Method and apparatus for inspecting defect of transparent body

Abstract

To provide a defect inspection apparatus and a defect inspection method that are intended to detect a defect of a transparent body used in a photomask.SOLUTION: A defect inspection apparatus for detecting a defect of a transparent body includes a light source, an inspection pattern part, an imaging device, and a detection circuit. Light emitted from the light source penetrates the inspection pattern part and the transparent body in this order so as to enter the imaging device. The imaging device can output an image signal corresponding to incident light to the detection circuit. The inspection pattern part can include, for example, a line and space pattern where a transmission region and a light-shielding region are disposed alternately. The detection circuit can acquire image data and determine the presence / absence of a defect of the transparent body.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method and an apparatus for inspecting defects in a transparent body, particularly a transparent body used for a photomask.

Background Art

[0002] In a lithography process for manufacturing an electronic circuit such as a flat panel display such as a liquid crystal panel, a photomask is used. A pellicle is attached to the surface of the photomask to prevent foreign matter from adhering. The pellicle includes a frame and a pellicle film. The pellicle film is attached to the frame, and the frame is fixed to the photomask. If there are foreign matters or unevenness on the pellicle film, in some cases, defects caused by the foreign matters or unevenness may occur on the transfer target in the exposure process using the photomask. In order to detect foreign matters attached to the pellicle film, there is known a foreign matter inspection apparatus that measures the transmittance, which is an optical property of the pellicle film, and detects foreign matters from abnormalities in the transmittance (Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, with conventional foreign matter inspection apparatuses, it has been difficult to detect foreign matters and unevenness in a transparent body such as a pellicle film used for a photomask with high sensitivity. Therefore, foreign matters are inspected manually using a microscope image, and unevenness in the pellicle film is inspected visually.

[0005] In view of the above problems, an object of the present invention is to provide a defect inspection apparatus and a defect inspection method capable of detecting foreign matters and unevenness in a transparent body used for a photomask, particularly in a pellicle film.

Means for Solving the Problem

[0006] The defect inspection apparatus according to the present invention is a defect inspection apparatus for a transparent body, and includes a light source, an inspection pattern section, an imaging device, and a detection circuit, and is configured such that light emitted from the light source passes through the inspection pattern section and the transparent body in this order and is incident on the imaging device. The imaging device outputs an image signal corresponding to the incident light to the detection circuit. It is characterized by this.

[0007] By using such a defect inspection apparatus, it becomes possible to detect defects in a transparent body such as a pellicle film that affect the exposure process.

[0008] Also, in the above configuration, the inspection pattern section may have a line and space pattern in which a transmission region and a light shielding region are arranged alternately.

[0009] By using such a defect inspection apparatus, defects in a transparent body can be effectively detected with a simple pattern.

[0010] Also, in the above configuration, the transparent body may be a pellicle film.

[0011] By using such a defect inspection apparatus, defects in the pellicle film of a photomask can be effectively detected.

[0012] Also, in the above configuration, it further includes an illumination lens, and the position of the focus of the light may be configured to be located on the light source side of the transparent body by the illumination lens.

[0013] By using such a defect inspection apparatus, effective defect inspection becomes possible.

[0014] Also, in the above configuration, The inspection pattern portion may be located between the illumination lens and the transparent body.

[0015] By using such a defect inspection apparatus, defect inspection can be performed in a configuration that is particularly close to the geometric conditions of the pellicle film, which is a transparent body.

[0016] Also, in the above configuration, The inspection pattern portion may be located between the light source and the illumination lens.

[0017] By using such a defect inspection apparatus, the space for arranging the transparent body to be inspected expands, and the operability of the defect inspection apparatus is improved.

[0018] Also, in the above configuration, Further include a review light source and a reflector, The reflector is disposed between the transparent body and the imaging device, The light irradiated from the review light source may be configured to be guided to the transparent body.

[0019] By using such a defect inspection apparatus, the observation of the detected defects becomes easier.

[0020] The defect inspection method according to the present invention is A method for inspecting defects in a transparent body, A first step of irradiating light emitted from a light source onto an inspection pattern portion and irradiating transmitted light from the inspection pattern portion onto the transparent body; A second step in which an imaging device that has received the light transmitted through the transparent body outputs image data to a detection circuit; A third step in which the detection circuit acquires the image data and determines the presence or absence of defects in the transparent body and is characterized by including.

