JPH0969480A - Alignment method and exposure apparatus using the method - Google Patents

Abstract

(57) [Abstract] [Problem] To detect a shift of the focal position of a wafer mark,
Position with high accuracy. SOLUTION: Effective exposure field IAR of a projection optical system
Spot light 9a to a plurality of measurement points that are almost evenly distributed to
A multi-point focus position detection system is provided which obliquely irradiates 9 m and detects the height (focus position) of those irradiation positions. Alignment illumination light for detecting the positions of the wafer marks 4a, 4b from the alignment sensor is used as slit light 1a, 1b.
The spot lights 9k and 9h are set to overlap the irradiation positions of the slit lights 1a and 1b, respectively. Sample shots in which the height measurement values at the irradiation positions of the spot lights 9k and 9h exceed the allowable range from the height measurement values at the other measurement points are excluded from the alignment data and the EGA method is used to measure the wafer. The coordinate position of each shot area is calculated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention transfers a mask pattern onto a substrate such as a wafer in a lithography process for manufacturing a semiconductor device, an imaging device (CCD or the like), a liquid crystal display device, a thin film magnetic head or the like. And a aligner method using this method, particularly when aligning each shot area on a wafer with a mask pattern based on array coordinates predicted using a statistical method. It is suitable for application.

[0002]

2. Description of the Related Art For example, a semiconductor element is formed by stacking a large number of layers of circuit patterns on a wafer. It is necessary to perform highly accurate alignment between each shot area in which the marks have been formed and the pattern of the reticle to be exposed, that is, wafer alignment (wafer alignment).

As an alignment sensor for this purpose,
LSA (Laser Step A) that irradiates a laser beam on a dot-line-shaped alignment mark on the wafer and detects the position of the mark using the light diffracted or scattered by the mark.
FIA (Field Image) that measures the image data of the alignment mark imaged by illuminating it with light with a wide wavelength band using a halogen lamp as the light source.
Alignment) method or a diffraction grating-like alignment mark on a wafer is irradiated with laser light of the same frequency or a slightly different frequency from two directions, and the two generated diffracted lights are caused to interfere with each other, and the phase of the alignment mark LIA (Laser Interferometric Alignment) for measuring position
There is an alignment sensor such as a method.

FIG. 4 shows a schematic structure of a projection exposure apparatus equipped with a conventional LSA type alignment sensor. In FIG. 4, the pattern of the reticle 5 passes through the projection optical system 6 and each shot area on the wafer 7. Is transcribed to. The wafer 7 is mounted on a wafer stage (not shown) via a wafer holder (not shown). Further, the Z axis is taken parallel to the optical axis of the projection optical system 6, and the Cartesian coordinate system on the plane perpendicular to the Z axis is the X axis and the Y axis. Then, the alignment illumination light LX and LY from the alignment sensors 11X and 11Y for the X-axis and the Y-axis of the LSA system and the TTL (through the lens) system are transmitted from the lower part of the reticle 5 through the projection optical system 6. The slit light beams 1a and 1b are applied to the ends of the projection optical system 6 on the effective exposure field IAR. The best focus planes of the alignment sensors 11X and 11Y are set at the same focus position with respect to the image plane of the projection optical system 6.

A light transmitting optical system 102 and a light receiving optical system 1
And an effective exposure field IAR from the light transmission optical system 102.
The measurement beam LE is emitted as spot light from a diagonal direction to a plurality of measurement points in the substantially central portion of, and the reflected light from the plurality of measurement points is received by the light receiving optical system 103. The plurality of spot lights are re-imaged in the light receiving optical system 103, and a plurality of focus signals corresponding to the lateral shift amount of the re-formed image are output. When the focus position of the wafer 7 (the position in the optical axis direction of the projection optical system 6) changes, the lateral shift amount of the re-formed images changes, so that the wafers at the plurality of measurement points are obtained from the plurality of focus signals. The focal positions of 7 are measured.

FIG. 5 shows a specific arrangement on the effective exposure field IAR of the spot light by the measurement beams LE from the focus position detection systems 102 and 103. As shown in FIG. 5, the projection optical system shown in FIG. 6 effective exposure field IAR
The spot lights 109a to 109e are irradiated onto the five measurement points arranged at substantially equal intervals on a substantially diagonal line. FIG.
The slit light beams 1a and 1b from the alignment illumination light beams LX and LY from the alignment sensors 11X and 11Y, respectively, are applied to substantially the center of the end portions of the effective exposure field IAR in the −Y direction and the + X direction.

Here, the X-axis wafer mark 4a for the LSA system and the Y-axis wafer mark 4b for the LSA method are respectively provided at the end portions of the shot area 8 surrounded by the dotted line on the wafer 7 in the -Y direction and the + X direction. Are formed. During alignment, the wafer 7 is moved via a wafer stage (not shown) so that the wafer mark 4a crosses the slit light 1a in the X direction, and then the wafer mark 4b crosses the slit light 1b in the Y direction. By moving, the X and Y coordinates of the wafer marks 4a and 4b are detected. After that, at the time of exposure, the shot area 8 on the wafer 7
The center of the effective exposure field IAR center (exposure center)
On the basis of the focus signals from the focus position detection systems 102 and 103, and the average value of the focus positions of the shot area 8 is adjusted to the focus position of the image plane of the projection optical system 6 (predetermined). In this state, the pattern image of the reticle 5 is projected and exposed on the shot area 8.

As shown in FIG. 5, conventionally, the oblique incidence type focus position detection system has been mainly focused on detecting the average focus position of the shot area during exposure. Therefore, only five spot lights 109a to 109e are irradiated on the diagonal line of the effective exposure field IAR.

[0009]

According to the above prior art, when the shot area 8 on the wafer is aligned, the wafer marks 4a and 4b are crossed by the slit light beams 1a and 1b for alignment, respectively. The two spot lights 109a to 109e are all on the wafer marks 4a and 4e.
It is not irradiated in the vicinity of b. Therefore, the focus position on the wafer marks 4a and 4b is not measured during alignment. For example, when a foreign substance such as a resist residue is present between the wafer and the wafer holder, the wafer mark 4
The focus positions of a and 4b are not necessarily the alignment sensor 11
Since it does not match the best focus position of X and 11Y,
There was a risk of causing focus offset during alignment. If the telecentricity of the alignment sensors 11X and 11Y is destroyed when such an offset occurs, there is a disadvantage that an error (jump of measurement data) is mixed in the measurement value accordingly.

In view of this point, the present invention accurately detects the state of the wafer mark (alignment mark) on the wafer even if the focal position of the wafer mark is misaligned as compared with the other areas in the shot area. An object of the present invention is to provide a positioning method for performing highly accurate positioning. Another object of the present invention is to provide an exposure apparatus which can carry out such an alignment method.

[0011]

According to the alignment method of the present invention, an alignment mark (4) attached to a shot area (8) on a substrate (7) onto which a mask pattern is transferred is provided.
A) is illuminated with alignment illumination light (1a) to detect the position of the alignment mark (4a), and the mask pattern and its substrate (7) are detected based on the detection result.
In the alignment method for aligning with the shot area (8) above, a plurality of measurement lights (9a-9m) on the substrate (7) are irradiated with predetermined measurement light, respectively. The height of the board at each of the measurement points is detected, and at least one (9k) of the plurality of measurement points is set on the alignment mark (4a). The height detection result at the measurement point is compared, and based on this comparison result, the alignment mark (4a)
It is to determine whether or not the height of the substrate (7) at the formation position is suitable for detecting the position of the alignment mark (4a).

According to such a positioning method of the present invention,
The actual height of the alignment mark (4a) is accurately detected at at least one measurement point (9k) of the plurality of measurement points (9a to 9m). Then, when the difference between this detection result and the detection results at other measurement points exceeds, for example, a predetermined permissible range, it is determined that the position detection by the alignment mark (4a) is inappropriate. By doing so, detection data that may include an error is excluded, and alignment is performed with high accuracy.

Further, the exposure apparatus according to the present invention is such that the alignment mark (4a) provided on each shot area (8) on the substrate (7) is illuminated with alignment illumination light (1a).
Has an alignment sensor (11X) that detects the position of the alignment mark (4a) by irradiating with a mask pattern and each shot area on the substrate (7) based on the detection result of this alignment sensor. Of the plurality of spot-shaped measurement lights on the substrate (7) in the plurality of measurement points (9a) on the transfer region of the mask pattern on the substrate (7). Up to 9 m) is obliquely irradiated and a multi-point type focus position detection system (2, 3) for detecting the height of the substrate (7) at the plurality of measurement points is provided. At least one (9k) of the plurality of measurement points (9a to 9m) by 2, 3) is attached to the alignment sensor (11).
X) is set at or near the position where the illumination light is emitted,
Based on the difference between the detection result at this measurement point (9k) and the detection result at other measurement points, the alignment sensor (11
The determination means (13) for determining whether or not the detection data can be used by X) is provided.

According to the exposure apparatus of the present invention, measurement is performed at a plurality of measurement points on the transfer area of the mask pattern on the substrate (7) by using the multi-point type focus position detection system (2, 3). Irradiation with light is performed, and the determination means (1
By 3), it is possible to judge whether or not the detection data can be used by the alignment sensor (11X). Therefore,
The alignment method of the present invention described above can be implemented.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION An example of an embodiment of the present invention will be described below with reference to FIGS. FIG. 1 shows an overall schematic configuration of a stepper type projection exposure apparatus of this example,
In FIG. 1, during exposure, the reticle 5 is irradiated with exposure illumination light from the exposure illumination system AL, and under the illumination light, the pattern of the reticle 5 is reduced to, for example, 1/5 via the projection optical system 6. It is projected on each shot area on the wafer 7 which is reduced in size and coated with the photoresist. Here, the Z axis is taken parallel to the optical axis AX of the projection optical system 6, the Y axis is taken parallel to the plane of FIG. 1 on the plane perpendicular to the Z axis, and the X axis is taken perpendicular to the plane of FIG.

In this case, the reticle 5 is held on the reticle stage 14, and the reticle stage 14 moves in the X direction, the Y direction, and the rotation direction (θ direction) in a plane perpendicular to the optical axis AX of the projection optical system 6. Position 5 On the other hand, the wafer 7 is placed on the wafer stage 15 via a wafer holder (not shown). The wafer stage 15 positions the wafer 7 in the X direction, the Y direction, and the rotation direction (θ direction) within a plane perpendicular to the optical axis AX of the projection optical system 6, and also moves the wafer 7 in the focal direction (Z direction). Positioning is also performed. An X coordinate, a Y coordinate, and a rotation angle of the wafer 7 are constantly measured by a movable mirror (not shown) fixed on the wafer stage 15 and a laser interferometer (not shown) installed outside,
The measured value is supplied to the central control system 13. In each shot area of the wafer 7 (typically, the shot area 8 is shown in FIG. 2B), a wafer mark 4a in the form of dot rows for the X axis for wafer alignment and a wafer in the form of dot rows for the Y axis are provided. The mark 4b (see FIG. 2B) is formed.

Further, in FIG. 1, a TTL type and LSA type alignment sensor 11X for the X-axis is installed near the upper side surface of the projection optical system 6 and below the reticle stage 14. This alignment sensor 11
X is used for alignment for final positioning of the reticle 5 and each shot area on the wafer 7. When the wafer is aligned, the alignment sensor 11
The alignment illumination light LX emitted from X is irradiated onto the wafer 7 as slit light 1a via the mirror 16X above the projection optical system 6 and the projection optical system 6. When the wafer stage 15 is driven in that state so that the wafer mark 4a in FIG. 2B crosses the slit light 1a in the X direction, for example, when the wafer mark 4a is exposed to the slit light 1a, Diffracted light is generated. The diffracted light from the wafer mark 4a reverses the incident optical path, returns to the alignment sensor 11X via the projection optical system 6, and enters the internal light receiving sensor. The alignment sensor 11X generates a detection signal obtained by photoelectrically converting the amount of light incident on the light receiving sensor. The detection signal is supplied to the alignment processing system 12, and in the alignment processing system 12, the X coordinate of the wafer stage 15 when the light amount becomes maximum is detected as the position of the wafer mark.

Although not shown, a Y-axis alignment sensor similar to the alignment sensor 11X is provided, and the illumination light from this alignment sensor is shown in FIG.
As shown in (b), the slit light 1b is applied to the end portion of the effective exposure field IAR in the + X direction. The Y-axis alignment sensor and the alignment processing system 12 measure the Y-coordinate of the Y-axis wafer mark 4b shown in FIG. 2B on the wafer 7. The X and Y coordinates of the wafer mark detected by the alignment processing system 12 are supplied to a central control system 13 that centrally controls the operation of the entire apparatus. Further, the focus positions of the best focus surfaces of the X-axis alignment sensor 11X and the Y-axis alignment sensor are set to be equal to the focus position (Z-direction position) of the image forming surface of the projection optical system 6. Has been done.

In FIG. 2B, the distance between the X coordinate of the center (detection center) of the slit light 1a from the X-axis alignment sensor 11X and the X coordinate of the center (exposure center) of the effective exposure field IAR. That is, the baseline amount of the alignment sensor 11X is obtained in advance and stored in the central control system 13 of FIG. Similarly, the baseline amount of the Y-axis alignment sensor (not shown), that is, the distance between the center Y coordinate of the slit light 1b and the center Y coordinate of the effective exposure field IAR is also stored in the central control system 13.
At the time of exposure, the center of each shot area is positioned at the center of the effective exposure field IAR based on the coordinates obtained by adding the baseline amount to the X and Y coordinates of the wafer mark detected by the alignment sensor 11X and the like.

Further, in the apparatus shown in FIG. 1, a photoresist layer for forming a slit image (or pin-hole image) obliquely toward the exposure surface of the wafer 7 in the effective exposure field IAR of the projection optical system 6 is exposed. Multiple measurement beams (hereinafter referred to as "AF beam") LF with weak wavelength range
Of the oblique incidence system including an irradiation optical system 2 for irradiating each shot area on the wafer 7 in a diagonal direction and a light receiving optical system 3 for receiving the reflected light flux of the AF beam LF on the exposure surface of the wafer 7. A point type focus position detection system (hereinafter, referred to as “focus position detection systems 2 and 3”) is arranged. As shown in FIG. 5, the measurement beam of the conventional focus position detection system is applied to five measurement points arranged diagonally in the effective exposure field of the projection optical system. The AF beams LF of the position detection systems 2 and 3 are applied to more measurement points.

FIG. 2A shows a state of slit-shaped spot light by the AF beam applied to 13 measurement points arranged in the effective exposure field IAR of the projection optical system 6, and FIG. ) Indicates the positional relationship between the effective exposure field IAR of the projection optical system 6 and the shot area 8 of the wafer 7 during alignment. As shown in FIG. 2A, the AF beam LF has slit-shaped spots parallel to the diagonal line of the effective exposure field IAR on 13 measurement points that are substantially evenly distributed over the entire effective exposure field IAR. It is emitted as light 9a to 9m. The spot lights 9a to 9m (measurement points) are effective exposure fields I
The five spot lights 9a to 9e arranged at equal intervals on the diagonal line of the AR are arranged at symmetrical positions.
Of these spot lights 9a to 9m, the spot light 9k at the end in the Y direction is the slit light 1a which is the irradiation position of the alignment illumination light from the X-axis alignment sensor 11X.
It is irradiated so that it almost overlaps. Further, the spot light 9h at the end portion in the + X direction is the spot light 1b which is the irradiation position of the alignment illumination light from the Y-axis alignment sensor.
It is irradiated so that it almost overlaps.

In this case, the images of the 13 spot lights 9a to 9m are re-imaged in the light-receiving optical system 3 of FIG. 1, and 13 corresponding to the lateral shift amounts of these re-imaged images, respectively.
Individual focus signals are generated. These focus signals are supplied to the AF processing system 10, and the AF processing system 10 obtains the focus positions at the irradiation positions (measurement points) of the spot lights 9a to 9m, and supplies these focus positions to the central control system 13. To be done.

As shown in FIG. 2B, assuming that the shot area 8 on the wafer 7 is the shot area to be measured, the X-axis alignment sensor 11X is used for alignment in the X direction, and the wafer of FIG. The wafer stage 15 on which 7 is mounted is scanned in the X direction so that the slit light 1a is crossed by the wafer mark 4a. At that time, the focus position of the wafer mark 4a is detected by the AF processing system 10. In addition, when performing the alignment in the Y direction, the slit light 1b is used for the wafer mark 4 by using the Y-axis alignment sensor.
The AF processing system 10 detects the focal position of the wafer mark 4b when "b" crosses.

Next, the alignment method of this example will be described. In this example, the X-axis alignment sensor 1 is based on the enhanced global alignment (EGA) method disclosed in Japanese Patent Laid-Open No. 61-44429.
The wafer is aligned using the 1X and Y axis alignment sensors. That is, the positions of the wafer marks of a predetermined number of shot areas (sample shots) selected from all the shot areas on the wafer 7 are measured, and the measurement results of these sample shots are statistically processed to determine the positions on the wafer 7. The array coordinates of all shot areas are calculated. FIG. 3 shows an example of a shot array on the wafer 7. As shown by hatching in FIG.
N (N = 9 in FIG. 3) sample shots 17A to 17I selected from all shot areas on the wafer 7.
The coordinates of the wafer mark attached to the are measured.

At the time of alignment, the central control system 13 in FIG. 1 is supplied with the measured values of the coordinates of the wafer marks of the sample shots 17A to 17I from the alignment processing system 12, but at the same time via the AF processing system 10. , Wafer mark is slit light 1a from alignment sensor
(Or 1b), the focus position detection system 2,
The spot lights 9a to 9m of FIG.
The focus position at the irradiation position (measurement point) of is also supplied,
These measured values for each sample shot are the central control system 1
3 is stored. Here, for example, when measuring the sample shot 17A of FIG. 3, the spot lights 9a to 9m of FIG.
The focal positions measured at the irradiation positions of
And That is, the slit light 1 from the alignment sensor
The focal positions measured by the spot lights 9k and 9h that are irradiated so as to substantially overlap the irradiation positions where a and 1b are irradiated are represented by fk and fh, respectively.

After that, when performing statistical processing by the EGA method, the spot light 9k,
Focus positions fk and fh of the irradiation position of 9h, and (N-2) spot lights 9a to 9g, 9i, 9j, and
The average value F (= (f
The difference with a + fb + ... + fm) / (N-2)) is calculated by the central control system 13. Here, spot light 9
If the differences with respect to the focus positions fk and fh at k and 9h are ΔFk and ΔFh, respectively, the central control system 13
Determines whether the differences ΔFk and ΔFh are within the allowable range ε. If at least one of the differences ΔFk and ΔFh exceeds the allowable range ε, the measurement data of the sample shot 17A is subject to statistical processing. Exclude from. The same calculation is performed for the remaining sample shots 17B to 17I, and the EGA method statistical processing is performed only on the measurement data of the remaining sample shots other than the excluded sample shots.

According to the alignment method of the present embodiment, the focus position of the wafer mark deviates from the best focus position of the alignment sensor due to the influence of foreign matter such as resist residue attached to the back surface of the wafer, and a jump occurs in the measurement data. Since the measurement data of such sample shots can be excluded from the processing target, it is possible to improve the overall alignment accuracy without lowering the throughput.

In the above example, the difference between the focus position of the wafer mark (spot light 9k, 9h) and the average value of the focus positions of the other spot lights is calculated. However, for example, during alignment and exposure, an average surface of the wafer surface in the effective exposure field is obtained based on the focal positions of the 13 spot lights 9a to 9m, and this average surface is adjusted to the image plane. In such a case, the difference between the focus position of the wafer mark (spot light 9k, 9h) and the average focus position of the surface determined from the focus positions of the 13 spot lights 9a to 9m is obtained, and from this difference Whether or not the measurement data can be used may be determined.

Further, in the above-mentioned example, in FIG. 3, after actually measuring the positions of all the sample shots 17A to 17I, the measurement data of the sample shots in which the focal position of the wafer mark is abnormal are excluded. However, instead, immediately before the measurement by the alignment sensor, the focus position detection systems 2 and 3 detect the deviation amount between the focal position of the wafer mark and the focal positions at the other measurement points, and the sample shot having the large deviation amount is detected. May not be measured by the alignment sensor. This can reduce the measurement time.

In the example of the above embodiment, TTL is used.
Although the alignment sensor of the LSA method and the alignment sensor of the LIA method is used, the present invention can be similarly applied to the case of using the alignment sensor of the LIA method and the TTL method. As described above, the present invention is not limited to the above-described embodiment, and can take various configurations without departing from the gist of the present invention.

[0031]

According to the alignment method of the present invention, the difference between the height of the alignment mark measured at at least one of the plurality of measurement points and the height at other measurement points is, for example, If it exceeds the predetermined allowable range, it is determined that the position detection of the alignment mark is inappropriate. Therefore, it is possible to accurately detect a large deviation between the height (focus position) of the alignment mark (wafer mark) and the height of the other area, and the measurement value of the alignment sensor may be abnormal. Since the value is removed in advance, the alignment accuracy is improved.

Further, according to the exposure apparatus of the present invention, the above-described alignment method of the present invention can be implemented.

[Brief description of drawings]

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

2A is an enlarged plan view showing a relationship between an irradiation position of alignment illumination light and spot light from a focus position detection system in the projection exposure apparatus of FIG. 1, and FIG. 2B is a shot area 8 on a wafer. FIG. 4 is an enlarged plan view showing the relationship between the wafer mark attached to the and the irradiation position of alignment illumination light.

FIG. 3 is a plan view showing an example of an array of sample shots on a wafer.

FIG. 4 is a perspective view showing a schematic configuration of an example of a conventional projection exposure apparatus.

FIG. 5 is an enlarged plan view showing a relationship between an irradiation position of alignment illumination light and spot light from a focus position detection system in a conventional projection exposure apparatus.

[Explanation of symbols]

 1a, 1b Slit light by alignment illumination light 2 Light-transmitting optical system (focus position detection system) 3 Light-receiving optical system (focus position detection system) 4a, 4b Wafer mark 5 Reticle 6 Projection optical system 7 Wafer 8 Shot area LF AF beam 9a ~ 9m Spot light 10 AF processing system 11X X-axis alignment sensor 12 Alignment processing system 13 Central control system

Claims (2)

[Claims] 1. A positioning mark provided on a shot area on a substrate to which a mask pattern is transferred is irradiated with alignment illumination light to detect the position of the positioning mark. In an alignment method for aligning the mask pattern and the shot area on the substrate based on, by irradiating a plurality of measurement points on the substrate with predetermined measurement light,
The heights of the substrate at the plurality of measurement points are respectively detected, and at least one of the plurality of measurement points is set on the alignment mark, and the height detection result at the measurement point and other measurement are performed. The height detection result at the point is compared, and based on the comparison result, it is determined whether or not the height of the substrate at the position where the alignment mark is formed is appropriate for the position detection of the alignment mark. A positioning method characterized by the above. 2. An alignment sensor that detects the position of the alignment mark by irradiating alignment marks attached to each shot area on the substrate with alignment illumination light. In an exposure device that positions a mask pattern and each shot area on the substrate based on a detection result and exposes the mask pattern on each shot area, a plurality of spot-shaped measurement lights on the substrate Irradiate multiple measurement points on the transfer area of the mask pattern diagonally,
A multi-point focus position detection system for detecting the height of the substrate at the plurality of measurement points is provided, and at least one of the plurality of measurement points by the focus position detection system is illuminated by the illumination light from the alignment sensor. Judgment means which is set at an irradiation position or in the vicinity thereof, and judges whether or not the detection data by the alignment sensor can be used based on the difference between the detection result at the measurement point and the detection result at another measurement point. An exposure apparatus comprising: