JP2001250760A - Aberration measuring method, mask detecting method to use said method and exposure method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To find coma in an optical system for detection, which causes the error between the detected values of the relative positions of patterns and the detected values of the relative positions of patterns due to a change in the line width of a mark and a change in the position of a focus, with high accuracy. SOLUTION: A first mark M1X consisting of two recessed patterns M1Xa and M1Xb of the same line width dI is imaged via an imaging optical system, which is used as an optical system for detection, while the position of a focus is changed and the relative positions MD1 of both patterns M1Xa and M1Xb are measured. Then a second mask M2 consisting of a recessed pattern M2Xa of a line width d2 and a recessed pattern M2Xb of the line width d1 is imaged while the position of the focus is changed and the relative positions MD2 of both patterns M2Xa and M2Xb are measured. The amount ΔMD of change of the detected values of the relative positions due to a coma is found from the difference between the relative positions MD1 and the relative positions MD2 and the coma of the imaging optical system is found from the relation between the amount ΔMD of change of the detected values of the relative positions previously found by a simulation and the amount of the coma of the imaging optical system.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring aberration of an optical system for detecting a light beam from a test mark.
For example, it is suitable for use as an alignment sensor provided in an exposure apparatus used in a lithography process for forming a fine pattern such as a semiconductor integrated circuit, an image pickup device (such as a CCD), a liquid crystal display, or a thin film magnetic head. .

[0002]

2. Description of the Related Art When manufacturing a semiconductor integrated circuit or the like, an image of a reticle pattern as a mask is projected onto each shot area on a wafer (or a glass plate or the like) coated with a photoresist through a projection optical system. A projection exposure apparatus (stepper or the like) for transferring is used. For example, a semiconductor integrated circuit is formed by stacking circuit patterns of several tens of layers on a wafer in a predetermined positional relationship. For example, when projecting and exposing the circuit patterns of the second and subsequent layers on the wafer, It is necessary to perform high-accuracy alignment (alignment) between the circuit pattern formed in each of the shot areas by the previous process and the image of the reticle pattern to be exposed.

For this purpose, the projection exposure apparatus is provided with an alignment sensor for detecting the position of an alignment mark (reticle mark or wafer mark) provided on a reticle or wafer. There are various types of alignment sensors, and the alignment sensor that detects the reticle mark illuminates the reticle mark with exposure illumination light (exposure light), captures an image with a CCD camera, etc., and obtains image data. And a method using exposure light such as a VRA (Visual Reticle Alignment) method for measuring the position of a reticle mark by image processing.

An alignment sensor for detecting a wafer mark is illuminated with light having a wide wavelength band, for example, using a halogen lamp or the like as a light source. FIA (Fiel) that measures the position of wafer mark by image processing data
d Image Alignment) method or the like is used.

[0005]

As described above, in the conventional imaging type alignment sensor, a system such as the VRA system or the FIA system has been used. However, when such an imaging type alignment sensor is used, if an aberration (coma aberration or the like) remains in a detection optical system such as an imaging system of the alignment sensor, position detection is performed due to the aberration. Since an error occurs in the value and accurate alignment between the reticle and the wafer cannot be performed, it is necessary to measure the residual aberration of the optical system for detection and adjust the optical system for detection.

Heretofore, as a method of measuring the residual aberration of the optical system for detection, a method of obtaining the aberration by using the focus dependence of the index of the asymmetry of the image corresponding to the edge of the predetermined mark, a method of measuring the predetermined aberration, A method has been used in which a mark for adjusting the line width is detected, and the aberration is obtained using the focus dependence of the position detection value. However, the error in the position detection value due to the residual aberration of the optical system for detection is mainly due to coma, and the amount of error in the position detection value due to coma varies depending on the line width of the alignment mark and the focus position. For this reason, even if the aberration of the optical system for detection is measured using the method described above, and the line width of the alignment mark to be detected is measured for coma even if the optical system for detection is adjusted, If the line width of the used mark is different from that of the used mark, there is a problem that an error occurs in the position detection value of the alignment mark.

In the above-described method of obtaining aberrations using the focus dependence of the index of asymmetry of an image corresponding to the edge of a predetermined mark, the index of asymmetry is not a mark position detection value itself but a direct mark. Was not. In view of the above, the present invention provides an aberration measurement method capable of measuring, with high accuracy, an aberration of a detection optical system that causes an error in a position detection value due to a change in a line width of a mark or a focus position. The purpose is to: Another object of the present invention is to provide a mark detection method and an exposure method using such an aberration measurement method.

[0008]

According to a first aberration measuring method of the present invention, a predetermined optical system (10, 9, 12, 15, 16, 16, 21) for condensing a light beam from a test mark is provided. Is an aberration measuring method for measuring the aberration information of the first mark and the second mark (M2X) having different line widths at a plurality of different focus positions via an optical system for the detection.
a, M2Xb), and based on the relative position information detected at each of the plurality of focus positions, the predetermined aberration information based on the change information between the plurality of focus positions. Is what you want.

According to the present invention, if coma remains in the optical system for detection, the position of the image of the test mark is determined according to the line width and focus position of the test mark. The relative position detection value as the relative position information of the first and second marks shifted and having different line widths changes according to the coma aberration of the optical system for the detection. In the present invention, the first and second focus positions are set at different focus positions.
The relative position information of the mark is detected. For example, a predetermined optical system for the detection is determined from the relationship between the relative positions of the first and second marks previously obtained by simulation and the coma of the optical system for the detection. Is obtained as coma aberration information. Thus, the aberration of the optical system for detection, which causes a position detection error due to a change in the line width or focus position of the test mark, can be obtained with high accuracy.

Next, a first mark detection method according to the present invention is based on the predetermined aberration information obtained by the aberration measuring method according to the present invention, and the optical system (10, 9, 12, 15, 15) is used.
16, 21), at least a part of the optical member is adjusted, and the position information of the mark formed on the substrate (W) is detected through the adjusted optical system.

