JP2011108974A - Wavefront measuring method and apparatus, and exposure method and apparatus - Google Patents

Abstract

A wavefront aberration of a test optical system is measured with high accuracy based on interference fringes obtained using a diffraction grating.
A measurement light beam that has passed through a measurement reticle 4 and a projection optical system PO is incident on a diffraction grating 10, and the wavefront aberration of the projection optical system PO is determined based on interference fringes 22 (i) generated from the diffraction grating 10. In the wavefront measurement method to be obtained, the light intensity distribution of the interference fringe 22 (i) is measured a plurality of times while the diffraction grating 10 moves one pitch of the diffraction grating 10 with respect to the periodic direction of the diffraction grating 10, and is measured a plurality of times. The wavefront information of the projection optical system PO corresponding to each of the light intensity distributions of the interference fringes 22 (i) is calculated, and the calculated wavefront information of the projection optical system PO is averaged to calculate the wavefront of the projection optical system PO. Obtain aberrations.
[Selection] Figure 2

Description

  The present invention relates to a wavefront measurement technique for measuring wavefront aberration information of a test optical system based on, for example, interference fringes generated by shearing interference, and an exposure technique using the wavefront measurement technique.

  In accordance with the miniaturization of semiconductor devices and the like, in exposure apparatuses, the exposure light has been shortened in order to increase the resolution. Recently, extreme ultraviolet light including soft X-rays having a wavelength of about 100 nm or less as exposure light (Extreme Ultraviolet). An exposure apparatus (EUV exposure apparatus) using a light (hereinafter referred to as EUV light) has also been developed. Since there is no optical material that transmits EUV light at present, the illumination optical system and the projection optical system of the EUV exposure apparatus are configured by reflective optical members except for specific filters and the like.

  Further, the wavefront aberration of a projection optical system using EUV light is required to be, for example, about 0.5 nm RMS or less, and the measurement accuracy of the wavefront aberration of the projection optical system is required to be about 0.1 nm RMS. Thus, as a highly accurate wavefront aberration measuring device, one or a plurality of pinholes or one or a plurality of slit patterns are arranged on the object plane of the projection optical system, and spherical waves generated from the pinholes, etc. There is known a shearing interference type measuring apparatus that receives interference fringes of wavefronts shifted laterally due to a plurality of diffracted lights generated from a diffraction grating through an optical projection system and a diffraction grating by an image sensor (see, for example, Patent Document 1). .

JP 2006-269578 A

When measuring the wavefront of a projection optical system with a conventional shearing interferometry measurement device, the measurement result of the wavefront that should be constant, regardless of the position of the diffraction grating, differs depending on the position of the diffraction grating. There is a risk that the difference between the two becomes larger than the required measurement accuracy.
In addition, in order to obtain a shearing wavefront, it is possible to make the wavefront shifted by an optical element other than the diffraction grating interfere with visible light or ultraviolet light, but it is very difficult with EUV light having a short wavelength. Therefore, it is necessary to use a diffraction grating in a wavefront measuring apparatus using EUV light.

  In view of such circumstances, an object of the present invention is to measure the wavefront aberration of a test optical system with high accuracy based on, for example, interference fringes obtained using a diffraction grating.

  According to the first aspect of the present invention, the measurement light beam that has passed through the measurement mask and the test optical system is incident on the diffraction grating, and the wavefront of the test optical system is based on the interference fringes generated from the diffraction grating. In the wavefront measurement method for determining aberration, the light intensity distribution of the interference fringes is measured a plurality of times while the diffraction grating moves one pitch of the diffraction grating with respect to the periodic direction of the diffraction grating, and is measured a plurality of times. Calculate wavefront information of the test optical system corresponding to each of the light intensity distributions of the interference fringes, average the calculated wavefront information of the test optical system, and calculate the wavefront aberration of the test optical system A wavefront measurement method for obtaining

According to the second aspect of the present invention, in the exposure method in which the pattern is illuminated with the exposure light and the substrate is exposed with the exposure light through the pattern and the projection optical system, the wavefront aberration of the projection optical system is reduced. In order to measure, an exposure method using the wavefront measuring method of the present invention is provided.
Further, according to the third aspect of the present invention, the measurement optical flux passing through the measurement pattern and the test optical system is incident on the diffraction grating, and the test optical system is based on the interference fringes generated from the diffraction grating. In the wavefront measuring apparatus for determining the wavefront aberration of the detector, a detector for detecting the light intensity distribution of the interference fringe, a moving mechanism for moving the diffraction grating in the period direction of the diffraction grating, and the interference detected by the detector A storage device for storing the light intensity distribution of the fringes, and a moving mechanism for moving the diffraction grating in the periodic direction to detect the light intensity distribution of the interference fringes by the detector and the storage device for the detection results. The control device repeats the memory a plurality of times while the diffraction grating moves one pitch of the diffraction grating, and the light intensity distribution corresponding to each of the light intensity distributions of the interference fringes detected and stored a plurality of times. Provided is a wavefront measuring device comprising: an arithmetic device that calculates wavefront information of a test optical system, averages the calculated plurality of wavefront information of the test optical system, and obtains wavefront aberration of the test optical system Is done.

