JP5554164B2 - Defect inspection equipment - Google Patents

Description

  The present invention relates to a defect inspection apparatus, and more particularly to a defect inspection apparatus for a nanoimprint mold.

  According to the roadmap of semiconductor lithography (for example, SEMATECH Lithography Forum 2008), the circuit line width HP in the next generation 2016 is assumed to be 16-22 nm. As the exposure apparatus and method of that generation, a reduction projection exposure method, which is a conventional extension, and a new nano-imprint (NIL) method have been studied.

  In the former optical system, the resolution using the ArF laser that oscillates at a wavelength of 193 nm, which is currently used, is insufficient in resolution, so double patterning by the immersion method and an EUV light source having a wavelength of 13.5 nm are necessary. These researches and developments are proceeding at a rapid pace. In the immersion double patterning method, there are problems in throughput reduction and cost increase due to the double exposure. The EUV light source has a wavelength shorter than that of an ArF laser by one digit or more, and research into practical use of the light source and the optical system is extremely difficult.

  In contrast, in recent years, nanoimprint technology, which is a molding technology that transfers a concavo-convex pattern onto a resin thin film by pressing a nanoimprint mold (mold) on which a nanoscale concavo-convex pattern has been formed against a substrate coated with a resin thin film, has been developed. Use in device manufacturing technology is under consideration.

  This method allows nanoscale processing at a simpler and lower cost than photolithography technology or the like.

  There are two major differences optically between a conventional exposure mask and a nanoimprint mold.

  (1) Miniaturization of defect size (effect of equal-magnification optical system)

  Conventional semiconductor exposure uses a 4 × reduction optical system, whereas nanoimprint uses a 1 × mold. Therefore, the defect size of the exposure mask is several tens of nm to 100 nm, which is four times the defect size of the semiconductor product, whereas the defect size of the nanoimprint mold needs to be suppressed to about 10 nm which is equal to the defect size of the semiconductor. The defect size is one order of magnitude or more smaller than the wavelength of light (DUV light / far ultraviolet ArF laser, 193 nm).

  (2) Optical properties of measurement samples

  The exposure mask has a pattern made of metal (mainly Cr) on a transparent quartz substrate. Since Cr is opaque and has a metallic luster, the light applied to the sample is reflected, scattered, and absorbed, and the amount of light is greatly changed in both transmitted light and reflected light. Therefore, the presence or absence of a defect can be directly detected as light brightness. On the other hand, since the nanoimprint mold forms a pattern by the unevenness of the quartz substrate itself, the defect is only a difference in the minute unevenness of the transparent body. For this reason, in a nanoimprint mold, even if a defect exists, only a slight phase shift occurs, and the intensity of transmitted light is equal regardless of the presence or absence of a defect (hereinafter, such an object is referred to as a “phase object”). Call).

  Any of these differences makes the defect inspection of the nanoimprint mold difficult.

  As a method of detecting the unevenness of the transparent material (phase object), for example, a method using an interference microscope as described in Patent Document 1 is conceivable.

  Patent Document 1 discloses an apparatus for detecting by optically erasing a defect-free portion of a pattern and optically extracting the defective portion with an interference microscope.

  Non-Patent Document 1 discloses a technique for increasing the scattered light intensity by causing the scattered light component and the illumination light to interfere with each other with a phase difference of π−Δ.

JP-A-8-327557

“Seventh Light Pencil”, verse 25, Ikuo Tsuruta

  However, in Patent Document 1, as shown in paragraphs “0026” to “0029” and FIGS. 10 to 12, an “optical image” corresponding to a circuit pattern and its amplitude (light intensity) pattern, that is, A real image pattern of a periodic pattern whose shape can be resolved at the wavelength of light is described.

  In the technique described in Patent Document 1, a defect is detected by causing interference between an optical image and a periodic pattern from two object points (periodic pattern) on the wafer. In order to eliminate the influence of the periodic pattern at that time, The phase difference between is π. In such a measurement, it is difficult to extract a signal from a defect having an optical wavelength or less that cannot obtain an optical image. Furthermore, as can be seen from the Rayleigh scattering equation, the amount of light scattered from the object is significantly reduced in proportion to the sixth power of the (defect) size. For example, the minimum size from which an optical image can be obtained is about several hundred nm, but the size of a defect required in the nanoimprint mold is 10 nm, which is 1.5 digits smaller. This means that the amount of scattered light from the object is attenuated by almost 10 orders of magnitude. As a result, the signal from the defect portion below the wavelength of the light (becomes scattered light) is small and buried in the level of background noise and scattered light, making it difficult to detect the defect.

