JP6131448B2 - Confocal optical inspection apparatus and confocal optical inspection method - Google Patents

Description

  The present invention relates to a confocal optical inspection apparatus and a confocal optical inspection method for inspecting an object using a confocal optical system.

  One apparatus for obtaining a high-resolution image of an object is a confocal microscope that focuses on a confocal optical system. A confocal microscope includes a pinhole plate in which a plurality of minute pinholes are formed between an image sensor and an objective lens, and a pinhole in which illumination light passes only through the image formed on the surface of the pinhole plate by the objective lens. Pass through the same pinhole. By blocking scattered light or the like that does not form an image on the surface of the pinhole plate by the pinhole plate, it becomes possible to generate a clear image free from noise due to defocusing or flare light.

  In the confocal microscope, when the observation area of the object is much larger than one image projected by the objective lens, processing such as taking a series of images while moving the object is necessary. For example, Patent Document 1 discloses a confocal microscope in which an object is placed on a moving stage, and an image formed by a confocal optical system is acquired by a TDI (Time Delayed Integration) camera.

Japanese Patent No. 3970998

  Here, the optical system is considered as a kind of transmission path, and distortion may occur there. When the optical transmission path is distorted, the resolution of the obtained image is reduced. However, the confocal microscope of Patent Document 1 does not consider the distortion of the optical transmission path and does not perform processing on the obtained image.

  Therefore, the present invention has been made in view of the above problems, and an object of the present invention is to acquire information on an object with higher accuracy in consideration of distortion of an optical transmission path. It is an object of the present invention to provide a new and improved confocal optical inspection apparatus and confocal optical inspection method.

  In order to solve the above problems, according to an aspect of the present invention, there is provided a confocal optical inspection apparatus that acquires a confocal image of an object and inspects the object. The confocal optical inspection apparatus includes a light source that emits illumination light, a first aperture member that has a plurality of apertures that convert illumination light emitted from the light source into a plurality of illumination lights, and is reflected by an object. From the TDI image obtained by the TDI operation of the imaging unit using the imaging unit that images each illumination light and acquires the image, and the PSF that represents the optical system characteristics of the confocal optical inspection device measured in advance And an information processing unit that acquires a corrected confocal image from which the optical transmission line distortion of the confocal optical inspection apparatus is removed.

  According to the present invention, the PSF representing the optical system characteristics of the confocal optical inspection apparatus is measured in advance, and the optical transmission path of the confocal optical inspection apparatus is obtained from the TDI image acquired by the imaging unit using the PSF. A corrected confocal image from which distortion has been removed is acquired. The corrected confocal image is an image obtained by estimating the confocal image acquired when there is no distortion of the optical transmission path based on the PSF and the TDI image. Therefore, by acquiring the corrected confocal image, it is possible to acquire an image representing the object shape of the target with higher accuracy than the TDI image acquired by the imaging unit.

Here, the confocal image of the object that is the PSF, TDI image, and original image satisfies the following Equation 1, and the information processing unit calculates the inverse matrix of the PSF, thereby correcting the confocal image that is an estimated image of the confocal image. Get an image.
Here, g (x) is a TDI image, p (x) is a PSF, and f (x) is a confocal image. Further, x indicates a pixel position of the TDI image, and i takes a value of 0 to N.

  Further, the PSF may be acquired by imaging the target object in a state where the target object is stopped.

  Each opening of the first opening member is formed in a lattice shape with a predetermined shift amount in the first direction which is the scanning direction of the object and in the second direction orthogonal to the scanning direction. The shift amount in the second direction of the opening may be an integer multiple of the pixel size of the TDI image.

  Further, each opening of the first opening member may be a pinhole, for example.

  Furthermore, the confocal optical inspection apparatus may include a second opening member having a plurality of openings through which reflected light from an object incident on the imaging unit passes. The opening of the second opening member is formed such that the opening length in the insertion / extraction direction in which the second opening member is inserted / extracted from the confocal optical inspection apparatus is larger than the opening length in the direction orthogonal to the insertion / extraction direction. Also good.

  The second opening member may be provided in the confocal optical inspection apparatus so that it can be inserted and removed in a second direction orthogonal to the scanning direction of the object.