  According to the fourth aspect of the present invention, in the exposure apparatus that illuminates the pattern with the exposure light and exposes the substrate with the exposure light through the pattern and the projection optical system, the wavefront aberration of the projection optical system is reduced. In order to measure, an exposure apparatus provided with the wavefront measuring apparatus of the present invention is provided.

  According to the present invention, the wavefront aberration of the optical system to be detected is detected from the wavefront obtained by detecting the interference fringes a plurality of times while moving the diffraction grating by one pitch in the periodic direction and averaging the wavefronts obtained from the interference fringes, for example. Is required. Therefore, the wavefront aberration of the test optical system can be measured with high accuracy regardless of the position of the diffraction grating due to the averaging effect.

1 is a partially cutaway view showing an exposure apparatus including a wavefront aberration measuring apparatus 30 according to an example of an embodiment. (A) is a diagram showing the projection optical system PO and the measurement main body 8 in FIG. 1 as a transmission optical system, (B) is an enlarged view showing a part of the diffraction grating 10 in FIG. 2 (A), and (C) is a diagram. The figure which shows the state which shifted the diffraction grating 10 by Pg / N to the diagonal direction, (D) is a figure which shows an example of the i-th interference fringe measured. It is a flowchart which shows an example of the measurement operation | movement of the wavefront aberration of projection optical system PO. It is a figure which shows the measurement result of 1st Example, (A) is a figure which shows the Zernike (Zernike) coefficient of the wave front decompress | restored from the measurement result of each time, (B) is every other one of measurement results sequentially. The figure which shows the Zernike coefficient of the wave front obtained by averaging a measurement result, (C) is a figure which shows the Zernike coefficient of the wave front obtained by averaging four continuous measurement results sequentially among measurement results. In a 2nd Example, it is a figure which shows the Zernike coefficient of the wave front obtained by averaging eight consecutive measurement results sequentially.

An exemplary embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a view schematically showing the overall configuration of the exposure apparatus 100 of the present embodiment. The exposure apparatus 100 is an EUV exposure apparatus that uses EUV light (Extreme Ultraviolet Light) within a wavelength range of, for example, about 11 to 15 nm as the illumination light EL (exposure light) for exposure. The wavelength of the illumination light EL is 13.5 nm as an example. In FIG. 1, an exposure apparatus 100 illuminates a laser plasma light source that generates illumination light EL and illumination area on a pattern surface (here, the lower surface) of a reticle R (mask) through the mirror 2 with the illumination light EL. An illumination device ILS including an optical system, a reticle stage RST that holds and moves the reticle R, and an image of a pattern in the illumination area of the reticle R on a wafer W (photosensitive substrate) coated with a resist (photosensitive material). And a projection optical system PO that projects onto the upper surface. The exposure apparatus 100 further includes a wafer stage WST that holds and moves the wafer W on the upper surface of the wafer base WB, a main control system 16 that includes a computer that controls the overall operation of the apparatus, and a projection optical system PO. A wavefront aberration measuring device 30 for measuring wavefront aberration and other drive systems are provided. Measurement main body 8 of wavefront aberration measuring apparatus 30 (described later in detail) is attached to wafer stage WST.

  In the present embodiment, since EUV light is used as the illumination light EL, the illumination optical system ILS and the projection optical system PO are configured by reflective optical members such as a plurality of mirrors except for a specific filter or the like (not shown). The reticle R is also a reflection type. The reflective optical member is obtained by, for example, processing the surface of a member made of quartz (or a metal having high heat resistance) into a predetermined curved surface or plane with high accuracy, and then, for example, molybdenum (Mo) and silicon (Si) on the surface. And a multilayer film (an EUV light reflecting film) is formed as a reflecting surface. The reticle R, for example, forms a multilayer film on the surface of a quartz substrate to form a reflective surface, and then absorbs EUV light such as tantalum (Ta), nickel (Ni), or chromium (Cr) on the reflective surface. A transfer pattern is formed by an absorption layer made of a material to be transferred.

Further, in order to prevent the EUV light from being absorbed by the gas, the exposure apparatus 100 is accommodated in a box-shaped vacuum chamber (not shown) as a whole.
In FIG. 1, the X axis is perpendicular to the plane of FIG. 1 and the Y axis is parallel to the plane of FIG. 1 within the plane (substantially horizontal plane in the present embodiment) on which wafer stage WST moves. The explanation will be given by taking the Z axis. In the present embodiment, the illumination area of the illumination light EL on the pattern surface of the reticle R has an arc shape elongated in the X direction (non-scanning direction), and the reticle R and the wafer W are Y with respect to the projection optical system PO during exposure. Scanning is performed in synchronization with the direction (scanning direction).

