JP2011118269A - Method for adjusting objective lens, objective lens unit, and surface inspection device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for adjusting an objective lens which prevents misdetections that accompany a change in the environmental temperature. <P>SOLUTION: The method for adjusting the objective lens composed of a plurality of lenses including a lens using a crystalline material, includes change amount calculating steps (steps S101 to S103) of obtaining a thermal stress produced in the objective lens by the change in the environmental temperature and obtaining the state change in the light that passes through the objective lens produced by the thermal stress; an adjustment amount calculating step (step S104) of calculating the crystal orientation of a lens (ninth lens) by using the crystalline material that cancels out the obtained state change of the light so that the state of the light passing through the objective lens becomes constant, regardless of the change in the environmental temperature; and an adjustment step (step S105) of making the lens (ninth lens) rotate by using the crystalline material around the optical axis so as to obtain the calculated crystal orientation. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a surface inspection apparatus for inspecting the surface of a semiconductor wafer, a liquid crystal substrate or the like, and more particularly to an objective lens used in such a surface inspection apparatus and an adjustment method thereof.

  Various methods for inspecting the cross-sectional shape by observation using a scanning electron microscope (hereinafter referred to as SEM) have been proposed as methods for determining the quality of a pattern formed on the surface of a semiconductor wafer (hereinafter referred to as wafer). ing. The cross-sectional shape inspection by the SEM was performed by scanning an electron beam applied to the pattern on the substrate to be inspected (sample) in the cross-sectional direction of the pattern, and detecting, analyzing, and analyzing reflected electrons and secondary electrons from the pattern. This is performed by a method for obtaining the cross-sectional shape of the portion. By performing the above scanning at several points on the pattern, the quality of the entire pattern is determined.

  In the inspection method using SEM, an operation of irradiating and scanning an electron beam on a pattern is repeated many times, so that it takes a long time to obtain the shape of the pattern. Further, since the observation magnification is high, as described above, it is difficult to obtain all pattern shapes on the wafer, and the quality of the entire wafer is determined by sampling some points. As a result, even if there is a defect in a portion other than the sampled pattern, it is overlooked. In the resist pattern, when the electron beam is irradiated, the electron beam is absorbed and charged by the resist by the acceleration voltage, and the pattern is lost. In some cases, discharge occurs and the pattern collapses, resulting in inconvenience in the subsequent process. Therefore, it is necessary to obtain optimum observation conditions while changing the acceleration voltage and the observation magnification in various ways. Therefore, more time is required for measurement.

  Other methods for determining the quality of the pattern include CD measurement using a scatterometer, in-line inspection technology for overlay, and the like. A spectroscopic scatterometer examines the properties of scattered light at a fixed angle as a function of wavelength. Normally, a broadband light source that is a halogen-based light source such as xenon, deuterium, or a xenon arc lamp is used. The fixed angle may be normal incidence or oblique incidence. Angle-resolved scatterometers characterize scattered light at a fixed wavelength as a function of incident angle. Normally, a laser is used as a single wavelength light source.

  The problem with angle resolved scatterometers is that they only detect one wavelength at a time. Therefore, a spectrum having a plurality of wavelengths must be detected by time-division multiplexing of the wavelengths, and it takes time to detect and process the spectrum, increasing the total data acquisition time. Further, in the spectroscopic scatterometer, since a small grating must be illuminated with a small incident angle, the amount of light from the extended light source is wasted. As a result, the level of light reaching the photodetector is lowered, the data acquisition time is lengthened, and the throughput is negatively affected. In addition, if the data acquisition time is shortened, the test result may not be stable.

  In view of such circumstances, a method for detecting a change in the line width of a fine pattern as a change in structural birefringence amount (hereinafter referred to as an APM-PER inspection method) has been proposed (see, for example, Patent Document 1). . In this method, when a fine pattern is condensed and illuminated with linearly polarized light, the reflected light becomes elliptically polarized light due to structural birefringence in the fine pattern. As a result, the amount of light passing through the analyzer in the crossed Nicols state (with the polarizer) changes in accordance with the line width of the pattern, and the amount of change is measured by pupil image observation. With this method, the relationship between the line width and the gradation value (the amount of light in the pupil image) can be detected as shown in FIG. That is, by measuring the gradation value in the pupil image and referring to the data table based on FIG. 13, the line width converted value of the fine pattern can be obtained.

International Publication No. 2008/015973 Pamphlet

  However, in such measurement by the APM-PER inspection method, when the environmental temperature changes, the amount of light passing through the analyzer through the objective lens changes, which may reduce the inspection accuracy.

  The present invention has been made in view of such problems, and an object of the present invention is to provide an objective lens adjustment method, an objective lens unit, and a surface inspection apparatus that prevent erroneous detection accompanying changes in environmental temperature. .

  In order to achieve such an object, an objective lens adjustment method according to the present invention is an objective lens adjustment method including a plurality of lenses including a lens using a crystalline material, and the objective lens is adjusted according to a change in environmental temperature. A thermal stress generated in the lens, a change amount calculating step for determining a change in the state of light passing through the objective lens caused by the thermal stress from the determined thermal stress, and a state of the light passing through the objective lens is the environmental temperature An adjustment amount calculating step for calculating the crystal orientation of the lens using the crystalline material so as to cancel the change in the obtained light state so as to be constant regardless of the change, and the calculated crystal orientation are obtained. An adjustment step of rotating the lens using the crystalline material around the optical axis.

