JP4826326B2 - Evaluation method and adjustment method of illumination optical system - Google Patents

Description

The present invention relates to an evaluation method and adjustment method of illumination optical system for performing telecentric illumination of the object.

For example, in an apparatus for detecting the position of a test mark on a substrate, the test mark is telecentric illuminated to capture an image of the test mark, and this image is processed to detect the position. In this apparatus, in order to improve the accuracy of position detection, the illumination telecentricity (hereinafter referred to as “illumination telecentric”) is uniformly adjusted within the field of view so as to reduce the error TIS (Tool Induced Shift) caused by the apparatus. (For example, refer to Patent Document 1).
JP 2004-158555 A

However, with the method of uniformly adjusting the illumination telecentricity within the field of view as described above, it is not possible to adjust the variation within the field of view of the illumination telecentricity. In addition, it is necessary to evaluate the variation in order to adjust the variation, but the above method cannot evaluate the variation in the illumination telecentric even if the average illumination telecentric in the field of view can be evaluated. It was.
An object of the present invention is to provide an illumination optical system evaluation method and adjustment method, and a position detection device that can evaluate variations in illumination telecentricity when an object is illuminated.

The illumination optical system evaluation method of the present invention includes a first step of irradiating illumination light onto a predetermined region of an object plane of an imaging optical system that forms an optical image of an object using the illumination optical system to be evaluated, In the state where the predetermined area is irradiated with the illumination light, one or more evaluation marks are sequentially or simultaneously positioned at a plurality of different evaluation points in the predetermined area, and auxiliary marks having a level difference lower than the evaluation mark are A second step of positioning at a point away from the evaluation mark within a predetermined area; and an image including the light / dark information of the auxiliary mark together with the light / dark information of the evaluation mark positioned at each of the plurality of evaluation points. a third step of capturing through the image optical system, based on the evaluation marks and brightness information of each of said auxiliary marks included in the image, the positional deviation amount between the auxiliary marks and the evaluation mark Because, based on the positional deviation amount and a fourth step of generating tilt information of the principal ray of the illumination light at each of the plurality of evaluation points, step h ₁ of the evaluation mark, the center of the illumination light The following conditional expression “(λ / NA ² ) <h ₁ <3 (λ / NA ² )” is satisfied with respect to the wavelength λ and the numerical aperture NA on the object side of the imaging optical system.

Further, the evaluation mark and the auxiliary mark constitute a double mark having different steps inside and outside, and in the fourth step, the double mark is reversed within a plane perpendicular to the optical axis of the imaging optical system. It is preferable that the amount of misalignment between the evaluation mark and the auxiliary mark is obtained before and after the tilting, and the tilt information is generated based on an average value of the amount of misalignment before and after the reversal.
In the second step, it is preferable that a plurality of the evaluation marks and a plurality of the auxiliary marks are alternately arranged in the predetermined area and positioned simultaneously.

Further, the step h _{1 of the} evaluation mark and the step h _{0 of the} auxiliary mark are respectively expressed by a conditional expression “h ₁ = m ₁ ×× with respect to the center wavelength λ of the illumination light and arbitrary integers m ₁ and m ₀ . It is preferable to satisfy (λ / 4) ”“ h ₀ = m ₀ × (λ / 4) ”.
In the illumination optical system adjustment method of the present invention, after the tilt information is generated by the illumination optical system evaluation method described above, the position of the aperture stop of the illumination optical system is parallel to the optical axis based on the tilt information. Shift adjustment in the direction.

  ADVANTAGE OF THE INVENTION According to this invention, the variation of the illumination telecentric at the time of illuminating an object can be evaluated.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
(First embodiment)
Here, the overlay measurement apparatus 10 in FIG. 1 will be described as an example.
The overlay measurement apparatus 10 is an apparatus that performs overlay inspection of a resist pattern on the substrate 11 in a manufacturing process of a semiconductor element, a liquid crystal display element, or the like. The substrate 11 is a semiconductor wafer, a liquid crystal substrate, or the like, and is in a state after exposure / development of the resist layer and before processing of a predetermined material film. A large number of measurement points are prepared on the substrate 11 for overlay inspection.

  At each measurement point on the substrate 11, 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. For example, in the case of the bar mark shown in FIG. 2, the base mark is formed on the outside and the resist mark is formed on the inside. In the overlay inspection, the position of each mark is detected, and the registration mark positional deviation amount L with respect to the base mark is measured. In the following description, the registration mark and the base mark are collectively referred to as “overlapping mark 11A”.

  As shown in FIG. 1A, the overlay measuring apparatus 10 includes a stage 12 that supports the substrate 11, illumination units (13 to 19, 40), measurement units (18 to 25), and pupil division type. A focus detection unit (17-19, 40-49) and a stage control unit 27 are provided. Further, on the upper surface of the stage 12, a substrate 28 used for evaluation of the optical system of the illumination units (13 to 19, 40) is provided, and two types of marks 30 to 39 having different steps are provided on the substrate 28 (FIG. 3). Is formed.

