JPH11251218A - Position detecting method and apparatus, and exposure apparatus provided with the apparatus - Google Patents

Abstract

(57) [Problem] To detect a position of a wafer mark with high accuracy and perform alignment even when a wafer mark has a low step. SOLUTION: Wafer marks MKX1 and MK on a wafer are provided.
By illuminating Y1 and the index marks IMX1, IMX2, IMY1 and IMY2 on the index plate in the wafer alignment sensor, an image signal of a projection image formed on the image plane of the image sensor is generated. Offset WI of wafer mark part of imaging signal
The amount of illumination light for illuminating the index mark is adjusted so that the offset KI of the index mark becomes equal to the offset KI of the index mark. Marks 19a to 19 having different line widths forming index marks
From the peaks SXa to SXc of the imaging signal corresponding to the image c, the center position X2 of the index mark is obtained from the peak whose amplitude is within a predetermined range. A positional shift amount of the center position X1 of the wafer mark MKX1 with respect to the center position X2 of the index mark 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 method and apparatus for detecting the position of a test mark on a substrate such as a wafer, and more particularly to a method for manufacturing a semiconductor element, a liquid crystal display element, a thin film magnetic head, or the like. For use in an alignment sensor for photoelectrically detecting an alignment mark on a substrate such as a wafer.

[0002]

2. Description of the Related Art For example, in a projection exposure apparatus such as a stepper used for manufacturing a semiconductor device or the like, an image of a circuit pattern formed on a reticle as a mask is transferred to a wafer (or glass) as a photosensitive substrate. Plate etc.)
In order to transfer with high overlay accuracy on the pattern formed in the previous steps in each shot area above,
An alignment mechanism is provided for positioning the reticle and each shot area of the wafer with high accuracy.

The main parts of this alignment mechanism are a reticle alignment microscope for detecting the position of an alignment mark (reticle mark) on a reticle, and an alignment sensor for detecting the position of an alignment mark (wafer mark) on a wafer. Further, as an alignment sensor for a wafer mark, a dedicated optical system for detecting a wafer mark is used as disclosed in JP-A-2-54103, and the position of the wafer mark is set at a position different from the exposure position. An image processing type alignment sensor that uses broadband illumination light in an off-axis type to be detected is often used. This alignment sensor is provided with an index mark, and measures the distance between the detection center position of the alignment sensor (the center position of the index mark) and the exposure center position (the center position of the reticle pattern image) before alignment. Baseline measurement was performed in advance. And
The amount of misalignment between the center position of the index mark and the center position of the wafer mark is measured, a baseline amount is added to the amount of misalignment, correction is performed, and the wafer is positioned and exposed based on the correction result. Was.

A conventional wafer mark has a step of 500.
In most cases, the alignment sensor has an imaging optical system having a numerical aperture (NA) of about 0.2 to 0.3, and sufficient accuracy has been obtained. In addition, since the measurement stability of the alignment sensor greatly affects the alignment accuracy, the index mark is provided in the optical system of the alignment sensor at a position where the number of relays of the image to the imaging surface is small.

In the case where the index mark is irradiated with return light from the wafer, if the surface of the wafer is rough, the detection light from the index mark includes noise due to flare or the like due to the roughness of the wafer surface. However, the detection accuracy of the index mark is deteriorated. Further, the wafer surface conjugate with the index mark needs to be a pattern forbidden zone in which a pattern must not be formed, and there is a problem that the effective use area of the wafer is reduced. To solve such a problem, Japanese Patent Application Laid-Open
As disclosed in JP-A-326375 or JP-A-6-77116, a method has been proposed in which an illumination system for illuminating an index mark is provided separately from an illumination system for illuminating a wafer mark on a wafer. .

Conventionally, a projection optical system is used as a part of an optical system for detecting the position of a wafer mark attached to each shot area on a wafer with a light beam other than the exposure wavelength and detecting the wafer mark. The TTL (through-the-lens) method was also used in combination.

[0007]

As described above, in the conventional alignment sensor, in addition to the off-axis method, TT
The L method is also used in combination, and most of the wafer marks have a step of about 500 nm or more, and the wafer mark is formed by an imaging optical system having a numerical aperture (NA) of about 0.2 to 0.3. Accuracy sufficient to detect the mark was obtained.

However, in recent years, 0.25 to 0.1
A resolution of about μm is required, and in order to respond to the demand, exposure is performed using KrF or Ar from an i-line of a mercury lamp or the like.
The wavelength of excimer laser light such as F is becoming shorter, and a projection optical system having a numerical aperture of, for example, 0.7 or more is required. At present, only fluorite or quartz is considered to be suitable as a lens glass material that can be used to manufacture such a projection optical system. In this case, since aberration remains for an alignment laser beam different from the exposure light or a light beam having a broadband wavelength (about 530 to 800 nm), it is difficult to use a TTL type position detection device (alignment sensor). .

[0009] Also, in the objective optical system of the alignment sensor, it is required to increase the numerical aperture to, for example, about 0.4 to 0.6 in order to increase the alignment accuracy. In addition, CMP (Chemical Mechanical Polishing:
There is a possibility that the level of the wafer mark may be reduced to about 30 to 500 nm by a flattening process such as a chemical mechanical polishing technique. However, when the level of the wafer mark is reduced, the contrast of the image of the wafer mark when detecting the wafer mark is reduced, and the center position of the wafer mark may not be accurately detected.

