JP2011123397A - Objective lens unit and surface inspection device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an objective lens unit capable of preventing false detection accompanied by the environmental temperature change. <P>SOLUTION: The objective lens unit includes an objective lens 51 including a plurality of lenses G1 to G13 including a lens using an amorphous material, and a lens barrel member for supporting the objective lens 51. With the premise that the linear expansion coefficient of the material of the lens barrel member is α1, the linear expansion coefficient of the material of the lens using the amorphous material out of the plurality of the lenses G1 to G13 is α2, the outer diameter of the lens using the amorphous material is D, the photoelastic constant of the material of the lens using the amorphous material is β, and an optical path length to have the maximum numerical aperture in the lens using the amorphous material is L, all the lenses using the amorphous material in the plurality of the lenses G1 to G13 satisfy conditional expression: ¾(α1-α2)×D×β×L¾<12,000. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a surface inspection apparatus that inspects the surface of a semiconductor wafer, a liquid crystal substrate, or the like using polarized light, and more particularly to an objective lens unit used in such a surface inspection apparatus.

  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, the line width converted value of the fine pattern can be obtained by measuring the gradation value in the pupil image and referring to the data table based on FIG.

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 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 unit according to the present invention includes an objective lens including a plurality of lenses including a lens using an amorphous material, and a lens barrel member that holds the objective lens. A lens using the amorphous material, where α1 is a linear expansion coefficient of the material of the lens barrel member, and α2 is a linear expansion coefficient of the lens material using the amorphous material among the plurality of lenses. And D is the photoelastic constant of the lens material using the amorphous material, and L is the optical path length that maximizes the numerical aperture in the lens using the amorphous material. Then, the lenses using all the amorphous materials in the plurality of lenses are represented by the following formula: | (α1-α2) × D × β × L | <12000
The conditions are satisfied.

If the direct stress light constant of the lens material using the amorphous material is c1, the following formula: | (α1-α2) × D × c1 × L | <12000
The conditions are satisfied.

Further, when the lateral stress light constant of the lens material using the amorphous material is c2, the following formula: | (α1-α2) × D × c2 × L | <12000
The conditions are satisfied.

In addition, an objective lens unit according to the present invention includes an objective lens including a plurality of lenses including a lens using an amorphous material, and a lens barrel member that holds the objective lens. The linear expansion coefficient of the lens material using the amorphous material is α2, the linear expansion coefficient of the lens material bonded to the lens using the amorphous material is α3, and the amorphous material An optical path where the outer diameter of the lens using the amorphous material is D, the photoelastic constant of the lens material using the amorphous material is β, and the numerical aperture in the lens using the amorphous material is maximized When the length is L, all the lenses using the amorphous material in the plurality of lenses are represented by the following formula: | (α3-α2) × D × β × L | <12000
The conditions are satisfied.

When the direct stress light constant of the lens material using the amorphous material is c1, the following expression: | (α3-α2) × D × c1 × L | <12000
The conditions are satisfied.

When the lateral stress light constant of the lens material using the amorphous material is c2, the following formula: | (α3-α2) × D × c2 × L | <12000
The conditions are satisfied.

An objective lens unit according to the present invention includes an objective lens including a plurality of lenses including a lens using an amorphous material, and a lens barrel member that holds the objective lens, and the material of the lens barrel member The linear expansion coefficient of the lens is α1, the linear expansion coefficient of the lens material using the amorphous material among the plurality of lenses is α2, and the lens material joined to the lens using the amorphous material The coefficient of linear expansion of the lens is α3, the outer diameter of the lens using the amorphous material is D, the photoelastic constant of the lens material using the amorphous material is β, and the amorphous material is When the optical path length at which the numerical aperture in the lens using the material is maximum is L, all the lenses using the amorphous material in the plurality of lenses are expressed by the following formulas (| α1-α2 | + | α3 −α2 |) × D × | β | × L <20000
The conditions are satisfied.

If the direct stress light constant of the lens material using the amorphous material is c1, the following formula (| α1-α2 | + | α3-α2 |) × D × | c1 | × L <20000
The conditions are satisfied.

When the lateral stress optical constant of the lens material using the amorphous material is c2, the following formula (| α1-α2 | + | α3-α2 |) × D × | c2 | × L <20000
The conditions are satisfied.

  Further, the surface inspection apparatus according to the present invention includes a stage that supports a substrate having a predetermined repeating pattern formed on the surface, an objective lens, and a lens barrel member that holds the objective lens so as to face the stage. An objective lens unit, an illumination unit for irradiating the surface of the substrate supported by the stage with linearly polarized light through the objective lens by epi-illumination, and reflected light from the surface of the substrate irradiated with the illumination light Of the reflected light received by the objective lens on a pupil plane of the objective lens or a plane conjugate with the pupil plane, and a polarization component substantially perpendicular to the polarization direction of the linearly polarized light. A detection unit for detecting the presence of defects in the repetitive pattern based on information on the polarization component detected by the detection unit, An objective 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 figure which shows the detail of an objective lens. 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 an example of the amount of retardation changes by a temperature fluctuation. It is a table | surface which shows the example of calculation of (4) Formula in embodiment. It is a table | surface which shows the example of calculation of (7) Formula in embodiment. 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. A surface inspection apparatus 1 according to the present embodiment is shown in FIG. 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 lens barrel member 52 that holds the objective lens 51 so as to face the stage 10. As shown in FIG. 1, the objective lens 51 is arranged in order from the wafer 5 side, a first lens G1 that is a convex meniscus lens on the image side, a second lens G2 that is 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. . The material of the lens barrel member 52 is brass. In FIG. 2, the description of the objective lens 51 is simplified.

  As shown in FIG. 2, 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 vibrates in the direction perpendicular to the paper surface of FIG. 2 (X-axis direction). Illumination light (linearly polarized light) irradiated on the surface of the wafer 5 by the coaxial incident illumination may be reflected on 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 is rotated by the repetitive pattern 6 on the surface of the wafer 5 (see FIG. 4), 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. 4) on the surface of the wafer 5 as a change in structural birefringence amount. 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.

  Further, for example, as shown in FIG. 3A, the pupil image 60 is divided into a circular region E in the center and four regions A, B, C, and D that radiate from the center to the surrounding region. 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. 3 (b), the pupil image 60 has eight circular shapes arranged concentrically so as to surround the central region I in the central region I and the peripheral region I. 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.

  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. 4) is the surface of 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. 4) 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.

  Incidentally, as shown in FIG. 4, 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.

  In the surface inspection apparatus 1 of the present embodiment, when retardation due to temperature change occurs in any optical member other than the wafer 5, the amount of light transmitted through the analyzer 31 in the crossed Nicols state is increased. Therefore, if the line width is converted based on the gradation value, a line width error occurs, and the measurement accuracy of the line width decreases. That is, when the environmental temperature changes, the line width measurement accuracy decreases. For example, when the data table as shown in FIG. 8 is used, when the environmental temperature rises by + 1 ° C. from the reference temperature, a difference of about 12 gradations is generated in the correlation between the gradation value and the line width, and the line width conversion is performed. An error of about 0.8 nm occurs.

  The cause is that 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 designed so that the light passing through the objective lens 51 is not affected by the environmental temperature change. In order to minimize the influence of the environmental temperature, it is important to reduce the stress distortion generated in the objective lens 51. For this purpose, it is necessary to reduce the stress received by each of the lenses G1 to G13 and to reduce the strain generated by the received stress. In order to reduce the stress received by each of the lenses G1 to G13, it is preferable that the linear expansion coefficient of the material of the lens barrel member 52 is close to the linear expansion coefficient of the material of the lenses G1 to G13.

  The stress received by each lens G1 to G13 is proportional to the inner diameter of the lens barrel member 52 (that is, the outer diameter of each lens G1 to G13). That is, when the stress is σ, the linear expansion coefficient of the material of the lens barrel member 52 is α1, the linear expansion coefficient of the material of each lens G1 to G13 is α2, and the outer diameter of each lens G1 to G13 is D, σ∝ (α1-α2) × D. In addition, the principal stresses are σ1, σ2, and σ3, respectively, the refractive indices felt by the electric field in the principal stress direction are n1, n2, and n3, respectively, the refractive index in a state where no stress is applied are n0, and the direct stress light constant is Assuming that c1 is the lateral stress light constant and c2, the refractive index when the lens receives a certain 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.

  n2−n1 = (c2−c1) × σ1 = β × σ1 (2)

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

  Since the retardation δ generated in the lens is obtained by multiplying the refractive index difference n2-n1 by the optical path length L, the following equation (3) is obtained.

  δ = (n2−n1) × L (3)

  Therefore, in consideration of the above-described equations (1) to (3), it is preferable that the material of the lens used for the objective lens 51 and the material of the lens barrel member 52 satisfy the following equation (4).

  | (Α1-α2) × D × β × L | <12000 (4)

  In addition, since the orientation of the crystal structure also affects the lens using a crystalline material, in the case of an equiaxed crystal material such as fluorite, the change in refractive index is expressed using a so-called piezo optical coefficient. It changes depending on the direction of the crystal axis, that is, the direction in which the lens is assembled. Therefore, for the fifth lens G5 and the ninth lens G9 made of fluorite, the equation (4) and the equations (5) to (12) described below are not considered. The optical path length L is the optical path length when the numerical aperture in each lens is maximized.

  Further, the equation (4) depends on the photoelastic constant β when the light beam passes through the lens parallel to the optical axis and the stress acts in the radial direction of the lens. In general, since the direction in which light passes and the direction in which stress acts are various, the following formula (5) or (6) should be satisfied in consideration of the direct stress light constant c1 and the lateral stress light constant c2. Is preferred.

| (Α1-α2) × D × c1 × L | <12000 (5)
| (Α1-α2) × D × c2 × L | <12000 (6)

  In the objective lens 51 composed of a plurality of lenses G1 to G13 as in the present embodiment, a configuration in which the lenses are joined to each other is often used. However, even if the linear expansion coefficients of the joined lenses are different, stress due to temperature change occurs. To do. In the present embodiment, the third lens G3 and the fourth lens G4 are cemented, the eighth lens G8 and the ninth lens G9 are cemented, the tenth lens G10 and the eleventh lens G11 are cemented, and the twelfth lens G12. The thirteenth lens G13 is cemented. Further, the fifth lens G5, the sixth lens G6, and the seventh lens G7 are respectively joined in this order. At this time, as in the case described above, the stress received by each of the lenses G1 to G13 is proportional to the outer diameter of each of the lenses G1 to G13. That is, the stress is σ, the linear expansion coefficient of the material of each of the lenses G1 to G13 is α2, and the linear expansion of the material of the lens (referred to as a cemented lens for convenience in this embodiment) that is cemented to the target lens. When the coefficient is α3 and the outer diameter of each lens G1 to G13 is D, σ∝ (α3−α2) × D.

  Therefore, as in the case described above, it is preferable that the lens material used for the objective lens 51 satisfies the following expression (7).

  | (Α3-α2) × D × β × L | <12000 (7)

  The photoelastic constant β and the optical path length L are the same as described above. Therefore, as in the case described above, it is preferable to satisfy the following expression (8) or (9) in consideration of the direct stress light constant c1 and the transverse stress light constant c2.

| (Α3-α2) × D × c1 × L | <12000 (8)
| (Α3-α2) × D × c2 × L | <12000 (9)

  Furthermore, in order to reduce both the influence of the linear expansion coefficient of the lens barrel member 52 and the lenses G1 to G13 and the influence of the linear expansion coefficient of the lenses joined to each other, the expression (7) is changed to the above-described expression (4). In addition, it is preferable to satisfy the following formula (10) considered.

  (| Α1-α2 | + | α3-α2 |) × D × | β | × L <20000 (10)

  Similarly, when the direct stress light constant c1 and the lateral stress light constant c2 are taken into consideration, it is preferable that the following expression (11) or expression (12) is satisfied.

(| Α1-α2 | + | α3-α2 |) × D × | c1 | × L <20000 (11)
(| Α1-α2 | + | α3-α2 |) × D × | c2 | × L <20000 (12)

  FIG. 5 shows the result of simulating the retardation with respect to the intrinsic polarization axis by obtaining the stress distribution by performing the thermal structure analysis in the conventional 100 × objective lens, calculating the refractive index distribution from the stress distribution. FIG. 5 shows the amount of change (nm) in retardation in each lens when the ambient temperature changes by 1 ° C. when light passes through the lens with a maximum NA = 0.9. The configuration of the lens group of the conventional objective lens used for the simulation is the same as the lens configuration shown in FIG.

  An example of calculating equation (4) is shown in FIG. As shown in FIG. 6, in the lens exceeding the upper limit value of the expression (4), specifically, in the third lens G3, the sixth lens G6, and the eighth lens G8, the change in retardation in the simulation result of FIG. The amount is large, and it can be seen that there is a correlation between the equation (4) and the like and the amount of change in retardation. Further, FIG. 7 shows a calculation example of the expression (7). As shown in FIG. 7, in the lenses exceeding the upper limit of the expression (7), that is, the third lens G3, the sixth lens G6, and the eighth lens G8, the amount of change in retardation in the simulation result of FIG. (7) etc. and the amount of change in retardation are correlated.

  Therefore, by designing the objective lens 51 so as to satisfy the expressions (4) to (12), it is possible to suppress a change in retardation that occurs in the conventional objective lens. In some cases, the retardation cancels out between the individual lenses. However, by reducing the amount of change in the retardation in each lens, even if a temperature difference occurs between the lenses, the total (that is, in the objective lens 51). )) The amount of change in retardation can be reduced.

  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.

  In the above-described embodiment, the change of 1 ° C. is described as an example of the change of the environmental temperature. However, the present invention is not limited to this. For example, even if the change is 2 ° C. or 3 ° C. Good.

  Moreover, in the above-mentioned embodiment, although the surface of the wafer 5 is inspected, it is not restricted to this, For example, it is also possible to inspect the surface of a glass substrate.

  In the above-described embodiment, 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. For example, polarized light such as a polarizing microscope can be used. The present invention can also be applied to an objective lens attached to an optical instrument to be handled.

  In the above-described embodiment, the objective lens 51 is composed of the 13 lenses G1 to G13. However, the objective lens 51 is not limited to this, and may be, for example, 10 or 15 depending on the device, and may be amorphous. What is necessary is just to be comprised from the some lens containing the lens using material.

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 barrel member 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 tenth Lens G11 11th lens G12 12th lens G13 13th lens

Claims (10)

An objective lens comprising a plurality of lenses including a lens using an amorphous material;
A lens barrel member that holds the objective lens;
A lens using the amorphous material, where α1 is a linear expansion coefficient of the material of the lens barrel member, and α2 is a linear expansion coefficient of the lens material using the amorphous material among the plurality of lenses. And D is the photoelastic constant of the lens material using the amorphous material, and L is the optical path length that maximizes the numerical aperture in the lens using the amorphous material. Then, the lenses using all the amorphous materials in the plurality of lenses are represented by the following formula: | (α1-α2) × D × β × L | <12000
An objective lens unit that satisfies the following conditions. An objective lens comprising a plurality of lenses including a lens using an amorphous material;
A lens barrel member that holds the objective lens;
A lens using the amorphous material, where α1 is a linear expansion coefficient of the material of the lens barrel member, and α2 is a linear expansion coefficient of the lens material using the amorphous material among the plurality of lenses. , The direct stress light constant of the lens material using the amorphous material is c1, and the optical path length that maximizes the numerical aperture in the lens using the amorphous material is L. Then, the lenses using all the amorphous materials in the plurality of lenses are expressed by the following formula: | (α1-α2) × D × c1 × L | <12000
An objective lens unit that satisfies the following conditions. An objective lens comprising a plurality of lenses including a lens using an amorphous material;
A lens barrel member that holds the objective lens;
A lens using the amorphous material, where α1 is a linear expansion coefficient of the material of the lens barrel member, and α2 is a linear expansion coefficient of the lens material using the amorphous material among the plurality of lenses. , The lateral stress optical constant of the lens material using the amorphous material is c2, and the optical path length that maximizes the numerical aperture in the lens using the amorphous material is L. When all of the plurality of lenses using the amorphous material are expressed by the following formula: | (α1-α2) × D × c2 × L | <12000
An objective lens unit that satisfies the following conditions. An objective lens comprising a plurality of lenses including a lens using an amorphous material;
A lens barrel member that holds the objective lens;
Of the plurality of lenses, the linear expansion coefficient of the lens material using the amorphous material is α2, the linear expansion coefficient of the lens material bonded to the lens using the amorphous material is α3, The outer diameter of the lens using the amorphous material is D, the photoelastic constant of the lens material using the amorphous material is β, and the aperture in the lens using the amorphous material is When the optical path length with the maximum number is L, all the lenses using the amorphous material in the plurality of lenses are expressed by the following formula: | (α3-α2) × D × β × L | <12000
An objective lens unit that satisfies the following conditions. An objective lens comprising a plurality of lenses including a lens using an amorphous material;
A lens barrel member that holds the objective lens;
Of the plurality of lenses, the linear expansion coefficient of the lens material using the amorphous material is α2, the linear expansion coefficient of the lens material bonded to the lens using the amorphous material is α3, The outer diameter of the lens using the amorphous material is D, the direct stress light constant of the lens material using the amorphous material is c1, and the inside of the lens using the amorphous material is When the optical path length at which the numerical aperture is maximized is L, the lenses using all the amorphous materials in the plurality of lenses are expressed by the following expression: | (α3-α2) × D × c1 × L | <12000
An objective lens unit that satisfies the following conditions. An objective lens comprising a plurality of lenses including a lens using an amorphous material;
A lens barrel member that holds the objective lens;
Of the plurality of lenses, the linear expansion coefficient of the lens material using the amorphous material is α2, the linear expansion coefficient of the lens material bonded to the lens using the amorphous material is α3, The outer diameter of the lens using the amorphous material is D, the lateral stress optical constant of the lens material using the amorphous material is c2, and the inside of the lens using the amorphous material is When the optical path length with the maximum numerical aperture is L, all the lenses using the amorphous material in the plurality of lenses are expressed by the following formula: | (α3-α2) × D × c2 × L | <12000
An objective lens unit that satisfies the following conditions. An objective lens comprising a plurality of lenses including a lens using an amorphous material;
A lens barrel member that holds the objective lens;
A lens using the amorphous material, where α1 is a linear expansion coefficient of the material of the lens barrel member, and α2 is a linear expansion coefficient of the lens material using the amorphous material among the plurality of lenses. The linear expansion coefficient of the lens material joined to α is α3, the outer diameter of the lens using the amorphous material is D, and the photoelastic constant of the lens material using the amorphous material is β. When the optical path length that maximizes the numerical aperture in the lens using the amorphous material is L, all the lenses using the amorphous material in the plurality of lenses are expressed by the following formula (| α1 −α2 | + | α3-α2 |) × D × | β | × L <20000
An objective lens unit that satisfies the following conditions. An objective lens comprising a plurality of lenses including a lens using an amorphous material;
A lens barrel member that holds the objective lens;
A lens using the amorphous material, where α1 is a linear expansion coefficient of the material of the lens barrel member, and α2 is a linear expansion coefficient of the lens material using the amorphous material among the plurality of lenses. The linear expansion coefficient of the lens material bonded to the lens is α3, the outer diameter of the lens using the amorphous material is D, and the direct stress light constant of the lens material using the amorphous material is c1. When the optical path length that maximizes the numerical aperture in the lens using the amorphous material is L, all the lenses using the amorphous material in the plurality of lenses are expressed by the following formula (| α1-α2 | + | α3-α2 |) × D × | c1 | × L <20000
An objective lens unit that satisfies the following conditions. An objective lens comprising a plurality of lenses including a lens using an amorphous material;
A lens barrel member that holds the objective lens;
A lens using the amorphous material, where α1 is a linear expansion coefficient of the material of the lens barrel member, and α2 is a linear expansion coefficient of the lens material using the amorphous material among the plurality of lenses. The linear expansion coefficient of the lens material bonded to the lens is α3, the outer diameter of the lens using the amorphous material is D, and the lateral stress optical constant of the lens material using the amorphous material is c2. When the optical path length that maximizes the numerical aperture in the lens using the amorphous material is L, all the lenses using the amorphous material in the plurality of lenses are expressed by the following formula (| α1-α2 | + | α3-α2 |) × D × | c2 | × L <20000
An objective lens unit that satisfies the following conditions. 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 lens barrel member 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;
10. The surface inspection apparatus according to claim 1, wherein the objective lens unit is the objective lens unit according to claim 1.

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