Although not shown, the stage 12 has a holder for supporting the substrates 11 and 28 in a horizontal state, an XY drive unit for driving the holder in the horizontal direction (XY direction), and the holder in the vertical direction (Z direction). It is comprised with the Z drive part to drive. The XY drive unit and the Z drive unit are connected to the stage control unit 27.
The stage control unit 27 controls the XY driving unit of the stage 12 to position the overlay mark 11A on the substrate 11 (or the evaluation marks 30 to 39 on the substrate 28) within the visual field region. Further, the Z drive unit of the stage 12 is controlled based on the focus signal output from the focus detection units (17-19, 40-49). By this focus adjustment, the overlay mark 11A (or the evaluation marks 30 to 39) can be focused on the imaging surface of the optical system of the measuring units (18 to 25) (autofocus operation).

  The illumination units (13 to 19, 40) include the light source unit 13, the illumination aperture stop 14, the condenser lens 15, the field stop 16, the beam splitter 40, the illumination relay lens 17, the beam splitter 18, and the first. And an objective lens 19. The beam splitters 18 and 40 are half prisms that perform light amplitude separation. In the following description, components other than the light source unit 13 in the illumination units (13 to 19, 40) are collectively referred to as “illumination optical systems (14 to 19, 40)” as appropriate.

  The light source unit 13 includes a light source 3A, a collector lens 3B, a relay lens 3C, a wavelength selection filter 3E, and a light guide fiber 3D. The light source 3A emits light having a wide wavelength band (for example, white light). The light from the light source 3A enters the light guide fiber 3D through the collector lens 3B, the wavelength selection filter 3E, and the relay lens 3C. The light exit end face of the light guide fiber 3D is disposed in the vicinity of the illumination aperture stop 14.

  The illumination aperture stop 14 limits the diameter of the light beam emitted from the light guide fiber 3D to a specific diameter. The condenser lens 15 collects the light from the illumination aperture stop 14 and illuminates the field stop 16 uniformly. The field stop 16 is an optical element for limiting the illumination area on the surface of the substrate 11, and has one rectangular AF slit 16a shown in FIG. The beam splitter 40 transmits the light from the AF slit 16a.

  The illumination relay lens 17 collimates the light from the beam splitter 40. The beam splitter 18 reflects light from the illumination relay lens 17 downward (illumination light L1). The first objective lens 19 receives and collects the illumination light L1 from the beam splitter 18. As a result, the overlay mark 11A on the substrate 11 (or the evaluation marks 30 to 39 on the substrate 28) is irradiated with the illumination light L1 transmitted through the first objective lens 19.

In the illumination optical system (14-19, 40), the illumination aperture stop 14 and the pupil of the first objective lens 19 are arranged in a substantially conjugate manner, and the center of the illumination aperture stop 14 and the optical axis O1 substantially coincide with each other. Therefore, the principal ray of the illumination light L1 from the first objective lens 19 travels substantially parallel to the optical axis O2, and then enters the respective points of the substrate 11 (or substrate 28) substantially perpendicularly.
For this reason, the overlay mark 11A on the substrate 11 (or the evaluation marks 30 to 39 on the substrate 28) is substantially formed by the illumination light L1 from the first objective lens 19 (the principal ray is substantially parallel to the optical axis O2). Vertical epi-illumination (telecentric illumination).

  In the illumination optical system (14-19, 40), the field stop 16 and the surfaces of the substrates 11 and 28 are substantially conjugated. Therefore, the illumination relay lens 17 and the first objective are formed on the surfaces of the substrates 11 and 28. The AF slit 16a (FIG. 1B) of the field stop 16 is projected by the action of the lens 19. And the predetermined area | region corresponding to AF slit 16a among the surfaces of the board | substrates 11 and 28 is telecentric illuminated by the illumination light L1.

  Then, when telecentric illumination is performed by the illumination light L1, 0th-order diffracted light (that is, reflected light), ± 1st-order diffracted light, and the like (generally “from the illumination regions on the surfaces of the substrates 11 and 28 (predetermined regions corresponding to the AF slits 16a)). Light L2 ") is generated. The light L2 from the illumination area is guided to a common optical path by the measurement unit (18 to 25) and the focus detection unit (17 to 19, 40 to 49), and then branched to each optical path.

The measurement unit (18-25) includes an imaging optical system (18-23), a CCD imaging device 24, and an image processing unit 25. In addition to the first objective lens 19 and the beam splitter 18 already described, the imaging optical system (18 to 23) includes a second objective lens 20, a first relay lens 21, an imaging aperture stop 22, The second relay lens 23 is used.
The light L2 from the illumination area travels on a shared optical path between the measurement unit (18-25) and the focus detection unit (17-19, 40-49), is collimated by the first objective lens 19, and enters the beam splitter 18 To do. The beam splitter 18 transmits a part (L3) of the light L2 from the first objective lens 19 and reflects the remaining part (L4). Then, the transmitted light L3 is guided to the subsequent optical path of the measurement unit (18-25), and the reflected light L4 is guided to the subsequent optical path of the focus detection unit (17-19, 40-49).

  In the subsequent optical path of the measurement unit (18 to 25), the light L3 transmitted through the beam splitter 18 is condensed through the second objective lens 20 to form an intermediate image on the primary imaging plane 10a, and then the first Guided to the relay lens 21. The first relay lens 21 collimates the light L3 from the primary imaging surface 10a. The imaging aperture stop 22 limits the diameter of light from the first relay lens 21 to a specific diameter. The second relay lens 23 re-images the light from the imaging aperture stop 22 on the secondary imaging surface (the imaging surface of the CCD image sensor 24).

