JP4691922B2 - Adjustment method of imaging optical system - Google Patents

Description

  The present invention relates to a method for adjusting an imaging optical system that forms an image of an object, and in particular, increases the position of a mark formed on a substrate (such as a semiconductor wafer or a liquid crystal substrate) in a manufacturing process of a semiconductor element or a liquid crystal display element. The present invention relates to a method for adjusting an imaging optical system suitable for an apparatus for detecting with accuracy.

  In manufacturing processes such as semiconductor elements and liquid crystal display elements, a circuit pattern is transferred to a resist layer through a well-known lithography process, and a circuit pattern is formed on a predetermined material film by performing processing such as etching through the resist pattern. Is transferred (pattern forming step). By repeating this pattern forming process many times, circuit patterns of various material films are stacked on a substrate (semiconductor wafer or liquid crystal substrate), and a circuit of a semiconductor element or a liquid crystal display element is formed. .

  Furthermore, in the manufacturing process described above, in order to accurately overlay circuit patterns of various material films (in order to improve product yield), the substrate is aligned before the lithography process in each pattern forming process. The registration inspection of the resist pattern on the substrate is performed after the lithography process and before the processing process. For alignment of the substrate, an alignment mark formed on the underlying layer in the previous pattern formation step is used. For overlay inspection of the resist pattern, the overlay mark formed on the resist layer in the current pattern forming process and the overlay mark formed on the underlying layer in the previous pattern forming process are used.

  Also, a device for detecting the position of the alignment mark or overlay mark (generally simply referred to as “mark”) is incorporated in a device for aligning the substrate or a device for performing overlay inspection of a resist pattern on the substrate. ing. In the position detection device, illumination light is irradiated to a mark to be detected, an image based on light from the mark (for example, reflected light) is captured by an image sensor such as a CCD camera, and predetermined image processing is performed on the image. As a result, the position of the mark is detected. The wavelength band of the illumination light is often in a wide range from the visible light band to the near infrared light band in order to obtain a stable reflection intensity with respect to various mark structures.

Further, in the position detection device, in order to improve the detection accuracy, an aperture stop or an objective lens of an imaging optical system (an optical system for forming an image of a mark) is used by using a method disclosed in Patent Document 1, for example. Is finely adjusted in the shift direction to reduce an error component (TIS value: Tool Induced Shift) caused by the apparatus.
JP 2000-77295 A

However, in the above-described adjustment method of the imaging optical system, due to a manufacturing error (decentration error of the optical component) at the time of arranging each optical component of the imaging optical system, the aperture stop surface of the imaging optical system When the imaging position of the pupil image differs depending on the wavelength band, the error component (TIS value) caused by the apparatus cannot be reduced satisfactorily.
Therefore, the present inventor newly arranges an optical element for adjustment between the pupil plane and the aperture stop surface of the imaging optical system, and uses the method disclosed in Patent Document 1 above. It has been proposed to make fine adjustments using the correction and to correct the image formation position shift corresponding to the wavelength band of the pupil image on the aperture stop surface (Japanese Patent Application No. 2003-54058). However, in the method disclosed in Patent Document 1, the sensitivity when finely adjusting the arrangement of the optical elements is low, and it is difficult to reduce the adjustment error. For this reason, the error component (TIS value) caused by the apparatus cannot be sufficiently reduced, and there is a limit to the improvement of detection accuracy.

  An object of the present invention is to provide a method for adjusting an imaging optical system capable of finely adjusting the arrangement of optical elements for adjustment with high sensitivity.

According to the first aspect of the present invention, on the object plane of the imaging optical system, the first or higher order diffracted light beam by the incident illumination light of a predetermined wavelength band is not less than a pitch that is inscribed in the pupil region of the imaging optical system. first and marks arranged in one pitch, the second mark + 1st-order diffracted light flux by the illumination light are arranged at a pitch smaller than the second pitch as circumscribing the pupil area of the image forming optical system Are arranged symmetrically with respect to the center of the visual field of the imaging optical system, and when the wavelength of the illumination light is set on the long wavelength side, the first optical system is formed by the imaging optical system. A relative position between the image of the mark and the image of the second mark, and the image of the first mark formed by the imaging optical system when the wavelength of the illumination light is set to the short wavelength side; based on the difference between the relative position between the image of the second mark, the pupil plane and the open of the imaging optical system And adjusts the arrangement of the disposed optical element between the stop surface.

According to a second aspect of the present invention, in the method for adjusting an imaging optical system according to the first aspect, the first pitch is P1 (μm), the second pitch is P2 (μm), and the imaging optical system When the numerical aperture of the system is NAima, the numerical aperture of the optical system used for irradiation of the illumination light is NAill, and the center wavelength of the illumination light is λ (μm), the following conditional expression is satisfied.
NAima> NAill
NAima-NAill> λ / P1
NAima + NAill / 2 ≤ λ / P2
According to a third aspect of the present invention, in the image forming optical system adjustment method according to the first or second aspect, information on a relative position between the image of the first mark and the image of the second mark is obtained. when obtaining the first mark and the second mark in each of the states of before and after the 180 ° rotation with respect to the field center, the first mark in the image formed by the imaging optical system and after measuring the distance between the second mark, the error component of device due represented by the measured two distances were, and acquires as the information of the relative position.

According to a fourth aspect of the present invention, in the image forming optical system adjusting method according to any one of the first to third aspects, the optical element is a plane-parallel plate, and the arrangement of the optical elements is adjusted. it is adjusted in the direction of tilting the parallel flat plate.

  According to the adjustment method of the imaging optical system of the present invention, the arrangement of the adjustment optical elements can be finely adjusted with high sensitivity.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
Here, the adjustment method of the imaging optical system of the present embodiment will be described using the overlay measurement apparatus 10 shown in FIG. 1 as an example. The overlay measurement apparatus 10 is an apparatus that performs overlay inspection of a resist pattern (not shown) of the substrate 11 in a manufacturing process of a semiconductor element, a liquid crystal display element, or the like. In the overlay inspection, the amount of displacement of the resist pattern with respect to a circuit pattern (hereinafter referred to as “underground pattern”) formed on the underlayer of the substrate 11 is measured.

As shown in FIG. 1A, the overlay measuring apparatus 10 includes a stage 12 that supports a substrate 11 or an adjustment substrate 30 (FIG. 2) described later, an illumination optical system (13 to 19), and imaging optics. A system (19-24), a CCD image pickup device 25, an image processing unit 26, a focus detection unit (41-48), and a stage control unit 27 are provided.
Although not shown, the stage 12 includes a holder that supports the substrate 11 or an adjustment substrate 30 (FIG. 2), which will be described later, in a horizontal state, an XY drive unit that drives the holder in the horizontal direction (XY direction), It is comprised with the Z drive part which drives a holder to a perpendicular direction (Z direction). The XY drive unit and the Z drive unit are connected to the stage control unit 27.

