JP2006196555A - Method and apparatus of measuring aberration and of exposure - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To measure the aberration of a projection optical system with high precision for a short time. <P>SOLUTION: An image 1AB by a projection optical system PL of a line pattern is scanned by a slit 9A, and the image surface amplitude function F1(X) of the image is found. The Fourier transformation is performed in the image surface function obtained from a predetermined image surface phase function G1(θ) and predetermined image surface amplitude function F1(X), and a pupil plane function (amplitude function f1(X) and a phase function g1(θ)) are found. The phase function g1(θ) is obtained when an image surface amplitude function obtained by performing inverse Fourier transform of the pupil plane function obtained from the function which gives the defocus effect to the phase function and the amplitude function f1(X), and the image surface phase function F2(X) measured by actually defocusing, are approximately matched. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an aberration measurement technique for measuring an aberration of a projection optical system, for example, a mask pattern in a lithography process for manufacturing devices such as a semiconductor element, an imaging element (CCD, etc.), and a liquid crystal display element. It is suitable for use in measuring the aberration of the projection optical system of the projection exposure apparatus used for transferring the image onto the substrate. The present invention further relates to an exposure technique using the aberration measurement technique.

  Conventionally, in a lithography process for manufacturing a semiconductor element or the like, a reticle (or photomask or the like) pattern as a mask is coated with a photosensitive material through a projection optical system (wafer or glass plate or the like). A batch exposure type projection exposure apparatus (such as a stepper) and a scanning exposure type projection exposure apparatus (such as a scanning stepper) are used for transferring the image onto the top. As the integration degree and fineness of semiconductor elements and the like are further improved, the accuracy of imaging characteristics such as various aberrations required for the projection optical system of the projection exposure apparatus is also increasing.

  In addition, the imaging characteristics of the projection optical system gradually vary due to changes in environmental conditions such as the thermal energy of the exposure light accumulated in the projection optical system and the atmospheric pressure and temperature around the projection optical system by continuing the exposure. . Therefore, in the projection exposure apparatus, the distortion is controlled by controlling the posture of some lens elements constituting the projection optical system or by controlling the atmospheric pressure in a space (lens chamber) between predetermined lens elements. An imaging characteristic control mechanism that can control predetermined imaging characteristics such as aberration and spherical aberration to a predetermined state is provided. In order to control the imaging characteristics of the projection optical system using this imaging characteristics control mechanism, the imaging characteristics are measured with high accuracy while the projection optical system is mounted on the projection exposure apparatus (on-body). There is a need to. Further, for example, it is necessary to measure the imaging characteristics of the projection optical system with high accuracy on-body during assembly adjustment or maintenance of the projection exposure apparatus.

  As a conventional method for measuring imaging characteristics, a test reticle on which a predetermined pattern is formed is used to expose a wafer with a projected image of the pattern and measure the resist image obtained by developing the wafer. The method of calculating the imaging characteristics based on the above (hereinafter referred to as “baking method”) has been mainly used. However, this baking method requires a long time for measurement.

Therefore, without actually exposing the wafer, the aerial image of the measurement mark of the test reticle illuminated by the exposure light is projected via the projection optical system, and the aerial image (projected image) is measured. Based on this, a method of calculating the imaging characteristics of the projection optical system (hereinafter referred to as “aerial image measurement method”) has been proposed (see, for example, Patent Document 1). As another example of this aerial image measurement method, a plurality of diffraction gratings are illuminated, and the image intensity of each diffraction grating obtained through the projection optical system is measured at a plurality of focus positions of the projection optical system, A method for obtaining the wavefront aberration of the projection optical system based on the result has also been proposed (see, for example, Patent Document 2). There has also been proposed a method for obtaining the wavefront aberration of the projection optical system based on the measurement result of the light intensity distribution of the projected image of the pinhole.
JP-A-10-170399 JP 2001-57337 A

  As described above, when the aberration of the projection optical system is measured on-body, the conventional measurement object is low-order aberration. In general, when an aberration function indicating wavefront aberration on the exit pupil (or pupil plane) of the projection optical system is W (ρ, θ), the aberration function W (ρ, θ) is expressed in a polar coordinate format, and ρ is It is a normalized position (radial radius) in the radial direction of the exit pupil (or pupil plane) of the projection optical system, and θ is an angle. The aberration function W (ρ, θ) is series-expanded by using a completely orthogonal system polynomial in which the radial ρ and the angle θ are separated, for example, Zernike's Polynomial represented by the following equation: Is possible.

Here, Z _i is a coefficient representing the magnitude of the aberration represented by the i-th order Zernike polynomial fi (ρ, θ) among the various aberrations of the projection optical system. Hereinafter, for convenience of explanation, the coefficient Z _i (i is an integer of 1 or more) is also regarded as an aberration (or aberration amount) represented by an i-th order Zernike polynomial.
In this case, the low-order aberration generally indicates an aberration represented by a Zernike polynomial up to the ninth order, that is, an aberration up to Z ₉ . Such low-order aberrations can change due to changes in the relative spacing and angle of the lens elements in the projection optical system, changes in curvature due to changes in the temperature of the lens elements, and the like. Therefore, the low-order aberration amount may change depending on time and temperature. Moreover, a part of such low-order aberrations can be corrected by the imaging characteristic control mechanism.

On the other hand, high-order aberrations are mostly determined by the error in the shape of the lens elements in the projection optical system. Conventionally, high-order aberrations were generally considered to be unlikely to change with temperature and time. . However, as a result of analyzing the aberration fluctuation depending on the temperature change of the projection optical system, the present inventor has found that the aberrations up to Z ₉ , Z ₁₆ , and Z ₂₅ change with respect to, for example, axially symmetric aberration. Therefore, it is desirable that high-order aberrations exceeding these 9th-order Zernike polynomials can be separated and accurately measured. If high-order aberrations can be accurately measured in this way, there is a possibility that the aberrations can be corrected using, for example, the imaging characteristic control mechanism described above.

Further, among the conventional measurement methods, a method for measuring a projected image of a pinhole has a low S / N ratio due to a small amount of light, and it is difficult to improve measurement accuracy, and a two-dimensional image sensor is required as a photoelectric sensor. There was a problem that became complicated.
In view of such a point, the present invention has a first object to provide an aberration measurement technique capable of measuring an aberration of a projection optical system with high accuracy in a short time.

A second object of the present invention is to provide an aberration measurement technique capable of measuring high-order aberrations of a projection optical system with high accuracy in a short time.
A third object of the present invention is to provide an exposure technique capable of measuring the aberration of the projection optical system in a short time with high accuracy in a state where the projection optical system is mounted on the projection exposure apparatus (exposure apparatus). And

  An aberration measurement method according to the present invention is an aberration measurement method for measuring an aberration of a projection optical system (PL), and projects an image of a line pattern (1A to 1F) through the projection optical system, and the line pattern A first step (step 111) for obtaining light intensity distribution information in the width direction of the image, and the image of the line pattern on the pupil plane of the projection optical system from the light intensity distribution information obtained in the first step. A second step (steps 113 to 121) for obtaining the phase distribution information of the image light beam, and a third step (step 122) for obtaining the aberration of the projection optical system based on the phase distribution information obtained in the second step. It is what you have.

  According to the present invention, in the second step, the pupil plane of the projection optical system is obtained, for example, by the phase recovery method using the light intensity distribution information (light amount distribution information) obtained by the aerial image measurement in the first step. The phase distribution information of the imaged light beam can be obtained in a short time. Then, from the phase distribution information, for example, a wavefront aberration represented by a Zernike polynomial up to a predetermined order can be obtained. At this time, since the light amount of the image of the line pattern is sufficiently larger than that of the pinhole image, the SN ratio becomes high, and high measurement accuracy can be obtained.

In the present invention, as an example, in the first step, the line pattern image and the slit-shaped opening patterns (9A to 9F) pass through the opening pattern while relatively scanning in the width direction of the line pattern image. It includes a step of receiving light. Thereby, the light intensity distribution in the width direction of the image of the line pattern can be measured with a simple mechanism and at a high S / N ratio.
Further, as an example, in the second step, the function obtained by multiplying the first image plane amplitude function by the first image plane amplitude function obtained from the light intensity distribution information obtained in the first step is Fourier-transformed. A fourth step (steps 113 to 116) for obtaining a first amplitude function and a first phase function on the pupil plane of the projection optical system, and an image of the line pattern is added to the first phase function obtained in the fourth step. A fifth step (step 117) for obtaining a second phase function by performing an operation corresponding to a predetermined change in the light intensity distribution, and the first amplitude function obtained in the fourth step is obtained in the fifth step. A sixth step (steps 118 and 119) for obtaining a second image plane amplitude function and a second image plane phase function on the image plane of the projection optical system by performing inverse Fourier transform on the function obtained by multiplying the second phase function. ) And the light of the line pattern image A seventh step (step 120) of obtaining light intensity distribution information in the width direction of the image of the line pattern and obtaining a third image plane amplitude function from the light intensity distribution information in a state where the predetermined change is given to the degree distribution; When the second image plane amplitude function obtained in the sixth step and the third image plane amplitude function obtained in the seventh step are within an allowable range, the second image plane amplitude function was obtained in the fourth step. And an eighth step (step 121) for obtaining phase distribution information of the imaged light beam on the pupil plane of the projection optical system from the first phase function.

Thus, by using the first phase function when the calculated second image plane amplitude function and the measured third image plane amplitude function are within the allowable range, the projection can be accurately performed by the phase recovery method. Phase distribution information on the pupil plane of the optical system can be obtained.
As an example, the first image plane phase function is a predetermined distribution constant, and the predetermined change in the light intensity distribution of the line pattern image in the fourth step is the line pattern image. This is a change in the light intensity distribution when the focus position is changed. Since the change of the phase function when the focus position is changed in this way is known, the second image plane amplitude function and the second image plane phase function on the image plane can be easily obtained in the sixth step. Can do.

Further, in the eighth step, when the second image plane amplitude function and the third image plane amplitude function match within the allowable range, the imaging light flux on the pupil plane of the projection optical system The phase distribution information may be obtained. Thereby, the phase distribution information can be easily obtained.
In the eighth step, when the second image plane amplitude function and the third image plane amplitude function do not match within the allowable range, the light intensity distribution information obtained in the seventh step is It is regarded as the light intensity distribution information obtained in the first step, the second image plane phase function obtained in the sixth step is regarded as the first image plane phase function, and the fourth step to the eighth step. You may repeat to a process (steps 123-136). By repeating the calculation, measurement, and comparison in this manner, the accuracy of the phase distribution information of the imaged light beam on the pupil plane can be gradually increased.

As an example, the line pattern projected in the first step includes six line patterns arranged in different directions.
According to the present inventor, when a predetermined integer equal to or greater than 2 is M, they are arranged on the pupil plane of the projection optical system along at least M different directions around the optical axis of the projection optical system. By obtaining the phase information of the imaged light flux at the at least M points, the wavefront aberration represented by the Zernike polynomial up to the M ² order of the projection optical system can be obtained. Further, by measuring images of six line patterns arranged in different directions, wavefront aberrations expressed by higher-order Zernike polynomials up to the 37th order (in the case of FIG. 9) can be obtained. Also, Zernike coefficients up to the 81st order in the 9 direction and the 121st order in the 11 direction can be decomposed.

