JP3064432B2 - Projection exposure apparatus, projection exposure method, and circuit manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a projection exposure apparatus, and more particularly to a projection optical apparatus for manufacturing a semiconductor integrated circuit requiring high-precision imaging characteristics.

[0002]

2. Description of the Related Art In recent years, a super LSI having a circuit line width of the order of submicron has been produced. With this, a projection exposure apparatus used in an optical lithography process for transferring and exposing a mask pattern onto a semiconductor wafer. Are increasingly demanding highly accurate devices.

[0003] As a projection exposure apparatus of this type, a stepper for reducing, projecting and transferring a pattern image of a reticle of an enlarged mask while sequentially moving a wafer is a mainstay. This stepper is required to project a reticle pattern superimposed on a pattern of a previous process already formed on a wafer with an alignment accuracy of about 1/5 to 1/10 of the resolution line width. In addition, since the manufacture of one LSI usually requires about 20 to 30 lithography steps, a plurality of steppers are required to optimize productivity.
For this reason, the distortion of the projection optical system of each stepper,
It is easily understood that the imaging characteristics such as the projection magnification must be matched to each other with an error of about 0.1 μm or less.

For this reason, the distance between the lens elements constituting the projection optical system must be adjusted with high precision at the time of assembly. However, at the stepper production stage, LSI
It is actually difficult to match the distortion (distortion) and magnification of the projection optical system of each device on the production line. Therefore, a drive element is attached to a part of the lens element (lens element) of the projection optical system, and when the apparatus is installed on the LSI production line, it is possible to accurately adjust the magnification and the field distortion of each apparatus. It is considered.

FIG. 5 is a simplified view of the structure of this mechanism.
The pattern of the reticle 101 is
The projection is transferred onto the work piece 103. Of the projection optics,
The three lens elements on the reticle side are drivable. As shown in the figure, the two lens elements on the reticle side are group A, and the three lens elements on the reticle side are group B. Here, the lens elements of the group A or the group B can be integrally tilted and translated in the vertical or horizontal direction.

FIG. 3 schematically shows an example of a change in an image due to the driving of the lens element. For example, when the lens elements (A) and (B) are viewed from above, they are tilted with R as the rotation axis as shown in FIG. In this case, when only the lens element of the A group is tilted, the image portion far from the rotation axis R is greatly deformed in the direction perpendicular to the rotation axis R as shown in FIG. When only the lens elements of the B group are tilted, the image portion close to the rotation axis R is greatly deformed in the direction perpendicular to the rotation axis R as shown in FIG.

For example, when both are inclined at the same time (however, (b) is in the opposite direction), as shown in (c) of the figure, the displacement is effected so that the effects of both are added, and the correction for the platform formation can be performed. As described above, by appropriately selecting the inclination directions and the amounts of the two lens element groups, it is possible to correct an asymmetric distortion component. The asymmetric distortion here includes so-called trapezoidal distortion due to the inclination of the reticle. If the lens element is translated in the vertical direction, the magnification of the image can be changed.

[0008]

However, when the lens is moved or tilted by a very small amount by the driving element, the image plane moves up and down or tilts accordingly.
For example, field curvature may occur. For this reason, although the pattern alignment accuracy can be improved, there is a problem that image quality is degraded due to defocus, and line width accuracy (substantial resolution) is reduced.

In particular, when the correction of the tilt component of the reticle and the correction due to the change in the atmospheric pressure are performed during the operation of the manufacturing line, it is difficult to stop the line each time and then measure the image plane again and readjust it. , Not allowed in terms of productivity.

SUMMARY OF THE INVENTION The present invention has been made in view of such problems, and corrects out-of-focus due to inclination or curvature of an image plane, thereby preventing distortion of line width accuracy and preventing distortion and magnification from being reduced. It is an object of the present invention to provide an apparatus and a method which can be adapted to the following.

[0011]

To solve the above problems, for example, in the invention according to claim 1, a mask (R) on which a predetermined pattern is formed is illuminated, and an image of the pattern is projected onto a projection optical system. In a projection exposure apparatus that forms an image on a projection target substrate (W) in a predetermined imaging state via (PL), some optical elements (6, 7, 8) of a projection optical system (PL) are projected. First control means (1) for adjusting the image formation state of the image of the pattern of the mask by inclining with respect to the optical axis of the optical system.
0, 11, 24, 25) and the image plane of the projection optical system according to the inclination of some optical elements of the projection optical system so that the image plane of the projection optical system and the surface of the substrate to be projected substantially coincide with each other. (IM)
And a second control means (14, 16, 21, 25, 27) for adjusting a relative positional relationship between the control unit and the projection target substrate.