  In Patent Document 1, as shown in FIG. 2, since there are shift adjusting means (lateral shift members) 46 and 56 for adjusting the shift amount and the shift direction in the convergent optical path, spherical aberration occurs. The interference signal deteriorates, for example, the signal light quantity decreases and noise (background) increases. This also causes a problem that the S / N with respect to a defect having a size of nm is remarkably lowered, and the defect detection becomes more difficult.

  Non-Patent Document 1 describes that the scattered light component and the illumination light are caused to interfere with each other with a phase difference of π−Δ to increase the scattered light intensity. However, pp. As shown in FIG. 3 of 421 and the text, it is merely a reference to a simple conventional phase contrast microscope. There is no description regarding the comparison between the sample and the reference, and the deletion of the pattern and the extraction of the defect. For this reason, it is difficult to use this technique for defect detection of a nanoimprint mold without reference to adjusting a lateral shift / distance with an appropriate reference (for example, an adjacent periodic pattern).

  The present invention has been made to solve the above-described problems, and an object thereof is to provide a defect inspection apparatus capable of detecting a defect in a nano-order pattern of a nanoimprint mold that is smaller than the wavelength of illumination light. To do.

In order to solve the above-mentioned problem, the invention according to claim 1 is a light irradiation means for irradiating a light-transmitting nanoimprint mold on which a nano-size predetermined pattern is formed with illumination light having a wavelength larger than the nano-size. And light splitting means for splitting the light transmitted through the nanoimprint mold irradiated with the illumination light into two lights, and the two lights so that the two split lights are laterally shifted in a predetermined direction. Each of the two lights is deflected so that a phase difference between the deflecting means for deflecting and the two lights deflected by the deflecting means is π−Δ (−90 ° <Δ <90 °, Δ: bias phase). The phase shift means for shifting the phase of at least one light, the multiplexing means for multiplexing the two lights phase-shifted by the phase shifting means, and the light combined by the multiplexing means are combined. An imaging lens for the provided with an imaging means for capturing an optical image formed by the image forming lens, wherein Δ is the contrast between the defective portion and the background light of the nano-imprint mold, the defective portion Is determined according to the amount of the background light so as to be equal to or higher than a detectable contrast .

  According to this invention, since the phase difference between the two lights deflected so as to be laterally shifted in a predetermined direction by the deflecting means is π−Δ (−90 ° <Δ <90 °), It becomes possible to detect a defect in the nano-order pattern of the nanoimprint mold that is smaller than the wavelength of the illumination light.

  According to a second aspect of the present invention, the pattern includes a plurality of the same patterns, and the deflecting unit is configured so that the two light images become two identical pattern images. May be deflected.

  In addition, as described in claim 3, the correlation image generation unit that generates a correlation image between the image captured by the imaging unit and a comparison image including a defect image having a predetermined shape, and the generated It is good also as a structure provided with the binarized image production | generation means which produces | generates the binarized image which binarized the correlation image.

  In addition, as described in claim 4, it is good also as a structure provided with the liquid immersion means to immerse the surface on the opposite side to the surface in which the said pattern of the said nanoimprint mold was formed in a pure water.

  Further, as described in claim 5, a configuration in which a mask means for cutting the optical image of the Fourier transform pattern is provided on a Fourier transform surface on which the optical image of the Fourier transform pattern corresponding to the pattern is formed. Good.

  According to the present invention, it is possible to detect a defect in a nano-order pattern of a nanoimprint mold that is smaller than the wavelength of illumination light.

  Further, according to the present invention, it is possible to detect not only a difference in dimension in the in-plane direction (that is, a defect, for example, a short circuit between adjacent wirings, thinning / missing of a line, etc.) but also a difference in the depth direction. Because the present invention basically detects a phase change, not only a difference in the in-plane dimensional difference, but also a difference in the depth direction of the concavo-convex gives a phase change, which is used as a phase difference signal. This is because it can be detected. Thereby, the chip | tip of a height direction and the change (for example, abrasion with time) of uneven | corrugated height can also be test | inspected.