  Here, the substrate 11 is a general product substrate such as a semiconductor wafer or a liquid crystal substrate, and is in a state after exposure / development of the resist layer and before processing of a predetermined material film. Many measurement points are prepared on the product substrate for overlay inspection. The positions of the measurement points are the four corners of each shot area. At each measurement point, a resist mark indicating the reference position of the resist pattern and a base mark indicating the reference position of the base pattern are formed. In the following description, the registration mark and the base mark are collectively referred to as “overlapping mark 11A”.

  The adjustment substrate 30 (FIG. 2) is designed for obtaining an index for adjusting the imaging optical system (19 to 24). The adjustment substrate 30 is provided with an adjustment mark 30 </ b> A including an outer mark 31 and an inner mark 32. The adjustment mark 30A is a double mark of the BAR in BAR type, and is created by etching a silicon wafer or the like. The step h of the adjustment mark 30A is, for example, 83 nm. 2A is a plan view, and FIG. 2B is a cross-sectional view.

  The outer mark 31 is composed of four bar marks 1A elongated in the X direction and four bar marks 1B elongated in the Y direction, and each of the two marks forms a quadrilateral around the inner mark 32. Has been placed. The four bar marks 1A are arranged at a pitch P1 for each group. Similarly, the four bar marks 1B are also arranged at a pitch P1 for each group. The pitch P1 is, for example, 3.8 μm, and corresponds to the “first pitch” in the claims.

  The inner mark 32 is composed of four bar marks 2A elongated in the X direction and four bar marks 2B elongated in the Y direction. Each of the inner marks 32 forms a quadrilateral shape inside the outer mark 31. Has been placed. Further, the four bar marks 2A are arranged with a pitch P2 different from the pitch P1 for each group. Similarly, four bar marks 2B are arranged at a pitch P2 for each group. The pitch P2 is 1 μm, for example, and corresponds to the “second pitch” in the claims.

  In a state where the substrate 11 (or the adjustment substrate 30) is supported by the holder of the stage 12, the stage control unit 27 controls the XY drive unit of the stage 12 and moves the holder in the XY direction to The upper overlay mark 11A (or the adjustment mark 30A on the adjustment substrate 30) is positioned in the visual field region. Further, based on a focus signal (described later) output from the focus detection unit (41 to 48), the Z drive unit of the stage 12 is controlled to move the holder up and down in the Z direction. By this focus adjustment, the substrate 11 (or the adjustment substrate 30) can be focused on the imaging surface of the CCD image sensor 25. At this time, the overlay mark 11A on the substrate 11 (or the adjustment mark 30A on the adjustment substrate 30) is arranged on the object plane of the imaging optical system (19 to 24).

  The illumination optical system (13 to 19) includes a light source unit 13, an illumination aperture stop 14, a condenser lens 15, a field stop 16, an illumination relay lens 17, a beam splitter 18, an optical axis, which are arranged in order along the optical axis O1. And a first objective lens 19 disposed on O2. The beam splitter 18 has a reflection / transmission surface inclined by about 45 ° with respect to the optical axis O1, and is also disposed on the optical axis O2. The optical axis O1 of the illumination optical system (13-19) is perpendicular to the optical axis O2 of the imaging optical system (19-24).

  The light source unit 13 includes a light source 3A, a collector lens 3B, an optical relay lens 3C, a wavelength switching mechanism 3D, and a light guide fiber 3E. The light source 3A emits light having a wide wavelength band (for example, white light). The wavelength switching mechanism 3D is provided with a plurality of optical filters having different transmission characteristics. By switching the optical filter and inserting it into the illumination optical path, the wavelength band of the light emitted from the light source 3A is any one of a wide band (for example, a wavelength width of about 270 nm in this embodiment), a long wavelength band, and a short wavelength band. Can be selected.

In the light source unit 13, the light having a wide wavelength emitted from the light source 3A is incident on the optical filter of the wavelength switching mechanism 3D via the collector lens 3B, and the wavelength band corresponding to the transmission characteristic (that is, the broadband or long wavelength). Band or short wavelength band). Thereafter, the light is guided to the illumination aperture stop 14 via the optical relay lens 3C and the light guide fiber 3E.
The center of the illumination aperture stop 14 is located on the optical axis O1, and limits the diameter of the light emitted from the light source unit 13 to a specific diameter. The condenser lens 15 condenses the light from the illumination aperture stop 14. The field stop 16 is an optical element that limits the field of view of the overlay measurement apparatus 10, and has one slit 16a that is a rectangular opening as shown in FIG. The illumination relay lens 17 collimates the light from the slit 16 a of the field stop 16. The beam splitter 18 reflects light from the illumination relay lens 17 downward.

  In the above configuration, the light emitted from the light source unit 13 uniformly illuminates the field stop 16 via the illumination aperture stop 14 and the condenser lens 15. Then, the light that has passed through the slit 16a of the field stop 16 is guided to the beam splitter 18 through the illumination relay lens 17, reflected by its reflection / transmission surface (illumination light L1), and then the first objective on the optical axis O2. Guided to the lens 19.

The first objective lens 19 receives and collects the illumination light L1 from the beam splitter 18. As a result, the substrate 11 (or the adjustment substrate 30) on the stage 12 is vertically illuminated by the illumination light L1 having a predetermined wavelength band transmitted through the first objective lens 19 (epi-illumination).
The incident angle of the illumination light L1 when entering the substrate 11 (or the adjustment substrate 30) is determined by the positional relationship between the center of the illumination aperture stop 14 and the optical axis O1. Further, the incident angle range of the illumination light L1 at each point of the substrate 11 (or the adjustment substrate 30) is determined by the aperture diameter of the illumination aperture stop 14. This is because the illumination aperture stop 14 has a conjugate positional relationship with the virtual pupil plane 19A of the first objective lens 19.

  Furthermore, since the field stop 16 and the substrate 11 (or the adjustment substrate 30) are in a conjugate positional relationship, a region corresponding to the slit 16a of the field stop 16 on the surface of the substrate 11 (or the adjustment substrate 30) is present. Illuminated by the illumination light L1. That is, the image of the slit 16 a is projected on the surface of the substrate 11 (or the adjustment substrate 30) by the action of the illumination relay lens 17 and the first objective lens 19.