[0012]

According to the first aspect of the present invention, some of the optical elements (6, 7, 8) of the projection optical system (PL) are inclined with respect to the optical axis of the projection optical system. Even if the image plane changes in the projection optical system (PL), the projection optical system (P
L) depending on the inclination of some of the optical elements (6, 7, 8)
Since the relative positional relationship between the image plane (IM) of the projection optical system and the projection target substrate is adjusted, the influence of a change in the image plane can be minimized.

Therefore, according to the present invention, a change in the imaging plane caused by driving the mask or the lens element of the projection optical system can be canceled, so that a good imaging state can be always maintained.

[0014]

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a plan view showing a schematic configuration of a projection optical device (stepper) according to an embodiment of the present invention. In FIG. 1, an illumination light source 1 for exposure, such as an ultra-high pressure mercury lamp or an excimer laser light source, has a wavelength range (exposure) for exposing a resist layer of g-line, i-line, or ultraviolet pulse light (for example, KrF excimer laser). (Illumination light IL) in the wavelength range, and the illumination light IL reaches the illumination optical system 2 including an optical integrator (fly-eye lens) and the like.

The illuminating light IL, in which the luminous flux has been made uniform and the speckle has been reduced in the illuminating optical system 2, reaches the mirror 4 through the main condenser lens 3, where it is reflected vertically downward. The pattern area PA of the reticle R is illuminated with uniform illuminance. The reticle R is placed on a reticle stage 5 that can move two-dimensionally in a horizontal plane, and is positioned so that the center point of the pattern area PA coincides with the optical axis AX. The initial setting of the reticle R is performed by finely moving the reticle stage 5 based on a mark detection signal from a reticle alignment system (not shown) that photoelectrically detects an alignment mark (not shown) around the reticle.

The illumination light IL that has passed through the pattern area PA is incident on a projection optical system PL that is telecentric on both sides. The projection optical system PL forms a projection image of the circuit pattern of the reticle R, and a resist layer is formed on the surface. The surface is superimposed and projected (imaged) on one shot area on the wafer W held so that its surface substantially coincides with the image plane IM. The wafer W is vacuum-sucked on a wafer holder (θ table) 12, held on a leveling stage 13 via the holder 12, and can be tilted in an arbitrary direction with respect to the image plane IM by a drive motor 14. . The configuration of the leveling stage 13 is described in, for example,
-274201.

The leveling stage 13 is provided on a Z stage 15 which can be finely moved in the optical axis direction (Z direction) by a drive motor 16, and the Z stage 15 is two-dimensionally driven by a drive motor 19 in a step-and-repeat manner. When the reticle R is placed on the movable XY stage 15 and the transfer exposure of the reticle R to one shot area on the wafer W is completed, stepping is performed to the next shot position. The two-dimensional position of the XY stage 18 is constantly detected by the interferometer 20 with a resolution of, for example, about 0.01 μm.
A movable mirror 17 that reflects the laser beam from the interferometer 20 is fixed to an end of the Z stage 15.

FIG. 1 also shows an off-axis type alignment system 28 which is mechanically fixed at a fixed interval from the projection optical system PL and magnifies and observes an alignment mark using an image pickup device such as an ITV or a CCD camera. Have been. The alignment system 28 irradiates the alignment mark on the wafer with white light, thereby simultaneously observing the index mark and the alignment mark of the index plate (focusing plate) arranged almost conjugate with the wafer W. The image signal from the image sensor is input to the alignment signal processing circuit 29, where the amount of shift of the mark image with respect to the index mark is detected based on the signal waveform. The main control unit 25 inputs the position information from the interferometer 20 together with the information on the deviation amount, and obtains the position (coordinate value) of the alignment mark based on the information.

Next, the configuration of the projection optical system PL constituting the first control means of the present invention together with the drive elements 10, 11 and the lens control unit 24 in the apparatus of the present embodiment will be described. This first control means makes the imaging characteristics of the projection optical system substantially the same among a plurality of steppers,
This is for controlling the image formation state (distortion aberration, projection magnification, etc.) of the image of the mask pattern to a predetermined value according to the shape distortion of each shot area due to expansion and contraction of the wafer.

The components of the projection optical system PL are movable. As shown in FIG.
The first group of lens elements 6 and 7 closest to are fixed integrally by a lens support member 30, and the second group of lens elements 8 are fixed by a lens support member 31. The lens elements below the lens element 9 are fixed to the lens barrel 32 of the projection optical system PL (here, the optical axis AX of the projection optical system PL is the lens barrel 3).
2 means the optical axis of the lens element).

