JP2006234517A - Optical characteristic measurement method and instrument, substrate used for the measurement method, and exposure method and device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To measure the optical characteristics of an optical system under test with high accuracy, by reducing the effects of manufacturing errors in marks for measurement. <P>SOLUTION: A first group of aberration measurement marks 1A to 1I and a second group of aberration measurement marks 2A to 2I, severally obtained by 180° turning about the first group of marks are formed on a reticle mark plate RFM. A first aberration of a projection optical system is found, based on the images of the measurement marks 1A to 1I obtained by the optical system. A second aberration of the optical system is found, based on images of the measurement marks 2A to 2I. The first and second aberrations are averaged for reducing the effect of depiction errors in the measurement marks 1A to 1I. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

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

  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 wafer (or glass plate) coated with a photosensitive material as a substrate via a projection optical system. Etc.) A batch exposure type projection exposure apparatus (stepper or the like) and a scanning exposure type projection exposure apparatus (scanning stepper or the like) to be transferred thereon are used. 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.

  As the disturbance factors of the aberration of the projection optical system, heating of the lens by irradiation of exposure light, change of refractive index due to atmospheric pressure fluctuation, change of laser wavelength when exposure light is laser light such as excimer laser, and The reticle expands due to exposure light exposure, and various aberrations of the projection optical system fluctuate depending on these factors. Further, in the projection exposure apparatus, distortion aberration or the like can be controlled by controlling the posture of some lenses constituting the projection optical system or controlling the atmospheric pressure in a space (lens chamber) between predetermined lenses. An imaging characteristic control mechanism for controlling predetermined imaging characteristics such as spherical aberration to a predetermined state is provided.

Conventionally, aberration variations due to lens heat among these aberration variations are determined by changing the best focus position and magnification while changing the exposure light irradiation amount using a predetermined measurement mark formed on the test reticle. By measuring, the relationship between the irradiation amount, the best focus position, and the amount of change in magnification was obtained in advance. When the actual reticle pattern for a device is exposed, the imaging characteristic control mechanism is controlled so as to cancel the amount of change in the best focus position and magnification in accordance with the exposure light irradiation amount. Further, in order to quickly measure a predetermined aberration of the projection optical system using the measurement mark, a method of measuring an aerial image (projection image) of the mark and calculating the aberration based on the measurement result ( Hereinafter, it is referred to as “aerial image measurement method” (see, for example, Patent Document 1).
JP-A-10-170399

  As described above, conventionally, the aberration of the projection optical system has been measured using a predetermined measurement mark formed on the test reticle. In addition, a conventional test reticle is produced by, for example, producing a master reticle by drawing an original pattern of measurement marks on a glass substrate by an electron beam drawing apparatus, and then projecting the master reticle pattern to a reduction magnification of, for example, 1/5. It was manufactured by transferring onto a glass substrate using a photo repeater comprising an exposure device. In this case, if a manufacturing error is included in the measurement mark of the test reticle due to a drawing error of the original pattern formed on the master reticle, it becomes a measurement error of the aberration of the projection optical system. there were.

  In view of the above, the present invention provides a measurement technique and an exposure technique that can reduce the influence of a manufacturing error of a measurement mark and accurately measure the optical characteristics of a test optical system such as a projection optical system. For the purpose.

  The optical characteristic measuring method according to the present invention is an optical characteristic measuring method for measuring the optical characteristic of a test optical system (PL), based on an image of the first mark (1A to 1I) by the test optical system. A first step of obtaining a first optical characteristic of the optical system, and a second mark (2A to 2I) obtained by rotating the first mark by a predetermined angle based on an image of the optical system to be tested. The second step for obtaining the second optical characteristic and the third step for obtaining the optical characteristic of the test optical system based on the first and second optical characteristics.

  According to the present invention, when the first mark as the measurement mark has a position shift due to a manufacturing error (relative position shift within the mark), the second mark has the position shift. There is a displacement in the direction rotated by a predetermined angle. Therefore, the first and second optical characteristics obtained based on the images of the first and second marks are subjected to calculations according to the predetermined angles, thereby reducing the influence of the manufacturing error. The optical characteristics of the test optical system can be measured with high accuracy.

In the present invention, as an example, the predetermined angle is 180 °. In this case, the positional deviation of the second mark is almost the same as the positional deviation of the second mark with respect to the positional deviation due to manufacturing error of the first mark. Therefore, for example, the influence of the manufacturing error can be reduced by a simple calculation of averaging the first and second optical characteristics.
Further, as an example, the first mark includes marks having pitches of six or more types arranged along two different directions. Thus, when the wavefront aberration is expressed by a Zernike polynomial, aberrations of 0θ, 1θ, and cos 2θ components among the aberrations expressed by the Zernike polynomial up to the 16th order can be measured.

As another example, the first mark includes marks with pitches of six or more types arranged along six different directions. As a result, aberrations represented by Zernike polynomials up to the 37th order can be measured.
An exposure method according to the present invention is an exposure method in which a second object (W) is exposed via an exposure beam via a first object (R) and a projection optical system (PL). It has a measurement process for measuring the optical characteristics of the projection optical system, and a correction process for correcting the imaging characteristics of the projection optical system based on the measurement results of the measurement process.

According to the present invention, it is possible to measure the optical characteristics of the projection optical system with high accuracy by reducing the influence of the manufacturing error of the measurement mark. By correcting the imaging characteristic of the projection optical system based on the measurement result, the imaging characteristic can be maintained in a desired state with high accuracy.
The first substrate according to the present invention is a substrate (RFM) used when measuring the optical characteristics of the test optical system, and forms an aerial image including information on the optical characteristics of the test optical system. The first mark (1A to 1I) to be formed and the second mark (2A to 2I) having a shape obtained by rotating the first mark by a predetermined angle are formed. By using this substrate, the optical property measuring method of the present invention can be implemented.

In this case, the substrate includes a first set of alignment marks (65A to 65D) used when the substrate is arranged at the first rotation angle, and the substrate is moved to the first rotation angle. A second set of alignment marks (64A to 64D) used when rotated by 180 ° with respect to each other may be formed.
In this case, as an example, the predetermined angle is 180 °. In addition, as an example, the first mark includes marks with pitches of six or more types arranged along two different directions. As another example, the first mark includes marks with pitches of six or more types arranged along six different directions.

  The second substrate according to the present invention is arranged such that the first and second marks are opposed to each other along the first direction (Y direction) in the first substrate. A plurality of pairs of marks having the same shape as the pair of marks (1A, 2A) are formed along a second direction (X direction) intersecting the first direction. By using the plurality of pairs of marks, for example, optical characteristics in a slit-shaped exposure region in a scanning exposure apparatus can be measured.

  Next, an optical characteristic measuring apparatus according to the present invention is an optical characteristic measuring apparatus for measuring the optical characteristics of a test optical system (PL), the substrate (RFM) of the present invention, and an illumination system (12, 14), an aerial image detection system (59) for detecting images of the first and second marks formed on the substrate by the optical test system, and the test based on the detection result of the spatial image detection system And an arithmetic unit (50) for obtaining optical characteristics of the optical system.

According to the present invention, in the arithmetic device, with respect to the first and second optical characteristics obtained based on the images of the first and second marks, the rotation angle of the second mark with respect to the first mark is determined. By performing a corresponding calculation, the influence of the manufacturing error of the first mark can be reduced, and the optical characteristics of the optical system to be measured can be measured with high accuracy.
Next, the first exposure apparatus according to the present invention illuminates the first object (R) with the exposure beam, and the second object (W) through the first object and the projection optical system (PL) with the exposure beam. In the exposure apparatus for exposing the substrate, the substrate (RFM) of the present invention, the stage (RST) for holding the substrate together with the first object, and the projection optical system of the first and second marks formed on the substrate An aerial image detection system (59) for detecting an image by the above and an arithmetic unit (50) for obtaining optical characteristics of the projection optical system based on the detection result of the aerial image detection system.