It is a block diagram of the defect inspection apparatus which concerns on 1st Embodiment. It is a block diagram of a control system of the defect inspection apparatus according to the first embodiment. It is a figure for demonstrating the detection of an isolated defect. It is a figure which shows the image which imaged the isolated defect. It is a graph which shows the measurement result of the contrast of a simulation defect, and the contrast of background light. It is a figure which shows the image which imaged the isolated defect. It is a figure for demonstrating the case where the defect of a cell is detected by making the image of an adjacent cell interfere. It is a figure for demonstrating the case where the image of an adjacent die is made to interfere and a defect of a die is detected. It is a block diagram of the defect inspection apparatus which concerns on 3rd Embodiment. It is a figure for demonstrating the image which imaged the isolated defect from which height differs. (A) is a figure which shows an example of an acquired image, (B) is a figure which shows an example of a comparison image. (A) is a diagram showing an example of a correlation image, (B) is a diagram showing an example of an image obtained by binarizing the correlation image, and (C) is a result of calculating the centroid position of the defective portion from the binarized image. FIG. It is a block diagram of the defect inspection apparatus which concerns on 5th Embodiment. (A) is a figure for demonstrating the amount of scattered light at the time of immersing the surface in which the uneven | corrugated pattern of the nanoimprint mold was formed in a pure water, (B) is the surface on the opposite side to the surface in which the uneven | corrugated pattern of the nanoimprint mold was formed. It is a figure for demonstrating the amount of scattered light when water is immersed in a pure water. It is a block diagram of the defect inspection apparatus which concerns on 6th Embodiment.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  (First embodiment)

  FIG. 1 shows a defect inspection apparatus 10 according to this embodiment. The defect inspection apparatus 10 is an apparatus for inspecting a defect of the nanoimprint mold 12 in which a nano-size predetermined pattern is formed.

  The nanoimprint mold 12 is produced by so-called nanoimprint lithography (NIL) using a light-transmitting material such as quartz, and a predetermined pattern having a pattern width or pattern pitch of several nm to several tens of nm on one surface 12A. Is formed.

  As shown in FIG. 1, the defect inspection apparatus 10 is an interference microscope that divides a field of view, a light source 14 that irradiates the nanoimprint mold 12 with parallel illumination light, and a collimator that collimates the light transmitted through the nanoimprint mold 12. The lens 16, the half mirror 18 for separating the parallel light from the collimating lens 16 in two directions, the deflector 20A for deflecting the light transmitted through the half mirror 18, and the light deflected by the deflector 20A in a predetermined direction A mirror 22 to be compensated, a phase compensation plate 24 for compensating the phase, a deflector 20B for deflecting the light reflected by the half mirror 18, and a mirror 26 for reflecting the light deflected by the deflector 20B in a predetermined direction; A phase shifter 28 that shifts the phase of light from the mirror 26, and transmits light from the phase shifter 28 and a phase compensation plate The half mirror 30 which combines both by reflecting the light from 4, the imaging lens 32 which images the light from the half mirror 30, and the image pick-up element which images the light imaged by the imaging lens 32 34.

  The light beam L transmitted through the nanoimprint mold 12 is converted into parallel light by the collimating lens 16 and is incident on the half mirror 18. The light beam L incident on the half mirror 18 is separated into a light beam L1 that is transmitted through the half mirror 18 and a light beam L2 that is reflected by the half mirror 18.

  The light beam L1 that has passed through the half mirror 18 passes through the deflector 20A, and is reflected by the mirror 22 toward the phase compensation plate 24.

  The phase compensation plate 24 has a function of adjusting the relative phase difference between the light beams L1 and L2, that is, a function of adjusting the optical path length of the light beam L1 and the optical path length of the light beam L2. The light beam L <b> 1 that has passed through the phase compensation plate 24 enters the half mirror 30.

  On the other hand, the light beam L2 reflected by the half mirror 18 passes through the deflector 20B and is reflected by the mirror 26 toward the phase shifter 28.

  The phase shifter 28 is composed of wedge-shaped prisms 28A and 28B. By shifting the prism 28A in the direction of the arrow P in the figure, the optical path difference between the light beams L1 and L2 according to the shift amount, that is, the phase shift amount. Can be adjusted.

  The light from the phase shifter 28 and the light from the phase compensation plate 24 are combined by the half mirror 30. The combined light is imaged on the image sensor 34 by the imaging lens 32.

