JP2002195912A - Method and apparatus for measuring optical property, exposure apparatus and method for producing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately calculate the best focus position in a projection optical system, regardless of the condition of illumination. SOLUTION: A slit 22 is relatively scanned with respect to a spatial image of a pattern PM formed near the image plane of the projection optical system PL by an illuminating light, and a signal corresponding to the strength of the illuminating light passing through the slit is obtained at each of plural positions of a slit plate 90 in the optical axis direction. A tentative position as the best focus position is determined from a first contrast curve that is calculated based on the contrast values of these signals. A second contrast curve is obtained from the tentative position set as the central point by weighting the contrast values using a weighting function including weighting parameters in accordance with the condition of illumination, thereby determines the true best focus position. Accordingly, the weighting parameters are determined beforehand so that the measurement accuracy is not deteriorated in each condition of illumination. As a result, the best focus position can be accurately calculated, regardless of the condition of illumination.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical characteristic measuring method and apparatus, an exposure apparatus, and a device manufacturing method.
More specifically, an optical characteristic measuring method and apparatus for measuring optical characteristics of a projection optical system, an exposure apparatus for transferring a circuit pattern formed on a mask to a substrate via a projection optical system, and an exposure apparatus using the exposure apparatus The present invention relates to a device manufacturing method to be performed.

[0002]

2. Description of the Related Art Conventionally, when a semiconductor element or a liquid crystal display element is manufactured by a photolithography process, a pattern of a photomask or a reticle (hereinafter, collectively referred to as “reticle”) is formed on a surface through a projection optical system. Exposure apparatus for transferring onto a substrate such as a wafer or a glass plate on which a photosensitive agent such as a photoresist is coated, for example, a step-and-repeat type reduction projection exposure apparatus (so-called stepper), a step-and-scan method (A so-called scanning stepper) or the like is used.

However, when a semiconductor device or the like is manufactured using a projection exposure apparatus, an exposure region (a region irradiated with illumination light) on a substrate is required to minimize the occurrence of exposure failure due to defocus. ) Must be within the range of the depth of focus of the best imaging plane of the projection optical system. For this purpose, it is important to accurately measure the best imaging plane or the best focus position of the projection optical system and to calibrate the focus position detection system (focus detection system) based on the measurement result.

As one method of measuring the best focus position of a projection optical system, a measurement mark formed on a reticle, for example, a line and space mark, is illuminated with illumination light and a spatial image of the measurement mark formed by the projection optical system is illuminated. There is a method of measuring a (projected image) using an aerial image measurement device and calculating a best focus position based on the measurement result.

[0005] The calculation of the best focus position by the conventional aerial image measurement is generally performed as follows. That is, for a spatial image of a measurement mark formed near the image plane of the projection optical system, a rectangular aperture pattern or a slit-shaped aperture pattern (hereinafter, referred to as a “measurement pattern”) arranged on the image plane side of the projection optical system. (Collectively referred to as "scan"), and the illumination light passing through the measurement pattern is received by the photoelectric conversion element and photoelectrically converted to measure the spatial image of the measurement mark. The aerial image measurement of such a measurement mark is performed in a predetermined step by centering the position of the measurement pattern in the optical axis direction of the projection optical system around the position estimated as the best focus position (for example, the best focus position at the previous measurement). The process is repeated at a pitch, for example, at an interval of 0.15 μm while changing about 15 steps. Then, for example, a contrast value for, for example, a fundamental frequency component of each photoelectric conversion signal obtained for each position in the optical axis direction of the measurement pattern is obtained, and these contrast values are determined by a predetermined higher-order function (for example, a sixth-order function). The fitting was performed, and the position in the optical axis direction of the measurement pattern corresponding to the peak point of the obtained contrast curve was calculated as the best focus position.

As a method of calculating the best focus position with higher accuracy by removing the influence of noise or the like,
Recently, the contrast value is weighted using an appropriate weighting function (for example, Gaussian function) centered on the best focus position (temporary best focus position) obtained as described above, and the higher-order function is again performed. (For example, a quadratic function), and the position of the measurement pattern corresponding to the peak point of the obtained contrast curve in the optical axis direction is calculated as the best focus position.

Incidentally, when the apparatus is initialized and loses the best focus position of the projection optical system, or when the state of the apparatus fluctuates greatly due to an external factor and the best focus position fluctuates greatly, the above-mentioned situation occurs. As described above, the best focus position may not be detected even when the above-described best focus position is measured centering on the best focus position at the time of the previous measurement. In such a case,
Twice the step pitch during normal measurement (for example, 0.3 μm)
m) at a relatively large interval of about m) in the optical axis direction of the projection optical system while stepping the measurement pattern in the same manner as described above.
By performing aerial image measurement of steps and covering a large measurement range (measurement range twice as large as usual), after performing measurement (also called "rough measurement") to roughly search for the best focus position, it is obtained. By performing the above-described normal measurement (hereinafter, appropriately referred to as “fine measurement”) around the best focus position, the best focus position is detected with high accuracy.

[0008]

In recent years, projection exposure apparatuses such as steppers have been required to improve the resolution in accordance with the miniaturization of patterns, and various high-resolution techniques have been adopted for that purpose. Have been. As one of them,
There is a change in lighting conditions corresponding to the target pattern. The illumination conditions in the exposure apparatus are determined by the numerical aperture (N.
A. ) And the numerical aperture of the projection optical system are changed by changing the coherence factor (σ value).
This is because the distribution of the illumination light on the pupil plane is changed by changing the illumination system aperture stop in the illumination optical system. In the current exposure apparatus, illumination conditions of normal illumination (large σ illumination), small σ illumination, annular illumination, deformed illumination (for example, quadrupole illumination, etc.) are selectively set according to the target pattern. It has become.

As a result of various experiments (including simulations) performed by the inventors, weighting by a weighting function performed for the purpose of improving the accuracy in measuring the best focus position described above depends on the lighting conditions. On the contrary, it has been found that the measurement accuracy may be reduced.

More specifically, for example, in the case of normal illumination, annular illumination, and deformed illumination, the contrast value of the fundamental frequency of the photoelectric conversion signal obtained by aerial image measurement decreases as the distance from the best focus position increases. However, in the case of small σ illumination, in a certain range centered on the best focus position, the contrast value gradually decreases as the distance from the best focus position increases, but outside the certain range, the contrast increases again. I do. For this reason, a contrast curve obtained by function-fitting the contrast value has sub-peaks at both ends in addition to the central peak. In this case, if there is no aberration in the projection optical system, there is no major problem since the sub-peaks at both ends are symmetric with respect to the best focus position. However, since a considerable amount of aberration exists (remains) in an actual projection optical system, the left and right sub-peaks are asymmetric with respect to the best focus position as shown by a dotted line in FIG. 14 due to the influence of the aberration. Therefore, when the contrast value is weighted and function fitting is performed using the least squares method, an approximate curve Pu indicated by a solid line in FIG. 14 is derived, and the position BF ′ deviated from the actual best focus position BF is determined as the best focus position. It will be calculated as

When performing the above-described conventional rough measurement, in addition to the fine measurement, an extra measurement time equivalent to or longer than the fine measurement is used only for finding the center position in the fine measurement. Will be hung. However, since the measurement of the best focus position by the aerial image measurement is performed between normal exposures, the time required for the measurement causes a decrease in throughput. Therefore, it is required to reduce the time required for measuring the best focus position as much as possible.

The present invention has been made under such circumstances, and a first object of the present invention is to measure the best focus position of a projection optical system by using at least one of an accuracy surface and a time surface. It is an object of the present invention to provide a new optical characteristic measuring method and an optical characteristic measuring device which contribute to improvement of optical characteristics.

It is a second object of the present invention to provide an exposure apparatus capable of realizing highly accurate exposure.

A third object of the present invention is to provide a device manufacturing method which contributes to improvement in productivity of a highly integrated microdevice.

[0015]

An optical characteristic measuring method according to claim 1 is an optical characteristic measuring method for measuring an optical characteristic of a projection optical system (PL), wherein a predetermined pattern is measured by illumination light (IL). (PM), and forming a spatial image (PM ′) of the pattern near the image plane via the projection optical system; and a measurement pattern (22) arranged on the image plane side of the projection optical system. ) Is relatively scanned with respect to the aerial image, and a photoelectric conversion signal corresponding to the intensity of the illumination light via the measurement pattern is obtained for each of a plurality of positions in the optical axis direction of the measurement pattern. Obtaining a temporary best focus position of the projection optical system based on a first contrast curve obtained by curve fitting the contrast values of the photoelectric conversion signals obtained for each of the plurality of positions; Optics A second contrast curve including a weighting parameter determined according to an illumination condition for illuminating the system, weighting the contrast value using a weighting function centered on the temporary best focus position, and calculating a second contrast curve; Calculating a true best focus position of the projection optical system based on a contrast curve.