The lens support member 31 moves in the optical axis direction (Z direction).
Sets of drive elements 11a, 11b, 11c which can be extended and retracted
(11c is not shown), the lens barrel 3 of the projection optical system PL
It is connected to 2. Similarly, the lens support member 30
Are three sets of extendable drive elements 10a, 10b, 10c
(10c is not shown) is connected to the lens support member 31. Here, the lens elements 6, 7, and 8 close to the reticle R can be moved, and these elements are easier to control the influence on magnification and distortion characteristics than other lens elements (that is, deterioration of other aberrations). Are few).

The movement of the lens element is performed within a range where the influence on other aberrations (eg, astigmatism) of the projection optical system PL can be ignored. Alternatively, a method is also conceivable in which the magnification and distortion characteristics are controlled and other aberrations are corrected by adjusting the distance between the lens elements.

Further, in order to sufficiently cope with the shape distortion of the shot area, it is necessary to increase the moving range of the lens element while suppressing other aberrations, and various shape distortions (trapezoidal, rhombic, barrel, pincushion) Type, etc.). For this purpose, the movable lens groups are 2
The present invention is not limited to the group configuration, and may be configured by, for example, three or more lens groups that satisfy the condition (1).

FIG. 2 is a view of the projection optical system PL as viewed from above (the reticle side). The driving elements 10a, 10b, and 10c are arranged at positions rotated by 120 °, respectively. Independent control is possible by the lens control unit 24. Drive elements 11a, 11b, 1
1c is similarly arranged at a position rotated by 120 °. 10a and 11a are arranged so as to be shifted from each other by 60 °, and 10b and 11b,
Similarly, 10c and 11c are also arranged so as to be shifted from each other by 60 °.

The driving elements 10 and 11 use, for example, an electrostrictive element or a magnetostrictive element. The amount of displacement of the drive element according to the voltage or magnetic field applied to the drive element is determined in advance. In consideration of the hysteresis of the drive element, if a capacitive position sensor, differential transformer, etc. is installed near the drive element as a position detection device, the position of the drive element corresponding to the voltage or magnetic field applied to the drive element should be monitored. Therefore, highly accurate driving is possible.

Thus, three points around the two lens elements (6, 7) and 8 are moved to the optical axis A of the projection optical system PL.
It can be independently moved in the X direction according to the drive amount of each drive element. As a result, each of the lens element groups (6, 7), 8 can be inclined with respect to a plane perpendicular to the optical axis AX. Note that the lens is inclined about the virtual optical axis of the lens elements 6, 7, 8 (optical axis AX when there is no inclination).

In the main controller 25, the drive amounts of the drive elements 10 and 11 are calculated by calculation in accordance with the imaging characteristics of the projection optical system PL of the plurality of steppers, and a drive command corresponding to the result is obtained. Is transmitted to the lens control unit 24, and the lens control unit 24 drives the driving elements 10 and 11 independently. As a result, the image forming characteristics of the projection lens PL are set to the predetermined values, and the image forming characteristics of each stepper substantially match.

The distortion characteristics of the projection optical system are changed by driving the two lens units as described above. These two lens groups
For example, when the first group tilts the lens element with the vertical bisector of the driving elements 10a and 10c as the virtual rotation axis RL, the first group rotates the image portion away from the rotation axis RL as shown in FIG. This is a lens group having a characteristic of largely deforming in a direction perpendicular to the axis RL. For example, when the second lens unit tilts the lens element about the same virtual rotation axis RL,
As shown in FIG. 3 (b), the lens group has a characteristic of largely deforming an image portion close to the rotation axis RL in a direction perpendicular to the rotation axis RL.

Since each of these lens groups can give an innumerable virtual rotation axis equivalently, each of the lens groups also has an infinite number of directions regarding image deformation. Therefore, the specific directionality of the image deformation determined by each lens group is obtained as a vector sum, and the distortion characteristics of each lens group are combined (the vector sum is obtained) to obtain a trapezoidal distortion, a rhombic distortion, or the like. The projection images can be superimposed even on anisotropic shape distortion.

The lens elements 6, 7, 8
Is moved two-dimensionally in an XY plane perpendicular to the optical axis AX, the distortion characteristic of the projection optical system can be changed anisotropically. In this case, the driving element is X
What is necessary is just to arrange | position in the direction which displaces in a Y plane, and to make a lens element movable in an XY plane. For example, two drive elements displaceable in the X direction are provided at positions facing each other along the X axis, and two drive elements displaceable in the Y direction are provided at positions facing each other along the Y axis.

Next, the focus detection system 21 for detecting the in-focus state between the wafer W and the projection optical system PL will be described. In FIG. 1, an image forming light beam for forming an image of a pinhole or a slit toward an image forming plane IM of the projection optical system PL is supplied obliquely with respect to the optical axis AX via a beam splitter 23a. An oblique incidence type focus detection system 21 including an irradiation optical system 21a and a light receiving optical system 21b that receives a light beam reflected by the surface of the wafer W of the image forming light beam via a beam splitter 23b is provided.

