JP2010206033A - Wavefront aberration measuring device, method of calibrating the same, and aligner - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain measurement errors when performing wavefront measurement, for example, by shearing interference systems. <P>SOLUTION: In a method of calibrating a wavefront measuring device 8, illumination light EL passing through a pattern for measurement and a projection optical system PO is divided via a diffraction grating 10, and wavefront aberration of the projection optical system PO is measured, based on interference fringes 22 obtained by allowing divided luminous flux to interfere. In this case, a pattern 7 for calibration is disposed at an object surface side of the projection optical system PO, a grating 11 for calibration, where a pattern corresponding to the pattern for measurement is formed, is disposed at an image plane side of the projection optical system PO, the luminous flux passing through the pattern 7 for calibration and the projection optical system PO is received via the grating 11 for calibration and diffraction grating 10, and the measurement error is obtained based on the light reception result. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a wavefront aberration measuring apparatus that measures wavefront aberration information of a test optical system based on, for example, interference fringes generated by shearing interference, a calibration method thereof, and an exposure apparatus provided with the wavefront aberration measuring apparatus.

  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

  In a conventional shearing interference type measuring apparatus, astigmatism due to a slight tilt of the diffraction grating or the image pickup element may be mixed into the wavefront to be measured and cause a measurement error. In addition, since the EUV exposure apparatus is generally installed in a vacuum chamber, for example, when the measurement apparatus is incorporated in the EUV exposure apparatus, the actual tilt angles of the diffraction grating and the imaging device of the measurement apparatus in the exposure apparatus are measured. It is difficult to do.

  In view of such circumstances, the present invention provides a calibration method and a wavefront aberration measuring apparatus capable of obtaining a measurement error when performing wavefront measurement using, for example, a shearing interference method, and an exposure apparatus including the wavefront aberration measuring apparatus. The purpose is to do.

  The wavefront aberration measuring apparatus calibration method according to the present invention is based on interference fringes obtained by dividing a measurement light beam that has passed through a measurement mask and a test optical system through a diffraction grating and causing the divided light beam to interfere with each other. A calibration method of a wavefront aberration measuring apparatus for measuring wavefront aberration information of the test optical system, wherein a first calibration mask different from the measurement mask is arranged on the object plane side of the test optical system. A second calibration mask on which a pattern corresponding to the pattern of the measurement mask is formed is disposed on the image plane side of the test optical system, and passes through the first calibration mask and the test optical system. The received light flux is received through the second calibration mask and the diffraction grating, and measurement error information of the wavefront aberration measuring device is obtained based on the light reception result.

  The wavefront aberration measuring apparatus according to the present invention is based on interference fringes obtained by dividing a measurement light beam that has passed through a measurement mask and a test optical system via a diffraction grating and causing the divided light beam to interfere with each other. A wavefront aberration measuring apparatus for measuring wavefront aberration information of the test optical system, a light receiver for detecting the interference fringes, and a first calibration different from the measurement mask on the object plane side of the test optical system And a second mask for arranging a second calibration mask having a pattern corresponding to the pattern of the measurement mask formed on the image plane side of the test optical system. The light beam that has passed through the placement unit, the first calibration mask, and the optical system to be detected is received by the light receiver through the second calibration mask and the diffraction grating, and the light reception result of the light receiver is obtained. Control to obtain measurement error information based on And, those with a.

  An exposure apparatus according to the present invention illuminates a pattern with exposure light, and measures wavefront aberration information of the projection optical system in the exposure apparatus that exposes the substrate with the exposure light through the pattern and the projection optical system. In addition, the wavefront aberration measuring apparatus of the present invention is provided.

  According to the present invention, the second calibration mask receives the light beam that has passed through the first calibration mask and the test optical system via the second calibration mask and the diffraction grating, so that the second calibration mask is the test optical system. Acts as an ideal image of a measurement mask when there is no aberration. Therefore, measurement error information that is an aberration amount caused by a member other than the optical system to be measured can be obtained from the light reception result, and for example, a shearing interference type wavefront aberration measuring apparatus can be calibrated using this result. it can.