Further, the second exposure apparatus according to the present invention illuminates the first object (R) with the exposure beam, and moves the first object and the second object (W) synchronously while moving the first object with the exposure beam. In an exposure apparatus that exposes an object and a second object via a projection optical system (PL), the second substrate (RFM) of the present invention and the substrate together with the first object have a first direction in the first direction. A stage (RST) that holds the object so as to be parallel to the scanning direction (Y direction) of the object, and an aerial image detection system that detects an image of the first and second marks formed on the substrate by the projection optical system ( 59) and an arithmetic unit (50) for obtaining the optical characteristics of the projection optical system based on the detection result of the aerial image detection system.
According to the exposure apparatus of the present invention, the optical characteristics of the projection optical system can be measured with high accuracy in the batch exposure type or scanning exposure type exposure apparatus.

According to the present invention, since the optical characteristics of the optical system to be measured can be obtained based on the image of the first mark as the measurement mark and the second mark rotated by this, the influence of the manufacturing error of the measurement mark. The optical characteristics of the test optical system can be measured with high accuracy.
Further, according to the exposure method and apparatus of the present invention, it is possible to measure the optical characteristics of the projection optical system with high accuracy by reducing the influence of the manufacturing error of the measurement mark. Based on the measurement result, the imaging characteristic of the projection optical system is corrected as necessary, so that the imaging characteristic can be maintained in a desired state.

Hereinafter, an example of a preferred embodiment of the present invention will be described with reference to FIGS.
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 step-and-scan type scanning exposure type projection exposure apparatus, that is, a scanning stepper.
In FIG. 1, a projection exposure apparatus 10 holds a reticle stage as a light source 14 (exposure light source) that generates a laser beam LB, an illumination optical system 12 (illumination unit), and a mask (first object) and moves. It includes an RST, a projection optical system PL, a wafer stage WST that holds and moves the wafer W as a substrate (second object or photoconductor), a control system that controls these, and the like. 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 to turn on / off the laser emission, the center wavelength, the spectral half-value width, the repetition frequency, and the like by a main controller 50 that is a computer that controls the overall operation of the apparatus. 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, an integrator sensor 46 including a condenser lens 44 and a light receiving element is 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. The beam splitter 26, the condenser lens 44, and the integrator sensor 46 serve as an irradiation amount control system. 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 forms an image of the pattern surface of the reticle R (first object) on the upper surface of the wafer W (second object). 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 the present example is provided with an imaging characteristic correction device for controlling (correcting) the predetermined imaging characteristics.
FIG. 2 is a cross-sectional view showing a part of the imaging characteristic correction apparatus for the projection optical system PL in FIG. 1. In FIG. 2, for convenience of explanation, the optical axis is configured to form 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 imaging characteristic correction apparatus is configured including the drive element 20 and the imaging characteristic correction controller 78. Thereby, the wavefront aberration or the predetermined aberration as the imaging characteristic (optical characteristic) of the projection optical system PL is corrected (details will be described later). The number of movable lens elements may be arbitrary. However, for example, 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, and the types of wavefront aberrations to be corrected (wavefronts represented by Zernike polynomials described later) The number of movable lens elements or the degree of freedom of driving as a whole of the movable lens elements may be determined according to the number of aberrations) or the type of imaging characteristics that need to be corrected.

  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. Alternatively, the end surface of reticle stage RST may be mirror-finished to form the reflection surface of movable mirror 52R described above.

  Also, a reticle fiducial mark plate (hereinafter referred to as “reticle mark plate”) as a reference member or substrate on which an aerial image measurement reference mark (measurement pattern) is formed in the vicinity of the end in the −Y direction of reticle stage RST. The RFM is abbreviated as "" and is aligned with the reticle R. This reticle mark plate RFM (described later in detail) is made of the same glass material as that of reticle R, for example, synthetic quartz, fluorite, lithium fluoride and other fluoride crystals, and is fixed to reticle stage RST (stage). Has been. 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, wafer stage WST includes XY stage 42 and Z tilt stage 38 mounted on XY stage 42. 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 driving 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, 21C (however, the actuator 21C on the back side of the paper in FIG. 2 is not shown), and the Z position drive units 27A, 27B, 27C of the Z tilt stage 38 are supported by the actuators 21A, 21B, 21C at the respective support points. It includes encoders 23A to 23C (however, encoder 23C on the back side in FIG. 2 is not shown) that detects a driving amount in the direction (displacement from the reference position).

  In this example, the actuators 21A, 21B, and 21C control the position of the Z tilt stage 38 (wafer W) in the optical axis AX direction (Z direction), the rotation angle θx around the X axis, and the rotation angle θy around the Y axis. To do. The stage controller 70 in FIG. 1 adjusts the position and leveling amount (rotation angle θx) 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. Note that the end surface of the Z tilt stage 38 may be mirror-finished to form the reflective surface of the movable mirror 52W.

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. And a relay optical system comprising a slit plate 90, lenses 84 and 86, a mirror 88 for bending an optical path, a light transmitting lens 87, and components outside the stage provided outside the wafer stage WST, that is, a mirror 96, a light receiving lens 89, And an optical sensor 94 (photoelectric sensor) composed of a photoelectric conversion element.

  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 is projected from above in a state of covering the opening with respect to the protruding portion 58 formed with an opening in the upper portion. It is inserted. The slit plate 90 is configured by forming a reflective 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 a slit shape having a predetermined width of 2D is formed on a part of the reflective film 83. The opening pattern (hereinafter referred to as “slit”) 122 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 ArF excimer laser light transmission property 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. In the Z tilt stage 38 below the slit 122, a relay optical composed of lenses 84 and 86 is interposed via a mirror 88 that horizontally bends the optical path of illumination light IL (imaging light beam) incident vertically downward through the slit 122. A system (84, 86) is 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 ° vertically upward by a mirror 96 having a predetermined length in the X direction and inclined at an inclination angle of 45 °. It can be bent. 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 measurement device 59 configured as described above, the measurement mark PM (or the mark formed on the reticle R) formed on the reticle mark plate RFM (or the reticle R) is projected via the projection optical system PL. When measuring the projection image (aerial image) obtained in this way, the slit plate 90 is illuminated by the illumination light IL (imaging light beam) transmitted through the projection optical system PL. The illumination light IL that has passed through the slit 122 of the slit plate 90 is guided to the outside of the wafer stage WST through the lens 84, the mirror 88, the lens 86, and the light transmission lens 87. The light guided to the outside of the wafer stage WST is received by the optical sensor 94 via the mirror 96 and the light receiving lens 89, and a photoelectric conversion signal (light quantity signal) PS corresponding to the amount of received light is received from the optical sensor 94. It is output to the main controller 50 via the signal processing device 80 of FIG.

  In this example, since the measurement of the projected image (aerial image) of the measurement mark is executed by the slit scan method, the light transmitting lens 87 is in the X direction and Y direction with respect to the light receiving lens 89 and the optical sensor 94 at that time. Will move in the direction. 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. Furthermore, 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 off-axis alignment system ALG 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. In this example, an image processing type alignment system, a so-called FIA (Field Image Alignment) system is used as the alignment system ALG. An imaging signal from the alignment system ALG is supplied to an alignment control device (not shown).

  Further, as shown in FIG. 1, the projection exposure apparatus 10 of this example is provided with an oblique incidence type multi-point 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 the multi-point focal position detection system similar to the multi-point focal position detection system (60a, 60b) is disclosed in, for example, Japanese Patent Application Laid-Open No. Hei 6-283403. The detailed explanation is omitted.

  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 for actual exposure based on an instruction from the operator. 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 characteristic (optical characteristic) of the projection optical system PL to be measured and corrected is a predetermined aberration.