  Moreover, in order to solve the said subject, according to another viewpoint of this invention, the confocal optical inspection method which acquires the confocal image of a target object and test | inspects a target object is provided. Such a confocal optical inspection method includes a step of obtaining a PSF representing the optical system characteristics of the confocal optical inspection apparatus, and a TDI obtained by TDI operation of an imaging unit of the confocal optical inspection apparatus using the PSF. Obtaining a corrected confocal image obtained by removing the optical transmission line distortion of the confocal optical inspection apparatus from the image.

  As described above, according to the present invention, a confocal optical inspection apparatus and a confocal optical inspection method capable of acquiring information on an object with higher accuracy in consideration of distortion of an optical transmission line. Can be provided.

It is a schematic explanatory drawing which shows the structure of the confocal optical inspection apparatus which concerns on this embodiment. It is a partial expanded sectional view of the micro lens array and pinhole member concerning the embodiment. It is a top view which shows one structural example of the pinhole member which concerns on the same embodiment. It is an image which shows an example of the spot image in the imaging surface of a TDI camera. It is explanatory drawing which shows the image of the integration result (one-dimensional) by a TDI camera. It is a block diagram which shows the function structure of the information processing part which concerns on the same embodiment. It is a flowchart which shows the correction process of the TDI image which concerns on the embodiment. It is a top view which shows the slit member which is an example of the opening member by the side of light reception.

  Exemplary embodiments of the present invention will be described below in detail with reference to the accompanying drawings. In addition, in this specification and drawing, about the component which has the substantially same function structure, duplication description is abbreviate | omitted by attaching | subjecting the same code | symbol.

<1. Configuration of Confocal Optical Inspection Device>
First, a configuration of a confocal optical inspection apparatus according to an embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a schematic explanatory diagram illustrating the configuration of the confocal optical inspection apparatus according to the present embodiment. FIG. 2 is a partially enlarged cross-sectional view of the microlens array 122 and the pinhole member 130 according to the present embodiment. FIG. 3 is a plan view illustrating a configuration example of the pinhole member 130 according to the present embodiment. FIG. 4 is an image showing an example of a spot image on the imaging surface of the TDI camera 150. FIG. 5 is an explanatory diagram showing an image of the integration result (one-dimensional) by the TDI camera 150. FIG. 6 is a block diagram illustrating a functional configuration of the information processing unit 160 according to the present embodiment.

  A confocal optical inspection apparatus 100 according to the present embodiment is an apparatus that optically inspects a defect of an object such as a semiconductor wafer 10 using a confocal optical system. The confocal optical inspection apparatus 100 according to the present embodiment can detect an object so that an object having a wide inspection area such as the semiconductor wafer 10 can be inspected with respect to a range where the image can be captured once. A moving stage that is placed and moved on a plane is provided. The confocal optical inspection apparatus 100 acquires an image formed by a confocal optical system of an object placed on a moving stage with a TDI camera 150 and acquires information on the shape of the object as a TDI image. .

  As shown in FIG. 1, the confocal optical inspection apparatus 100 emits light irradiating an object from a light source 110 and irradiates the semiconductor wafer 10 as the object, and the reflected light from the semiconductor wafer 10 is captured by an imaging device. By receiving light with a certain TDI camera 150, information on the shape of the semiconductor wafer 10 is acquired. Transmission of light among the light source 110, the semiconductor wafer 10, and the TDI camera 150 is performed by the relay lenses 121, 123, 125, 126, the microlens array 122, the objective lens 124, and the beam splitter 140. The microlens array 122 is provided with a pinhole member 130 on the light exit surface side.

  The light source 110 of the confocal optical inspection apparatus 100 according to the present embodiment emits laser light. The emitted laser light is incident on the microlens array 122 via the relay lens 121. The microlens array 122 is a member formed by arranging a plurality of microlenses in a lattice shape. For example, as shown in FIG. 2, a plurality of microlenses having a curved surface on the light incident surface 122a side and a flat surface on the exit surface 122b side are provided. It is arranged and configured. A pinhole member 130 is provided on the emission surface 122 b side of the microlens array 122.