  Therefore, when the overlay mark 11A on the substrate 11 (or the evaluation marks 30 to 39 on the substrate 28) is positioned in the visual field region, the imaging optical system (18 to 24) described above An optical image of each mark can be formed on the image pickup surface of the CCD image pickup device 24 based on a part of the light L2 generated from the illumination regions 11 and 28 (light L3 transmitted through the beam splitter 18).

The CCD image pickup device 24 is an area sensor in which a plurality of pixels are two-dimensionally arranged. The CCD image pickup device 24 picks up a light image of the overlay mark 11A (or the evaluation marks 30 to 39) formed on the image pickup surface to obtain an image. An imaging signal is output to the processing unit 25. The imaging signal represents a distribution (luminance distribution) related to the luminance value for each pixel on the imaging surface of the CCD imaging device 24.
The image processing unit 25 captures the image of the overlay mark 11A (or the evaluation marks 30 to 39) based on the image pickup signal from the CCD image pickup device 24, and performs predetermined image processing on the image. Image processing for overlay inspection is performed on the image of the overlay mark 11A. The images of the evaluation marks 30 to 39 are subjected to image processing necessary for the evaluation of the illumination optical system (14 to 19, 40). Note that visual observation with a television monitor (not shown) is also possible via the image processing unit 25.

  In addition to the first objective lens 19, the beam splitter 18, the illumination relay lens 17, and the beam splitter 40 described above, the focus detectors (17 to 19 and 40 to 49) are provided with an AF field stop 41 and a first relay. A lens 42, a deflection mirror 43, a plane parallel plate 44, a pupil division mirror 45, a second relay lens 46, a cylindrical lens 47, an AF sensor 48, and a signal processing unit 49 are provided. The AF sensor 48 is a line sensor.

The focus detectors (17-19, 40-49) align the substrate 11 (or substrate 28) on the stage 12 with the imaging surface of the CCD image sensor 24 based on the light L4 reflected by the beam splitter 18. Whether or not it is in focus is detected, and the detection result (focus signal) is output to the stage controller 27.
Details of the pupil division type AF operation using the focus detection units (17 to 19, 40 to 49) are described in, for example, Japanese Patent Application Laid-Open No. 2002-40322, and the description thereof is omitted here. After the AF operation, the overlay mark 11A on the substrate 11 (or the evaluation marks 30 to 39 on the substrate 28) is brought into focus with respect to the imaging surface of the CCD image sensor 24, and the imaging optical system (18 ˜23) on the object plane.

  In the overlay measurement apparatus 10 having the above-described configuration, the overlay mark 11A on the substrate 11 is positioned in the visual field region during overlay inspection, and the tessellation is performed by the illumination light L1 from the illumination optical system (14-19, 40). The trick is illuminated. Then, an optical image of the overlay mark 11A is formed on the imaging surface of the CCD imaging device 24 via the imaging optical system (18 to 23), and an image signal related to this mark image is taken into the image processing unit 25.

  The wavelength band of the illumination light L1 can be arbitrarily selected within the range of 470 nm to 800 nm, for example, by switching the wavelength selection filter 3E. However, the width of the wavelength band of the illumination light L1 is preferably 60 nm or more. Since the overlay mark 11A is measured through a transparent film (not shown), if the illumination light L is a single wavelength light, the return light L2 may be weak depending on the variation in film thickness. For this reason, it is preferable to set the wavelength width to 60 nm or more so that measurement can be performed with good SN even if the film thickness varies.

  The image processing unit 25 performs image processing for overlay inspection on the image of the overlay mark 11A, detects the position of each of the registration mark and the base mark constituting the overlay mark 11A (FIG. 2), and A registration mark misregistration amount L with respect to the mark is calculated. The positional shift amount L is a relative shift amount of the center position of each mark, and represents the overlay shift amount of the resist pattern with respect to the base pattern on the substrate 11. This overlay deviation amount is also called a overlay measurement value.

Incidentally, in recent years, with the miniaturization of semiconductor devices, it has become desirable to improve the overlay accuracy during exposure (that is, to reduce the above-mentioned positional deviation amount L). Therefore, the required specifications for the accuracy of position detection and the measurement accuracy of the positional deviation amount L in the overlay measuring apparatus 10 are becoming stricter.
When the chief ray of the illumination light L1 from the illumination optical system (14 to 19, 40) is slightly inclined with respect to the optical axis O2, and the inclination is different for each point of the substrate 11 (that is, for illumination telecentric in the field of view) In the case of an image of the overlay mark 11A, the shift amount differs for each edge image of each mark, and a systematic measurement error (TIS) occurs. Further, when overlay inspection is performed using such illumination optical systems (14 to 19, 40), the overlay measurement value changes for each position (measurement position) of the overlay mark 11A in the visual field region. Reproducibility deteriorates.

For this reason, it is necessary to evaluate the performance of the illumination optical system (14 to 19, 40) at an appropriate timing (for example, at the time of manufacturing the apparatus) and to stabilize the measurement accuracy of the overlay measurement apparatus 10. . Furthermore, when evaluating the illumination optical system (14-19, 40), it is desirable to simply perform the evaluation with the illumination optical system (14-19, 40) incorporated in the apparatus.
Next, the evaluation method of the illumination optical system (14-19, 40) of this embodiment is demonstrated.