  Further, assuming that the aberration function indicating the wavefront aberration on the exit pupil (or pupil plane) of the projection optical system PL is W (ρ, θ), using wavefront aberration to classify the aberration, the aberration function W (Ρ, θ) is expressed in a polar coordinate format, ρ 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, the coefficient Z _i is a coefficient representing the magnitude of the aberration represented by the i-th order (i = 1, 2,...) Zernike polynomial fi (ρ, θ) among the various aberrations of the projection optical system. is there. 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. 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. For example, for f7 and f8 shown in Table 1, the radial functions are both (3ρ ³ −2ρ) and are odd functions, and f5 and f6 are both radial functions of ρ ² and are even functions and It has become. The function of the angle θ in each order Zernike polynomial is sin (mθ) (m is an integer of 1 or more) or cos (mθ) (m is an integer of 0 or more). When the integer m that defines the angle mθ is an odd number, the corresponding radial function is an odd function, and when the integer m is 0 or an even number, the corresponding radial function is an even function. . As described above, 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. In this example, the wavefront aberration represented by the Zernike polynomial up to a predetermined order can be individually corrected by the imaging characteristic correction device of the projection optical system PL including the imaging characteristic correction controller 78 of FIG. If the aberration Z _i represented by the coefficient of the i-th order Zernike polynomial is used, the spherical aberration (even function aberration) is the aberration Z ₉ , Z ₁₆ , and the coma aberration (odd function aberration) is the aberration Z ₇ , Z ₈ , Z ₁₄ and Z ₁₅ , and distortion (odd function aberration) are aberrations Z ₂ and Z ₃ . Therefore, when the imaging characteristic correction apparatus is used, for example, spherical aberration, coma aberration, and distortion can be individually corrected.

In this example, the aerial image measuring device 59 described above is used to measure the wavefront aberration. Hereinafter, aerial image measurement by the aerial image measurement device 59, measurement of wavefront 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. In place of the reticle mark plate RFM, a test reticle dedicated to aerial image measurement, or an actual exposure reticle R used for manufacturing a device having a dedicated measurement pattern formed thereon can be used as a substrate. is there. Here, on the reticle mark plate RFM, a line-and-space pattern (hereinafter referred to as a ratio of the width of the line portion to the width of the space portion (duty ratio)) having a periodicity in the Y direction at a predetermined location is 1: 1. It is assumed that a measurement mark PM composed of “L & S pattern” is formed. Such a measurement mark PM is actually one of a plurality of marks provided on the reticle mark plate RFM.

  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. In the measurement of 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 area of the illumination light IL of the reticle R It is limited only to a predetermined area including the measurement mark PM.

In addition, by controlling the illumination system aperture stop plate 24 (illumination σ changing means) in the illumination optical system 12, the illumination condition is set to a small annular illumination with a coherence factor (σ value) of about 0.068 to 0.044, for example. Or set to illumination with a minimum σ value.
In this state, when the illumination light IL is irradiated onto the reticle mark plate RFM, as shown in FIG. 4A, the light diffracted and scattered by the measurement mark PM (illumination light IL) is projected onto the projection optical system PL. And a spatial image (projected image) PM ′ of the measurement mark PM is formed on the image plane of the projection optical system PL. At this time, wafer stage WST is set at a position where the aerial image PM ′ is formed on the + Y direction side (or the −Y direction side) of slit 122 on slit plate 90 of aerial image measurement device 59. And A plan view of the slit plate 90 at this time when viewed from the projection optical system PL side is shown in FIG. If the projection magnification of the projection optical system PL is 1/4, the pitch (period) of the spatial image PM ′ is 1/4 of the pitch of the L & S pattern of the measurement mark PM. In the following description, it is assumed that the line width and pitch of each measurement mark and the like indicate the line width and pitch of the aerial image, respectively.

  When the main controller 50 drives the wafer stage WST (scanning mechanism) in the + Y direction as indicated by the arrow F in FIG. 4A via the wafer stage drive system 56W, the slit 122 becomes a space. The image PM ′ is scanned in the Y direction. 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, the mirror 96, and the light receiving lens 89, and the photoelectric conversion signal PS is converted into a signal processing device. 80 to the main controller 50. Main controller 50 acquires light intensity distribution information corresponding to aerial image PM ′ based on the photoelectric conversion signal. Note that the aerial image PM ′ and the slit 122 may be relatively scanned in a direction perpendicular to 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 aerial image PM ′ is averaged by the influence of the width (2D) of the slit 122 in the scanning direction (Y direction). 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. In this example, the slit width 2D is set to about 200 nm or less, for example, about 100 to 150 nm. Note that the aerial image PM ′ may be scanned using a pinhole instead of the slit 122. In the case of a pinhole, there is no directionality, but the amount of light is reduced. Therefore, pinholes can be used particularly when the pitch of the aerial image PM 'is large. When using a pinhole, in order to increase the amount of received light, the diameter is set to about twice the slit width 2D, that is, about 400 nm or less, for example, about 200 to 300 nm.

  Thus, the light intensity distribution in the aerial image (projected image) PM ′ of the measurement 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 odd-function aberration and even-function aberration, and hence wavefront aberration. 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 periodic marks having different directions and pitches 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 arrangement of a plurality of slits as opening patterns formed on the slit plate 90 of this example. In FIG. 5, the slit plate 90 has a slit width 2D extending in the Y direction and a length L. And a slit 122a that extends in the X direction and is formed by rotating the slit 122b by 90 °. Further, six aberration measuring slits 9A, 9B, 9C, 9D, 9E, and 9F each having a width 2D and a length L1 are formed on the slit plate 90. In this case, the slits 9A and 9D are arranged on the extensions of the slits 122b and 122a, respectively, and the remaining four slits 9B, 9C, 9F, and 9E are located at the positions of the four apexes of a substantially square, and a set of slits. 122b and 9A and another set of slits 122a and 9D substantially constitute two adjacent sides of the square. In addition, a pin hole 123 having a diameter of about 4D is formed at substantially the center of the square. The illumination light that has passed through the slits 122a, 122b, 9A to 9F, and the pinhole 123 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 and 9D, the slits 122b and 9A, the slit 9B, the slit 9C, the slit 9E, the slit 9F, and the pinhole 123, for example, a slit is formed on the bottom surface of the slit plate 90. A liquid crystal panel as a selection member may be provided so that only illumination light that has passed through the selected set or one slit or pinhole may enter the optical sensor 94.

  In this example, the slit width 2D of each slit image is about 100 nm, the length L of the slits 122a and 122b is about 8 μm, and the length L1 of the slits 9A to 9F is about 3 μm. These slit widths and lengths are values at the stage of the projected image. The distance between the slit 122a and the slit 9D and the distance between the slit 122b and the slit 9A are about 1 to 2 μm. In this case, the slits 122a and 122b are used for calibration of the best focus position and position measurement of the mark image. Further, when the slits 122a and 122b are used, the aberration measuring slits 9D and 9A on the extensions are also used at the same time. By simultaneously using the aberration measurement slits 9D and 9A for the slits 122a and 122b in this way, a sufficient amount of light can be secured when measuring the best focus position and the image position, and measurement reproducibility is improved. To do.

  The longitudinal directions (arrangement directions) of the aberration measurement slits 9A, 9B, 9C, 9D, 9E, and 9F in FIG. 5 are 90 °, φ5, φ6, and 0 ° counterclockwise with respect to the X axis, respectively. , Φ7, and φ8. 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 °, φ1 (= φ5-90 °), φ2 (= φ6) counterclockwise with respect to the X axis, respectively. -90 °), 90 °, φ3 (= φ7 + 90 °), and φ4 (= φ8 + 90 °). As an example, the angle φ1 is 30 °, the angle φ2 is 45 °, the angle φ3 is 120 °, and the angle φ4 is 135 °. In this way, by using the slit plate 90 of this example, the aberration of the projection optical system PL can be measured on-body.

When the aberration to be measured is 0θ, 1θ, and cos2θ components up to Z ₃₇ as will be described later, the two slits 9A and 9D on the slit plate 90 in FIG. Only two slits (opening patterns) intersecting at 0 ° and 90 ° may be used.
Then, when measuring the aberration of the even function component, one or more terms of the even function component such as the defocus aberration, the fourth term Z ₄ , the ninth term Z ₉ , and the sixteenth term Z ₁₆ of the Zernike polynomial The amplitude of the fundamental frequency component of the target mark is measured using the slit plate 90 while changing the amount of aberration. At this time, the even function aberration amount at the corresponding point in the wavefront can be calculated from the even function aberration amount giving the maximum amplitude. The aberrations Z ₄ , Z ₉ , Z _{16 and the} like can be controlled by moving the corresponding lens element of the projection optical system PL using the imaging characteristic correction device shown in FIG.