The configuration of the focus detection system 21 is as follows.
For example, Japanese Patent Application Laid-Open No. 60-1681 filed by the present applicant earlier
No. 12 discloses an image forming surface IM of a wafer surface.
Of the wafer W in the vertical direction (Z direction) with respect to
And a focus state of the projection optical system PL.

Here, in the present embodiment, the sensor control section 26 outputs an offset signal to the light receiving optical system 21b so that the best focus position of the projection optical system in the focus detection system 21 becomes a zero point reference. Then, the angle of the parallel flat glass (not shown) provided inside the light receiving optical system 21b is adjusted according to the offset signal, and the zero point calibration of the focus detection system 21 is performed. As a result, the main control unit 25 controls the Z stage 15 to a zero point in a closed loop, that is, by driving the motor 16 via the stage controller 27 based on a detection signal from the focus detection system 21, so that the best condition is always obtained. The focus position almost coincides with the wafer surface.

Further, the parallel light beam is transmitted to the beam splitter 2.
A horizontal position composed of an irradiation optical system 22a for supplying an oblique direction with respect to the optical axis AX via the optical axis AX and a light receiving optical system 22b for receiving, via a beam splitter 23b, a parallel light beam reflected on the surface of the wafer W via a beam splitter 23b. A detection system 22 is provided. The configuration of the horizontal position detecting system 22 is described in, for example, Japanese Patent Application Laid-Open No.
It is disclosed in Japanese Patent No. 3706 and detects the inclination of a predetermined area on the wafer W with respect to the image plane IM.

In the horizontal position detecting system 22, as in the case of the focus detecting system 21, the sensor control unit is so set that the best image forming plane of the projection optical system PL taking into account the image plane inclination and the field curvature becomes the zero point reference. 26 outputs an offset signal to the light receiving optical system 22b.

That is, when the wafer surface coincides with the best imaging plane, the light beam from the irradiation optical system 22a is
It is assumed that the horizontal position detection system 22 has been calibrated so as to be condensed at the center position of the four-divided light receiving element (not shown) inside 2b. As a result, the main control unit 25
By controlling the leveling stage 13 in a closed loop, that is, by driving the motor 14 via the stage controller 27 based on a detection signal from the horizontal position detection system 22, the best imaging surface and the wafer W The surface of the predetermined area is almost the same.

Here, in the present embodiment, the main controller 25 obtains the best image forming plane (including the best focus position) of the projection optical system PL by trial printing or the like in advance, and performs sensor control on the information regarding the best image forming plane. Output to the unit 26. Then, the sensor control unit 26 gives an offset signal corresponding to the information to each of the light receiving optical systems 21b and 22b, thereby performing offset setting for the focus detection system 21 and the horizontal position detection system 22. Also, when the imaging characteristics between the steppers are made to coincide with each other at the time of initialization of the stepper (hereinafter, referred to as matching), trial printing or the like is performed after driving the lens elements 6, 7, and 8, and the imaging characteristics are obtained. It is desirable to check.

The main control section 25 stores therein data relating to the driving amounts (displacement amounts of the driving elements 10, 11) of the lens elements 6, 7, 8 from the initial state at the time of matching as initial data therein. Shall be kept. Also, since the imaging characteristics of the projection optical system PL may fluctuate in the matching operation, the calibration of the focus detection system 21 and the horizontal position detection system 22 is performed by the lens element 6,
This is performed at the time when the matching operation by the driving of 7 and 8 is completed. In the present embodiment, the focus detection system 21 and the horizontal position detection system 22 are optically offset. However, for example, the detection signals from the light receiving optical systems 21b and 22b are electrically offset. It does not matter.

Next, when correcting the distortion or the magnification in accordance with the wafer shape distortion or the like, the fluctuation of the image plane IM caused by driving the lens elements 6, 7, 8
That is, an operation for correcting a deviation between the best image forming plane and the wafer surface due to the image plane inclination or curvature will be described.

FIG. 4 (a) shows how the image plane tilt when the lens element C of the projection optical system PL is tilted in order to control the distortion or projection magnification of the image of the reticle pattern as described above. This is a schematic drawing of what will occur. This figure shows a state in which the image plane IM is inclined by an angle θ as compared to before the driving of the lens element C (indicated by a dotted line in the figure). However, since the lens interval is not changed, no curvature of field occurs.

In this embodiment, the lens element group (6,
7) or how one of (6, 7, 8) or both are driven simultaneously, how the image plane changes is determined in advance by experiment or simulation, etc.
The above relationship is stored in a storage unit or the like inside the main control unit 25 in the form of a table or a mathematical expression. The main control unit 25 calculates the image plane tilt amount from the drive amount of the lens element group using these tables or mathematical expressions.