That is, as shown in FIG. 7A, an image pickup signal obtained by picking up an image of a wafer mark and an index mark having a reduced level is obtained by the same image pickup device. The amplitude is smaller than the amplitude of the portion corresponding to the index mark on both sides. In FIG. 7A, the horizontal axis is the position X in the measurement direction (X direction), and the vertical axis is the position X.
Represents the level of the imaging signal SXA. At this time,
When the image signal SXA is amplified in an analog manner around a predetermined level in order to increase the amplitude of the wafer mark portion, as shown by the image signal SXB in FIG. Since the waveform is distorted due to saturation, the center position of the index mark cannot be detected with high accuracy, and the alignment accuracy is reduced.

In order to avoid the saturation of the image pickup signal at the index mark portion, a method of detecting the index mark and the wafer mark by separate image pickup devices is conceivable. However, the projection image of the wafer mark and the projection of the index mark are considered. When the contrast and the offset from the image are largely different, there is a disadvantage that an error easily occurs when adjusting the gain or the offset for each imaging signal of each imaging element.

In view of the foregoing, it is a first object of the present invention to provide a position detecting method capable of detecting a position of a wafer mark having a low step with high accuracy. It is a second object of the present invention to provide a position detecting method capable of detecting the positions of wafer marks at various steps with high accuracy. Another object of the present invention is to provide a position detection device and an exposure device that can perform such a position detection method.

[0013]

According to a first position detecting method of the present invention, a mark (MKX1, MKX, MKX1, MKX) on a substrate (4) is detected.
2) image and predetermined index marks (IMX1, IMX2),
Alternatively, by comparing the image of the index mark (IMX1, IMX2) with the image of the test mark (MKX1, MK2).
In the position detection method for detecting the position of X2), the index marks (IMX1 and IMX2) have a plurality of marks (19a to 19c) different from each other, and according to the images of the test marks (MKX1 and MKX2). , A mark serving as a reference for comparison is selected from the plurality of marks (19a to 19c). Preferably, the plurality of different marks (19a to 19c) are, for example, a plurality of marks having different line widths.

According to the first position detecting method of the present invention, when the detected mark to be detected is at a high step and the detection level (amplitude) of the image is large, the index mark (IMX1, IMX1) is used.
MX2), the image of the thick mark is selected from among the images of the marks (19a to 19c) constituting the image as a reference for comparison,
When the test mark is a low step and the detection level of the image is low, by selecting a thin mark image, the positions of the test marks at various steps can be detected with high accuracy.

Next, a second position detecting method according to the present invention uses an image of a test mark (MKX2, MKY2) and an image of a predetermined index mark (IMX1, IMX2, IMY) on a substrate (4).
1, IMY2), and in the position detecting method for detecting the position of the test mark (MKX2, MKY2), the index mark (IMX1, IMX2,
IMY1, IMY2) are images of this index mark (IMX
1, IMX2, IMY1, IMY2) on a predetermined detection surface (31X, 31Y). The mark (19c) has a line width smaller than the resolution limit of the objective optical system.

According to the second position detecting method of the present invention, the image of the index mark (IMX1, IMX2, IMY1,
An index mark having a smaller line width than the resolution limit of the objective optical system that forms (IMY2) on the predetermined detection surface (31X, 31Y) has a low image contrast. Therefore, even if the test mark (MKX2, MKY2) is a test mark with a low contrast and a low step, the image of the index mark with a small line width is selected as a reference for comparison, thereby achieving high accuracy. The position of the test mark (MKX2, MKY2) can be detected.

If the numerical aperture of the objective optical system is NA and the average wavelength of the illumination light is λ, the Rayleigh resolution limit △ is as follows, and the line width of the index mark may be smaller than △. Δ = λ / (2 · NA) (1) Therefore, suppose that the numerical aperture NA is 0.6 and the average wavelength λ is 650.
nm, the resolution limit △ is approximately 540 nm (a value converted into a projected image on the substrate), and the numerical aperture N is the same at the same average wavelength.
If A is 0.4, the resolution limit △ is approximately 812 nm (a value converted into a projected image on the substrate).

Further, the test mark and the index mark are illuminated by different illumination systems (25, 27), and different from each other in accordance with the detection levels of the image of the test mark and the image of the index mark. Lighting system (25, 2
It is desirable to adjust the relative illuminance of 7). In this case, for example, the average detection level of the image of the test mark and the image of the index mark can be equalized, and the position detection accuracy of the test mark can be improved.

The image of the test mark and the image of the index mark are projected onto the image pickup surface of the same image pickup device (31X, 31Y), and the detection signal of the image pickup device corresponds to the image of the test mark. Gain control so that the signal portion to be controlled has a predetermined range of amplitude, that is, auto gain control (AGC).
It is desirable that the gain-controlled detection signal be processed to detect the amount of displacement of the image of the test mark with respect to the image of the index mark. In this case, by controlling the gain of the detection signal, it is possible to detect the position of the detection mark with high accuracy even if the detection mark is a low-level test mark having a low image contrast.