According to the present invention, since the optical system is adjusted based on the predetermined aberration information obtained by the first aberration measuring method of the present invention, the line width and the focus of the mark on the substrate are adjusted. Even if the position changes, the position of the mark formed on the substrate can be detected with high accuracy. The first exposure method of the present invention positions the substrate (W) based on the position information of the mark detected by the mark detection method of the present invention, and forms a predetermined pattern on the positioned substrate. It is to be transcribed. According to the present invention, since the position information of the mark detected by the mark detection method of the present invention is used, the substrate can be positioned with high accuracy for exposure.

Next, a second aberration measuring method according to the present invention measures aberration information of a detection optical system (10, 9, 12, 15, 16, 21) for condensing a light beam from a test mark. A plurality of focus positions different from each other through a predetermined mark (M2) through the optical system.
Xa) is detected, and first aberration information of the optical system is obtained based on change information corresponding to the focus position of the detected position information of the image of the predetermined mark. The second aberration information of the optical system is obtained based on the change information according to the focus position of the asymmetry of the image of the predetermined mark, and the predetermined aberration information is obtained based on the first and second aberration information. It is.

According to the present invention, the coma of the optical system contains a relatively large number of distortion components of a predetermined order (for example, the third order) or less as a distortion component of the wavefront, and is corrected by adjusting the optical system. A component (hereinafter, referred to as “low-order coma aberration”) and a distortion component of a higher order than the predetermined order as a distortion component of the wavefront, which are relatively difficult to correct by adjustment in the optical system (hereinafter, components). , “Higher order coma”). The amount of change due to the change of the focus position of the asymmetry of the image of the predetermined mark changes according to the aberration including the low-order coma and the high-order coma of the optical system, and the position of the image of the predetermined mark is changed. The amount of change due to the change in the focus position changes according to the low-order coma aberration of the optical system for detection.

In the present invention, as an example, low-order coma aberration as first aberration information of the optical system is obtained based on change information of the position information of the image of the predetermined mark in accordance with the focus position, and the detection thereof is performed. Based on the information on the change of the asymmetry of the image of the predetermined mark according to the focus position, an aberration including low-order coma and high-order coma as second aberration information of the optical system is obtained. And this second
The first-order aberration information is subtracted from the aberration information to obtain a high-order coma aberration amount as predetermined aberration information. by this,
The aberration of the optical system for detection, which causes a position detection value error due to a change in the line width or focus position of the test mark, can be obtained with high accuracy.

Next, a second mark detecting method according to the present invention adjusts at least a part of an optical member constituting the optical system based on the first aberration information obtained by the aberration measuring method according to the present invention. Then, the position information of the mark formed on the substrate (W) is detected through the adjusted optical system, and the position information of the detected mark is corrected based on the predetermined aberration information. Things.

According to the present invention, the optical system is adjusted based on the first aberration information obtained by the aberration measurement method of the present invention, and the detected mark is adjusted based on the predetermined aberration information. Is corrected, the position of the mark formed on the substrate can be detected with high accuracy even when the line width or the focus position of the mark on the substrate changes.

The second exposure method of the present invention positions the substrate (W) based on the position information of the mark obtained by the mark detection method of the present invention, and places the substrate (W) on the positioned substrate. This is for transferring a predetermined pattern. According to the present invention, since the position information of the mark obtained by the mark detection method of the present invention is used, the substrate can be positioned with high accuracy for exposure.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a position detecting device of the present embodiment. In FIG. 1, the surface of an adjustment wafer 11 is arranged on a surface to be inspected by the position detecting device of the present embodiment. On the surface of the wafer 11, a plurality of pairs of concave and convex lattice marks (step marks) are formed as described later.

In FIG. 1, a light source 1 such as a halogen lamp is shown.
Is emitted from the optical axis AX1 of the illumination system.
Along a condenser lens 2, an illumination system aperture stop (hereinafter, referred to as “σ stop”) 3, a first relay lens 6, a field stop 7, and a second relay lens 8 to enter the half prism 9. The illumination light AL <b> 1 reflected downward by the half prism 9 illuminates the adjustment wafer 11 through the objective lens group 10. The σ stop 3 sets a σ value that is a coherence factor of the illumination system.

The light beam AL2 reflected by the wafer 11 enters the half prism 9 through the objective lens group 10.
The light beam AL2 transmitted through the half prism 9 forms an image of a lattice mark on the wafer 11 on the pattern surface of the index plate 13 via the third relay lens 12. That is,
The pattern surface of the index plate 13 is conjugate with the surface of the wafer 11, and the pattern surface has an index mark 14 as a reference for a detection position when performing alignment in the projection exposure apparatus.
a and 14b are formed.

The luminous flux AL2 transmitted through the index plate 13 is
A relay lens 15 and an optical system for correcting coma aberration (hereinafter, referred to as
The frame-like marks and index marks 14a, 14b on the wafer 11 are passed through an aperture stop 18, a field lens 21, an image pickup surface of a two-dimensional image pickup device 22 such as a CCD type, and the like. An image is formed. Image sensor 2
2 is supplied to the control operation system 23. In this example, the objective lens group 10, the half prism 9, the third relay lens 12, and the fourth relay lens 1
5, the frame correction optical system 16 and the field lens 21 constitute an imaging optical system as a detection optical system. Hereinafter, the Z axis is taken parallel to the optical axis AX2 of the imaging optical system, 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.

In this case, the aperture stop 18 in the imaging optical system
Is the numerical aperture of this imaging optical system (N
A) is determined and, depending on the position, the deviation of the mark position detection result due to the positional deviation amount (defocus amount) of the surface of the wafer 11 in the direction of the optical axis AX2 with respect to the best focus position of the imaging optical system. (Hereinafter referred to as “telecentric shift”). Therefore, the aperture stop 18
Is held by holding members 19a and 19b,
Under the control of the control calculation system 23, the feed screw system, a telescopic drive element system such as a piezo element, a voice coil motor (VCM) system, a linear motor system, etc. are held by aperture stop position adjusting mechanisms 20a and 20b. Member 19a, 1
By shifting 9b, the center of the aperture stop 18 can be shifted by an arbitrary amount in the X and Y directions. The position of the aperture stop 18 is adjusted so that the telecentric displacement does not occur before starting the measurement.