When the illumination optical system (14-19, 40) is evaluated, the illumination optical system (14-19, 40) to be evaluated is used to form the imaging optical system (18- The illumination light L1 is irradiated to a predetermined area (a predetermined area corresponding to the AF slit 16a) of the object plane of 23). Also in this case, the width of the wavelength band of the illumination light L1 is preferably 60 nm or more.
Further, the evaluation marks 30 to 39 (FIG. 3) on the substrate 28 are positioned in the illumination area in a state where the illumination light L1 is irradiated. At this time, the evaluation marks 30 to 39 are illuminated by tessellentic illumination with the illumination light L1 from the illumination optical system (14 to 19, 40), and the evaluation mark 30 is passed through the imaging optical system (18 to 23). To 39 are formed on the imaging surface of the CCD image sensor 24. Then, an image signal related to the mark image is taken into the image processing unit 25.

Here, the evaluation marks 30 to 39 (FIG. 3) are convex bar marks created by etching a silicon wafer or the like. Marks 30 to 34 elongated in the X direction are used for evaluation of the illumination optical system (14 to 19, 40) in the Y direction. The marks 35 to 39 elongated in the Y direction are used for evaluation in the X direction.
The elongated marks 35 to 39 in the Y direction have a shape obtained by rotating the elongated marks 30 to 34 in the X direction by 90 degrees. The evaluation method using the elongated marks 35 to 39 in the Y direction is the same as the evaluation method using the elongated marks 30 to 34 in the X direction. For this reason, the description related to the elongated marks 35 to 39 in the Y direction is omitted, and the description related to the elongated marks 30 to 34 in the X direction will be described below.

The long and narrow marks 30 to 34 in the X direction include two kinds of marks having a constant line width (for example, 3 μm) in the short direction and a distance (for example, 7 μm) from each other and having different steps. Further, the high step marks 30, 32, 34 and the low step marks 31, 33 are alternately arranged.
For this reason, the center of the marks 30 to 34 is a high step mark 32, and low step marks 31 and 33 are arranged at ± 10 μm from the mark 32. In addition, other high step marks 30 and 34 are arranged at a point of ± 20 μm from the mark 32.

Mark 30-34 configured as described above, evaluation of the illumination optical system (14～19,40), the center point P ₀ of the center mark 32 is positioned at the center of the viewing area (object height 0 .mu.m). For this reason, the low step marks 31 and 33 are positioned at the object height of ± 10 μm away from the central mark 32 in the visual field region. Further, the other high step marks 30 and 34 are positioned at the object height of ± 20 μm in the field of view.

The step h ₁ of the high step marks 30, 32, and 34 is expressed by the following conditional expression (1) with respect to the center wavelength λ of the illumination light L1 and the numerical aperture NA on the object side of the imaging optical system (18 to 23). , (2) is satisfied. M ₁ of the formula (2) is an arbitrary integer. In the present embodiment, the level difference h _{1 is set} to 4 μm, for example.
(λ / NA ² ) <h ₁ <3 (λ / NA ² ) (1)
h ₁ = m ₁ × (λ / 4) (2)
Further, the step h ₀ of the low step marks 31 and 33 satisfies the following conditional expressions (3) and (4) with respect to the same central wavelength λ and numerical aperture NA as described above. M _{0 in the} formula (4) is an arbitrary integer. In this embodiment, the step h _{0 is set} to 0.16 μm, for example.

λ / 4 ≦ h ₀ <(λ / NA ² ) (3)
h ₀ = m ₀ × (λ / 4) (4)
At the time of evaluation of the illumination optical system (14-19, 40), the marks 30-34 having the above-described configuration are positioned in the visual field region, telecentric illuminated by the evaluation target illumination optical system (14-19, 40), and an image processing unit. 25, the images of the marks 30 to 34 are captured. And the evaluation process of the illumination optical system (14-19, 40) is performed according to the procedure of the flowchart of FIG. 4 while repeatedly capturing the images of the marks 30-34 as necessary.

  The images of the marks 30 to 34 include light / dark information reflecting variations in illumination telecentricity. The influence of illumination telecentricity appears greatly in the light / dark information of the high step marks 30, 32, 34, and is very small in the light / dark information of the low step marks 31, 33. This can also be seen from the fact that, as shown in FIGS. 5 (a) and 5 (b), even if the chief ray inclination (angle θ) of the illumination light L1 is the same, the shadow portion becomes wider as the step becomes larger. This shadow portion occurs asymmetrically with respect to the center of the mark, and becomes a dark portion in the images of the marks 30 to 34.

Therefore, when the illumination optical system (14-19, 40) is evaluated, when the images of the marks 30-34 are captured (step S1 in FIG. 4), the index for evaluation is based on the asymmetry of the brightness information of each mark in the image. As a TIS value (step S2).
For example, assume that the variation in illumination telecentricity is in the state shown in FIG. In the present embodiment, attention is first focused on the high step mark 32 at the center of the visual field (object height 0 μm) and the low step marks 31 and 33 having an object height of ± 10 μm. Then, considering that these three marks 31 to 33 constitute double marks having different steps inside and outside, a TIS value is obtained.