The calculated inclination amount is calculated by the sensor controller 26.
And an offset is set in the horizontal position detection system 22 as in the calibration operation. As a result, the image plane inclined by a predetermined amount becomes the zero point reference of the horizontal position detection system 22. By controlling the leveling stage 13 based on the detection signal of the horizontal position detection system 22, the image plane becomes parallel to the image plane. The wafer is tilted so that

On the other hand, the field curvature occurs when the lens element interval is changed to correct the projection magnification. This is schematically illustrated in the example of FIG. In the figure, when the distortion and the magnification are corrected at the same time, for example, the imaging surface originally matching the reference surface 41 of the detection systems 21 and 22 changes to the surface 42 by the calibration operation.

At this time, when no correction is made for the image plane tilt and the image field curvature, that is, when no offset is given to the focus detection system 21 and the horizontal position detection system 22, the wafer surface is set to the reference. It is fitted to the surface 41. However, in the present invention, since the correction is made for the curvature of field as well as the tilt of the image plane, the surface of the wafer can be adjusted to the best image plane 43 determined from the plane 42.

That is, in this case, the average position of the image plane 42 (the best imaging plane 43) is determined by, for example, the method of least squares or the method of minimizing the maximum error by using the above-described mathematical expression in the main control unit 25. Etc. The position 43 is instructed to the sensor control unit 26 as a zero point reference for the detection systems 21 and 22.

Thus, an offset is set in the detection systems 21 and 22. That is, the reference plane 41 coincides with the best imaging plane 43 in FIG. When only the curvature of field occurs, it goes without saying that the offset may be set only for the focus detection system 21.

Thus, the lens elements 6, 7
Alternatively, the focus detection system 21 and the horizontal position detection system 22 detect the deviation between the best image plane and the wafer surface due to the inclination or curvature of the image plane, which is generated when driving 6, 7, 8 to correct the distortion or magnification. Can be corrected by giving an offset.

Now, the operation of the apparatus having the above configuration will be briefly described. As shown in FIG. 1, the main control unit 25 executes a matching operation prior to the exposure operation so that a difference in distortion among all exposure apparatuses used until the semiconductor element is completed is minimized. The calibration of the focus detection system 21 and the horizontal position detection system 22 is performed based on the imaging characteristics.

As a result, the detection reference planes of the detection systems 21 and 22 almost coincide with the best imaging planes.
If the Z stage 15 and the leveling stage 13 are controlled based on the detection signal from 22, the surface of the shot area on the wafer W and the best imaging plane can be accurately matched.

Next, as disclosed in, for example, JP-A-61-44429, the main control unit 25 uses the alignment system 28 to attach to a plurality of (3 to 15) shot areas on the wafer. After measuring the positions of the two sets of alignment marks (sample alignment), the shot arrangement coordinates on the wafer (stepping coordinates of the wafer stage) are calculated by statistical calculation based on these measured values.

Further, the main controller 25 includes an alignment system 28
In addition to the alignment marks, the position of the shape distortion measurement pattern provided at, for example, the four corners of the shot area is measured, and the shape distortion of the shot area is calculated based on the measurement result. At this time, shape distortion may be obtained for all shot areas on the wafer, but time is required for position measurement.

Therefore, in this embodiment, the shot area on the wafer is divided into several areas (blocks), and the shape distortion of only a part of the shot area in each block is obtained. It is desirable to set each block so that the shape distortion is considered to have substantially the same property. And
By averaging the measured values for each block, the shape distortion of the shot area is determined for each block.

Next, the main controller 25 calculates the amount of drive of the lens elements 6, 7, 8 for each block on the basis of the shape distortion, and forms an image plane produced by driving the lens elements 6, 7, 8 Is obtained for each block, and the best imaging plane IM of the projection optical system PL is determined from the calculation result.

In the exposure operation, the main control unit 25 drives the lens elements 6, 7, 8 by the lens control unit 24 for each block according to the above calculation result, and sets the image forming characteristics to predetermined values. An offset is set in the focus detection system 21 and the horizontal position detection system 22 by the sensor control unit 26, and the best imaging plane is set as a zero point reference.

Thereafter, the main control unit 25 uses the detection systems 21 and 22 for each shot to make the best imaging plane and the surface of the shot area substantially coincide with each other, and adjusts the wafer stage in accordance with the shot arrangement coordinates previously obtained. 18 is univocally moved, and the projected image of the reticle pattern and the shot area on the wafer are sequentially superimposed to perform exposure.

