JP2007285911A - Surface inspection device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface inspection device capable of performing inspection of surface flaws of high accuracy, without being affected by a white damage generating luminance of a predetermined value or higher at all times, varying the luminance or gradually becoming large in luminance. <P>SOLUTION: Before a surface is inspected on the basis of image due to the scattered light from the surface of a wafer W photographed by a camera 5, a first camera image position, having luminance higher than a first predetermined luminance A and a second camera image position having luminance higher than a second predetermined luminance C but below the first predetermined luminance A (however, A>C) are detected from a genuine black image obtained by photographing the surface of the wafer W, in a state where light is not incident on the imaging surface of the camera 5. The detected first camera image position is decided as being a permanent flaw, and the detected second camera image position is decided as being a temporary flaw. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a surface inspection apparatus that images a surface of a semiconductor wafer, a liquid crystal display element panel or the like (hereinafter referred to as a semiconductor wafer or the like) using a camera and performs surface inspection based on the obtained image.

  Semiconductor wafers, etc. are configured with a large number of circuit element patterns formed on the surface, and if there are defects on the surface, the performance of chips or panels made of circuit element patterns will be impaired. Is important to. For this reason, various apparatuses for inspecting surface defects such as semiconductor wafers have been conventionally known. Such a surface inspection apparatus irradiates a surface of a semiconductor wafer or the like with predetermined inspection light (light suitable for generating reflected light, diffracted light, scattered light), and reflects light, diffracted light from this surface, or The scattered light is collected by a condensing optical system, and this collected light is irradiated onto the image device (imaging device) of the camera to form an image of the inspection target surface on the image receiving surface (the inspection target surface is an image device). Based on the obtained captured image, it is configured to inspect pattern defects on the surface of the semiconductor wafer to be inspected, film pressure unevenness, presence or absence of scratches, adhesion of foreign matters, etc. Yes. (See Patent Document 1 and Patent Document 2).

  For example, an apparatus that performs surface inspection using scattered light is an apparatus that mainly detects scratches on the surface of a semiconductor wafer, adhesion of dust, etc., and irradiates the wafer surface with light at a shallow incident angle from the lateral direction. The wafer surface is imaged by a camera disposed at a position where neither the regular reflection light nor the diffracted light of the incident light is received, and the presence or absence of scattered light from the wafer surface is detected. If there are scratches or dirt on the wafer surface, the light hitting the scratches and dust will be reflected as scattered light to the surroundings, so the camera will pick up the scattered light and obtain an image with a bright spot at that position. Therefore, the presence / absence of a flaw and dust and the location of the flaw are detected from this image.

Japanese Patent Laid-Open No. 11-351848 JP 2002-5851 A

  By the way, when a surface of a semiconductor wafer or the like is imaged by such a camera and the surface defect is inspected, a so-called white scratch is output that outputs a signal having a certain luminance or more even though no light is incident on the image sensor of the camera. If there is, there is a problem that an erroneous determination is made if there is a flaw or dust on this part, and the inspection becomes inaccurate. This problem has been considered in the past, and before performing surface inspection, a camera image position having a luminance of a predetermined luminance or higher from an image obtained by imaging in a state where light does not enter the imaging surface of the imaging element of the camera. The image of the part corresponding to this position of the camera is not used as the inspection image.

  However, the white scratches present in the image sensor of the camera include not only white scratches that constantly generate a luminance higher than a predetermined level, but also white scratches that vary in luminance or gradually increase in luminance. For this reason, it is possible to detect a camera image position having a luminance equal to or higher than a predetermined luminance from an intrinsic black image before performing a surface inspection, and not to use an image corresponding to this position as an inspection image. When surface defects are inspected, white scratches that generate a brightness higher than a predetermined level may appear even though there is no light from the wafer, and it may be erroneously determined that there are scratches or dust, resulting in a decrease in inspection accuracy. There was a problem.

  The present invention has been made in view of such a problem, and not only white scratches that constantly generate a luminance of a predetermined level or more, but also the effects of white scratches in which the luminance fluctuates or the luminance gradually increases. An object of the present invention is to provide an apparatus capable of performing surface defect inspection with high accuracy without being subjected to the above.