  An aberration measuring apparatus according to the present invention is an aberration measuring apparatus for measuring the aberration of the projection optical system (PL), and includes line patterns (1A to 1F) arranged on the object plane side of the projection optical system, and An illumination system (12) for illuminating the line pattern, and a slit-like shape arranged on the image plane side of the projection optical system and extending in a direction substantially parallel to the longitudinal direction of the image of the line pattern by the projection optical system A scanning mechanism (WST) that relatively scans the aperture pattern (9A to 9F), the image of the line pattern by the projection optical system, and the aperture pattern in the width direction of the image of the line pattern, and the aperture pattern. A photoelectric sensor (94) that receives light and detects the light intensity distribution information of the image of the line pattern, and the projection optical system based on the light intensity distribution information detected by the photoelectric sensor. A first computing device (50) for obtaining the phase distribution information of the imaging light beam of the image of the line pattern on the surface, and obtaining the aberration of the projection optical system based on the phase distribution information obtained by the first computing device And a second arithmetic unit (50). With this aberration measuring apparatus, the aberration measuring method of the present invention can be implemented.

  In this case, as an example, the line pattern includes six line patterns arranged in different directions, and the opening pattern includes six opening patterns corresponding to the six line patterns. A stage mechanism (38) that relatively displaces the pattern image and the opening pattern in the optical axis direction of the projection optical system may be further provided. By defocusing the image of the line pattern by the stage mechanism, the phase distribution information of the imaged light beam on the pupil plane of the projection optical system can be easily obtained.

The exposure method according to the present invention illuminates the first object (R) with an exposure beam, and exposes the second object (W) with the exposure beam via the first object and the projection optical system (PL). In the method, the aberration of the projection optical system is measured by the aberration measuring method of the present invention. According to the present invention, the aberration of the projection optical system can be easily measured even during the exposure process.
In the present invention, the imaging characteristics of the projection optical system may be corrected according to the aberration measured by the aberration measuring method. Thereby, the imaging characteristics of the projection optical system can be maintained in a predetermined state.

  The exposure apparatus according to the present invention illuminates the first object (R) with an exposure beam, and exposes the second object (W) with the exposure beam via the first object and the projection optical system (PL). The apparatus is provided with the aberration measuring apparatus of the present invention in order to measure the aberration of the projection optical system. According to the present invention, the aberration of the projection optical system can be measured on-body.

According to the present invention, the aberration of the projection optical system can be measured with high accuracy in a short time by measuring the aerial image of the line pattern.
Further, in the present invention, when the line pattern projected in the first step includes six line patterns arranged in different directions, the wavefront aberration represented by a higher-order Zernike polynomial up to the 37th order is obtained. Can be sought.

  Further, according to the exposure method and apparatus of the present invention, the aberration of the projection optical system can be measured with high accuracy in a short time in a state where the projection optical system is mounted on the exposure apparatus.

Hereinafter, an example of a preferred embodiment of the present invention will be described with reference to the drawings.
FIG. 1 shows a schematic configuration of a projection exposure apparatus 10 of this example. The projection exposure apparatus 10 corresponding to the exposure apparatus of the present invention is a scanning stepper type scanning exposure type projection exposure apparatus.
In FIG. 1, a projection exposure apparatus 10 includes a light source 14 (exposure light source) that generates a laser beam LB, an illumination optical system 12 (illumination unit or illumination system), a reticle stage RST that holds and moves a reticle R as a mask, Projection optical system PL, wafer stage WST (scanning mechanism) that holds and moves wafer W as a substrate (or photoconductor), a control system that controls these, and the like are provided. The parts other than the light source 14 and the control system are actually housed in an environmental chamber (not shown) in which environmental conditions such as the internal temperature are controlled with high accuracy and are maintained constant.

In this example, an ArF excimer laser light source (oscillation wavelength 193 nm) is used as the light source 14. The light source 14 is controlled by a main controller 50 (first and second arithmetic units) comprising a computer that controls the overall operation of the apparatus, on / off of the laser emission, center wavelength, spectral half width, repetition frequency, and the like. Is done. As an exposure light source, KrF excimer laser (wavelength 248 nm), F ₂ laser (wavelength 157 nm), harmonic generator of YAG laser, harmonic generator of solid-state laser (semiconductor laser, etc.), or mercury lamp (i-line etc.) ) Etc. can also be used.

  The illumination optical system 12 includes a beam shaping optical system 18 that shapes the cross-sectional shape of the laser beam LB supplied from the light source 14, a fly-eye lens 22 as an optical integrator (a homogenizer or a homogenizer), an illumination system aperture stop plate 24, A relay optical system including a first relay lens 28A and a second relay lens 28B, a fixed reticle blind 30A, a movable reticle blind 30B, a mirror M, a condenser lens 32, and the like are provided. As the optical integrator, an internal reflection type integrator (for example, a rod integrator) or a diffractive optical element may be used. A large number of microlenses constituting the fly-eye lens 22 each focus the laser beam LB from the beam shaping optical system 18 on the focal plane on the emission side, and a secondary light source (surface light source) is formed on the focal plane. . Hereinafter, the laser beam LB emitted from the secondary light source formed by the fly-eye lens 22 is referred to as “illumination light IL” as an exposure beam (exposure light).

  The light source 14 and the illumination optical system 12 are also used as an illumination system for a later-described aerial image measurement. In the illumination optical system 12, an illumination system aperture stop plate 24 made of a disk-like member is disposed in the vicinity of the exit-side focal plane of the fly-eye lens 22. The illumination system aperture stop plate 24 is provided with an aperture stop (small aperture) made up of, for example, a normal circular aperture, and an aperture stop (small size) for reducing the σ value that is a coherence factor made up of a small circular aperture at substantially equal angular intervals. σ stop), an annular aperture stop for annular illumination (annular aperture stop), and a modified aperture stop (for example, for dipole illumination or quadrupole illumination) in which a plurality of apertures are decentered for the modified light source method. ) And the like are arranged. The illumination system aperture stop plate 24 is rotated by a drive device 40 such as a motor controlled by the main control device 50, and any one of the aperture stops is on the optical path of the illumination light IL by this rotation operation. Selectively set.

A beam splitter 26 having a low reflectance and a high transmittance is disposed on the optical path of the illumination light IL emitted from the illumination system aperture stop plate 24, and further, relays are provided on the rear optical path with reticle blinds 30A and 30B interposed therebetween. Optical systems (28A, 28B) are arranged.
The fixed reticle blind 30A is disposed on a surface slightly defocused from the conjugate plane with respect to the pattern surface of the reticle R, and the fixed reticle blind 30A is formed with a rectangular opening that defines the illumination area IAR on the reticle R. Has been. Also, in the vicinity of the fixed reticle blind 30A, there is a movable reticle blind 30B having an opening whose position and width are optically corresponding to the scanning direction at the time of scanning exposure and the non-scanning direction orthogonal thereto. Has been placed. At the start and end of scanning exposure, the illumination area IAR defined by the fixed reticle blind 30A is further restricted by the movable reticle blind 30B according to instructions from the main controller 50, so that unnecessary portions (reticles) The exposure of the portion other than the portion to be transferred such as the circuit pattern on R is prevented. In this example, the movable reticle blind 30B is also used for setting an illumination area when performing aerial image measurement, which will be described later, as necessary.

On the other hand, a condenser lens 44 and an integrator sensor 46 including a light receiving element are disposed on the optical path of the illumination light IL reflected by the beam splitter 26 in the illumination optical system 12.
The laser beam LB emitted from the light source 14 at the time of exposure becomes illumination light IL in the illumination optical system 12, and the illumination light IL is bent vertically downward by the mirror M and then passes through the condenser lens 32. A slit-like illumination area IAR elongated in the non-scanning direction of the pattern surface (lower surface) of the reticle R is illuminated with a uniform illuminance distribution.

  On the other hand, a part of the illumination light IL reflected by the beam splitter 26 is received by the integrator sensor 46 via the condenser lens 44, and the photoelectric conversion signal of the integrator sensor 46 passes through the peak hold circuit and the A / D converter. It is supplied to the main controller 50 through the signal processing device 80 having the same. In this example, the measurement value of the integrator sensor 46 is used not only for exposure amount control on the wafer W but also for calculation of the irradiation amount for the projection optical system PL. This irradiation amount is not only the wafer reflectivity (which can also be obtained based on the output of the integrator sensor 46 and the output of the reflectivity monitor (not shown)) and the imaging characteristics due to the absorption of illumination light of the projection optical system PL. It is also used to calculate the amount of change.

In this example, the main controller 50 measures the irradiation amount of the illumination light IL at predetermined time intervals based on the output of the integrator sensor 46, and the measurement result is stored in the memory 51 (storage device) as an irradiation history. It has come to be remembered.
Under the illumination light IL, an image formed by the telecentric projection optical system PL on both sides (or one side on the wafer side) of the pattern in the illumination area IAR of the reticle R is coated with a photoresist as a photosensitive material. And projected onto an exposure area IA on one shot area of the wafer W. The exposure area IA is conjugate with the illumination area IAR, and the projection optical system PL converts the pattern image (first surface or object surface) of the reticle R (first object) to the upper surface of the wafer W (second object). It is formed on the (second surface or image surface). The projection magnification of the projection optical system PL is, for example, a reduction magnification such as 1/4 or 1/5. In the following description, it is assumed that the projection magnification of the projection optical system PL is 1/4. Although the projection optical system PL of this example is a refraction system, a catadioptric system or the like can also be used as the projection optical system PL. As shown in FIG. 3, a variable aperture stop AS for controlling the numerical aperture NA of the projection optical system PL is disposed in the vicinity of the pupil plane PP of the projection optical system PL.

  Hereinafter, the Z-axis is taken in a direction parallel to the optical axis AX of the projection optical system PL, the X-axis is taken in a direction perpendicular to the paper surface of FIG. 1 within a plane perpendicular to the Z-axis, and the direction parallel to the paper surface of FIG. A description will be given taking the Y axis. In this example, the scanning direction of the reticle R and the wafer W during scanning exposure is a direction parallel to the Y axis (Y direction), and the illumination area IAR on the reticle R and the exposure area IA on the wafer W are not in each case. This is an elongated region in the scanning direction (X direction).

The projection optical system PL of this example is provided with an imaging characteristic control mechanism for controlling (correcting) the predetermined imaging characteristics.
2 is a cross-sectional view showing a part of the imaging characteristic control mechanism of the projection optical system PL in FIG. 1. In FIG. 2, for convenience of explanation, the optical axis is configured so as to constitute the projection optical system PL. Of the many lens elements arranged along AX, only eight lens elements 13 ₁ , 13 ₂ ,..., 13 ₈ are shown. In this case, some of the lens elements 13 ₁ , 13 ₂ ,..., 13 ₈ , for example, the lens elements 13 ₁ , 13 ₂ , are respectively arranged in the direction of the optical axis AX by a plurality of drive elements (for example, piezoelectric elements) 20 It is configured so that it can be finely driven in an inclination direction with respect to the XY plane. A clean gas such as nitrogen is supplied between the lens elements via a pressure adjusting mechanism 41 from a gas supply mechanism (not shown).

  In this example, the drive voltage (drive amount of the drive element) applied to each drive element 20 is controlled by the imaging characteristic correction controller 78 in accordance with a command from the main controller 50 in FIG. As described above, the image formation characteristic control mechanism is configured including the drive element 20 and the image formation characteristic correction controller 78. This corrects the imaging characteristics of the projection optical system PL, such as field curvature, distortion, magnification, coma aberration, astigmatism, spherical aberration, and the like. The number of movable lens elements may be arbitrary. However, in this case, since the number of movable lens elements corresponds to the types that can correct the imaging characteristics of the projection optical system PL, excluding the focus, the movable lens elements can be adjusted according to the types of imaging characteristics that need to be corrected. The number should be determined.