  In the adjustment method described above, the state of the light is a phase of polarized light passing through the objective lens, and in the change amount calculation step, a lens excluding a lens using the crystalline material among the plurality of lenses. In each of the above, the phase change amount of the polarized light passing through the lens caused by the thermal stress is obtained individually, and the sum of the individually obtained phase change amounts is calculated, and in the adjustment amount calculating step, the polarized light passing through the objective lens is calculated. It is preferable to calculate the crystal orientation of the lens using the crystalline material so as to cancel the total of the calculated phase change amounts so that the phase of the lens becomes constant regardless of the change in the environmental temperature.

  In the adjustment method described above, the light state is a polarization state of polarized light passing through the objective lens, and the change amount calculating step excludes a lens using the crystalline material from the plurality of lenses. For each lens, the polarization state change amount of the polarized light passing through the lens caused by the thermal stress is obtained individually, and the sum of the individually obtained polarization state change amounts is calculated, and in the adjustment amount calculating step, the objective lens The crystal orientation of the lens using the crystalline material is calculated so as to cancel the total of the calculated amount of change in the polarization state so that the polarization state of the polarized light passing through is constant regardless of the change in the environmental temperature. You may do it.

  In addition, an objective lens unit according to the present invention includes an objective lens including a plurality of lenses including a crystalline lens, and a holding unit that holds the objective lens, and the holding unit emits light to the crystalline lens. The objective lens is adjusted using the objective lens adjustment method according to the present invention by having a rotation mechanism that rotates about an axis, and rotating the crystalline lens by the rotation mechanism. .

  Further, the surface inspection apparatus according to the present invention includes an objective having a stage for supporting a substrate having a predetermined repetitive pattern formed on the surface, and an objective lens and a holding portion for holding the objective lens so as to face the stage. A lens unit; an illumination unit that irradiates linearly polarized light on the surface of the substrate supported by the stage via the objective lens by epi-illumination; and reflected light from the surface of the substrate irradiated with the illumination light. A polarization component substantially perpendicular to the polarization direction of the linearly polarized light in the reflected light received by the objective lens on the pupil plane of the objective lens or a plane conjugate with the pupil plane. A detection unit for detecting, and an inspection unit for inspecting the presence or absence of a defect in the repetitive pattern based on information on the polarization component detected by the detection unit, Object lens unit is in an objective lens unit according to the present invention.

  According to the present invention, it is possible to prevent erroneous detection associated with a change in environmental temperature.

It is a flowchart which shows the adjustment method of the objective lens which concerns on 1st Embodiment. It is a flowchart which shows the adjustment method of the objective lens which concerns on 2nd Embodiment. It is a figure which shows the outline | summary of a surface inspection apparatus. (A), (b) is a figure which shows the example of the division | segmentation of a pupil image. It is a figure which shows the surface of a wafer. It is a figure which shows the detail of an objective lens. It is a figure which shows an example of the amount of retardation changes by the temperature fluctuation of a 9th lens. It is a figure which shows an example of the total amount of retardation changes except a 9th lens. It is a figure which shows an example of the result of adding the retardation variation | change_quantity by the temperature fluctuation of a 9th lens to the total retardation variation | change_quantity except the 9th lens. It is a figure which shows an example of the leakage light variation | change_quantity by the temperature fluctuation of a 9th lens. It is a figure which shows an example of the total amount of leakage light changes except a 9th lens. It is a figure which shows an example of the result of having added the amount of leakage light changes by the temperature fluctuation | variation of a 9th lens to the total amount of leakage light changes except a 9th lens. It is a figure which shows the relationship between line width and a gradation value.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. FIG. 3 shows a surface inspection apparatus 1 according to this embodiment. The surface inspection apparatus 1 includes a stage 10 that supports a wafer 5, an objective lens unit 50 and a half mirror 12, and illumination light on the surface of the wafer 5 supported by the stage 10 via the half mirror 12 and the objective lens unit 50. Illuminating unit 20, a detection unit 30 that detects the reflected light reflected by the surface of the wafer 5 through the objective lens unit 50 and the half mirror 12, and a data processing unit 45. Composed.

  The objective lens unit 50 includes an objective lens 51 and a holding portion 52 that holds the objective lens 51 so as to face the stage 10. The holding unit 52 incorporates a rotation mechanism 53 that rotates a part of the objective lens 51 (a ninth lens G9 described later) about the optical axis.