An example of an embodiment of the present invention will be described with reference to FIGS.
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 an illumination area on a pattern surface (here, the lower surface) of a reticle R (mask) through a mirror 2 with a laser plasma light source that generates illumination light EL and the illumination light EL. A resist (photosensitive material) is applied to an illumination device ILS including an illumination optical system, a reticle stage RST that moves while holding the reticle R via the reticle holder RH, and an image of a pattern in the illumination area of the reticle R. And a projection optical system PO that projects onto a wafer W (photosensitive substrate). Further, exposure apparatus 100 includes wafer stage WST that holds and moves wafer W, main control system 16 that includes a computer that comprehensively controls the operation of the entire apparatus, a stage drive mechanism (not shown), and the like. In addition, a wavefront measuring device 8 for measuring the wavefront aberration of the projection optical system PO is mounted on the 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 reticle R has an arc shape elongated in the X direction (non-scanning direction), and the reticle R and the wafer W are exposed to the projection optical system PO in the Y direction (at the time of exposure). Scanning is performed in synchronization with the 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. 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, and the image side For example, the numerical aperture NA is 0.25. In this case, the numerical aperture NAin on the object side of the projection optical system PO is 0.0625 (= 0.25 / 4).

  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 projection optical system PO. The configuration of the projection optical system PO is arbitrary. The illumination light EL reflected by the illumination area of the reticle R forms a reduced image of a part of the pattern of the reticle R in the exposure area (area conjugate to the illumination area) on the wafer W via the projection optical system PO. .

  When one die (shot area) on the wafer W is exposed, the illumination light EL is irradiated to the illumination area of the reticle R via the mirror 2 by the illumination device ILS, and the reticle R and the wafer W are directed to the projection optical system PO. On the other hand, it moves synchronously in the Y direction at a predetermined speed ratio according to the projection magnification β (reduction magnification) (synchronized scanning). In this way, the pattern image of the reticle R is exposed to one die on 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 pattern of the reticle R is scanned and exposed to the next die on the wafer W. In this way, the pattern R image of the reticle R is sequentially exposed to a plurality of dies on the wafer W by the step-and-scan method.

  Next, the configuration of the wavefront measuring apparatus 8 of the present embodiment and the principle of measuring the wavefront aberration of the projection optical system PO will be described. The wavefront measuring apparatus 8 in the wafer stage WST is arranged substantially parallel to the XY plane and has a diffraction grating 10 on which a two-dimensional grating pattern is formed, and interference of shearing interference by a plurality of diffracted lights from the diffraction grating 10. A CCD-type or CMOS-type two-dimensional imaging device 14 for detecting fringes and a calibration grid 11 used when the wavefront measuring device 8 is calibrated are provided. Further, the wavefront measuring apparatus 8 includes a drive mechanism 12 including a rotation motor that sets the calibration grating 11 at the same height as the image plane of the projection optical system PO above the diffraction grating 10 at the time of calibration. . The detection signal of the image sensor 14 is supplied to a calculation unit in the main control system 16.

  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 wavefront measuring apparatus 8 by driving the wafer stage WST. A calculation unit in the main control system 16 obtains the wavefront aberration of the projection optical system PO from the detection signal of the image sensor 14. Further, during calibration of the wavefront measuring apparatus 8, the main control system 16 measures the wavefront aberration by disposing the calibration grating 11 above the diffraction grating 10 via the drive mechanism 12 (details will be described later).

  At the time of measuring the wavefront aberration, the reticle R on 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 is set as the illumination area of the illumination device ILS. The A pinhole array 6 and a calibration pattern 7 described later are formed on the pattern surface of the measurement reticle 4. As an example, the pinhole array 6 and the calibration pattern 7 can be manufactured by forming an absorption layer on a reflective film for EUV light, except for a portion that becomes a pinhole. The measurement reticle 4 can also be regarded as a part of the wavefront measuring apparatus 8. 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 the optical system in which the wavefront aberration of the projection optical system PO is being measured by the wavefront measuring apparatus 8 of FIG. 1 as a transmission optical system. The optical system in FIG. 2A is a Talbot interferometer that performs shearing interference. In FIG. 2A, the pinhole array 6 of the measurement reticle 4 is installed on the object plane of the projection optical system PO, and the pinhole array 6 is illuminated with the illumination light EL.
As shown in an enlarged view in FIG. 2B, the pinhole array 6 is formed by arranging pinhole groups 6S including a plurality of pinholes 6a in the X direction and the Y direction at a period (pitch) Ps / β. is there. In this case, β is the projection magnification of the projection optical system PO, and the period in the X direction and Y direction of the image (the pinhole group image 6SP) obtained by projecting the pinhole array 6 through the projection optical system PO is Ps. . The diameter of each pinhole 6a 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 6a ≦ λ / (2NAin) (1)
Here, when 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 6a is about 100 nm or smaller.
Moreover, the space | interval of the several pinhole 6a in the pinhole group 6S should just be more than the distance from which the coherence coefficient of illumination light EL becomes 0 as an example. Using the wavelength λ and the numerical aperture NA _IL of the illumination optical system, the shortest distance at which the coherence coefficient becomes 0 is 0.61λ / NA _IL , that is, about 132 nm in this case. By using such a pinhole array 6 in which a large number of pinholes are periodically formed, the amount of interference fringes on the image sensor 14 increases, so shearing interference wavefront measurement can be performed with a high S / N ratio. It can be carried out.