On the other hand, when measuring the aberration of the odd function component, the phase of the fundamental frequency component of the aerial image intensity signal may be measured and converted to the aberration amount at the corresponding point in the wavefront.
In the above aberration measurement method, the odd-function aberration and the even-function aberration are individually detected. Hereinafter, a method for unifying and calculating odd-function aberration and even-function aberration will be described by regarding the aberration as a phase distribution at the exit pupil (or pupil plane) of the projection optical system PL. First, the even function aberration at the position (ρ, θ) is set to H_even (ρ, θ) using the normalized radius ρ and angle θ on the exit pupil. At this time, as an example, if a method of measuring the even function aberration in terms of the aberration Z ₉ represented by the above 9th-order Zernike polynomial f9 (ρ, θ) (= 6ρ ⁴ -6ρ ² +1) is used, The even function aberration H_even (ρ, θ) represented by the Zernike polynomial of even order Feven (ρ, θ) can be expressed as follows. In this case, it is assumed that the position at which the aberration (phase) is measured is a position (ρ = ρ _p , θ = Ψ _p ) where diffracted light from a periodic mark having a predetermined pitch Pmes passes. The even function aberration amount is a relative aberration amount from the center of the pupil plane where ρ = 0. In addition to the aberration Z ₉ , the aberration at the pupil center and the measurement point can be measured by an even function aberration that can be controlled, such as defocusing.

H_even (ρ _p , Ψ _p ) = [feven (ρ _p , Ψ _p ) −1] λ even-mes
= [F9 (ρ _p , Ψ _p ) −1] λmes = (6ρ _p ⁴ −6ρ _p ² ) λmes (18)
Here, the Zernike polynomial feven (ρ, θ) is, for example, f16, f25, etc., and λeven-mes is the amount (coefficient) of the aberration represented by the Zernike polynomial feven (ρ, θ) of the even order. . Also, λeven is the amount of aberration Z ₉ when the amplitude or contrast (= first-order component amplitude / 0th-order amplitude) of the first-order component obtained by Fourier-transforming the spatial image of the periodic mark with the pitch P is maximized. is there.

Equation (18) is an aberration 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, an aberration determined by the Zernike polynomial (for example, feven (ρ _{For p} , Ψ _p )), an average value within the area of the effective light source is used.
On the other hand, if the odd function aberration at the position (ρ, θ) on the exit pupil is H_odd (ρ, θ), this odd function aberration is, for example, a plurality of odd function aberrations as described in the method for measuring the odd function aberration. It can be obtained by measuring the relative phase difference Φ of the fundamental wave components of the aerial images of the L & S patterns having different pitches. Odd function aberration can also be obtained by measuring the phase difference Φ from the pattern design position of the fundamental wave component. A method of reducing the influence of the drawing error of the reticle measurement mark when performing this measurement will be described later. Further, Δ is the amount of horizontal shift of the aerial image corresponding to the phase difference Φ. At this time, using the phase difference Φ (lateral shift amount Δ) and the wavelength λ of the illumination light, at a position (ρ = ρ _p , θ = Ψ _p ) where diffracted light from a periodic mark having a predetermined pitch Pmes passes. The odd-function aberration H_odd (ρ _p , Ψ _p ) can be expressed by the following equation. The odd function aberration amount has a relationship of H_odd (ρ _p , Ψ _p ) = − H_odd (ρ _p , Ψ _p + 180 °). The phase difference Φ may be obtained as a phase shift from the design value of the primary component obtained by Fourier transforming the aerial image.

H_odd (ρ _p , Ψ _p ) = (Δ / Pmes) λ = [Φ / (2π)] λ (19)
The wavefront aberration H (ρ _p , Ψ _p ), which is the phase distribution at the position (ρ _p , Ψ _p ) on the exit pupil of the projection optical system PL, is an even function aberration of the equation (18) as follows: This is the sum of the odd function aberration of equation (19) and the offset H_off (ρ _p , Ψ _p ) consisting of higher order aberrations that are not measured on-body. Note that the offset H_off (ρ _p , Ψ _p ) is obtained in advance by calculation, for example, and the information is stored in the memory 51 of FIG.

H (ρ _p , Ψ _p ) = H_even (ρ _p , Ψ _p ) + H_odd (ρ _p , Ψ _p )
+ H_off (ρ _p , Ψ _p ) (20)
Next, the wavefront aberration H (ρ _p , Ψ _p ) on the exit pupil (or pupil plane) of the projection optical system PL of the equation (20) is expressed as an nth order (n is an integer greater than 9) as in the equation (1). ) To the Zernike polynomial fj (ρ _p , Ψ _p ) (j = 1 to n) and the coefficient Z _j thereof. 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. In this case, the wavefront aberration of the actual projection optical system PL includes a higher-order aberration component expressed by a Zernike polynomial of the 16th order or higher, but the 17th-order or higher component does not substantially change with time. The phase distribution due to the aberration expressed by the Zernike polynomial of the 17th order or higher of the optical system PL is obtained in advance by calculation and stored as the inherent offset H_off (ρ _p , Ψ _p ) of the projection exposure apparatus of this example. May be.

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. The even function of equation (18) at the measurement points on the positions (ρ _k , Ψ _k ) (k = _{1 to} m) at m places (m is an integer of approximately n or larger) on the pupil (or pupil plane). The aberration and the odd function aberration of the equation (19) are measured, and the result obtained by adding the measured value and the offset H_off (ρ _k , Ψ _k ) stored in advance as described above is the wavefront aberration H (ρ _k , Ψ _k ). The m wavefront aberrations H (ρ _k , Ψ _k ) correspond to phase information on the pupil plane of the projection optical system. In the following, the measurement points on the position (ρ _k , Ψ _k ) are referred to as measurement points (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 measurement mark PM in FIG. 3 (an error from a design value measured by a coordinate measuring device or the like), a measurement error of the X coordinate and the Y coordinate of the wafer stage WST, and the slit plate 90. This is a phase error obtained in advance based on a focus position measurement error or the like.

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 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. As a result, 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 improve the measurement reproducibility of the aberration amount, it is better that the condition number is smaller. The minimum value of the condition number is 1. The condition number is the square root of the result of dividing the largest singular value of the matrix D by the smallest 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)
In this way, wavefront aberration represented by Zernike polynomials up to an arbitrary nth order can be obtained (measurement step of fluctuation amount of wavefront aberration).

  Thereafter, the main controller 50 passes through an imaging characteristic correction apparatus including the imaging characteristic correction controller 78 of FIG. 2 so as to cancel out the fluctuation amount of the aberration expressed by the Zernike polynomial up to the nth order. The aberration of the projection optical system PL is corrected (image characteristic correction process). 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.
Next, there is actually a solution in the equation (21) or (23), and the wavefront aberration of the projection optical system PL in FIG. 1 can be obtained by dividing it into aberrations represented by Zernike polynomials up to the nth order. The case will be described. In this case, in equation (21), the number m of measurement points (ρ _k , Ψ _k ) (k = 1 to m) for measuring phase information on the exit pupil (or pupil plane) of the projection optical system PL is n It is necessary to do more. In the following, for convenience of explanation, the measurement points (ρ _k , Ψ _k ) are set on standardized coordinates (hereinafter referred to as “normalized pupil coordinates”) on the pupil plane of the projection optical system PL. It shall be. The inventor has measured points (ρ _k , Ψ _k ) at m (m ≧ n) positions (ρ _k , Ψ _k ) arranged along a plurality of predetermined directions around the optical axis AX on the normalized pupil coordinates. Sampling points) were set, and it was confirmed whether or not equation (21) could be solved by computer simulation. That is, m rows × n based on the values fj (ρ _k , Ψ _k ) (j = 1 to n; k = 1 to m) of the j-th order Zernike polynomial at each measurement point (ρ _k , Ψ _k ). a matrix of rows as D, in which case the transposed matrix was D ^T, and see if n rows × n columns (D ^T D) of the inverse matrix (D ^T D) ^-1 exists. When the inverse matrix exists and the equation (21) can be solved, the actual measured value is substituted as the wavefront aberration H (ρ _k , Ψ _k ) (k = 1 to m) of the equation (21), The aberration coefficient a _j represented by Zernike polynomials up to the nth order can be obtained.