According to this, a predetermined pattern is illuminated by the illumination light, and is arranged on the image plane side of the projection optical system with respect to the spatial image of the pattern formed near the image plane via the projection optical system. Relative scanning of the measurement pattern
A photoelectric conversion signal corresponding to the intensity of illumination light via the measurement pattern is obtained for each of a plurality of positions in the optical axis direction of the measurement pattern. Then, a temporary best focus position of the projection optical system is obtained based on a first contrast curve obtained by curve-fitting the obtained contrast values of the plurality of photoelectric conversion signals, with the temporary best focus position as a center,
Further, a second contrast curve is calculated by weighting a contrast value using a weighting function including a weight parameter determined according to an illumination condition for illuminating the projection optical system, and the projection optical system is calculated based on the second contrast curve. Calculate the true best focus position. As described above, the second contrast curve for calculating the true best focus position by weighting the contrast value using the weighting function including the weight parameter determined according to the lighting condition centering on the temporary best focus position Is calculated, a weighting parameter can be determined in advance for each illumination condition so that the measurement accuracy under each illumination condition does not decrease. This allows the best focus position of the projection optical system to be determined regardless of the illumination condition. Can be calculated with high accuracy. In particular, it is possible to improve the measurement accuracy of the best focus position under a small σ illumination condition.

In this case, various weighting functions can be considered. For example, the weighting function may be a Gaussian function including a standard deviation as the weight parameter, as in the optical characteristic measuring method according to claim 2, or the optical characteristic measuring method according to claim 3, for example. As described above, the weighting function may be a step function in which the value of the weight is 1 at a central portion of a predetermined width determined according to the illumination condition, and is 0 at both sides.

In each of the optical characteristic measuring methods according to any one of the first to third aspects, as in the optical characteristic measuring method according to the fourth aspect, the illumination condition may include an aperture of an illumination optical system (12) for illuminating the pattern. The condition may correspond to a coherence factor obtained by dividing the number by the numerical aperture of the projection optical system.

An optical characteristic measuring method according to a fifth aspect is an optical characteristic measuring method for measuring an optical characteristic of a projection optical system (PL), wherein a predetermined pattern (P) is measured by illumination light (IL).
Illuminating M) to form an aerial image (PM ') of the pattern near the image plane via the projection optical system; and a measurement pattern (22) arranged on the image plane side of the projection optical system. Relative to the aerial image, and obtain a photoelectric conversion signal corresponding to the intensity of the illumination light via the measurement pattern at at least two positions in the optical axis direction of the measurement pattern. And comparing a contrast value of at least two points respectively corresponding to the obtained photoelectric conversion signal with a reference contrast curve prepared in advance, and a first curve obtained by curve fitting the contrast values of the at least two points. A peak point on a contrast curve is calculated, and a position in the optical axis direction of the measurement pattern corresponding to the peak point is set as a first best focus position of the projection optical system. And calculating.

According to this, a predetermined pattern is illuminated by the illumination light, and is arranged on the image plane side of the projection optical system with respect to the spatial image of the pattern formed near the image plane via the projection optical system. The measurement pattern is relatively scanned, and a photoelectric conversion signal corresponding to the intensity of the illumination light via the measurement pattern is obtained at at least two positions in the optical axis direction of the measurement pattern. Then, the contrast values of at least two points respectively corresponding to the obtained photoelectric conversion signals are compared with a reference contrast curve prepared in advance, and the first contrast curve obtained by curve-fitting the contrast values of at least two points is obtained. And a position in the optical axis direction of the measurement pattern corresponding to the peak point is calculated as a first best focus position of the projection optical system.

That is, the position of the measurement pattern in the optical axis direction is sequentially set to at least two positions, and the aerial image measurement of the pattern is performed at each position, and at least two positions in the optical axis direction of the measurement pattern are measured. A photoelectric conversion signal corresponding to the measured aerial image is obtained, and a contrast value (contrast value at a minimum of two points) of each photoelectric conversion signal is compared with a reference contrast curve.
A first contrast curve having the same shape as a reference contrast curve including a contrast value at a point is obtained by fitting, and a first best focus position of the projection optical system is calculated based on a peak point on the first contrast curve. . Therefore, the first aerial image is obtained by two aerial image measurements.
Can be calculated in an extremely short time as compared with the conventional rough measurement. In particular, this contributes to shortening the measurement time of the best focus position when the best focus position greatly changes.

In this case, as in the optical characteristic measuring method according to claim 6, the measurement pattern is scanned relative to the aerial image and the intensity of the illumination light through the measurement pattern is measured. Obtaining a photoelectric conversion signal corresponding to each of a plurality of positions in the optical axis direction of the measurement pattern within a range of a predetermined width including the first best focus position; and a photoelectric conversion for each of the obtained plurality of positions. Calculating a position in the optical axis direction of the measurement pattern corresponding to a peak point of a second contrast curve obtained by curve fitting the contrast value of the signal as a second best focus position of the projection optical system; May be further included.

An optical characteristic measuring device according to a seventh aspect of the present invention is an optical characteristic measuring device for measuring an optical characteristic of a projection optical system (PL), and comprises a spatial image (P) of a predetermined pattern (PM).
M ') is formed on the image plane via the projection optical system, so as to illuminate the pattern (12, 14).
A pattern forming member (90) arranged on the image plane side of the projection optical system and having a measurement pattern formed thereon; and photoelectrically converting the illumination light via the measurement pattern to convert the measurement pattern. A photoelectric conversion element (24) for outputting a photoelectric conversion signal according to the intensity of the illumination light transmitted therethrough; and the predetermined pattern is illuminated by the illumination device and the aerial image is formed on the image plane. Scanning the pattern forming member relative to the aerial image, and applying a photoelectric conversion signal from the photoelectric conversion element corresponding to the aerial image to the pattern forming member in the optical axis direction of the projection optical system. Measurement processing device for measuring at each of a plurality of positions (50)
Calculating a temporary best focus position of the projection optical system based on a first contrast curve obtained by curve-fitting the contrast values of the photoelectric conversion signals obtained for each of the plurality of positions; A second contrast curve is calculated by weighting the contrast value using a weighting function centered on the temporary best focus position, including a weight parameter determined according to the lighting condition, and based on the second contrast curve. A calculating device (50) for calculating a true best focus position of the projection optical system.

According to this, in the measurement processing apparatus, a predetermined pattern is illuminated by the illuminating device, and a pattern forming member (measurement for measurement) is formed in a state where a spatial image of the predetermined pattern is formed on the image plane of the projection optical system. ) Is scanned relative to the aerial image, and a photoelectric conversion signal from the photoelectric conversion element corresponding to the aerial image is measured at each of a plurality of positions of the pattern forming member in the optical axis direction of the projection optical system. And
In the calculation device, a first value obtained by curve-fitting a contrast value of the photoelectric conversion signal obtained for each of the plurality of positions is obtained.
Calculates the temporary best focus position of the projection optical system based on the contrast curve of the projection optical system, includes a weight parameter determined according to the lighting conditions of the lighting device, and calculates the contrast value using a weighting function centered on the temporary best focus position. A second contrast curve is calculated by weighting, and a true best focus position of the projection optical system is calculated based on the second contrast curve. As described above, the second contrast curve for calculating the true best focus position by weighting the contrast value using the weighting function including the weight parameter determined according to the lighting condition centering on the temporary best focus position , The best focus position can be calculated with high accuracy regardless of the lighting conditions by pre-determining weighting parameters for each lighting condition so that the measurement accuracy under each lighting condition does not decrease. Becomes In particular, it is possible to improve the measurement accuracy of the best focus position under a small σ illumination condition.

In this case, the weighting by the calculation device can be performed using various weighting functions.
For example, as in the optical characteristic measuring device according to claim 8, the calculating device may perform the weighting using a Gaussian function including a standard deviation as the weighting parameter as the weighting function, or As in the optical characteristic measuring device according to item 9, the calculating device includes a step function in which a weight value is 1 at a central portion of a predetermined width determined according to the illumination condition and is 0 at both sides as the weighting function. May be used to perform the weighting.

In the exposure apparatus according to the present invention, the circuit pattern formed on the mask (R) is projected onto the projection optical system (PL).
10. An exposure apparatus for transferring an image onto a substrate (W) via a substrate stage (WST) holding and moving the substrate; and wherein the pattern forming member is provided on a part of the substrate stage. 9. The optical characteristic measuring device according to any one of 9.

According to this, since each of the optical characteristic measuring devices according to claim 7 is provided with the pattern forming member provided on a part of the substrate stage, the substrate can be formed without using a special driving device. By scanning a measurement pattern with respect to a predetermined pattern aerial image via a stage, the best focus position of the projection optical system can be accurately measured without being affected by illumination conditions. Then, it is possible to make the substrate surface substantially coincide with the best imaging plane of the projection optical system at the time of exposure in consideration of the measurement result. Therefore, it is possible to perform high-precision exposure in which the occurrence of exposure failure due to defocus is suppressed as much as possible.

A device manufacturing method according to claim 11 is
A device manufacturing method including a lithography step, wherein exposure is performed using the exposure apparatus according to claim 10 in the lithography step.

[0029]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIG.
This will be described with reference to FIG.

FIG. 1 shows an exposure apparatus 10 according to one embodiment.
Is schematically shown. This exposure apparatus 10
This is a step-and-scan type scanning projection exposure apparatus, that is, a so-called scanning stepper.

The exposure apparatus 10 holds an illumination system as an illumination device including a light source 14 and an illumination optical system 12, a reticle stage RST for holding a reticle R as a mask, a projection optical system PL, and a wafer W as a substrate. A wafer stage WST as a substrate stage that can freely move in the XY plane, and a control system for controlling these.