  The pinhole member 130 has a plurality of pinholes 132 formed therein. For example, as shown in FIG. 3, each pinhole 132 of the pinhole member 130 has a predetermined shift amount in the first direction that is the scanning direction of the object and in the second direction that is orthogonal to the scanning direction. Is formed. Note that the scanning direction of the object, which is the first direction, corresponds to a TDI integration direction in which a TDI camera 150 described later integrates spot light collected on the TDI camera 150. The second direction is also referred to as the TDI longitudinal direction. Here, out of the shift amounts in each direction, the shift amount d in the second direction is preferably an integer multiple of the pixel size of the TDI image. Thereby, the calculation process for acquiring the confocal image which removed the optical system transmission distortion mentioned later can be performed efficiently, and a processing speed can be raised.

  In the confocal optical inspection apparatus 100, the microlens array 122 is not necessarily provided. However, in the present embodiment, the microlens array 122 is provided in order to ensure the amount of laser light from the light source 110. The microlens array 122 and the pinhole member 130 are arranged so that the condensing position of each microlens of the microlens array 122 corresponds to each pinhole 132 formed in the pinhole member 130.

  The laser light that has passed through the pinhole 132 enters the beam splitter 140 through the relay lens 123. As the beam splitter 140, for example, a non-polarizing beam splitter is used. The beam splitter 140 reflects the laser beam incident from the pinhole member 130 side to the objective lens 124 side. The laser beam reflected by the beam splitter 140 is collected by the objective lens 124 and irradiated onto the surface of the semiconductor wafer 10 that is the object.

  The laser light applied to the surface of the semiconductor wafer 10 is reflected by the surface, passes through the objective lens 124 again, and enters the beam splitter 140. The beam splitter 140 guides laser light incident from the semiconductor wafer 10 side to the TDI camera 150 side. The reflected light that has passed through the beam splitter 140 is condensed on the TDI camera 150 via the relay lenses 125 and 126.

  The TDI camera 150 acquires a TDI image based on the intensity of each collected spot light. The TDI camera 150 is formed by arranging a plurality of line units in which image pickup elements are arranged in a row in a direction orthogonal to the arrangement direction of the image pickup elements. When the object is imaged without moving the moving stage on which the object is placed, an image on which a plurality of spot images as shown in FIG. 4 appear is formed on the imaging surface of the TDI camera 150, for example. This confocal image acquired without moving the object is an image including distortion of the optical transmission path of the confocal optical system, and represents the PSF at each position.

  On the other hand, when inspecting the entire surface of the object, the TDI camera 150 sequentially images the surface of the object while moving the object by moving the moving stage. At this time, the TDI camera 150 integrates, in the first direction, images obtained by forming spot lights aligned in a second direction orthogonal to the scanning direction of the object on the imaging surface. To obtain a TDI image representing the whole.

  That is, in each line unit of the TDI camera 150, as shown in FIG. 5, an image in which spot lights arranged in the second direction overlap is acquired. For such imaging, the TDI camera 150 first transfers the imaging obtained by the line unit of the first column to the line unit of the second column, and then the second column is subjected to the imaging sent from the first column. The image obtained by the line unit is added and accumulated, and transferred to the third line unit. Similarly, the TDI camera 150 adds the imaging obtained by the line unit of the nth column to the imaging accumulated up to the (n−1) th column and transfers it to the (n + 1) th column. The TDI image finally obtained by such integration processing is a highly sensitive image having sufficient brightness. The TDI camera 150 outputs a TDI image obtained by integrating the image obtained by each line unit in the scanning direction (first direction) to the information processing unit 160.

  The information processing unit 160 performs processing for acquiring an original image obtained by removing distortion of the optical transmission path from the TDI image acquired by the TDI camera 150. As illustrated in FIG. 6, the information processing unit 160 includes a TDI image acquisition unit 162, a correction processing unit 164, and an output unit 166.

  The TDI image acquisition unit 162 receives the TDI image output from the TDI camera 150 and outputs it to the correction processing unit 164. The correction processing unit 164 acquires an original image obtained by removing distortion of the optical system transmission path from the TDI image input from the TDI image acquisition unit 162 using PFS (Point Spread Function). PSF is a function that represents the characteristics of an optical transmission line. Based on the characteristics of the optical transmission path, the correction processing unit 164 corrects the TDI image by calculating and acquiring an original image from which distortion of the optical transmission path of the TDI image acquired by the TDI camera 150 is removed. . Details of the correction processing by the correction processing unit 164 will be described later. The correction processing unit 164 outputs the original image to the output unit 166. The output unit 166 appropriately outputs the acquired original image to a display device (not shown) or a storage device (not shown) that stores information.