When the image of the test mark and the image of the index mark are detected by different image sensors, the gain of the detection signal of the image sensor is controlled under the same conditions, thereby obtaining the image of the test mark. The same effect as in the case where the image of the index mark and the image of the index mark are detected by the same image sensor is obtained. Further, when the image of the test mark and the image of the index mark are projected on the imaging surface of the same imaging device, there is no influence of the change in the sensitivity characteristic of the imaging device that occurs when the gain of the detection signal is controlled. Further, the marks constituting the index mark may be formed from a plurality of linear patterns having the same line width. In this case, by averaging the positions of the plurality of linear patterns, the position of the index mark can be detected with higher accuracy, and the alignment can be performed with higher accuracy.

On the other hand, when the image of the test mark and the image of the index mark are detected by different image sensors, the size of the index mark is not affected by the size of the measurement visual field for detecting the test mark. There is the advantage that the sheath arrangement can be determined. Next, the position detecting device of the present invention is an image pickup device (31X, 31Y) that picks up an image of a test mark (MKX2, MKY2) on a substrate and an image of a predetermined index mark (IMX1, IMX2, IMY1, IMY2). ) For detecting the position of the test mark (MKX2, MKY2) based on the index mark (IMX1, IMX2, IMY1, IMY2) by processing the detection signal of the image sensor (31X, 31Y). In the device, the index mark (I
MX1, IMX2, IMY1, IMY2) have a plurality of marks (19a to 19c) having different line widths, and the image (MKX2, MKY2) of the test mark in the detection signal of the image sensor (31X, 31Y). ) According to the level of the portion corresponding to the plurality of marks (1) in the detection signal.
A signal processing system (13) for selecting a reference portion for comparison from portions corresponding to 9a to 19c) is provided.

According to the position detecting device of the present invention, the first position detecting method of the present invention can be carried out, and the index marks (IMX1, IMX) can be obtained by the signal processing system (13).
2, IMY1, IMY2), by selecting an optimum part as a reference for comparison from a plurality of marks (19a to 19c) forming an image, the position of the test mark (MKX2, MKY2) with high accuracy. Detection can be performed. Further, when detecting a test mark (MKX2, MKY2) having a low step and a low image contrast, the image sensor (3
1X, 31Y), the gain control is performed such that the level of the test mark portion in the detection signal falls within a predetermined range.
By selecting an image of the index mark whose level of the detection signal is within the same range as the reference as a reference for comparison, the position of the test mark with respect to the index mark can be detected with high accuracy.

Next, an exposure apparatus according to the present invention comprises a position detecting device (5) according to the present invention and a positioning mark (MKX).
A substrate stage (3) for positioning a substrate (4) on which (2, MKY2) is formed, and an exposure unit (1, 8, 10) for exposing a pattern of a mask (9) on the substrate (4). An exposure apparatus having an alignment mark (MK) on the substrate (4) by the position detection device (5).
X2, MKY2) is detected, and the position of the substrate (4) and the position of the mask (9) are adjusted based on the detection result.

According to the exposure apparatus of the present invention, the position detecting mark (MKX2, MKY2) on the substrate is detected using the position detecting apparatus (5) of the present invention. Even when the mark is lowered, the alignment between the substrate (4) and the mask (9) can be performed with high accuracy. Further, the position detection device of the present invention, a substrate stage for positioning the substrate on which the alignment mark is formed, and an exposure unit for exposing a pattern of a mask on the substrate so as to achieve the above functions. By electrically, mechanically, or optically connecting, the exposure apparatus of the present invention is assembled.

[0025]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. In the present embodiment, the present invention is applied to an off-axis type alignment sensor provided in a step-and-repeat type projection exposure apparatus. FIG. 1 shows a schematic configuration of a projection exposure apparatus used in the present embodiment. In FIG. 1, an exposure light source, an optical integrator for uniformizing the illuminance distribution, a reticle blind, a condenser lens system and the like are used at the time of exposure. The pattern area on the pattern surface of the reticle 9 as a mask is illuminated with the exposure light IL from the illumination optical system 10. As the exposure light IL, a bright line such as an i-line (wavelength 365 nm) of a mercury lamp or KrF (wavelength 248)
nm), excimer lasers such as ArF (wavelength 193 nm), or F ₂ (wavelength 157 nm) laser or the like can be used.

Under the exposure light IL, the pattern image of the reticle 9 passes through the telecentric projection optical system 1 on both sides (or one side on the wafer side) at a predetermined magnification β (β is 1/4,
1/5) and projected onto each shot area on the wafer 4. A photoresist is applied to the surface of the wafer 4, and the surface is held so as to match the image plane of the projection optical system 1. Hereinafter, the Z axis is taken parallel to the optical axis AX of the projection optical system 1, the X axis is taken parallel to the plane of FIG. 1 in a plane perpendicular to the Z axis, and the Y axis is taken perpendicular to the plane of FIG. explain.

The reticle 9 is held on the reticle stage 8, and the reticle stage 8 positions the reticle 9 on the reticle base 8B in the X, Y, and rotation directions.
The two-dimensional position of the reticle stage 8 is
The stage driving unit 12 controls the operation of the reticle stage 8 based on the measurement result and the control information of the main control system 11.