  Then, diffracted light L2 is generated from the region of the substrate 11 (or the adjustment substrate 30) irradiated with the illumination light L1 having the predetermined wavelength band described above. The diffracted light L2 includes 0th order diffracted light (that is, reflected light), ± 1st order diffracted light, and the like. In the case of the adjustment substrate 30, the wavelength characteristic of the diffracted light L2 is the same for the outer mark 31 and the inner mark 32 of the adjustment mark 30A, and is substantially the same as the wavelength characteristic of the illumination light L1. Further, in the case of the substrate 11 (general product substrate), it differs depending on the structure and physical properties of the registration mark and the base mark of the overlay mark 11A. This is because the reflection characteristics of the mark change according to the structure and physical properties of the mark. The diffracted light L2 from the substrate 11 (or the adjustment substrate 30) is guided to an imaging optical system (19 to 24) described later.

  The imaging optical system (19-24) includes a first objective lens 19, a second objective lens 20, a first imaging relay lens 21, a parallel plane plate 22, and an imaging aperture stop arranged in order along the optical axis O2. 23 and a second imaging relay lens 24. The optical axis O2 of the imaging optical system (19 to 24) is parallel to the Z direction. A beam splitter 18 of the illumination optical system (13 to 19) is disposed between the first objective lens 19 and the second objective lens 20, and the second objective lens 20 and the first imaging relay lens 21 are connected to each other. Between them, the beam splitter 41 of the focus detection units (41 to 48) is arranged. The beam splitters 18 and 41 are half prisms that perform light amplitude separation.

The first objective lens 19 collimates the diffracted light L2 from the substrate 11 (or the adjustment substrate 30). The diffracted light L 2 collimated by the first objective lens 19 passes through the beam splitter 18 and enters the second objective lens 20. The second objective lens 20 condenses the diffracted light L2 from the beam splitter 18 on the primary imaging surface 10a.
The beam splitter 41 of the focus detection unit (41 to 48) disposed at the subsequent stage of the primary image formation surface 10a includes the optical axis O3 of the focus detection unit (41 to 48) and the light of the imaging optical system (18 to 24). The reflection / transmission surface is inclined by approximately 45 ° with respect to the axis O2. The beam splitter 41 transmits a part (L3) of the diffracted light L2 from the second objective lens 20 and reflects the remaining part (L4). A part of the light L3 transmitted through the beam splitter 41 is guided to the first imaging relay lens 21 of the imaging optical system (18 to 24). The first imaging relay lens 21 collimates the light L3 from the beam splitter 41.

  The plane parallel plate 22 can be tilted within a range of several degrees around two axes perpendicular to the optical axis O2 (each parallel to the X axis and the Y axis). That is, the arrangement of the plane parallel plate 22 can be finely adjusted in the tilt direction. FIG. 3 shows the fine adjustment of the tilt direction around the axis parallel to the X axis. As shown in FIG. 3, the direction in which the optical axis 22a (axis parallel to the thickness direction) of the plane-parallel plate 22 is tilted with respect to the optical axis O2 corresponds to the “tilt direction”. The fine adjustment of the tilt direction of the arrangement of the plane parallel plates 22 corresponds to the fine adjustment of the tilt angle θ of the plane parallel plates 22.

  As described above, the arrangement of the plane parallel plate 22 can be finely adjusted in the tilt direction (details will be described later), and the light from the first imaging relay lens 21 is transmitted. The imaging aperture stop 23 is disposed on a plane conjugate with the virtual pupil plane 19A of the first objective lens 19, and limits the diameter of light from the parallel plane plate 22 to a specific diameter. The second imaging relay lens 24 re-images the light from the imaging aperture stop 23 on the imaging surface (secondary imaging surface) of the CCD image sensor 25.

  In the imaging optical system (18 to 24), when the overlay mark 11A on the substrate 11 (or the adjustment mark 30A on the adjustment substrate 30) is positioned in the visual field region, an image of the mark is displayed. It is formed on the imaging surface of the CCD imaging device 25. Further, the plane parallel plate 22 arranged between the virtual pupil plane 19A of the first objective lens 19 and the arrangement plane of the imaging aperture stop 23 (hereinafter referred to as “aperture stop plane 23A”) is arranged in the tilt direction. Fine adjustment is possible, and the imaging optical system (18 to 24) is adjusted using the plane parallel plate 22 (details will be described later). The plane parallel plate 22 corresponds to “an optical element for adjustment” in the claims.

  The CCD image pickup device 25 is arranged such that its image pickup surface coincides with the image surface of the imaging optical system (18 to 24). The CCD image pickup element 25 is an area sensor in which a plurality of pixels are two-dimensionally arranged, picks up an image of the overlay mark 11A on the substrate 11 (or the adjustment mark 30A on the adjustment substrate 30), and outputs an image signal. Is output to the image processing unit 26. The image signal represents a distribution (luminance distribution) related to the luminance value for each pixel on the imaging surface of the CCD imaging device 25.

  The image processing unit 26 captures an image of the overlay mark 11A on the substrate 11 (or the adjustment mark 30A on the adjustment substrate 30) based on the image signal from the CCD image pickup device 25, and performs a predetermined process on the image. The image processing is performed. Incidentally, the image of the overlay mark 11A is subjected to image processing for overlay inspection. The image of the adjustment mark 30A is subjected to predetermined image processing (described later) in order to obtain an index when finely adjusting the arrangement of the plane-parallel plate 22 in the tilt direction. Note that visual observation with a television monitor (not shown) is also possible via the image processing unit 26.

Next, the focus detection units (41 to 48) will be described. The focus detection units (41 to 48) detect whether or not the substrate 11 (or the adjustment substrate 30) on the stage 12 is in focus with respect to the imaging surface of the CCD image sensor 25.
The focus detection units (41 to 48) include a beam splitter 41, an AF first relay lens 42, a parallel plane plate 43, a pupil division mirror 44, an AF second relay lens 45, and a cylindrical lens arranged in order along the optical axis O3. 46, an AF sensor 47, and a signal processing unit 48. The AF sensor 47 is a line sensor, and a plurality of pixels are arranged one-dimensionally on the imaging surface 47a. The cylindrical lens 46 has a refractive power in a direction perpendicular to the pixel arrangement direction (A direction in the figure) on the imaging surface 47 a of the AF sensor 47.

  In the focus detection unit (41 to 48), a part of the light L4 reflected by the beam splitter 41 (hereinafter referred to as “AF light”) is collimated by the AF first relay lens 42, passes through the parallel plane plate 43, and The light enters the pupil division mirror 44. On the pupil division mirror 44, an image of the illumination aperture stop 14 of the illumination optical system (13 to 19) is formed. The plane parallel plate 43 is an optical element for adjusting the position of the image of the illumination aperture stop 14 at the center of the pupil division mirror 44, and has a mechanism capable of tilt adjustment.