The wafer 11 is mounted on a wafer stage (not shown) for controlling the position of the wafer 11 in the X, Y and rotation directions via a wafer holder (not shown). Are measured by a laser interferometer (not shown). The position of the wafer 11 in the Z direction (focus position) is determined by the wafer stage.
And the tilt angle are also controlled.

In the position detecting device of the present embodiment, the objective lens group 10 and other optical systems are all manufactured and assembled with extremely high accuracy, but various aberrations due to manufacturing errors still remain. If such a residual aberration exceeds a predetermined allowable range, it causes the position detection accuracy to be worse than the required accuracy. Aberrations that deteriorate the position detection accuracy are mainly coma aberrations, which occur due to eccentricity of each optical member and insufficient precision of the polished surface. Therefore, even when the test mark is on the optical axis AX2 of the image forming optical system, such a bad influence of the coma aberration is given.

The coma correction optical system 16 is an optical system for correcting such residual coma aberration, and can change the state of the coma aberration of the imaging optical system by changing its position. For this reason, the frame correction optical system 16 is held by the holding members 16a and 16b, and the frame correction optical system position adjusting mechanism 17 is controlled under the control of the control operation system 23.
By shifting the holding members 16a and 16b by a and 17b, the center of the coma correction optical system 16 can be shifted by an arbitrary amount in the X and Y directions.
It should be noted that at least one optical element other than the coma correction optical system 16 is moved so that the optical characteristics of the imaging optical system, that is, aberrations other than coma, telecentricity, and the focal position can be adjusted. At least one of the optical elements may be moved so as to substantially cancel a change in the optical characteristics that may be caused by the movement of the correction optical system 16.

When the coma aberration remaining in the optical system is extremely large, the amount of position adjustment of the coma correction optical system 16 increases, and the position of the principal ray of the image forming light beam is largely shifted from the optical axis AX2. In some cases. The positional relationship between the position of the aperture stop 18 and the principal ray greatly changes, and in the worst case, the position of the aperture stop 18 needs to be readjusted every time the position of the frame correction optical system 16 is adjusted. May occur. Therefore, the aperture stop 18 and the frame correction optical system 1
6 is reversed from that in FIG.
By arranging it on the side closer to the wafer than the frame correction optical system 16, such fear of readjustment can be completely eliminated.

The coma correction optical system 16 is provided in the image forming optical system.
It is desirable to be arranged near the pupil plane (aperture stop 18), but of course, it may be arranged on the conjugate plane via a relay system. By arranging them on a conjugate plane via a relay optical system, there is an advantage in that the degree of freedom with respect to the arrangement space increases. On the other hand, when the relationship between the position of the σ stop 3 in the illumination system from the light source 1 to the second relay lens 8 and the position of the aperture stop 18 in the above-described imaging optical system changes, the detection position of the mark to be detected. Is adversely affected. However, as described above, the aperture stop 1
If the position of 8 is adjusted (moved), a telecentric shift occurs. Therefore, the positional relationship between them is adjusted by adjusting the position of the σ stop 3. Therefore, σ aperture 3
Is held by the holding members 4a and 4b, and the σ stop position adjusting mechanisms 5a and 5
b by shifting the holding members 4a and 4b by
The center of the stop 3 can be shifted by an arbitrary amount in the directions corresponding to the X direction and the Y direction on the wafer 11.

Next, an example of the measurement and adjustment of the coma aberration of the imaging optical system of the position detecting device of FIG. 1 will be described. FIG.
2 is a plan view showing an adjustment wafer 11 in FIG.
In FIG. 2, a silicon wafer is used as an example of the wafer 11 for adjustment. On the surface of the wafer 11, an X-axis first mark M1X in which two concavo-convex patterns having the same line width are arranged in the X direction, and an X-axis in which two concavo-convex patterns having different line widths are arranged in the X direction Second mark M
A third mark M3X composed of a pattern of irregularities that is periodic in the 2X and X directions is formed. In addition, each of the marks M1Y to M3Y is rotated by 90 ° to form a Y
A first mark M1Y, a second mark M2Y, and a third mark M3Y of the axis are formed. The coma aberration of the imaging optical system includes a component whose wavefront distortion component is equal to or lower than a predetermined order (for example, third order) (hereinafter, referred to as “low-order coma aberration”) and a component whose wavefront distortion component is equal to or higher than the predetermined order. (Hereinafter, referred to as “high-order coma aberration”). In this example, the first and second coma are used.
The low-order coma is measured using the marks M1X, M1Y, M2X, and M2Y, and the high-order coma is measured using the third marks M3X and M3Y.

In the case where, for example, a silicon wafer is used as the wafer 11, these concave and convex grid marks are coated with a photoresist on the surface thereof, a projection image of a corresponding reticle pattern is exposed, and a photoresist is developed. ,
It can be formed with extremely high precision by processes such as etching and resist peeling. FIG. 3A shows FIG.
FIG. 3 is an enlarged plan view showing a first mark M1X on the X axis of FIG.
This is a pattern in which book concave patterns M1Xa and M1Xb are formed at a pitch P in the X direction. The distance between the center of the concave pattern M1Xa and the center of the concave pattern M1Xb in the X direction, which is the measurement direction, is set to D as a design value.

FIG. 3C is an enlarged plan view showing the second mark M2X on the X axis in FIG.
A thin concave pattern M2X having a line width d2 is formed on the surface of the wafer 11.
a, and concave patterns M1Xa, M1 of the first mark M1X
This is a pattern in which a thick concave pattern M2Xb having the same line width d1 as Xb is formed. Then, in the X direction which is the measurement direction, the center of the concave pattern M2Xa and the concave pattern M2X
The distance from the center of b is set to D with the same design value as the distance between the first marks M1X.