[0021] By adopting such a defect inspection method, it becomes possible to detect defects that affect the exposure process of a transparent body such as a pellicle film, for example.

[0022] Also, in the above configuration, in the third step, the detection circuit may have a step of comparing the acquired image data with reference image data and determining that there is a defect in the transparent body when a difference is confirmed.

[0023] By adopting such a defect inspection method, it is possible to determine the presence or absence of defects in a transparent body by using a known pattern defect inspection method.

Advantages of the Invention

[0024] According to the present invention, it is possible to obtain a defect inspection apparatus and a defect inspection method capable of detecting foreign matters and unevenness in a transparent body, particularly a pellicle film, used for a photomask.

Brief Description of the Drawings

[0025]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Embodiments for Carrying Out the Invention

[0026] Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, none of the following embodiments gives a limiting interpretation in the determination of the gist of the present invention. Also, the same or similar members may be denoted by the same reference numerals, and the description thereof may be omitted.

[0027] Furthermore, with regard to terms used in this specification for specifying shapes, geometric conditions, and their degrees, such as terms like "parallel", "orthogonal", "identical", etc., and values of lengths and angles, etc., they shall not be bound by a strict meaning and shall be interpreted to include a range to the extent that similar functions can be expected.

[0028] (Embodiment 1) Hereinafter, with reference to the drawings, a pellicle inspection apparatus 100 (defect inspection apparatus) for inspecting a pellicle, particularly defects in a pellicle film, will be described. As described above, the pellicle is used for protecting a photomask and is provided on the pattern formation side of the photomask. In order not to affect the exposure process in the lithography process using the photomask, the pellicle film attached to the pellicle is a transparent body having transparency to exposure light. Since the pellicle is integrated with the photomask, in a broad sense, it constitutes a part of the photomask.

[0029] FIG. 1(A) is a schematic diagram showing the main configuration of the pellicle inspection apparatus 100, and FIG. 1(B) is a plan view schematically showing the inspection mask 7 (inspection pattern portion) used in the pellicle inspection apparatus 100. As shown in FIG. 1(A), the pellicle inspection apparatus 100 includes an illumination device 1, an objective lens 4, an imaging device 5 (camera), and a detection circuit 6. In FIG. 1(A), the Y direction indicates a direction parallel to the optical axis, and the X direction indicates a direction perpendicular to the optical axis.

[0030] The pellicle inspection apparatus 100 has an inspection mask 7 between the illumination device 1 and the objective lens 4. The inspection mask 7 may be, for example, a binary photomask. The illumination device 1 includes a light source 2 that emits light L and an illumination lens 3. Note that, for example, a lamp light source or a laser light source can be used as the light source 2. The wavelength of the light L emitted from the light source 2 is preferably the same as the exposure light used in the lithography process, but is not limited thereto. The illumination lens 3 is composed of, for example, but not limited to, a combination of a condenser lens, a condenser lens, and a projection lens. The imaging device 5 has, for example, but not limited to, a two-dimensional imaging element such as a CCD image sensor. The objective lens 4 has an arbitrary magnification, for example, a field width of 100 μm to 2000 μm. The objective lens 4 can guide the light L to the imaging device 5 and form (project) an image of the inspection mask 7 on the imaging element of the imaging device 5. The objective lens 4 can set the magnification according to the imaging element. The imaging element of the imaging device 5 can generate two-dimensional image data corresponding to the formed image (projection image). The image data can be configured as, for example, a combination of the luminance information of two-dimensional pixels and their coordinates. The imaging device 5 can convert the projection image into an electrical signal as image data and output it.

[0031] The pellicle inspection apparatus 100 has a mask support portion 9 for supporting the inspection mask 7, and the mask support portion 9 supports the inspection mask 7 such that the inspection mask 7 is positioned between the illumination device 1 and the objective lens 4.

[0032] As shown in FIG. 1(B), the inspection mask 7 is provided with a transmissive region and a light-shielding region. Specifically, the inspection mask 7 is configured as a mask in which a pattern 7b is formed as an inspection pattern on a light-transmissive substrate 7a. The pattern 7b is formed of, for example, a light-shielding film, and a plurality of patterns extending along the Z direction in the drawing are formed, for example. In the transmissive region, the light-transmissive substrate 7a is exposed, and in the light-shielding region, a pattern composed of a light-shielding film is formed on the light-transmissive substrate 7a.

[0033] Preferably, the pattern 7b constitutes a line of a line-and-space in which the light-shielding region and the transmissive region are alternately arranged. The width of the pattern 7b (light-shielding region) can be preferably set to the resolution limit value of the assumed exposure process, and can be, for example, 1 μm to 5 μm, but is not limited thereto. Also, the space between the patterns 7b may be, for example, equal to the line width. It is a simple repeating pattern and is easy to create, while being able to effectively detect defects. As the shape of the pattern 7b, for example, a line-and-space with a stable edge shape can be used, and defect inspection using a pattern inspection method also becomes easy. Note that the shape of the pattern 7b is not limited to a line-and-pattern, and all patterns capable of detecting defects such as a dot pattern can be adopted. The size of the inspection mask 7 and the width of the pattern 7b can be determined by the required detection sensitivity and the processing time of the inspection process of the pellicle 8. The inspection mask 7 can be created by a known method for manufacturing a photomask.

[0034] The pellicle inspection apparatus 100 has a pellicle support portion 10 (inspection object support portion) for supporting the pellicle 8. The pellicle support portion 10 supports the pellicle 8 such that the pellicle 8, particularly the pellicle film 8a of the pellicle 8, is positioned between the inspection mask 7 and the objective lens 4. The flat pellicle film 8a is arranged in parallel with the inspection mask 7. The relationship between the inspection mask 7 and the pellicle film 8a is configured to be close to the relationship between the actual photomask and the pellicle film 8a. The pellicle 8 includes a pellicle film 8a and a frame 8b for fixing to the photomask, and the pellicle film 8a is fixed to the frame 8b. The pellicle support portion 10 supports the frame 8b.

[0035] The illumination lens 3 is configured such that the focal point F of the light L can be adjusted to be positioned at the pattern 7b of the inspection mask 7. Therefore, the focal point F of the light L is positioned on the light source 2 side from the pellicle film 8a. By simulating and reproducing the geometric positional relationship between the actual pellicle film 8a and the focal point F, the sensitivity of the defect inspection can be increased, and the detection of excessive defects can be prevented, thereby realizing an effective defect inspection. The distance between the focal point F and the pellicle film 8a can be, for example, a distance approximately the same as the height of the frame 8b (the length in the Y direction in FIG. 1(A)) (for example, a value exceeding 1 to 3 times), but is not limited thereto.

[0036] The light L emitted from the light source 2 passes through the inspection mask 7 by the illumination lens 3 and is incident on the pellicle film 8a. Then, the light L transmitted through the pellicle film 8a is guided to the imaging device 5 by the objective lens 4, and an image of the pattern 7b is projected onto the imaging device 5. The imaging device 5 generates image data corresponding to the image of the projected light L (i.e., the image of the projected pattern 7b), and transmits (outputs) the image data as an image signal to the detection circuit 6. The detection circuit 6 can store the image data (input) acquired by the received image signal in the storage device. The image data can reproduce the image of the pattern 7b projected onto the imaging device 5. Note that the storage device may be built in the detection circuit 6 or may be externally attached.

[0037] As described above, the image of the pattern 7b is formed on the imaging device 5 (particularly, on its imaging element). If there is an optical abnormality in the pellicle film 8a, an abnormality (e.g., an abnormality in dimensional width or luminance) occurs in the formed pattern due to defocusing of the exposure light or the like. By comparing the image of the formed pattern 7b with the image of the normal pattern 7b, an abnormality in the pellicle film 8a can be detected.

[0038] By relatively moving the pellicle film 8a with respect to the inspection mask 7 and the illumination device 1, image data of the entire pellicle film 8a can be acquired. The relative movement direction of the pellicle film 8a can preferably be the direction perpendicular to the longitudinal direction (Z direction in FIG. 1(B)) of the pattern 7b (light-shielding region), which is a line pattern (X direction in FIG. 1(B)). By relatively moving the pellicle film 8a so as to cross the line pattern, it is possible to avoid the line pattern from interfering with the detection of the abnormal portion of the pellicle film 8a.

[0039] FIG. 2 schematically shows the direction in which the inspection region SA where the pattern 7b is formed scans over the pellicle film 8a to be inspected. The inspection region SA is a region for inspecting the presence or absence of an abnormality in the pellicle film 8a. The dotted arrow in FIG. 2 schematically shows the scanning direction of the inspection region SA. The inspection region SA can be relatively moved back and forth in a zigzag manner with respect to the pellicle film 8a to scan the entire surface of the pellicle film 8a. The detection circuit 6 stores the image data acquired using the imaging device 5 in the inspection region SA in a storage device in association with the position (coordinates) of the inspection region SA.

[0040] As shown in FIG. 2(A), the illumination device 1, inspection mask 7, objective lens 4, and imaging device 5 are fixed, and only the pellicle film 8a is moved. Note that, in order to move the pellicle film 8a, the pellicle support portion 10 can be moved. The pellicle support portion 10 can be moved by a driving device (not shown). The position information (coordinates) of the inspection area SA is transmitted to the detection circuit 6. The detection circuit 6 can store, for example, the ID number for identifying the inspection area SA and its position information in association with each other in a storage device. Note that the time may be used as the ID number.

[0041] Alternatively, as shown in FIG. 2(B), conversely, the pellicle film 8a can be fixed and the inspection area SA can be moved by moving other components such as the illumination device 1. In this case, the illumination device 1 and the like may be moved by a driving device (not shown). The position information (coordinates) of the inspection area SA is transmitted to the detection circuit 6. In either case, the positional relationship of the components (illumination device 1, inspection mask 7, objective lens 4, and imaging device 5) other than the pellicle 8 to be inspected is fixed.

[0042] While relatively moving the pellicle film 8a, image data may be continuously acquired by the imaging device 5, or the pellicle film 8a may be moved by a predetermined distance like step and repeat and then stopped, and the imaging device 5 may be configured to acquire image data in the stopped state. Note that, when the movement by step and repeat is adopted, if the above-mentioned predetermined distance is an integer multiple of the pitch of the line and space, foreign matter located in the pattern 7b (light-shielding area) may not be detected. Therefore, the above-mentioned predetermined distance can be a value obtained by adding a distance equal to the width of the light-shielding area to an integer multiple of the pitch. All areas of the pellicle film 8a can be inspected by being projected at least once by the transmission area of the inspection pattern portion. The same applies when other patterns such as a dot pattern are adopted as the pattern 7b. The above-mentioned predetermined distance may be determined based on the pitch of the adopted pattern.

[0043] By adopting a minute dot pattern, it is possible to detect even minute defects as compared with a line and space pattern. The corner portions of the dot pattern are greatly affected by defocus and tend to become rounded. In the corner portions, a large difference in luminance tends to appear, and the detection sensitivity can be improved.

[0044] The detection circuit 6 compares the acquired projection image of the inspection area SA with the projection image of the optically normal pellicle film 8a. When a difference is confirmed between the two projection images, it can be determined that there is an optical abnormality in the pellicle film 8a of the inspection area SA. Note that a projection image (optically normal image) from the pellicle film 8a in which no defect (foreign matter, unevenness, etc.) exists may be referred to as a "reference image", and the image data generated from the "reference image" may be referred to as "reference image data". The reference image data, which is optically normal image data, may be stored in the storage device as reference reference data. Also, for simplicity, an "optically normal image" may be referred to as a "normal image".

[0045] The detection circuit 6 can store the acquired image data in the storage device in association with the time or position at which the image data was acquired. Further, the detection circuit 6 includes a difference detection circuit such as a simple comparison difference circuit or a density difference type detection circuit, and can compare the image data acquired several seconds ago or the image data at a position several millimeters ago. Note that since there are many normal image data among the normal image data, it is easy to determine whether the acquired image data is normal image data. Such a method of comparing image data can use the die-to-die comparison method employed in a known pattern inspection apparatus. The detection circuit 6 can register the inspection area SA in which an abnormality has been detected in the storage device as an abnormal area.

[0046] Note that the detection circuit 6 may have a function of correcting the variation in light intensity. The correction function can, for example, softly reduce the influence of the variation in the intensity of light within the field of view, or the influence of changes over time in the illumination device 1, the imaging device 5, etc. It is possible to maintain the pellicle inspection apparatus 100 in a more stable state.

[0047] In this way, by detecting the imaging image of the inspection pattern 7b that has passed through the pellicle film 8a and inspecting the image, it is possible to detect defects in the pellicle film 8a that were difficult in the past.

[0048] In the case of a conventional inspection apparatus that detects transmittance, when the detection sensitivity is increased to detect unevenness in the pellicle film 8a, noise is detected or a slight change in optical characteristics that does not affect the actual lithography process is detected. Therefore, it has been difficult to actually detect unevenness in the pellicle film 8a. However, in this pellicle inspection apparatus 100, by utilizing the optical characteristics of the light L that has passed through the inspection pattern section, it is possible to sensitively detect defects in the pellicle film 8a that affect the exposure process.

[0049] Note that this pellicle inspection apparatus 100 is not limited to the pellicle film 8a and can also be applied to the defect inspection of a light-transmitting substrate (quartz substrate, soda-lime glass, low-expansion glass, etc.) used for a photomask. It is only necessary to support the light-transmitting substrate to be inspected on the pellicle support section 10 (specimen support section) instead of the pellicle film 8a. The light-transmitting substrate is a flat transparent body that is transparent to the exposure light. By inspecting the image of the pattern 7b that forms an image after passing through the light-transmitting substrate, it is possible to detect optical unevenness, foreign matter, etc. in the light-transmitting substrate. In short, the pellicle inspection apparatus 100 is applicable not only to the pellicle film but to all transparent bodies that transmit light.

[0050] (Embodiment 2) The pellicle inspection apparatus 100 may incorporate an inspection pattern section inside the illumination device 1. FIG. 3(A) is a schematic diagram showing the main configuration of the pellicle inspection apparatus 100 according to Embodiment 2, and FIG. 3(B) is a plan view schematically showing the projection pattern unit 11 (inspection pattern unit) used in the pellicle inspection apparatus 100.

[0051] As shown in FIG. 3(A), the illumination device 1 includes a light source 2 that emits light L, a projection pattern unit 11, and an illumination lens 12. The illumination lens 12 is composed of, for example, a combination of a condenser lens, a condenser lens, and a projection lens. The light source 2, the projection pattern unit 11, and the illumination lens 12 are housed in the housing of the illumination device 1. The projection pattern unit 11 is supported so as to be located between the light source 2 and the illumination lens 12. The projection pattern unit 11 can be appropriately replaced according to the sensitivity and throughput of defect inspection.

[0052] As shown in FIG. 3(B), the projection pattern unit 11 has a light-transmissive substrate 11a, and a pattern 11b constituting an inspection pattern used for inspection is formed on the light-transmissive substrate 11a. The projection pattern unit 11 may have the same configuration as the inspection mask 7 of Embodiment 1, and the configuration of the pattern 11b may be the same as that of the pattern 7b.

[0053] The illumination lens 12 is adjusted so that the focal point F of the light L emitted from the light source 2 is located on the intermediate image projection plane MP. Note that the intermediate image projection plane MP is a virtual plane and there is no actual plane. The pellicle film 8a of the pellicle 8 is installed between the intermediate image projection plane MP and the objective lens 4, and the focal point F of the light L is located on the light source 2 side from the pellicle film 8a. The flat pellicle film 8a is arranged parallel to the intermediate image projection plane MP. The light L emitted from the illumination device 1 passes through the pellicle film 8a, and an image of the pattern 11b is formed on the imaging device 5 by the objective lens 4. The imaging device 5 transmits an image signal corresponding to the detected image data to the detection circuit 6, and the detection circuit 6 can investigate the presence or absence of defects on the pellicle film 8a based on the acquired image data.

[0054] Since the illumination device 1 incorporates the projection pattern section 11, there is no need to secure an area for installing the inspection mask 7 between the illumination device 1 and the pellicle film 8a. Therefore, it is possible to set a longer distance between the illumination device 1 and the objective lens 4. The space for arranging the pellicle 8 between the illumination device 1 and the objective lens 4 expands, improving the operability of the pellicle inspection apparatus 100.

