal when the intensity of the diffracted light modulated by the structure of the position detection mark becomes maximum or minimum, The position detecting method according to claim 5, wherein the position is detected. 7. The position detecting mark has a length ratio of a first region and a second region along the predetermined direction from the center of the position detecting mark to the position detecting mark. The position ratio of the length of the first region and the length of the second region along the predetermined direction decreases from the center of the position detection mark to the one of the position detection marks while monotonically decreasing toward one end along the predetermined direction. The third step is to output the detection signal when the intensity of the diffracted light modulated by the structure of the position detection mark is maximum, which has a structure that monotonically decreases toward the other end along the predetermined direction. The position detection method according to claim 6, wherein the center position of the position detection mark is detected based on the position detection mark. 8. The position detecting mark has a length ratio of a first region and a second region along the predetermined direction from one end of the position detecting mark along the predetermined direction to another. Having a structure that changes monotonically toward the end, the third step, based on the output of the detection signal when the intensity of the diffracted light modulated by the structure of the position detection mark is in a predetermined state, The position detection method according to claim 5, wherein the center position of the position detection mark is detected.