When measuring the low-order coma aberration of the imaging optical system shown in FIG. 1, first, the first mark M1X is imaged while the focus position is changed by the image pickup device 22 of the position detecting device shown in FIG. Next, in the imaging surface of the imaging element 22, the first
The second mark M2X is moved to a position where the mark M1X is imaged, and the second mark M2X is imaged while the focus position is changed by the image sensor 22 of the position detection device in FIG.

FIGS. 3B and 3D show each mark M
FIG. 3B and FIG. 3B show image signals SD obtained by reading the images of the marks M1X and M2X in the X direction by the image sensor 22 when 1X and M2X are observed by the position detection device of FIG. In FIG. 3D, the horizontal axis represents the position X in the measurement direction, and the position X is actually the image pickup device using the magnification B from the surface of the wafer 11 to the image pickup surface of the image pickup device 22 in FIG. A position obtained by multiplying a position from a predetermined reference point on the imaging surface of No. 22 by 1 / B is shown. Further, in the image signal SD, the edge portion becomes a dark portion in the portion ID1 corresponding to the image of the concave pattern M1Xa, and similarly, the portions ID2, ID3, and ID4 corresponding to the images of the other concave patterns M1Xb, M2Xa, M2Xb have the same edge. The part is a dark part. In FIGS. 3B and 3D, the image signal SD is obtained by scanning the image of the first mark M1X or the second mark M2X in the X direction in the non-measurement direction (Y direction). May be averaged.

The control operation system 23 shown in FIG.
The distance MD1 between the center position X1 of the part ID1 and the center position X2 of the part ID2 is obtained from the X image signal SD, and the center position X3 of the part ID3 and the center position X4 of the part ID4 are obtained from the image signal SD of the second mark M2X. Is obtained. This distance MD2 should be equal to the distance MD1 between the first marks M1X and a designed distance D when the imaging optical system has no aberration, but low order coma remains in the imaging optical system. The bi-concave patterns M2Xa, M2X
b, the biconcave patterns M2Xa, M2X
Since the amount of change in the image position due to the low-order coma aberration b differs from each other, the interval MD2 does not match the designed interval D.

FIG. 4 shows an example of the relationship between the focus position and the amount of change in the image position due to coma. In FIG. 4, the horizontal axis represents the defocus amount ΔF with respect to the best focus position, and the vertical axis represents Represents a change amount ΔX of the image position and a change amount ΔMD of the relative position due to coma aberration. In FIG. 4, the change amount .DELTA.X of the image position due to coma when observing a mark having a line width d of 6 .mu.m hardly changes with respect to the change of the defocus amount .DELTA.F, but is stable. .5μ
The amount of change ΔX in the image position when observing the mark of m greatly fluctuates due to the change in the amount of defocus ΔF, and has a line width of 0.5
The change amount ΔMD of the relative position between the mark of μm and the mark having a line width of 6 μm also largely fluctuates due to the change of the defocus amount ΔF.

Such a change in the image position is due to the low-order coma aberration as described above, and the control operation system 23 shown in FIG.
Is the variation ΔMD (= MD) of the relative position detection value between the concave pattern M2Xa and the concave pattern M2Xb due to low-order coma aberration by calculating the difference between the interval MD1 and the interval MD2.
1−MD2), and the lower order coma of the imaging optical system is obtained from the relationship between the lower order coma of the imaging optical system and the variation ΔMD of the relative position, which is obtained in advance by simulation.

Further, the focus dependency of ΔMD as shown in FIG.
Find the second order coefficient of the fitted quadratic function,
Coma aberration may be obtained based on the relationship between this coefficient and coma aberration (this relationship is obtained in advance by simulation). That is, a method of changing ΔMD with respect to the focus (how the graph of FIG. 4 is bent) may be obtained, and the coma aberration may be obtained based on the obtained method.

Also, the measured relative position change amount ΔMD
From the magnitude of the low-order coma aberration, it is possible to determine the sign, so that the relative amount of change ΔMD
Control operation system 23 of FIG.
Adjusts the position of the frame correction optical system 16 via the frame correction optical system position adjusting mechanisms 17a and 17b so that the change amount ΔMD of the relative position becomes minimum at each focus position.

After the adjustment of the position of the frame correction optical system 16, the intervals between the patterns of the first and second marks M1X and M2X are measured again, and the change amount ΔMD of the relative position is measured.
Is outside the allowable range, the above adjustment is performed again.
By repeating the above steps until the change amount ΔMD of the relative position falls within the allowable range, low-order coma aberration of the imaging optical system can be corrected with high accuracy.

Next, measurement of higher-order coma aberration of the imaging optical system will be described. Of the coma of the imaging optical system, low-order coma can be measured as described above and adjusted by the coma correction optical system 16, but it is difficult at this time to adjust high-order coma. is there. For this reason, in the position detecting device of this example, the higher-order coma aberration of the imaging optical system is measured using the third mark M3X of FIG.
When the position is detected, the position detection value of the test mark is corrected based on the measured higher-order coma aberration.

FIG. 5A shows a cross section of the third mark M3X in FIG. 2. The third mark M3X is formed by forming a pattern having a predetermined line width on the surface of the wafer 11 at a pitch P in the X direction. It is. FIG. 5B shows the third mark M3X in FIG.
5B shows an image signal SD obtained by reading the image of the third mark M3X in the X direction by the image sensor 22 when observed by the position detection device of FIG. 5A. In FIG. 5B, the horizontal axis represents the position X in the measurement direction. 1, the position X is actually set to a position from a predetermined reference point on the imaging surface of the imaging device 22 by using the magnification B from the surface of the wafer 11 to the imaging surface of the imaging device 22 in FIG. / B represents a position obtained by multiplication. Also,
The image signal SD is an integrated signal ΔV obtained by integrating the signal V corresponding to the light intensity of the image of the third mark M3X in the non-measurement direction.