Further, the period Ps / β of the pinhole array 6 is not less than the spatial coherence length of the illumination light EL. When using the spatial coherency is low laser plasma light source as in this embodiment, by using the numerical aperture NA _IL and wavelength of the exit side of the illumination optical system lambda, its spatial coherence length at most, lambda / NA _IL It is. Therefore, the period Ps / β only needs to satisfy the following condition.
Ps / β ≧ λ / NA _IL ≈λ / NAin (2)
In this case, when the wavelength λ is 13.5 nm and the numerical aperture NAin is 0.0625, the spatial coherence length is approximately 216 nm, and therefore the period Ps / β only needs to be greater than about 200 nm. However, as will be described later, the period Ps of the image of the pinhole array 6 needs to satisfy a predetermined condition and has a problem in manufacturing technology. Therefore, the period Ps is, for example, about 1 μm or more. In this case, if the projection magnification β is ¼, the period Ps / β of the pinhole array 6 is about 4 μm or more, and the condition of the expression (2) is sufficiently satisfied.

In FIG. 2A, an image formed by the projection optical system PO of the pinhole array 6 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. Below this, the light receiving surface of the image sensor 14 is disposed at a distance Lc from the image plane 18.
In the diffraction grating 10, as shown in FIG. 2D, a large number of opening patterns 10a through which the illumination light EL passes with a light shielding film (or absorption layer) as a background are formed with a period Pg in the X and Y directions. . The illumination light EL that has passed through the pinhole array 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 of shearing interference as shown in FIG. 2 (E) is formed on the light receiving surface of the image sensor 14 by the folded light 20B or the like.

The period Pg of the diffraction grating 10 is set according to a desired lateral shift amount (shear amount) of the diffracted light. However, since there is actually a manufacturing limit, it is about several hundred nm to several μm, for example, about 1 μm. Set to
In this case, in order for the interference fringes 22 to be formed on the light receiving surface of the image sensor 14, the distance Lg from the image surface 18 of the diffraction grating 10 and the distance Lc from the image surface 18 of the light receiving surface of the image sensor 14 are: Using the exposure wavelength λ, the period Pg of the diffraction grating 10, and the Talbot order n, it is necessary to satisfy the following condition (Talbot condition). 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)
Further, in order to form interference fringes with high contrast on the image sensor 14, the period Ps of the image of the pinhole array 6 is the period Pg, the distance Lg, the distance Lc, and a predetermined integer m (for example, 2 or 4). ) To satisfy the following conditions: About this condition, it is disclosed by Unexamined-Japanese-Patent No. 2006-269578, for example.

この条件は、図２（Ａ）において、撮像素子１４上の干渉縞２２上の或る点２２ａに、ピンホールアレー６の一つのピンホール群の像６ＳＰからの光束Ｅ１が到達する場合に、他のピンホール群の像６ＳＰからの光束Ｅ２も達する条件である。言い換えると、この条件によって、高いコントラストの干渉縞２２が形成される。

This condition is shown in FIG. 2A when a light beam E1 from an image 6SP of one pinhole group of the pinhole array 6 reaches a certain point 22a on the interference fringe 22 on the image sensor 14. This is a condition that the light beam E2 from the image 6SP of the other pinhole group also reaches. In other words, the high-contrast interference fringes 22 are formed under this condition.

Since Lg / Lc is a value considerably smaller than 1, the following approximate expression may be used instead of Expression (5).
Ps = Pg × m (6)
In this equation, when the period Pg is 1 μm and m is 2, the period Ps of the image of the pinhole array 6 is 2 μm. In this case, the projection magnification β is 1/4, and the period of the pinhole array 6 is 8 μm.