First, the illumination optical system in the illumination device ILS includes an optical integrator, a variable aperture stop, a reticle blind, a condenser optical system, and the like. Illumination light EL from the illumination device ILS illuminates a circular arc-shaped illumination area elongated in the X direction on the pattern surface of the reticle R through the mirror 2 with a uniform illuminance distribution obliquely from below.
The reticle R is attracted and held on the bottom surface of the reticle stage RST via the electrostatic chuck RH. Reticle stage RST is driven with a predetermined stroke in the Y direction by a drive system (not shown) based on the measurement value of a laser interferometer (not shown) and control information of main control system 16, and in the X direction and θz direction. Also, it is driven by a minute amount (rotational direction around an axis parallel to the Z axis).

  The illumination light EL reflected by the illumination area of the reticle R forms an image of a part of the pattern of the reticle R in the exposure area (area conjugate to the illumination area) on the upper surface of the wafer W via the projection optical system PO. . The projection optical system PO forms a reduced image of the pattern on the object plane (first surface) on the image plane (second surface), and the projection magnification β of the projection optical system PO is, for example, ¼. The numerical aperture NA is, for example, 0.25.

  As an example, the projection optical system PO is configured by holding six aspherical mirrors M1 to M6, for example, by a lens barrel (not shown), and is non-telecentric on the object plane (pattern surface of the reticle R) side. It is a substantially telecentric reflective optical system on the surface (the surface of the wafer W) side. An aperture stop (not shown) is provided in the vicinity of the pupil plane in the projection optical system PO. The projection optical system PO is also provided with an imaging characteristic correction mechanism (not shown) that corrects the wavefront aberration by adjusting the position and inclination of a predetermined mirror. The configuration of the projection optical system PO is arbitrary.

  On the other hand, wafer W is attracted and held on top of wafer stage WST via an electrostatic chuck (not shown). Wafer stage WST performs predetermined strokes in the X and Y directions by wafer stage control system 17 and a drive mechanism (not shown) based on measurement values of a laser interferometer (not shown) and control information of main control system 16. And is also driven in the θz direction or the like as necessary. An alignment system (not shown) for aligning the reticle R and the wafer W is also provided.

  When exposing the wafer W, the illumination light EL is irradiated onto the illumination area of the reticle R by the illumination device ILS, and the reticle R and the wafer W are set to a predetermined magnification according to the projection magnification β (reduction magnification) with respect to the projection optical system PO. It moves synchronously in the Y direction at the speed ratio (synchronized scanning) In this way, the pattern image of the reticle R is exposed to one shot area (die) of the wafer W. Thereafter, the wafer stage WST is driven to move the wafer W stepwise in the X and Y directions, and then the reticle R pattern is scanned and exposed to the next shot area of the wafer W. In this way, a pattern image of the reticle R is sequentially exposed to a plurality of shot areas of the wafer W by the step-and-scan method.

In such exposure, the wavefront aberration of the projection optical system PO needs to be within a predetermined allowable range. For this purpose, it is first necessary to measure the wavefront aberration of the projection optical system PO with high accuracy.
Hereinafter, the configuration of the wavefront aberration measuring apparatus 30 of the present embodiment and the wavefront aberration measuring method of the projection optical system PO will be described. The wavefront aberration measuring device 30 includes a measurement main body 8 provided in the vicinity of the wafer W of the wafer stage WST, an arithmetic device 12 for processing a detection signal from the measurement main body 8, and a storage device connected to the arithmetic device 12. 12m. In the present embodiment, the wafer stage WST (movement mechanism) used for moving the measurement main body 8 with respect to the projection optical system PO also constitutes a part of the wavefront aberration measuring apparatus 30.

  First, the measurement main body 8 detects a fringe of shearing interference caused by a plurality of diffracted lights from the diffraction grating 10 that is arranged substantially parallel to the XY plane and has a two-dimensional grating pattern formed thereon. A two-dimensional imaging element 14 such as a CCD type or a CMOS type, and a holding member 8 a that holds the diffraction grating 10 and the imaging element 14 are provided. A detection signal from the image sensor 14 is supplied to the arithmetic unit 12.

  In addition, the calculation device 12 includes a first calculation unit 12a that obtains a wavefront (phase distribution) from a light intensity distribution obtained from a detection signal of the image sensor 14 by, for example, a Fourier transform method, and a wavefront measured N times (N is 2 or more). A second arithmetic unit 12b that averages an integer) and a third arithmetic unit 12c that obtains a Zernike coefficient as wavefront aberration information from the averaged wavefront. Note that the first calculation unit 12a to the third calculation unit 12c may each have a function on the software of a computer, or may be separate calculation devices.

At the time of measuring the wavefront aberration of the projection optical system PO, the exposure stage of the projection optical system PO is set above the diffraction grating 10 of the measurement main body 8 by driving the wafer stage WST. The arithmetic unit 12 obtains the wavefront aberration of the projection optical system PO from the detection signal of the image sensor 14 and supplies the obtained wavefront aberration to the main control system 16.
Further, at the time of measuring the wavefront aberration, the reticle R held by the reticle stage RST is exchanged with the measurement reticle 4 via a reticle loader system (not shown), and the pattern surface of the measurement reticle 4 becomes the illumination area of the illumination device ILS. Is set. A pinhole pattern 6 (actually a minute mirror) is formed on the pattern surface of the measurement reticle 4. As an example, the pinhole pattern 6 can be manufactured by forming an absorption layer on the EUV light reflecting film except for a portion serving as a pinhole. The measurement reticle 4 can also be regarded as a part of the wavefront aberration measuring device 30. In the following description, for convenience, the measurement reticle 4 and the projection optical system PO are expressed by a transmission optical system arranged on one optical axis. However, this measurement principle holds true for the reflective optical system as well.