  Returning to FIG. 1, the reticle R is fixed on the reticle stage RST by, for example, vacuum suction (or electrostatic suction). Reticle stage RST is two-dimensionally (X direction, Y direction, and rotational direction (rotation angle θz) around the Z axis) in the XY plane on reticle base RBS by reticle stage drive system 56R including a linear motor or the like. ) It can be driven minutely and can move on the reticle base RBS at a scanning speed designated in the Y direction.

  A movable mirror 52R that reflects a laser beam from a laser interferometer (hereinafter referred to as “reticle interferometer”) 54R is fixed on the reticle stage RST. The position of the reticle stage RST in the XY plane is the reticle stage RST. For example, the interferometer 54R always detects with a resolution of about 0.1 to 1 nm. In other words, the moving mirror 52R is actually composed of two Y-axis moving mirrors for measuring the position in the Y direction at two locations, and the X-axis moving mirror, and the laser interferometer 54R also corresponds thereto. And a three-axis laser interferometer.

Position information of reticle stage RST from reticle interferometer 54R is sent to stage controller 70 and main controller 50 via this. The stage controller 70 controls the movement of the reticle stage RST via the reticle stage drive system 56R according to an instruction from the main controller 50.
In addition, a reticle fiducial mark plate (hereinafter referred to as a “reticle mark plate”) as a mark forming member in which an aerial image measurement reference mark (measurement pattern) is formed in the vicinity of the end in the −Y direction of the reticle stage RST. The RFM is abbreviated to be aligned with the reticle R. This reticle mark plate RFM (described later in detail) is made of a glass material that transmits the illumination light IL of the same material as the reticle R, such as synthetic quartz, fluorite, or lithium fluoride or other fluoride crystals. It is fixed to the stage RST. Reticle stage RST has a movement stroke in the Y direction such that the entire surface of reticle R and the entire surface of reticle mark plate RFM can cross at least optical axis AX of projection optical system PL. In addition, openings for passing illumination light IL are formed in reticle stage RST below reticle R and reticle mark plate RFM, respectively. Also, a rectangular opening at least larger than the illumination area IAR, which is a passage for the illumination light IL, is formed in a portion almost directly above the projection optical system PL of the reticle base RBS (portion centered on the optical axis AX). ing.

  Also, above the reticle R, a mark on the reticle R or on the reticle mark plate RFM and a reference mark on a later-described reference mark plate (not shown) on the wafer stage WST are simultaneously provided via the projection optical system PL. A pair of TTR (Through The Reticle) type reticle alignment microscopes (hereinafter referred to as “RA detection system” for convenience) (not shown) (not shown) using light having an exposure wavelength for observation is provided. The detection signals of these RA detection systems are supplied to the main controller 50 through an alignment controller (not shown). A configuration equivalent to that of the RA detection system is disclosed in, for example, JP-A-7-176468.

  In FIG. 1, a wafer stage WST relatively displaces an XY stage 42 and a Z tilt stage 38 (projected image and aerial image measurement system) mounted on the XY stage 42 in the optical axis direction of the projection optical system PL. Stage mechanism). The XY stage 42 is levitated and supported above the upper surface of the wafer base 16 by an air bearing (not shown) with a clearance of about several μm, for example. Further, the XY stage 42 is configured to be capable of two-dimensional driving in the Y direction which is the scanning direction and the X direction orthogonal thereto by a linear motor (not shown) constituting the wafer stage drive system 56W. A Z tilt stage 38 is mounted on the XY stage 42, and the wafer holder 25 is fixed on the Z tilt stage 38. The wafer W is held by the wafer holder 25 by vacuum suction or the like.

  As shown in FIG. 2, the Z tilt stage 38 is placed on the XY stage 42 by three Z position driving units 27A, 27B, and 27C (however, the Z position driving unit 27C on the back side in FIG. 2 is not shown). Supported by a point. These Z position driving units 27A to 27C have three actuators (for example, a voice coil motor) that independently drive the respective support points on the lower surface of the Z tilt stage 38 in the optical axis direction (Z direction) of the projection optical system PL. 21A, 21B, and 21C (however, the actuator 21C on the back side of FIG. 2 is not shown) and the encoder 23A that detects the driving amount (displacement from the reference position) in the Z direction by the Z position driving units 27A, 27B, and 27C. , 23B, 23C (however, the encoder 23C on the back side of FIG. 2 is not shown).

  In this example, the position of the Z tilt stage 38 (wafer W) in the optical axis AX direction (Z direction or focus direction), the rotation angle θx about the X axis, and the rotation angle θy about the Y axis are set by the actuators 21A to 21C. Control. The stage controller 70 in FIG. 1 adjusts the position and leveling amount (rotation angle θx, rotation angle θx, Z) of the Z tilt stage 38 so that the upper surface of the wafer W is focused on the image plane of the projection optical system PL during exposure. θy) is calculated, and the actuators 21A to 21C are driven using the calculation result. In FIG. 1, the linear motor and the like for driving the XY stage 42 and the Z position driving units 27A to 27C in FIG. 2 are collectively shown as a wafer stage driving system 56W.

  In FIG. 1, a movable mirror 52 </ b> W that reflects a laser beam from a laser interferometer (hereinafter referred to as “wafer interferometer”) 54 </ b> W is fixed on the Z tilt stage 38. The position of the Z tilt stage 38 (wafer stage WST) in the XY plane is always detected by the wafer interferometer 54W with a resolution of, for example, about 0.1 to 1 nm. Actually, on the Z tilt stage 38, a movable mirror having a reflective surface orthogonal to the scanning direction (Y direction) and a movable mirror having a reflective surface orthogonal to the non-scanning direction (X direction) are provided. The wafer interferometer is also provided with a plurality of axes in the X direction and the Y direction, respectively, and the position of the Z tilt stage 38 in the direction of five degrees of freedom (the position in the X direction, the Y direction, and the rotation angles θx, θy, θz). Measurement is possible. Position information (or speed information) of wafer stage WST is supplied to stage controller 70 and main controller 50 via this. Stage control device 70 controls the position of wafer stage WST in the XY plane via wafer stage drive system 56W in accordance with an instruction from main control device 50.

Further, the projection exposure apparatus of the present example is provided with an aerial image measurement device 59 (aerial image measurement system) used for measuring the imaging characteristics (optical characteristics) of the projection optical system PL. A part of the optical system constituting the aerial image measurement device 59 is arranged inside the Z tilt stage 38.
FIG. 3 is a partially cutaway view showing the aerial image measuring device 59. In FIG. 3, the aerial image measuring device 59 is a stage side component provided on the Z tilt stage 38, that is, a pattern forming member. As a slit plate 90, a relay optical system comprising lenses 84 and 86, a mirror 88 that bends the optical path in a substantially horizontal direction, a light transmission lens 87, and a component outside the stage provided outside the wafer stage WST, that is, the optical path upward. A mirror 96, a light receiving lens 89, an optical sensor 94 (photoelectric sensor) including a photoelectric conversion element, and the like.

  More specifically, the slit plate 90 is provided on the upper surface of the end portion of the Z tilt stage 38 of the wafer stage WST, and the projecting portion 58 formed with an opening in the upper portion is covered with the opening from above. It is inserted. The slit plate 90 is configured by forming a reflection film 83 also serving as a light shielding film on the upper surface of a rectangular flat glass substrate 82 parallel to the XY plane, and illumination light having a predetermined width of 2D is formed on a part of the reflection film 83. A slit-like opening pattern (hereinafter referred to as “slit”) 122 that transmits IL is formed. 3 representatively shows one of a plurality of slits (see FIG. 5) provided in the slit plate 90. As the material of the glass substrate 82, here, synthetic quartz or fluorite having good transparency to ArF excimer laser light is used.

  In the state of FIG. 3, the measurement mark PM (measurement pattern) formed on the reticle mark plate RFM is located in the illumination area of the illumination light IL, and the image of the mark is slit by the projection optical system PL. Projected onto the plate 90. A part of the imaging light beam made of the illumination light IL passes through the slit 122. Inside the Z tilt stage 38 below the slit 122, lenses 84 and 86 are formed by interposing a mirror 88 that bends the optical path of the illumination light IL (imaging light beam) incident substantially vertically downward through the slit 122 almost horizontally. Relay optical systems (84, 86) are arranged. In addition, illumination light relayed by the relay optical system (84, 86) is almost outside the wafer stage WST on the side wall on the + Y direction side of the Z tilt stage 38 behind the optical path of the relay optical system (84, 86). A light transmission lens 87 that transmits light in the + Y direction is fixed.

  The optical path of the illumination light IL sent out of the wafer stage WST by the light sending lens 87 is 90 substantially vertically upward by a mirror 96 having a predetermined length in the X direction and inclined at an inclination angle of 45 °. ° Folded. On the bent optical path, a light receiving lens 89 that is larger than the light transmitting lens 87 is disposed, and an optical sensor 94 is disposed above the light receiving lens 89. The light receiving lens 89 and the optical sensor 94 are housed in the case 92 while maintaining a predetermined positional relationship, and the mirror 96 is also fixed to the case 92 via a support member (not shown). The illumination light IL reflected upward by the mirror 96 is condensed on the light receiving surface of the optical sensor 94 by the light receiving lens 89. The case 92 is fixed to the vicinity of the upper end portion of the support column 97 implanted on the upper surface of the wafer base 16 via the mounting member 93.

  As the optical sensor 94, a photoelectric conversion element (photoelectric sensor) capable of accurately detecting weak light, for example, a photomultiplier tube (PMT, photomultiplier tube) or the like is used. The photoelectric conversion signal PS from the optical sensor 94 is sent to the main controller 50 via the signal processing device 80 of FIG. The signal processing device 80 can be configured to include, for example, an amplifier, a sample hold circuit, an A / D converter, and the like. The arrangement and shape of the actual plurality of slits represented by the slit 122 will be described later.

  According to the aerial image measuring device 59 configured as described above, the measurement mark PM (or mark formed on the reticle R) formed on the reticle mark plate RFM (or reticle R) is projected via the projection optical system PL. In the measurement of the projection image (aerial image) obtained in this manner, a photoelectric conversion signal (light amount signal) PS corresponding to the amount of light (light reception amount) that has passed through the slit 122 is transferred from the optical sensor 94 to the signal processing device 80 of FIG. To the main controller 50.

  In this example, the measurement of the light intensity distribution (light quantity distribution) of the projected image (aerial image) of the measurement mark is performed by the slit scan method. In this case, the light transmission lens 87 is replaced by the light receiving lens 89 and the optical sensor. It moves in the X direction and the Y direction with respect to 94. Therefore, in the aerial image measuring device 59, the diameter of the light receiving lens 89 is set larger than the diameter of the light transmitting lens 87 so that all the light passing through the light transmitting lens 87 moving within a predetermined range is incident on the light receiving lens 89. Has been. In the aerial image measurement device 59 of this example, the moving unit including the slit plate 90 provided in the Z tilt stage 38 and the fixed unit including the optical sensor 94 provided in the case 92 are mechanically separated. Yes. The moving part and the fixed part are optically connected via the mirror 96 only when the aerial image is measured. Thereby, a decrease in measurement accuracy due to heat generation of the optical sensor 94 is suppressed.