As a result, the projected image of the reticle pattern and the shape of the shot area almost coincide with each other regardless of the shape distortion due to the expansion and contraction of the wafer in all the shot areas on the wafer, and high-accuracy overlay exposure can be performed. Main control unit 2
5 indicates that after the superposition exposure of the first wafer is completed, the imaging characteristics of the projection optical system PL are set to the initial values by driving the lens elements 6, 7, 8 based on the initial data stored previously. By setting and performing pattern exposure by the same operation as described above, high-precision overlay can be realized on all wafers.

Since the expansion and contraction characteristics of the wafers stored in the same lot are considered to be substantially the same, the shape distortion of the shot area on the wafer is measured only for the first wafer and the second wafer is measured. For the wafers after the first lens, the lens elements 6, 7, 8 may be driven based on the data of the first wafer.

In this embodiment, the shape distortion of the shot area is obtained by actually measuring the position of the pattern for measuring the shape distortion. However, the method of obtaining the shape distortion may be arbitrary. In the case where the shape is deformed as described above, it is possible to obtain not only the shot arrangement coordinates but also the shape distortion by a statistical operation at the time of alignment. Furthermore, here, the shape of the projected image of the reticle pattern is controlled to a predetermined value by driving the lens element for each block, but for example, an average shape distortion of a shot area on a wafer is obtained, and only once before exposure. The shape of the projected image may be controlled by driving the lens element, or the shape of the projected image may be controlled for each shot.

It is not necessary to set an offset for the detection systems 21 and 22 each time the lens element is driven. In practice, the amount of change in the imaging plane due to the driving of the lens element is a predetermined allowable value. The offset may be set with respect to the detection systems 21 and 22 only when the number exceeds the threshold value.
At this time, the detection systems 21 and 22 may be electrically offset.

Here, for example, the distortion characteristic (initial value) of the projection optical system when the apparatus is started may change over a long period of time. This is because the stress generated at the time of manufacturing is released for a long period of time, and can be almost prevented by management in manufacturing. However, the above change may rarely occur. In such a case, the lens elements 6, 7, and 8 are driven according to the above change, and the distortion characteristics of the projection optical system (the same applies to the projection magnification and the like) are reset to new initial values.

As a result, the fluctuation of the distortion characteristic of the projection optical system due to the above change can be substantially suppressed, and a state where there is almost no distortion is always set as the initial value. When performing the above operation,
It is necessary to set the initial values of the detection systems 21 and 22 again, that is, set an offset for the detection systems 21 and 22 again.

In the present embodiment, the amount of change in the imaging plane of the projection optical system that occurs in accordance with the driving of the lens element is obtained by calculation as a function of the amount of driving of the lens element. If the amount of change in the image plane can be measured directly, sequentially, or when the lens element is driven,
There is no need to perform the above operation. In addition, the amount of change in the imaging plane can be determined with higher accuracy. Can be suppressed.

However, actually, the amount of change of the image plane,
That is, it is very difficult to directly and sequentially measure the focus positions at a plurality of points in the exposure field of the projection optical system, and it is particularly difficult to measure the focus position near the center of the exposure field. An example of a known measurement method will be briefly described.

Generally, a TTR for aligning a projected image of a reticle pattern with a circuit pattern on a wafer is used.
In the case of an exposure apparatus equipped with a (through-the-reticle) type alignment sensor, a method of measuring the amount of change using the alignment sensor, for example, projecting a reference mark provided on a wafer stage by the alignment sensor There is known a method of observing through an optical system and obtaining a focus position from the contrast.

In this method, an image of a reference mark observed by an alignment sensor (microscope) provided above the reticle is taken in, and for example, the difference between the maximum value and the minimum value of the amount of received light is obtained to obtain the contrast thereof. By moving the wafer stage up and down, the height position of the stage having the best contrast is determined.

Therefore, when the distortion characteristic is corrected by driving the lens element, the focus position (image plane position) is obtained at a plurality of positions in the exposure field (corresponding to the image plane) by the above method. The amount of change in the surface may be determined, and an offset may be set for the detection systems 21 and 22 according to the determined amount of change.

The focus detection system and the horizontal position detection system may be arbitrary, for example, may be configured to irradiate a plurality of slit images having different wavelengths into the exposure area to simultaneously detect the focus and tilt.

In the above-described embodiment, the imaging state of the projection optical system PL is controlled to a predetermined value by driving the lens elements 6, 7, and 8. However, the same applies when the reticle R is driven. The effect can be obtained. In particular, when controlling a pincushion-type or barrel-type distortion, it is effective to tilt the reticle.

For this reason, the distortion may be controlled by driving the reticle together with the lens element. In the case of a double-sided telecentric projection optical system, the projection magnification cannot be controlled even if the reticle is moved up and down. In such a case, the distortion is controlled by the inclination of the reticle, and the projection magnification is moved up and down, or a sealed space is formed between the two lens elements to control the pressure in the sealed space. The adjustment may be made by the following.