As the light source 14, here, for example, an excimer laser light source such as a KrF excimer laser (output wavelength 248 nm) or an ArF excimer laser (output wavelength 193 nm) is used. This light source 1
4 indicates that the main controller 50 turns on / off the laser emission.
Off, center wavelength, spectral half width, repetition frequency, and the like are controlled.

The illumination optical system 12 includes a beam shaping optical system 18, a fly-eye lens 22 as an optical integrator (homogenizer), an illumination system aperture stop plate 24,
It includes a first relay lens 28A, a second relay lens 28B, a fixed reticle blind 30A, a movable reticle blind 30B, a mirror M for bending an optical path, a condenser lens 32, and the like.

In the beam shaping optical system 18, the light source 1
The sectional shape of the laser beam LB pulsed in step 4 is
For shaping the laser beam LB so that it efficiently enters a fly-eye lens 22 provided behind the optical path of the laser beam LB;
For example, a cylinder lens and a beam expander (both not shown) are included. The beam shaping optical system 18 also includes a zoom optical system that can continuously change the cross-sectional area of the laser beam according to the setting of an illumination aperture stop by an illumination system aperture stop plate 24 described later. .

The fly-eye lens 22 is arranged on the optical path of the laser beam LB emitted from the beam shaping optical system 18, and has a large number of point light sources on its exit-side focal plane to illuminate the reticle R with a uniform illuminance distribution. (A light source image), that is, a secondary light source is formed. In this specification, the laser beam emitted from the secondary light source is referred to as “illumination light I.
L ".

An illumination system aperture stop plate 24 is arranged near the exit-side focal plane of the fly-eye lens 22. As shown in FIG. 2, the illumination system aperture stop plate 24 is, for example, a large illumination aperture stop 2 having a normal circular aperture for normal illumination.
3a, a small σ aperture stop 23b composed of a small circular aperture for reducing the σ value which is a coherence factor, an annular aperture stop 23c for annular illumination, and a plurality of eccentrically arranged apertures for a modified light source method The modified aperture stop (quadrupole stop) 23d and the like are constituted by disk-shaped members arranged at substantially equal angular intervals. This illumination system aperture stop plate 2
1 is rotated by a driving device 40 such as a motor controlled by a main controller 50, as shown in FIG. 1, so that one of the aperture stops is positioned on the optical path of the illumination light IL. Set selectively. In FIG. 1,
Only two of the above four aperture stops are shown.

Illumination light IL emitted from the illumination system aperture stop plate 24
A beam splitter 26 having a small reflectance and a large transmittance is disposed on the optical path of the first relay lens 28A and the second relay lens 28A on the optical path behind the fixed reticle blind 30A and the movable reticle blind 30B. A relay optical system including a lens 28B is provided.

The fixed reticle blind 30A is disposed on a plane slightly defocused from a plane conjugate to the pattern plane of the reticle R, and has a rectangular opening defining an illumination area IAR on the reticle R. Also, in the scanning direction (here, X-direction) near the fixed reticle blind 30A.
A movable reticle blind 30B having an opening whose position and width are variable in directions respectively corresponding to the axial direction) and the non-scanning direction (Y-axis direction) is arranged, and the movable reticle blind is provided at the start and end of scanning exposure. By further restricting the illumination area IAR via 30B, exposure of unnecessary portions is prevented. In the present embodiment, the movable reticle blind 30B is also used for setting an illumination area at the time of aerial image measurement described later.

On the optical path of the illumination light IL behind the second relay lens 28B constituting the relay optical system, a bending mirror M for reflecting the illumination light IL passing through the second relay lens 28B toward the reticle R is arranged. And this mirror M
A condenser lens 32 is arranged on the optical path of the rear illumination light IL.

On the other hand, on the optical path of the illuminating light IL reflected by the beam splitter 26 in the illuminating optical system 12, a condenser lens 44 and a pulsed light emitted from the light source 14 having high sensitivity in the far ultraviolet region are detected. With high response frequency due to
An integrator sensor 46 including a light receiving element such as an N-type photodiode is provided.

The operation of the illumination system configured as described above will be briefly described. The laser beam LB pulse-emitted from the light source 14 is incident on the beam shaping optical system 18 where the rear fly-eye lens 22 After the cross-sectional shape of the fly-eye lens 2 is
2 is incident. Thus, the above-described secondary light source is formed on the exit-side focal plane of the fly-eye lens 22 (the pupil plane of the illumination optical system 12). Illumination light I emitted from this secondary light source
After passing through one of the aperture stops on the illumination system aperture stop plate 24, L reaches a beam splitter 26 having a large transmittance and a small reflectance. The illumination light IL transmitted through the beam splitter 26 passes through the first relay lens 28A, the rectangular opening of the fixed reticle blind 30A and the movable reticle blind 30B, and then the second relay lens 2B.
After passing through 8B, the optical path is bent vertically downward by the mirror M, and passes through the condenser lens 32 to illuminate the illumination area IAR on the reticle R held on the reticle stage RST with a uniform illuminance distribution.

On the other hand, the illumination light IL reflected by the beam splitter 26 is received by an integrator sensor 46 via a condenser lens 44, and a photoelectric conversion signal of the integrator sensor 46 is converted to a peak hold circuit (not shown) and an A / D converter.
Main controller 5 via signal processor 80 with converter
0 is supplied.

A reticle R is fixed on the reticle stage RST by, for example, vacuum suction (or electrostatic suction). Here, reticle stage RST is driven by an unillustrated reticle stage drive system including a linear motor or the like, and XY perpendicular to optical axis AX of projection optical system PL described later.
Two-dimensionally in the plane (the X-axis direction and the Y-axis direction orthogonal thereto, and the rotation direction (θz
Direction), and can be moved on a reticle base (not shown) at a designated scanning speed in the X-axis direction. The reticle stage RST has a moving stroke in the X-axis direction that allows the entire surface of the reticle R to cross at least the optical axis AX of the projection optical system PL.

On reticle stage RST, a reticle laser interferometer (hereinafter, referred to as “reticle interferometer”) 54
A movable mirror 52R that reflects the laser beam from R is fixed, and the position of the reticle stage RST in the XY plane is, for example, 0.5 to 1 nm by a reticle interferometer 54R.
It is always detected with a resolution of the order. Here, actually, the scanning direction (X
A moving mirror having a reflecting surface perpendicular to the non-scanning direction (Y-axis direction) and a moving mirror having a reflecting surface perpendicular to the non-scanning direction (Y-axis direction) are provided.
At least one axis is provided in the axis and the Y-axis direction.
These are typically the moving mirror 52R, the reticle interferometer 5
Shown as 4R.

The position information of the reticle stage RST from the reticle interferometer 54R is sent to the stage controller 70 and, via the stage controller 70, to the main controller 50 comprising a workstation (or microcomputer). Below, the reticle stage RST is controlled via a reticle stage drive system (not shown).
Control movement.

The projection optical system PL is disposed below the reticle stage RST in FIG. 1 and its optical axis AX is in the Z-axis direction. Here, it is a reduction system that is telecentric on both sides, and extends in the optical axis AX direction. A refractive optical system including a plurality of lens elements arranged at predetermined intervals along the optical axis is used. Here, the projection magnification of the projection optical system PL is, for example, 1/4. Therefore, when the illumination light IL from the illumination optical system 12 illuminates the slit illumination area IAR on the reticle R, the illumination light IL passing through the reticle R causes the illumination of the slit illumination via the projection optical system PL. A reduced image (partially inverted image) of the circuit pattern of the reticle R in the area IAR is formed in an exposure area IA conjugate to the illumination area IAR on the wafer W having a surface coated with a photoresist.

The wafer stage WST is freely driven along the upper surface of the stage base 16 in an XY two-dimensional plane (including θz rotation) by a wafer stage drive system (not shown) composed of, for example, a magnetic levitation type two-dimensional linear actuator. It has become so. Here, since the two-dimensional linear actuator also has a Z drive coil in addition to the X drive coil and the Y drive coil, the wafer stage WST
The micro drive can be performed in three degrees of freedom, that is, a rotation direction (θx) around the Z and X axes and a rotation direction (θy) around the Y axis.

A wafer holder 25 is mounted on wafer stage WST, and wafer W is held by wafer holder 25 by vacuum suction (or electrostatic suction).

Incidentally, instead of wafer stage WST, XY is driven by a drive system such as a linear motor or a planar motor.
When a two-dimensional moving stage driven only in a two-dimensional plane is used, the wafer holder 25 is set to three of Z, θx, and θy.
It may be mounted on the two-dimensional moving stage via a Z-leveling table that is minutely driven by a voice coil motor or the like in the direction of freedom.

On wafer stage WST, a wafer laser interferometer (hereinafter referred to as "wafer interferometer") 54W
The movable mirror 52W for reflecting the laser beam from the wafer stage is fixed, and the position in the XY plane of the wafer stage WST is set to, for example, 0.5 to 1 by the wafer interferometer 54W arranged outside.
It is always detected with a resolution of about nm.