As shown in FIG. 5B, the image signal SD
(Integrated signal ΔV) changes along the X direction at every cycle BP (B is the magnification of the imaging optical system). In this example, in order to quantify the asymmetry of the image of the third mark M3X, in the distribution of the integrated signal ΣV, the minimum value of the left and right signals (the dip in the figure) in the i-th (second in FIG. 5B) cycle is shown. The signal values of the edge portion) are ViL and ViR (i = 1, 2, 2, 3), respectively.
3 ...). In addition, the maximum value and the minimum value of the signal are set to Vmax and Vmin, respectively, in the entire region over each period except for both ends of the integrated signal ΔV. And
An index β of asymmetry of the phase pattern image is obtained based on the following equation.

Β = {ViL−ViR / (Vmax−Vmin)} / n (1) where n is the number of periods, and Σ is a sum symbol for i = 1 to n. FIG. 6 shows the focus position and the third mark M3.
FIG. 6 shows the relationship between the asymmetry of X and the index β. In FIG. 6, when there is a coma in the imaging optical system, the index β is a defocus amount ΔF as shown by a straight line L having a slope C in FIG. , And shows a substantially linear change, and is expressed by the following equation.

Β = C · ΔF (2) The slope C of the straight line L is a sum of a component due to low-order coma aberration and a component due to high-order coma aberration. Then, the high-order coma aberration amount Ch is expressed by the following equation. C = al · Cl + ah · Ch Ch = (C−al · Cl) / ah (3) where al and ah are proportional coefficients for low-order coma aberration and high-order coma aberration, respectively, and are obtained in advance by simulation. Can be kept. Therefore, using the first and second marks M1X and M2X, the low-order coma aberration amount C
1 is obtained in advance, and from the relationship between the index β measured using the third mark M3X and the defocus amount, for example, the value of the slope C is obtained by linear approximation or the like. Can be obtained.

When detecting the position of the test mark at the time of the overlay exposure or the like, the position detection value of the test mark is corrected based on the high-order coma aberration amount Ch, whereby the position due to the high-order coma aberration is corrected. The detection error can be reduced, and the position of the test mark can be detected with high accuracy. In addition,
The region where the image of the third mark M3X is detected may be limited to a desired range. That is, in the equation (1), i = 1 to
The range of n may be limited. By limiting in this way, coma at an arbitrary position on the object plane can be inspected.

As described above, according to the position detecting device of the present embodiment, the low-order and high-order coma aberrations of the imaging optical system are measured, and the imaging optical system is adjusted based on the low-order coma aberration. Since the position detection value is corrected based on the higher-order coma aberration, even if the line width or the focus position of the mark to be inspected fluctuates,
The position of the test mark can be detected with high accuracy. Note that there are various methods such as a slice method and a correlation method for the position detection algorithm of each mark image in the above-described position detection process. In the present embodiment, any of these methods may be used. For example, in the slice method, position detection is performed based on the slice position of the image signal SD at a predetermined slice level. In the correlation method, the image signal SD is compared with a predetermined reference waveform, and the degree of correlation with the reference waveform is determined. The highest position is the position of the mark image. Note that FIG. 3B and FIG.
In (d), the signal waveforms corresponding to the images of the index marks 14a and 14b are not shown, but for example,
The distance ΔMD may be obtained after detecting the amount of displacement of the marks M1X and M2X with respect to the marks a and 14b.

It is desirable that the step (depth) of each mark M1X, M2X, M3X is about 40 to 100 nm. If the level difference is too small, the contrast of the mark images decreases (the mark portions do not become sufficiently dark), and the position detection accuracy decreases. Conversely, the step is 100n
When the step is higher than about m, adverse effects such as geometrical optical vignetting due to the step occur, and it becomes difficult to perform highly accurate measurement. Further, in order to obtain a good contrast image for each mark, the step is desirably 40 to 60 nm.

The index β of the asymmetry of the concave pattern of the mark M3X is determined by the manufacturing error of the reticle pattern used when transferring the concave pattern and the etching error when forming a step on the wafer 11. And other manufacturing errors. Therefore, before the above adjustment, it is desirable to measure the amount of cheating (error) caused by the wafer included in the index β. For this purpose, the pattern M3 in FIG.
After measuring the X image, the wafer 11 is rotated by 180 ° to measure an image of the same pattern M3X. From the difference between the two measured values, the characteristic of the wafer (the forming process or the formed (Such as mark asymmetry), a larger error can be obtained. Then, by correcting the inclination C in the equation (2) using the obtained error, the amount of the indicator β deceived by the wafer (an amount unrelated to the aberration of the optical system) can be removed. The coma of the system can be obtained with high accuracy.

By the way, generally, the position detecting device needs to measure a mark position in a two-dimensional direction (X direction, Y direction) or a relative positional relationship. Therefore, similarly to the adjustment in the X direction, the measurement and adjustment of the coma aberration in the Y direction are performed by measuring the interval between the images of the Y-axis marks (M1Y, M2Y, M3Y) on the wafer 11 in FIG. It can be carried out.

In this embodiment, the coma correction optical system 16 in FIG. 1 is adjusted to remove the residual coma aberration. However, the present invention is not limited to this. The residual coma may be adjusted and removed by adjusting the position or rotation angle of another optical member. In adjusting the illumination state, not only is the position of the σ stop 3 adjusted, but also
The position of the light source 1 or the position or the rotation angle of the first relay lens 6 or the second relay lens 8 may be adjusted.

In this example, two-dimensional coma aberration is measured.
Although the second mark M2X having two concave patterns is used, the mark used for measuring low-order coma aberration is not limited to this. For example, a mark as shown in FIG. 7 may be used. . The fourth mark M4X shown in FIG. 7A has five thick lines (only two or more marks are required).
Are formed in a lattice pattern at a predetermined pitch in the X direction, and the fifth mark M5X has five linear concave patterns M5Xn (n = 1 to 5) having a small line width.
Are formed in a lattice at a predetermined pitch in the X direction. When these marks M4X and M5X are used for measurement, the center of the fourth mark M4X and the fifth mark M5X
By measuring the distance from the center of the lens, the focus is shaken, and the change in the relative positional relationship is determined, the low-order coma aberration of the imaging optical system is determined.