  In the aerial image measuring device 59, the optical path between the light transmitting lens 87 and the light receiving lens 89 may be connected by a flexible optical fiber cable. Further, for example, when the heat generation of the optical sensor 94 is small, or when the influence of the heat generation can be reduced by the cooling mechanism, the optical sensor 94 and the light receiving lens 89 are fixed to the side surface in the + Y direction of the projection optical system PL, for example. It is also possible. Further, the optical sensor 94 can be provided inside the wafer stage WST (Z tilt stage 38). The aerial image measurement and the aberration measurement method performed using the aerial image measurement device 59 will be described in detail later.

  Returning to FIG. 1, an alignment system ALG of an off-axis image processing system as a mark detection system for detecting an alignment mark on the wafer W or a predetermined reference mark is provided on the side surface of the projection optical system PL. Based on the imaging signal from alignment system ALG and the position information of wafer stage WST which is the output of wafer interferometer 54W, main controller 50 determines the center of the projection image of the pattern on reticle R and the detection center of alignment system ALG. And the calculation of the array coordinates of each shot area on the wafer W, etc.

  Further, as shown in FIG. 1, the projection exposure apparatus 10 of this example is provided with an oblique incidence type multipoint focal position detection system (60a, 60b) comprising an irradiation system 60a and a light receiving system 60b. The irradiation system 60a projects a plurality of slit images obliquely with respect to the optical axis AX on the test surface that is the surface of the wafer W or the surface of the slit plate 90, and the light receiving system 60b reflects the reflected light from the test surface. It receives light and re-images those slit images. Then, the light receiving system 60b supplies a detection signal corresponding to the lateral shift amount of the re-imaged slit images to the stage controller 70. In the stage control device 70, as an example, these detection signals are converted into defocus amounts, and the defocus amount in the Z direction with respect to the image plane of the projection optical system PL of the test surface from the plurality of defocus amounts, and X An inclination angle about the axis and the Y axis is obtained. The detailed configuration of a multipoint focal position detection system similar to the multipoint focal position detection system (60a, 60b) is disclosed in, for example, Japanese Patent Laid-Open No. Hei 6-283403.

  During normal exposure, the stage controller 70 uses the detection result of the multipoint focal position detection system (60a, 60b) to automatically focus the surface of the wafer W on the image plane of the projection optical system PL. The position and tilt angle of the Z tilt stage 38 are controlled via the wafer stage drive system 56W by the focus method and the auto leveling method. Further, based on a command from the main controller 50 during exposure or aerial image measurement, the stage controller 70 projects the surface of the wafer W or the surface of the slit plate 90 via the wafer stage drive system 56W. It is also possible to defocus the image plane by an amount designated in the Z direction.

  In addition, an environmental sensor 81 for detecting atmospheric pressure fluctuations and temperature fluctuations is provided in the vicinity of the projection optical system PL in FIG. The measurement result by the environment sensor 81 is supplied to the main controller 50. Further, in the memory 51 connected to the main control device 50, for example, information on predetermined higher-order aberrations previously measured at the time of assembly adjustment of the projection optical system PL and the like and an aberration measurement method described later are obtained. Information on aberrations of the projection optical system PL is stored.

  Next, the scanning exposure operation in the projection exposure apparatus 10 of this example will be briefly described. First, main controller 50 sets an illumination condition optimal for exposure using reticle R based on an operator's instruction. Next, the alignment of the reticle R and the alignment of the wafer W are performed using the reticle alignment microscope and the wafer side alignment system ALG. Thereafter, the next shot area to be exposed on the wafer W is positioned on the front side of the optical axis AX by stepping the wafer stage WST. Then, the irradiation of the illumination light IL is started, and in synchronization with the movement of the reticle R in the Y direction at the speed Vr with respect to the illumination area via the reticle stage RST, the exposure area via the wafer stage WST. Thus, one shot area on the wafer W moves in the Y direction at a velocity β · Vr (β is the projection magnification of the projection optical system PL). In this way, the stepping operation between shots and the synchronous scanning operation for each shot are repeated, and the pattern image of the reticle R is transferred to all shot regions on the wafer W by the step-and-scan method.

  By the way, in the above-described scanning exposure operation, in order to transfer the pattern of the reticle R onto the wafer W with high resolution and high accuracy via the projection optical system PL, the imaging characteristics of the projection optical system PL are in a predetermined state. It needs to be adjusted. For this purpose, it is necessary to measure the imaging characteristics with high accuracy. In the following, it is assumed that the imaging characteristics of the projection optical system PL to be measured and adjusted are predetermined aberrations.

In addition, assuming that wavefront aberration is used to classify the aberration, an aberration function indicating the wavefront aberration on the exit pupil (or pupil plane) of the projection optical system PL is W (ρ, θ). In this case, ρ is a normalized position (radial radius) in the radial direction of the exit pupil of the projection optical system PL, and θ is an angle, the aberration function W (ρ, θ) is the above ( As shown in equation (1), series expansion can be performed using i-th order (i = 1, 2,...) Zernike's Polynomial fi (ρ, θ) and its coefficient Z _i . The Zernike polynomials may also be referred to as Fringe Zernike polynomials or Zernike circle polynomials.

As an example, the Zernike polynomials fi of the first order to the 37th order are illustrated together with the corresponding coefficients Z _i as shown in Table 1 below.

  As shown in Table 1, the Zernike polynomial fi (ρ, θ) of each order is expressed in a form in which a radial function that is a function of the radial diameter (ρ) and a function of the angle (θ) are separated. The Zernike polynomials can be classified into those whose radial function is an odd function and those that are an even function. An aberration corresponding to a Zernike polynomial whose radial function is expressed by an odd function is called an odd function aberration, and an aberration corresponding to a Zernike polynomial whose radial function is expressed by an even function is called an even function aberration.

The aberrations of the projection optical system PL can be classified into lateral aberrations, which are lateral shifts of the image, and longitudinal aberrations, which are changes in the contrast of the image. The former lateral aberration is an odd function aberration, and the latter longitudinal aberration is an even function aberration. It is. Accordingly, spherical aberration, defocus, and the like among the aberrations of the projection optical system PL are even function aberrations, and the coma aberration is an odd function aberration. Further, the coefficient Z _i of the i-th order Zernike polynomial represents the aberration expressed by the i-th order Zernike polynomial. In this example, the aberration Z ₉ and Z ₁₆ , which are spherical aberrations (even function aberrations), and coma aberration (odd function aberrations) are performed by the imaging characteristic control mechanism of the projection optical system PL including the imaging characteristic correction controller 78 of FIG. A plurality of aberrations including aberrations Z ₇ , Z ₈ , Z ₁₄ , Z ₁₅ , and aberrations Z ₂ , Z ₃ , which are distortion (odd function aberration), can be corrected. In this example, the above-described aerial image measurement device 59 is used to measure these odd-function aberration and even-function aberration. Hereinafter, aerial image measurement by the aerial image measurement device 59, measurement of aberration of the projection optical system PL, and the like will be described in detail.

  FIG. 3 shows a state in which the aerial image of the measurement mark PM formed on the reticle mark plate RFM is measured using the aerial image measuring device 59. Instead of the reticle mark plate RFM, it is also possible to use a test reticle dedicated to aerial image measurement, or a reticle R used for manufacturing a device on which a dedicated measurement pattern is formed. Here, on the reticle mark plate RFM, it is assumed that a measurement line mark PM (line pattern) composed of an elongated rectangular opening pattern having the X direction as a longitudinal direction is formed at a predetermined location. Note that such a line mark PM is actually one of a plurality of marks provided in a plurality of measurement areas on the reticle mark plate RFM in different directions.

  Here, a method of aerial image measurement using the aerial image measurement device 59 will be briefly described. For example, as shown in FIG. 4A, the slit plate 90 is formed with a slit 122 (opening pattern) having a predetermined width 2D extending in the X direction. The width of the projected image of the line mark PM is set wider than the width 2D of the slit 122, and the length of the projected image of the line mark PM in the longitudinal direction is set longer than the length of the slit 122.

In measuring the aerial image, the main reticle 50 of FIG. 1 drives the movable reticle blind 30B via a blind driving device (not shown). As shown in FIG. 3, the illumination light IL of the reticle R is illuminated. The area is limited only to a predetermined area including the line mark PM.
In this state, when the illumination light IL is irradiated onto the reticle mark plate RFM, as shown in FIG. 4A, the light (illumination light IL) diffracted and scattered by the line mark PM is transmitted by the projection optical system PL. Refracted and a spatial image (projected image) PM ′ of the line mark PM is formed on the image plane of the projection optical system PL. At this time, it is assumed that the aerial image PM ′ is formed on the + Y direction side (or the −Y direction side) of the slit 122 on the slit plate 90. If the projection magnification of the projection optical system PL is ¼, the line width of the spatial image PM ′ is approximately ¼ of the line width of the line mark PM. In the following description, it is assumed that the line width or the like of each line mark indicates the line width or the like of the aerial image.

  When the main controller 50 drives the wafer stage WST (scanning mechanism) in the + Y direction as shown by the arrow F in FIG. 4A via the wafer stage drive system 56W of FIG. 122 is scanned in the Y direction with respect to the aerial image PM ′. During this scanning, light (illumination light IL) that passes through the slit 122 is received by the optical sensor 94 via the optical system in the wafer stage WST in FIG. 3, the mirror 96, and the light receiving lens 89, and the photoelectric conversion signal PS is obtained. The signal is supplied to the main controller 50 via the signal processing device 80. Main controller 50 acquires light intensity distribution information corresponding to aerial image PM ′ based on the photoelectric conversion signal and a coordinate position (Y coordinate in this case) that gradually changes on wafer stage WST. Note that the aerial image PM ′ and the slit 122 may be relatively scanned in the width direction of the slit 122. Therefore, the aerial image PM ′ side may be moved by moving the reticle mark plate RFM via the reticle stage RST (scanning mechanism) in FIG.

  FIG. 4B shows an example of a photoelectric conversion signal (light intensity signal) PS obtained in the above aerial image measurement. In this case, the change in the amount of light of the aerial image PM ′ becomes gentle due to the integration effect of the width (2D) of the slit 122 in the scanning direction (Y direction). Therefore, if the transmittance distribution in the scanning direction (here Y direction) of the slit 122 is p (y), the light intensity distribution of the aerial image is i (y), and the observed light intensity signal is m (y). The relationship between the intensity distribution i (y) of the aerial image and the observed intensity signal m (y) is expressed by the following equation (2). In equation (2), the unit of intensity distribution i (y) and intensity signal m (y) is the intensity per unit length, and the u axis is the same coordinate axis as the y axis.

  However, the function p (y) of the transmittance distribution of the slit 122 is expressed by the following equation (3).

That is, the observed intensity signal m (y) is a convolution of the function p (y) of the slit 122 and the light intensity distribution i (y) of the aerial image.
Therefore, in terms of measurement accuracy, the width (hereinafter simply referred to as “slit width”) 2D of the slit 122 in the scanning direction (Y direction) is preferably as small as possible. As in this example, when a photomultiplier tube (PMT) is used as the optical sensor 94, even if the slit width becomes very small, if the scanning speed is slowed and the measurement takes time, the light intensity (light intensity ) Can be detected. However, in reality, since there is a certain restriction on the scanning speed at the time of aerial image measurement from the viewpoint of throughput, if the slit width 2D is too small, the amount of light transmitted through the slit 122 becomes too small and measurement is difficult. turn into.