The AF light that has entered the pupil division mirror 44 is separated into light in two directions, and then condensed in the vicinity of the imaging surface 47 a of the AF sensor 47 via the AF second relay lens 45 and the cylindrical lens 46. The At this time, on the imaging surface 47a, images of the two field stops 16 are formed in the measurement direction at positions separated along the pixel arrangement direction (A direction in the figure).
Then, the AF sensor 47 outputs a light reception signal regarding the imaging center of the two images formed on the imaging surface 47 a to the signal processing unit 48. Based on the output from the AF sensor 47, the signal processing unit 48 calculates the distance between the imaging centers of the images of the two field stops 16 in the measurement direction, and the difference from the distance in the in-focus state stored in advance. And a focus signal is output to the stage control unit 27. Details of such an AF operation of the pupil division method are described in, for example, JP-A-2002-40322.

  By the way, in the overlay measuring apparatus 10 (FIG. 1) configured as described above, when the optical components of the imaging optical system (18 to 24) are arranged, the optical components are fixed with hardware. The blocks are arranged in parallel to the optical axis O2 while being adjusted with a tool such as a collimator. However, each optical component may have an eccentric error due to block processing accuracy or adjustment error.

When an eccentric error of the optical component occurs between the virtual pupil surface 19A of the imaging optical system (18 to 24) and the aperture stop surface 23A, the pupil image of the aperture stop surface 23A is caused by the eccentric error. The imaging position varies depending on the wavelength band. FIG. 4 schematically shows the positional relationship of the pupil image in such a case. FIG. 4 shows the pupil image H _G corresponding to the center wavelength band of the illumination light L1, and the pupil image H _B corresponding to the short wavelength band, the positional relationship between the pupil image H _R corresponding to the long wavelength band. The pupil images H _R , H _G , and H _{B in} FIG. 4 are components of the same diffraction order (for example, a 0th-order diffraction component) in the diffracted light L3 incident on the imaging aperture stop 23A.

In addition, as an example of causing an imaging position shift (FIG. 4) of the pupil images H _R , H _G , H _{B on} the aperture stop surface 23A, an eccentric error (tilt error) of the beam splitter 18 as shown in FIG. Conceivable. In FIG. 5, the illustration of the beam splitter 41 among the optical components on the optical axis O2 is omitted, and the tilt angle θ = 0 of the parallel flat plate 22 (similar to FIG. 3A). Further, in FIG. 5, in the diffracted light L3, the optical path of the diffracted light L _B of the short wavelength band, showing separately the optical path of the diffracted light L _R of the long wavelength band.

As can be seen from FIG. 5, for example when the beam splitter 18 has an eccentric error, not to perform fine adjustment of the parallel flat plate 22 (that is set to the tilt angle theta = 0), and the diffracted light L _B of the short wavelength band The long-wavelength band diffracted light L _R is incident on the aperture stop surface 23A while being shifted in position, and image formation position shifts of the pupil images H _R , H _G , H _B on the aperture stop surface 23A occur (FIG. 4). . The same applies to the case where the second objective lens 20, the beam splitter 41, and the first imaging relay lens 21 are not limited to the beam splitter 18, but have an eccentric error.

If the imaging positions of the pupil images H _R , H _G , and H _{B on} the aperture stop surface 23A differ depending on the wavelength band (FIG. 4), the imaging aperture stop 23 arranged there is moved to each wavelength band. When the diffracted light L3 passes, the symmetry / asymmetric property of vignetting differs for each wavelength band. For example, when the vignetting in the central wavelength band is symmetric, the vignetting in the short wavelength band and the vignetting in the long wavelength band are asymmetric.

And if vignetting is asymmetric is the case as shown in FIG. 6 (a), that with respect to the center C ₂₃ of the imaging aperture stop 23, are out of position of the center C _H of the pupil image H. FIG. 6A illustrates the 0th-order diffraction component and the ± 1st-order diffraction component of the pupil image H. In the case of FIG. 6A, a part (point hatched portion) of the + 1st order diffraction component of the pupil image H is blocked by the image forming aperture stop 23, but the -1st order diffraction component is The image forming aperture stop 23 is not limited. For this reason, the vignetting is asymmetric with respect to the center C _{H of the} pupil image H.

In contrast, in the case vignetting is symmetric is the case as shown in FIG. 7 (a), the position of the center C _H of the pupil image H is coincident with the center C ₂₃ of the imaging aperture stop 23. FIG. 7A also illustrates the 0th-order diffraction component and the ± 1st-order diffraction component of the pupil image H. In the case of FIG. 7A, a part of the + 1st order diffracted component and the −1st order diffracted component (point hatched portion) of the pupil image H are blocked by the imaging aperture stop 23 by the same amount and vignetted. It has become. Therefore, with respect to the center C _H of the pupil image H, vignetting is symmetrical.

  Further, when the vignetting is asymmetric (FIG. 6A), considering the diffracted light L3 after passing through the imaging aperture stop 23, the light amounts of the 0th-order diffraction component and the −1st-order diffraction component do not change, but +1 The light amount of the next diffraction component will decrease. That is, the light amount of the + 1st order diffraction component is smaller than that of the −1st order diffraction component. In the first place, when the diffracted light L2 is generated from the concavo-convex structure mark as shown in FIG. 6B arranged on the object plane of the imaging optical system (19 to 24), it is +1 from the −1st order diffraction component. The light amount of the next diffraction component is reduced, and a difference appears in the imaging state regarding the left and right edge images.

  Further, when the asymmetry of the diffracted light L2 as described above occurs, the appearance of the two edges E1 and E2 of the mark shown in FIG. Therefore, the intensity profile of the images of the edges E1 and E2 formed on the imaging surface of the CCD imaging device 25 via the imaging optical system (18 to 24) is distorted as shown in FIG. ) Will be included. In this case, when the position of the mark shown in FIG. 6B is detected based on the image signal from the CCD image sensor 25, the detection result includes an error component (TIS value) corresponding to the imbalance between the left and right edge images. Will be included.