Incidentally, for example, the distance between the center of the mark M4X and the concave pattern M5Xn (n = 1 to 5 in this example) is measured, and the change in the relative positional relationship is obtained by shaking the focus to obtain an arbitrary value within the observation range. The coma at the position of can be obtained. The seventh mark M7X shown in FIG. 7B is a pattern in which three linear concave patterns having a small line width are formed in a lattice at a predetermined pitch in the X direction.
The sixth mark M6X and the eighth mark M6X sandwich the seventh mark M7X.
The mark M8X is formed. The sixth mark M6X is
This is a pattern in which three (though it is sufficient if two or more) linear concave patterns having a large line width are formed in a grid pattern at a predetermined pitch in the X direction, and the shape of the eighth mark M8X is the sixth mark M6.
Same as X. When these marks M6X to M8X are used for measurement, the center position of each mark M6X to M8X is determined as the position of each mark M6X to M8X, and then the average position of the marks M6X and M8X at both ends is calculated. The marks M6X at both ends with respect to the position of the seventh mark M7X,
By obtaining the deviation of the average position of M8X as a relative positional relationship, low-order coma aberration of the imaging optical system is obtained.

In this example, the biconcave pattern M2Xa,
M2Xb is imaged at the same time to obtain biconcave patterns M2Xa and M2.
Although the relative position of Xb was detected, for example, the concave pattern M2X
a, the wafer 11 is moved by the design interval D based on the position of the wafer stage measured by the laser interferometer, and the concave pattern M2Xb is positioned at the position where the concave pattern M2Xa is imaged. Only the pattern M2Xb may be imaged, and the difference in the amount of change in the image position due to the difference in line width may be determined.

It is desirable that the line width of the mark used for measurement be appropriately selected according to the characteristics of the imaging optical system. In general, the amount of change in the image position due to coma is
Since the narrower the line width, the larger the focus position changes, the larger the value, the larger the line width of one pattern, for example, so that the amount of change in the image position due to coma is stable with respect to the change in the focus position. However, it is desirable that the line width of the other pattern is set to be thin so that the amount of change in the image position due to coma varies in response to the change in the focus position. For example, as shown in FIG. 3, one of the patterns has a line width such that a signal obtained at the time of imaging is a single-edge signal, and the other pattern has a double-edge signal at the time of imaging. The line width may be such that the signal of

In this embodiment, the line width of the mark used for measurement is set to two types. However, by increasing the line width of the mark used for measurement, the line width of the mark can be increased with higher accuracy. Coma can be measured. Next, a case where the position detecting device of FIG. 1 is applied to an alignment sensor of a projection exposure apparatus will be described with reference to FIG.

FIG. 8 shows a projection exposure apparatus used in this embodiment. In FIG. 8, during exposure, an exposure light source such as a mercury lamp or an excimer laser light source, an optical integrator, a variable field stop, and a condenser lens system are used. The reticle R is irradiated with exposure light IL from the illumination optical system 51 composed of. Then, the image of the pattern formed on the reticle R is converted into a projection magnification α via the projection optical system PL.
(Α is 1/5, 1/4, etc.) and projected onto one shot area on the wafer W coated with the photoresist. At this time, the exposure control system 52 optimizes the exposure based on the control information of the main control system 53.

Hereinafter, the Z axis is taken parallel to the optical axis AX of the projection optical system PL, the X axis is taken parallel to the plane of FIG. 8 in a plane perpendicular to the Z axis, and the Y axis is taken perpendicular to the plane of FIG. Take and explain. At this time, the reticle R is sucked and held on the reticle stage 54, and the reticle stage 54 is placed on the reticle base 55 based on the control information of the drive system 57 based on the measured value of the coordinates of the reticle stage 54 by the laser interferometer 56. To position the reticle R in the X, Y, and rotation directions.

On the other hand, the wafer W is held on a wafer holder (not shown) by vacuum suction. The wafer holder is fixed on a sample table 58, and the sample table 58 is floated on a surface plate 60 via an air bearing. X supported
It is fixed on a Y stage 59. The sample stage 58 controls the position (focus position) and the tilt angle of the wafer W in the Z direction to adjust the surface of the wafer W to the image plane of the projection optical system PL by the autofocus method.
Based on the control information of the drive system 62 based on the position of the sample table 58 measured by the laser interferometer 61, the sample table 58
Is stepped in the X and Y directions. XY stage 5
By repeating the step movement by No. 9 and the exposure of the pattern image of the reticle R in a step-and-repeat manner, each shot area on the wafer W is exposed.

When performing the overlay exposure, it is necessary to perform alignment between the reticle R and the wafer W before the exposure. Therefore, a fiducial mark member 65 having various fiducial marks formed thereon is fixed on the sample table 58, and the reticle R is fixed to the fiducial mark member 65 based on the measurement result of a reticle alignment microscope (not shown) on the reticle R. Is aligned with Further, an off-axis type image processing type alignment sensor 63 having the same configuration as that of the optical system of the position detecting device of FIG. 1 is disposed on a side surface of the projection optical system PL.
The image signal from the image sensor 22 (see FIG. 1) is supplied to the alignment signal processing system 64. The alignment signal processing system 64 obtains, in addition to the function of the control operation system 23 in FIG. 1, the amount of displacement of the image of the alignment mark (wafer mark) on the detection target wafer W with respect to the index marks 14a and 14b in FIG. Has functions.

When the alignment sensor 63 is used, the adjustment wafer 11 shown in FIG. 2 is first placed on the sample table 58 via a wafer loader system (not shown). Then, the low-order and high-order coma aberrations of the imaging optical system are measured via the alignment sensor 63, and the position of the coma correction optical system 16 in FIG. 1 is adjusted. Thereafter, in FIG. 8, in parallel with the alignment of the reticle R, the position of a predetermined reference mark on the reference mark member 65 is detected via the alignment sensor 63, so that the center position of the pattern image of the reticle R (the exposure center ) And the distance between the detection center of the alignment sensor 63 (base line amount BL). Thereafter, the XY stage 59 is driven based on the coordinates obtained by correcting the position of the wafer mark detected via the alignment sensor 63 by the base line amount BL, thereby obtaining high overlay accuracy.