  Under the conditions of the equations (4) and (6), the intensity distribution of the interference fringes 22 formed on the light receiving surface of the image sensor 14 is taken into the arithmetic unit of the main control system 16 in FIG. The phase distribution of the shearing wavefront (Fourier image fringe distortion) is obtained by Fourier transform. Further, the calculation unit can obtain the wavefront of the projection optical system PO and, consequently, the wavefront aberration from the phase distribution.

Next, when the wavefront measuring device 8 is calibrated, the calibration pattern 7 of the measurement reticle 4 is arranged in the illumination area of the illumination light EL, and the drive mechanism 12 in FIG. The calibration grid 11 is arranged on the upper image plane 18.
FIG. 3A shows the arrangement of the wavefront measuring device 8 when the wavefront measuring device 8 is calibrated. As shown in FIG. 3B, the calibration pattern 7 shown in FIG. 3A has a pinhole group 7S including a plurality of pinholes 7a in a period Pca / β (β is a projection optical system) in the X direction and the Y direction. (PO projection magnification). The size of the pinhole 7a and the interval between the pinholes 7a in the pinhole group 7S are the same as those of the pinhole 6a in FIG. Further, the period Pca of the image (pinhole group image 7SP) of the calibration pattern 7 by the projection optical system PO is the period Pg of the diffraction grating 10, the distance Lg from the image plane 18 of the diffraction grating 10, and the light reception of the image sensor 14. The distance Lc from the image surface 18 of the surface and the half integer x are used to satisfy the following condition.

ここで、整数ｉ（ｉ＝１，２，３，４，…）を用いて半整数ｘは次のように表すことができる。
ｘ＝ｉ＋０．５ …（８）
また、校正用格子１１には、図３（Ｃ）に示すように、遮光膜（又は吸収層）を背景として照明光ＥＬを通す多数の開口パターン１１ａがＸ方向、Ｙ方向に周期Ｐｃｂで形成されている。校正用格子１１の周期Ｐｃｂは、図３（Ｄ）に示す回折格子１０の周期Ｐｇ、距離Ｌｇ、及び距離Ｌｃを用いて次の条件を満たすように設定される。

Here, a half integer x can be expressed as follows using an integer i (i = 1, 2, 3, 4,...).
x = i + 0.5 (8)
Further, as shown in FIG. 3C, a large number of opening patterns 11a through which the illumination light EL passes with the light shielding film (or absorption layer) as a background are formed in the calibration grid 11 with a period Pcb in the X direction and the Y direction. Has been. The period Pcb of the calibration grating 11 is set so as to satisfy the following condition using the period Pg, the distance Lg, and the distance Lc of the diffraction grating 10 shown in FIG.

式（５）と式（９）との比較より、式（９）の校正用格子１１の周期Ｐｃｂは、投影光学系ＰＯの収差計測時に使用されるピンホールアレー６の像の式（５）の周期Ｐｓのｍ分の１（整数分の１）であることが分かる。これは、校正用格子１１の周期Ｐｃｂをピンホールアレー６の像の周期Ｐｓの可能な最小値と等しくすることを意味している。なお、次式のように、校正用格子１１の周期Ｐｃｂをピンホールアレー６の像の周期Ｐｓと等しく設定することも可能である。

From the comparison between Expression (5) and Expression (9), the period Pcb of the calibration grating 11 in Expression (9) is the expression (5) of the image of the pinhole array 6 used when measuring the aberration of the projection optical system PO. It can be seen that this is 1 / m (an integer) of the period Ps. This means that the period Pcb of the calibration grating 11 is made equal to the minimum possible value of the period Ps of the image of the pinhole array 6. It is also possible to set the period Pcb of the calibration grating 11 equal to the period Ps of the image of the pinhole array 6 as in the following equation.