Here, actually, wafer stage WST
A moving mirror having a reflecting surface orthogonal to the X-axis direction, which is the scanning direction at the time of scanning exposure, and a moving mirror having a reflecting surface orthogonal to the Y-axis direction, which is the non-scanning direction, are provided on the upper side. 54W are provided in a plurality of axes in the X-axis direction and the Y-axis direction, respectively, so that the positions of the remaining five degrees of freedom (X, Y, θx, θy, θz) except the Z-axis direction of the wafer stage WST can be measured. However, in FIG. 1, these are typically shown as a moving mirror 52W and a wafer interferometer 54W. Position information (or speed information) of wafer stage WST is sent to stage controller 70 and main controller 50 via the same, and under the direction of main controller 50, stage controller 70 The position of wafer stage WST in the XY plane is controlled via a stage drive system.

Further, inside wafer stage WST,
A part of an optical system constituting the aerial image measuring device 59 used for measuring the optical characteristics of the projection optical system PL is arranged.
Here, the configuration of the aerial image measurement device 59 will be described in detail.
This aerial image measurement device 59 includes, as shown in FIG. 3, a stage-side component provided on wafer stage WST,
That is, a slit plate 90 as a pattern forming member, a relay optical system including lenses 84 and 86, a mirror 88 for bending an optical path, a light transmitting lens 87, and a wafer stage WS
A component outside the stage provided outside the T, that is, a mirror 96, a light receiving lens 89, an optical sensor 24 as a photoelectric conversion element, and the like are provided.

More specifically, the slit plate 90
As shown in FIG. 3, is fitted from above into a protruding portion 58 provided on the upper surface of one end of wafer stage WST and having an open top, in a state of closing the opening.
The slit plate 90 has a rectangular light receiving glass 82 in a plan view.
A reflection film 83 also serving as a light-shielding film is formed on the upper surface of the substrate, and a slit-shaped opening pattern (hereinafter, referred to as a “slit”) 22 having a predetermined width 2D as a measurement pattern is patterned on a part of the reflection film 83. It is formed.

Here, as a material of the light receiving glass 82, synthetic quartz, fluorite, or the like, which has good transmittance of KrF excimer laser light or ArF excimer laser light, is used.

Wafer stage WST below slit 22
Inside, a mirror 8 for horizontally bending the optical path of the illumination light beam (image light beam) that has entered vertically downward through the slit 22.
8, a relay optical system (84, 86) composed of lenses 84, 86 is arranged, and the relay optical system (84, 86) is arranged.
A light transmitting lens 87 for transmitting an illumination light beam relayed by a predetermined optical path length by a relay optical system (84, 86) to the outside of the wafer stage WST is provided on the + X side wall of the wafer stage WST behind the optical path 86). Fixed.

The wafer stage W is moved by the light transmitting lens 87.
A mirror 96 having a predetermined length in the Y-axis direction is inclined at an inclination angle of 45 ° on the optical path of the illumination light beam sent out of the ST. By this mirror 96, the optical path of the illumination light beam sent out of wafer stage WST is bent 90 ° vertically upward. A light receiving lens 89 having a larger diameter than the light transmitting lens 87 is arranged on the bent optical path. This light receiving lens 8
Above 9, an optical sensor 24 is arranged. The light receiving lens 89 and the optical sensor 24 are housed in a case 92 while maintaining a predetermined positional relationship, and the case 92 is mounted on the upper surface of the base 16 via a mounting member 93.
7 is fixed near the upper end.

As the optical sensor 24, a photoelectric conversion element (light receiving element) capable of accurately detecting weak light, for example, a photomultiplier tube (PM)
T, photomultiplier tube, etc. are used. The photoelectric conversion signal P from the optical sensor 24 is sent to the main controller 50 via the signal processor 80 in FIG. In addition,
The signal processing device 80 includes, for example, an amplifier, a sample holder,
It can be configured to include an A / D converter (usually, one having a resolution of 16 bits is used).

As described above, the slits 22 are formed in the reflection film 83, but the following description will be made on the assumption that the slits 22 are formed in the slit plate 90 for convenience.

According to the aerial image measuring device 59 configured as described above, a projection image (aerial image) of the measurement mark formed on the reticle R via the projection optical system PL, which will be described later.
Of the illumination light I transmitted through the projection optical system PL during the measurement of
The slit plate 9 constituting the aerial image measuring device 59 by L
When 0 is illuminated, the slit 2 on the slit plate 90
The illumination light IL that has passed through the wafer stage W passes through a lens 84, a mirror 88, a lens 86, and a light transmitting lens 87.
It is led out of ST. Then, the light guided to the outside of wafer stage WST has its optical path bent vertically upward by mirror 96, received by optical sensor 24 via light receiving lens 89, and responds to the amount of light received from optical sensor 24. The photoelectric conversion signal (light amount signal) P is output to the main controller 50 via the signal processor 80.

In the case of the present embodiment, the measurement of the projected image (spatial image) of the measurement mark is performed by the slit scan method.
9 and the optical sensor 24. Therefore, in the aerial image measurement device 59, the size of each lens and the mirror 96 are set such that all light passing through the light transmitting lens 87 moving within a predetermined range enters the light receiving lens 89.

As described above, in the aerial image measuring device 59, the light deriving section for guiding the light through the slit 22 to the outside of the wafer stage WST by the slit plate 90, the lenses 84 and 86, the mirror 88, and the light transmitting lens 87. , And a light receiving unit that receives the light led out of the wafer stage WST is formed by the light receiving lens 89 and the optical sensor 24. In this case, the light guiding section and the light receiving section are mechanically separated. And only for aerial image measurement,
The light guiding section and the light receiving section are optically connected via a mirror 96.

That is, in the aerial image measurement device 59, since the optical sensor 24 is provided at a predetermined position outside the wafer stage WST, the heat generation of the optical sensor 24 adversely affects the measurement accuracy of the laser interferometer 54W. Or give. Further, since the outside and inside of wafer stage WST are not connected by a light guide or the like, the driving accuracy of wafer stage WST is adversely affected as in the case where the outside and inside of wafer stage WST are connected by a light guide. Not even.

Of course, if the influence of heat can be eliminated, optical sensor 24 may be provided inside wafer stage WST. In addition, regarding the aerial image measurement method and the optical characteristic measurement method performed using the aerial image measurement device 59,
Details will be described later.

Returning to FIG. 1, on the side of the projection optical system PL,
Alignment mark (alignment mark) on wafer W
An off-axis alignment system ALG is provided as a mark detection system for detecting a mark. In the present embodiment, the alignment system ALG is an image processing type alignment sensor, so-called FIA (Field Image Alignment).
nt) system is used. The detection signal of alignment system ALG is supplied to main controller 50.

Further, as shown in FIG. 1, the exposure apparatus 10 of this embodiment has a light source whose ON / OFF is controlled by the main controller 50, and a large number of light sources are directed toward the image forming plane of the projection optical system PL. An irradiation system 60a for irradiating an imaging light beam for forming an image of a pinhole or a slit obliquely to the optical axis AX, and a light receiving system for receiving the reflected light beam of the imaging light beam on the surface of the wafer W 60b is provided. The detailed configuration of the multipoint focal position detection system similar to the focal position detection system (60a, 60b) of the present embodiment is described in, for example, Japanese Patent Laid-Open No. 6-28.
It is disclosed in, for example, Japanese Patent No. 3403.

The main controller 50 (not shown) operates such that the defocus becomes zero based on the defocus signal (defocus signal) from the light receiving system 60b, for example, the S-curve signal at the time of the scanning exposure to be described later. The movement of the wafer stage WST in the Z-axis direction and the two-dimensional inclination (that is, the rotation in the θx and θy directions) of the wafer stage WST are controlled via the wafer stage drive system, that is, the multipoint focal position detection system (60a, 60b) Is used to control the movement of the wafer stage WST so that the image plane of the projection optical system PL and the surface of the wafer W substantially match within the irradiation area of the illumination light IL (the imaging relation with the illumination area IAR). Execute auto focus (auto focus) and auto leveling.

Next, the operation of the exposure step in the exposure apparatus 10 of the present embodiment will be briefly described.

First, the reticle R is transported by a reticle transport system (not shown), and is held by suction on the reticle stage RST at the loading position. Next, under the instruction of main controller 50, the positions of wafer stage WST and reticle stage RST are controlled by stage controller 70, and a projection image (spatial image) of a reticle alignment mark (not shown) formed on reticle R is formed. Measurement is performed using the aerial image measurement device 59 as described later, and the projection position of the reticle pattern image is obtained. That is, reticle alignment is performed.

Next, under the instruction of main controller 50, stage controller 70 controls wafer stage WS so that slit plate 90 is positioned immediately below alignment system ALG.
T is moved, and the slit 22 serving as the position reference of the aerial image measurement device 59 is detected by the alignment system ALG. Main controller 50 detects the detection signal of alignment system ALG and the measured value of wafer interferometer 54W at that time,
And a relative position between the projection position of the pattern image of the reticle R and the alignment system ALG, that is, the alignment system AL, based on the projection position of the reticle pattern image obtained previously.
The baseline amount of G is obtained.

When the baseline measurement is completed, the main controller 50 performs wafer alignment such as EGA (enhanced global alignment) disclosed in detail in, for example, JP-A-61-44429. The positions of all shot areas on W are determined. At the time of this wafer alignment, a wafer alignment mark of a predetermined sample shot of a plurality of shot areas on the wafer W is measured using the alignment system ALG.