In the alignment sensor 63, the characteristic adjustment mark formed on the wafer 11 or the wafer W
The upper alignment mark is irradiated with broadband illumination light, and the light reflected by the wafer is used as the index mark 14a,
Although the illumination system 14b is illuminated, an illumination system for an index mark may be provided separately from an illumination system for illuminating a mark on a wafer.

In this embodiment, since the marks for characteristic adjustment are formed on the wafer 11 dedicated to measurement, the exposure apparatus used for manufacturing the marks for characteristic adjustment does not need to improve the transport mechanism and the wafer holder. In the projection exposure apparatus of No. 8, the measurement wafer can be placed on the XY stage by the wafer loader without providing a special transfer mechanism. However, the characteristic adjustment mark is
It may be formed on a plate other than the process wafer or the wafer, and furthermore, the plate may be detached from the sample tables 59 and 71 on the XY stage by an operator or the like. Even if the plate on which the characteristic adjustment mark is formed is not a wafer, if the shape and size are the same as the substrate (wafer or the like) carried into the projection exposure apparatus in FIG. It can be placed on an XY stage.

Further, since a rectangular substrate is used in an exposure apparatus used for manufacturing a liquid crystal display or the like, a plate on which marks for adjusting characteristics are formed is not a circle but a square.
Further, the reference plate on which the characteristic adjustment mark is formed is
It may be fixed to a part of the Y stage, and the adjustment may be performed periodically or when the diaphragm is replaced in the position detecting device. In this case, the time required for the measurement can be reduced as compared to using a wafer dedicated to the measurement.

In the projection exposure apparatus shown in FIG. 8, the position detection apparatus shown in FIG. 1 is used as an off-axis type alignment sensor, but the alignment sensor used in this projection exposure apparatus is transmitted through a projection optical system PL. A TTL (through-the-lens) method for detecting a mark on a wafer or a TTR (through-the-reticle) method for detecting a mark on a reticle and a mark on a wafer may be used. Although not shown in FIG. 8, a large number of optical elements constituting the off-axis type alignment sensor 63 are separately held in a plurality of lens barrels, and a stand on which the projection optical system PL is mounted is provided. Each lens barrel is fixed to hardware integrally provided.

Further, the projection exposure apparatus shown in FIG.
Is generally provided with an auto-focus mechanism for detecting the focus position (position in the optical axis direction of the alignment sensor 63) and focusing the surface of the wafer W to the best focus position of the alignment sensor 63. In this case, when detecting the position of a wafer mark on the wafer W or the interval between a pair of wafer marks, the measurement may be performed while operating the autofocus mechanism while focusing on the test mark. Note that the autofocus mechanism uses a TTL method in which a detection beam is irradiated onto the wafer through the objective lens group 10, or tilts the optical axis and the wafer surface without passing through the objective lens group 10 so that the detection beam is projected onto the wafer. May be applied to the oblique incident light system.

Further, the projection exposure apparatus shown in FIG. 8 is not limited to the step-and-repeat method, and the projection exposure apparatus shown in FIG. 8 is not limited to a step-and-scan method or a mirror projection method. It may be configured as a step-and-stitch method in which a plurality of patterns are partially overlapped and transferred on a substrate. In addition, a soft X-ray region (wavelength of about 5 to 50 nm) generated from a laser plasma light source or an SOR (Synchrotron Orbital Radiation) ring as exposure illumination light,
For example, EUV (Ex: 13.4 nm or 11.5 nm wavelength)
treme UltraViolet) Reduction projection exposure apparatus using light (E
UV exposure apparatus), a proximity type X-ray exposure apparatus using hard X-rays, or an exposure apparatus using a charged particle beam such as an electron beam or an ion beam. In the EUV exposure apparatus, a plurality of reduction projection optical systems (3
(Approximately 6) of reflective optical elements, and a reflective reticle is used as the reticle.

A reticle or a mask used in an exposure apparatus for manufacturing a device for manufacturing a semiconductor element or the like may be manufactured by an exposure apparatus using, for example, far ultraviolet light or vacuum ultraviolet light. The present invention can also be applied to an exposure apparatus used in a lithography process for manufacturing a semiconductor device. Further, as the exposure light, a mercury lamp of g-line or i-line, KrF excimer laser light, laser light such as ArF excimer laser light or F ₂ laser beam, or the like may be used harmonic of a YAG laser. Alternatively, DFB (Distributed feedbac
k) A semiconductor laser is amplified by, for example, a fiber amplifier doped with erbium (Er) (or both erbium and ytterbium (Yb)), and using a harmonic that is wavelength-converted to ultraviolet light using a nonlinear optical crystal. You may.

The exposure apparatus (projection exposure apparatus) according to the above embodiment incorporates an illumination optical system and a projection optical system composed of a plurality of lenses into the exposure apparatus main body, performs optical adjustment, and controls the projection optical system. The position detection device shown in FIG. 1 is incorporated into a hardware integrally provided on the holding stand to perform connection such as wiring, and optical adjustment thereof is performed as described in each of the above-described embodiments. The reticle stage and the wafer stage are connected to the exposure apparatus main body, wiring and piping are connected, and further, overall adjustment (electric adjustment, operation confirmation, etc.) can be performed. It is desirable that the exposure apparatus be manufactured in a clean room in which the temperature, cleanliness, and the like are controlled.

Further, when a semiconductor device is manufactured on a wafer by using the exposure apparatus of the above-described embodiment, the semiconductor device manufactures a reticle based on the step of designing the function and performance of the device. Step, producing a wafer from a silicon material, exposing the reticle pattern to the wafer by performing alignment using the exposure apparatus of the above-described embodiment, device assembling step (including dicing step, bonding step, and package step). It is manufactured through an inspection step and the like.

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.