  FIG. 6 shows an example of the arrangement of measurement points of phase information on the normalized pupil coordinates (X, Y) of the projection optical system PL (see FIG. 1) of this example. In FIG. The origin of (X, Y) is assumed to be the optical axis AX of the projection optical system PL. Further, the plurality of measurement points in FIG. 6 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.

In the following description, as a general rule, the measurement points on the normalized pupil coordinates using the offset (Xof, Yof) of the entire arrangement in FIG. 6, the offsets rof, rof2 for each direction, and the intervals rr, rr2 for each direction. The arrangement of
7A and 7B show specific measurement point arrangements. In the arrangement shown in FIG. 7A, (Xof, Yof) = (0, 0), rr = 0.166, rof. = 0.1, rr2 = 0.046, and rof2 = 0.7. In this case, there are no measurement points in the directions D3 and D6 in FIG. 6, and the measurement points SP2 in the directions D2 and D5 are set to overlap the measurement points SP1 in the direction D1 (0 °) and the direction D4 (90 °), respectively. .

  Actually, as shown in Table 2, there are 12 types of measurement marks that produce diffracted light by perpendicular incidence at a plurality of measurement points arranged as shown in FIG. 7A (6 types of fine marks and course marks). A plurality of line and space patterns (hereinafter referred to as “L & S patterns”) having six types of pitches. In Table 2, (A) shows six L & S patterns (course marks whose pitch changes greatly) that generate first-order diffracted light at six measurement points in directions of 0 ° and 90 °, and (B) shows 0. 6 L & S patterns (fine marks whose pitches are close to each other as a whole) that generate first-order diffracted light at 6 measurement points in the directions of ° and 90 ° are shown. In Table 2, the numbers 0 to 5 at the top indicate the order of the measurement points from the center in the radial direction, and thus the order of the L & S pattern that generates the first-order diffracted light at the measurement points, and Norm indicates the corresponding measurement point. Indicates the position in the radial direction on the normalized pupil coordinates, NA_equ indicates a value obtained by multiplying the radius Norm by the numerical aperture (0.92 in this case) of the projection optical system PL, and L / S indicates the corresponding L & S pattern. A half value (nm) of the pitch at the stage of the projected image is shown. The exposure wavelength is 193 nm.

When 12 measurement points are provided in two orthogonal directions as shown in FIG. 7A, the 0θ, 1θ, and cos 2θ components of the wavefront aberration expressed by the Zernike polynomial up to Z ₃₇ can be measured. It is. As a result of a computer simulation in which the illumination for the measurement marks of this arrangement is coherent illumination (illumination size is 0.05 on the normalized pupil), the condition number Cond (D) in the expression (24D) is 5.649 and 10 The measurement reproducibility is good as follows.

Further, the measurement points in FIG. 7B correspond to only the measurement points set by six kinds of course marks in two directions among the measurement points in FIG. This as in FIG. 7 (B), even in the case where the six measurement points in two orthogonal directions, 0Shita to Z _16, 1θ, cos2θ component can be measured. As a result of the computer simulation using the coherent illumination as the illumination for the measurement marks of this arrangement, the condition number Cond (D) of the equation (24D) is very small as 2.228. Since the coarse marks are six types of L & S patterns in the vertical and horizontal directions, aberrations can be measured in a short time by scanning them collectively with the slits 9A and 9D in FIG.

Next, in the arrangement of FIG. 8, (Xof, Yof) = (0, 0), rr = 0.166, rof = 0.1, rr2 = 0.036, rof2 = 0.75, the maximum value of σ value rmax = 0.932 is set. In this case, the measurement points SP2 in the 30 ° direction and the 120 ° direction are set by the fine marks in the following Table 3 (B), and the measurement in the other directions of 0 °, 45 °, 90 °, and 135 ° is performed. The point SP1 is set by the course mark in Table 3 (A). In this way, an arrangement is used in which six types of L & S patterns are set in each of the six directions, and a plurality of measurement points are set in two directions within 50% of the radial direction from the outer periphery of the pupil of the projection optical system PL. Thus, all aberrations up to Z ₃₇ can be measured. As a result of computer simulation using the coherent illumination for the measurement marks with this arrangement, the condition number Cond (D) in equation (24D) was 5.727, which is 10 or less.

The breakdown of each term of the Zernike polynomial of 2θ or less is as follows.
Lower frame: Z ₇ , Z ₈ (1θ)
Higher frame: Z ₁₄ , Z ₁₅ , Z ₂₃ , Z ₂₄ , Z ₃₄ , Z ₃₅ (1θ)
Low-order asses: Z ₅ (cos 2θ), Z ₆ (sin 2θ)
Low-order spherical surface: Z ₄ , Z ₉ (0θ)
Higher order spherical surface: Z ₁₆ , Z ₂₅ , Z ₃₆ , Z ₃₇ (0θ)
Distortion: Z ₂ , Z ₃ (1θ)
Next, in order to measure the phase information of all the measurement points SP1 and SP2 on the normalized pupil coordinates of the projection optical system PL of FIG. 6, all of the measurement points are placed on the reticle mark plate RFM of FIG. It is only necessary to form a measurement pattern that generates diffracted light that passes through. If the measurement points in the six directions in FIG. 6 can be set, the measurement points in the two directions in FIGS. 7A and 7B can be easily set. FIG. 9 shows an example of a measurement pattern for generating diffracted light passing through measurement points arranged along the six directions of FIG.

  FIG. 9 shows an example of a measurement pattern formed on the pattern surface of the reticle mark plate RFM (substrate) in FIG. 1. In FIG. 9, the Y direction (scanning direction or first direction) of the reticle mark plate RFM in FIG. A first set of nine aberration measurement marks (first marks) 1A, 1B, 1C, each including a plurality of periodic marks, as will be described later, along the X direction (non-scanning direction or second direction) at the center. 1D, 1E, 1F, 1G, 1H, and 1I are formed with a pitch ΔX. The pitch ΔX is, for example, several mm. On the reticle mark plate RFM, a second set of nine aberration measurement marks (second marks) 2A and 2B are provided so as to be in contact with and in contact with the first set of aberration measurement marks 1A to 1I in the Y direction. , 2C, 2D, 2E, 2F, 2G, 2H, 2I are also formed. The aberration measurement marks 1A to 1I and the aberration measurement marks 2A to 2I are formed, for example, by transferring a common original pattern drawn by an electron beam drawing apparatus at a predetermined magnification. However, the second set of aberration measurement marks 2A to 2I is relatively rotated by 180 ° with respect to the first set of aberration measurement marks 1A to 1I.

  In FIG. 9, the first set of aberration measurement marks 1 </ b> A to 1 </ b> I is marked with the letter “F”, and the second set of aberration measurement marks 2 </ b> A to 2 </ b> I is rotated with the letter “F” by 180 °. Although the letter is attached, the letter “F” is given for convenience in order to represent the relative rotation angles of the two sets of marks, and is not related to the actual pattern. In this example, the relative rotation angle (predetermined angle) of the aberration measurement marks 2A to 2I with respect to the aberration measurement marks 1A to 1I is 180 °, and the calculation for obtaining the aberration as described later becomes easy. However, even if the operation is somewhat complicated, the relative rotation angle can be any angle other than 0 °, such as 45 ° or 90 °.

  As described above, the reticle mark plate RFM of this example has a total of nine aberration measurement marks 1A to 1I, 2A to the same shape as the pair of aberration measurement marks 1A and 2A arranged to face each other in the Y direction. 2I is arranged along the X direction. At this time, the widths of the aberration measurement marks 1A to 1I and 2A to 2I in the X direction are set to be slightly narrower than the width of the illumination area IAR of the illumination light IL in FIG. With this arrangement, the reticle stage RST of FIG. 1 is driven, and the aberration measurement marks 1A to 1I and 2A to 2I of the reticle mark plate RFM of FIG. 9 are moved into the illumination area IAR. The aberration of the projection optical system PL can be measured by the aerial image measurement method at a plurality of positions (image heights) arranged in the non-scanning direction within the exposure area IA of the projection optical system PL corresponding to this.