FIG. 2A shows a transmission optical system representing an optical system that is measuring the wavefront aberration of the projection optical system PO in the measurement main body 8 of FIG. The optical system in FIG. 2A is a Talbot interferometer that performs shearing interference. In FIG. 2A, the pinhole pattern 6 of the measurement reticle 4 is installed on the object plane of the projection optical system PO, and the pinhole pattern 6 is illuminated with the illumination light EL. The diameter of the pinhole pattern 6 is about the diffraction limit or less as an example as follows. If the wavelength λ of the illumination light EL and the numerical aperture NAin on the object side of the projection optical system PO are used, the diffraction limit is λ / (2NAin).

Diameter of pinhole pattern 6 ≦ λ / (2NAin) (1)
Here, if the wavelength λ is 13.5 nm and the numerical aperture NAin is 0.0625, the diffraction limit is approximately 108 nm, so the diameter of the pinhole pattern 6 is about 100 nm or less.
Further, in FIG. 2A, an image 6SP of the pinhole pattern 6 by the projection optical system PO is formed on the image plane 18, and the diffraction grating 10 is disposed at a distance Lg from the image plane 18 in the −Z direction. The light receiving surface of the image sensor 14 is disposed at a distance Lc from the image plane 18 below this.

  As shown in FIG. 2B, the diffraction grating 10 is formed with a large number of opening patterns 10a through which the illumination light EL passes with the light shielding film (or absorption layer) as a background at the same pitch Pg in the X direction and the Y direction. ing. The illumination light EL that has passed through the pinhole pattern 6 enters the diffraction grating 10 via the projection optical system PO, and the 0th-order light (0th-order diffracted light) 20, the + 1st-order diffracted light 20A, and the −1st order generated from the diffraction grating 10. An interference fringe (Fourier image) 22 (i) (i-th interference fringe described later) as shown in FIG. 2D is formed on the light receiving surface of the image sensor 14 by the folded light 20B or the like.

The pitch Pg of the diffraction grating 10 is set in accordance with a desired lateral shift amount (shear amount) of the diffracted light, but actually has a manufacturing limit, for example, about several hundred nm to several μm, for example, about 1 μm. Set to
In this case, in order for the interference fringes 22 (i) to be formed on the light receiving surface of the image sensor 14, the distance Lg from the image plane 18 of the diffraction grating 10 and the distance from the image surface 18 of the light receiving surface of the image sensor 14. Lc needs to satisfy the following condition (Talbot condition) using the exposure wavelength λ, the pitch Pg of the diffraction grating 10, and the Talbot order n. Details of the Talbot condition (Talbot condition) are described in “Applied Optics 1 (Tsuruta)” (p.178-181, Baifukan, 1990).

なお、ｎ＝０，０．５，１，１．５，２，…である。即ち、タルボ次数ｎは整数又は半整数である。
本実施形態では、Ｌｃ≫Ｌｇが成立するため、式（３）の代わりに次の近似式を使用することができる。

Note that n = 0, 0.5, 1, 1.5, 2,. That is, the Talbot degree n is an integer or a half integer.
In this embodiment, since Lc >> Lg is satisfied, the following approximate expression can be used instead of Expression (3).

Lg = 2n × Pg ² / λ (4)
Under the condition of the expression (4), the intensity distribution of the interference fringes 22 (i) formed on the light receiving surface of the image sensor 14 is taken into the first calculation unit 12a of the calculation device 12 in FIG. By performing Fourier transform, the phase distribution (distortion of the fringes in the Fourier image) of the differential wavefront (shearing wavefront) between the wavefront WF of the projection optical system PO and the wavefront WFS shifted from the wavefront WF is obtained. Further, the first calculation unit 12a can obtain the wavefront WF (phase distribution) of the projection optical system PO by integrating the shearing wavefront (phase distribution), for example. Based on the wavefront WF, the third computing unit 12c, for example, a coefficient (Zernike coefficient) of, for example, a fifth to 36th order Zernike polynomial Zi of the wavefront WF of the projection optical system PO.
Can be requested.

Note that the diffraction grating 10 may be disposed above the image plane 18. In this case, the distance Lg may be handled as a negative value.
Hereinafter, an example of the operation of measuring the wavefront aberration of the projection optical system PO using the wavefront aberration measuring apparatus 30 in the exposure apparatus 100 of the present embodiment will be described with reference to the flowchart of FIG. This measurement operation is controlled by the main control system 16.

  First, in step 102, the measurement reticle 4 is loaded onto the reticle stage RST of FIG. 1, the reticle stage RST is driven, and the pinhole pattern 6 of the measurement reticle 4 is moved to the illumination area of the illumination device ILS. In the next step 104, wafer stage WST is driven via wafer stage control system 17, and as shown in FIG. 2A, the center of diffraction grating 10 of measurement main body 8 is centered on the image of pinhole pattern 6. Move to position.