  The configuration of the confocal optical inspection apparatus 100 according to this embodiment has been described above. The confocal optical inspection apparatus 100 according to the present embodiment performs a correction for removing distortion of the optical transmission path by the information processing unit 160 on the TDI image acquired by the TDI camera 150, thereby providing a clearer image of the object. Can be obtained, and performance degradation due to variations in the optical system can be avoided. Hereinafter, a TDI image correction process performed by the information processing unit 160 of the confocal optical inspection apparatus 100 will be described with reference to FIG. FIG. 7 is a flowchart showing a TDI image correction process according to this embodiment.

<2. TDI image correction processing>
In the TDI image correction process by the information processing unit 160 of the confocal optical inspection apparatus 100 according to the present embodiment, first, as shown in FIG. A PSF representing the characteristics of the optical transmission path is acquired (S110). As described above, PSF is a function representing the characteristics of the optical transmission line. In step S110, with the moving stage stopped, the pinhole member 130 is set so that the spot size on the surface of the object sample placed on the moving stage is about the diffraction limit. An image is acquired by the camera 150. The TDI image obtained at this time is, for example, a spot image as shown in FIG. 4, and this is a PSF representing the characteristics of the optical transmission line of the confocal optical inspection apparatus 100. The acquired PSF is recorded in a storage unit (not shown) that can be referred to by the correction processing unit 164.

  Next, the confocal optical inspection apparatus 100 integrates the images obtained by scanning the object and acquires a TDI image (S120). The TDI image is acquired by the TDI camera 150 and input to the TDI image acquisition unit 162 of the information processing unit 160. The TDI image acquisition unit 162 outputs the input TDI image to the correction processing unit 164.

  Receiving the input of the TDI image, the correction processing unit 164 acquires the original image from which the distortion of the optical transmission path is removed from the TDI image using the PSF acquired in step S110 (S130). First, the following Equation 1 is established between the TDI image g (x), PSFp (x), and the original image f (x) of the object from which distortion of the optical transmission path is not removed. Note that x indicates the pixel position of the TDI image, and i takes a value of 0 to N. x0 to xN can take discrete values.

  Here, in the confocal optical system, coherent light (laser light) is used, but at the same time, the images are separated so as not to overlap each other. Therefore, since the light intensity is only integrated in TDI, it is not necessary to consider the phase as in the case of imaging with ordinary coherent light, and only the light intensity needs to be considered.

  Further, in the confocal optical inspection apparatus 100 according to the present embodiment, the pinholes 132 of the pinhole member 130 are arranged at predetermined intervals in the second direction (TDI longitudinal direction) for each row as shown in FIG. It is formed shifted by one. This shift amount d is preferably an integer multiple of the pixel size of the TDI image in order to efficiently perform the calculation of Equation 1 above. For example, when the shift amount d is set to 3 times the pixel size, x0 is the 0th pixel value in the first direction (TDI integration direction), x1 is the third pixel value in the first direction, and x2 is the first pixel value. The sixth pixel value in the direction of 2 is as follows. On the other hand, the second direction is usually a movement for each pixel. However, for example, the data may be acquired every other pixel by blinking the illumination. In this case, the same operation as described above is required.

  When the above formula 1 is represented by a matrix, the following formula 2 is obtained. Note that p (0) = 1.

  In Equation 2, p (x) is acquired in step S110 and is known. Also, g (x) is known because it has been acquired in step S120. Therefore, if the inverse matrix of PSF is calculated, an original image (observed object image) free from distortion due to the optical transmission path can be acquired. That is, the original image f (x) obtained by taking the PSF matrix in Equation 2 is a corrected confocal image, and is expressed by Equation 3 below.