On the other hand, the wafer 4 is a wafer holder (not shown).
The wafer holder is held by suction on the wafer stage, and the wafer holder is fixed on the sample stage 3, and the sample stage 3 is fixed on the wafer stage 2.
The wafer stage 2 controls the position (focus position) and the tilt angle of the sample table 3 in the Z direction, and controls the X
Stepping in the direction and the Y direction and high-precision positioning are performed. Therefore, the side surface of the sample stage 3 is a mirror surface as a movable mirror, and the laser interferometer 6 is arranged so as to face the mirror surface, and the position of the sample stage 3 is measured by the laser interferometer 6. . The stage drive unit 12 drives the wafer stage 2 based on the measurement result and the control information of the main control system 11.

At the time of exposure, when the exposure of the pattern image of the reticle 9 onto one shot area on the wafer 4 is completed, the next shot area on the wafer 4 is moved to the exposure area of the projection optical system 1 via the wafer stage 2. Then, the operation of exposing the pattern image of the reticle 9 is repeated in a step-and-repeat manner, and each shot area on the wafer 4 is exposed. In order to align the image plane of the projection optical system 1 with the surface of the wafer 4, a position (focus position) in the Z direction of the surface of the wafer 4 located in the exposure area is measured below the projection optical system 1. The oblique incidence autofocus device (not shown) is installed.

When performing the overlay exposure, it is necessary to perform high-precision alignment between the reticle 9 and each shot area of the wafer 4 in advance. Therefore, a reticle mark (not shown) for alignment is formed near the pattern area on the pattern surface of the reticle 9, and a reticle microscope (not shown) for reticle alignment is arranged above the reticle mark. Further, the projection optical system 1
An alignment sensor 5 of an off-axis system and an image processing system for detecting the position of an alignment wafer mark attached to each shot area on the wafer 4 is arranged on the side surface of the sensor 4. The signal is supplied to the image processing device 13.

A reference mark (not shown) is provided on the wafer stage 2, and the center (exposure center) of the image projected by the projection optical system 1 on the reticle 9 and the alignment sensor 5
The center of the index mark on the index plate 19 (see FIG. 2)
The fiducial mark is used to measure a distance (base line) from a conjugate point (detection center) on the wafer 4. Then, the image sensor 13 measures the amount of misalignment between the center position of the index mark and the center position of the wafer mark via the alignment sensor 5, and the image processing device 13 uses the main control system 11
To supply. The main control system 11 performs a correction by adding a base line amount to the coordinates of the wafer mark obtained by adding the positional deviation amount to the coordinates of the wafer stage 2, positions the wafer based on the correction result, and performs exposure. Do.

Next, the alignment sensor 5 of the projection exposure apparatus of this embodiment will be described. FIG. 2 shows the alignment sensor 5 of the present embodiment. In FIG. 2, a light source 27 for illuminating a wafer mark MK1 to be detected on the wafer 4 is shown.
Has a configuration in which illumination light from a halogen lamp is collected by an elliptical mirror, and then filtered so that the illumination light has a wavelength band of about 500 to 800 nm. The illumination light from the light source 27 uniformly illuminates the light-shielding slit 20 via the lenses 24 and 22 after the illuminance distribution is uniformed by the randomly bundled optical fiber bundle 26. The illumination light transmitted through the light shielding slit 20 is
Is deflected by the half mirror 16 and travels downward, passes through the dichroic mirror 15 and passes through the first objective lens 14 to the wafer mark M on the surface of the wafer 4.
Illuminate K1.

The wafer mark MK1 has a step of 500.
It is a high step mark of about nm, but in this example, the step is 50
Wafer mark M having a low level difference of about 0 nm to 30 nm
K2 can also perform position detection with high accuracy. Wafer 4
Is transmitted again through the first objective lens 14, the dichroic mirror 15, and the half mirror 16, and is reflected by the second objective lens 33 at a position conjugate with the surface of the wafer 4 to provide a CCD type two-dimensional image sensor. An image of the wafer mark MK1 is formed on the imaging surface of 31Y. Similarly, the light deflected by the half mirror 30 between the second objective lens 33 and the image sensor 31Y is the image pickup surface of the CCD type two-dimensional image sensor 31X disposed at a position conjugate with the surface of the wafer 4. Also, an image of the wafer mark MK1 is formed. The numerical aperture of the imaging optical system including the first objective lens 14 and the second objective lens 33 of this example is variable by an aperture stop (not shown) within a range of about 0.3 to 0.6 as an example. I have.

On the other hand, the illumination light from the light emitting diode (LED) 25 for illuminating the index mark, which can be regarded as quasi-monochromatic light having a wavelength of about 850 nm, illuminates the index plate 19 provided with the index mark via the lenses 23 and 21. I do. The light amount of the light emitting diode 25 is adjustable by a light amount control device 28 under the control of the image processing device 13.
The illumination light transmitted through the index plate 19 is deflected upward by the dichroic mirror 15 through the lens 17 and transmitted through the half mirror 16, and then, by the second objective lens 33, the imaging devices 31 </ b> X and 31 </ b> Y at positions conjugate with the wafer surface. Project the image of the index mark on the image pickup surface of. Also, the image sensor 31
In X and 31Y, the directions corresponding to the X direction and the Y direction on the wafer 4 are defined as the pixel scanning direction (readout direction). Supplied. Note that the index marks may be formed directly on the imaging surfaces of the imaging elements 31X and 31Y. By electrically, mechanically, or optically connecting these elements so as to achieve the above-described functions, the projection exposure apparatus of this embodiment is assembled.