For example, when controlling the distortion by controlling the inclination of the reticle and adjusting the projection magnification by controlling the pressure in the sealed space, the focus detection system 21 and the horizontal position detection system 22 can be used without using the projection optical system. By driving at least a part of the lens elements, it is possible to prevent a change in the imaging plane caused by the adjustment of the distortion and the projection magnification, thereby suppressing the deviation amount between the best imaging plane and the wafer surface to almost zero. It becomes possible. In addition,
In the projection optical apparatus shown in FIG. 1, data or calculation formulas relating to the relationship between the amount of drive of the mask or the lens element of the projection optical system and the change amount of the image plane are stored in advance in the control unit as mathematical formulas or tables. ing. Then, in the arithmetic means, the amount of change in the imaging plane caused by the driving of the mask or the lens element is calculated based on the data and the like, and the correction amount is calculated. Then, the correction amount is input as an electrical or optical offset to the means for detecting the inclination of the wafer as the workpiece and correcting the inclination and the focusing means, and corrects the variation. Thereafter, the image forming plane of the projection optical system and the wafer surface are made substantially coincident by using the above two means. In this way, it is possible to minimize the influence of the inclination of the image plane or the curvature of the image plane that occurs when adjusting the magnification.

[0071]

As described above, according to the present invention, in a stepper for driving a part of lens elements of a projection optical system to correct a distortion or a projection magnification, the inclination or curvature of an image plane generated at the time of correction can be reduced. By correcting the target position of the inclination correcting means or the focusing means, it is possible to minimize the defocus on average.

For this reason, the distortion or the projection magnification can be corrected without lowering the line width accuracy of the circuit, so that the shape of the projected image of the mask pattern can be controlled in accordance with the shape change of the predetermined area due to the expansion and contraction of the substrate. In addition, it is possible to improve the alignment accuracy in the entire exposure region, thereby improving the LSI manufacturing yield.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an embodiment of an apparatus according to the present invention.

FIG. 2 is a view of the projection optical system according to the embodiment of the present invention as viewed from above.

FIG. 3 is a conceptual diagram showing a deformation of an image due to driving of a lens element.

FIG. 4 is a schematic view showing occurrence of an image plane inclination accompanying driving of a lens element.

FIG. 5 is a simplified schematic diagram of a lens element driving mechanism.

[Explanation of symbols]

 R Reticle PL Projection optical system 6, 7, 8 Driven lens element 13 Leveling stage 15 Z stage 21 Focus detection system 22 Horizontal position detection system

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int. Cl. ⁷ , DB name) H01L 21/027 G03F 7/20

Claims (29)