On the other hand, when the vignetting is symmetric (FIG. 7A), considering the diffracted light L3 after passing through the imaging aperture stop 23, the light amount of the 0th-order diffraction component does not change, but the −1st-order diffraction component and +1 The light amount of the next diffraction component decreases by the same amount.
Further, when the symmetry of the diffracted light L2 as described above is maintained, the two edges E1 and E2 of the mark shown in FIG. That is, one edge E1 looks good by securing the light amount of the −1st order diffraction component, and the other edge E2 looks good by securing the light amount of the + 1st order diffraction component. Therefore, the intensity profiles of the images of the edges E1 and E2 formed on the imaging surface of the CCD imaging device 25 via the imaging optical system (18 to 24) are equal on the left and right as shown in FIG. Balance). In this case, when the position of the mark shown in FIG. 7B is detected based on the image signal from the CCD image sensor 25, an accurate detection result that does not include an error component (TIS value) can be obtained.

Therefore, as described above, if the imaging positions of the pupil images H _R , H _G , and H _{B on} the aperture stop surface 23A differ depending on the wavelength band (FIG. 4), the vignetting symmetry / asymmetric property is different for each wavelength band. Since they are different (FIGS. 6A and 7A), even the images of the edges E1 and E2 of the same mark (FIGS. 6B and 7B) have their intensity profiles (FIG. In FIG. 7 (c)), the left / right balance / unbalance differs for each wavelength band. For example, when the vignetting in the center wavelength band is symmetric and the vignetting in the long wavelength band or short wavelength band is asymmetric, the intensity profile of the former edge image is as shown in FIG. 7C, and the intensity profile of the latter edge image. Is as shown in FIG.

As a result, an accurate detection result of the mark position can be obtained in the symmetric center wavelength band of the vignetting, whereas the detection result of the mark position is an error component (in the asymmetrical long wavelength band and short wavelength band of the vignetting. Inaccurate data including TIS value.
Incidentally, when the vignetting asymmetry in the long wavelength band has a directional characteristic as shown in FIG. 6A, the vignetting asymmetry in the short wavelength band has an inverted directional characteristic as shown in FIG. become. The light intensity of each component of the diffracted light L2 generated from the mark and the intensity profiles of the images of the edges E1 and E2 are as shown in FIGS. For this reason, the error component (TIS value) of the mark position detection result in the short wavelength band has a directional characteristic that is reversed from the error component (TIS value) of the mark position detection result in the long wavelength band.

Next, a method for adjusting the imaging optical system (18 to 24) of this embodiment will be described. The adjustment of the imaging optical system (18 to 24) corrects an imaging position shift (FIG. 4) corresponding to the wavelength bands of the pupil images H _R , H _G , and H _{B on} the aperture stop surface 23A, and depends on the wavelength band. This is performed to form pupil images H _R , H _G , and H _B at the same imaging position (for example, the position in FIG. 7). For this adjustment, the adjustment substrate 30 shown in FIG. 2 and the plane parallel plate 22 disposed between the virtual pupil plane 19A of the imaging optical system (18 to 24) and the aperture stop plane 23A are used.

  As described above, the adjustment mark 30A provided on the adjustment substrate 30 (FIG. 2) is composed of the outer mark 31 and the inner mark 32, and the pitch P1 of the outer mark 31 is, for example, 3.8 μm. The pitch P2 of the inner marks 32 is 1 μm, for example. With such pitches P1 and P2, the numerical aperture of the illumination optical system (13 to 19) is NAill, the numerical aperture of the imaging optical system (19 to 24) is NAima, and the center wavelength of the illumination light L1 is λ (μm). The following conditional expressions (1) to (3) are satisfied.

NAima> NAill (1)
NAima-1.2 × NAill = λ / P1 (2)
NAima + NAill / 2 = λ / P2 (3)
When the conditional expression (1) is satisfied, the size of the pupil image H (see FIGS. 6 to 8) on the aperture stop surface 23A of the image forming optical system (19 to 24) is the image forming aperture stop 23 for each component. Smaller.

Conditional expression (2) relates to the outer mark 31 of the adjustment mark 30A. When the conditional expression (2) is satisfied, the pupil image H ₃₁ of the wavelength λ of the outer mark 31 on the aperture stop surface 23A is all of the 0th-order diffraction component and the ± 1st-order diffraction component as shown in FIG. Is incident on the inside of the imaging aperture stop 23 with a margin. FIG. 9A shows the positional relationship when the position of the center C _H of the pupil image H ₃₁ coincides with the center C ₂₃ of the imaging aperture stop 23.

Further, when the conditional expression (2) is satisfied, even if there is an image formation position shift of the pupil images H _R , H _G , H _B for each wavelength band shown in FIG. All of the ± first-order diffraction components can be incident on the inside of the imaging aperture stop 23. That is, the outer mark 31 can maintain vignetting symmetry not only in the center wavelength λ of the illumination light L1, but also in both the long wavelength band and the short wavelength band (see FIG. 7).

On the other hand, the conditional expression (3) relates to the inner mark 32 of the adjustment mark 30A. When the conditional expression (3) is satisfied, the pupil image H ₃₂ of the wavelength λ of the inner mark 32 on the aperture stop surface 23A has a 0th-order diffraction component inside the imaging aperture stop 23 as shown in FIG. Incidently, ± 1st order diffraction components are incident outside the imaging aperture stop 23. FIG. 9B shows a positional relationship when the position of the center C _H of the pupil image H ₃₂ coincides with the center C ₂₃ of the imaging aperture stop 23. In this case, the vignetting symmetry is maintained.

Further, when the conditional expression (3) is satisfied, if there is an imaging position shift of the pupil images H _R , H _G , H _B for each wavelength band shown in FIG. 4, the center C of the pupil image H _{32 in} the long wavelength band. _H is shifted to the left in the figure from the center C ₂₃ of the imaging aperture stop 23 (see FIG. 6), the center C ₂₃ of the center C _H is imaging aperture stop 23 of the pupil image H ₃₂ as opposed to the short wavelength band Since it shifts to the right in the figure (see FIG. 8), the symmetry of the vignetting is broken and becomes asymmetric.

  In the adjustment method of the imaging optical system (18 to 24) of the present embodiment, the imaging optical system (19 to 24) is added in consideration of the vignetting symmetry / asymmetry for each wavelength band in the inner mark 32 as described above. An index for adjusting is obtained, and the arrangement of the plane-parallel plate 22 is finely adjusted in the tilt direction based on the index (see FIG. 3). Adjustment of the imaging optical system (18 to 24) is performed according to the procedure of the flowchart of FIG.

  In step S <b> 1, the adjustment substrate 30 is placed on the holder of the stage 12, and the adjustment mark 30 </ b> A is positioned in the visual field region of the overlay measurement apparatus 10. After this positioning, an AF operation is performed based on the focus signal from the focus detectors (41 to 48), and the adjustment mark 30A is focused on the imaging surface of the CCD image sensor 25. That is, the adjustment mark 30A is arranged on the object plane of the imaging optical system (19 to 24).