Next, a method of detecting the amount of misalignment of the wafer mark with respect to the index mark when performing alignment will be described. For simplicity, only the alignment in the X direction will be described, and the description of the alignment in the Y direction will be omitted. When the detection target is the wafer mark MK1 having a high step, the imaging optical system (14, 33) shown in FIG.
Is set, for example, to about 0.3.

FIG. 3 (a1) shows the wafer 4 when the light source 27 for illuminating the wafer mark MK1 is used in FIG.
3A shows the wafer mark MK1 in the observation field of view by the imaging element 31X. In FIG. 3A, the light-shielding slit 20 in FIG.
0V to limit the field of view, and the wafer mark MK1 includes an X-axis wafer mark MKX1 on which an uneven line and space pattern is arranged in the X direction;
A Y-axis wafer mark M having an uneven line and space pattern arranged in the Y direction so as to sandwich it in the Y direction
KY1. Wafer mark MKX1
Is used for position detection in the X direction.
X1 is a lattice-shaped multi-pattern in which five concave linear patterns extending in the Y direction are arranged at a substantially constant pitch in the X direction.

Similarly, two wafer marks MKY1
Is a lattice-shaped multi-pattern in which three concave linear patterns (bar marks) each extending in the X direction are arranged at a substantially constant pitch in the Y direction. On the imaging surface of the imaging element 31X in FIG. 2, pixels are arranged in directions corresponding to the X direction and the Y direction, and the scanning direction is the X direction.

In the image sensor 31X, the photoelectric signal at each pixel of the image in the sampling area VSA in FIG. 3A is read out in the direction corresponding to the X direction (hereinafter also referred to as the "X direction"). The imaging signal SX obtained thereby has one bottom (minimum value) for each bar mark because the wafer mark MKX1 is a bar mark with a high step. Further, since only one scanning line is disadvantageous in terms of the S / N ratio, the image processing apparatus 13 uses the sampling area V
After correcting the offsets and gains of the imaging signals obtained by scanning in a plurality of X directions within the SA as described below, the obtained imaging signals are averaged to obtain an image signal. By this averaging process, the influence of noise components due to the roughness of the surface of the wafer 4 and the like is reduced. Then, the averaged image signal is interpolated between pixels to be binarized at an appropriate slice level SL, and the center of the binarized image signal in the scanning direction (X direction) is set in the X direction of the wafer mark MKX1. Consider position. Here, as an example, the slice level SL is obtained for each signal portion corresponding to each bar mark.

FIG. 3 (b1) shows an image pickup signal SX obtained from a certain column of pixels in the sampling area VSA of FIG. 3 (a1). In FIG. 3 (b1), the horizontal axis represents the corresponding wafer. Represents the position in the X direction above. In this example, the wafer mark MKX1 is composed of five bar marks with high steps, and a total of five bottom waveforms are obtained in the area A.
The number of bar marks constituting a wafer mark is 5
The number is not limited to the number, and the number may be increased in order to improve the detection accuracy. Conversely, when the roughness of the wafer surface is small, the number may be four or less.

FIG. 3A2 shows the index plate 19 in FIG.
3A shows an index mark detected in the observation field of view of the image sensor 31X when the light emitting diode 25 for illuminating is used. In FIG. 3 (a2), the index plate 19 is shielded from light at the center by chrome. X-axis index mark IMX is provided on the substrate where the chrome surface and the glass surface of slit 20 are reversed.
1, IMX2, and Y-axis index marks IMY1, IMY
2 is attached. Also, the X-axis index mark IMX1 is formed by arranging in the X direction marks 19a to 19c formed of a plurality of rectangular light-shielding films extending in the Y direction and having different line widths, and is paired with the index mark IMX2. I have. Also, index marks IMY1 and IMY2 on the Y axis
Are marks obtained by rotating the X-axis index marks IMX1 and IMX2 by 90 °. The line width of each mark 19a to 19c is
The outer mark 19a is the thickest, and the inner mark 19c is the thinnest.

The index marks IMX1, IMX2, I
MY1 and IMY2 are not limited to those formed of a light-shielding film such as a chrome film, but may be any as long as they shield or reflect illumination light. FIG. 3B2 shows an image signal SX obtained by capturing an image in the sampling area VSA of FIG. 3A2 with the image sensor 31X and reading out from a certain column of pixels. , The horizontal axis represents the position in the X direction converted on the wafer, and marks 19a to 19c having different line widths.
Peaks SXa to SXc respectively corresponding to 19c appear. Here, since the marks 19a to 19c have different line widths, the contrasts of the corresponding images are also different, and the sizes of the peaks SXa to SXc become smaller as the line width becomes narrower.