  Specifically, assuming that the exposure wavelength is λ and the numerical aperture of the projection optical system PL is NA, as an example, the width 2D is set to λ / (2 · NA) or less. When λ is 193 nm and the numerical aperture NA is 0.9, the width 2D is set to 107 nm or less, for example, about 100 nm. However, depending on the required measurement accuracy, the width 2D may be set to a value larger than λ / (2 · NA), for example, about 100 to 150 nm. The data sampling pitch is preferably λ / (4 · NA) or less. As the line mark, a mark whose line width design value is λ / (2 · NA) or less on the wafer can be used. The line width of the mark on the reticle is a value obtained by multiplying λ / (2 · NA) by the reciprocal of the reduction ratio.

  Thus, the light intensity distribution in the aerial image (projected image) PM ′ of the line mark PM can be measured by the aerial image measuring operation using the aerial image measuring device 59. Information on the measured light intensity distribution is supplied to the main controller 50 of FIG. Since the information on the light intensity distribution includes information on the horizontal image formation position (lateral shift) and amplitude (contrast) of the aerial image PM ′, the main controller 50 (arithmetic unit) determines that information. Can be used to determine the aberration (details will be described later). Furthermore, using the light intensity distribution information, it is possible to calibrate the best focus position with respect to the projection optical system PL, and it is also possible to obtain the positions of a predetermined mark image in the X direction and the Y direction.

In this example, it is assumed that the aberration represented by the Zernike polynomial up to a predetermined order exceeding 9th order is measured. For this purpose, as the aerial image PM ′, it is necessary to measure aerial images of various line marks having different directions as described later. For this purpose, it is necessary to form slits (opening patterns) arranged in a plurality of directions on the slit plate 90 as well.
FIG. 5 shows an actual arrangement of a plurality of slits as opening patterns formed in the slit plate 90 of this example. In FIG. 5, the slit plate 90 has a slit width 2D extending in the Y direction. An L-shaped slit 122b and a slit 122a that extends in the X direction and is formed by rotating the slit 122b by 90 ° are formed. Further, four slits 9B, 9C, 9E, and 9F each having a width 2D and a length L1 are formed on the slit plate 90. The four slits 9B to 9F are substantially at the positions of the four apexes of the square, and the two slits 122a and 122b constitute two adjacent sides of the square. The illumination light that has passed through these slits 122a, 122b, 9B to 9F is received by the optical sensor 94 in FIG. In this case, in order to individually detect the illumination light that has passed through the slits 122a, 122b, and 9B to 9F, for example, a liquid crystal panel as a slit selection member is provided on the bottom surface of the slit plate 90 and passes through one selected slit. Only the illuminated light may be incident on the optical sensor 94.

  As an example, the slit width 2D of each slit is about 100 to 150 nm as described above, the length L of the slits 122a and 122b is 18 μm, and the length L1 of the slits 9B, 9C, 9E, and 9F is 3 μm. In this case, the slits 122a and 122b are both used for calibration of the best focus position and position measurement of the mark image. Specifically, for example, on the pattern surface of the reticle mark plate RFM of FIG. 3, the X-axis and Y-axis marks for measuring the best focus position (focus marks) and the X-axis and Y-axis marks for position measurement ( Image position marks) are formed, and these projected images are images 62XP and 62YP and images 63XP and 63YP of FIG. In this case, the X-axis focus mark image 62XP is an image in which a plurality of line patterns (bright portions) extending in the Y direction having a line width of 110 nm are arranged in the X direction with a duty ratio of 1: 1. The Y-axis focus mark image 62YP is obtained by rotating the X-axis image 62XP by 90 °. Further, the image 63XP of the X-axis image position mark is an image in which a plurality of line patterns (bright portions) extending in the Y direction with a line width of 1 μm are arranged in the X direction with a duty ratio of 1: 1. The Y-axis image position mark image 63YP is obtained by rotating the X-axis image 63XP by 90 °. In this case, the width in the Y direction of the images 62XP and 63XP and the width in the X direction of the images 62YP and 63YP are set longer than the length L of the slits 122a and 122b, respectively.

  When obtaining the best focus position of the projection optical system PL, the wafer stage WST in FIG. 3 is sequentially driven in the X direction and the Y direction, and the focus mark images 62XP and slits 122b and 122a in FIG. The operation of scanning 62YP and detecting the light intensity distribution is performed by changing the position in the Z direction of the Z tilt stage 38 in FIG. Are executed multiple times while gradually changing. At this time, the best focus position can be obtained from the focus position at which the contrast (amplitude) of the obtained light intensity distribution becomes the largest. Thereby, for example, calibration of the best focus position of the multipoint focus position detection system (60a, 60b) of FIG. 1 can be performed. Thereafter, the defocus amount detected by the multipoint focal position detection system (60a, 60b) accurately indicates the amount of deviation from the image plane of the projection optical system PL.

  When obtaining the positions of the image position mark images 63XP and 63YP, the wafer stage WST in FIG. 3 is sequentially driven in the X direction and the Y direction, and the images 63XP and 63YP are scanned by the slits 122b and 122a, respectively. Thus, the light intensity distribution is detected, and the centers of the light intensity distribution in the X direction and the Y direction may be obtained. By forming the image position mark on the reticle R, for example, the reticle R can be aligned.

  Further, the slits 9B, 9C, 9E, and 9F are used for measuring aberrations, respectively. In this example, the slits 122a and 122b also serve as aberration measurement slits 9D and 9A, respectively. At this time, the longitudinal direction (arrangement direction) of the six slits 9A (122b), slit 9B, slit 9C, slit 9D (122a), slit 9E, and slit 9F is 90 counterclockwise with respect to the X axis. The directions intersect at degrees, 120 degrees, 135 degrees, 0 degrees, 30 degrees, and 45 degrees, and these arrangement directions are different from each other. In this case, each of the slits 9A to 9F is scanned relative to a corresponding aerial image in a direction (measurement direction) orthogonal to the longitudinal direction. In other words, the measurement directions of the six slits 9A, 9B, 9C, 9D, 9E, and 9F are 0 °, 30 °, 45 °, 90 °, 120 °, and counterclockwise with respect to the X axis, respectively. Cross at 135 °.

As described above, the six slits 9A to 9E (opening patterns) of this example are sequentially scanned in the corresponding measurement directions, thereby allowing the space of the six-direction line marks having different measurement directions (directions orthogonal to the longitudinal direction). The light intensity distribution information of the image can be measured.
FIG. 6 shows an example of the arrangement of such six-direction line marks 1A, 1B, 1C, 1D, 1E, and 1F (line patterns). The line marks 1A to 1F in FIG. 6 are the reticle marks in FIG. It is formed on the pattern surface of the plate RFM. These line marks may be formed on a part of reticle R, or may be formed on a test reticle loaded on reticle stage RST.

  In FIG. 6, the attached mark area 61 of the reticle mark plate RFM includes an X-axis mark 62X for measuring the best focus position and a Y-axis mark 62Y (focus mark) and an X-axis for measuring the position of the projected image. A mark 63X and a Y-axis mark 63Y (image position mark) are formed. The size of the attached mark region 61 is approximately 60 μm square when represented by a projection image by the projection optical system PL, and the arrangement of the marks 62X, 62Y, 63X, and 63Y represents the arrangement in the state of the projection image. Further, the projection images of the former marks 62X and 62Y are the images 62XP and 62YP in FIG. 5, and the projection images of the latter marks 63X and 63Y are the images 63XP and 63YP in FIG.

  Further, line marks 1A to 1F are formed in an area close to the attached mark area 61 of the reticle mark plate RFM. Each of the line marks 1A to 1F is a transmission pattern having the same shape as the line mark PM described with reference to FIG. 3 and having a width d, and has the same or different rotation angle. The measurement directions that are the width directions of the line marks 1A and 1D are parallel to the X direction and the Y direction, respectively, and the measurement directions of the line marks 1B, 1C, 1E, and 1F are counterclockwise with respect to the X axis, respectively. The angles φ1, φ2, φ3, and φ4 cross each other. In this example, the angle φ1 is 30 °, the angle φ2 is 45 °, the angle φ3 is 120 °, and the angle φ4 is 135 °. Accordingly, the light intensity distributions of the projected images of the line marks 1A, 1B, 1C, 1D, 1E, and 1F in FIG. 6 are respectively slits 9A, 9B, 9C, 9D, 9E, and 9F on the slit plate 90 in FIG. Can be measured by relative scanning in the corresponding measurement direction.

According to the present inventor, when a predetermined integer equal to or greater than 2 is M, they are arranged on the pupil plane of the projection optical system along at least M different directions around the optical axis of the projection optical system. By obtaining the phase information of the imaged light flux at the at least M points, the wavefront aberration represented by the Zernike polynomial up to the M ² order of the projection optical system can be obtained. Accordingly, by measuring the images of the line patterns 1A to 1F arranged in six different directions, the wavefront aberration represented by the higher-order Zernike polynomial up to at least the 36th order can be obtained. Further, as in the example of FIG. 9, the Zernike coefficients up to the 37th order (coefficients of the Zernike polynomial) can be decomposed by changing the radial sample pitch according to the angular direction.

  When the aberration to be measured may be an aberration expressed by a Zernike polynomial from the 9th order to the 16th order, the four slits 9A, 9C, 9D and 9F on the slit plate 90 in FIG. That is, it is possible to use only four slits (opening patterns) whose measurement directions intersect with the X axis at 0 °, 45 °, 90 °, and 135 °. At this time, only four line marks 1A, 1C, 1D and 1F are used in the line marks 1A to 1F in FIG.

  Next, in order to theoretically and quantitatively express aberrations including odd-function aberration and even-function aberration, the following calculation is performed. The aerial image to be measured in this case is the aerial image PM ′ of the line mark PM in FIG. Here, in the spatial image PM ′ of the line mark PM, the complex amplitude distribution in the Y direction in FIG. 4A is o (y), and the spatial frequency spectrum is O (s) (s is on the spatial frequency axis) Coordinates). Of the spatial frequency components included in the periodic pattern of the spatial image PM ′ of the line mark PM, if two spatial frequency components are f ′ and f ″, beats of the spectra O (f ′) and O (f ″) are obtained. The intensity distribution i (y) of the aerial image PM ′ of the line mark PM is obtained by integrating the interference fringes generated by the above by applying a certain weight at the entire spatial frequency. This weight is referred to as the cross modulation coefficient T (f ′, f ″), and the cross modulation coefficient T (f ′, f ″) is defined by the following equation (4).

In this equation, F is a pupil function at the exit pupil (or pupil plane) of the projection optical system PL ( ^* indicates a complex conjugate), and σ (ξ, η) is an effective light source. Note that ξ and η are orthogonal coordinate axes on the exit pupil of the projection optical system PL. Therefore, the imaging formula of the line mark PM by partial coherent illumination is represented by the following formula (5).

Next, the aberration represented by the Zernike polynomial will be described taking the aberrations Z ₇ and Z ₈ represented by the 7th and 8th order Zernike polynomials as an example. FIG. 7 shows the seventh-order aberration Z ₇ , and FIG. 8 shows the eighth-order aberration Z ₈ . 7 and 8, the orthogonal coordinate system (pupil coordinates) (X444, Y444) of the pupil QA of the projection optical system is parallel to the orthogonal coordinate system (X, Y) of the image plane QB of the projection optical system. However, the direction of the X444 axis is opposite to the X axis. A point on the pupil coordinates is usually indicated by the polar coordinates (ρ, θ).