Pcb = Ps (10)
When Expression (7) is satisfied, in FIG. 3A, a light beam E1 from an image 7SP of one pinhole group of the calibration pattern 7 is at a certain point 22a on the interference fringe 22 on the image sensor 14. When reaching, the light flux E3 from the image 7SP of the other pinhole group is shielded by the diffraction grating 10, and the high-contrast interference fringes 22 are not formed. In other words, the illumination light EL that has passed through the calibration pattern 7 and the projection optical system PO illuminates the calibration grating 11 as illumination light that does not include information on the wavefront aberration of the projection optical system PO. In this case, the calibration grating 11 substantially acts as an ideal image of the pinhole array 6 for measurement, that is, a light beam without wavefront aberration from the projection optical system PO, and therefore processes the detection signal of the image sensor 14. By doing so, it is possible to obtain a measurement error corresponding to the system error of the wavefront measuring device 8 other than the projection optical system PO (such as the deviation of the tilt angle of the calibration grating 11 and / or the image sensor 14).

Next, an example of a method for calibrating the wavefront measuring apparatus 8 by obtaining the measurement error of the wavefront measuring apparatus 8 will be described with reference to the flowchart of FIG. The method is controlled by the main control system 16. This calibration is performed periodically, for example.
First, in step 101 of FIG. 4A, the reticle R of the reticle stage RST is exchanged with the measurement reticle 4 via the reticle loader system (not shown in FIG. 1), and then the reticle stage RST is driven. 3A, the calibration pattern 7 of the measurement reticle 4 is arranged on the object plane of the projection optical system PO, and the diffraction grating 10 of the wavefront measuring device 8 is arranged on the image plane side of the projection optical system PO. . Next, the calibration grating 11 is set on the image plane 18 of the projection optical system PO above the diffraction grating 10 via the drive mechanism 12 (step 102). Thereafter, the illumination light EL is irradiated onto the calibration pattern 7 to measure the intensity distribution of the interference fringes 22 formed on the image sensor 14 of the wavefront measuring device 8 (step 103). Based on the intensity distribution, the calculation unit of the main control system 16 obtains a wavefront by, for example, a Fourier transform method (step 105).

In this case, to explain with a one-dimensional example along the y-axis, the shear wavefront of the wavefront to be detected W ′ (y) measured by the shearing interference via the calibration pattern 7, the projection optical system PO, and the diffraction grating 10. Is {W ′ (y + Δy) −W ′ (y)}. Δy is the shear amount. Further, when the system error of the wavefront measuring device 8 composed of the Talbot interferometer is a measurement error S, the wavefront measurement result W _T1 obtained in step 105 is as follows.

W _T1 = {W ′ (y + Δy) −W ′ (y)} + S (11)
In this case, since the period Pca of the image of the calibration pattern 7 satisfies the condition of the equation (7), the wavefront W ′ (y) to be detected does not include the aberration information of the projection optical system PO as described above. The shear wavefront {W ′ (y + Δy) −W ′ (y)} is almost zero. Accordingly, the measurement result W _T1 is only the measurement error S as follows.

W _T1 = S (12)
Therefore, the calculation unit of the main control system 16 stores the measurement error S, which is the measurement result W _T1 obtained in step 104, in the storage unit in the main control system 16 as calibration data (step 105). Thereafter, the calibration grid 11 is retracted to a position where the illumination light EL is not irradiated by the drive mechanism 12 of FIG.

Thereafter, when the wavefront aberration of the projection optical system PO is measured during exposure, the pinhole array 6 of the measurement reticle 4 is used for measurement in step 110 of FIG. 4B as shown in FIG. The pattern is arranged on the object plane of the projection optical system PO, and the diffraction grating 10 of the wavefront measuring device 8 is arranged on the image plane side of the projection optical system PO. Next, the illumination light EL is irradiated onto the pinhole array 6 to measure the intensity distribution of the interference fringes 22 formed on the image sensor 14 of the wavefront measuring device 8 (step 111). Furthermore, based on the intensity distribution, the calculation unit of the main control system 16 obtains a measurement result W _T2 that is a wavefront by, for example, a Fourier transform method (step 112).

In this case as well, in a one-dimensional example along the y-axis, the wavefront to be measured measured by shearing interference via the pinhole array 6, the projection optical system PO, and the diffraction grating 10 is the projection optical system PO's. It is divided into a true wavefront W (y) and a part corresponding to a system error. Therefore, when the shear wavefront {W (y + Δy) −W (y)} of the true wavefront W (y) is used, the measurement result W _T2 is the sum of the shear wavefront and the measurement error S as follows.