(57) [Claims] 1. A projection exposure apparatus which illuminates a mask on which a predetermined pattern is formed and forms an image of the pattern on a substrate to be projected in a predetermined imaging state via a projection optical system. A first control unit that adjusts an image forming state of an image of the pattern of the mask by inclining a part of optical elements of the optical system with respect to an optical axis of the projection optical system; and an image plane of the projection optical system. And the relative positional relationship between the image plane of the projection optical system and the projection target substrate in accordance with the inclination of a part of the optical elements of the projection optical system so that the surface of the projection target substrate substantially matches the surface of the projection target substrate. A projection exposure apparatus, comprising: second control means for adjusting. 2. The image processing apparatus according to claim 1, wherein said second control means is configured to control an image plane of said projection optical system and said projection target in accordance with a change in an image plane of said projection optical system caused by an inclination of a part of optical elements of said projection optical system. 2. The projection exposure apparatus according to claim 1, wherein the projection exposure apparatus moves relatively to a substrate. 3. The projection exposure apparatus according to claim 1, wherein a part of the optical elements of the projection optical system includes a plurality of lens groups each of which can be tilted independently. 4. The image forming apparatus according to claim 1, wherein the adjustment of the image forming state is performed in consideration of an image forming characteristic of a projection optical system in another projection exposure apparatus. Projection exposure equipment. 5. A projection according to claim 1, wherein said part of optical elements is inclined to adjust a magnification of a projection image formed by said projection optical system. Exposure equipment. 6. The projection according to claim 1, wherein the optical elements are inclined to adjust a distortion of a projection image formed by the projection optical system. Exposure equipment. 7. A circuit manufacturing method using the device according to claim 1. 8. A projection exposure method for illuminating a mask on which a predetermined pattern is formed, and forming an image of the pattern on a substrate to be projected in a predetermined image formation state via a projection optical system. Tilting some optical elements of the projection optical system with respect to the optical axis of the projection optical system in order to adjust the image formation state of the image of the pattern; and the image plane of the projection optical system and the substrate to be projected. A relative position relationship between an image plane of the projection optical system and the projection target substrate is adjusted in accordance with the inclination of the optical element so that the surface substantially coincides with the surface of the projection optical system. 9. A relative positional relationship between the image plane of the projection optical system and the substrate to be projected in consideration of a change in the image plane of the projection optical system caused by the inclination of some optical elements of the projection optical system. The projection exposure method according to claim 8, wherein is adjusted. 10. The image plane change of the projection optical system caused by the inclination of some optical elements of the projection optical system includes a change in the position of the image plane in the optical axis direction of the projection optical system. The projection exposure method according to claim 8 or 9, wherein 11. The projection exposure method according to claim 8, wherein the change in the image plane of the projection optical system caused by the inclination of the optical element includes a change in the inclination of the image plane. 12. The projection exposure method according to claim 8, wherein the change in the image plane of the projection optical system caused by the inclination of the optical element includes a change in the curvature of the image plane. 13. The projection exposure according to claim 8, wherein the adjustment of the image forming state is performed in consideration of a shape distortion of a shot area on the projection target substrate. Method. 14. The projection exposure method according to claim 13, wherein the shape distortion of the shot area on the projection target substrate includes an anisotropic trapezoidal distortion. 15. The projection exposure method according to claim 13, wherein the shape distortion of the shot area on the projection target substrate includes an anisotropic rhombic distortion. 16. A projection exposure apparatus which illuminates a mask on which a predetermined pattern is formed, and forms an image of the pattern on a projection target substrate via a projection optical system in a predetermined image forming state. First control means for adjusting at least one of the projection magnification and distortion of the pattern image of the above, based on information on a change in the image plane inclination of the projection optical system caused by adjustment of at least one of the projection magnification and distortion. Second control means for adjusting the relative positional relationship between the image plane of the projection optical system and the substrate so that the image plane of the projection optical system substantially coincides with the surface of the substrate to be projected. A projection exposure apparatus. 17. The projection according to claim 16, wherein at least one of the projection magnification and the distortion of the pattern image of the mask is adjusted by moving some optical elements of the projection optical system. Exposure equipment. 18. The projection exposure apparatus according to claim 17, wherein some optical elements of said projection optical system are constituted by a plurality of lens groups each of which can move independently. 19. The apparatus according to claim 16, wherein the adjustment of at least one of the projection magnification and the distortion is performed in consideration of an imaging characteristic of a projection optical system in another projection exposure apparatus. Item 6. The projection exposure apparatus according to Item 1. 20. A circuit manufacturing method using the device according to claim 16. 21. A projection exposure method for illuminating a mask on which a predetermined pattern is formed, and forming an image of the pattern on a substrate to be projected in a predetermined image-forming state via a projection optical system. A projection exposure method for obtaining information on a change in image plane tilt of the projection optical system, which is caused by adjusting at least one of the projection magnification and distortion of the image of the pattern. 22. The projection exposure method according to claim 21, wherein the adjustment of at least one of the projection magnification and the distortion is performed by adjusting the position of a part of optical elements of the projection optical system. 23. The projection exposure method according to claim 22, wherein the position of the optical element is adjusted by adjusting a tilt amount of the projection optical system with respect to an optical axis. 24. The projection exposure method according to claim 21, wherein the adjustment of the distortion is performed by tilting the mask. 25. The apparatus according to claim 2, wherein at least one of the projection magnification and the distortion is adjusted in consideration of the shape distortion of the shot area on the projection target substrate.
25. The projection exposure method according to any one of 1 to 24. 26. The projection exposure method according to claim 25, wherein the shape distortion of the shot area on the projection target substrate includes an anisotropic trapezoidal distortion. 27. The projection exposure method according to claim 25, wherein the shape distortion of the shot area on the projection target substrate includes an anisotropic rhombic distortion. 28. The image plane of the projection optical system and the substrate to be projected such that the image plane of the projection optical system substantially coincides with the surface of the substrate to be projected based on the obtained information. 3. A relative positional relationship is adjusted.
28. The projection exposure method according to any one of 1 to 27. 29. A projection exposure method for illuminating a mask on which a predetermined pattern is formed and forming an image of the pattern on a substrate to be projected in a predetermined image-forming state via a double-sided telecentric projection optical system. Tilting the mask with respect to the optical axis of the projection optical system to adjust the distortion of the pattern image of the mask; and adjusting the projection magnification of the image of the pattern of the mask in the projection optical system. Controlling the pressure in the sealed space; preventing a change in the image plane of the projection optical system caused by adjusting the distortion and the projection magnification by moving some optical elements of the projection optical system. Projection exposure method.