  In the next step 106, the main control system 16 sets (initializes) the value of the parameter i for control to 1. In the next step 108, illumination light EL is applied to the pinhole pattern 6 from the illumination device ILS, and the light of the interference fringes 22 (i) of the i-th shearing interference caused by the 0th-order light and the 1st-order diffracted light generated from the diffraction grating 10 The intensity distribution is detected by the image sensor 14, and the detection signal is supplied to the first calculation unit 12 a of the calculation device 12.

  In the next step 110, the first calculation unit 12a stores the light intensity distribution of the interference fringes 22 (i) in the storage device 12m. In the next step 112, the main control system 16 determines whether or not the parameter i has reached N (N is an integer of 2 or more) indicating a predetermined number of measurements. At this stage, since the parameter i is smaller than N and the parameter i is not N, the operation proceeds to step 114 and the main control system 16 adds the value 1 to the parameter i.

  In the next step 116, the main control system 16 drives the wafer stage WST via the wafer stage control system 17, and moves the diffraction grating 10 of the measurement main body 8 to the X-axis and the X-axis as shown in FIG. It moves in the direction D that intersects the Y axis at 45 ° and so that the amount of movement along the X axis is Pg / N (1 / N of the pitch). Thereafter, returning to step 108, the detection of the light intensity distribution of the interference fringes 22 (i) of the i-th shearing interference by the diffracted light generated from the diffraction grating 10 and the storage of the light intensity distribution (step 110) are repeated. Steps 108 and 110 are repeated N times. Therefore, the final movement amount with respect to the direction D of the diffraction grating 10 is (N−1) Pg / N.

  Thereafter, when the parameter i reaches N in step 112, the operation proceeds to step 118. And the 1st calculating part 12a of the calculating device 12 reads the information of the light intensity distribution of the i-th (i = 1-N) interference fringe sequentially from the memory | storage device 12m, and uses the X direction by the Fourier-transform method from the light intensity distribution. The two differential wavefronts in the Y direction are obtained, and the wavefront WFi (phase distribution) of the projection optical system PO is obtained from the two differential wavefronts. That is, in step 112, N wavefronts WFi (phase distribution) of i = 1 to N of the projection optical system PO are obtained.

  In the next step 120, the second computing unit 12b of the computing device 12 obtains a wavefront WFa obtained by averaging the N wavefronts WFi of the projection optical system PO. Thereafter, in step 122, the third computing unit 12c of the computing device 12 obtains a fifth-order to 36th-order Zernike coefficient ak (wavefront aberration) from the averaged wavefront WFa. The Zernike coefficient ak (wavefront aberration) obtained here is supplied to the main control system 16.

In the next step 124, the main control system 16 corrects the wavefront aberration of the projection optical system PO using an imaging characteristic correction mechanism (not shown) as necessary. Thereafter, in step 126, the reticle 4 for actual exposure is loaded onto the reticle stage RST, and in step 128, the pattern image of the reticle 4 is scanned and exposed on a plurality of shot areas of the wafer sequentially placed on the wafer stage RST.

  As described above, in the exposure apparatus 100 of the present embodiment, the interference fringes are detected a plurality of times (N times) while the diffraction grating 10 is moved by one pitch (Pg) in the periodic direction, and the wavefront (phase distribution) is detected from each interference fringe. And the obtained wavefronts are averaged to obtain the wavefront aberration of the optical system to be tested. Thus, even when the wavefront aberration is obtained using the diffraction grating 10, the wavefront aberration can be obtained with the required accuracy by increasing the number of times of measurement N, for example.

[First embodiment]
Next, the first embodiment, which is the result of actually measuring the wavefront aberration of the projection optical system PO using the wavefront aberration measuring apparatus 30, will be described with reference to FIGS. 4 (A) to 4 (C).
In the first embodiment, in the optical system of FIG. 2A (actually a reflective optical system), the diameter of the pinhole pattern 6 of the measurement reticle 4 is set to 100 nm, and the two-dimensional diffraction grating 10 is formed. A tantalum (Ta) thin film (membrane) having a thickness of 300 μm on which a two-dimensional lattice with a pitch Pg of 1.0 μm is formed is disposed 148 μm below the image plane 18 of the projection optical system PO. Then, the interference fringes due to the diffracted light from the diffraction grating 10 were received by the image sensor 14, and the detected light intensity distribution was taken into the arithmetic device 12 to restore the wavefront.

  In the first embodiment, a total of nine interference fringes were measured while driving the wafer stage WST and moving the diffraction grating 10 by a quarter pitch (0.25 μm). Therefore, the first embodiment corresponds to the case where the integer N in step 112 in FIG. Then, the wavefront (phase distribution) is obtained from the light intensity distribution of each interference fringe, and the coefficient (Zernike coefficient) of the 5th to 35th order Zernike polynomials Zi is obtained from each wavefront, as shown in FIG. Has been. 4A, 4B, and 4C, the horizontal axis is the Zernike polynomial Zi, and the vertical axis is the corresponding Zernike coefficient (the unit is the wavelength λ of the illumination light).