FIG. 3 (a3) shows the wafer mark MK at the same time.
FIG. 3 (a3) shows the observation field of view of the image sensor 31X when the light source 1 and the index plate 19 are illuminated. In FIG. 3 (a3), the patterns observed in FIG. 3 (a1) and FIG. It will be synthesized. FIG. 3 (b3) shows an image signal SX on a certain column of pixels obtained by imaging the image in the sampling area VSA of FIG. 3 (a3) with the image sensor 31X. The imaging signal SX is shown in FIG.
The image signal of (b1) and the image signal of FIG. 3 (b2) are synthesized. In this manner, the simple synthesis only results in the offset WI of the image signal of the wafer mark MKX1.
And the offsets KI of the image signals of the index marks IMX1 and IMX2 are usually different. Therefore, the image processing device 13 applies the illuminance of the bright portion (offset KI) of the detection region of the index marks IMX1 and IMX2 to the illuminance of the bright portion (offset WI) of the detection region of the wafer mark MKX1 via the light amount control device 28. The light amount of the light emitting diode 25 is adjusted to match. Note that the wafer mark MKX
Since the illuminance of the bright portion of the first detection area differs depending on the reflectance of the wafer 4, the light amount adjustment of the light emitting diode 25 is performed for each wafer. FIG. 3B4 shows the image pickup signal SX1 after adjusting the illuminance of the illumination light of the light emitting diode 25, and FIG.
4) shows the observation visual field corresponding thereto.

In FIG. 3 (b4), the image pickup signal SX
In FIG. 1, since the amplitude of the portion A corresponding to the wafer mark MKX1 is large enough to detect the position with high accuracy, the image signal SX1 is subjected to analog / digital (A / D) conversion.
The digital image signal SX is obtained by averaging in the non-measurement direction (Y direction) of the image of the sampling area VSA in FIG.
Get 1 '. Thereafter, the slice level SL is set at the center of the amplitude of the portion A of the image signal SX1 ', and the coordinates at which the portion A crosses the slice level SL are averaged, whereby the center position X1 of the wafer mark is obtained.

Next, in the image signal SX1 'corresponding to the index marks IMX1 and IMX2, a new slice level SL is set at the center of the amplitude at the peak SXb closest to the portion A, and the two peaks SXb By averaging the coordinates that cross the slice level SL, the center position X2 of the index mark is obtained, the amount of displacement of the position X1 with respect to the position X2 is obtained, and supplied to the main control system 11.

Next, a case where alignment is performed by detecting a wafer mark having a low level difference of about 500 nm or less will be described with reference to FIG. Hereinafter, it is assumed that the step of the wafer mark is 30 to 50 nm as an example. In FIG. 4, portions corresponding to FIG. 3 are denoted by the same reference numerals, and detailed description thereof will be omitted. FIG. 4 (a1) shows a pattern in the observation field of view of the image sensor 31X when detecting the low level wafer mark MK2 of another layer on the wafer 4 in FIG. 2, and the wafer mark MK2 has five concave portions. An X-axis wafer mark MK2 in which bar marks extending in the Y direction are arranged at a constant pitch in the X direction, and a bar mark extending in the X direction consisting of three concave portions each sandwiching the mark are fixed in the Y direction. And two Y-axis wafer marks MKY2 arranged at a pitch. The step of the concave portion of the wafer mark MK2 is 30 to 50 nm, and the numerical aperture of the imaging optical system (14, 33) in FIG. 2 is set to about 0.4 to 0.6 as an example. .

FIG. 4 (b1) shows an image pickup signal SX of an image in the sampling area VSA of FIG. 4 (a1). In FIG. 4 (b1), since the wafer mark MK2 has a low step, it corresponds thereto. FIG. 3B shows the contrast of the portion B.
It is lower than section A of 1). Also, the image sensor 3
An imaging signal SX obtained from one row of pixels in the 1X X direction
Becomes the bottom (minimum value) at the edge positions on both sides of each concave portion of the wafer mark MKX2, so that ten bottoms are detected. Further, as in the case of FIG.
5 with the light quantity control, the wafer mark MKX2 and the index mark IM
FIG. 4 obtained when X1 and IMX2 are simultaneously detected.
By adjusting the offset of the imaging signal SX in (b3), FIG.
The imaging signal SX1 as shown in (b4) is generated.

As described above, when the wafer mark MKX2 has a low step, the contrast of the portion B corresponding to the wafer mark MKX2 in the imaging signal SX of FIG. 4B is low, and the center position can be detected. It becomes difficult. If the influence of the noise component due to the roughness of the surface of the wafer 4 is large, the center position of the wafer mark MKX2 cannot be detected. Therefore, the wafer mark MKX2
In order to detect the center position of the image signal SX1, an analog auto gain control (AGC) circuit in the image processing apparatus 13 of FIG.

FIG. 5 shows the image pickup signal before and after the gain adjustment. The gain of the image pickup signal SX1 shown in FIG. 5 (a) is increased within a range where the portion B does not saturate, and the image pickup signal shown in FIG. The signal SX2 is generated. Here, the imaging signal SX2 in FIG. 5B is obtained by enlarging the imaging signal SX1 in FIG. 5A in the vertical direction. By adjusting the gain and setting the slice level SL at the center of the amplitude of the portion B corresponding to the wafer mark MKX2, the center position X1 can be obtained with high accuracy.