  Here, an example of a method for manufacturing the reticle mark plate RFM on which the aberration measurement marks 1A to 1I and 2A to 2I are formed will be described. First, for example, an original pattern obtained by enlarging one aberration measurement mark 1A with a predetermined magnification (here, 5 times) is used to form a first glass substrate (a metal film is deposited on the first glass substrate by using an electron beam drawing apparatus on the basis of design data. The master reticle on which the original pattern is formed is manufactured by drawing on the material coated) and developing and etching. Next, using a photo repeater composed of a projection exposure apparatus having a reduction ratio of 1/5, the second glass substrate (a metal film is deposited and a photosensitive material is applied) is arranged in a row (X in FIG. 9). The master reticle pattern is transferred at a pitch ΔX along the direction corresponding to the direction). For example, an alignment mark is formed on the second glass substrate in advance.

  Next, after rotating the second glass substrate by 180 °, using the same photo repeater, the master reticle is positioned at a position corresponding to the aberration measurement marks 2A to 2I in FIG. 9 on the second glass substrate. Transfer the original pattern. If necessary, images of a focus mark and an image position mark described later are also transferred. Thereafter, the reticle mark plate RFM of FIG. 9 as a working reticle can be manufactured by performing development, etching, and the like. At this time, a manufacturing error (in this example, a pitch error of the periodic marks) of each of the first set of aberration measurement marks 1A to 1I includes a drawing error by the electron beam drawing apparatus and a transfer error by the photo repeater. And the sum. In addition, the manufacturing error of each of the second set of aberration measurement marks 2A to 2I is an error obtained by rotating the drawing error by 180 ° (an error of opposite polarity with the signs of the drawing errors in the X direction and Y direction having opposite polarities, respectively). ) And the error at the time of transfer by a photo repeater. In this case, an error (for example, magnification error) at the time of transfer by a photo repeater can be measured and corrected in advance. On the other hand, the drawing error is slightly different for each of the plurality of periodic marks in one aberration measurement mark 1A and for each part in each periodic mark. May remain. Therefore, in this example, the influence of the drawing error on the measurement result of the aberration is reduced by using the fact that the drawing error is opposite in polarity between the aberration measuring marks 1A to 1I and the aberration measuring marks 2A to 2I as described later. To do.

The number of the aberration measurement marks 1A to 1I and 2A to 2I is arbitrary. Alternatively, a pair of marks similar to the aberration measurement marks 1A and 2A may be provided at the center of the rectangular illumination area IAR and the positions of the four vertices of the rectangular area surrounding it.
In FIG. 9, an X-axis mark 62XA for measuring the best focus position, a Y-axis mark 62YA (focus mark), and the position of the projected image are included in the attached mark area 61A in the −X direction of the reticle mark plate RFM. An X-axis mark 63XA for measurement and a Y-axis mark 63YA (image position mark) are formed. The size of the attached mark area 61A is approximately 60 μm square when represented by a projection image by the projection optical system PL, and the arrangement of the marks 62XA, 62YA, 63XA, and 63YA represents the arrangement in the state of the projection image. Further, the projected images of the X-axis marks 62XA and 63XA can be detected by scanning with the slits 122b and 9A in FIG. 5, and the projected images of the Y-axis marks 62YA and 63YA are scanned with the slits 122a and 9D in FIG. Can be detected. By processing these projected images, the best focus position and the position of the attached mark area 61A can be obtained.

  Similarly, an X-axis mark 62XB and a Y-axis mark 62YB for measuring the best focus position, and the position of the projection image are arranged in the + X direction auxiliary mark area 61B of the reticle mark plate RFM in the same arrangement as the auxiliary mark area 61A. An X-axis mark 63XB for measurement and a Y-axis mark 63YB are formed. By processing the projected images of these marks, the best focus position and the position of the attached mark area 61B can be obtained. In addition, the positional relationships of the aberration measurement marks 1A to 1I and 2A to 2I with respect to the attached mark areas 61A and 61B are measured and stored in the memory 51 of FIG. Therefore, the positions of the projection images of the aberration measurement marks 1A to 1I and 2A to 2I can be obtained based on the positions of the two attached mark regions 61A and 61B.

Next, among the aberration measurement marks 1A to 1I and 2A to 21 in FIG. 9, the configuration of the aberration measurement marks 1A and 2A will be described representatively.
FIG. 10 is an enlarged view showing the aberration measurement marks 1A and 2A formed on the reticle mark plate RFM of FIG. 9, and in FIG. 10, the aberration measurement mark 1A has six periodic directions (pitch directions) different from each other. It consists of periodic marks 3A, 3B, 3C, 3D, 3E, 3F. Among these, the first periodic mark 3A is formed with six L & S patterns (line and space patterns) 4A, 4B, 4C, 4D, 4E, having a duty ratio of 1: 1, which are formed at a pitch gradually decreasing in the X direction. 4F, and the third, fourth, and sixth periodic marks 3C, 3D, and 3F are marks obtained by rotating the first periodic mark 3A by a predetermined angle. The periodic direction of the fourth periodic mark 3D is parallel to the Y axis.

Further, the second periodic marks 3B are formed, for example, at six pitches of L & S patterns 5A, 5B, 5C, and 5D having a duty ratio of 1: 1 with a gradually decreasing pitch in a direction rotated by a predetermined angle with respect to the X axis. , 5E, 5F, and the fifth periodic mark 3E is a mark obtained by rotating the periodic mark 3B by a predetermined angle.
FIG. 11 is an enlarged view showing the aberration measurement mark 1A in FIG. 10. In FIG. 11, the measurement direction which is the periodic direction of the L & S pattern in the periodic marks 3A, 3B, 3C, 3D, 3E, 3F is Each of them is inclined counterclockwise by 0 °, angle φ1, angle φ2, 90 °, angle φ3, and angle φ4 with respect to the X axis. The angles φ1, φ2, φ3, and φ4 in this example are 30 °, 45 °, 120 °, and 135 °, respectively, as are the corresponding angles in FIG. 6 (and FIG. 5). The L & S patterns 4A to 4F in the period marks 3A, 3C, 3D, and 3F have a pitch as a course mark for setting the rough measurement point SP1 in FIG. 6, and the L & S patterns 5A to 5L in the period marks 3B and 3E are set. 5F has a pitch as a fine mark for setting the dense measurement points SP2 in FIG. That is, the period marks 3A to 3F are marks for setting six measurement points on one side in each of six directions. An example of the pitch of the projected images of the L & S patterns 4A to 4F as the course marks is shown in Table 3 (A), and an example of the pitch of the projected images of the L & S patterns 5A to 5F as the fine marks is shown in Table 3 (B). It is described in.

  Further, when the measurement points on the pupil plane of the projection optical system PL are set along two directions of the X direction and the Y direction as shown in FIG. 7A, two periodic marks including the fine mark of FIG. The periodic directions of 3B and 3E are set in the X direction and the Y direction, respectively, and the two periodic marks 3C and 3F can be omitted. Further, when the measurement points are set along the two directions of the X direction and the Y direction in this way, an example of the pitch of the projected images of the L & S patterns 4A to 4F as the course marks is shown in Table 2 (A). An example of the pitch of the projected images of the L & S patterns 5A to 5F as marks is shown in Table 2 (B).

  The periodic directions of the six periodic marks 3A to 3F in FIG. 11 are parallel to the directions D1 to D6 in which the measurement points SP1 and SP2 on the normalized pupil coordinates of the projection optical system PL of FIG. 6 are arranged, respectively. . Further, each of the periodic marks 3A to 3F includes six L & S patterns. Therefore, when the measurement pattern of FIG. 11 is illuminated with the illumination light IL of FIG. 3, the ± first-order diffracted lights from the periodic marks 3A to 3F are respectively in six directions D1 to D6 on the normalized pupil coordinates of FIG. Pass through 12 positions (6 on each side) arranged along. Therefore, the position through which those ± 1st order diffracted light passes is the measurement point.