  A surface inspection apparatus according to the present invention includes a camera that images a surface to be inspected and an image processing apparatus that obtains an image of the surface to be inspected captured by the camera, and is obtained by the image processing apparatus. Further, the inspection target surface is inspected based on the image. In the surface inspection apparatus configured as described above, a first black having a luminance equal to or higher than a first predetermined luminance is obtained from an intrinsic black image obtained by the image processing device by imaging in a state where light does not enter the imaging surface of the camera. An image position and a second image position having a luminance that is greater than or equal to a second predetermined luminance smaller than the first predetermined luminance and less than the first predetermined luminance are detected, and the detected first image position is detected as a permanent of the camera. In the subsequent inspection, it is removed from the image of the inspection target surface obtained by the image processing apparatus, and the detected second image position is determined as a temporary defect of the camera. An image correction device that removes an image of the surface of the inspection object obtained by the image processing device in an inspection over a predetermined time or number of times;

  The image correction apparatus performs a process of detecting the first image position by capturing the true black image by imaging with the camera a plurality of times, and the first image position obtained in at least one of the processes is determined by the camera. It is preferable that the defect is determined as a permanent defect and is removed from the image on the inspection target surface obtained by the image processing apparatus in the subsequent inspection.

  The image correction device is configured to detect an intrinsic black image obtained by imaging in a state where light is not incident on the imaging surface of the camera again after the inspection for the predetermined time or number of times, at the second predetermined luminance or more. A process of detecting the second image position having a luminance less than the first predetermined luminance is performed, and if the previously detected second image position is currently less than the second predetermined luminance, the image position is set to the next You may comprise so that it may use as a normal image position in the inspection over predetermined time or frequency | count.

  According to the surface inspection apparatus according to the present invention, not only white scratches that constantly generate a luminance of a predetermined level or more, but the influence of white scratches that change in luminance or gradually increase in luminance are removed, Highly accurate surface defect inspection can be performed

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows an example of a surface inspection apparatus according to the present invention. This apparatus detects surface defects (scratches, dust) and the like of a semiconductor wafer W by scattered light. This surface inspection apparatus has a holder 2 for mounting and holding a wafer W, and the wafer W transferred by a transfer apparatus (not shown) is mounted on the holder 2 and fixed and held by means such as vacuum suction. To do.

  The apparatus further includes an illumination light source 1 that irradiates the surface of the wafer W fixedly held by the holder 2 with the inspection illumination light Li at a shallow incident angle, and the surface of the wafer W that has been irradiated with the inspection illumination light Li. The wafer 5 which is arranged at a position where it does not receive the regular reflected light Lo (1) and the diffracted light Lo (2) and which has been converted by the imaging device (image device) 6 of the camera 5 An image processing device 10 that receives an image signal of the surface of W and performs image processing, and a display device 15 that displays a wafer surface image processed by the image processing device 10 are provided. The image processing apparatus 10 includes an image correction apparatus 11 described later.

  The surface inspection of the wafer W by this surface inspection apparatus will be briefly described below. In order to perform inspection using this apparatus, first, as described above, a wafer W to be inspected is transferred and placed at a predetermined position of the holder 2 by a transfer apparatus (not shown), and a vacuum suction device built in the holder 2 is mounted. To attract and hold the wafer W. Then, the illumination light source 1 irradiates the surface of the wafer W with the inspection illumination light Li. The inspection illumination light Li is specularly reflected on the surface of the wafer W, and specularly reflected light Lo (1) is emitted as shown. Further, a circuit pattern is periodically and repeatedly formed on the surface of the wafer W, and the diffracted light Lo (() in a direction corresponding to the repetition pitch of lines forming the circuit pattern and the wavelength of the inspection illumination light Li. 2) is emitted as shown. Therefore, if the surface of the wafer W is imaged by placing a camera at the position where the regular reflection light Lo (1) is received, the surface inspection based on the regular reflection light is possible, and the position where the diffracted light Lo (2) is received. If the surface of the wafer W is imaged by placing a camera on the surface, surface inspection based on diffracted light can be performed.

  In the surface inspection apparatus of the present embodiment, the camera 5 is disposed at a position where neither the regular reflection light Lo (1) nor the diffracted light Lo (2) is received, and the surface of the wafer W is imaged. Yes. When the surface of the wafer W is imaged by the imaging device 6 of the camera 5 in this way, since the regular reflected light Lo (1) and the diffracted light Lo (2) are not incident on the camera 5, the surface of the wafer W is damaged. If the wafer W is normal and free of dust, dust, etc., a black image is obtained as an image displayed on the screen 16 of the display 15 by processing the image signal from the image sensor 6 by the image processing device 10. It is only done.