  In step S2, the adjustment mark 30A is irradiated with broadband illumination light L1 (for example, a wavelength width of about 270 nm), and a mark image is captured based on the broadband diffracted light L2 generated from the adjustment mark 30A at this time. . The mark image is captured in each of the states before and after the adjustment mark 30A is rotated 180 degrees. Then, based on the luminance information of the two mark images, the amount of positional deviation between the outer mark 31 and the inner mark 32 is calculated.

Further, according to the following equation (4), the positional deviation amount L ₀ at the 0-degree direction (initial state), the average value of the positional deviation amount L ₁₈₀ in the direction of 180 degrees, is calculated as a TIS value. This TIS value is the center of a wide-band pupil image (including the pupil image H ₃₁ and pupil image H ₃₂ of the center wavelength λ shown in FIG. 9 as well as the pupil image of the long wavelength band and the short wavelength band) shown in FIG. represents the center C _H wavelength lambda, the positional deviation between the center C ₂₃ of the imaging aperture stop 23.

TIS = (L ₀ + L ₁₈₀ ) / 2 (4)
In step S3, the calculated TIS value in step S2 (that positional deviation of the center C _H of the center wavelength λ of the pupil image), is compared with a predetermined threshold value. The threshold value is a sufficiently small standard value. If the TIS value is larger than the threshold (S3 is No), the arrangement of the imaging aperture stop 23 is finely adjusted in the shift direction using the TIS value as an index (step S4). Thereafter, the process returns to step S2. Process of step S2~S4 described above are, TIS value (i.e. positional deviation of the center C _H of the center wavelength λ of the pupil image) is smaller than the threshold value (S3 becomes Yes) is repeated until.

When the TIS value calculated in step S2 is smaller than the threshold value, the center C _H of the center wavelength λ of the pupil image and the center C ₂₃ of the imaging aperture stop 23 are as shown in FIGS. 9 (a) and 9 (b). , They are almost identical to each other. In this case, the vignetting at the center wavelength λ is symmetrical for both the outer mark 3 and the inner mark 32 of the adjustment mark 30A. The vignetting symmetry of the outer mark 31 is due to the fact that all ± first-order diffraction components of the pupil image H ₃₁ are incident on the inside of the imaging aperture stop 23. Further, the vignetting symmetry of the inner mark 32 is due to the fact that all ± first-order diffraction components of the pupil image H ₃₂ are incident on the outside of the imaging aperture stop 23.

  In the next step S5, the wavelength band of the illumination light L1 is changed, and the adjustment mark 30A is irradiated with the short wavelength band illumination light L1, and at this time, the short wavelength band diffracted light L2 generated from the adjustment mark 30A. Based on the above, a mark image is captured. The diffracted light L2 in the short wavelength band includes light generated at a spread angle corresponding to the pitch P1 of the outer mark 31 and light generated at a spread angle corresponding to the pitch P2 of the inner mark 32. Of the diffracted light L2, the mark image is captured based on the light that has passed through the imaging aperture stop 23 and has reached the image plane of the imaging optical system (19 to 24).

When there is an imaging position shift of the pupil images H _R , H _G , H _B for each wavelength band shown in FIG. 4, the pupil image of the outer mark 31 by the diffracted light L2 in the short wavelength band is shown in FIG. Although it shifts to the right in the figure with respect to the pupil image H _{31 having the} center wavelength λ, since the conditional expression (2) is satisfied, the −1st order diffraction component does not protrude outside the imaging aperture stop 23. Therefore, the outer mark 31 can maintain vignetting symmetry even in a short wavelength band. In this case, the intensity information of the outer mark 31 of the mark image has the same intensity profile on the left and right (see FIG. 7C).

On the other hand, in the case of the inner mark 32 which satisfies the above conditional expression (3), the pupil image by the diffracted light L2 of the short wavelength band, than pupil image H ₃₂ of center wavelength λ shown in FIG. 9 (b) Shifting to the right in the figure, part of the + 1st order diffraction component is incident on the inside of the imaging aperture stop 23. That is, the amount of vignetting of the + 1st order diffraction component decreases, and the amount of vignetting of the −1st order diffraction component does not change. Therefore, in the inner mark 32, the vignetting becomes asymmetric in the short wavelength band. In this case, the intensity information of the inner mark 32 in the mark image includes distortion (left and right imbalance) in the intensity profile (see FIG. 6C).

Capture of the mark image using the illumination light L1 in the short wavelength band is also performed in each of the states before and after the adjustment mark 30A is rotated 180 degrees. Based on the luminance information of the two mark images, the symmetry / asymmetric property of the luminance information related to the outer mark 31 is taken into account, and the symmetry / asymmetric property of the luminance information related to the inner mark 32 is taken into account, respectively. The amount of positional deviation between the mark 31 and the inner mark 32 is calculated. Further, according to the above equation (4), an average value of the positional deviation amount L _{0 in the 0} degree direction and the positional deviation amount L ₁₈₀ in the 180 degree direction is calculated as a TIS value. This TIS value represents a positional deviation between the center C _H of the pupil image in the short wavelength band on the aperture stop surface 23A and the center C ₂₃ of the imaging aperture stop 23.

  Further, in step S6, the wavelength band of the illumination light L1 is changed, and the adjustment mark 30A is irradiated with the long wavelength band illumination light L1, and at this time, the long wavelength band diffracted light L2 generated from the adjustment mark 30A. Based on the above, a mark image is captured. The diffracted light L2 in the long wavelength band includes light generated at a spread angle corresponding to the pitch P1 of the outer mark 31 and light generated at a spread angle corresponding to the pitch P2 of the inner mark 32. Of the diffracted light L2, the mark image is captured based on the light that has passed through the imaging aperture stop 23 and has reached the image plane of the imaging optical system (19 to 24).

When there is an imaging position shift of the pupil images H _R , H _G , H _B for each wavelength band shown in FIG. 4, the pupil image of the outer mark 31 by the diffracted light L2 in the long wavelength band is shown in FIG. Although it shifts to the left in the figure from the pupil image H ₃₁ of the center wavelength λ, the above-mentioned conditional expression (2) is satisfied, so that the + 1st order diffraction component does not protrude outside the imaging aperture stop 23. Therefore, the outer mark 31 can maintain vignetting symmetry even in a long wavelength band. In this case, the intensity information of the outer mark 31 of the mark image has the same intensity profile on the left and right (see FIG. 7C).