Next, a plurality of measurement points SP are generated from the periodic marks 3A to 3F in FIG. 11 and arranged along the six directions D1 to D6 on the normalized pupil coordinates of the projection optical system PL in FIG. In order to measure the phase information of the diffracted light, when the periodic marks 3A to 3F in FIG. 11 are regarded as aerial images, each spatial image is shown on the slit plate 90 in FIG. The corresponding slits 9A to 9F may be relatively scanned in the periodic direction, and the light intensity distribution information of these aerial images may be obtained by the aerial image measuring device 59 of FIG. Then, the wavefront aberration H (ρ _p , Ψ _p ) of equation (20) is obtained by obtaining the even function aberration of equation (18) and the odd function aberration of equation (19) from the light intensity distribution information. Can do. By substituting the wavefront aberration H (ρ _p , Ψ _p ) (p = k) into the equation (21), the aberration (first optical characteristic) represented by the Zernike polynomial up to the nth order can be obtained. (First step).

  In this case, the measurement directions (relative scanning directions with respect to the aerial image) of the six slits 9A, 9B, 9C, 9D, 9E and 9F in FIG. 5 are 0 °, 30 ° counterclockwise with respect to the X axis, respectively. Since they intersect at 45 °, 90 °, 120 °, and 135 °, diffracted light that passes through the measurement points arranged along the six directions D1 to D6 in FIG. 6 using these slits 9A to 9F. Can be detected.

  Returning to FIG. 10, the aberration measurement mark 2A facing the aberration measurement mark 1A is a mark obtained by rotating the aberration measurement mark 1A by 180 °. Accordingly, the six periodic marks 6A, 6B, 6C, 6D, 6E, and 6F constituting the aberration measurement mark 2A are marks obtained by rotating the six periodic marks 3A to 3F constituting the aberration measurement mark 1A by 180 °. is there. From the periodic marks 3A to 3F in this example, diffracted light passing through the measurement points along the six directions D1 to D6 in FIG. 6 is generated, but also from the periodic marks 6A to 6F obtained by rotating them 180 degrees. Diffracted light passing through measurement points along the six directions D1 to D6 is generated. Therefore, the diffracted light generated from the six periodic marks 6A to 6F of the aberration measurement mark 2A in FIG. 10 and passing through the measurement points in FIG. 6 is also detected through the six slits 9A to 9F in FIG. Based on the detection result, the aberration (second optical characteristic) represented by the Zernike polynomial up to the nth order can be obtained (second step).

Further, the aberration represented by the Zernike polynomial up to the nth order can be measured independently with respect to the respective positions (image heights) of the aberration measurement marks 1A to 1I and 2A to 2I in FIG.
Next, an example of a method for reducing the influence of the drawing error of the aberration measurement marks 1A to 1I and 2A to 2I will be described. As described above, the drawing errors of the second set of aberration measurement marks 2A to 2I are opposite in polarity to the drawing errors of the first set of aberration measurement marks 1A to 1I. Therefore, as an example, the main controller 50 (arithmetic unit) in FIG. 1 averages the aberration measurement results at each measurement point in FIG. 9 (third step). Specifically, the coefficient (aberration) of the Zernike polynomial up to the nth order obtained by the aerial image measurement of the aberration measurement mark 1A is set as Z1 _Ak (k = 1 to n), and the aerial image measurement of the aberration measurement mark 2A facing it is performed. When the Zernike polynomial coefficients (aberrations) up to the n-th order are Z2 _Ak (k = 1 to n), the Zernike polynomial coefficients (aberrations) Z _Ak up to the n-th order at the positions of the aberration measurement marks 1A and 2A are It becomes like this.

_{Z AK = (Z1 AK + Z2} AK) / 2 (k = 1~n)
Similarly, the two aberrations are averaged at the positions of the other pair of aberration measurement marks 1B, 2B, etc., respectively. As a result, lateral aberration, which is an aberration of an odd function component, for example, distortion represented by aberrations Z ₂ and Z ₃ and coma aberration represented by aberrations Z ₇ , Z ₈ , Z ₁₄ , and Z ₁₅ are obtained by averaging. Since the drawing errors of the two opposing aberration measurement marks are offset, the true aberration amount can be measured by eliminating the influence of manufacturing errors.

Further, with respect to longitudinal aberration, which is an aberration of the even function component, for example, spherical aberration represented by aberrations Z ₉ and Z ₁₆ , improvement in measurement accuracy can be expected by averaging.
In addition, a measurement error of longitudinal aberration (even function component aberration) is actually caused by a position error of the measurement mark in the optical axis direction. Therefore, the flatness of the areas where the aberration measurement marks 1A to 1I and 2A to 2I of the reticle mark plate RFM in FIG. 9 are formed in advance is measured with an interferometer, and the positional error of each aberration measurement mark in the optical axis direction is measured. May be stored. Then, at the time of aberration measurement, the longitudinal aberration measurement error is adjusted by adjusting the position of the slit plate 90 in FIG. 1 in the Z direction so as to cancel the position error in the optical axis direction for each aberration measurement mark to be measured. Can be corrected. At this time, for example, the positions in the optical axis direction of the aberration measurement marks 1A, 2A and 1I, 2I close to the attached mark areas 61A and 61B (or the corresponding best focus positions) are used as the reference for the position in the optical axis direction. Can do.

  Note that measurement marks corresponding to one image height (for example, aberration measurement marks 1A and 2A) are localized within 1 mm square on the object surface, and the positional error of the measurement mark in the optical axis direction is Usually, it is about 20 nm or less. Therefore, if the projection magnification of the projection optical system PL is 1/4, the position error of the projected image in the optical axis direction is about 1/16 of 1/16, and the error is 5 mλ or less with respect to the exposure wavelength (λ) of 193 nm. It becomes. This is a normally negligible error. However, in order to remove this error as well, the flatness of reticle mark plate RFM may be measured as described above.

  In the above embodiment, the aberration measurement mark is formed on the reticle mark plate RFM built in the projection exposure apparatus. However, the reference reticle (or test reticle) for exchanging the mark with the reticle R, Alternatively, it may be formed on a part of a reticle for device manufacture (for actual exposure) and loaded on the reticle stage RST when measuring the aberration of the projection optical system PL.

  Further, for example, only one set of aberration measurement marks 1A to 1I is formed on the reticle mark plate RFM in FIG. 9, and the aberration measured using the reticle mark plate RFM and the error measured using the reference reticle are used. A difference from an aberration with a small amount may be stored in the memory 51 of FIG. 1 as initial value data. Thereafter, when the aberration is measured using only the aberration measurement marks 1A to 1I, the influence of the drawing error of the aberration measurement marks 1A to 1I can be reduced by correcting the result with the stored initial value data.

  Next, another embodiment of the present invention will be described with reference to FIG. In FIG. 12, parts corresponding to those in FIG. Although the projection exposure apparatus of FIG. 1 is also used in this example, the aberration measurement mark of the projection optical system PL of this example is formed on an evaluation reticle exchangeable with the reticle R. Therefore, when measuring the aberration of the projection optical system PL, the reticle R on the reticle stage RST is exchanged with the reticle for evaluation.

  12A shows a state in which the evaluation reticle R1 of this example is loaded on the reticle stage RST of FIG. 1 at a rotation angle of 0 °. In FIG. 12A, the central portion of the pattern area of the reticle R1 is shown. Nine aberration measurement marks 1A to 1I are formed in the X direction (non-scanning direction) at a pitch ΔX (ΔX is 3 mm, for example). The symbol “F” in the aberration measurement marks 1 </ b> A to 1 </ b> I is virtually added to indicate the rotation angle of each mark. The positions of the aberration measurement marks 1A to 1I in the X direction are such that the positions of the aberration measurement marks 1A to 1I become the positions of the aberration measurement marks 1I to 1A, respectively, when the reticle R1 is rotated 180 ° on the reticle stage RST. Is set. The entire X-direction width of the aberration measurement marks 1A to 1I is approximately within the illumination area IAR in FIG.