  As shown in FIG. 6, the objective lens 51 is arranged in order from the wafer 5 side, the first lens G1 being a convex meniscus lens on the image side, the second lens G2 being a convex meniscus lens on the image side, A third lens G3 that is a concave lens, a fourth lens G4 that is a convex lens, a fifth lens G5 that is a convex lens, a sixth lens G6 that is a concave lens, a seventh lens G7 that is a convex lens, and the object side (wafer 5) The eighth lens G8 that is a convex meniscus lens, the ninth lens G9 that is a convex lens, the tenth lens G10 that is a convex lens, the eleventh lens G11 that is a concave lens, and the twelfth lens G12 that is a convex lens. And a thirteenth lens G13 which is a concave lens. Of the first to thirteenth lenses G1 to G13, the fifth lens G5 and the ninth lens G9 are made of crystalline fluorite, and the remaining lenses are made of an amorphous glass material. . In FIG. 3, the description of the objective lens 51 is simplified.

  As shown in FIG. 3, the illumination unit 20 includes, in order from the light source side, a light source 21 such as a white LED or a halogen lamp, a condenser lens 22, a uniformizing illumination unit 23 including an interference filter, an aperture stop 24, The first field stop 25, the relay lens 26, and the polarizer 27 are configured, and are arranged in this order on the optical axis. In such an illumination unit 20, the light emitted from the light source 21 passes through the aperture stop 24 and the first field stop 25 via the condenser lens 22 and the uniformizing illumination unit 23, and is collimated by the relay lens 26. . The light collimated by the relay lens 26 is transmitted through the polarizer 27, reflected downward by the half mirror 12, and then guided to the surface of the wafer 5 placed on the stage 10 through the objective lens 51.

  The aperture stop 24 and the first field stop 25 are respectively the shape of the opening (particularly, the size of the diameter in the linear direction connecting the optical axis and the opening) and the opening in the plane orthogonal to the optical axis. The structure can change the position. Therefore, when the shape and position of the opening of the aperture stop 24 are changed, the opening angle of the illumination light irradiated on the surface of the wafer 5 is changed, and the shape and position of the opening of the first field stop 25 is changed. The size of the illumination area (illumination range) on the surface of the wafer 5 can be changed.

  The pupil planes of the aperture stop 24 and the objective lens 51 are arranged at positions approximately twice the focal length of the relay lens 26 with the relay lens 26 interposed therebetween. Therefore, an image of the aperture of the aperture stop 24 is formed on or near the pupil plane of the objective lens 51, and is further condensed by the objective lens 51 and irradiated onto the surface of the wafer 5. That is, the aperture stop 24 and the pupil plane of the objective lens 51 have a conjugate relationship. Further, the optical axis of the illuminating unit 20 is arranged so as to substantially coincide with the optical axis of the detecting unit 30 by the half mirror 12, and is configured to coaxially illuminate the wafer 5 on the stage 10.

  Here, assuming that the optical axis of the coaxial epi-illumination is the Z-axis, and the axes that pass through the Z-axis and are orthogonal to each other in a plane perpendicular to the Z-axis are the X-axis and the Y-axis, respectively, , Movable in the Z-axis direction and rotatable about an axis parallel to the Z-axis. The polarizer 27 is set so as to emit linearly polarized light that oscillates in a direction perpendicular to the paper surface of FIG. 3 (X-axis direction). Illumination light (linearly polarized light) irradiated on the surface of the wafer 5 by the coaxial incident illumination may be reflected by the surface of the wafer 5, return to the objective lens 51 again, pass through the half mirror 12, and enter the detection unit 30. it can.

  The detector 30 includes an analyzer 31, a first imaging lens 32, a half prism 33, a second imaging lens 34, a second field stop 35, two image sensors 41, in order from the wafer 5 side. 42 and arranged in this order on the optical axis. In such a detector 30, the reflected light from the wafer 5 that has passed through the half mirror 12 passes through the analyzer 31, is collected by the first imaging lens 32, and enters the half prism 33. The half prism 33 transmits part of the light and reflects the remaining light. The light reflected by the half prism 33 reaches the second image sensor 42 and forms an image of the wafer 5. . On the other hand, the light transmitted through the half prism 33 is further condensed by the second imaging lens 34, reaches the second field stop 35, forms an image of the wafer 5, and reaches the first imaging element 41. A pupil image of the objective lens 51 is formed.

  The first image sensor 41 is disposed at a position for detecting an image (pupil image) of the pupil plane of the objective lens 51, that is, at a position conjugate with the pupil plane of the objective lens 51. Imaging (detection) is performed, and a detection signal is output to the data processing unit 45. The second image sensor 42 is disposed at a position where the image of the wafer 5 is detected, that is, a position conjugate with the surface of the wafer 5, images (detects) the image of the wafer 5, and outputs a detection signal to the data processing unit 45. Output to. The second field stop 35 is disposed at a position conjugate with the surface of the wafer 5 and has an aperture shape that can move in the X-axis and Y-axis directions with respect to the optical axis (Z-axis). Images detected by the first image sensor 41 and the second image sensor 42 can be observed by the image display device 46 via the data processing unit 45. Therefore, by observing the image detected by the second image sensor 42 with the image display device 46, it is possible to confirm which position on the wafer 5 is irradiated with the illumination light. The data processing unit 45 is electrically connected to a storage unit 47 that stores a data table to be described later.

  The polarizer 27 and the analyzer 31 are set so as to satisfy the crossed Nicols condition. For this reason, unless the polarization main axis rotates in the repetitive pattern 6 on the surface of the wafer 5 (see FIG. 5), the detected light amount becomes almost zero.

  As described above, the surface inspection apparatus 1 of the present embodiment is configured to detect a change in the line width of the fine repetitive pattern 6 (see FIG. 5) on the surface of the wafer 5 as a structural birefringence change. The reflected light from the pattern having structural birefringence has a phase difference between a component parallel to the vibration plane of incident light (linearly polarized light) and a component perpendicular to the surface depending on the pattern shape on the surface of the wafer 5 and the underlying structure. The amplitude changes and becomes elliptically polarized light. For this reason, in the surface inspection apparatus 1 of the present embodiment, the fine repetitive pattern 6 on the surface of the wafer 5 is condensed and illuminated by the linearly polarized light by the polarizer 27, and the reflected light elliptically polarized by the fine repetitive pattern 6 is crossed. A change in the amount of light transmitted through the Nicol analyzer 31 is measured using a pupil image. That is, the linearly polarized light irradiated on the surface of the wafer 5 becomes elliptically polarized light, is reflected, passes through the analyzer 31, and changes in luminance and hue are generated in the pupil image formed on the imaging surface of the first image sensor 41. Therefore, this is measured and the surface inspection of the wafer 5 is performed.

  As a specific inspection method, for example, a pupil image (reference image) of a wafer (a reference wafer, hereinafter referred to as “reference wafer”) having a normal pattern by the surface inspection apparatus 1 of the present embodiment is used. Image acquisition is performed, and then a pupil image (detection image) of the wafer 5 to be inspected is acquired and the data processor 45 compares the difference in luminance (gradation value) for each pixel between the reference image and the detection image. However, it may be determined that there is a defect when the difference exceeds a predetermined threshold in a certain pixel. The pixels to be compared need not be all pixels, and only pixels on a predetermined line (radiation direction) passing through the optical axis may be compared. In addition, if there is a defect, the symmetry of the reflected light is lost and a difference occurs in the luminance or hue between the symmetrical portions with respect to the optical axis of the pupil image. By detecting this difference, the defect is detected. be able to.

  Further, as described above, the surface inspection apparatus 1 of the present embodiment can change the opening angle of the illumination light irradiated on the wafer 5 by changing the position of the opening of the aperture stop 24. In other words, in the pupil image captured by the first image sensor 41, the optical axis corresponds to an aperture angle of 0 °, and the aperture angle increases toward the periphery of the pupil image. Therefore, the pupil image is divided into regions inside and outside the corresponding circle when the incident angle to the wafer 5 is 45 °, and the difference between the reference image and the detection image in each region is detected. The presence or absence of defects may be inspected based on the above.

  Also, for example, as shown in FIG. 4A, the pupil image 60 is divided into a circular area E at the center and four areas A, B, C, and D that radiate from the center to the surrounding area. It is possible to divide and detect a difference between the reference image and the detected image in each of the five areas A to E, and detect a defect based on the result. Alternatively, as shown in FIG. 4 (b), the pupil image 60 has eight circular shapes arranged concentrically so as to surround the central region I and the peripheral region I in the peripheral portion. In other words, the difference between the reference image and the detected image in each of the nine regions A to I is detected, and a defect may be detected based on the result.

  Note that, as a method for detecting such a defect, the comparison of the image of the pupil plane of the objective lens 51 is used because the pitch of the repetitive pattern 6 (see FIG. 5) is the surface in a simple image of the surface of the wafer 5. This is because the resolution is below the resolution of the inspection apparatus 1 and optical detection is not possible even if there is a defect. The reason why the position and shape of the opening of the second field stop 35 are variably configured is that information on a region of an appropriate position and size on the wafer 5 can be detected. Further, the illumination σ (the illumination NA / the objective lens NA) is variable by the aperture stop 24, and the wafer 5 can be illuminated with an appropriate brightness.

  As described above, the defect of the wafer 5 to be inspected can be detected by comparing the gradation values of the reference image and the detection image. The gradation values having the relationship shown in FIG. If the data table in which the line width is associated is stored in the storage unit 47, the line width of the repetitive pattern 6 (see FIG. 5) formed on the surface of the wafer 5 is calculated from the gradation value of the detected image. be able to. Thereby, numerical management of the line width for each wafer 5 can be performed.

  By the way, as shown in FIG. 5, a repeated pattern 6 for a plurality of semiconductor chips is baked on the surface of the wafer 5. Therefore, the inspection of the wafer 5 by the surface inspection apparatus 1 of the present embodiment is performed on a plurality of inspection points on the surface of the wafer 5. For example, in the case of FIG. 5, the inspection is started from the inspection start point P1, and the inspection is repeatedly performed up to the inspection end point Pe while sequentially inspecting at the adjacent inspection points P2, P3,. Therefore, as described above, the pupil image (reference image) of the reference pattern formed on the surface of the reference wafer is captured and acquired using the reference wafer before the inspection is started, and then detected at each inspection point on the surface of the wafer 5. If the procedure is to take an image and compare the detected image at each inspection point with the reference image, if the ambient temperature changes during that time, the gradation value of each image will change and the image will be accurate. There is a possibility that inspection cannot be performed. For example, when the data table as shown in FIG. 13 is used, if the environmental temperature rises by + 1 ° C. from the reference temperature, a difference of about 12 gradations occurs in the correlation between the gradation value and the line width, and the line width conversion An error of about 0.8 nm occurs.

  The cause is that retardation (retardation) occurs in light passing through the objective lens 51 due to stress distortion caused by lens expansion in the objective lens 51 due to a change in environmental temperature. As a result, the linearly polarized light (illumination light) incident on the objective lens 51 changes to elliptically polarized light before reaching the wafer 5, and the amount of light transmitted through the analyzer 31 in the crossed Nicols state changes. . For this reason, the reliability of the inspection deteriorates due to the temperature difference between the inspection start time and the inspection end time of the wafer 5, the difference between the environmental temperature at the time of imaging the reference wafer and the environmental temperature at the time of inspection of the wafer 5, or the like.

  On the other hand, in the present embodiment, the objective lens 51 is adjusted so that the light passing through the objective lens 51 is not affected by the environmental temperature change. Therefore, an adjustment method of the objective lens 51 according to the first embodiment will be described with reference to the flowchart shown in FIG. First, the amount of thermal stress generated in the objective lens 51 is calculated by simulation using structure analysis software (step S101). Specifically, for the objective lens 51, a finite element model is created using structural analysis software (I-DEAS or the like), and due to the difference in thermal expansion coefficient between the materials of the lenses G1 to G13 and the material of the holding portion 52, For example, the stress distribution data of the lenses G1 to G13 generated when the environmental temperature rises by 1 ° C. is calculated. Note that the material of the holding portion 52 that holds the objective lens 51 is brass in this embodiment.

  When the amount of thermal stress generated in the objective lens 51 is calculated, one of the lenses G5 and G9 whose material is fluorite is selected (a fluorite lens having a large amount of retardation change with respect to the stress is preferable) and passes through a certain pupil position. For example, the amount of change in retardation due to thermal stress distortion of the fluorite lens (in this embodiment, the ninth lens G9) generated when the ambient temperature rises by 1 ° C., for example, is selected. ) While changing the crystal axis direction (around the optical axis) (step S102). The direction (crystal orientation) of the crystal axis of the fluorite lens is a rotation direction around the optical axis of the crystal axis with respect to the polarization direction of linearly polarized light incident on the objective lens 51, and is fluorite perpendicular to the optical axis. Is set to the (1,1,1) plane. Thereby, when the fluorite lens is rotated about the optical axis, the direction of the crystal axis of the fluorite lens changes at a period of 120 °.

  In order to obtain the retardation change amount, first, the stress distribution data calculated in step S101, the refractive indexes of the lenses G1 to G13, and the photoelastic constants of the lenses G1 to G13 (when the material is fluorite, the piezo optical coefficient) From the above, the inverse dielectric constant tensor of each of the lenses G1 to G13 is calculated. In the case of a lens using a normal glass material, the principal stresses are σ1, σ2, and σ3, respectively, and the refractive indexes felt by the electric field in the principal stress direction are n1, n2, and n3, respectively. When the rate is n0, the direct stress light constant is c1, and the lateral stress light constant is c2, the refractive index change due to stress can be expressed as the following equation (1).

  When light travels in the σ3 direction, the electric field directions are the σ1 direction and the σ2 direction. When stress in the σ1 direction is applied to the lens, the following equation (2) is obtained.

  Here, the proportional coefficient c is a photoelastic constant, and this number is generally described in catalogs and the like.

In the case of a lens using fluorite, when the piezo optical coefficient is π _ijkl , the reverse dielectric constant is β _ij , the stress is T _kl , and the vacuum dielectric constant is ε ₀ , the stress and the reverse dielectric constant change _slightly (The details of this relationship are described in Tomoya Ogawa, “Fundamentals of Crystal Engineering”, etc.) (Omitted). Here, subscripts i and j designate components of the electric flux density vector, and subscripts k and l designate components of the stress tensor.

  If the material has no absorption, the reverse dielectric constant β is expressed as the following equation (4) using the refractive index n.

  That is, the inverse dielectric constant tensor shows the difference in refractive index for each stress direction.

Next, when linearly polarized light is incident on the objective lens 51, the phase difference (retardation) between the phase eigenvector and the delay eigenvector of light passing through the pupil (45 ° direction) where NA = 0.58 is obtained by polarization. The calculation is performed by performing a ray tracing simulation considering the difference in refractive index depending on the direction. When the refractive index difference depending on the polarization direction is Δn, the in-lens optical path length is d, and the reference wavelength is λ ₀ , the retardation Δφ is expressed as the following equation (5).

  Next, when the reverse dielectric constant tensor obtained by using the equation (3) is input as a parameter of the ninth lens G9 that is the selected fluorite lens, the environmental temperature of the ninth lens G9 increases by 1 ° C. Is calculated by performing the ray tracing simulation described above.

  Then, by taking the difference between the normal retardation obtained earlier and the retardation when the environmental temperature rises by 1 ° C. for the ninth lens G9, the amount of change in retardation due to the temperature fluctuation of the ninth lens G9 is obtained. At this time, the amount of retardation change every time the crystal axis direction (crystal orientation) of the ninth lens G9 rotates by a predetermined angle (for example, 1 °, 5 °, etc.) while rotating the ninth lens G9 around the optical axis. For each. An example of the retardation change amount thus obtained is shown in FIG.

  When the amount of retardation change due to the thermal stress strain of the ninth lens G9 is obtained, the amount of retardation change due to the thermal stress strain of each lens other than the ninth lens G9 that occurs when the environmental temperature rises by 1 ° C. is investigated, respectively, and the total change The amount is obtained (step S103). Specifically, the retardation change amount due to the temperature fluctuation of the lens other than the ninth lens G9 is calculated in the same manner as in the previous step S102, and the total retardation change amount due to the temperature fluctuation of the lens other than the ninth lens G9 is calculated. . That is, the total retardation change amount due to the temperature fluctuation excluding the ninth lens G9 is obtained by adding the retardation change amount due to the temperature fluctuation of the lenses other than the ninth lens G9. At this time, the rotation of each lens such as the fifth lens G5 is not performed. An example of the total retardation change obtained in this way is shown in FIG.

  When the total retardation change amount by each lens other than the ninth lens G9 is obtained, the total retardation change amount obtained in step S103 is canceled out of the retardation change amounts obtained while changing the direction of the crystal axis of the ninth lens G9. The direction (crystal orientation) of the crystal axis of the ninth lens G9 is calculated (step S104). Specifically, as a result of adding the retardation variation due to the temperature variation of the ninth lens G9 to the total retardation variation due to the temperature variation of the lenses other than the ninth lens G9, the ninth lens G9 having the smallest retardation variation. The direction of the crystal axis (crystal orientation) is calculated.

  In the present embodiment, when the direction of the crystal axis of the ninth lens G9 is rotated by 105 °, the added total retardation change amount becomes the smallest. On the other hand, when the direction of the crystal axis of the ninth lens G9 is rotated by 30 ° or 60 °, the total retardation change amount increases. Further, when the direction of the crystal axis of the ninth lens G9 is rotated by 15 ° or 75 °, the total retardation change amount does not change so much and the ninth lens G9 does not contribute to the retardation change. The result of adding the retardation change amount due to the temperature variation of the ninth lens G9 to the total retardation change amount due to the temperature variation of the lenses other than the ninth lens G9 is 30 ° in the direction of the crystal axis of the ninth lens G9. FIG. 9 shows the cases of rotation by 75 ° and 105 °. FIG. 9 shows that the amount of retardation change due to temperature fluctuation can be controlled by the direction (crystal orientation) of the crystal axis of the ninth lens G9.

  Then, when the crystal axis direction (crystal orientation) of the ninth lens G9 that cancels the total retardation change amount is obtained, the rotation mechanism 53 can obtain the obtained crystal axis direction (crystal orientation). The lens G9 is rotated around the optical axis (step S105). In the present embodiment, the ninth lens G9 is rotated so that the crystal axis direction (crystal orientation) of the ninth lens G9 is 105 °. The rotation mechanism 53 may be configured to rotate the ninth lens G9 by an electric motor or the like, and may rotate the ninth lens G9 in response to a drive signal from the data processing unit 45 or the like. The ninth lens G9 may be rotated.

  As a result, according to the present embodiment, it is possible to realize a lens system in which the amount of retardation change due to temperature fluctuation is small. Therefore, it is possible to prevent erroneous detection accompanying changes in the environmental temperature, and high-precision inspection is possible.

  The retardation change amount also corresponds to a change in the amount of leakage light that passes through the analyzer 31 in the crossed Nicols state. The amount of leakage light can be calculated from the amount of change in the Stokes parameter. The Stokes parameter S0 is expressed by the following equation (6), where Ix is the amount of light in the polarization direction in the X-axis direction and Iy is the amount of light in the polarization direction in the Y-axis direction.

  The Stokes parameter S1 is expressed as the following equation (7).

  Assuming that the linearly polarized light from the polarizer 27 is light polarized in the X-axis direction, the light transmitted through the analyzer 31 in the crossed Nicol state is only light polarized in the Y-axis direction. That is, the amount of light leaking through the analyzer 31 in the crossed Nicols state is the amount of light Iy in the polarization direction in the Y-axis direction, and is expressed as in the following equation (8).

  Therefore, it is possible to pass through the objective lens 51 caused by the environmental temperature change by evaluating how much the amount of leakage light when the stress is applied changes with respect to the amount of leakage light when the stress is not applied. The change in the amount of light can be evaluated in the same manner as in the first embodiment. Therefore, an adjustment method of the objective lens 51 according to the second embodiment will be described with reference to the flowchart shown in FIG. First, the amount of thermal stress generated in the objective lens 51 is calculated by simulation using structure analysis software (step S201). That is, the stress distribution data of the lenses G1 to G13 is calculated in the same manner as in the first embodiment.

  When the amount of thermal stress generated in the objective lens 51 is calculated, the fluorite ninth lens G9 having a large amount of change in leakage light with respect to the stress is selected, and when the ambient temperature rises by 1 ° C. for a light beam passing through a certain pupil position. The amount of change in leakage light due to the thermal stress strain of the ninth lens G9 is examined while changing the direction of the crystal axis of the ninth lens G9 (around the optical axis) (step S202). In order to obtain the amount of change in leakage light, first, as in the case of the first embodiment, the inverse dielectric constant tensors of the lenses G1 to G13 are respectively calculated.

  Next, when linearly polarized light whose polarization direction is the X-axis direction is incident on the objective lens 51, the polarization component in the Y-axis direction of light passing through the pupil (45 ° direction) where NA = 0.58, that is, The amount of light leaking through the analyzer 31 in the crossed Nicols state is calculated by performing a ray tracing simulation considering polarization. Next, by inputting the inverse dielectric constant tensor obtained previously as a parameter of the ninth lens G9, the above-described ray tracing simulation is performed on the amount of leakage when the environmental temperature rises by 1 ° C. for the ninth lens G9. To calculate.

  Then, the amount of leakage light change due to temperature fluctuation of the ninth lens G9 is obtained by taking the difference between the normal amount of leakage light obtained previously and the amount of leakage light when the environmental temperature rises by 1 ° C. for the ninth lens G9. . At this time, the leakage light changes each time the direction of the crystal axis (crystal orientation) of the ninth lens G9 rotates by a predetermined angle (for example, 1 °, 5 °, etc.) while rotating the ninth lens G9 around the optical axis. Find each quantity. An example of the amount of change in leakage light obtained in this way is shown in FIG.

  When the amount of change in leakage light due to the thermal stress strain of the ninth lens G9 is obtained, the amount of change in leakage light due to the thermal stress strain of each lens other than the ninth lens G9 that occurs when the environmental temperature rises by 1 ° C. is investigated, respectively, Is obtained (step S203). Specifically, the amount of change in leakage light due to temperature fluctuations of lenses other than the ninth lens G9 is calculated in the same manner as in the previous step S202, and the total amount of change in light leakage due to temperature fluctuations of lenses other than the ninth lens G9 is calculated. calculate. That is, the total amount of change in leaked light due to temperature fluctuations excluding the ninth lens G9 is obtained by adding the amount of change in leaked light due to temperature fluctuations of lenses other than the ninth lens G9. At this time, the rotation of each lens such as the fifth lens G5 is not performed. An example of the total amount of change in leakage light obtained in this way is shown in FIG.

  When the total amount of leakage light change by each lens other than the ninth lens G9 is obtained, the total amount of leakage light change obtained in step S203 out of the amount of leakage light change obtained while changing the direction of the crystal axis of the ninth lens G9. The direction (crystal orientation) of the crystal axis of the ninth lens G9 that cancels the amount is calculated (step S204). Specifically, as a result of adding the leakage light change amount due to the temperature fluctuation of the ninth lens G9 to the total leakage light change amount due to the temperature fluctuation of the lenses other than the ninth lens G9, the leakage light change amount is the smallest. The direction (crystal orientation) of the crystal axis of the 9 lens G9 is calculated.

  In the present embodiment, when the direction of the crystal axis of the ninth lens G9 is rotated by 95 °, the added total leakage light change amount becomes the smallest. On the other hand, if the direction of the crystal axis of the ninth lens G9 is rotated by 30 ° or 60 °, the total amount of change in leakage light becomes large. Note that the result of adding the amount of leakage light change due to the temperature variation of the ninth lens G9 to the total amount of leakage light variation due to the temperature variation of the lens other than the ninth lens G9 is 30 directions of the crystal axis direction of the ninth lens G9. FIG. 12 shows the case where the angle is rotated by °, 95 °, and 105 °. From FIG. 12, it can be seen that the amount of change in retardation due to temperature fluctuation can be controlled by the direction (crystal orientation) of the crystal axis of the ninth lens G9.

  Then, when the direction of the crystal axis (crystal orientation) of the ninth lens G9 that cancels the total amount of leakage light change is obtained, the rotation mechanism 53 can obtain the obtained crystal axis direction (crystal orientation). The nine lens G9 is rotated around the optical axis (step S205). In the present embodiment, the ninth lens G9 is rotated so that the crystal axis direction (crystal orientation) of the ninth lens G9 is 95 °. The rotation mechanism 53 may be configured to rotate the ninth lens G9 by an electric motor or the like, and may rotate the ninth lens G9 in response to a drive signal from the data processing unit 45 or the like. The ninth lens G9 may be rotated.

  As a result, according to the present embodiment, it is possible to realize a lens system in which the amount of change in leakage light due to temperature fluctuation is small. Therefore, it is possible to prevent erroneous detection accompanying changes in the environmental temperature, and high-precision inspection is possible.

  In each of the above-described embodiments, the reason why the ninth lens G9 is selected as the fluorite lens for adjusting the direction of the crystal axis (crystal orientation) is that the retardation change amount with respect to the environmental temperature change (in comparison with the fifth lens G5) And the amount of change in leakage light) is large, and the amount of change in retardation (and change in the amount of leaked light) can be controlled effectively with a simple calculation. Therefore, by selecting the fifth lens G5 in addition to the ninth lens G9 as the fluorite lens for adjusting the crystal axis direction (crystal orientation), the calculation becomes complicated, but the retardation change amount (and the leakage light amount change) ) Can be expanded. That is, the rotation mechanism 53 is not limited to the ninth lens G9, and may have a configuration capable of independently rotating the ninth lens G9 and the fifth lens G5.

  Further, in each of the above-described embodiments, the calculation is performed by taking an increase of 1 ° C. as an example of a change in the environmental temperature, but the present invention is not limited to this. For example, the increase is 2 ° C. or 3 ° C. It may be 1 ° C. or 2 ° C. The change in the environmental temperature may be set so as to be different for each of the lenses G1 to G13 constituting the objective lens 51.

  In each of the above-described embodiments, the surface of the wafer 5 is inspected. However, the present invention is not limited to this. For example, the surface of a glass substrate can be inspected.

  In each of the above-described embodiments, the objective lens 51 (objective lens unit 50) attached to the surface inspection apparatus 1 is described as an example. However, the present invention is not limited to this. The present invention can also be applied to an objective lens that is attached to an optical apparatus that handles the above.

  In each of the above embodiments, a fluorite lens is used as a lens for adjusting the direction of the crystal axis (crystal orientation). However, the present invention is not limited to this, and a lens using a crystalline material is used. I just need it. Further, the objective lens 51 is composed of 13 lenses G1 to G13, but is not limited thereto, and may be 10 or 15 depending on the apparatus, including a lens using a crystalline material. What is necessary is just to be comprised from the some lens.

DESCRIPTION OF SYMBOLS 1 Surface inspection apparatus 5 Wafer 6 Repeat pattern 10 Stage 20 Illumination part 30 Detection part 45 Data processing part (inspection part)
50 Objective lens unit 51 Objective lens 52 Holding part 53 Rotating mechanism G1 First lens G2 Second lens G3 Third lens G4 Fourth lens G5 Fifth lens G6 Sixth lens G7 Seventh lens G8 Eighth lens G9 Ninth lens G10 10th lens G11 11th lens G12 12th lens G13 13th lens

Claims (5)

A method for adjusting an objective lens including a plurality of lenses including a lens using a crystalline material,
A change amount calculating step for obtaining a thermal stress generated in the objective lens due to a change in environmental temperature, and obtaining a change in the state of light passing through the objective lens caused by the thermal stress from the obtained thermal stress;
Adjustment for calculating the crystal orientation of the lens using the crystalline material so as to cancel the obtained change in the state of the light so that the state of the light passing through the objective lens is constant regardless of the change in the environmental temperature. A quantity calculating step;
An adjustment step of rotating a lens using the crystalline material around an optical axis so as to obtain the calculated crystal orientation. The light state is a phase of polarized light passing through the objective lens,
In the change amount calculating step, for each of the lenses other than the lens using the crystalline material among the plurality of lenses, the phase change amount of polarized light passing through the lens caused by the thermal stress is individually obtained, and the individual Calculate the total amount of phase change found in
In the adjustment amount calculating step, the crystalline material that cancels the calculated total amount of phase change is used so that the phase of polarized light passing through the objective lens is constant regardless of the change in the environmental temperature. 2. The method for adjusting an objective lens according to claim 1, wherein the crystal orientation of the lens is calculated. The light state is a polarization state of polarized light passing through the objective lens,
In the change amount calculating step, for each of the lenses excluding the lens using the crystalline material among the plurality of lenses, the polarization state change amount of the polarized light passing through the lens caused by the thermal stress is obtained individually, and Calculate the total amount of polarization state change obtained individually,
In the adjustment amount calculating step, the crystalline material that cancels the calculated total amount of change in the polarization state so that the polarization state of the polarized light passing through the objective lens is constant regardless of the change in the environmental temperature. The method for adjusting an objective lens according to claim 1, wherein the crystal orientation of the lens using the lens is calculated. An objective lens composed of a plurality of lenses including a crystalline lens;
A holding unit for holding the objective lens,
The holding portion has a rotation mechanism that rotates the crystalline lens about the optical axis,
The objective lens, wherein the objective lens is adjusted using the objective lens adjustment method according to claim 1 by rotating the crystalline lens by the rotating mechanism. unit. A stage for supporting a substrate having a predetermined repeating pattern formed on the surface;
An objective lens unit having an objective lens and a holding portion that holds the objective lens so as to face the stage;
An illumination unit that irradiates the surface of the substrate supported by the stage with linearly polarized light through the objective lens by epi-illumination;
The reflected light from the surface of the substrate irradiated with the illumination light is received through the objective lens, and the reflected light received by the objective lens on the pupil plane of the objective lens or a plane conjugate with the pupil plane. A detection unit for detecting a polarization component substantially perpendicular to the polarization direction of the linearly polarized light in the light;
An inspection unit that inspects the presence or absence of defects in the repetitive pattern based on the information of the polarization component detected by the detection unit;
5. The surface inspection apparatus according to claim 4, wherein the objective lens unit is the objective lens unit according to claim 4.

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