Also in this example, the imaging signal SX2 is
/ D conversion to obtain the sampling area VSA in FIG.
The digital image signal SX2 is obtained by averaging in the Y direction. In this example, the index marks IMX1 and IMX1 of the image signal SX2 ′ are used.
Since the peaks SXa and SXb corresponding to the thick marks 19a and 19b of the IMX2 are saturated at the output of the AGC circuit, the signal of the saturated part is delayed, and the image signal SX2 'of the part is displaced. Would. Therefore, the index mark IMX is within the range where the amplitude is not saturated.
1 and IMX2, using a peak SXc corresponding to the finest mark 19c, setting a slice level SL at the center of the amplitude of the peak SXc on both sides, and setting two slices SL
The center of the coordinates where Xc crosses the slice level SL is determined as the center position X2 of the index marks IMX1 and IMX2,
Position X1 of wafer mark MKX2 with respect to this position X2
Alignment is performed by calculating the amount of positional deviation of.

As described above, in this example, even when the gain is adjusted by the AGC circuit when detecting a wafer mark having a low level difference, a plurality of images having different image contrasts are obtained by changing the line width as the index mark. Mark 19a
Since the center position of the index mark within the range where the amplitude of the imaging signal is not saturated is obtained,
Alignment can be performed with high accuracy even for a low step mark.

In order to match the centers of the images of the marks 19a to 19c constituting the index marks in the respective measuring directions, the offsets of the center positions are measured in advance, and when the alignment is performed. Needs to correct the offset according to the mark used. In the above-described embodiment, the position of each mark is obtained by the slice level method. However, template images are prepared for each image of the mark of each line width of the wafer mark and the index mark, and each mark is obtained by the pattern matching method. The position of the mark may be specified.

The thinnest mark 19c of the plurality of marks 19a to 19c having different line widths constituting the index marks IMX1 and IMX2 is connected to the imaging optical system (17, 3) of FIG.
A pattern having a line width smaller than the resolution limit of 3) may be used.
In this case, the contrast of the image of the pattern 19c easily becomes as small as the image of the low step mark. In this example, the index marks IMX1 and IMX2 are constituted by marks 19a to 19c having different line widths to change the contrast of the image of the index mark.
To 19c having the same thickness, making a notch finer than the resolution of the imaging optical system in the non-measurement direction (Y direction) (providing more notches as the inner mark 19c is provided), and a plurality of chrome transmittances different from each other. Each mark 19a ~ from the mark
By configuring the index mark 19c, the contrast between a plurality of marks constituting the index mark can be changed. Further, instead of the two-dimensional image sensor 31X, X
When a one-dimensional line sensor or the like in which pixels elongated in the direction are arranged is used, each mark 19a to 19c in the non-measurement direction is used.
May vary in length.

Next, another example of the embodiment of the present invention will be described. In this example, the configuration of the index marks is changed from the above-described embodiment. In FIG. 2, an index plate 32 is used instead of the index plate 19 in FIG. FIG. 6 (a)
FIG. 6 shows an observation field of view of the image sensor 31X of FIG. 2 on the index plate 32 when the index plate 32 used in the present example is illuminated. In FIG. A multi-pattern 32a in which linear patterns made of films are arranged at a constant pitch in a direction corresponding to the X direction, and multi-patterns 32b and 32c whose line widths gradually become smaller than the multi-pattern 32a are provided. The index mark IMX3 on one of the axes is formed by the multi patterns 32a to 32c.
It is composed of The other index mark IMX4 on the X axis is provided symmetrically with the index mark IMX3. Similarly, for alignment in the Y direction, multi-patterns 32d to 32d arranged in the direction corresponding to the Y direction
An index mark IMY3 composed of f and an index mark IMY4 symmetrical to the index mark IMY3 are provided as a pair.

FIG. 6B shows an image pickup signal SX obtained by picking up an image in the sampling area VSA of FIG. 6A. In FIG.
Three bottoms are formed corresponding to 32c so that the contrast gradually decreases. When the alignment is performed, similarly to the embodiment of FIGS. 4 and 5, an index mark portion within a range where the amplitude is not saturated is selected, and for example, each of the multi patterns (any one of 32a to 32c) is selected. By averaging the position where the signal crosses the predetermined slice level and performing position detection, alignment can be performed with high accuracy by the averaging effect. The number of linear patterns constituting the multi patterns 32a to 32c is three.
The number is not limited to two and may be two or four or more. However, when the number is increased, the detection accuracy is improved by the averaging effect, and alignment can be performed with higher accuracy.

In the above embodiment, the reference mark on the wafer stage used at the time of the baseline measurement may be composed of a plurality of marks having different line widths, like the index mark. In this case, the gain and offset of the imaging signal are adjusted to, for example, index marks IMX1, IMX
By selecting the optimum reference mark for each of the marks 19a to 19c of each line width of X2 and performing the baseline measurement, it is possible to perform the baseline measurement with high accuracy for each of the marks 19a to 19c of each line width. it can.