[0070]

According to the first or second aberration measuring method of the present invention, the aberration of the detection optical system which causes a position detection value error due to a change in a mark line width or a focus position can be corrected with high accuracy. Can be sought. Further, according to the first or second mark detection device of the present invention, the first or second mark detection device of the present invention can be used.
Alternatively, the second aberration measurement method can be performed, and the position of the test mark can be detected with high accuracy even when the line width or the focus position of the test mark changes. According to the first or second exposure method of the present invention,
Exposure can be performed by positioning the substrate with high precision.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a part of a position detecting device used in an embodiment of the present invention.

FIG. 2 is a plan view showing a plurality of grid marks on a wafer used for adjustment in the embodiment of the present invention.

FIG. 3 shows first and second marks M1X, M2X,
FIG. 4 is a diagram showing image signals obtained from images of these marks.

FIG. 4 is a diagram illustrating an example of a relationship between a focus position and a change amount of an image position due to coma aberration.

5A is a sectional view showing a third mark M3X in FIG. 2, and FIG. 5B is a view showing an image signal obtained from an image of the third mark M3X.

FIG. 6 is a diagram illustrating a relationship between a focus position and an index β of asymmetry of a mark image.

FIG. 7 is a plan view showing another example of a mark for adjusting the characteristics of the imaging optical system.

8 is a configuration diagram illustrating a projection exposure apparatus including the position detection device of FIG. 1 as an alignment sensor.

[Explanation of symbols]

M1X to M3X, M1Y to M3Y: marks for adjusting the characteristics of the imaging optical system, PL: projection optical system, R: reticle, W:
Wafer, 1 light source, 2 condenser lens, 3 σ stop, 4a, 4b holding member, 5a, 5b σ stop position adjusting mechanism, 6 first relay lens, 7 field stop, 8 second relay Lens, 9 half prism, 10 objective lens group, 11 wafer for adjusting the characteristics of the imaging optical system, 12
Third relay lens, 15: fourth relay lens, 16: coma correction optical system, 16a, 16b: holding member, 17a, 1
7b: Frame correction optical system position adjustment mechanism, 21: Field lens, 22: Image sensor, 23: Control operation system, 53: Main control system, 58: Sample stage, 59: XY stage, 63: Alignment sensor, 64: Alignment Signal processing system

Continued on the front page (72) Inventor Hiroshi Chiba 3-2-3 Marunouchi, Chiyoda-ku, Tokyo F-term in Nikon Corporation (reference) 2F065 AA03 AA20 BB27 CC19 EE08 FF01 FF04 FF51 GG02 JJ03 JJ26 LL30 LL50 MM22 PP12 QQ14 QQ29 TT02 5F046 BA04 DA13 EA03 EA12 EB01 EC05 FA10 FA16 FB04 FB09 FB12 FC04

Claims (11)

[Claims] 1. An aberration measuring method for measuring predetermined aberration information of a detection optical system for condensing a light beam from a test mark, comprising: a plurality of focuses different from each other via the detection optical system And detecting relative position information regarding relative positions of the first and second marks having different line widths from each other at the position, and detecting the relative position information detected at the plurality of focus positions. An aberration measurement method, wherein the predetermined aberration information is obtained based on change information. 2. The aberration measurement method according to claim 1, wherein the predetermined aberration information is low-order coma aberration including a relatively large number of distortion components of a predetermined order or less as a distortion component of a wavefront. . 3. The relative position information includes a first relative distance between the first and second marks, and the line width is substantially the same at the plurality of focus positions via the optical system for detection. Detecting a second relative interval between the third and fourth marks having the following. The change information is a change amount of the difference between the first relative interval and the second relative interval between the plurality of focus positions. The aberration measurement method according to claim 1, wherein the method includes: 4. An image of the test mark is detected at a plurality of focus positions different from each other via the optical system, and asymmetry of the image of the detected mark is converted into change information according to the focus position. Based on the specific aberration information of the optical system including the low-order coma aberration, and subtracting the low-order coma aberration from the specific aberration information, the order larger than the predetermined order as a distortion component of the wavefront. 4. The aberration measuring method according to claim 3, wherein a higher-order coma aberration including a relatively large amount of distortion component is obtained. 5. The method according to claim 1, wherein at least a part of an optical member constituting the optical system is adjusted based on the predetermined aberration information obtained by the aberration measurement method according to claim 1. A mark detection method comprising: detecting position information of a mark formed on a substrate via an adjusted optical system. 6. An exposure method comprising: positioning the substrate based on position information of the mark detected by the mark detection method according to claim 5; and transferring a predetermined pattern onto the positioned substrate. Method. 7. An aberration measuring method for measuring aberration information of a detection optical system for condensing a light beam from a test mark, wherein the predetermined mark is provided at a plurality of different focus positions via the optical system. Detecting the first aberration information of the optical system based on the change information according to the focus position of the detected position information of the image of the predetermined mark, and detecting the detected predetermined mark. The second aberration information of the optical system is obtained based on the change information according to the focus position, which is the asymmetry of the image, and the predetermined aberration information is obtained based on the first and second aberration information. Aberration measurement method. 8. The first aberration information is a low-order coma aberration including a relatively large number of distortion components of a predetermined order or less as a distortion component of a wavefront, and the second aberration information is obtained by converting the first aberration information to The predetermined aberration information is the first aberration information from the second aberration information.
8. The aberration measurement method according to claim 7, wherein the wavefront distortion component obtained by subtracting the aberration information is a high-order coma aberration including a relatively large number of distortion components of an order larger than the predetermined order. 9. The aberration measuring method according to claim 7, wherein the predetermined mark includes a plurality of line-shaped marks having different line widths. 10. An optical member constituting the optical system, wherein at least a part of the optical member is adjusted based on the first aberration information obtained by the aberration measurement method according to claim 7. A mark detecting the position information of the mark formed on the substrate via the adjusted optical system, and correcting the detected position information of the mark based on the predetermined aberration information; Detection method. 11. A method according to claim 10, wherein the substrate is positioned based on the position information of the mark obtained by the mark detecting method according to claim 10, and a predetermined pattern is transferred onto the positioned substrate. Method.