In step S1, the double mark (31-33) is inverted in the plane perpendicular to the optical axis O2 of the imaging optical system (18-23) (that is, rotated 180 degrees) before and after the image processing unit. 25, the images of the marks 30 to 34 are captured. Then, the image processing unit 25, based on each image before and after inversion to determine the relative positional deviation amount between the center position C ₁ of the high step difference mark 32 and the center position C ₂ of the low step difference mark 31, 33 . Further, an average value (TIS value) of the positional deviation amounts before and after inversion is obtained.

This TIS value reflects the influence of the illumination telecentre (the inclination of the principal ray of the illumination light L1) at the point where the high step mark 32 is positioned (object height 0 μm). The influence of illumination telecentricity at the point where the low step marks 31 and 33 are positioned (object height ± 10 μm) is very small and can be ignored.
Usually, in the overlay measurement apparatus 10, a difference in illumination telecentric for each object height in the visual field region becomes a problem. For this reason, in the present embodiment, the processing in steps S1 to S4 is repeatedly performed so that the absolute value of the TIS value at the center of the visual field (object height 0 μm) is smaller than a predetermined threshold (for example, 0.2 nm), and then illumination is performed. The optical system (14-19, 40) was evaluated.

  In step S3, the absolute value of the TIS value at the visual field center (object height 0 μm) obtained in step S2 is compared with a threshold value (for example, 0.2 nm). If the TIS value obtained in step S2 is greater than or equal to the threshold value, the process of step S4 is performed. In step S4, the illumination aperture stop 14 of the illumination optical system (14-19, 40) is shifted and adjusted in a direction perpendicular to the optical axis O1. By this shift adjustment, the illumination telecentricity in the field of view can be adjusted uniformly.

  When the processes of steps S1 to S4 are repeatedly performed and the TIS value at the center of the visual field (object height 0 μm) becomes smaller than the threshold value, the variation of the illumination telecentric becomes, for example, as shown in FIG. That is, the illumination telecentricity at the center of the visual field (object height 0 μm) is substantially zero, and the principal ray of the illumination light L1 incident on the center mark 32 is substantially parallel to the optical axis O2. The image processing unit 25 stores the TIS value at the center of the visual field (object height 0 μm) in this state as TIS (0) in a memory (not shown) (step S5).

  Next (step S6), the image processing unit 25 uses the images before and after the reversal of the marks 30 to 34 last captured in step S1, and uses the high step mark 32 at the center of the visual field (object height 0 μm) and the object height. Attention is paid to the low step mark 33 of +10 μm and the high step mark 34 of the object height +20 μm (FIG. 7A). Then, considering that these three marks 32 to 34 constitute double marks having different steps inside and outside, a TIS value is obtained.

  This TIS value reflects the influence of illumination telecentricity (inclination of the principal ray of the illumination light L1) at the point where the high step mark 34 is positioned (object height + 20 μm). The influence of the illumination telecentre at each of the point where the low step mark 33 is positioned (object height +10 μm) and the point where the high step mark 32 is positioned (object height 0 μm) is very small and can be ignored. . Then, the TIS value at this point (object height + 20 μm) is stored in the memory as TIS (+20).

  Next (step S7), the image processing unit 25 uses the same image as in step S6, and includes a high step mark 32 at the center of the visual field (object height 0 μm), a low step mark 31 with an object height −10 μm, Attention is paid to the high step mark 30 of −20 μm (FIG. 7B). Then, considering that these three marks 30 to 32 constitute double marks having different steps inside and outside, a TIS value is obtained.

  This TIS value reflects the influence of the illumination telecentre (the inclination of the principal ray of the illumination light L1) at the point where the high step mark 30 is positioned (object height −20 μm). The influence of the illumination telecentre at each of the point where the low step mark 31 is positioned (object height −10 μm) and the point where the high step mark 32 is positioned (object height 0 μm) is very small and can be ignored. it can. Then, the TIS value at this point (object height −20 μm) is stored in the memory as TIS (−20).

  At this time, the memory of the image processing unit 25 includes TIS (-20) at a point where the object height is −20 μm in the field of view area, TIS (0) at the center of the field of view (point where the object height is 0 μm), TIS (+20) at the point of high +20 μm is stored. These TIS (-20), TIS (0), and TIS (+20) reflect the effect of illumination telecentric at different evaluation points in the field of view (for example, object heights of 0 μm and ± 20 μm). .

  Therefore, as described above, high-level marks 30, 32, and 34 are positioned at a plurality of different evaluation points in the field of view (for example, points having an object height of 0 μm and ± 20 μm), and an image is obtained using these marks as evaluation marks. In order to generate inclination information (for example, TIS (−20), TIS (0), TIS (+20), etc.) of the chief ray of the illumination light L1 at each evaluation point based on the brightness information included in the captured image, Variations in illumination telecentricity within the field of view can be evaluated.

  In addition to the above-mentioned TIS values, indices used for evaluating the variation of illumination telecentric values include correlation values related to the asymmetry of the light / dark information of the image (light / dark information of the high step marks 30, 32, 34), the width of the dark portion, etc. May be used. The illumination optical system (14-19, 40) illuminates an object such as the substrate 11 by generating tilt information of the principal ray of the illumination light L1 based on the brightness information of the high step marks 30, 32, and 34. It is possible to evaluate the variation of the lighting telecentre. In the case where the above correlation value, the width of the dark portion, or the like is used as an index, the low step marks 31 and 33 may be omitted.