The aberration is the advance or delay of the phase of the pupil plane, and the seventh-order aberration Z ₇ in FIG. ₇ is a 1θ component in the Y444 direction. In FIG. 7, the aberration H is a phase delay −H ₀ at a point (ρ ₀ , φ ₀ ) in the region of Y444> 0, and the aberration H is a phase at a point (ρ ₁ , φ ₁ ) in the region of Y444 <0. a of proceeds + H _0, the shift of the image QC is H ₀ in the + Y direction (in phase). The aerial image is represented by a line and space pattern with a pitch P ₀ .

Further, the eighth-order aberration Z ₈ in FIG. ₈ is a 1θ component in the X444 direction. In FIG. 8, at the point (ρ ₃ , φ ₃ ) in the region of X444> 0, the aberration H is the phase delay −H ₁ , and at the point (ρ ₄ , φ ₄ ) in the region of X444 <0, the aberration H is the phase. a of proceeds + H _1, the shift of the image QD is H ₁ in the -X direction (in phase). The aerial image is represented by a line and space pattern with a pitch P ₁ .

The absolute value of the aberration amount and the image shift amount at the measurement point in the pupil coincide with each other if the unit is a phase. Conversion from the unit of length to the unit of phase is expressed by the following equation.
Image shift amount (phase) = (image shift amount (length) / mark pitch) × 360 ° (K1)
Note that the amount of aberration at the measurement point in the pupil is determined by the effective illumination size (the size of the secondary light source on the pupil plane of the illumination optical system), and an example of the secondary light source is a small annular zone.

Further, when the measurement point in the pupil is represented by polar coordinates (ρ, θ), θ coincides with the mark periodic direction (width direction for the line mark), and the radius ρ is the mark pitch P and the numerical aperture of the projection optical system. Using NA and exposure wavelength λ:
ρ = λ / (P · NA) (K2)
Thus, the aberration (coefficient) of the Zernike polynomial of each order is determined by the phase distribution on the pupil plane of the projection optical system PL.

Also, consider a coordinate system in which the polar coordinates (ρ, θ) on the pupil (exit pupil) of the projection optical system PL are normalized so that the maximum radius is 1, and the phase measurement position on the normalized coordinate system is ( Let ρ _p , Ψ _p ) (p = 1, 2,...). The wavefront aberration H (ρ _p , Ψ _p ), which is the phase distribution at this position (ρ _p , Ψ _p ), is obtained by measuring the light intensity distribution of the projected images of the six-direction line marks 1A to 1F as will be described later. be able to.

Next, the wavefront aberration H (ρ _p , Ψ _p ) of the projection optical system PL is changed to the Zernike polynomial fj (ρ _p , Ψ _p ) up to the nth order (n is an integer larger than 9) as shown in the equation (1). It is expressed by the sum of products of (j = 1 to n) and its coefficient Z _j . That is, function fitting of the wavefront aberration H (ρ _p , Ψ _p ) is performed using a Zernike polynomial. The function fitting of the wavefront aberration of the projection optical system PL is usually performed using Zernike polynomials up to the 37th order. However, since this example assumes that the aberration of the projection optical system PL is measured on-body, the function fitting up to, for example, a 36th order (n = 36) Zernike polynomial is also practical.

Further, when the wavefront aberration H (ρ _p , Ψ _p ) is function-fitted using the Zernike polynomials fj (ρ _p , Ψ _p ) (j = 1 to n) up to the nth order, the projection optical system PL emits light. Wavefront aberration H (ρ _k , _k ) at measurement points on positions (ρ _k , Ψ _k ) (k = _{1 to} m) at m points (m is an integer greater than or equal to n) on the pupil (or pupil plane). Ψ _k ) needs to be obtained. The m wavefront aberrations H (ρ _k , Ψ _k ) correspond to phase distribution information on the pupil plane of the projection optical system of the present invention. Hereinafter, the position (ρ _k , Ψ _k ) is referred to as a measurement point (ρ _k , Ψ _k ). At this time, for example, from the reference document ("Adaptive optics and optical structures", SPIE, Vol. 1271, p. 80-86 (1990)), the value of the j-th order Zernike polynomial at the measurement point (ρ _k , Ψ _k ) Using fj (ρ _k , Ψ _k ) (j = 1 to n), its coefficient a _j (unknown number corresponding to coefficient Z _j ), and measurement error ε _k , wavefront aberration H (ρ _k , Ψ _k ) Can be expressed as follows: The measurement error ε _k is, for example, a drawing error of the line mark PM of FIG. 3 (line marks 1A to 1F of FIG. 6), a measurement error of the X coordinate and the Y coordinate of the wafer stage WST, and a measurement error of the focus position of the slit plate 90. This is a phase error obtained in advance based on the above.

Here, H is an m-dimensional vector based on the measured wavefront aberration H (ρ _k , Ψ _k ) (k = 1 to m), and the value fj (ρ _k) of the j-th order Zernike polynomial that can be calculated from Table 1. , Ψ _k ) (j = 1 to n; k = 1 to m) based on m rows × n columns matrix D, unknown n-dimensional vector based on unknown coefficient a _j , A, measurement If an m-dimensional vector based on the error ε _k is ε, the equation (21) becomes the following equation (22).

H = DA + ε (22)
The computing unit (second computing device) in the main controller 50 in FIG. 1 finds n elements (coefficients a _j ) of the vector A by solving equation (22). These coefficients a _j are the coefficients of the j-th order (j = 1 to n) Zernike polynomial fj in the case where the wavefront aberration of the projection optical system PL is represented by the Zernike polynomial up to the n-th order. This corresponds to the third step of the present invention, whereby the wavefront aberration of the projection optical system PL is obtained.

To actually solve the equation (22), the transposition matrix of the matrix D is set to D ^T , and the vector (H−ε) is set to G, so that the equation (22) is transformed as follows.
(D ^T D) A = D ^T G (23)
Then, the vector A can be obtained as follows by multiplying both sides of this equation by an inverse matrix (D ^T D) ⁻¹ of an n-row × n-column matrix (D ^T D).

A = (D ^T D) ⁻¹ D ^T G (24)
Therefore, the condition for solving the vector A is that an inverse matrix (D ^T D) ⁻¹ exists. In principle, if m = n, the vector A can be uniquely obtained from the equation (24). On the other hand, when m> n, Equation (22) becomes an overdetermined system, and the vector A can be solved by the least square method. In order to apply the least square method to the equation (22), each element of the vector A may be determined so that the inner product of the vector (H-DA-ε) and the transposed vector is minimized.

In order to solve the equation (21), the inverse matrix (D ^T D) ⁻¹ appearing in the equation (24) is as stable as possible (the amount of fluctuation is small when the position of the measurement point is slightly shifted). ) Is desirable. A numerical value representing the stability is called a condition number, and the smaller the condition number, the more stable the inverse matrix. The condition number represents the influence of the raw data error on the solution. The condition number is the square root of the result of dividing the maximum singular value of the matrix D by the minimum singular value as follows, and the condition number may be expressed as “Cond (D)”.

Condition number = (maximum singular value of matrix D / minimum singular value of matrix D) ^1/2 (24D)
Further, the error propagation rate matrix Ed is defined using the matrix D as follows.
Ed = D ⁺ (D ⁺ ) ^T (24E)
Note that D ⁺ = (D ^T D) ⁻¹ D ^T. The square root of each diagonal component of the error propagation rate matrix Ed indicates the error propagation rate to the Zernike coefficient, and the smaller the error propagation rate, the smaller the wavefront aberration measurement error corresponding to the Zernike coefficient.

  After that, the main controller 50 performs a projection optical system via an imaging characteristic control mechanism including the imaging characteristic correction controller 78 of FIG. PL aberration is corrected (imaging characteristic correction step). Thereafter, the pattern of the reticle R is exposed onto the wafer W via the corrected projection optical system PL (exposure process), so that the pattern of the reticle R can be transferred with high accuracy.

The above description can be applied when the effective light source of the illumination optical system is sufficiently small and can be regarded as coherent illumination. However, when the effective light source is somewhat large, the value fj determined by the Zernike polynomial in equation (21). (Ρ _k , Ψ _k ) may be an average value within the area of the effective light source.
In this example, the measurement point of phase information on the normalized pupil coordinates of the projection optical system PL (actually, so that the condition number Cond (D) of the expression (24D) becomes a sufficiently small value of about 10 or less, for example. Is the point of estimating the phase by calculation). Below, arrangement | positioning of the measurement point of the phase information of this example is demonstrated.

  FIG. 9 shows an example of the arrangement of phase information measurement points on the normalized pupil coordinates (X, Y) of the projection optical system PL (see FIG. 1) of this example. The origin of (X, Y) is assumed to be the optical axis AX of the projection optical system PL. In addition, the plurality of measurement points in FIG. 9 include a 0 ° direction D1, a 30 ° direction D2, a 45 ° direction D3, a 90 ° direction D4, and a 120 ° direction D5, counterclockwise with respect to the X axis. And 6 directions composed of a direction D6 of 135 °. Also in this case, in each of the directions D1 to D6, the plurality of measurement points are arranged symmetrically with respect to the center. Further, for the directions D1, D3, D4, and D6, the measurement point SP1 is set so that the radial offset from the symmetry center of the measurement point is rof and the interval is rr. For the directions D2 and D5, The measurement point SP2 is set so that the radial offset from the center of symmetry is rof2 and the interval is rr2. Furthermore, it is assumed that the entire measurement point arrangement has offsets Xof and Yof in the X and Y directions with respect to the optical axis AX. In order to give such an offset (Xof, Yof), the chief ray of the illumination light for illuminating the measurement mark may be inclined by an angle corresponding to the X direction and the Y direction.

  As an example, (Xof, Yof) = (0, 0), rr = 0.166, rof = 0.1, rr2 = 0.036, and rof2 = 0.75 were set. In this case, the measurement points SP2 in the 30 ° direction and the 120 ° direction (directions D2 and D5) are arranged near the outermost periphery of the pupil. In other words, as for the measurement points in the 30 ° direction and the 120 ° direction, a plurality of measurement points (measurement positions) are arranged within 50% in the radial direction from the outer periphery of the pupil of the projection optical system PL, and the interval rr2 ( = 0.036) is 5% or less of the radius of the pupil (normalized to 1). When this mark is used, it is possible to extract aberrations represented by Zernike polynomials up to the 37th order.

As a result of simulation by a computer in which the illumination for the measurement mark in this case is coherent illumination (illumination with a small σ value), the condition number Cond (D) in Expression (24D) is 5.727, which is 10 or less. Further, the error propagation rate, which is the square root of each diagonal component of the error propagation rate matrix Ed represented by the equation (24E), is 1.7 (in the case of aberration Z ₂₅ ) at the maximum, and the wavefront aberration can be obtained with extremely high accuracy. It can be measured.

Next, a method for obtaining the wavefront aberration H (ρ _k , Ψ _k ) on the pupil plane of the projection optical system PL in the above equation (21) will be described. Here, it is assumed that wavefront aberrations are obtained at a plurality of measurement points along a straight line passing through the optical axis AX on the normalized pupil coordinates in FIG. 9 and parallel to the X axis. In this case, the line mark 1A whose measurement direction in the line marks 1A to 1F in FIG. 6 is the X direction and the corresponding slit 9A in the slits 9A to 9E in FIG. 5 are used. When obtaining wavefront aberration at measurement points in other directions in FIG. 9, corresponding line marks and slits may be used.
For example, the width of the data acquisition range of FIG. 11 described later is IL, the sampling interval is SL, and IL = SL × m (m is an integer). When the light quantity distribution in this region is Fourier-transformed, it is represented by a trigonometric function series up to the maximum frequency fs = m / (2 · IL) at the basic frequency fo = 1 / IL. Further, since the frequency of the pattern of the pitch P is 1 / P and the normalized pupil coordinate is λ / (P · NA), the sampling point (measurement point) on the desired pupil coordinate can be sampled from the relationship. It is desirable to determine the widths IL and SL.