On the other hand, in the case of the inner mark 32 which satisfies the above conditional expression (3), the pupil image by the diffracted light L2 in a long wavelength band, than pupil image H ₃₂ of center wavelength λ shown in FIG. 9 (b) Shifting to the left in the figure, a part of the −1st order diffraction component is incident on the inside of the imaging aperture stop 23. That is, the amount of vignetting of the −1st order diffraction component decreases, and the amount of vignetting of the + 1st order diffraction component does not change. Therefore, in the inner mark 32, vignetting becomes asymmetric in the long wavelength band. In this case, the intensity information of the inner mark 32 of the mark image includes distortion (left and right imbalance) in the intensity profile (see FIG. 8C).

Capture of the mark image using the illumination light L1 in the long wavelength band is also performed in each of the states before and after the adjustment mark 30A is rotated 180 degrees. Based on the luminance information of the two mark images, the symmetry / asymmetric property of the luminance information related to the outer mark 31 is taken into account, and the symmetry / asymmetric property of the luminance information related to the inner mark 32 is taken into account, respectively. The amount of positional deviation between the mark 31 and the inner mark 32 is calculated. Further, according to the above equation (4), an average value of the positional deviation amount L _{0 in the 0} degree direction and the positional deviation amount L ₁₈₀ in the 180 degree direction is calculated as a TIS value. This TIS value represents a positional shift between the center C _H of the long-wavelength pupil image on the aperture stop surface 23A and the center C ₂₃ of the imaging aperture stop 23.

As can be seen from the description of steps S5 and S6 described above, the vignetting asymmetry in the short wavelength band and the vignetting asymmetry in the long wavelength band have inverted directional characteristics. Therefore, the TIS value calculated in step S5 (position shift of the center C _H of the short wavelength band pupil image) and the TIS value calculated in step S6 (position shift of the center C _H of the long wavelength band pupil image) are also obtained. , The direction characteristics are reversed.

In step S7, the TIS value calculated in step S5 (position shift of the center C _H of the short wavelength band pupil image) and the TIS value calculated in step S6 (position of the center C _H of the long wavelength band pupil image). Find the difference from the deviation. The “difference in TIS value” represents a positional deviation between the center C _H of the short wavelength band pupil image and the center C _H of the long wavelength band pupil image on the aperture stop surface 23A.
In step S8, the “TIS value difference” calculated in step S7 is compared with a predetermined threshold value (a sufficiently small standard value). When the “TIS value difference” is larger than the threshold (No in S8), the arrangement of the plane parallel plates 22 is finely adjusted in the tilt direction using the “TIS value difference” as an index (step S4). Thereafter, the process returns to step S5. The processes in steps S5 to S9 described above are repeated until the “TIS value difference” becomes smaller than the threshold value (S8 becomes Yes).

The positional shift amount of the outer mark 31 and the inner mark 32 of the adjustment mark 30A (position shift amount of 0 degree direction L ₀ and the position deviation amount L ₁₈₀ in the direction of 180 degrees) has an imaging aperture stop 23 It changes sensitively depending on the relative positional relationship with the pupil image H. Further, when the TIS value of the adjustment mark 30A is measured, the characteristic of the inner mark 32 is inverted for each wavelength band, so that the change of the TIS value is large. This means that the “difference in TIS value” is an index that changes with high sensitivity depending on the wavelength band.

When the “difference in TIS value” calculated in step S7 is smaller than the threshold value (when S8 is Yes), the center C _H of the short wavelength band pupil image and the center of the long wavelength band pupil image on the aperture stop surface 23A C _H substantially coincides with each other. In this case, the center C _H of the pupil image H ₃₁ of center wavelength λ also substantially coincides with the center C _H of the short wavelength band and a long wavelength band. However, if the TIS value in step S2 is calculated again at this time, there is a possibility that it is out of the threshold (S3 becomes No).

  Accordingly, the processes in steps S2 to S9 are repeated, and the TIS value in step S2 and the “difference in TIS value” in step S7 are driven to be smaller than the respective threshold values. Adjustment processing of the imaging optical system (19 to 24) of the present embodiment when both the TIS value in step S2 and the “difference in TIS value” in step S7 are within the standard values (No in step S10). Exit.

At this time, the imaging position shift (FIG. 4) corresponding to the wavelength bands of the pupil images H _R , H _G , H _{B on} the aperture stop surface 23A is corrected, and the same imaging position (for example, FIG. 7) regardless of the wavelength band. ), Pupil images H _R , H _G , H _B can be formed. Further, the vignetting on the aperture stop surface 23A can be maintained in a symmetric state (FIG. 7) regardless of the wavelength band.
As described above, in the adjustment method of the imaging optical system (19 to 24) of the present embodiment, an index (difference in TIS value) is obtained from the image of the adjustment mark 30A on the adjustment substrate 30, and based on this index. Since the arrangement of the plane parallel plate 22 is finely adjusted in the tilt direction, the arrangement of the plane parallel plate 22 can be finely adjusted with high sensitivity. Therefore, the adjustment error (tilt angle θ error) of the plane parallel plate 22 can be reliably reduced, and the error component (TIS value) caused by the apparatus can be reduced satisfactorily.

Furthermore, the setting of the illumination wavelength in step S5 is the shortest wave side of the light source 3A, and the setting of the illumination wavelength in step S6 is the longest wave side of the light source 3B, so that a wide band from the visible light band to the near infrared light band can be obtained. In a range (for example, a range in which the wavelength width is about 270 nm), the error component (TIS value) caused by the apparatus can be reduced well.
As a result, at the time of overlay inspection of the substrate 11 (general product substrate) in the overlay measurement apparatus 10, the wavelength characteristic of the diffracted light L2 depends on the structure and physical properties of the registration mark and the base mark of the overlay mark 11A. Even if they are different, it is possible to obtain an accurate value that does not include an error component (TIS value) as the detection result of each mark position, and the detection accuracy is improved. Furthermore, the amount of misalignment between the registration mark and the base mark can be obtained accurately, and high-precision overlay inspection can be performed.
(Modification)
In the above-described embodiment, the example in which the pitch P1 of the outer mark 31 of the adjustment mark 30A satisfies the conditional expression (2) has been described, but the present invention is not limited to this. The present invention can also be applied when the following conditional expression (4) is satisfied.

NAima-NAill> λ / P1 (4)
Further, in the above-described embodiment, the example in which the pitch P2 of the inner mark 32 of the adjustment mark 30A satisfies the conditional expression (3) has been described, but the present invention is not limited to this. The present invention can also be applied when the following conditional expression (5) is satisfied.
NAima + NAill / 2 ≤ λ / P2 (5)
In the above-described embodiment, the pitch P1 of the outer mark 31 is larger than the pitch P2 of the inner mark 32, but the present invention is not limited to this. As long as the pitches P1, P2 of the outer mark 31 and the inner mark 32 are different, the present invention can be applied even if the magnitude relationship between the pitches P1, P2 is reversed.