_{W T2 = {W (y +} Δy) -W (y)} + S ... (13)
Therefore, the arithmetic unit of the main control system 16 subtracts the measurement error (calibration data) S stored in step 105 from the measurement result W _T2 to obtain a shear wavefront of the true wavefront of the projection optical system PO as follows. W ₀ can be determined (step 113).
W ₀ = W _T2 −S = W (y + Δy) −W (y) (14)
By using this shear wavefront W ₀ , the calculation unit of the main control system 16 can obtain the wavefront aberration of the projection optical system PL.

Effects and the like of this embodiment are as follows.
(1) The shearing interference type wavefront measuring apparatus 8 of the present embodiment diffracts the illumination light EL that has passed through the pinhole array 6 (measurement mask) and the projection optical system PO (test optical system) of the measurement reticle 4. A measuring device that measures the wavefront aberration of the projection optical system PO based on an interference fringe 22 obtained by dividing the grating 10 and causing the divided illumination light EL to interfere with each other. Image sensor 14, reticle stage RST (first mask placement unit) for placing calibration pattern 7 (first calibration mask) different from pinhole array 6 on the object plane side of projection optical system PO, and projection optical system A drive mechanism 12 (second mask placement section) for placing a calibration grid 11 (second calibration mask) in which a pattern corresponding to the pinhole array 6 of the measurement reticle 4 is formed on the image plane side of PO; Proofreading A main control system 16 (calculation unit) that receives the light beam that has passed through the pattern 7 and the projection optical system PO by the imaging element 14 via the calibration grating 11 and the diffraction grating 10 and obtains a measurement error based on the light reception result; It has.

  Further, in the calibration method of the wavefront measuring apparatus 8, the calibration pattern 7 is arranged on the object plane side of the projection optical system PO (step 101), and the calibration grid 11 is arranged on the image plane side of the projection optical system PO ( Step 102), the light beam that has passed through the calibration pattern 7 and the projection optical system PO is received through the calibration grating 11 and the diffraction grating 10, and the measurement error of the wavefront measuring device 8 is obtained based on the light reception result. (Steps 103-105).

  According to the present embodiment, the light beam obtained by irradiating the diffraction grating 10 with the light beam that has passed through the calibration pattern 7 and the projection optical system PO substantially does not include information on the wavefront aberration of the projection optical system PO. The calibration grating 11 generates an ideal image intensity distribution of the pinhole array 6 when there is substantially no aberration of the projection optical system PO. Therefore, by illuminating the diffraction grating 10 via the calibration grating 11, a measurement error that is a wavefront aberration caused by a portion other than the projection optical system PO can be easily obtained. Therefore, for example, the wavefront measuring device 8 can be easily calibrated by periodically obtaining a measurement error.

  (2) Further, the period Ps / β of the pinhole array 6 is β times the expression (5), and the period Pca / β of the calibration pattern 7 is β times the expression (7). Therefore, the calibration pattern 7 can be easily manufactured in the same manner as the pinhole array 6, and by combining the calibration pattern 7 and the diffraction grating 10, a light beam that does not include information on the wavefront aberration of the projection optical system PO can be obtained with high accuracy. Can be generated.

Note that the period Pca of the image of the calibration pattern 7 does not need to satisfy the equation (7) exactly, and may only approximately satisfy the equation (7).
(3) The pinhole array 6 has a periodic pattern. The calibration grating 11 is disposed on the image plane 18 of the projection optical system PO, and the period Pcb of the calibration grating 11 is an image of the pinhole array 6. The period is the same as or a whole number. Therefore, the calibration grating 11 can be regarded as an ideal image of the pinhole array 6 when the projection optical system PO has no aberration, and only the measurement error can be easily obtained by using the calibration grating 11. It can be measured.

  (4) In addition, the exposure apparatus 100 of the present embodiment illuminates the pattern of the reticle R with the illumination light EL and exposes the wafer W with the illumination light EL through the pattern and the projection optical system PO. In order to measure the wavefront aberration of the optical system PO, the wavefront measuring device 8 is provided. Therefore, the wavefront aberration of the projection optical system PO can be efficiently measured on-body, and the wavefront aberration can always be measured with high accuracy by, for example, performing regular calibration.

Further, by using the result of measuring the wavefront aberration of the projection optical system PO with the wavefront measuring apparatus 8 of the present embodiment, it is possible to manufacture a high-performance projection optical system PO. 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.