  FIG. 10 shows a state in which the image of the line mark 1A is projected onto the vicinity of the slit 9A in FIG. 5 via the projection optical system PL. In FIG. 10, the orthogonal coordinate system (pupil coordinates) of the pupil QA of the projection optical system PL is shown. ) (X444, Y444) is parallel to the Cartesian coordinate system (X, Y) of the image plane QB, but the direction of the X444 axis is opposite to the X axis. In FIG. 10, the light beam from the line mark 1A becomes the diffraction pattern 1AA in the pupil QA, and the light beam from the diffraction pattern 1AA becomes the image 1AB on the image plane QB. Further, the diffraction pattern 1AA is distributed on the X444 axis, and the phase at an arbitrary measurement point SP on the diffraction pattern 1AA becomes the wavefront aberration at the measurement point SP. The arrangement of the measurement points SP is determined based on the arrangement shown in FIG.

  FIG. 11 shows the light intensity distribution of the image 1AB on the image plane of FIG. 10. In FIG. 11, the light intensity distribution of the image 1A can be measured by scanning the slit 9A in the X direction. Information on the light intensity distribution as a function of the measured coordinate X is supplied to the phase recovery unit (first arithmetic unit) in the main controller 50 of FIG. The phase recovery unit in the main controller 50 obtains the phase distribution on the diffraction pattern 1AA of the pupil QA from the information of the light intensity distribution (hereinafter referred to as H1 (X)) by the phase recovery method described below.

Here, the principle of the phase recovery method will be described with reference to FIG. First, in step 101 of FIG. 12, a measured image plane amplitude function is obtained. In this case, the square root function (H1 (X)) ^1/2 of the light intensity distribution H1 (X) as a function of the measured coordinate X is the image plane amplitude function. Next, in step 102, an initial phase between -π and π is generated as an image plane phase function using a uniform random noise generator. In the next step 103, a function obtained by multiplying the image plane amplitude function by the image plane phase function is defined as an image plane function. At this stage, the operation shifts to the next step 104, where the image plane function is Fourier transformed by the FFT (Fast Fourier Transfomrm) method, and is a function of the imaged light flux on the pupil plane of the projection optical system PL. Find the pupil plane function. In the next step 105, only the phase function is obtained from the pupil plane function. In step 106, an amplitude function (Fourier plane amplitude function) on the pupil plane of the projection optical system PL is measured.

In the next step 107, a new pupil plane function is obtained by multiplying the amplitude function on the pupil plane by the phase function on the pupil plane. Next, in step 108, the new pupil plane function is subjected to inverse Fourier transform using an IFFT (Inverse Fast Fourier Transfomrm) technique to obtain a new image plane function. In the next step 109, the new image plane function is separated into an image plane amplitude function and an image plane phase function. Subsequently, returning to step 103, when the image plane amplitude function measured in step 101 and the image plane amplitude function calculated in step 109 are within a predetermined allowable range, preferably the measured image plane amplitude function is And the calculated image plane amplitude function match within a predetermined allowable range, the phase recovery operation ends, and the phase function at the pupil plane calculated in step 105 is the pupil plane of the projection optical system PL. This is the wavefront aberration. By substituting the wavefront aberration H (ρ _k , Ψ _k ) at the measurement position (ρ _k , Ψ _k ) in the wavefront aberration into the equation (21), the coefficient (aberration) of the Zernike polynomial of each order is obtained. Can do.

  In step 103, when the image plane amplitude function measured in step 101 and the image plane amplitude function calculated in step 109 do not match within a predetermined allowable range, the image plane amplitude measured in step 101 is determined. A function obtained by multiplying the function by the image plane phase function calculated in step 109 is defined as a new image plane function. Then, the operations from Step 103 to Step 109 are repeated until the image plane amplitude function measured in Step 101 matches the image plane amplitude function calculated in Step 109 within a predetermined allowable range. Thereby, the phase distribution information on the pupil plane of the projection optical system PL can be recovered.

However, in this example, since the measurement of the amplitude function on the pupil plane of the projection optical system PL, which is the operation of step 106, is not performed, the operation of FIG. 12 cannot be executed as it is. Therefore, an example of an operation capable of performing phase recovery without measuring the amplitude function on the pupil plane of the projection optical system PL will be described with reference to FIG.
First, in step 111 of FIG. 13, the light intensity distribution (image intensity) of the image 1AB of the line mark is measured on the upper image plane (referred to as “image plane 1”) in FIG. The initial value θi (predicted value) of the phase function at the X coordinate Xi (i = 1, 2,...) Of the surface 1 is set. In this example, the initial values θi are all 0, but a distribution of values obtained theoretically or empirically may be used, for example. In the next step 113, a function of the square root of the measured image intensity is set as an image plane amplitude function F1 (X) (see FIG. 11), and an image generated from the initial value θi in the image plane amplitude function F1 (X). An image surface function is obtained by multiplying the surface phase function G1 (θ).

  In the next step 114, the image plane function is Fourier-transformed by the FFT technique, and then in step 115, the inverse of the equation (3) (deconvolution) is performed, whereby the slit width of the slit 9A in FIG. Eliminate the effects of 2D integration effects. As a result, a pupil plane function that is a function of the imaging light flux on the pupil plane of the projection optical system PL is obtained. When the slit width 2D is narrow, the deconvolution calculation in step 115 can be omitted. In the next step 116, an amplitude function f1 (X) and a phase function g1 (θ) are obtained from the pupil plane function (see FIG. 11).

  Next, in this example, the Z tilt stage 38 (stage mechanism) in the wafer stage WST in FIG. 1 is driven to defocus the slit plate 90 (image plane) by ΔZ along the Z axis. In FIG. 11, the image plane after such defocusing is defined as an image plane 2. In step 120, the light intensity distribution (image intensity) of the line mark image 1AB on the image plane 2 is measured in advance. Then, the function of the square root of the measured image intensity is stored as the image plane amplitude function F2 (X). In this example, the defocus corresponds to a state that gives a predetermined change to the light intensity distribution of the projected image.

In parallel with this operation, in step 117, the phase function g1 ^* (θ) is obtained by multiplying the phase function g1 (θ) obtained in step 116 by the known phase function of ΔZ defocus. Then, a new pupil plane function is obtained by multiplying the phase function g1 ^* (θ) by the amplitude function f1 (X) on the pupil plane. Next, in step 118, the new pupil plane function is subjected to inverse Fourier transform by the IFFT method, and then in step 119, the same calculation (convolution) as in the equation (3) is performed, whereby the slit 9A in FIG. The integration effect of the slit width 2D is given. As a result, an image plane function measured through the slit 9A on the image plane of the projection optical system PL is obtained. If the deconvolution operation in step 115 is omitted, the convolution operation in step 119 is also omitted (the same applies hereinafter).

In the next step 121, the image plane function is separated into an image plane amplitude function F2 ^* (X) and an image plane phase function G2 (θ). When the image plane amplitude function F2 (X) measured in step 120 matches the calculated image plane amplitude function F2 ^* (X) within a predetermined allowable range (both are within the allowable range). This phase recovery operation ends, and the phase function g1 (θ) at the pupil plane calculated at step 116 is the wavefront function Φ (= | Φ | exp ( iθ)). Then, the process proceeds to step 122, and the wavefront aberration H (ρ _k , Ψ _k ) at the measurement position (ρ _k , Ψ _k ) in the wavefront function (wavefront aberration) is substituted into the equation (21), The coefficient (aberration) of the Zernike polynomial of each order can be obtained. Step 111 corresponds to the first process, steps 113 to 121 correspond to the second process, and step 122 corresponds to the third process. Steps 113 to 116, step 117, steps 118, 119, step 120, and step 121 correspond to the fourth step, the fifth step, the sixth step, the seventh step, and the eighth step, respectively.

In step 121, when the image plane amplitude function F2 (X) measured in step 120 and the calculated image plane amplitude function F2 ^* (X) do not match within a predetermined allowable range, step 120 is performed. A function obtained by multiplying the image plane amplitude function F2 (X) measured in step 1 by the calculated image plane phase function G2 (θ) is defined as a new image plane function.
In the next step 123, the image plane function is Fourier-transformed by the FFT method, and then in step 124, a deconvolution operation is performed to obtain a pupil plane function on the pupil plane of the projection optical system PL. In the next step 125, an amplitude function f2 (X) and a phase function g2 (θ) are obtained from the pupil plane function (see FIG. 11).

  Next, the Z tilt stage 38 (stage mechanism) in the wafer stage WST of FIG. 1 is driven to further defocus the slit plate 90 (image plane) by ΔZ along the Z axis. In FIG. 11, the image plane after such defocusing is defined as an image plane 3. In step 129, the light intensity distribution (image intensity) of the line mark image 1AB on the image plane 3 is measured in advance. Then, the function of the square root of the measured image intensity is stored as the image plane amplitude function F3 (X).

In parallel with this operation, in step 126, the phase function g2 ^* (θ) is obtained by multiplying the phase function g2 (θ) obtained in step 125 by the known phase function of ΔZ defocus. Then, a new pupil plane function is obtained by multiplying the phase function g2 ^* (θ) by the amplitude function f2 (X) on the pupil plane. Next, in step 127, the new pupil plane function is subjected to inverse Fourier transform using the IFFT method, and in step 128, the image plane function on the image plane of the projection optical system PL is obtained by performing a convolution operation. .

In the next step 130, the image plane function is separated into an image plane amplitude function F3 ^* (X) and an image plane phase function G3 (θ). Then, after the image plane amplitude function F3 ^* (X) is replaced with the image plane amplitude function F3 (X) measured in step 129, the calculated image plane phase function G3 is replaced with the image plane amplitude function F3 (X). A function obtained by multiplying (θ) is defined as a new image plane function. In the next step 131, the image plane function is Fourier-transformed by the FFT method, and in step 132, a deconvolution operation is performed to obtain a pupil plane function on the pupil plane of the projection optical system PL. In the next step 133, an amplitude function f2 (X) and a phase function g2 ^* (θ) are obtained from the pupil plane function. In the next step 134, the phase function g 2 (θ) is obtained by multiplying the phase function g 2 ^* (θ) obtained in step 133 by the known phase function of −ΔZ defocus. Then, a new pupil plane function is obtained by multiplying the phase function g2 (θ) by the amplitude function f2 (X) on the pupil plane. Next, in step 135, the new pupil plane function is subjected to inverse Fourier transform by the IFFT method, and in step 136, a convolution operation is performed to obtain an image plane function on the image plane of the projection optical system PL.

Next, returning to step 121, the image plane function is separated into an image plane amplitude function F2 ^* (X) and an image plane phase function G2 (θ). Then, when the image plane amplitude function F2 (X) measured in step 120 matches the calculated image plane amplitude function F2 ^* (X) within a predetermined allowable range, the phase recovery operation ends. Then, the phase function g2 (θ) at the pupil plane calculated at step 134 becomes the wavefront function Φ (= | Φ | exp (iθ)) at the pupil plane of the projection optical system PL, and the operation shifts to step 122. To do. On the other hand, when the image plane amplitude function F2 (X) measured in step 120 and the calculated image plane amplitude function F2 ^* (X) do not match within a predetermined allowable range in step 121, step 120 is performed. A function obtained by multiplying the image plane amplitude function F2 (X) measured in step 1 by the calculated image plane phase function G2 (θ) is defined as a new image plane function.