  Furthermore, in the above-described embodiment, the ± first-order diffraction components of the pupil image H on the aperture stop surface 23A and the imaging aperture stop are expressed by the conditional expressions (2) and (3) and the conditional expressions (4) and (5). 23, the pitches P1 and P2 of the adjustment mark 30A are determined. However, the present invention is not limited to this. Instead of the ± 1st order diffraction component, the pitches P1 and P2 may be determined using the positional relationship between the ± 2nd order diffraction component or higher order component and the imaging aperture stop 23.

Further, in the above-described embodiment, the example of the adjustment mark 30A configured by two types of marks (the outer mark 31 and the inner mark 32) has been described, but the present invention is not limited to this. The present invention can also be applied to the case where the adjustment mark 30A includes three or more types of marks having different pitches.
Further, in the above-described embodiment, the plurality of marks (for example, the outer mark 31 and the inner mark 32) constituting the adjustment mark 30A are configured by bar marks, but the present invention is not limited to this. The present invention can also be applied to other shapes (for example, dot shapes). Further, the adjustment mark 30A is not limited to a double mark (a mark whose design positional deviation amount is 0) which is a plurality of marks arranged so that their centers coincide with each other. It is also possible to arrange them side by side with a design displacement amount ≠ 0).

  In the above-described embodiment, the example in which the arrangement of the plane-parallel plate 22 is finely adjusted using the difference in the error component (TIS value) when the wavelength band of the illumination light L1 is different as an index has been described. It is not limited. The present invention can also be applied when finely adjusting the arrangement of the plane-parallel plates 22 based on the amount of displacement when the wavelength bands of the illumination light L1 are different. At this time, for example, a difference in positional deviation amount may be used as an index.

  Furthermore, in the above-described embodiment, the example in which the imaging optical system (19 to 24) is adjusted using the plane parallel plate 22 has been described, but the present invention is not limited to this. As an adjustment optical element, it is conceivable to use two wedge-shaped prisms having different refractive indexes. In this case, the slopes of the two wedge-shaped prisms face each other and slide along the direction perpendicular to the optical axis O2 (change the relative position) to obtain the same effect as the tilt adjustment of the parallel flat plate 22. be able to.

  In the embodiment described above, the adjustment method has been described by taking the imaging optical system (19 to 24) incorporated in the overlay measurement apparatus 10 as an example, but the present invention is not limited to this. The present invention can also be applied when adjusting an imaging optical system of an optical apparatus (for example, an optical microscope or an appearance inspection apparatus) for observing an object.

1 is a diagram illustrating an overall configuration of an overlay measurement apparatus 10. FIG. 5 is a diagram showing a configuration of an adjustment mark 30A on the adjustment substrate 30. It is a figure explaining the fine adjustment of arrangement | positioning of the plane parallel plate. It is a figure explaining the imaging position shift according to the wavelength band of the pupil images H _R , H _G , H _{B on} the aperture stop surface 23A. It is a figure explaining the imaging position shift in 23 A of aperture stop surfaces by the eccentric error (tilt error) of the beam splitter 18. FIG. It is a figure explaining the case where vignetting is asymmetrical (only the + 1st order diffraction component is reduced in light amount). It is a figure explaining the case where vignetting is symmetrical. It is a figure explaining the case where vignetting is asymmetric (only -1st-order diffracted component is reduced in light amount). Positional relationship between the pupil image H ₃₁ of the imaging aperture stop 23 and the outer mark 31 (a), a diagram showing positional relationship (b) of the pupil image H ₃₂ of the inner mark 32 and the imaging aperture stop 23. It is a flowchart which shows the adjustment procedure of the imaging optical system (19-24) of this embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Overlay measuring apparatus 11 Board | substrate 12 Stage 13 Light source part 14 Illumination aperture stop 15 Condenser lens 16 Field stop 17 Illumination relay lens 18, 41 Beam splitter 19 1st objective lens 20 2nd objective lens 21 1st imaging relay lens 22, 43 Parallel plane plate 23 Imaging aperture stop 24 Second imaging relay lens 25 CCD imaging device 26 Image processing device 27 Stage controller 30 Adjustment substrate 30A Adjustment mark 31 Outer mark 32 Inner mark 42 AF first relay lens 44 Pupil Split mirror 45 AF second relay lens 46 Cylindrical lens 47 AF sensor 48 Signal processing unit

Claims (4)

First ± first-order diffracted light beams produced by epi-illumination light in a predetermined wavelength band are arranged on the object plane of the imaging optical system at a first pitch that is greater than or equal to a pitch that is inscribed in the pupil region of the imaging optical system. And the second mark arranged at a second pitch smaller than the pitch at which the + 1st order diffracted light beam by the illumination light circumscribes the pupil region of the imaging optical system, respectively. Are arranged symmetrically with respect to the visual field center of
A relative position between the image of the first mark and the image of the second mark formed by the imaging optical system when the wavelength of the illumination light is set on the long wavelength side ; Based on the difference between the relative position between the image of the first mark and the image of the second mark formed by the imaging optical system when the wavelength is set to the short wavelength side, the imaging A method for adjusting an imaging optical system, characterized by adjusting an arrangement of optical elements disposed between a pupil plane and an aperture stop surface of the optical system. In the adjustment method of the imaging optical system according to claim 1,
The first pitch is P1 (μm), the second pitch is P2 (μm), the numerical aperture of the imaging optical system is NAima, the numerical aperture of the optical system used for irradiation of the illumination light is NAill, When the center wavelength of the illumination light is λ (μm), the following conditional expression is satisfied. NAima> NAill
NAima-NAill> λ / P1
NAima + NAill / 2 ≤ λ / P2
An imaging optical system adjustment method characterized by the above. In the adjustment method of the imaging optical system according to claim 1 or 2,
When obtaining information on the relative position between the image of the first mark and the image of the second mark,
Said first mark and said second mark in each of the states before and after rotating 180 ° with respect to the field center, and the first mark in the image formed by the imaging optical system and the second after measuring the distance between the mark, the measured error component of device due represented by two distances, the adjustment method of the image forming optical system and acquires as the information of the relative position. In the adjustment method of the imaging optical system of any one of Claims 1-3 ,
The optical element is a plane parallel plate;
The adjustment of the arrangement of the optical elements, the adjustment method of the image forming optical system, characterized in that an adjustment in the direction of tilting the parallel flat plate.

Images