  Further, alignment marks 65A, 65B, 65C and 65D (first set of alignments) associated with the positions of the aberration measurement marks 1A to 1I at the rotation angle of 0 ° are provided at the four corners of the pattern surface of the reticle R1. Mark) is formed. Further, in the vicinity of the alignment marks 65A to 65D on the pattern surface of the reticle R1, alignment marks 64A, 64B, 64C, which are associated with the positions of the aberration measurement marks 1A to 1I when the reticle R1 is rotated 180 °, 64D (second set of alignment marks) is also formed. The alignment marks 65A to 65D for a rotation angle of 0 ° and the alignment marks 64A to 64D for a rotation angle of 180 ° are formed at positions that substantially overlap when the reticle R1 is rotated 180 ° around the center of the reticle R1. .

  When the reticle R1 shown in FIG. 12A is manufactured, the same original pattern is used as a reticle by using a photo repeater as in the case where only the aberration measurement marks 1A to 1I are formed on the reticle mark plate RFM shown in FIG. What is necessary is just to transfer to 9 places on the board | substrate of R1 in order. Since the formed aberration measurement marks 1A to 1I are transferred almost simultaneously through the same optical repeater projection optical system using the same original pattern, the same drawing error causes the influence of the aberration of the same optical repeater projection optical system. Is receiving. Accordingly, since the aberration measurement marks 1A to 1I have substantially the same shape, when the reticle R1 is rotated by 180 ° as shown in FIG. 12B, the aberration measurement marks 1A to 1I in FIG. The shape error has opposite polarity in the X direction and the Y direction with respect to the shape error of the aberration measurement marks 1I to 1A in FIG. In this example, using this, only the reticle R1 is used to measure the aberration of the projection optical system PL in FIG. 1 while eliminating the influence of the drawing error and the aberration of the photo repeater.

  That is, when measuring the aberration of the projection optical system PL in FIG. 1, first, the reticle R1 is set to the state of the rotation angle 0 ° in FIG. 12A, and the aberration is measured using the aberration measurement marks 1A to 1I. Next, the reticle R1 is set to the state of the rotation angle of 180 ° shown in FIG. 12B, and the positions of the aberration measurement marks 1A to 1I are set to the positions of the aberration measurement marks 1I to 1A in FIG. Then, the aberration is measured. Next, by averaging the two measurement results at nine locations, the effects of manufacturing errors (errors due to drawing errors and photo repeater aberrations) of the aberration measurement marks 1A to 1I are canceled out, resulting in high accuracy. In addition, the aberration of the projection optical system PL can be measured.

  The reticle R1 of this example is suitable for a reference reticle for absolute aberration measurement. This is because, in general, a small fiducial mark plate mounted in the exposure apparatus cannot be transported and is not easily rotated by 180 °. Therefore, the absolute aberration amount of the projection optical system PL is obtained with the reference reticle (reticle R1) of this example, the aberration amount is then measured with the reference mark plate built in the apparatus, and the difference is obtained as a manufacturing error of the reference mark plate. If the data file is stored in, for example, a storage device in the projection exposure apparatus, then the absolute value of the aberration can be measured using the reference mark plate. Since an offset caused by such a drawing error occurs only with an odd function aberration as previously described, a manufacturing error data file may be provided only for the odd function component.

12A shows the basic principle, the aberration measurement marks 1A to 1I are arranged in one row and nine columns on the reticle R1, but in reality, aberration measurement marks are formed in a plurality of rows. Random measurement errors can be reduced by averaging the aberration measurement values.
Note that the reticle mark plate RFM of FIG. 1 can be installed in a dedicated aberration measuring apparatus separate from the exposure apparatus. In this case, the test optical system can be not only a projection optical system for a projection exposure apparatus but also an objective lens for an optical microscope, for example.
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 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, it is possible to measure the optical characteristics of the projection optical system with high accuracy by reducing the influence of the manufacturing error of the measurement mark. And based on this measurement result, by correcting the imaging characteristics of the projection optical system as necessary, the imaging characteristics can be maintained in a desired state. Can be transferred onto an object.

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 correction device 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 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 two examples of arrangement | positioning of the measurement point of the phase information in the pupil plane of a projection optical system. It is a figure which shows the other example of arrangement | positioning of the measurement point of phase information in the pupil plane of a projection optical system. It is a top view which shows an example of the pattern for a measurement of the pattern surface of the reticle mark board RFM of FIG. FIG. 10 is an enlarged plan view showing aberration measurement marks 1A and 2A in FIG. It is an enlarged plan view which shows the aberration measurement mark 1A of FIG. FIG. 13A is a plan view showing a reticle used in another embodiment of the present invention, and FIG. 12B is a plan view showing a state where the reticle shown in FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1A-1I ... Aberration measurement mark, 2A-2I ... Aberration measurement mark, 3A-3F, 6A-6F ... Periodic mark, 4A-4F, 5A-5F ... L & S pattern, 9A-9F ... Slit, 12 ... Illumination optical system, DESCRIPTION OF SYMBOLS 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, 123 ... Pinhole, SP1, SP2 ... Measurement Point, PL ... projection optical system, AS ... variable aperture stop, R ... reticle, RST ... reticle stage, RFM ... reticle mark plate, W ... wafer, WST ... wafer stage

Claims (14)

In an optical property measurement method for measuring optical properties of a test optical system,
A first step of obtaining a first optical characteristic of the test optical system based on an image of the first mark by the test optical system;
A second step of obtaining a second optical characteristic of the test optical system based on an image of the second mark obtained by rotating the first mark by a predetermined angle by the test optical system;
And a third step of obtaining an optical characteristic of the test optical system based on the first and second optical characteristics.   The optical characteristic measurement method according to claim 1, wherein the predetermined angle is 180 °.   3. The optical characteristic measuring method according to claim 1, wherein the first mark includes marks with pitches of six or more types arranged along two different directions. 4.   3. The optical characteristic measuring method according to claim 1, wherein the first mark includes marks with pitches of six or more types arranged along six different directions. 4. In an exposure method of exposing a second object with an exposure beam via a first object and a projection optical system,
A measurement step of measuring the optical characteristics of the projection optical system by the optical characteristic measurement method according to any one of claims 1 to 4,
An exposure method comprising: a correction step of correcting an imaging characteristic of the projection optical system based on a measurement result of the measurement step. A substrate used for measuring optical characteristics of a test optical system,
A first mark for forming an aerial image including information on optical characteristics of the test optical system;
A substrate having a second mark formed by rotating the first mark by a predetermined angle.   The substrate includes a first set of alignment marks used when the substrate is disposed at a first rotation angle, and when the substrate is rotated 180 ° with respect to the first rotation angle. The substrate according to claim 6, wherein a second set of alignment marks used for the substrate is formed.   The substrate according to claim 6 or 7, wherein the predetermined angle is 180 °.   9. The substrate according to claim 6, wherein the first mark includes marks having pitches of six kinds or more arranged along two different directions. 10.   9. The substrate according to claim 6, wherein the first mark includes marks of six or more kinds of pitches arranged along six different directions. The first and second marks are arranged to face each other along the first direction,
The pair of marks having the same shape as the pair of marks made of the first and second marks are formed in a plurality along a second direction intersecting the first direction. The substrate according to any one of the above. In an optical property measuring device that measures the optical properties of a test optical system,
A substrate according to any one of claims 6 to 11,
An illumination system for illuminating the substrate;
An aerial image detection system for detecting images of the first and second marks formed on the substrate by the test optical system;
An optical characteristic measuring apparatus comprising: an arithmetic unit that obtains optical characteristics of the optical system to be detected based on a detection result of the aerial image detection system. 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,
A substrate according to any one of claims 6 to 11,
A stage for holding the substrate together with the first object;
An aerial image detection system for detecting an image of the first and second marks formed on the substrate by the projection optical system;
An exposure apparatus comprising: an arithmetic unit that obtains optical characteristics of the projection optical system based on a detection result of the aerial image detection system. 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 the projection optical system while moving the first object and the second object synchronously ,
A substrate according to claim 11;
A stage for holding the substrate together with the first object such that the first direction is parallel to the scanning direction of the first object;
An aerial image detection system for detecting an image of the first and second marks formed on the substrate by the projection optical system;
An exposure apparatus comprising: an arithmetic unit that obtains optical characteristics of the projection optical system based on a detection result of the aerial image detection system.

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