  Since the defect inspection apparatus 10 having such a configuration has a visual field division function, two object points conjugate with one image point on the image sensor 34 can be formed. Specifically, when the deflectors 20A and 20B are tilted in opposite directions by a predetermined angle θ with respect to the optical axis, the light beams L1 and L2 are moved away from each other in the direction parallel to the imaging plane of the image sensor 34 (arrow P direction). Can be shifted in parallel. Therefore, by tilting the deflectors 20A and 20B by a predetermined angle θ, the light beam L1 that is light from the object point P1 out of the two object points P1 and P2 separated by the distance D in the arrow P direction on the nanoimprint mold 12 is used. An interference image obtained by causing the visual field image to interfere with the visual field image by the light beam L2 that is the light from the object point P2 can be formed on the image sensor 34.

  In this way, by tilting the deflectors 20A and 20B by a predetermined angle θ corresponding to the distance D, light from two separated object points on the nanoimprint mold 12 can interfere with each other to form an image on the image sensor 34. it can.

  FIG. 2 shows a block diagram of a control system of the defect inspection apparatus 10. As shown in the figure, the defect inspection apparatus 10 includes a control unit 40. Connected to the control unit 40 are a drive unit 42A for driving the deflector 20A, a drive unit 42B for driving the deflector 20B, a drive unit 44 for driving the prism 28A of the phase shifter 28, an image sensor 34, and a memory 46. Yes.

  Next, the result of simulating the detection of isolated defects in the defect inspection apparatus 10 by electromagnetic field optical simulation will be described.

  In this simulation, as shown in FIG. 3, as an example, a case was detected in which a protrusion 52 as an isolated defect having a rectangular parallelepiped shape with a length of 300 nm and a height of 200 nm present on the planar region 50 of the nanoimprint mold 12 was detected.

  Here, the object point P1 is on the projection 52, and the object point P2 is on the plane region 50 separated from the projection 52 by the distance D, and the deflectors 20A and 20B are inclined in the opposite direction by an angle θ corresponding to the distance D. The phase difference between the light beam L1 and the light beam L2 is determined by the phase shifter 28 as to how the interference image obtained by causing the image of the light beam L1 from the projection 52 to interfere with the image of the light beam L2 from the plane region 50 is changed. A case where simulation is performed while changing φ = π−Δ will be described. Note that Δ is a phase shift amount (bias phase). Moreover, the wavelength of illumination light is 638 nm as an example.

  FIG. 4 shows a phase difference φ = 0 ° (Δ = π, Δ; bias phase) and φ = π−60 ° (Δ = 60 °) for each of the case without background light and the case with background light. ), Φ = π−30 ° (Δ = 30 °), φ = π (Δ = 0 °), and the simulation result of the interference image is shown. The background light is light generated by scattered light due to defects in the optical member, dirt, scratches, dust, etc., stray light from the lens barrel and holder, dark current, noise, or the like.

  The case where there is no background light is an ideal case where there is no background light due to defects or dirt on the nanoimprint mold 12 or other optical members.

  In the case where there is background light, the amount of light is set to 0.05. This value is a value when the phase difference φ = 0 °, that is, when the light quantity of the bright field image that does not cause the light beams L1 and L2 to interfere with each other is 1.

  In the case of a bright field image with a phase difference φ = 0 °, the protrusion 52 cannot be detected whether or not there is background light. In the case of the phase difference φ = π, in the ideal state without background light, the images of the light beams L1 and L2 are interfered with the phase being shifted by π. It is canceled out, and only the different part of both images, that is, the part of the protrusion 52 becomes brighter. For this reason, the contrast becomes 1 and becomes extremely high, but since the light quantity is proportional to the sixth power of the size, the signal light quantity becomes very small.

  However, in practice, there is usually background light due to defects in the optical member, dirt, scratches, dust, or the like. For this reason, as shown in FIG. 4, when φ = π in the presence of background light, the contrast is as low as 0.065 due to the influence of background light, and it is difficult to detect the protrusion 52. is there.

  On the other hand, as shown in FIG. 4, even in the presence of background light, the contrast is improved when φ = π−30 ° and π−60 ° compared to when φ = 0 ° and π. The protrusion 52 can be detected. Thus, the signal light quantity from the protrusion 52 can be amplified by setting the phase difference φ between the light beams L1 and L2 to π−Δ. Therefore, even in an actual measurement system in which background light exists, by controlling the phase difference φ, it is possible to accurately detect even a nano-sized defect smaller than the wavelength of the illumination light.

  FIG. 5 shows the result of measuring the contrast of the simulated defect 54 and the contrast of the background light in the measurement image when the simulated defect 54 as shown in FIG. 6 is imaged by the defect inspection apparatus 10. The size of the simulated defect 54 is 500 nm in length and width, the height is 200 nm, and the aperture NA of the optical system of the defect inspection apparatus 10 is 0.45. A line 56 in FIG. 6 indicates the luminance on the line including the simulated defect 54. In FIG. 5, the horizontal axis indicates the bias phase, that is, Δ, and the vertical axis indicates the contrast. As shown in the figure, in the case of Δ = 0 °, that is, a dark field image with φ = π, the simulated defect contrast and the contrast of the background light are substantially the same, so it is difficult to detect the defect. In the case of Δ = π, that is, in the case of a bright field image with φ = 2π (0 °), the simulated defect contrast is low and it is difficult to detect the defect. Further, the contrast is maximized in the vicinity of Δ = −30 °.

  As described above, even if the defect has a size equal to or smaller than the wavelength of the illumination light, the defect can be detected by setting the phase difference between the light beam L1 and the light beam L2 to π−Δ instead of π. Note that Δ is determined according to the amount of background light, and is set to increase as the amount of background light increases, for example. Then, the contrast between the defective portion and the background light is determined so as to be equal to or higher than the contrast at which the defective portion can be detected.

  In the defect inspection apparatus 10, the control unit 40 instructs the drive unit 44 to drive the prism 28A so that the phase difference φ between the light beam L1 and the light beam L2 becomes φ = π−Δ. The mold 12 is imaged by the image sensor 34. Thereby, an interference image in which the defect portion is emphasized can be obtained, and an isolated defect having a size smaller than the wavelength of the illumination light can be detected with high accuracy.

  (Second Embodiment)

  Next, a second embodiment of the present invention will be described.

  In the present embodiment, a case where the nanoimprint mold 12 is used for manufacturing a semiconductor circuit substrate, for example, and a periodic circuit pattern defect formed in the nanoimprint mold 12 is detected will be described.

  As shown in FIG. 7, when detecting defects in the nanoimprint mold 12 used when forming a plurality of dies 64 including a plurality of cells 62 having the same circuit pattern on a semiconductor wafer 60, nearby, desirably adjacent to each other. By making the reference light from the cell 62 interfere with the measurement light, the circuit pattern can be erased and a defect can be detected. That is, the distance D is set to the distance from the reference cell, the deflectors 20A and 20B corresponding to the distance D are tilted, and the phase difference between the light beam L1 and the light beam L2 is φ = π−Δ. By driving the prism 28 </ b> A of the phase shifter 28 so that the light beam L <b> 1 and the light beam L <b> 2 from the reference cell interfere with each other, the image sensor 34 captures an interference image. Note that Δ is determined according to the amount of background light, as described above.

  For example, when a defect 66 exists in the cell 62C and the cell 62B that is referred to is a normal cell that does not have a defect, the interference image 68B between them is, as shown in FIG. Only the defect 66 is emphasized (white circle portion in the figure), and the other portion is a canceled image. The same applies to interference images with other reference cells 68D. Thereby, the defect of the cell of the circuit pattern of a periodic structure is detectable.

  Similarly, when a plurality of dies 64 having the same pattern are adjacent to each other, a defect can be detected by capturing an interference image in which reference light from a nearby, preferably adjacent die 64 is interfered with measurement light. For example, as shown in FIG. 8, when defects 66A and 66B exist in the die 64B, the interference image 68A with the normal die 64A becomes as shown in FIG. 8, and the defect portions 66A and 66B are emphasized. The same applies to the interference image with the die 64C.

  (Third embodiment)

  Next, a third embodiment of the present invention will be described. In addition, the same code | symbol is attached | subjected to the same part as the defect inspection apparatus 10, and the detailed description is abbreviate | omitted.

  FIG. 9 shows the configuration of the defect inspection apparatus 70 according to the present embodiment. As shown in the figure, the defect inspection apparatus 70 includes a light source 14, lenses 72 and 74, a λ / 2 plate 76, a birefringent polarization separator 78, a phase shifter 80, lenses 82 and 84, a birefringent polarization detector. The waver 86, the analyzer 88, the imaging lens 90, and the image sensor 34 are configured.

  In the defect inspection apparatus 70 having such a configuration, the nanoimprint mold 12 to be inspected is set between the lenses 82 and 84.

  The illumination light emitted from the light source 14 passes through the lenses 72 and 74 and the λ / 2 plate 76 and enters the birefringent polarization separator 78. The light incident on the birefringent polarization separator 78 is separated into two linearly polarized light beams L1 and L2 having orthogonal polarization components.

  The light beams L1 and L2 are phase-adjusted by the phase shifter 80 so as to have a phase difference φ = π−Δ, pass through the lens 82, and enter the nanoimprint mold 12. The light beams L 1 and L 2 that have passed through the nanoimprint mold 12 pass through the lens 84 and enter the birefringent polarization multiplexer 86. The birefringent polarization multiplexer 86 multiplexes the incident light beams L1 and L2. The combined light passes through the analyzer 88 and the lens 90 and forms an image on the image sensor 34. As the phase shifter 80, an EO element, a Babinet Soleil, or the like can be used. The phase shifter 80 may be placed not behind the nanoimprint mold 12 but behind (after transmission).

  Also in this case, the lateral shift amount in the direction of arrow P in FIG. 9 of the light beams L1 and L2 by the birefringent polarization separator 78 is adjusted according to the distance D between the adjacent cells 62 on the nanoimprint mold 12, and the light beams L1 and L2 By adjusting the amount of phase shift by the phase shifter 80 so that the phase shift difference φ of L2 becomes π−Δ, the reference light from a nearby, preferably adjacent cell 62 can interfere with the measurement light. . Thereby, when any of the adjacent cells 62 has a defect, an interference image in which the defect is emphasized can be obtained, and the defect can be detected. Of course, as in the second embodiment, it is also possible to detect a defect by capturing an interference image between adjacent, preferably adjacent dies, instead of comparing cells.

In order to adjust the distance between two points to be referred to and compared, the birefringent polarization separator 78 and the birefringent polarization multiplexer 86 may be mechanically moved. Preferably, when an element having an electro-optic effect, specifically, a birefringent crystal such as LiNbO ₃ or a photochromic material such as liquid crystal is used for the polarization separator 78 and the polarization multiplexer 86, an external electric Since the distance between the two points can be adjusted by the signal, the apparatus can be simplified.

  (Fourth embodiment)

  Next, a fourth embodiment of the present invention will be described. In the present embodiment, image signal processing executed by the control unit 40 of the defect inspection apparatuses 10 and 70 will be described.

When the size of the defect is less than the wavelength of the illumination light, the vertical and horizontal size of the defect is not related to the vertical and horizontal size of the image formed on the image sensor 34 but is related to the contrast. The contrast C is proportional to (a / λ) ² where the defect size is a and the wavelength of the illumination light is λ, and the contrast is greatly reduced as the defect size is smaller than the wavelength of the illumination light.

  For example, as shown in FIG. 10, when defects 92 </ b> A, 92 </ b> B, and 92 </ b> C having a wavelength less than that are imaged by the imaging device 34 with an interference microscope 94 (configuration is omitted), a captured image 96 is obtained. The defects 92A, 92B, and 92C have the same vertical and horizontal sizes but have different heights. The higher the height, the stronger the signal intensity and the brighter. Therefore, even if the vertical and horizontal sizes of the defect are the same, the ease of detection varies depending on the height.

  The image size is determined by a PSF (point spread function) determined by the diffraction limit of light. For example, if the wavelength of the illumination light is 193 nm and the aperture NA of the interference microscope 94 is 0.9, the diffraction limit size is 260 nm. For example, if the target defect size is 10 nm, it is difficult to detect the position of the defect. Become.

  Therefore, in the present embodiment, an intensity pattern image of the captured image is acquired, and a defect position is specified by image processing and threshold processing.

  For example, when the acquired image acquired by the image sensor 34 is an acquired image 98 as shown in FIG. 11A, the protruding defects 100A to 100C become brighter and the defective defects 102A and 102B become darker. If a defect is determined based on the magnitude of intensity, all defects cannot be detected.

  Therefore, the control unit 40 generates a correlation image between the acquired image 98 captured by the image sensor 34 and a predetermined comparison image 104 as shown in FIG. 11B, and sets the generated correlation image to a predetermined threshold value. A binarized image is generated based on the binarization. This binarized image is an image in which defects are reflected.

Here, it is assumed that the pixel value (luminance value) of the coordinates (m, n) of the acquired image 98 is i (m, n) and the pixel value of the comparison image is j (m, n). The pixel value j (m, n) of the comparison image 104 is defined by the following equation using the Bessel function J ₁ (r), for example.

j (m, n) = J ₁ (r) / r

r = c · sqrt (m ² + n ² )

Here, J ₁ () is a linear Bessel function. C is a proportional constant determined in advance by the NA of the optical system of the defect inspection apparatus of the optical system, the magnification, the pixel size of the image sensor 34, and the like. Further, assuming that the size of the comparison image 104 is (2N + 1), (−N / 2 ≦ m, n ≦ N / 2) (the origin is the center of the image), and the size of the comparison image 104 is larger than the size of the acquired image 98. The size is small and larger than the size corresponding to the first dark ring of the diffraction limited spot.

  The correlation image between the pixel value i (m, n) of the acquired image 98 and the pixel value j (m, n) of the comparative image 104 is calculated by the following equation while moving the comparison image 104 on the acquired image 98 in an overlapping manner. A correlation image is obtained by calculating the pixel value r (m, n).

R (m, n) obtained by the above formula represents a spatial shape similarity, and is a value normalized to a range of −1 to 1. In this case, the closer to “1” or “−1”, the higher the correlation. That is, among the defects shown in FIG. 11A, r (m, n) in the regions of the defects 100A to 100C having high luminance is a value close to '1', and r (m) in the regions of the defects 102A and 102B having low luminance. , N) is a value close to “−1”.

  Then, a pixel value r ′ (m, n) obtained by binarizing the pixel value r (m, n) of the correlation image is obtained by the next threshold processing.

r ′ (m, n) = 1 (| r (m, n) | ≧ x)

r '(m, n) = 0 (| r (m, n) | <x)

Here, x is a predetermined set value, for example, x = 0.7.

  The image binarized in this way becomes an image 108 as shown in FIG. Then, the position of the center of gravity of a set of pixels where r ′ (m, n) = 1, which is a defect portion (the white portion in the figure), is calculated, and the center of gravity of the defect is obtained as shown in FIG. Defect information 110 including information indicating the signal intensity of the position 108 and its gravity center position is generated.

  In this way, a correlation image between the acquired image 98 and the comparative image 104 is generated and binarized with a threshold value, so that even if the defect has a size smaller than the wavelength of the illumination light, the defect position can be detected with high accuracy. can do.

  (Fifth embodiment)

  Next, a fifth embodiment of the present invention will be described. In this embodiment, a defect inspection apparatus using an immersion optical system will be described.

  FIG. 13 shows the configuration of the defect inspection apparatus 120 according to the present embodiment. The defect inspection apparatus 120 shown in FIG. 13 has a liquid immersion part 124 filled with pure water 122. The collimating lens 16 is provided at the bottom of the liquid immersion part 124, and the nanoimprint mold 12 is formed above the liquid immersion part 124, and the surface opposite to the surface on which the uneven pattern of the nanoimprint mold 12 is formed is pure water 122. Set to be immersed. Since other configurations are the same as those of the defect inspection apparatus 10, description thereof will be omitted.

  Thus, by adopting an immersion optical system in which the surface opposite to the surface on which the uneven pattern of the nanoimprint mold 12 is formed is immersed in pure water, even if the wavelength of the illumination light is the same, non-immersion The resolution can be made higher than when an optical system is employed. The resolution R is expressed by the following equation.

R = k ₁ · λ / NA

NA = n · sinθ

Here, k1 is a proportionality constant, λ is the wavelength of illumination light in vacuum, and n is the refractive index.

  Since air is n = 1 and pure water is n = 1.475, the resolution of the immersion optical system is 1.475 times that of the non-immersion optical system.

  Here, as shown in FIG. 14A, when the surface of the nanoimprint mold 12 on which the concave / convex pattern is formed is soaked in pure water 122, the refractive index of the nanoimprint mold 12 made of quartz and pure water are arranged. Since the difference from the refractive index is small and the amount of scattered light decreases, the S / N ratio cannot be increased. For example, when the wavelength of illumination light is 193 nm, the refractive index of pure water is 1.475, the refractive index of quartz is 1.554, the difference in refractive index is small, and the S / N ratio cannot be increased.

  On the other hand, as shown in FIG. 14B, when the surface opposite to the surface on which the uneven pattern of the nanoimprint mold 12 is formed is soaked in pure water 122, the difference in refractive index between quartz and air. Therefore, the amount of scattered light can be increased and the S / N ratio can be increased. For this reason, it is preferable to arrange | position so that the surface on the opposite side to the surface in which the uneven | corrugated pattern of the nanoimprint mold 12 was formed may be immersed in the pure water 122. FIG.

  (Sixth embodiment)

  Next, a sixth embodiment of the present invention will be described. This embodiment demonstrates the defect inspection apparatus using the periodic pattern cut mask for cutting the diffracted light by the periodic pattern formed in the nanoimprint mold 12. FIG.

  For example, a memory element such as an SRAM generally has a regular periodic circuit pattern in one chip. In this case, the nanoimprint mold 12 for forming the circuit pattern may have a repetitive pattern having a period longer than the wavelength. In this case, since this repetitive pattern acts as a diffraction grating for light, diffracted light is emitted in a specific direction. Therefore, when the diffracted light of the periodic circuit pattern becomes brighter with respect to the signal light amount from the defect of several nm to several tens of nm, the defect detection capability may be lowered.

  Therefore, as shown in FIG. 15, the defect inspection apparatus 130 according to the present embodiment performs this Fourier transform on a Fourier transform plane on which an optical image of a Fourier transform pattern corresponding to the periodic pattern formed on the nanoimprint mold 12 is formed. A periodic pattern cut mask 132 on which a pattern is formed is provided.

  The periodic pattern cut mask 132 is composed of, for example, an EO element or a liquid crystal. In this case, the control unit 40 controls the periodic pattern cut mask 132 so that a Fourier transform pattern corresponding to the periodic pattern formed on the nanoimprint mold 12 is formed (displayed).

  By disposing such a periodic pattern cut mask 132 on the Fourier transform plane, it is possible to cut diffracted light due to a periodic circuit pattern, so that a defective portion can be detected with high accuracy.

  In addition, this invention is not limited to the said Example, Of course, a various change and correction are possible in the range which does not deviate from the technical idea described in the claim. For example, as the method for obtaining the interference image of the defect detection apparatus according to the present invention, the Mach-Zehnder method (see FIG. 1) and the polarization separation / combination method (see FIG. 9) are exemplified in this embodiment. The Jaman method, Michelson method, Fizeau method, Twiman-Green method, etc. may be used as appropriate.

10, 70, 120, 130 Defect inspection device 12 Nanoimprint mold 14 Light source 16 Collimating lens 18 Half mirror 20A, 20B Deflector 22, 26 Mirror 24 Phase compensation plate 28 Phase shifter 28A, 28B Prism 30 Half mirror 32 Imaging lens 34 Imaging Element 40 Control unit 42A, 42B Drive unit 44 Drive unit 46 Memory 72, 82, 84, 90 Lens 76 λ / 2 plate 78 Polarization separator 80 Phase shifter 86 Polarization multiplexer 88 Analyzer 90 Imaging lens 122 Pure water 124 Immersion part 132 Periodic pattern cut mask

Claims (5)

A light irradiating means for irradiating illumination light having a wavelength larger than the nano size to a nanoimprint mold having translucency in which a predetermined pattern of nano size is formed;
A light splitting means for splitting the light transmitted through the nanoimprint mold irradiated with the illumination light into two lights;
Deflecting means for deflecting each of the two lights so that the two divided lights are laterally shifted in a predetermined direction;
Phase shift means for shifting the phase of at least one of the two lights so that the phase difference between the two lights deflected by the deflection means is π−Δ (−90 ° <Δ <90 °). When,
A multiplexing unit that combines the two lights phase-shifted by the phase-shifting unit;
An imaging lens that forms an image of the light combined by the combining means;
Imaging means for imaging an optical image formed by the imaging lens;
Equipped with a,
The Δ is determined according to the amount of the background light so that the contrast between the defective portion of the nanoprint mold and the background light is equal to or higher than the contrast capable of detecting the defective portion . The pattern includes a plurality of the same patterns,
The defect inspection apparatus according to claim 1, wherein the deflecting unit deflects the two lights so that the images of the two lights become two images of the same pattern. The defect inspection apparatus according to claim 1, further comprising a correlation image generation unit configured to generate a correlation image between an image captured by the imaging unit and a comparison image including a defect image having a predetermined shape. The defect inspection apparatus of any one of Claims 1-3 provided with the liquid immersion means to immerse the surface on the opposite side to the surface in which the said pattern of the said nanoimprint mold was formed in pure water. The mask means for cutting the optical image of the Fourier transform pattern is provided on a Fourier transform surface on which an optical image of the Fourier transform pattern corresponding to the pattern is formed. Defect inspection equipment.