(1) First, as a measurement mask on the object plane side of the projection optical system PO, instead of the pinhole array 6 in which a plurality of pinholes in FIG. 2B are periodically arranged in the X and Y directions, FIG. As shown in FIG. 2C, a pinhole array 6H in which single pinholes 6a are arranged in the X direction and the Y direction at a period Ps / β can be used as a measurement mask.
Furthermore, instead of the pinhole array 6, it is possible to use only one pinhole 6a. In this case, although the intensity of the interference fringes is reduced, the condition of the expression (2) is not necessary.

  (2) Further, as a calibration pattern disposed on the object plane side of the projection optical system PO in order to calibrate the wavefront measuring apparatus, instead of the periodic calibration pattern 7 shown in FIG. As shown in FIG. 5B, a calibration pattern 7D in which a large number of pinholes 7DAa are randomly formed may be used. In FIG. 5B, the minimum value of the size and interval of the pinhole 7Da is the minimum size of the pinhole 7a in the pinhole group 7S constituting the calibration pattern 7 of FIG. Same as value.

  FIG. 5A shows a wavefront measuring apparatus 8A that uses the measurement reticle 4A on which the pinhole array 6 and the calibration pattern 7D shown in FIG. 5B are formed. 5A, the configuration other than the calibration pattern 7D is the same as that of the wavefront measuring apparatus 8 in FIG. When the measurement error of the wavefront measuring apparatus 8A is measured and calibrated, the calibration pattern 7D is arranged on the object plane side of the projection optical system PO as shown in FIG. The calibration grid 11 is arranged on the image plane 18. In this case, since the image of the calibration pattern 7D by the projection optical system PO is a large number of pinhole images 7DaP randomly arranged on the image plane 18, the calibration grating 11 substantially has the projection optical system PO. The illumination light EL is not affected by the wavefront aberration. Therefore, by using the detection signal of the image sensor 14, a measurement error that is a wavefront caused by an optical member other than the projection optical system PO can be obtained, and as a result, the wavefront measuring device 8A can be accurately calibrated.

As a calibration pattern on the object plane side of the projection optical system PO (test optical system), not only a random calibration pattern 7D but also an arbitrary aperiodic pattern having no periodicity in the X direction and the Y direction. Can be used.
Further, as the calibration pattern, a diffusion plate or the like that diffuses the illumination light EL at random can be used.

  (3) In the wavefront measuring apparatus 8 of the above-described embodiment, the diffraction grating 10 is disposed between the image plane 18 of the projection optical system PO and the image sensor 14 (below the image plane 18). However, as shown by the wavefront measuring device 8B in FIG. 6, even if the diffraction grating 10 is arranged between the image plane 18 of the projection optical system PO and the projection optical system PO (above the image plane 18), the shearing is similarly performed. Wavefront measurement by interference can be performed. However, in this case, the distance Lg between the image plane 18 and the diffraction grating 10 in the equations (3) and (5) needs to be regarded as a negative value. In this case, in order to calibrate the wavefront measuring apparatus 8B, for example, the calibration pattern 7 shown in FIG. 3A is arranged instead of the pinhole array 6 shown in FIG. The calibration grid 11 shown in FIG.

  (4) In the above embodiment, the diffraction grating 10 is stationary during the wavefront measurement, and the wavefront is obtained by the Fourier transform method from the intensity distribution of one interference fringe. For example, the diffraction grating 10 in FIG. The image sensor 14 may capture the intensity distribution of a plurality of interference fringes while moving the image by a predetermined amount (for example, 1/4 of the period Pg) in the Y direction. In this case, the wavefront can be obtained by the phase shift method. The same applies to the calibration of the wavefront measuring device 8 or the like.

  (5) 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. 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.

It is the figure which notched a part which shows the exposure apparatus provided with the wavefront measuring device of an example of embodiment. 1A is a view showing the projection optical system PO and the wavefront measuring device 8 in FIG. 1 as a transmission optical system, FIG. 2B is an enlarged view showing a part of the pinhole array 6 in FIG. 2A, and FIG. Is an enlarged view showing another example of a pinhole array, (D) is an enlarged view showing a part of the diffraction grating 10 of FIG. 2 (A), and FIG. 2 (E) is a view showing an example of interference fringes to be measured. It is. (A) is a diagram showing the arrangement of the optical system when the wavefront measuring apparatus is calibrated, (B) is an enlarged view showing a part of the calibration pattern 7 of FIG. 3 (A), and (C) is FIG. (A) is an enlarged view showing a part of the calibration grating 11, (D) is an enlarged view showing a part of the diffraction grating 10 of FIG. 3 (A). (A) is a flowchart showing an example of a calibration method for the wavefront measuring apparatus, and (B) is a flowchart showing an example of a wavefront aberration measuring method. (A) is a figure which shows the wavefront measuring device and projection optical system of the modification of embodiment as a transmission optical system, (B) is an enlarged view which shows a part of calibration pattern 7D of FIG. 5 (A). It is a figure which shows the wavefront measuring device and projection optical system of another modification of embodiment.