  However, for example, when a scratch (or dust) d exists on the surface of the wafer W, the inspection illumination light Li irradiated to the scratch d is irregularly reflected here, and a part of the irregularly reflected light Lo (3) is partly reflected. It also enters the camera 5. For this reason, a bright spot indicating the position of the scratch d appears in an image displayed on the screen 16 of the display 15 by processing the image pickup signal from the image sensor 6 by the image processing device 10, thereby causing a scratch on the wafer W, Presence of dust etc. can be detected.

  By the way, as described above, there may be a defect called a white flaw that outputs a light reception signal without receiving light in the image pickup device 6 of the camera. There is a risk of judging it as a scratch or garbage. For this reason, in the surface inspection apparatus shown in the present embodiment, this white scratch is detected in advance before performing the surface inspection with scattered light, and correction processing is performed so that the portion where the white scratch exists is not used for the surface inspection. An image correction apparatus 11 to be performed is provided in the image processing apparatus 10.

  White spot detection by the image correction apparatus 11 will be described with reference to the flowchart of FIG. In this white spot detection, the imaging process by the camera 5 is performed in a state where light is not incident on the imaging surface of the imaging element 6 of the camera 5. The illumination light source 1, the holder 2, and the camera 5 constituting the surface inspection apparatus are provided in a case sealed from the outside, and light from outside the case does not enter the case. Therefore, by stopping the emission of the illumination light from the illumination light source 1, the light incident on the camera 5 can be eliminated, and the light can be prevented from entering the imaging surface of the image sensor 6 of the camera 5. When this white spot detection is performed in a state in which illumination light is emitted or light from the outside is not blocked by the housing, an image of the camera 5 is captured by covering the front surface of the imaging lens of the camera 5. A state in which no light enters the imaging surface of the element 6 can be achieved. When imaging is performed with the camera 5 in such a state, an image displayed on the screen 16 of the display 15 from the imaging device 6 via the image processing device 10 should be a black image. The image obtained at this time is hereinafter referred to as an intrinsic black image.

  However, if there are white scratches on the image sensor 6 of the camera 5, the image displayed on the screen 16 has white scratches as bright spots d1 to d5, for example, as shown in FIG. The relationship between the pixel positions (coordinate positions) of these bright spots d1 to d5 and the luminance is shown in the graph of FIG. In FIG. 3, the luminance D is a luminance that serves as a reference for determining whether the wafer W is scratched or dust when the wafer W is actually inspected, and is referred to as a determination reference luminance D. The first predetermined luminance A, the second predetermined luminance B, and the third predetermined luminance C are set as shown in the luminance range lower than the judgment reference luminance D, and the magnitudes of these luminances are good from FIG. As can be seen, D> A> C> B.

  The second predetermined brightness B is the brightness of a substantially black camera image, and there is no bright spot with a brightness lower than this. The third predetermined luminance C is set between the determination reference luminance D and the second predetermined luminance B. Further, the first predetermined luminance A is set to a luminance value obtained by adding the amount of change in luminance due to noise in the image sensor 6 of the camera 5 to the third predetermined luminance C. Specific values of these luminances are appropriately set according to the performance of the image sensor 6, the scratches used for detection, the size of dust, and the like.

  The brightness of the bright spots d1 to d5 appearing in the image obtained by imaging in step S1 is measured, and a bright spot having the first brightness A or higher is detected (step S2). In this example, the bright spots d1 and d5 are equal to or higher than the first luminance A, and these are detected in step S2. Then, the coordinates (pixel positions) of the bright spots d1 and d5 detected in this way are additionally registered as permanent defect data indicating a white flaw position as a permanent defect. This coordinate position corresponds to the “first camera image position” defined in the claims. In addition, this permanent defect data is data that is not deleted or changed only by adding data, and when the same coordinates as those registered as permanent white scratches are detected by the previous detection, The registered coordinate data is held as it is (step S3). As a result, a portion that may be changed to a white scratch that is erroneously determined as a scratch, dust, or the like in a future surface inspection is registered as a permanent defect.

  Next, the process proceeds to step S4, and it is determined whether or not the current imaging is the designated imaging. The white scratch detection based on the flow shown in FIG. 4 is performed by imaging the sample wafer W placed on the holder 5 a plurality of times, and steps S5 to S7 are designated from among the plurality of times of imaging. This is performed only in the first imaging. For this reason, the determination in step S4 is made, and if the current imaging is the designated time of imaging, the steps S5 to S7 are performed. move on.