  Here, for the sake of simplification in the above formula 3, PSF (p (x)) is a single function, but actually, the aberration generated by the optical system differs for each image position. Different for each position. For example, aberrations such as coma and astigmatism tend to increase as the distance from the optical axis increases, and even when there is field curvature, the defocus amount differs between on the optical axis and off the optical axis. These are all factors that change the PSF. However, in the confocal optical inspection apparatus 100 according to the present embodiment, the PSF at the actual position as shown in FIG. By using the PSF at such an actual position, it is possible to avoid performance degradation due to variations in the optical system, and it is possible to acquire a corrected confocal image in which the original image is restored with high accuracy.

  The correction processing unit 164 outputs the corrected confocal image to the output unit 166 when acquiring the corrected confocal image that is the original image obtained by removing the distortion of the optical transmission path from the TDI image in step S130. The output unit 166 outputs this corrected confocal image to an external device or the like.

  The TDI image correction process by the confocal optical inspection apparatus 100 according to the present embodiment has been described above. In the above description, noise due to vibration or the like during scanning of the sensor or the object is ignored. However, considering the noise w (x), the above formulas 1 and 2 become the following formulas 4 and 5. .

  Then, the corrected confocal image, which is the estimated amount of the original image, can be expressed by Equation 6 below.

  If PSF (p (x)) is known in Equation 6 and the second term on the right side of the above equation is zero, the original image can be estimated completely uniquely. However, in the actual image, the second term on the right side of the above expression may be enlarged. For this, for example, the influence of noise can be suppressed by using a Wiener filter or the like. In the TDI image correction processing described above, a one-dimensional example is shown, but it can be extended to two dimensions.

<3. Installation of light receiving side opening member>
In the confocal optical inspection apparatus 100 according to the present embodiment, as shown in FIG. 1, the pinhole member 130 as shown in FIG. 3 is provided only on the illumination side where the light source 110 is provided. Here, before the spot light reflected by the object forms an image on the TDI camera 150 (that is, on the light receiving side), the confocal optical inspection apparatus 100 may be provided with an aperture member that allows each spot light to pass therethrough. . Thereby, the diffraction pattern of the spot light reflected by the object can be cut, and a clearer TDI image can be acquired.

  Here, in the confocal optical system, if a positional deviation occurs between the pinhole member 130 on the illumination side and the opening member on the light receiving side, the performance is degraded. Depending on the size of the opening formed in each member, position adjustment between the illumination-side pinhole member 130 and the light-receiving-side opening member requires an accuracy of several μm. When the opening member is used in a fixed manner, these positions may be secured by initial adjustment. On the other hand, when switching between a conventional optical system and a confocal optical system, the light-receiving side optical system is used in common, so the light-receiving side opening member is inserted and removed, and switching adjustment is performed. It is important to ensure accuracy each time a member is inserted or removed.

  Therefore, in the confocal optical inspection apparatus 100 according to the present embodiment, for example, a slit member 170 having a plurality of slits as shown in FIG. Position accuracy with the pinhole member 130 is ensured. The slit member 170 shown in FIG. 8 has a plurality of slits 172 corresponding to the arrangement positions of the respective image sensors of the TDI camera 150.

  Each slit 172 is formed to extend long in a second direction (TDI longitudinal direction) orthogonal to the scanning direction. This is for inserting / removing the slit member 170 in the second direction. Since the slit member 170 is moved in the insertion / removal direction, the displacement in the second direction, which is the insertion / removal direction, is larger than the displacement in the first direction. Cheap. If the opening formed in the light receiving side opening member is circular or square like the pinhole member 130, the same positional accuracy is required in the first direction and the second direction. Therefore, by forming a slit 172 that is long in the insertion / removal direction as in the slit member 170 of FIG. 8, the positional accuracy in the insertion / removal direction is eased. If the positional accuracy in one direction can be relaxed, the light receiving side opening member can be easily switched by the opening member insertion / extraction mechanism using the direction as a guide.

  The confocal optical inspection apparatus 100 according to the present embodiment can acquire an original image from which distortion of the optical transmission path is removed using PSF by the above-described correction processing of the TDI image. Therefore, when acquiring an image of an object using TDI, the images in the second direction, which is the longitudinal direction of TDI, are integrated, and thus the image in the second direction is not separated in principle. By acquiring the PSF with the member 170 provided, the original image can be acquired in the same manner as described above even if the positional accuracy in the second direction is relaxed. It should be noted that the opening of the opening member on the light receiving side is desirably large enough not to hinder the spread of the PSF even when a positional shift occurs in the opening.