Next, the main controller 50 sends the position information sent from the interferometers 54W and 54R via the stage controller 70 based on the position information of each shot area on the wafer W and the base line amount obtained above. While monitoring
The wafer stage WST is positioned at the scanning start position of the first shot area via the stage control device 70, and the reticle stage RST is positioned at the scanning start position, and scanning exposure of the first shot area is performed.

In other words, main controller 50 starts relative scanning of reticle stage RST and wafer stage WST in the direction opposite to the X-axis direction. Both stages RST, WST
Reaches the respective target scanning speeds, the pattern area of the reticle R starts to be illuminated by the illumination light IL, and scanning exposure is started.

The main controller 50 controls the moving speed Vr of the reticle stage RST in the X-axis direction especially during the above-described scanning exposure.
The reticle stage RST and the wafer stage WST are instructed so that the speed ratio of the wafer stage WST and the moving speed Vw in the X-axis direction are maintained at a speed ratio corresponding to the projection magnification of the projection optical system PL. Perform synchronous control.

Then, different areas of the pattern area of the reticle R are sequentially illuminated with the illumination light IL, and the illumination of the entire pattern area is completed.
The scanning exposure of the shot area ends. Thus, the circuit pattern of the reticle R is reduced and transferred to the first shot area via the projection optical system PL.

When the scanning exposure of the first shot area is completed, a stepping operation between shots for moving wafer stage WST to the scanning start position of the second shot area is performed. Then, the scanning exposure of the second shot area is performed in the same manner as described above. Thereafter, the same operation is performed in the third shot area and thereafter.

As described above, the stepping operation between shots and the scanning exposure operation for shots are repeated, and the pattern of the reticle R is transferred to all the shot areas on the wafer W by the step-and-scan method.

Here, during the above-mentioned scanning exposure, the main controller 50 executes the auto-focusing and the auto-leveling based on the output of the multi-point focal position detecting system (60a, 60b).

In order to transfer the pattern of the reticle R to the shot area on the wafer W with high accuracy during the scanning exposure, the above-mentioned auto focus and auto leveling are performed with high accuracy. Exposure needs to be performed in a state where the region substantially matches the image plane of the projection optical system PL. For this purpose, the best focus position (best image plane position) of the projection optical system PL is measured with high accuracy, and the calibration of the multi-point focal position detection system (60a, 60b) is performed based on the measurement result. It needs to be done. In the present embodiment, the main controller 50 sets, for example, the detection offset of the multipoint focal position detection system (60a, 60b) based on the measurement result of the best focus position (best image plane position), or The inclination of the reflected light flux of the parallel plate (not shown) in the optical plate 60b with respect to the optical axis is controlled to control the multi-point focal position detection system (60a, 6b).
The calibration is performed by resetting the origin (detection reference point) of 0b). However, the present invention is not limited to this, and calibration can be performed by giving an electrical offset to the detection signal.

In the present embodiment, an aerial image measuring device 59 is used for measuring the best focus position of the projection optical system. Hereinafter, the measurement of the best focus position will be described. Prior to that, the aerial image measurement using the aerial image measurement device 59 will be described.

FIG. 3 shows an aerial image measuring device 59
The state in which the aerial image of the measurement mark PM formed on the reticle R is being measured is shown. As the reticle R, a reticle R dedicated to aerial image measurement, or a device reticle used for manufacturing a device in which a dedicated measurement mark is formed is used. Instead of these reticles, a fixed mark plate (also called a reticle fiducial mark plate) made of the same glass material as the reticle is provided on the reticle stage RST, and measurement marks (measurement marks) are formed on the mark plate. You may use what was done.

Here, the reticle R has X
It is assumed that a measurement mark PM composed of a line-and-space (L / S) mark having a ratio (duty ratio) of the width of the line portion to the width of the space portion having a periodicity in the axial direction (duty ratio) of 1: 1 is formed. In addition, as shown in FIG. 4A, the slit plate 90 constituting the aerial image measuring device 59 has Y
It is assumed that a slit 22 having a predetermined width 2D extending in the axial direction is formed.

In measuring the aerial image, the movable reticle blind 30B shown in FIG. 1 is driven by the main controller 50 via a blind drive device (not shown), and the illumination area of the illumination light IL includes the measurement mark PM. It is limited to a predetermined area (see FIG. 3). In this state, main controller 50
When the illumination light IL is irradiated on the measurement mark PM, the light (illumination light IL) diffracted and scattered by the measurement mark PM is refracted by the projection optical system PL, and the projection optical system PL A spatial image (projection image) of the measurement mark PM is formed on the image plane of. At this time, as shown in FIG. 4A, wafer stage WST is at a position where spatial image PM ′ of measurement mark PM is formed on + X side (or −X side) of slit 22 on slit plate 90. It has been set.

Then, under the instruction of main controller 50, stage controller 70 moves wafer stage WST to the position shown in FIG.
When driven in the + X direction as shown by the arrow F in (A), the slit 22 scans the aerial image PM ′ in the X-axis direction. During this scanning, the light (illumination light IL) passing through the slit 22 is received by the optical sensor 24 via the light receiving optical system in the wafer stage WST, the reflection mirror 96 and the light receiving lens 89 outside the wafer stage WST, and the light The converted signal P is supplied to the signal processing device 80 shown in FIG. The signal processing device 80 performs predetermined processing on the photoelectric conversion signal, and supplies a light intensity signal corresponding to the aerial image PM ′ to the main control device 50. At this time, in the signal processing device 80, in order to suppress the variation in the emission intensity of the illumination light IL from the light source 14, a signal obtained by standardizing the signal from the optical sensor 24 based on the signal from the integrator sensor 46 shown in FIG. Is supplied to the main controller 50.

FIG. 4B shows an example of a photoelectric conversion signal (light intensity signal) P obtained at the time of the aerial image measurement.

Hereinafter, detection of the best focus position using the aerial image measuring device 59 in the exposure apparatus 10 of the present embodiment will be described with reference to the flowchart of FIG.
FIG. 5 shows a simplified control flow of main controller 50. It is assumed that table data of the weight attenuation rate corresponding to the σ value shown in FIG. 7A (or FIG. 7B) is stored in advance in the memory of main controller 50. I do. Further, a reticle R is formed with, for example, a 0.8 μmL / S pattern as a measurement pattern, and the width 2D of the slit 22 is, for example, 0.3 μm. Since the projection magnification of the projection optical system PL is 1/4 as described above, the measurement pattern on the reticle R becomes a 0.2 μmL / S pattern image on the slit plate 90.

First, main controller 50 executes step 102
, The best focus position stored in the memory is set as the measurement center of the fine measurement. As the best focus position set as the measurement center of the fine measurement, in the normal case, the previous measurement value is used. However, if the previous measurement has not been performed or the measured value has been lost, the design value set in the adjustment stage of the exposure apparatus 10 is used. However, the design value may be used even when the previous measurement value is not lost.

In the next step 104, main controller 50
Performs fine measurement around the fine measurement center set in step 102. Specifically, main controller 50 sets a reticle R at a predetermined point in the field of view of projection optical system PL where the best focus position should be measured, for example, reticle R on the optical axis.
The reticle stage RST is moved so that the upper measurement mark PM is positioned. Next, the main controller 50 controls the driving of the movable reticle blind 30B so as to irradiate only the measurement mark PM with the illumination light IL, thereby defining an illumination area. In this state, main controller 50
Irradiation light IL is applied to reticle R, and wafer stage W
While scanning ST in the X-axis direction, the aerial image measurement of the measurement mark PM is performed by the slit scan method using the aerial image measurement device 59 in the same manner as described above. At this time, the main controller 50
Then, the position of the slit plate 90 in the Z-axis direction (that is, the Z position of the wafer stage WST) is changed by, for example, about 15 steps at a pitch of 0.15 μm within a predetermined width centered on the fine measurement center set in step 102. The light intensity signal (photoelectric conversion signal) of each time is stored in an internal memory.

In the next step 106, main controller 50
Is the temporary best focus position of the projection optical system PL (first
Is calculated as follows.

First, the contrast value of the photoelectric conversion signal obtained at each position in the Z-axis direction of the slit plate 90 in the measurement in step 104 is calculated from the coefficient by Fourier transforming each signal waveform. Hereinafter, this will be described in more detail.

The photoelectric conversion signal obtained by the measurement is represented by I
If (x) is expressed as a fundamental frequency component and a higher-order frequency component, it can be expressed as the following equation (1).

[0091]

(Equation 1)

Here, a ₀ , a _n , and b _n are represented by the following equations (2) to (4), respectively.

[0093]

(Equation 2)

P is the period of the signal, and ω ₀ = 2π
/ P.

The contrast value (Cont) is expressed by the following equation (5). Cont = (Max−Min) / (Max + Min) (5)

[0096] Here, the waveform is assumed to be formed only by 0-order component and the first-order component of the Fourier series expansion, the amplitude c ₀ of the DC component of the waveform, the amplitude c ₁ of the fundamental frequency component, the following equation ( 6) and (7). c ₀ = a ₀ (6)

[0097]

(Equation 3)

In this case, Max = c ₀ + c _1/2 (8) Min = c ₀ -c _1/2 (9) Therefore, the expression (5) can be expressed by the above expressions (8) and (9). Than,
It is expressed as the following equation (5) ′. Cont = c ₁ / (2c ₀ ) (5) ′

When the best focus position is obtained, the contrast value including the (first order / zero order) amplitude ratio is used because the contrast value changes sensitively according to the focus position (Z position). By using this, the focus position (Z position) at which the contrast value becomes maximum can be easily and reliably determined as the best focus position.

In FIG. 6A, the contrast values of the respective photoelectric conversions obtained at the respective Z positions of the slit plate 90 are obtained as described above. An example of data plotted on an orthogonal coordinate system having a vertical axis as a contrast value (an example under normal illumination conditions with a large σ illumination stop) is shown.

Main controller 50 performs function fitting by the least squares method based on each plot point, and
A first contrast curve P1 consisting of a sixth-order approximation curve as shown in (B) is obtained, and the contrast values on the first contrast curve P1 are compared between measurement ranges at, for example, 0.05 μm intervals. , Is set as a temporary maximum value Ma. Next, the main control device 50
As shown in (C), a predetermined amount S is calculated from the provisional maximum value Ma.
A straight line (slice line) SL of Cont = a is set at the position where the distance is lowered, and two intersection coordinates Ja and Ka with the above-described sixth-order approximation curve P1 are obtained. Further, in the main controller 50, a straight line S of the obtained two points Ja and Ka is obtained.
The midpoint Oa on L is calculated, and the Z position corresponding to the midpoint Oa is determined as a temporary best focus position (Z ′) of the projection optical system PL.

Returning to FIG. 5, in the next step 108, main controller 50 determines whether or not temporary best focus position Z 'has been calculated in step 106. If this determination is affirmed, the process proceeds to the next step 110, where main controller 50 checks the set lighting conditions. The confirmation of the illumination condition is performed by checking the setting state of the aperture of the illumination system aperture stop plate 24 in the illumination optical system 12, that is, FIG.
Is performed based on which of the aperture stops is being used (whether the aperture stop is set on the optical path of the illumination light).

Next, main controller 50 executes step 1
At 12, based on the confirmation result of step 110,
The illumination coherence factor σ (= the numerical aperture of the illumination optical system / the numerical aperture of the projection optical system), which is a value obtained by dividing the numerical aperture of the illumination optical system 12 that illuminates the pattern on the reticle R by the numerical aperture of the projection optical system, At the same time, the weight attenuation rate γ is determined based on the coherence factor σ and the table data stored in the memory (see FIG. 7A). In the present embodiment, the coherence factor σ
Is calculated in advance for each aperture stop, and is stored in the memory in association with information on the aperture stop. Therefore, step 1
At 12, the coherence factor σ is not calculated, but may be calculated. For example, in the case of a large σ aperture stop, the coherence factor σ = 0.8 and the small σ
In the case of the aperture stop, the coherence factor σ = 0.3 or the like.

Here, the weight decay rate γ is given by the following equation (10).
Means the weight parameter of the weighting function represented by.

Η = exp ｛−0.5 ｛(Z−Z ′) / γ｝ ² ｝ (10)

In the equation (10), Z is the measured Z position, Z ′ is the center of weighting (the above-mentioned temporary best focus position), and γ is the weight damping rate (Weight Dumping).
Rate). The weighting function η in this equation (10) is
As is clear when γ in the equation (10) is replaced by the standard deviation s, there is nothing but a Gaussian function.

Here, for example, when the large σ aperture stop 23a of the illumination system aperture stop plate 24 is in use, the σ value is usually 0.8, although it depends on the numerical aperture of the projection optical system PL. , And the weight attenuation rate γ is determined to be 1.0 based on the table data of FIG. Also, the annular aperture stop 23
c, when the modified aperture stop 23d and the like are in use, the σ value is 0.6 or more, so the weight attenuation rate γ is determined to be 1.0.

On the other hand, for example, the large σ of the illumination system aperture stop plate 24
When the aperture stop 23b is in use, the σ value = 0.3
Therefore, based on the table data of FIG.
The weight decay rate γ = 0.3 is determined.

Note that the table data of the weight decay rate according to the σ value is not limited to the data that can be classified into the two stages described above, and the table data that can be classified into the three stages as shown in FIG. 7B. Data may be used, or table data that can be classified in multiple stages in which values of the weight attenuation rate predetermined for each lighting condition are set may be used.
In short, weight decay rate (weight parameter) according to lighting conditions
May be used.

In the next step 114, each contrast value is weighted around the temporary best focus position Z 'using a weighting function η obtained by substituting the value determined in step 112 for γ in the above equation (10). The least squares fitting is performed on each of the weighted contrast values, and a second contrast curve composed of, for example, a fourth-order approximation curve is calculated.

In the next step 116, main controller 50
Calculates the true best focus position (second best focus position) Z _best of the projection optical system PL based on the second contrast curve obtained in step 114. Specifically, the contrast values on the second contrast curve are compared at, for example, 0.05 μm intervals, the maximum value (peak point of the second contrast curve) is obtained, and the Z position corresponding to this maximum value is set to true. _Is calculated as the best focus position Z _best and stored in the memory. Thus, the detection of the best focus position ends.

Here, as an example, a large σ aperture stop 23a
The case where is being used will be described. In this case, as described above, in step 112, the weight decay rate γ is determined to be 1.0, so that the weighting function η represented by the following equation (11) is used. η = exp ｛−0.5 × (Z−Z ′) ² … (11)

In step 114, as described above, each contrast value is weighted around the temporary best focus position Z 'using the weighting function of the above equation (11), and each weighted contrast value is used. The fitting by the least squares method is performed for
A second contrast curve P2 composed of a fourth-order approximation curve as shown in (D) is calculated. Then, in step 116, the true best focus position (second best focus position) Z _best shown in FIG. 6D is calculated.

If the annular aperture stop 23c or the modified aperture stop 23d is in use, for example, as a result of the fine measurement in step 104, the first contrast curve P1 shown in FIG. Since the first contrast curve having a gentle peak is obtained, the true best focus position is calculated in the same manner as in the case of the large σ aperture stop 23a.

When the small σ aperture stop 23b is in use, as a result of the fine measurement in step 104, for example, as shown in FIG. A contrast curve P3 is obtained. The deviation (asymmetry) of the sub-peaks on both sides in FIG. 8A is due to the influence of the aberration of the projection optical system PL.

In this case, in step 112,
Since the weight decay rate γ is determined to be 0.3, a function expressed by the following equation (12) is used as the weighting function η. η = exp [−0.5 × {(Z−Z ′) / 0.3} ² ] (12)

According to the weighting function expressed by the above equation (12), the weight near the center of the weight (the value of the weighting function) is larger than the weighting function at the time of the large σ aperture stop expressed by the above equation (11). Is large, and the weight at a position distant from the center to some extent becomes very small. Therefore, by using the weighting function of the above equation (12), it is possible to reduce the influence of the contrast value at a position away from the peak when calculating the true best focus position.

[0118] As a result, second contrast curve calculated in step 116, for example, the contrast curve P4 becomes as shown in FIG. 8 (B), resulting in fact substantially coincident position and best focus position Z ₀ of the Z _best is calculated as the true best focus position. As is apparent from a comparison between FIG. 8B and FIG. 14 described above, in the present embodiment, the measurement accuracy of the true best focus position of the projection optical system PL under the small σ illumination condition is significantly improved. You can see that.

On the other hand, in step 108,
If it is determined that the provisional best focus position Z ′ cannot be calculated, the main control device 50 proceeds to step 118
Is performed. Here, the temporary best focus position Z '
Is not calculated when the calculated contrast of the 15 points indicates a monotonic increase (or a monotonous decrease) as shown in FIG. 9A. One of the reasons why such a phenomenon occurs is when the focus fluctuation from the previous measurement is abnormally large, or when the apparatus is initialized and the best focus position stored in the memory at the time of adjustment is different from the true best position. It is possible that the focus position is greatly different from the focus position. Even when the apparatus is initialized, if the difference between the best focus position stored in the memory at the time of adjustment and the true best focus position is small, in step 104, the fine measurement center is stored in the memory at the time of adjustment. This is because the provisional best focus position can be easily calculated by setting the best focus position stored in the above.

At step 118, main controller 50
Of the 15 points measured in step 104, for example, two points, for example, Z ₁ and Z ₂ in FIG. 9A are selected, and the two points and the contrast curve ( For example, a comparison is made between a contrast curve obtained when the best focus position was measured last time, a contrast curve stored in a memory at the time of adjustment, or a designed contrast curve. Then, main controller 50 performs the following based on the comparison result as shown in FIG.
(B) Contrast curve P as shown by the dotted line in FIG.
The peak position of (Z) is estimated to determine the fine measurement center (Z ₀ ′).

That is, since the function of the contrast curve (P (Z)) stored in the memory is obtained as a result of least squares approximation, for example, the function P (Z) of the position Z in the focus direction is obtained. ) = F (Z−Z ₀ ′), the main controller 50 sets the contrast measurement value C obtained as a result of the above measurement.
(Z ₁ ) and C (Z ₂ ) are: C (Z ₁ ) = f (Z ₁ −Z ₀ ′) (13) C (Z ₂ ) = f (Z ₂ −Z ₀ ′) (14) the value Z ₀ that satisfies both 'the (fine measurement center) is determined by the minimum square method. By changing the contrast curve stored in the memory in the focusing direction, f (Z−Z ₀ ) can be changed to f (Z−Z ₀ ′).
That is, it can be determined whether the contrast curve stored in the memory overlaps with the contrast curve including the two points (for example, Z ₁ and Z _{2 in} FIG. 9A) selected earlier.

In addition to the above, by comparing the magnitude of two points out of 15 points, it is possible to determine whether the contrast is monotonically increasing or monotonically decreasing, and to determine which contrast curve is stored based on one point. It is also possible to determine whether only the shift has occurred.

As described above, the fine measurement center Z ₀ ′
Is estimated, the process returns to step 104, and fine measurement is performed around the fine measurement center (Z ₀ ′) measured in step 118. Thereafter, the temporary best focus position Z ′ and true Of the best focus position Z _best is obtained.

The estimated fine measurement center Z ₀ ′
When performing fine measurement centering on, the same Z position as the 15 points (points shown in FIGS. 9A and 9B) measured in the previous measurement, or a Z position in the vicinity thereof is a measurement scheduled position. In the case, for example, when the absolute value of the difference between the measurement scheduled Z position of the fine measurement and the previous measurement Z position is less than の of the measurement interval, the fine measurement at the nearest Z position is omitted, The number of measurements can be reduced, which in turn
Throughput can be improved.

In the above description, two of the previous measurement points are selected and compared with the stored contrast curve. However, the present invention is not limited to this, and three or more points can be selected. It is also possible to improve the measurement accuracy.

When a small σ aperture stop having a contrast curve with a sub-peak is used, the above step 1 is used.
In 18, it is desirable to increase the number of points selected from the measurement points (15 points).

If the exposure apparatus is initialized and the stored best focus position (and contrast curve) at the time of the previous measurement is lost, it is stored at the time of adjustment in step 104 as described above. prior to performing the fine measuring about the best focus position, as shown in FIG. 10 (a), around the best focus position Z _f in the adjustment step, apart 0.6μm, for example, in the optical axis direction for 2-point (Z _s, Z _t) (hereinafter referred to as "rough measurement") aerial image measurement, the said two points on the basis of the measurement result of the rough measurement (Z _s, Z _t) for calculating a contrast value of (FIG. 10B). Then, the two contrast values obtained at this time and FIG.
0 (B) is compared with the contrast curve Pi stored in the memory at the time of the adjustment indicated by the two-dot chain line, and the contrast curve Pi ′ indicated by the one-dot chain line in which the contrast curve Pi is translated in the Z-axis direction is compared. it is also possible to estimate the peak location as a fine measure center Z _0.

Then, in step 104,
The Z ₀ as fine measurement center, may be set to be performed fine measurement.

Thus, when the apparatus is initialized, for example, a detailed measurement (for example, 0.15 μm
Since the center of fine measurement can be obtained without performing ordinary rough measurement, such as performing measurement over a wide range with an accuracy (interval) of μ (0.30 μm interval), the throughput is improved. There is expected.

In this case, as described above,
The absolute value of the difference between the position measured at the time of obtaining the fine measurement center or a position in the vicinity thereof, for example, the position at which the fine measurement is to be measured and the position measured at the time of obtaining the fine measurement center is 1 / of the measurement interval. If less than 2,
If the fine measurement at the closest focus position is omitted, the number of fine measurements itself can be reduced.

As described above, in the present embodiment, regardless of the lighting conditions, whether the apparatus is initialized, or if there is a large change in the focus, the present embodiment is applicable. In addition, the best focus position of the projection optical system PL can be obtained with high accuracy. Therefore, the main control device uses the multi-point focus position detection system (6) based on the best focus position thus obtained.
0a, 60b), and the multi-point focal position detection system (60a, 60b) after the calibration is performed.
By executing the above-described auto-focusing and auto-leveling during the scanning exposure using b), it is possible to realize high-precision exposure with almost no defocus.

Further, in the present embodiment, especially when the apparatus is initialized, the rough measurement for performing the aerial image measurement at at least two Z positions is employed, so that the time required for the rough measurement and, consequently, the best focus Since the time required for the position measurement can be reduced, the throughput can be improved accordingly.

As is clear from the above description, in the present embodiment, the main control device 50 constitutes a measurement processing device and a calculation device.

In the above embodiment, a case has been described in which a Gaussian function in which the standard deviation is replaced by a weight parameter is used as the weighting function, but the present invention is not limited to this. That is, as the weighting function, for example, a step function having values of 0 and 1 as shown in FIG. 11 is used, and the measured value near the temporary best focus position (first best focus position) is 1 and the temporary value is 1. It is also possible to set the measured value at a position away from the best focus position by a predetermined amount to 0, and to widen or narrow the range Rg of 1 (weight parameter) according to the lighting conditions. Thereby, even when aberration is present in the projection optical system PL in the case of small σ illumination, the true best focus position can be calculated without being affected by the sub-peak.

In the above embodiment, the amplitudes of the 0th-order and 1st-order frequency components are used. However, the amplitudes of the second-order and higher-order frequency components are generally small, and electrical noise and optical noise In some cases, it is not possible to obtain sufficient amplitude with respect to periodic noise, but if there is no problem with respect to the S / N (signal / noise) ratio, the best focus can be obtained by observing changes in the amplitude ratio of higher-order frequency components. It is possible to determine the position.

In the above embodiment, the weight decay rate, which is a weighting parameter, is determined based on the state of the illumination system aperture stop plate. However, when the numerical aperture of the projection optical system PL can be changed. Or even higher N.D. A.
Similarly, the coherence factor σ is calculated based on the numerical aperture of the projection optical system PL and the numerical aperture of the illumination optical system, and the optimum weight attenuation factor can be set accordingly. It is also possible.

In the above embodiment, the measurement is performed at 15 points in the Z direction. However, the present invention is not limited to this. The measurement can be arbitrarily determined in consideration of the time required for the measurement and the measurement accuracy. is there.

Note that the image plane of the projection optical system PL, that is,
The best imaging plane is a plane composed of a set of best focus points at innumerable points at different distances from the optical axis (that is, so-called innumerable points at different image heights). Also, the image plane shape can be easily and accurately obtained.

In each of the above embodiments, the case where the present invention is applied to the step-and-scan type projection exposure apparatus has been described. However, the present invention is not limited to this. Transferring the pattern onto the substrate and moving the substrate step by step
The present invention can be applied to an AND-repeat type exposure apparatus.

In each of the above embodiments, the case where the present invention is applied to an exposure apparatus for manufacturing a semiconductor has been described. However, the present invention is not limited to this. For example, a liquid crystal display element pattern is transferred to a square glass plate. The present invention can be widely applied to an exposure apparatus for a liquid crystal, an exposure apparatus for manufacturing a thin film magnetic head, an image sensor, a micromachine, a DNA chip, a reticle, a mask, and the like.

In each of the above embodiments, KrF excimer laser light (248 nm) and ArF
The case where excimer laser light (193 nm) or the like is used has been described.
i-line (365 nm), F ₂ laser light (157 nm), harmonics of a copper vapor laser, a YAG laser, and the like can be used as illumination light for exposure.

In each of the above embodiments, the case where a reduction system and a refraction system are used as the projection optical system has been described. However, the present invention is not limited to this, and an equal magnification or enlargement system may be used as the projection optical system. System, a catadioptric system, or a reflective system may be used.

An illumination optical system composed of a plurality of lenses;
The projection optical system is incorporated into the exposure apparatus main body to perform optical adjustment, and a reticle stage and wafer stage consisting of many mechanical parts are attached to the exposure apparatus main body to connect wiring and piping, and are further adjusted (electrical adjustment, operation confirmation, etc.) 2), the exposure apparatus of the present embodiment can be manufactured. It is desirable that the manufacture of the exposure apparatus be performed in a clean room in which the temperature, cleanliness, and the like are controlled.

<< Device Manufacturing Method >> Next, an embodiment of a device manufacturing method using the above-described exposure apparatus in a lithography process will be described.

FIG. 12 shows devices (semiconductor chips such as ICs and LSIs, liquid crystal panels, CCDs, thin film magnetic heads,
The flowchart of the example of manufacture of a micromachine etc. is shown. As shown in FIG.
In 1 (design step), a function / performance design of a device (for example, a circuit design of a semiconductor device) is performed, and a pattern design for realizing the function is performed. Subsequently, in step 202 (mask manufacturing step)
A mask on which the designed circuit pattern is formed is manufactured. On the other hand, in step 203 (wafer manufacturing step)
A wafer is manufactured using a material such as silicon.

Next, in step 204 (wafer processing step), using the mask and the wafer prepared in steps 201 to 203, an actual circuit or the like is formed on the wafer by a lithography technique or the like as described later. . Next, in step 205 (device assembly step), device assembly is performed using the wafer processed in step 204. In this step 205,
Steps such as a dicing step, a bonding step, and a packaging step (chip encapsulation) are included as necessary.

Finally, step 206 (inspection step)
In step S205, inspections such as an operation check test and a durability test of the device created in step 205 are performed. After these steps, the device is completed and shipped.

FIG. 13 shows a detailed flow example of step 204 in the semiconductor device. In FIG. 13, in step 211 (oxidation step), the surface of the wafer is oxidized. Step 212 (CV
In step D), an insulating film is formed on the wafer surface. In step 213 (electrode formation step), electrodes are formed on the wafer by vapor deposition. Step 214
In the (ion implantation step), ions are implanted into the wafer. Each of the above steps 211 to 214 constitutes a pre-processing step in each stage of wafer processing, and is selected and executed according to a necessary process in each stage.

In each stage of the wafer process, when the above-mentioned pre-processing step is completed, the post-processing step is executed as follows. In this post-processing step, first, in step 2
In 15 (resist forming step), a photosensitive agent is applied to the wafer. Subsequently, in step 216 (exposure step), the circuit pattern of the mask is transferred onto the wafer by the lithography system (exposure apparatus) and the exposure method described above. Next, in step 218 (etching step), the exposed members other than the portion where the resist remains are removed by etching. Then, in step 219 (resist removing step), unnecessary resist after etching is removed.

By repeatedly performing the pre-process and the post-process, multiple circuit patterns are formed on the wafer.

By using the device manufacturing method of this embodiment described above, the exposure apparatus of the above embodiment is used in the exposure step (step 216), so that the reticle pattern can be transferred onto the wafer with high accuracy. As a result, it is possible to improve the productivity (including the yield) of a highly integrated device.

[0152]

As described above, according to the optical characteristic measuring method and apparatus according to the present invention, when measuring the best focus position of the projection optical system, measurement is performed on at least one of the precision surface and the temporal surface. This has the effect of improving the ability.

Further, according to the exposure apparatus of the present invention, there is an effect that highly accurate exposure can be realized.

In addition, the device manufacturing method according to the present invention
This has the effect of contributing to an improvement in the productivity of highly integrated microdevices.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a schematic configuration of an exposure apparatus according to an embodiment.

FIG. 2 is a diagram showing a configuration of an illumination system aperture stop plate constituting an illumination optical system.

FIG. 3 is a diagram showing an internal configuration of the aerial image measurement device of FIG. 1;

FIG. 4A is a plan view showing a state where a spatial image PM ′ is formed on a slit plate at the time of measuring an aerial image, and FIG. 4B is a photoelectric image obtained at the time of measuring the aerial image; FIG. 3 is a diagram illustrating an example of a converted signal (light intensity signal) P.

FIG. 5 is a flowchart illustrating a method of detecting a best focus position of a projection optical system using the aerial image measurement device.

FIGS. 6A to 6D are diagrams for explaining calculation of a true best focus of the projection optical system when a large σ aperture stop is used.

FIG. 7A is a diagram illustrating a weighting classification table according to the present embodiment, and FIG. 7B is a modified example of the weighting classification table.

FIGS. 8A and 8B are diagrams for explaining calculation of a true best focus position of the projection optical system when a small σ aperture stop is used.

9 (A) and 9 (B) show Step 1 of FIG. 5;
FIG. 18 is a diagram for explaining the process of No. 18;

FIGS. 10A and 10B are diagrams illustrating rough measurement when the apparatus is initialized. FIG.

FIG. 11 is a diagram showing best focus position measurement using a step function as a weighting function.

FIG. 12 is a flowchart illustrating an embodiment of a device manufacturing method according to the present invention.

FIG. 13 is a flowchart showing details of step 204 in FIG.

FIG. 14 is a diagram for explaining a conventional technique.

[Explanation of symbols]

12: illumination optical system (part of illumination device), 14: light source (part of illumination device), 22: slit (measurement mark), 24
... Optical sensor (photoelectric conversion element), 50 ... Main control device (measurement processing device, calculation device), 59 ... Aerial image measurement device (optical characteristic measurement device), 90 ... Slit plate (pattern forming member), 100 ... Exposure device , IL: illumination light, PL: projection optical system, PM: pattern, PM ': aerial image, R: reticle (mask), W: wafer (substrate), WST: wafer stage (substrate stage).

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Koji Saito 3-2-2 Marunouchi, Chiyoda-ku, Tokyo Nikon Corporation (72) Inventor Tsuneyuki Hagiwara 3-2-2 Marunouchi, Chiyoda-ku, Tokyo Stock Company F term in Nikon Corporation (reference) 2G086 HH01 5F046 AA25 BA04 BA05 CB17 CC01 CC03 CC05 DA14 DB01 DB05 DC10 DC12

Claims (11)

[Claims] An optical characteristic measuring method for measuring an optical characteristic of a projection optical system, wherein a predetermined pattern is illuminated by illumination light, and a spatial image of the pattern is formed near an image plane via the projection optical system. And scanning the measurement pattern arranged on the image plane side of the projection optical system relative to the aerial image, and performing photoelectric conversion according to the intensity of the illumination light via the measurement pattern. Obtaining a signal at each of a plurality of positions in the optical axis direction of the measurement pattern; based on a first contrast curve obtained by curve-fitting a contrast value of a photoelectric conversion signal obtained at each of the plurality of positions. Obtaining a temporary best focus position of the projection optical system by using the weighting parameter determined according to an illumination condition for illuminating the projection optical system. Calculating a second contrast curve by weighting the contrast value using a weighting function to be calculated, and calculating a true best focus position of the projection optical system based on the second contrast curve. Characteristics measurement method. 2. The method according to claim 1, wherein the weighting function is a Gaussian function including a standard deviation as the weight parameter. 3. The weighting function according to claim 1, wherein the weighting function is a step function in which a weight value is 1 at a central portion of a predetermined width determined according to the illumination condition, and is 0 at both sides. Optical property measurement method. 4. The illumination condition according to claim 1, wherein the illumination condition is a condition corresponding to a coherence factor obtained by dividing a numerical aperture of an illumination optical system for illuminating the pattern by a numerical aperture of the projection optical system. The optical characteristic measuring method according to any one of the above. 5. An optical characteristic measuring method for measuring an optical characteristic of a projection optical system, wherein a predetermined pattern is illuminated by illuminating light, and a spatial image of the pattern is formed near an image plane via the projection optical system. And scanning the measurement pattern arranged on the image plane side of the projection optical system relative to the aerial image, and performing photoelectric conversion according to the intensity of the illumination light via the measurement pattern. Obtaining a signal at each of at least two positions in the optical axis direction of the measurement pattern; comparing at least two contrast values respectively corresponding to the obtained photoelectric conversion signals with a reference contrast curve prepared in advance. Calculating a peak point on a first contrast curve obtained by curve fitting the at least two contrast values, and calculating the peak value corresponding to the peak point. Step and calculating the position of the optical axis of the use pattern as the first best focus position of said projection optical system; optical characteristic measuring method comprising. 6. The method according to claim 1, wherein the measurement pattern is relatively scanned with respect to the aerial image, and a photoelectric conversion signal corresponding to the intensity of the illumination light via the measurement pattern is transmitted to the first image.
Obtaining the measurement pattern for each of a plurality of positions in the optical axis direction within a range of a predetermined width including the best focus position; and obtaining the obtained contrast value of the photoelectric conversion signal for each of the plurality of positions by curve fitting. Calculating a position in the optical axis direction of the measurement pattern corresponding to a peak point of the second contrast curve to be obtained as a second best focus position of the projection optical system. 6. The optical characteristic measuring method according to 5. 7. An illumination device for measuring an optical characteristic of a projection optical system, the illumination device illuminating the pattern for forming a spatial image of a predetermined pattern on an image plane via the projection optical system. An apparatus; a pattern forming member disposed on the image plane side of the projection optical system and having a measurement pattern formed thereon; and a photoelectric conversion of the illumination light passing through the measurement pattern to pass through the measurement pattern. A photoelectric conversion element for outputting a photoelectric conversion signal according to the intensity of the illumination light; and the pattern forming member in a state where the predetermined pattern is illuminated by the illumination device and the aerial image is formed on the image plane. Is scanned relative to the aerial image, a plurality of the pattern forming member in the optical axis direction of the projection optical system from the photoelectric conversion signal from the photoelectric conversion element corresponding to the aerial image A measurement processing device for measuring each position; a temporary best focus position of the projection optical system based on a first contrast curve obtained by curve-fitting the contrast values of the photoelectric conversion signals obtained for the plurality of positions. And a weighting parameter determined according to the lighting conditions of the lighting device, and weighting the contrast value using a weighting function centered on the temporary best focus position.
And a calculating device for calculating a true best focus position of the projection optical system based on the second contrast curve. 8. The optical characteristic measuring device according to claim 7, wherein the calculating device performs the weighting using a Gaussian function including a standard deviation as the weighting parameter as the weighting function. 9. The calculation device performs the weighting using a step function in which a weight value is 1 at a central portion of a predetermined width determined according to the illumination condition and is 0 on both sides as the weighting function. The optical characteristic measuring device according to claim 7, wherein: 10. An exposure apparatus for transferring a circuit pattern formed on a mask to a substrate via a projection optical system, wherein the substrate stage moves while holding the substrate; An optical device comprising: the optical characteristic measuring device according to any one of claims 7 to 9 provided in a part thereof. 11. A device manufacturing method including a lithography step, wherein in the lithography step, exposure is performed using the exposure apparatus according to claim 10.