[0055] (Embodiment 3) The pellicle inspection apparatus 100 may have a review function. FIG. 4 is a schematic diagram for explaining the review function provided in the pellicle inspection apparatus 100. FIG. 4(A) shows a configuration example having a review function employing coaxial epi-illumination, and FIG. 4(B) shows a configuration example having a review function employing side illumination. With the pellicle inspection apparatus 100 having a review function, it is possible to easily observe the detected defects.

[0056] In the configuration shown in FIG. 4(A), the pellicle inspection apparatus 100 has a first light source 13a (first review light source 13a) for review, and further has a reflecting mirror 14 between the objective lens 4 and the imaging device 5. The reflecting mirror 14 may be, for example, a half mirror. The first light source 13a emits light L perpendicular to the optical axis of the objective lens 4. When a half mirror is employed as the reflecting mirror 14, it becomes possible to perform coaxial epi-illumination on the inspection region SA of the inspection target. Note that, for example, a lamp light source or a laser light source can be used as the light source 13.

[0057] Furthermore, the pellicle inspection apparatus 100 has a display device 15 that receives the image signal of the imaging device 5. The light L emitted from the first light source 13a enters the reflecting mirror 14, and at least a part (for example, 50%) of the light L is reflected by the reflecting mirror 14 and guided to the pellicle film 8a via the objective lens 4. The objective lens 4 can be adjusted so that the focal point of the light L is located on the surface of the pellicle film 8a.

[0058] The detection circuit 6 moves the pellicle 8 relative to the objective lens 4 and moves the inspection area SA registered in the storage device as an abnormal area into the field of view of the objective lens 4. The light L reflected in the inspection area SA is guided by the objective lens 4 to the imaging device 5, and the imaging device 5 transmits an image signal to the display device 15. The display device 15 displays a surface image of the pellicle film 8a in the inspection area SA based on the image signal. Using the reflected light of the light L, unevenness of the pellicle film 8a can also be detected, for example, as interference fringes.

[0059] In the configuration shown in FIG. 4(B), the pellicle inspection device 100 has a second light source 13b (second review light source 13b) for review. The second light source 13b emits light L having a predetermined angle with respect to the optical axis of the objective lens 4 and can perform side illumination on the inspection area SA of the inspection object. The light L reflected in the inspection area SA is guided by the objective lens 4 to the imaging device 5. The surface of the pellicle film 8a in the inspection area SA can be observed by the display device 15 connected to the imaging device 5. Note that the second light source 13b may be composed of, for example, a plurality of small light sources and arranged so as to draw a circle around the optical axis of the objective lens 4. In this case, the second light source 13b constitutes ring illumination.

[0060] The pellicle inspection device 100 may have a configuration including the first light source 13a, the mirror 14, and the second light source 13b, and having both the configuration shown in FIG. 4(A) and the configuration shown in FIG. 4(B). With such a configuration, an operator can appropriately select coaxial epi-illumination by the first light source 13a or side illumination by the second light source 13b according to the inspection object and observe defects of the inspection object. Note that even if the pellicle inspection device 100 has a configuration including the mirror 14, by using the mirror 14 as a half mirror, a part (for example, 50%) of the reflected light of the light L of the second light source 13b from the inspection object is transmitted, so that an image of the inspection object can be detected by the imaging device 5.

[0061] As described above, the operator can confirm the abnormal portion of the pellicle film 8a by observing in detail the portion where the abnormality is detected from the image displayed on the display device 15. Note that the display device 15 may be incorporated in the imaging device 5.

[0062] (Defect inspection method) Hereinafter, the inspection process of the pellicle 8 using the pellicle inspection device 100 will be described. Step 1: Optical system adjustment Irradiate the light L, and adjust the illumination lens 3 (or illumination lens 12) and the objective lens 4 so that the light L that has passed through the inspection pattern portion (inspection mask 7, projection pattern portion 11) is focused on the imaging device 5. Note that the in-plane variation in the intensity of the light L detected by the imaging device 5, the change over time, etc. may be corrected by the light intensity variation correction function of the detection circuit 6. Step 2: Preparation of the inspection object Install the pellicle film 8a (transparent body) that is the inspection object. The pellicle film 8a is arranged at a predetermined position (between the illumination device 1 and the objective lens 4 and on the objective lens 4 side from the focal point F) by fixing the pellicle 8 to the pellicle support portion 10 (specimen support portion). Step 3: Light irradiation Irradiate the light L emitted from the light source 2 onto the inspection pattern portion, and irradiate the inspection region SA of the pellicle film 8a with the transmitted light (or the transmitted image of the inspection pattern) from the inspection pattern portion, specifically. Step 4: Image data generation The light L (or the image formed by the light L) transmitted through the inspection region SA of the pellicle film 8a is imaged on the imaging device 5. The imaging device 5 generates image data corresponding to the received light (or the formed image), converts it into an image signal, and transmits (outputs) it to the detection circuit 6. The detection circuit 6 receives the image signal and acquires (inputs) the image data of the inspection region SA. The detection circuit 6 can store the acquired image data. Step 5: Detection of Abnormality (Defect Judgment) The detection circuit 6 determines the presence or absence of a defect in the pellicle film 8a in the inspection area SA based on the received image signal. Specifically, the inspection circuit 6 reproduces image data from the image signal, compares the image data at each coordinate in the inspection area SA, and identifies abnormal locations. Note that as the determination method, a known determination method for pattern inspection of the die-to-die method used in the photomask manufacturing process or the semiconductor manufacturing process can be adopted. For example, the image data of the newly acquired inspection area SA is compared with the image data of the inspection area SA acquired a predetermined time before (or a predetermined distance before). The predetermined time is, for example, several seconds, and the predetermined distance is several millimeters, but it can be set according to the size of the inspection pattern and the scanning speed of the inspection area SA. Mutually compare the acquired image data of the inspection area SA, When there is no difference between the image data to be determined and the normal image data (reference image data), it is determined that the pellicle film 8a in the inspection area SA is normal (without defects), When there is a difference between the image data to be determined and the normal image data, it is determined that the pellicle film 8a in the inspection area SA is abnormal (with defects). The position coordinates of the inspection area SA determined to be abnormal are registered and stored in the storage device in association with the image data as abnormal locations. Step 6: Review Observe the locations determined to be abnormal as necessary. Observe the pellicle film 8a in the inspection area SA at the coordinates registered as abnormal locations, and classification and analysis of the abnormal locations can be performed.

[0063] Move the inspection area SA to the pellicle film 8a to be inspected, and repeat steps 2 to 5. The inspection area SA moves over the entire surface of the object to be inspected and is scanned to acquire image data. Note that the detection circuit 6 may scan the entire surface of the inspection target, store the image data of the inspection area SA at each scanning position in the storage device, and finally determine the presence or absence of defects in the inspection area SA at each scanning position in step 5.

[0064] The pellicle 8 having the pellicle film 8a where an abnormality is confirmed is subjected to necessary processes such as recreation, and the pellicle 8 having the pellicle film 8a determined to have no abnormality is fixed to the photomask.

[0065] Note that an optical system of reduction projection or enlargement projection may be adopted as the optical system of the illumination lens 3 of the pellicle inspection apparatus 100, and a corresponding inspection pattern 7 may be adopted. In this case, the image of the inspection pattern 7 can be directly projected onto the imaging device 5, and the objective lens 4 can be made unnecessary. As a result, the space for installing the inspection target (pellicle film 8a) can be enlarged, and the operability of the pellicle inspection apparatus 100 can be improved. Also, in the case of enlargement projection, the spatial resolution of the imaging device 5 can be optically improved.

[0066] (Defect examples of pellicle film) FIG. 5 shows an example of an image acquired by the imaging device 5. FIG. 5(A) is a normal image of the inspection pattern (pattern 7b), FIGS. 5(B) and (C) are images of the inspection pattern (pattern 7b) determined to be abnormal, and FIGS. 5(D) and (E) are review images of the pellicle film 8a in the inspection area SA determined to be abnormal. The review image in FIG. 5(D) corresponds to the inspection area SA shown in FIG. 5(B), and the review image in FIG. 5(E) corresponds to the inspection area SA shown in FIG. 5(C).

[0067] It can be understood that the image shown in FIG. 5(B) has an unclear edge portion and an increased luminance of the edge portion as compared with the inspection pattern shown in FIG. 5(A). As shown in the review image in FIG. 5(D), stripe-like unevenness of the pellicle film 8a is observed in the area corresponding to the image shown in FIG. 5(B), and it is considered that there is an abnormality in the optical characteristics in this uneven portion.

[0068] The image shown in FIG. 5(C) has a clear edge. Compared with the inspection pattern shown in FIG. 5(A), although the difference in luminance at the edge portion is considered to be small, it can be understood that there are dark regions between the inspection patterns and locations where the luminance decreases. As shown in the review image of FIG. 5(E), foreign matter was observed on the pellicle film 8a in the region corresponding to the image shown in FIG. 5(C).

[0069] With conventional inspection apparatuses, it was difficult to detect unevenness particularly based on slight differences in the transmittance of the pellicle film 8a. However, by inspecting the image of the pattern 7b formed through the pellicle film 8a, it is considered that optical effects such as unevenness of the pellicle film 8a are emphasized and automatic detection has become possible. In addition, since an image having an abnormality due to unevenness of the pellicle film 8a (FIG. 5(D)) and an image having an abnormality due to foreign matter (FIG. 5(E)) exhibit different appearances, it is also possible to classify the abnormal locations based on the detected images.

Industrial Applicability

[0070] According to the present invention, it is possible to obtain an inspection method and an inspection apparatus capable of detecting defects in a pellicle film, which have been difficult in the past. This inspection apparatus can contribute to the quality control of the pellicle, and as a result, can also contribute to the quality control of the photomask. In addition, this inspection method and inspection apparatus are not limited to the pellicle film, and can also be applied to the transparent substrate used for the photomask. The industrial applicability of the present invention is high.

Explanation of Signs

[0071] 100 Pellicle inspection apparatus (defect inspection apparatus) 1 Lighting apparatus 2 Light source 3 Illumination lens (first illumination lens) 4 Objective lens 5 Imaging apparatus (camera) 6 Detection circuit 7 Inspection mask (inspection pattern section) 7a Translucent substrate 7b Pattern 8 Pericle 8a Pericle film 8b Frame 9 Mask support section 10 Pericle support section (specimen support section) 11 Projection pattern section (inspection pattern section) 11a Translucent substrate 11b Pattern 12 Illumination lens (second illumination lens) 13a First light source (first review light source) 13b Second light source (second review light source) 14 Reflecting mirror 15 Display device F Focus L Light MP Intermediate image projection plane SA Inspection area

Claims

1. A defect inspection apparatus for a transparent body, comprising a light source, an inspection pattern section, an imaging device, and a detection circuit, configured such that light emitted from the light source passes through the inspection pattern section and the transparent body in this order and is incident on the imaging device, wherein the imaging device outputs an image signal corresponding to the incident light to the detection circuit characterizing the defect inspection apparatus.

2. The inspection pattern section has a line and space pattern in which a transmission region and a light-shielding region are arranged alternately characterizing the defect inspection apparatus according to Claim 1.

3. The transparent body is a pellicle film, characterizing the defect inspection apparatus according to Claim 1 or 2.

4. Further comprising an illumination lens, wherein the position of the focus of the light is configured to be located on the light source side of the transparent body by the illumination lens characterizing the defect inspection apparatus according to Claim 1 or 2.

5. The inspection pattern section is located between the illumination lens and the transparent body, characterizing the defect inspection apparatus according to Claim 4.

6. The inspection pattern section is located between the light source and the illumination lens, characterizing the defect inspection apparatus according to Claim 4.

7. Further comprising a review light source and a mirror, wherein the mirror is disposed between the transparent body and the imaging device, and is configured to guide light irradiated from the review light source to the transparent body characterizing the defect inspection apparatus according to Claim 1.

8. A method for inspecting defects of a transparent body, comprising a first step of irradiating light emitted from a light source to an inspection pattern section and irradiating transmitted light from the inspection pattern section to the transparent body, a second step of an imaging device that has received the light transmitted through the transparent body outputs image data to a detection circuit, and a third step in which the detection circuit acquires the image data and determines whether there are defects in the transparent body characterizing the defect inspection method.

9. In the third step, the detection circuit compares the acquired image data with reference image data, and when a difference is confirmed, has a step of determining that there are defects in the transparent body characterizing the defect inspection method according to Claim 8.

Images