In order to obtain an index (for example, TIS value) used for evaluating the variation of the illumination telecentre with high sensitivity, it is preferable to increase the step h ₁ of the high step marks 30, 32, and 34. However, if the level difference h ₁ is too large, the brightness / darkness information of the image becomes broad due to the focus shift, and the reproducibility when obtaining the index decreases. For this reason, in this embodiment, the upper limit “3 (λ / NA ² )” and the lower limit “(λ / NA ² )” as in the conditional expression (1) are set for the step h ₁ . . “Λ / NA ² ” in conditional expression (1) corresponds to twice the focal depth of the overlay measurement apparatus 10.

  In the present embodiment, the low step marks 31 and 33 are positioned at points away from the high step marks 30, 32, and 34 in the field of view, and the low step marks 31 and 33 are used as auxiliary marks. Therefore, based on the brightness information of each mark included in the image, the amount of positional deviation between the high step evaluation mark and the low step auxiliary mark is obtained, and the inclination information of the principal ray of the illumination light L1 is obtained from this positional deviation amount. Can be generated. In this case, the variation of the illumination telecentricity can be more accurately evaluated as compared with the case where the correlation value or the width of the dark part is used as an index. The double mark does not have to be constituted by the high step evaluation mark and the low step auxiliary mark.

  Further, in the present embodiment, a double mark is constituted by a high step evaluation mark and a low step auxiliary mark, and a positional deviation amount is obtained before and after the double mark is inverted, and an average value of the positional deviation amount before and after the inversion is obtained. The principal ray tilt information of the illumination light L1 is generated from the (TIS value). For this reason, it is possible to accurately and accurately evaluate the variation of the illumination telecentric as compared with the case where the correlation value or the amount of positional deviation is used as an index.

In the present embodiment, since the plurality of high step marks 30, 32, 34 and the plurality of low step marks 31, 33 are alternately arranged in the field of view and positioned simultaneously, illumination at each evaluation point in the field of view is performed. When generating the tilt information of the chief ray of the light L1, it is not necessary to move the stage 12, and the variation in illumination telecentricity can be evaluated in a short time.
However, one high step evaluation mark may be sequentially positioned at each evaluation point in the field of view by moving the stage 12. Therefore, the present invention can be applied if the number of high step marks provided on the substrate 28 is one or more.

Further, in the present embodiment, the step h ₁ of the high step marks 30, 32, 34 satisfies the conditional expression (2), and the step h ₀ of the low step marks 31, 33 satisfies the conditional expression (4). . For this reason, in the images of the marks 30 to 34, it is possible to reduce the influence of the decentration coma aberration of the imaging optical system (18 to 23). For this reason, it is possible to evaluate the variation of the illumination telecentricity without being affected by the eccentric coma aberration.

  In the present embodiment, the line width of the marks 30 to 34 is, for example, about 3 μm. For this reason, in the images of the marks 30 to 34, each edge image is shifted in the opposite direction, and the amount of change in the center position of each mark may be considered to be minute. That is, the influence of field curvature can be reduced. For this reason, the variation in illumination telecentricity can be evaluated without being affected by the curvature of field.

Furthermore, in the present embodiment, the illumination optical system (14-19, 40) is added to the overlay measuring apparatus 10 as long as the substrate 28 on which the processing of the evaluation marks 30-39 and the like are performed and the image analysis software are prepared. Evaluation can be performed easily and in a short time in the built-in state.
(Second Embodiment)
When evaluating variations in illumination telecentricity, decentration coma and curvature of field of the imaging optical system (18 to 23) can be reduced by the above-mentioned mark shape, but the effect of distortion may remain. For this reason, it is preferable to correct the influence of the distortion of the imaging optical system (18 to 23) by performing the following processing.

In this case, marks 50 to 59 shown in FIG. 8 are used. The marks 50 to 59 have the same line width and interval as the above-described marks 30 to 39 (FIG. 3), and the steps h ₃ are all the same as the steps h ₀ of the low steps 31 and 33 (for example, 0.5. 16 μm).
After positioning the marks 50 to 59 (FIG. 8) in the field of view and taking the images of the marks 50 to 59 into the image processing unit 25, the same double mark setting as described above (see FIGS. 6 and 7) is performed. Go to find the TIS value for each double mark.

In this case, since all the marks 50 to 59 have low steps, the influence of the illumination telecentricity is not reflected in the TIS value. For the same reason as described above, the influence of decentration coma aberration and field curvature in the TIS value is also slight. Therefore, each TIS value obtained from the images of the marks 50 to 59 is considered to be an influence of distortion.
When the image processing unit 25 obtains the TIS value from the images of the marks 50 to 59, the TIS _dis (−20) at the point where the object height is −20 μm in the visual field region and the TIS at the center of the visual field (the point where the object height is 0 μm). _Dis (0), TIS _dis (+20) at the point of object height +20 μm is stored in the memory.

Then, according to the following formulas (5) to (7), TIS values including the influence of distortion (TIS (−20), TIS (0), TIS) obtained from the images of the marks 30 to 39 (FIG. 3) described above. Calculate the difference with (+20)).
TIS _tel (-20) = TIS (-20) -TIS _dis (-20) (5)
TIS _tel (0) = TIS (0) −TIS _dis (0) (6)
TIS _tel (+20) = TIS (+20) −TIS _dis (+20) (7)
The TIS values obtained in this way (TIS _tel (-20), TIS _tel (0), TIS _tel (+20)) eliminate the effects of distortion and represent the variation of illumination telecentricity within the field of view. ing. Therefore, by performing the processing as described above, it is possible to accurately evaluate the variation in illumination telecentricity without being affected by distortion.