In FIG. 4A, the nine bar graphs at the positions of the respective Zernike polynomials Zi are the values of the Zernike coefficients obtained from the nine interference fringes. At this stage, the measurement results vary, and the wavefront measurement results differ depending on the position of the diffraction grating 10, and it can be seen that the measurement reproducibility is not very good.
Next, FIG. 4B shows the diffraction grating 10 using the measurement result of FIG. 4A, like the average of the first and third wavefronts, the average of the second and fourth wavefronts, and so on. Represents the Zernike coefficient of the wavefront obtained by averaging the wavefronts measured by shifting by a half pitch. As can be seen from a comparison with FIG. 4A, the processing result of FIG. 4B has a small variation, but there is a variation in the Zernike coefficients between the averaged sets. Therefore, variations remain in the measurement reproducibility depending on the position of the diffraction grating 10.

  Next, FIG. 4C shows the average of the first, second, third, and fourth wavefronts, the second, third, fourth, and 5 using the measurement result of FIG. The Zernike coefficients of the wave fronts obtained by averaging four wave fronts continuously measured while moving the diffraction grating 10 substantially by one pitch, such as the average of the first wave front,... In the processing result of FIG. 4C, there is almost no variation between the averaged sets. This result shows that the influence that the measurement result differs depending on the position of the diffraction grating 10 can be removed. Therefore, it can be seen that when N = 4, the measurement operation of FIG. 3 can reduce the influence of variations in the measurement result due to the position of the diffraction grating 10.

[Second Embodiment]
Next, a second embodiment, which is the result of actually measuring the wavefront aberration of the projection optical system PO using the wavefront aberration measuring apparatus 30, will be described with reference to FIG.
In the second embodiment, in the optical system of FIG. 2A (actually a reflective optical system), the diameter of the pinhole pattern 6 of the measurement reticle 4 is set to 100 nm, and the two-dimensional diffraction grating 10 is formed. A tantalum (Ta) thin film (membrane) is disposed 199 μm above the image plane 18 of the projection optical system PO and a two-dimensional lattice having a pitch Pg of 1.64 μm is formed. Then, the interference fringes due to the diffracted light from the diffraction grating 10 were received by the image sensor 14, and the detected light intensity distribution was taken into the arithmetic device 12 to restore the wavefront.

  In the first embodiment, a total of 27 interference fringes were measured while driving the wafer stage WST and moving the diffraction grating 10 by 1/8 pitch (0.205 μm). Therefore, this second embodiment corresponds to the case where the integer N in step 112 in FIG. Then, the wavefront (phase distribution) was obtained from the light intensity distribution of each interference fringe, and the coefficient (Zernike coefficient) of the fifth to 35th order Zernike polynomials Zi was obtained from each wavefront. In the case of the second embodiment, the wavefront restored from each interference fringe varies depending on the position of the diffraction grating 10, and the measurement reproducibility is 0.13 nm RMS.

  In the second embodiment, since eight interference fringes are measured while the diffraction grating 10 is moved by one pitch, among the measurement results of the 27 wavefronts, the first to eighth, second to ninth, As shown in FIG. 5, the average wavefront of the wavefront measured continuously eight times is obtained, and the Zernike coefficients obtained from the average wavefront are shown in FIG. Also in FIG. 5, the horizontal axis represents the Zernike polynomial Zi from the fifth order to the 35th order, and the vertical axis represents the Zernike coefficient (unit: λ) corresponding to each order. As is apparent from FIG. 5, there is almost no variation in the Zernike coefficient (wavefront aberration). The measurement reproducibility at this time is greatly improved to 0.002 nm RMS. Therefore, it can be seen that even when N = 8, the measurement operation of FIG. 3 can greatly reduce the influence of variations in the measurement result due to the position of the diffraction grating 10.

The effects and the like of this embodiment are as follows.
(1) In the wavefront measuring method by the wavefront aberration measuring apparatus 30 of the present embodiment, the diffraction grating 10 moves by one pitch of the diffraction grating 10 with respect to the periodic direction (X direction and Y direction) of the diffraction grating 10. The light intensity distribution of the interference fringe 22 (i) obtained by the diffraction grating 10 through the projection optical system PO is measured a plurality of times (steps 108 to 116), and the light intensity of the interference fringe 22 (i) measured a plurality of times. The wavefront of the test optical system PO corresponding to each of the distributions is calculated (step 118), the plurality of calculated wavefronts of the test optical system PO are averaged (step 120), and the wavefront of the test optical system PO is calculated. A Zernike coefficient (wavefront aberration) is obtained (step 122).

  Further, the shearing interference type wavefront aberration measuring apparatus 30 (wavefront measuring apparatus) of the present embodiment uses the illumination light EL that has passed through the measurement reticle 4 (pinhole pattern 6) and the projection optical system PO (test optical system). A measurement device that measures the wavefront aberration of the projection optical system PO based on the interference fringes 22 (i) obtained by dividing the diffraction light through the diffraction grating 10 and interfering with the divided illumination light EL. The image sensor 14 (detector) for detecting the light intensity distribution of), the wafer stage WST (moving mechanism) that moves the diffraction grating 10 in this periodic direction, and the light intensity distribution of the interference fringes detected by the image sensor 14. The storage device 12m for storing and the diffraction grating 10 is moved in the periodic direction by the wafer stage WST, the detection of the light intensity distribution of the interference fringes by the image sensor 14 and the storage device 12m for this detection result. The main control system 16 (control device) that repeats a plurality of times while the diffraction grating 10 moves by one pitch, and the test corresponding to each of the light intensity distributions of the interference fringes that are detected and stored a plurality of times And an arithmetic unit 12 that calculates wavefront information of the optical system PO, averages the calculated plurality of wavefront information of the optical system PO, and obtains the wavefront aberration of the optical system PO.

According to the present embodiment, the interference fringes are detected a plurality of times while the diffraction grating 10 is moved by one pitch in the periodic direction, the wave front (phase distribution) is obtained from each interference fringe, the obtained wave fronts are averaged, The wavefront aberration of the analyzing optical system PO is obtained. Therefore, even when the wavefront aberration is obtained using the diffraction grating 10, the wavefront aberration can be obtained with high accuracy.
(2) Further, the image sensor 14 detects interference fringes of shearing interference of a plurality of light beams obtained by dividing the light beam by the diffraction grating 10, and the arithmetic unit 12 calculates the difference between the light beams that pass through the optical system PO to be detected. Find the wavefront. Therefore, the wavefront aberration of the projection optical system PO can be measured on-body with a simple configuration.

(3) In the present embodiment, the number of times the diffraction grating 10 is moved while the diffraction grating 10 is moved by one pitch (the integer N in Step 112) is preferably at least three. This increases the averaging effect and improves the measurement reproducibility.
(4) Further, the diffraction grating 10 is a two-dimensional grating having the same pitch Pg in the X direction (first direction) and the Y direction orthogonal to each other. The wafer stage WST moves the diffraction grating 10 to 45 in the X direction. Move in the crossing direction at °. Therefore, an averaging effect is obtained in both the X direction and the Y direction.

(5) Further, in the present embodiment, the number of interference fringe measurements is N, and the diffraction grating 10 having a period Pg in the X direction and the Y direction is moved by Pg / N for each measurement. Therefore, measurement can be easily performed.
In addition, you may make it move the diffraction grating 10 only about Pg / N for every measurement.
(6) In the exposure method of this embodiment, the pattern of the reticle R is illuminated with illumination light EL (exposure light), and the wafer W (substrate) is exposed with the illumination light EL via the pattern and the projection optical system PO. In this exposure method, the wavefront measuring method of this embodiment is used to measure the wavefront aberration of the projection optical system PO.

In addition, the exposure apparatus 100 of this embodiment includes a wavefront aberration measuring device 30 for measuring the wavefront aberration of the projection optical system PO.
Accordingly, since the wavefront aberration of the projection optical system PO can be measured with high accuracy, the projection optical system PO is corrected by correcting the wavefront aberration of the projection optical system PO using, for example, an imaging characteristic correction mechanism (not shown) based on the measurement result. The wavefront aberration of the optical system PO can be maintained within an allowable range. Accordingly, the pattern image of the reticle R can be exposed onto the wafer with high accuracy via the projection optical system PO.

Note that it is also possible to manufacture a high-performance projection optical system PO by using the result of measuring the wavefront aberration of the projection optical system PO by the wavefront aberration measuring apparatus 30 of the present embodiment. It is also possible to optimize predetermined parameters when the exposure apparatus 100 exposes the pattern of the reticle R onto the wafer W from the measurement result of the wavefront aberration of the projection optical system PO.
In the above embodiment, the following modifications are possible.

In the measurement main body 8 of FIG. 2A, an order selection window for forming an interference fringe with only a specific order of diffracted light may be disposed between the diffraction grating 10 and the imaging device 14. Even with the interferometer of this configuration, the wavefront aberration of the projection optical system PO can be measured with high accuracy by the measurement operation of FIG.
In the above embodiment, since the two-dimensional periodic pattern is formed on the diffraction grating 10, the two-dimensional wavefront of the projection optical system PO can be obtained by one measurement. However, instead of the diffraction grating 10, for example, an X-axis one-dimensional diffraction grating in which a pattern having periodicity only in the X direction may be used. At this time, the diffraction grating may be moved by 1 / N of the pitch in the X direction for each measurement.

In this case, the measurement using the diffraction grating is followed by the measurement using the Y-axis one-dimensional diffraction grating in which the pattern having periodicity in the Y direction is formed, thereby obtaining the two-dimensional wavefront of the projection optical system PO. Can be requested.
The present invention can be applied to the case where an interference fringe due to shearing interference or the like is detected using an arbitrary interferometer other than the Talbot interferometer and the wavefront aberration of the optical system to be measured is measured.

In the above-described embodiment, the laser plasma light source is used as the EUV light source. However, the present invention is not limited to this, but a SOR (Synchrotron Orbital Radiation) ring, a betatron light source, a discharged light source (discharge excitation plasma light source, rotary discharge) Any of an excitation plasma light source or the like) or an X-ray laser may be used.
In the embodiment of FIG. 1, the case where EUV light is used as exposure light and an all-reflection projection optical system including a plurality of mirrors is used is described as an example. For example, the present invention can be applied to measure the wavefront aberration even when a projection optical system composed of a catadioptric system or a refractive system using ArF excimer laser light (wavelength 193 nm) or the like as exposure light.

Furthermore, the present invention can also be applied to measuring wavefront aberration of an optical system other than the projection optical system of the exposure apparatus, for example, an objective lens of a microscope or an objective lens of a camera.
In addition, this invention is not limited to the above-mentioned embodiment, A various structure can be taken in the range which does not deviate from the summary of this invention.

  ILS: Illumination device, R: Reticle, RST: Rectile stage, PO: Projection optical system, W: Wafer, WST ... Wafer stage, WB ... Wafer base, 4 ... Measurement reticle, 6 ... Pinhole pattern, 8 ... Measurement body , 10 ... Diffraction grating, 12 ... Calculation device, 14 ... Image sensor, 16 ... Main control system, 17 ... Wafer stage control system, 30 ... Wavefront aberration measuring device

Claims (12)

In the wavefront measuring method of making the measurement light beam that has passed through the measurement mask and the test optical system enter the diffraction grating, and obtaining the wavefront aberration of the test optical system based on the interference fringes generated from the diffraction grating,
While the diffraction grating moves one pitch of the diffraction grating with respect to the periodic direction of the diffraction grating, the light intensity distribution of the interference fringes is measured a plurality of times,
Calculating wavefront information of the test optical system corresponding to each of the light intensity distributions of the interference fringes measured a plurality of times;
A wavefront measuring method, comprising: averaging a plurality of calculated wavefront information of the test optical system to obtain a wavefront aberration of the test optical system.   The wavefront measuring method according to claim 1, wherein the interference fringes are interference fringes of a plurality of light beams obtained by dividing the light beam by the diffraction grating.   The wavefront measuring method according to claim 1 or 2, wherein the number of times of measurement of the light intensity distribution is at least three.   The diffraction grating is a two-dimensional grating having the same pitch periodicity in first and second directions orthogonal to each other, and the moving direction of the diffraction grating is a direction crossing the first direction at 45 °. The wavefront measuring method according to any one of claims 1 to 3, wherein:   The pitch of the diffraction grating in the periodic direction is p, and the number of measurements of the light intensity distribution is N (N is an integer of 2 or more), and the amount of movement of the diffraction grating is p / N. The wavefront measuring method according to any one of claims 1 to 4. In an exposure method of illuminating a pattern with exposure light and exposing the substrate with the exposure light through the pattern and a projection optical system,
An exposure method using the wavefront measuring method according to any one of claims 1 to 5, in order to measure the wavefront aberration of the projection optical system. In the wavefront measuring apparatus for making the measurement light beam passing through the measurement pattern and the test optical system enter the diffraction grating, and obtaining the wavefront aberration of the test optical system based on the interference fringes generated from the diffraction grating.
A detector for detecting a light intensity distribution of the interference fringes;
A moving mechanism for moving the diffraction grating in the periodic direction of the diffraction grating;
A storage device for storing a light intensity distribution of the interference fringes detected by the detector;
The diffraction mechanism is moved in the periodic direction by the moving mechanism to detect the light intensity distribution of the interference fringes by the detector and to store the detection result by the storage device. A control device that repeats multiple times during pitch movement;
Calculate wavefront information of the test optical system corresponding to each of the light intensity distributions of the interference fringes detected and stored a plurality of times, and average the calculated wavefront information of the test optical system. , An arithmetic device for obtaining the wavefront aberration of the test optical system,
A wavefront measuring apparatus comprising: The detector detects interference fringes of a plurality of light beams obtained by dividing the light beam with the diffraction grating,
The wavefront measuring apparatus according to claim 7, wherein the arithmetic unit obtains a differential wavefront of a light beam passing through the optical system to be measured.   The wavefront measuring apparatus according to claim 7 or 8, wherein the number of times of measurement of the light intensity distribution is at least three. The diffraction grating is a two-dimensional grating having a periodicity with the same pitch in first and second directions orthogonal to each other;
10. The wavefront measuring apparatus according to claim 7, wherein the moving mechanism moves the diffraction grating in a direction intersecting with the first direction at 45 °. The pitch in the periodic direction of the diffraction grating is p, and the number of times of measurement of the light intensity distribution is N (N is an integer of 2 or more),
11. The wavefront measuring apparatus according to claim 7, wherein the moving mechanism moves the diffraction grating by p / N for each measurement of the light intensity distribution. In an exposure apparatus that illuminates a pattern with exposure light and exposes the substrate through the pattern and the projection optical system with the exposure light,
An exposure apparatus comprising the wavefront measuring apparatus according to any one of claims 7 to 11 for measuring wavefront aberration of the projection optical system.

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