  ILS ... illumination device, R ... reticle, PO ... projection optical system, W ... wafer, 4 ... reticle for measurement, 6 ... pinhole array, 7 ... pattern for calibration, 8,8A, 8B ... wavefront measurement device, 10 ... diffraction Grating 11 Calibration grid 12 Driving mechanism 14 Image sensor 16 Main control system 18 Image plane

Claims (10)

Measurement light wave aberration information of the test optical system is measured based on interference fringes obtained by dividing the measurement light beam that has passed through the measurement mask and the test optical system via a diffraction grating and causing the divided light beam to interfere with each other. A wavefront aberration measuring device calibration method,
Disposing a first calibration mask different from the measurement mask on the object plane side of the test optical system,
A second calibration mask having a pattern corresponding to the pattern of the measurement mask formed on the image plane side of the test optical system;
The light flux that has passed through the first calibration mask and the optical system to be tested is received through the second calibration mask and the diffraction grating, and measurement error information of the wavefront aberration measuring device based on the light reception result A method for calibrating a wavefront aberration measuring apparatus, characterized by: The measurement mask has a periodic pattern arranged with a period of PM × m, when the length is represented by PM and the integer is represented by m,
The first calibration mask has a periodic pattern having a period PM × x in the same direction as the arrangement direction of the periodic pattern of the measurement mask when a half integer is represented by x. The wavefront aberration measuring device calibration method according to claim 1, wherein the wavefront aberration measuring device is calibrated.   The wavefront aberration measuring apparatus calibration method according to claim 1, wherein the first calibration mask has an aperiodic pattern. The measurement mask has a periodic pattern;
The second calibration mask is arranged on the image plane of the test optical system, and the pattern of the measurement mask pattern is the same as the period of the image by the test optical system or a pattern with a period of a fraction of an integer. The wavefront aberration measuring device calibration method according to claim 1, wherein the wavefront aberration measuring device is calibrated. Measurement light wave aberration information of the test optical system is measured based on interference fringes obtained by dividing the measurement light beam that has passed through the measurement mask and the test optical system via a diffraction grating and causing the divided light beam to interfere with each other. A wavefront aberration measuring device,
A light receiver for detecting the interference fringes;
A first mask placement section for placing a first calibration mask different from the measurement mask on the object plane side of the test optical system;
A second mask placement section for placing a second calibration mask having a pattern corresponding to the pattern of the measurement mask formed on the image plane side of the test optical system;
The light beam that has passed through the first calibration mask and the optical system to be tested is received by the light receiver through the second calibration mask and the diffraction grating, and a measurement error based on the light reception result of the light receiver. A control unit for seeking information;
A wavefront aberration measuring apparatus comprising: The measurement mask has a periodic pattern having a period of PM × m when the length is represented by PM and the integer is represented by m.
The first calibration mask has a periodic pattern having a period PM × x in the same direction as the arrangement direction of the periodic pattern of the measurement mask, when a half integer is represented by x. The wavefront aberration measuring apparatus according to claim 5.   6. The wavefront aberration measuring apparatus according to claim 5, wherein the first calibration mask has an aperiodic pattern. The measurement mask has a periodic pattern;
The second calibration mask has a pattern having the same period as the image of the measurement mask pattern by the optical system to be detected or a period of an integer.
The wavefront according to any one of claims 5 to 7, wherein the second mask arrangement unit arranges the second calibration mask on an image plane of the optical system to be measured. Aberration measuring device. 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 aberration measuring device according to any one of claims 5 to 8, in order to measure wavefront aberration information of the projection optical system. The exposure light is EUV light;
The exposure apparatus according to claim 9, wherein the wavefront aberration measuring apparatus uses the exposure light as the measurement light beam.

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