It should be noted that TIS _tel (0) at the center of the visual field (the point where the object height is 0 μm) after the influence of the distortion is removed may be equal to or higher than the above threshold (for example, 0.2 nm). For this reason, the shift adjustment of the illumination aperture stop 14 (similar to step S4 in FIG. 4) is performed so that TIS _tel (0) after the influence of distortion is removed becomes smaller than a threshold value (for example, 0.2 nm). Is preferred.

Then, after this shift adjustment, TIS _dis (−20) and TIS _dis (+20) at the point where the object height is ± 20 μm are obtained, so that the difference in illumination telecentric for each object height in the field of view (with respect to the center of the field of view). The difference in lighting telecentricity) can be obtained more accurately.
(Third embodiment)
Here, a method for adjusting the illumination optical system (14 to 19, 40) will be described.

When there is variation in illumination telecentricity within the field of view, even if the illumination telecentricity at the center of the field of view is substantially zero, the illumination telecentric around the field of view is not zero (see FIG. 7). In order to reduce such an error of the illumination telecentric, the following adjustment is performed.
The adjustment of the illumination optical system (14-19, 40) is performed by evaluating the illumination optical system (14-19, 40) described above, and the tilt information (for example, TIS (-20), TIS (0) of the principal ray of the illumination light L1. ), TIS (+20), TIS _tel (-20), TIS _tel (0), TIS _tel (+20), etc.), and the position of the illumination aperture stop 14 is determined based on the tilt information. This is done by adjusting the shift by a small amount in the direction parallel to the axis O1.

For example, shift adjustment in the optical axis direction of the illumination aperture stop 14 is performed so that TIS _tel (0) at the center of the field of view and TIS _tel (+20) at the object height +20 μm satisfy the following expression (8). .
| TIS _tel (+20) −TIS _tel (0) | <0.3 (8)
Here, assuming that TIS _tel (+20) = 0.3 nm and TIS _tel (0) = 0 nm, the tilt angle of the illumination telecentre (angle θ in FIG. 5) is evaluated on the object side. At the point where the object height is +20 μm, It is estimated to be 0 (mrad) at a point where the inclination angle = 0.27 (mrad) and the object height is 0 μm.

Further, in the illumination optical system (14 to 19, 40) of the present embodiment, it is assumed that the illumination aperture stop 14 is shifted by about 0.28 mm in the optical axis direction, and the tilt angle of the illumination telecentre (angle θ in FIG. 5) When the amount of change is evaluated on the object side, the amount of change is about 0.27 (mrad) at a point where the object height is +20 μm.
Therefore, if the illumination aperture stop 14 is shifted and adjusted in the optical axis direction based on these numerical values, the inclination of the principal ray of the illumination light L1 (for example, TIS _tel (-20), TIS _tel (+20), etc.) can be appropriately adjusted. Can be adjusted. That is, it is possible to appropriately adjust the variation of the illumination telecentricity within the field of view.

If the adjustment is performed so as to satisfy the above formula (8), not only the illumination telecentric error at the center of the field of view but also the illumination telecentric error around the field of view (for example, at an object height of ± 20 μm) is reduced. be able to. As a result, the illumination telecentric is in an ideal state as shown in FIG. 9, for example, and all the principal rays of the illumination light L1 are substantially parallel to the optical axis O2.
If the variation of the illumination telecentric is adjusted and managed to be smaller than a specific numerical value (for example, the threshold value 0.3 in the equation (8)) for each unit when the overlay measuring apparatus 10 is manufactured, the manufacturing for each unit is performed. Errors can be reduced, and stable device manufacturing is possible.

Furthermore, in the overlay measurement apparatus 10 in which the variation of the illumination telecentricity is managed, the accuracy of position detection and the measurement accuracy of the positional deviation amount L (FIG. 2) are improved, and it is possible to cope with the recent miniaturization of semiconductor devices. .
(Modification)
In the above-described embodiment, the example in which the high step marks 30, 32, 34 used for the evaluation of the illumination optical system (14-19, 40) are the step h ₁ = 4 μm has been described. It is not limited. As long as conditional expression (1) is satisfied, step h ₁ may be set to another value.

In the above-described embodiment, the example in which the low step marks 31 and 33 are the step h ₀ = 0.16 μm has been described, but the present invention is not limited to this. The step h ₀ may be set to another value within a range that satisfies the conditional expression (3), or may be set to a value smaller than the lower limit value of the conditional expression (3).
Furthermore, in the above-described embodiment, the steps h ₁ and h ₀ of the marks 30 to 34 have been described as satisfying the conditional expressions (2) and (4), but the present invention is not limited to this. If the influence of the decentration coma aberration of the imaging optical system (18 to 23) can be ignored, the steps h ₁ and h ₀ may not satisfy the conditional expressions (2) and (4).

In the above-described embodiment, the line width of the marks 30 to 34 is 3 μm, but the present invention is not limited to this. When the influence of the field curvature of the imaging optical system (18 to 23) can be ignored, the line width of the marks 30 to 34 may be set to a value other than 3 μm.
Furthermore, in the above-described embodiment, the interval between the marks 30 to 34 is 7 μm, but the present invention is not limited to this. The interval between the marks 30 to 34 may be set to a value other than 7 μm according to the object height at the evaluation point of the variation of the illumination telecentricity.

In the above-described embodiment, the example in which the evaluation marks 30 to 39 are convex bar marks has been described, but the present invention is not limited to this. In addition, a concave bar mark may be used for evaluation, or a BOX mark may be used.
Furthermore, in the above-described embodiment, the evaluation substrate 28 is fixed to the upper surface of the stage 12, and the evaluation marks 30 to 39 (FIG. 3) are formed on the substrate 28. However, the present invention is not limited to this. A tool substrate on which marks 30 to 39 similar to those described above are formed may be prepared, and this tool substrate may be mounted on the stage 12 instead of the substrate 11 and evaluated in the same procedure.

Further, in the above-described embodiment, when the variation in illumination telecentricity is evaluated, the processing for adjusting the illumination telecentricity at the center of the visual field to substantially zero (the processing in steps S3 and S4 in FIG. 4) is performed. It is not limited to this. Without such adjustment (for example, in the state shown in FIG. 6), the tilt information (for example, TIS (-20), TIS (0), TIS (+20), TIS) of the chief ray of the illumination light L1 from the mark image. _tel (-20), TIS _tel (0), TIS _tel (+20), etc.) may be generated and used as a result of the evaluation.

  Furthermore, in the above-described embodiment, the evaluation method has been described by taking the illumination optical system (14 to 19, 40) of the position detection device incorporated in the overlay measurement device 10 as an example, but the present invention is not limited to this. The present invention can also be applied to evaluation of an illumination optical system incorporated in an apparatus (for example, an alignment system of an exposure apparatus) that detects the position of an alignment mark. In this apparatus, the position of the alignment mark can be detected with high accuracy, which can contribute to the improvement of the alignment accuracy of the substrate.

1 is a diagram illustrating an overall configuration of an overlay measurement apparatus 10. It is a figure explaining the overlay mark 11A. It is a figure explaining the marks 30-39 used for evaluation of the variation of illumination telecentricity. It is a flowchart which shows the evaluation procedure of the variation of illumination telecentricity. It is a figure explaining the influence of illumination telecentricity. It is a figure explaining TIS (0) in the visual field center (object height 0 micrometer). It is a figure explaining TIS (+20) and TIS (-20) in a visual field periphery (object height +/- 20micrometer). It is a figure explaining the marks 50-59 used for distortion correction. It is a figure explaining the state after carrying out the shift adjustment of the illumination aperture stop 14 to an optical axis direction.

Explanation of symbols

10 overlay measurement apparatus; 11, 28 substrate; 12 stage;
13-19,40 illumination optical system; 18-23 imaging optical system;
24 CCD image sensor; 25 Image processing part; 30-39 Evaluation mark

Claims (5)

A first step of irradiating illumination light onto a predetermined region of an object plane of an imaging optical system that forms an optical image of an object using an illumination optical system to be evaluated;
In the state where the illumination light is irradiated on the predetermined area, one or more evaluation marks are sequentially or simultaneously positioned at a plurality of different evaluation points in the predetermined area, and auxiliary marks having a lower step than the evaluation mark, A second step of positioning at a point away from the evaluation mark within the predetermined region ;
A third step of capturing an image including light and dark information of the auxiliary mark together with light and dark information of the evaluation mark positioned at each of the plurality of evaluation points through the imaging optical system;
Based on the brightness information of each of the evaluation mark and the auxiliary mark included in the image, a positional deviation amount between the evaluation mark and the auxiliary mark is obtained, and each of the plurality of evaluation points is determined based on the positional deviation amount. A fourth step of generating tilt information of the chief ray of the illumination light in
The step h _{1 of the} evaluation mark satisfies the following conditional expression with respect to the center wavelength λ of the illumination light and the numerical aperture NA on the object side of the imaging optical system.
(λ / NA ² ) <h ₁ <3 (λ / NA ² )
A method for evaluating an illumination optical system. In the evaluation method of the illumination optical system according to claim 1,
The evaluation mark and the auxiliary mark constitute a double mark having different steps inside and outside ,
In the fourth step, the amount of positional deviation between the evaluation mark and the auxiliary mark is obtained before and after the double mark is reversed in a plane perpendicular to the optical axis of the imaging optical system. The tilt information is generated based on an average value of the amount of positional deviation of the illumination optical system. In the evaluation method of the illumination optical system according to claim 1 or 2 ,
In the second step, a plurality of the evaluation marks and a plurality of the auxiliary marks are alternately arranged in the predetermined area and simultaneously positioned . In the evaluation method of the illumination optical system according to any one of claims 1 to 3,
The step h _{1 of the} evaluation mark and the step h _{0 of the} auxiliary mark satisfy the following conditional expression with respect to the center wavelength λ of the illumination light and arbitrary integers m ₁ and m ₀ , respectively.
h ₁ = m ₁ × (λ / 4)
h ₀ = m ₀ × (λ / 4)
A method for evaluating an illumination optical system. After more generate the gradient information to the evaluation method of the illumination optical system according to claims 1 to any one of claims 4, based on the inclination information, the optical axis position of the aperture stop of the illumination optical system method of adjusting the illumination optical system, wherein you shift adjustment in a direction parallel to the.

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