In the next step 137, the image plane function is Fourier-transformed by the FFT method, and then in step 138, a deconvolution operation is performed to obtain a pupil plane function on the pupil plane of the projection optical system PL. In the next step 139, an amplitude function f1 (X) and a phase function g1 ^* (θ) are obtained from the pupil plane function. In the next step 140, the phase function g1 (θ) is obtained by multiplying the phase function g1 ^* (θ) obtained in step 139 by the known phase function of −ΔZ defocus. Then, a new pupil plane function is obtained by multiplying the phase function g1 (θ) by the amplitude function f1 (X) on the pupil plane. Next, in step 141, the new pupil plane function is subjected to inverse Fourier transform by the IFFT method, and in step 142, a convolution operation is performed to obtain an image plane function on the image plane of the projection optical system PL. . Next, the operation returns to step 113 again, and the operations from steps 114 to 142 are repeated. At this time, when the measured image plane amplitude function matches the calculated image plane amplitude function within a predetermined allowable range in step 121, the phase recovery operation ends, and the step is performed as described above. At 122, an aberration is determined.

  As described above, according to this example, the phase distribution information on the pupil plane of the projection optical system PL can be obtained with high accuracy by only measuring the light intensity distribution of the defocused line mark image. Therefore, the aberration of the projection optical system PL can be obtained in a short time and with high accuracy based on the phase distribution information. In addition, since the measurement of the image of the line mark can be performed by the aerial image measurement device provided with the focus position and alignment position measurement slits provided in the projection exposure apparatus, a dedicated measurement device is newly provided. There is no need to provide it.

  Note that it is desirable to adjust the projection optical system PL of FIG. 1 based on the aberration amount measured by the aberration measurement method of each of the above embodiments, and ideally, the aberration of the projection optical system PL is set to 0. Actually, some aberrations may remain even after the projection optical system PL is adjusted. Therefore, when the projection exposure apparatus of the above embodiment is operated, after the projection optical system PL is adjusted, the residual aberration of the projection optical system PL is again measured as the initial aberration amount by using the aberration measurement method of the above embodiment. It may be left. In this case, when the aberration fluctuation amount of the projection optical system PL is periodically measured by the aberration measurement method of the above-described embodiment and the aberration changes due to a change over time, the main controller 50 performs the operation shown in FIG. The imaging characteristics of the projection optical system PL may be adjusted via the imaging characteristic correction controller 78 so that these aberration amounts return to the initial aberration amounts. In addition, it is desirable from the viewpoint of measurement stability that periodic aberration measurement is performed using a measurement pattern formed on the reticle mark plate RFM or the like.

In each of the above embodiments, the case where the reduction system is used as the projection optical system has been described. However, the present invention is not limited to this, and the projection optical system may be an equal magnification or an enlargement system. Either a catadioptric system or a reflective system may be used.
Further, for example, for a semiconductor device, a step of designing the function / performance of the device, a step of manufacturing a reticle based on the design step, a step of manufacturing a wafer from a silicon material, and the projection exposure apparatus (exposure apparatus) of the above-described embodiment Thus, the wafer is manufactured through a step of transferring a reticle pattern to a wafer, a device assembly step (including a dicing process, a bonding process, and a package process), an inspection step, and the like.

  In each of the above embodiments, the case where the present invention is applied to a scanning exposure type projection exposure apparatus has been described. However, the present invention is not limited thereto, and the mask pattern is transferred to the wafer while the mask and the wafer are stationary. The present invention can also be applied to a static exposure type (collective exposure type) projection exposure apparatus such as a stepper. The present invention can also be applied to the case where the aberration of the projection optical system is measured by an immersion type exposure apparatus disclosed in, for example, WO 99/49504.

  Further, the present invention is not limited to an exposure apparatus for manufacturing a semiconductor device, but is used for manufacturing a display including a liquid crystal display element, a plasma display, and the like. An exposure apparatus for transferring a device pattern onto a glass plate and a thin film magnetic head. The present invention can also be applied to an exposure apparatus for transferring a device pattern used in the above to a ceramic wafer, and an exposure apparatus used for manufacturing an imaging device (CCD, etc.), an organic EL, a micromachine, a DNA chip, and the like. In addition to microdevices such as semiconductor elements, circuits for glass substrates or silicon wafers are used to manufacture masks used in optical exposure equipment, EUV exposure equipment, X-ray exposure equipment, and electron beam exposure equipment. The present invention can also be applied to an exposure apparatus that transfers a pattern.

  In addition, this invention is not limited to the above-mentioned embodiment, Of course, a various structure can be taken in the range which does not deviate from the summary of this invention.

  According to the exposure method and apparatus of the present invention, the aberration of the projection optical system can be measured with high accuracy in a short time with the projection optical system mounted on the exposure apparatus. Therefore, for example, by correcting the aberration of the projection optical system according to the measurement result, the mask pattern can be transferred onto the substrate with high accuracy.

It is the figure which partly cut off showing the schematic structure of the projection exposure apparatus of an example of embodiment of this invention. FIG. 2 is a partially cutaway view showing an imaging characteristic control mechanism of projection optical system PL of FIG. 1 and a Z tilt stage of wafer stage WST. It is a figure which shows the internal structure of the aerial image measuring device with which the projection exposure apparatus of FIG. 1 was equipped. (A) is a figure which shows an example of the slit on the slit board 90 of FIG. 3, (B) is a figure which shows an example of the photoelectric conversion signal obtained in the case of an aerial image measurement. It is an enlarged plan view which shows arrangement | positioning of the actual slit on the slit board 90 of FIG. It is an enlarged plan view showing an example of the arrangement of line marks on reticle mark plate RFM. It is a figure which shows an example of the aberration component represented by a 7th-order Zernike polynomial. It is a figure which shows an example of the aberration component represented by an 8th-order Zernike polynomial. It is a figure which shows an example of arrangement | positioning of the measurement point of phase information in embodiment of this invention. It is a figure which shows the line mark in the embodiment of this invention, its diffraction pattern, and its projection image. It is a figure which shows an example of the light intensity distribution of the projection image of the line mark of FIG. It is a flowchart which shows the principle of the phase recovery operation | movement in embodiment of this invention. It is a flowchart which shows an example of the phase recovery operation | movement in embodiment of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1A-1F ... Line mark, 9A-9F ... Slit, 12 ... Illumination optical system, 14 ... Light source, 50 ... Main controller, 51 ... Memory, 59 ... Aerial image measuring device, 78 ... Imaging characteristic correction controller, 80 ... Signal processing device, 90 ... slit plate, PL ... projection optical system, R ... reticle, RST ... reticle stage, RFM ... reticle mark plate, W ... wafer, WST ... wafer stage

Claims (12)

An aberration measurement method for measuring an aberration of a projection optical system,
A first step of projecting a line pattern image through the projection optical system to obtain light intensity distribution information in the width direction of the line pattern image;
A second step of obtaining phase distribution information of the imaged light flux of the image of the line pattern on the pupil plane of the projection optical system from the light intensity distribution information obtained in the first step;
And a third step of obtaining an aberration of the projection optical system based on the phase distribution information obtained in the second step.   The first step includes a step of receiving light passing through the opening pattern while relatively scanning the line pattern image and the slit-shaped opening pattern in the width direction of the line pattern image. The aberration measurement method according to claim 1. The second step includes
A function obtained by multiplying the first image plane amplitude function by the first image plane amplitude function obtained from the light intensity distribution information obtained in the first step is subjected to Fourier transform, and the first on the pupil plane of the projection optical system. A fourth step of obtaining an amplitude function and a first phase function;
A fifth step of obtaining a second phase function by performing an operation corresponding to a predetermined change in the light intensity distribution of the image of the line pattern on the first phase function obtained in the fourth step;
A function obtained by multiplying the first amplitude function obtained in the fourth step by the second phase function obtained in the fifth step is subjected to inverse Fourier transform to obtain a first on the image plane of the projection optical system. A sixth step of obtaining a two image plane amplitude function and a second image plane phase function;
In the state where the predetermined change is given to the light intensity distribution of the image of the line pattern, light intensity distribution information in the width direction of the image of the line pattern is obtained, and a third image plane amplitude function is obtained from the light intensity distribution information. 7 steps,
When the second image plane amplitude function obtained in the sixth step and the third image plane amplitude function obtained in the seventh step are within an allowable range, the obtained in the fourth step The aberration measurement method according to claim 1, further comprising an eighth step of obtaining phase distribution information of the imaged light beam on the pupil plane of the projection optical system from the first phase function. The first image plane phase function is a predetermined distribution constant,
The predetermined change in the light intensity distribution of the line pattern image in the fourth step is a change in the light intensity distribution when the focus position of the line pattern image is changed. Aberration measurement method.   In the eighth step, the phase of the imaging light beam on the pupil plane of the projection optical system when the second image plane amplitude function and the third image plane amplitude function match within the allowable range. The aberration measurement method according to claim 3, wherein distribution information is obtained. In the eighth step, when the second image plane amplitude function and the third image plane amplitude function do not match within the allowable range,
The light intensity distribution information obtained in the seventh step is regarded as the light intensity distribution information obtained in the first step, and the second image plane phase function obtained in the sixth step is used as the first image plane phase. The aberration measurement method according to claim 5, wherein the fourth to eighth steps are repeated as a function.   The aberration measurement method according to claim 1, wherein the line pattern projected in the first step includes six line patterns arranged in different directions. An aberration measuring apparatus for measuring the aberration of the projection optical system,
A line pattern disposed on the object plane side of the projection optical system;
An illumination system for illuminating the line pattern;
A slit-like opening pattern disposed on the image plane side of the projection optical system and extending in a direction substantially parallel to the longitudinal direction of the image of the line pattern by the projection optical system;
A scanning mechanism for relatively scanning an image of the line pattern by the projection optical system and the opening pattern in a width direction of the image of the line pattern;
A photoelectric sensor that receives light passing through the aperture pattern and detects light intensity distribution information of the image of the line pattern;
A first arithmetic unit that obtains phase distribution information of an image forming light beam of the image of the line pattern on the pupil plane of the projection optical system based on light intensity distribution information detected by the photoelectric sensor;
An aberration measuring device comprising: a second computing device that obtains aberrations of the projection optical system based on phase distribution information obtained by the first computing device. The line pattern includes six line patterns arranged in different directions, and the opening pattern includes six opening patterns corresponding to the six line patterns,
9. The aberration measuring apparatus according to claim 8, further comprising a stage mechanism that relatively displaces the image of the line pattern and the opening pattern in an optical axis direction of the projection optical system. In an exposure method of illuminating a first object with an exposure beam and exposing the second object with the exposure beam via the first object and a projection optical system,
An exposure method, comprising: measuring an aberration of the projection optical system by the aberration measurement method according to claim 1.   The exposure method according to claim 10, wherein the imaging characteristics of the projection optical system are corrected according to the aberration measured by the aberration measurement method. In an exposure apparatus that illuminates a first object with an exposure beam and exposes the second object with the exposure beam via the first object and a projection optical system,
An exposure apparatus comprising the aberration measuring apparatus according to claim 8 or 9 for measuring aberrations of the projection optical system.

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