  In step S5, a bright spot existing in a range lower than the first predetermined luminance A and higher than or equal to the third predetermined luminance C (in the hatched range in FIG. 3) is detected. Thereby, the bright spots d3 and d4 in the region between the lines A and C in the graph of FIG. 3 are detected, and the coordinates (pixel positions) of the bright spots d3 and d4 thus detected are temporarily stored. Is additionally registered as temporary defect data indicating the position of the white defect as a typical defect (step S6). This coordinate position corresponds to the “second camera image position” defined in the claims. Note that the same coordinates as those registered as temporary white scratches are detected by previous detection (previous white scratch detection performed prior to previous surface inspection, not detection based on the current flow). If registered, the registered coordinate data is held as it is. Further, although not detected as temporary defect data this time, the data registered in the past inspection is deleted from the temporary defect data (step S7). Thereby, although there is little possibility that it will be erroneously determined as a scratch, dust or the like in a future surface inspection, a portion that may change to a white scratch is registered as a temporary permanent defect. Note that the bright spot d2 having a luminance lower than the third predetermined luminance C is not included in any defect data because there is no possibility of being erroneously determined as a scratch or dust at least at the present time.

  Next, the process proceeds to step S8, where it is determined whether white spot detection by imaging based on the flow from step S1 to step S7 has been performed a specified number of times, and when it is determined that the specified number of times has been performed, the white spot inspection is terminated. To do. After the white scratch inspection is completed in this way, the surface inspection of the actual wafer W is performed by the surface inspection apparatus of FIG. 1. At this time, the image correction apparatus 11 registers the permanent defect data and the temporary defect data. Surface inspection is performed except for the detection data at the coordinates (pixel positions). As a result, not only white scratches that constantly generate a brightness higher than a predetermined level, but also the presence of white scratches that vary in brightness or gradually increase in brightness are accurately determined, and the image of that portion is excluded. Can inspect the surface defects with high accuracy.

  In the surface inspection apparatus according to the present embodiment, a predetermined period (for example, one week, one month, etc.) elapses or inspection is performed for a predetermined number of times (for example, the number of wafer inspections for several lots). After being performed, white scratch detection is again performed according to the flow of FIG. In this case, when the permanent defect data is newly found, the previous data is added as it is, and for the temporary defect data, the newly found data is added or retained. If it is not detected (below the second predetermined luminance B), it is deleted from the temporary defect data, and the detected data at this position is used for the inspection for the subsequent surface inspection.

It is a schematic diagram which shows the structure of the surface inspection apparatus which is one Embodiment of this invention. It is a top view which shows the image obtained by imaging in the state in which light does not enter into the imaging surface of a camera. It is a graph which shows the relationship between the brightness | luminance of a bright spot and the pixel position of the image obtained by imaging in the state in which light is not incident on the imaging surface of a camera. It is a flowchart which shows a white wound detection process.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Illumination light source 2 Holder 5 Camera 6 Image pick-up element 10 Image processing apparatus 11 Image correction apparatus 15 Display apparatus 16 Screen W Wafer

Claims (3)

The inspection object is configured to include a camera that images the inspection target surface and an image processing device that obtains an image of the inspection target surface imaged by the camera, and based on the image obtained by the image processing device In surface inspection equipment that inspects the surface,
A first image position having a luminance equal to or higher than a first predetermined luminance from an intrinsic black image acquired by the image processing device by imaging in a state where light does not enter the imaging surface of the camera, and smaller than the first predetermined luminance Detecting a second image position having a luminance that is greater than or equal to a second predetermined luminance and less than the first predetermined luminance;
The detected first image position is determined as a permanent defect of the camera, and removed from the image of the inspection target surface obtained by the image processing apparatus in a subsequent inspection,
An image correction device that judges the detected second image position as a temporary defect of the camera and removes it from the image of the surface to be inspected obtained by the image processing device in an inspection over a predetermined time or number of times thereafter. A surface inspection apparatus comprising:   The image correction apparatus performs a process of detecting the first image position by capturing the true black image by imaging with the camera a plurality of times, and the first image position obtained in at least one of the processes is determined by the camera. The surface inspection apparatus according to claim 1, wherein the surface inspection apparatus determines that the defect is a permanent defect and removes the defect from the image of the inspection target surface obtained by the image processing apparatus in a subsequent inspection.   The image correction device is configured to detect an intrinsic black image obtained by imaging in a state where light is not incident on the imaging surface of the camera again after the inspection for the predetermined time or number of times, at the second predetermined luminance or more. A process of detecting the second image position having a luminance less than the first predetermined luminance is performed, and if the previously detected second image position is currently less than the second predetermined luminance, the image position is set to the next 3. The surface inspection apparatus according to claim 1, wherein the surface inspection apparatus is used as a normal image position in an inspection over a predetermined time or number of times.

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