Note that the present invention provides a step
The present invention can be applied not only to an AND repeat type projection exposure apparatus, but also to an alignment sensor of a step-and-scan type projection exposure apparatus that has become mainstream in recent years. In the present embodiment, the present invention is applied to a projection exposure apparatus having a projection optical system of a refractive optical system. However, the present invention can be applied to an exposure apparatus using a catadioptric optical system or a reflection optical system using X-rays.

It should be noted that the present invention is not limited to the above-described embodiment, and it is needless to say that various configurations can be adopted without departing from the gist of the present invention.

[0058]

According to the first position detecting method of the present invention,
By selecting the image of the index mark having the optimum contrast as a reference for comparison in accordance with the contrast of the image of the test mark to be detected, it is possible to detect the positions of the test marks at various steps with high accuracy. it can.

Next, according to the second position detection method of the present invention, since the index mark having a line width smaller than the resolution limit of the objective optical system for forming an image of the index mark on a predetermined detection surface is provided. Even if the test mark is a test mark having a low contrast and a low step, the position of the test mark can be detected with high accuracy by selecting the image of the index mark as a reference for comparison. it can.

Next, according to the position detecting device of the present invention, the position detecting method of the present invention can be implemented, and the signal processing system can be used to select an optimum part from a part corresponding to a plurality of marks forming an image of the index mark. Is selected as a reference for comparison, the position of the test mark can be detected with high accuracy. In addition, when detecting a target mark having a low contrast and a low contrast of the image, when the gain control is performed so that the detection signal of the image sensor has a predetermined range of amplitude, an index mark that is not saturated is used. By selecting an image as a reference for comparison, the position of the test mark can be detected with high accuracy.

Further, according to the exposure apparatus of the present invention, by using the position detecting apparatus of the present invention to detect the alignment mark on the substrate, even if the substrate has gone through the step-difference process, The alignment between the substrate and the mask can be performed with high accuracy.

[Brief description of the drawings]

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

FIG. 2 is a schematic configuration diagram showing an alignment sensor 5 of FIG.

FIG. 3 is a diagram illustrating an observation field of view of an image sensor when detecting the position of a high step mark, and an image signal corresponding thereto.

FIG. 4 is a diagram illustrating an observation field of view of an image sensor when detecting the position of a low step mark, and an image signal corresponding thereto.

FIG. 5A is a diagram showing the imaging signal of FIG. 4B4;
FIG. 5B is a diagram illustrating an image signal obtained by increasing the gain of the image signal in FIG.

FIG. 6 is a diagram showing a multi-marked index mark used in another example of the embodiment of the present invention, and an image pickup signal of the image.

FIG. 7 is an explanatory diagram of a case where the position of a low step mark is detected by a conventional position detecting device.

[Explanation of symbols]

 Reference Signs List 1 projection optical system 4 wafer 5, alignment sensor 6, 7 laser interferometer 9 reticle 11 main control system 12 stage drive unit 13 image processing device 15 dichroic mirror 16 half mirror 19, 32 index plate 20 field slit 25 light emitting diode 26 randomly Bundled fiber bundle 27 light source 31X, 31Y two-dimensional image sensor

Claims (8)

[Claims] 1. A position detecting method for detecting a position of a test mark by comparing an image of a test mark on a substrate with a predetermined index mark or an image of the index mark, wherein the index mark is Has a plurality of different marks,
A position detection method, wherein a mark serving as a reference for comparison is selected from the plurality of marks according to an image of the test mark. 2. The position detection method according to claim 1, wherein the plurality of different marks are a plurality of marks having different line widths. 3. A position detecting method for detecting a position of the test mark by comparing an image of the test mark on a substrate with an image of a predetermined index mark, wherein the index mark is A position detection method comprising a mark having a line width smaller than a resolution limit of an objective optical system for forming an image on a predetermined detection surface. 4. The position detection method according to claim 1, wherein said mark to be detected and said index mark are illuminated by different illumination systems, and an image of said mark to be detected and said index. A position detecting method comprising: adjusting relative illuminance of said different illumination systems according to a detection level of a mark image. 5. The position detection method according to claim 1, wherein the image of the test mark and the image of the index mark are projected on an imaging surface of the same imaging device. The detection signal of the image sensor is gain-controlled so that the signal portion corresponding to the image of the test mark has an amplitude within a predetermined range, and the gain-controlled detection signal is processed to perform the test on the image of the index mark. A position detection method, comprising detecting a position shift amount of a mark image. 6. The position detection method according to claim 1, wherein each of the marks constituting the index mark comprises a plurality of linear patterns having the same line width. Detection method. 7. An image pickup device for picking up an image of a test mark on a substrate and an image of a predetermined index mark, and processing a detection signal of the image pickup device to process the detection mark based on the index mark. In a position detection device that detects a position, the index mark has a plurality of marks having different line widths from each other, and according to a level of a portion corresponding to the image of the test mark in a detection signal of the imaging element, A position detecting device, comprising: a signal processing system for selecting a portion serving as a reference for comparison from portions corresponding to the plurality of marks in the detection signal. 8. An exposure apparatus comprising: the position detection device according to claim 7; a substrate stage for positioning a substrate on which a positioning mark is formed; and an exposure unit for exposing a pattern of a mask on the substrate. An exposure apparatus, wherein the position detection device detects the position of a mark for alignment on the substrate, and performs alignment between the substrate and the mask based on the detection result.