  In the confocal optical system, a high resolution in the focus direction and a high in-plane resolution are advantageous over a normal optical system. Therefore, in the confocal optical inspection apparatus 100, it is possible to further improve the resolution by providing a slit member as shown in FIG. 8 as an opening member on the light receiving side. On the other hand, when the resolution in the focus direction is unnecessary, the confocal optical inspection apparatus 100 does not have to be provided with the light receiving side opening member as shown in FIG. Even if the opening member on the light receiving side is omitted, the in-plane resolution is ensured by using the above-mentioned PSF.

  The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the present invention is not limited to such examples. It is obvious that a person having ordinary knowledge in the technical field to which the present invention pertains can come up with various changes or modifications within the scope of the technical idea described in the claims. Of course, it is understood that these also belong to the technical scope of the present invention.

  Note that the information processing unit 160 (particularly the function of the correction processing unit 164) of the confocal optical inspection apparatus according to the above embodiment includes hardware such as a CPU, ROM, and RAM incorporated in an information processing apparatus such as a computer. It can also be realized by a computer program for functioning. The computer program can also be provided by a storage medium that records the computer program.

DESCRIPTION OF SYMBOLS 100 Confocal optical inspection apparatus 110 Light source 122 Micro lens array 124 Objective lens 130 Pinhole member 132 Pinhole 140 Beam splitter 150 TDI camera 160 Information processing part 162 TDI image acquisition part 164 Correction processing part 166 Output part 170 Slit member 172 Slit

Claims (7)

A confocal optical inspection apparatus for acquiring a confocal image of an object and inspecting the object,
A light source that emits illumination light;
A first opening member having a plurality of openings, wherein the illumination light emitted from the light source is converted into a plurality of illumination lights;
Each illumination light reflected by the object is imaged, and an imaging unit that acquires an image;
A second opening member having a plurality of apertures through which reflected light from the object incident on the imaging unit passes, and being insertable / removable in a direction orthogonal to the scanning direction of the object;
The optical transmission line distortion of the confocal optical inspection apparatus is removed from the TDI image obtained by the TDI operation of the imaging unit using the PSF representing the optical system characteristic of the confocal optical inspection apparatus measured in advance. An information processing unit for acquiring the corrected confocal image,
A confocal optical inspection apparatus comprising: The confocal image of the object that is the PSF, the TDI image, and the original image satisfies the following Equation 1;
The confocal optical inspection according to claim 1, wherein the information processing unit obtains the corrected confocal image that is an estimated image of the confocal image by calculating an inverse matrix of the PSF. apparatus.
Here, g (x) is a TDI image, p (x) is a PSF, and f (x) is a confocal image. Further, x indicates a pixel position of the TDI image, and i takes a value of 0 to N.   The confocal optical inspection apparatus according to claim 1, wherein the PSF is acquired by imaging the target object in a state where the target object is stopped. Each of the openings of the first opening member has a predetermined shift amount in a lattice shape in a first direction that is a scanning direction of the object and a second direction that is orthogonal to the scanning direction. Formed,
The shift amount in the second direction of each opening of the first opening member is an integral multiple of the pixel size of the TDI image, according to any one of claims 1 to 3. Confocal optical inspection device.   5. The confocal optical inspection device according to claim 1, wherein each opening of the first opening member is a pinhole. 6.   The opening of the second opening member is formed such that an opening length in the insertion / extraction direction in which the second opening member is inserted / extracted from the confocal optical inspection apparatus is larger than an opening length in a direction perpendicular to the insertion / extraction direction. The confocal optical inspection device according to any one of claims 1 to 5, wherein: A confocal optical inspection method for acquiring a confocal image of an object and inspecting the object,
Obtaining a PSF representing the optical system characteristics of the confocal optical inspection device;
Using the PSF, obtaining a corrected confocal image obtained by removing the optical transmission line distortion of the confocal optical inspection device from the TDI image obtained by the TDI operation of the imaging unit of the confocal optical inspection device. When,
Inserting / removing an aperture member having a plurality of apertures that allow reflected light from the object incident on the imaging unit to pass in a direction perpendicular to the scanning direction of the object;
A confocal optical inspection method, comprising: