JP2009250653A - Surface inspection method and surface inspection device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a surface inspection method capable of performing the accurate inspection of a flaw by excluding the effect of the offset of difference output caused by the roughness or the like of a surface. <P>SOLUTION: The surface inspection method is constituted of a step of imaging the surface of an inspection target while relatively moving an imaging device with respect to the inspection target, a step of extracting the inspection signal value corresponding to a predetermined inspection item from the taken surface image of the inspection target at each region of a plurality of regions obtained by dividing the surface of the inspection target into a plurality of parts along the relative moving direction, a step of calculating the moving average value of the inspection signal value in the relative moving direction with respect to a plurality of the regions, a step of calculating a corrected inspection signal value by subtracting the moving average value from the inspection signal value with respect to a plurality of the regions and a step of performing inspection with respect to the predetermined inspection item on the basis of the corrected inspection signal value. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a surface inspection method and apparatus for inspecting the presence or absence of surface defects in an object such as a semiconductor wafer or a liquid crystal glass substrate.

  In recent years, the degree of integration of circuit element patterns formed on semiconductor wafers has increased, and the types of thin films used for wafer surface treatment in semiconductor manufacturing processes have increased. Along with this, defect inspection near the edge of the wafer where the boundary portion of the thin film is exposed has become important. This is because if there is a defect such as a foreign substance near the edge of the wafer, the foreign substance or the like will enter the surface side of the wafer in a later step and adversely affect the yield of circuit elements produced from the wafer. .

Therefore, the periphery of the test object formed in a disk shape such as a semiconductor wafer (eg apex and upper and lower bevels) is observed from multiple directions to remove foreign matter and film, bubbles in the film, and wrap around the film. An inspection apparatus for inspecting the presence or absence of defects such as these has been devised (see, for example, Patent Document 1). Such an inspection apparatus has a configuration in which foreign matter or the like is detected by using scattered light generated by irradiation with laser light or the like, or a foreign object or the like is detected by forming an image of the test object in a belt shape with a line sensor. There are things of composition.
JP 2004-325389 A

  In addition, there is a configuration in which an image acquisition device partially acquires an image around the end face of a test object one by one, and detects a foreign substance or the like based on signal values in a plurality of image data. For example, there is an inspection apparatus that detects surface defects by irradiating illumination light onto an end surface of a wafer and imaging regular reflection light of the illumination light. In this inspection apparatus, an area adjacent to an image area Thus, the defect inspection is performed based on the intensity of the luminance difference for each pixel.

  In this inspection apparatus, even if there are no scratches or the like that are regarded as defects on the wafer surface, surface roughness that exists over the entire circumference of the edge region of the wafer is detected as a differential signal, which becomes an offset component of the detection signal, and the defect There is a problem that detection becomes inaccurate. In particular, since the surface condition such as the processing roughness of the wafer surface is not uniform over the entire wafer surface, the offset signal itself of the image difference detection based on the surface roughness fluctuates and should be detected as a defect under the influence of this fluctuation. There is a problem that detection of a differential signal due to scratches or the like becomes inaccurate.

  The present invention has been made in view of such a problem, and provides a surface inspection method and apparatus capable of performing accurate defect inspection by eliminating the influence of differential output offset due to surface roughness or the like. Objective.

  In order to achieve such an object, the surface inspection method according to the present invention is a step of imaging the surface of the test object while relatively moving an imaging device capable of imaging the surface of the test object with respect to the test object. And an inspection signal value corresponding to a predetermined inspection item for each of a plurality of regions obtained by dividing the surface of the test object into a plurality of parts along the relative movement direction from the captured image of the surface of the test object Extracting a moving average value of the inspection signal values in the relative movement direction for each of the plurality of regions, and correcting the inspection signal value by subtracting the moving average value for each of the plurality of regions. The method includes a step of obtaining an inspection signal value and a step of inspecting the predetermined inspection item based on the corrected inspection signal value.

  In this surface inspection method, it is preferable that the moving average value is calculated by calculating an average value of the inspection signal values in a predetermined number of regions before and after the corresponding region in each of the plurality of regions as a moving average value of the corresponding region. Is calculated as

  In the surface inspection method, preferably, the test object is a disk-shaped semiconductor wafer, and the outer peripheral end of the semiconductor wafer is imaged by the imaging device while rotating the semiconductor wafer.

  On the other hand, a surface inspection apparatus according to the present invention includes a holding device that holds a test object, an imaging device that can image the surface of the test object held by the holding device, and the holding device that holds the test object. A relative movement device that moves the test object relative to the imaging device, a control device that performs imaging control by the imaging device and a relative movement control of the test object by the relative movement device, and imaging by the imaging device An inspection processing device that inspects a surface defect from a captured image of the surface of the test object, and the control device uses the relative movement device to position the test object relative to the imaging device. The imaging apparatus divides the surface of the test object into a plurality of divided areas while moving the image, and the inspection processing apparatus performs predetermined processing on images of the plurality of divided areas picked up by the imaging apparatus. An inspection signal value corresponding to an inspection item is extracted, a moving average value of the inspection signal value is calculated for each of the plurality of divided regions, and correction is performed by subtracting the moving average value from the inspection signal value for each of the plurality of regions. An inspection signal value is obtained, and the predetermined inspection item is inspected based on the corrected inspection signal value.

  In the surface inspection apparatus, preferably, the test object is a disk-shaped semiconductor wafer, and the relative movement device rotates the semiconductor wafer held by the holding device to move relative to the imaging device. Configured.

  According to the present invention, since the inspection signal value is corrected using the moving average value, it is possible to accurately detect the surface defect.

  Hereinafter, preferred embodiments of the present invention will be described. An example of a surface inspection apparatus according to the present invention is shown in FIG. 1, and this inspection apparatus 1 uses a semiconductor wafer 10 (hereinafter referred to as a wafer 10) as an object to be tested, and surface defects ( It is for inspecting the presence or absence of scratches, foreign matters, etc.).

  The wafer 10 is formed in a thin disk shape, and an insulating film and electrodes are formed on its surface in order to form a circuit pattern (not shown) corresponding to a plurality of semiconductor chips (chip regions) taken out from the wafer 10. A thin film (not shown) such as a wiring film or a semiconductor film is formed over multiple layers. Thus, a circuit pattern is formed on the outer peripheral edge of the portion where the circuit pattern is formed on the surface (upper surface) of the wafer 10, that is, on the upper bevel portion 11 which is a ring-shaped region shown in FIG. The substrate is exposed without being exposed. Further, a lower bevel portion 12 is formed symmetrically with the upper bevel portion 11 with respect to the wafer 10 on the inner side of the outer peripheral end portion on the back surface (lower surface) of the wafer 10. The wafer end surface connected to the upper bevel portion 11 and the lower bevel portion 12 is referred to as an apex portion 13.

  The inspection apparatus 1 includes a wafer support unit 20 that supports and rotates the wafer 10, an imaging unit 30 that images the outer peripheral end portion of the wafer 10 supported by the wafer support unit 20 and the vicinity of the outer peripheral end unit, and an imaging unit 30. An image processing unit 40 that obtains image data based on an image signal of the imaged wafer 10, a control unit 50 that performs rotational drive control of the wafer 10 by the wafer support unit 20 and imaging control by the imaging unit 30, an image display and an external An interface unit 60 using a personal computer capable of input and the like and an inspection processing unit 70 for performing defect inspection processing are configured.

  The wafer support unit 20 includes a base 21, a rotary shaft 22 that extends vertically upward from the base 21, and is mounted substantially horizontally on the upper end of the rotary shaft 22 so that the wafer 10 is coaxially mounted on the upper surface side. And a wafer holder 23 that is positioned and supported. A vacuum suction mechanism (not shown) is provided inside the wafer holder 23, and the wafer 10 is suctioned and held on the wafer holder 23 coaxially with the rotation axis using the vacuum suction by the vacuum suction mechanism.

  A rotation drive mechanism (not shown) that rotates the rotation shaft 22 is provided inside the base 21, and the wafer holder attached to the rotation shaft 22 by rotating the rotation shaft 22 by the rotation drive mechanism. 23, the wafer 10 sucked and held on the wafer holder 23 is rotationally driven with the center (rotation symmetry axis O) of the wafer 10 as the rotation axis. The wafer holder 23 is formed in a substantially disk shape having a diameter smaller than that of the wafer 10, and includes an upper bevel portion 11, a lower bevel portion 12, and an apex portion 13 with the wafer 10 being sucked and held on the wafer holder 23. The vicinity of the outer peripheral end of the wafer 10 protrudes from the wafer holder 23.

  The imaging unit 30 is a so-called two-dimensional camera, and mainly includes a lens barrel unit 31 including an objective lens (not shown) and epi-illumination, and a camera body 32 including an image sensor (not shown). Illumination light by illuminates the wafer 10 via the objective lens, and reflected light from the wafer 10 is guided to the image sensor via the objective lens, and an image of the outer peripheral portion of the wafer 10 is captured by the image sensor. In this embodiment, the end surface of the wafer 10 is inspected for scratches, adhesion of foreign matter, and the like. The camera is provided at a position where the illumination light is regularly reflected, and the surface of the end surface of the wafer 10 is detected. It is configured to capture an image.

  The imaging unit 30 is disposed so as to face the apex portion 13 of the wafer 10, and partially captures the apex portion 13 from a direction orthogonal to the rotation axis (rotation symmetry axis O) of the wafer 10. Accordingly, when the wafer 10 supported by the wafer support unit 20 is rotated, the outer peripheral end portion of the wafer 10, that is, the apex portion 13 rotates relative to the imaging region of the imaging unit 30 in the circumferential direction of the wafer 10. The imaging unit 30 disposed so as to face the apex unit 13 can continuously image the apex unit 13 in the circumferential direction (that is, the relative rotation direction), and images the apex unit 13 over the entire circumference of the wafer 10. It becomes possible to do. The image signal captured by the imaging unit 30 in this way is output to the image processing unit 40, where image processing is performed, and image data of the apex unit 13 is obtained for each position.

  As shown in FIG. 2, the imaging unit 30 is arranged at a position facing the upper bevel portion 11 in the vertical direction, and the upper bevel portion 11 is imaged, and this portion is inspected or the imaging unit is moved to the lower bevel. The lower bevel portion 12 can be imaged by placing it at a position facing the portion 12 in the vertical direction, and this portion can be inspected.

  The control unit 50 includes a control board that performs various controls, and performs operation control of the wafer support unit 20, the imaging unit 30, the image processing unit 40, and the like according to control signals from the control unit 50. Specifically, the rotation driving control of the rotation shaft 22 by the wafer support unit 20 (rotational position control of the wafer 10 held by the wafer holder 23), the imaging control by the imaging unit 30, and the imaging unit 30 in the image processing unit 40. Image processing control for obtaining image data from the image signal obtained by processing is performed based on control by the control unit 50.

  The image data of the apex unit 13 obtained by the image processing in the image processing unit 40 in this way is sent to the inspection processing unit 70 to inspect for the presence of surface defects such as scratches on the surface of the apex unit 13 and adhesion of foreign matter. Done. At this time, the inspection processing result and the like are simultaneously displayed on the display screen of the interface unit 60.

  The contents of the inspection process performed by the inspection apparatus 1 configured as described above will be described with reference to the flowchart of FIG. In this inspection processing, first, under the control of the control unit 50, the imaging unit 30 images the apex unit 13 of the wafer 10 and the rotation support control of the rotation shaft 22 by the wafer support unit 20 (the wafer held on the wafer holder 23). 10 rotation position control) is performed (step S1). The image signal of the part facing the imaging unit 30 in the apex unit 13 obtained by imaging by the imaging unit 30 in this way is sent to the image processing unit 40, and image data of this part (this is divided into divided images). Data)). This operation is repeated for each predetermined index angle by the rotational drive control of the rotary shaft 22. In other words, the divided image of the apex unit 13 is repeatedly imaged by the imaging unit 30 for each index angle over the entire circumference of the wafer 10 (step S2).

  As a result, the image processing unit 40 obtains a series of images of the apex unit 13 imaged by the imaging unit 30 for each index angle, and sends these series of image data to the inspection processing unit 70. As described above, the image processing unit 40 obtains the image of the apex unit 13 corresponding to each index position, and these images are continuously connected to be set so as to indicate the image over the entire circumference of the apex unit 13. ing. Then, adjacent images are compared on a pixel basis to obtain a divided image indicating a luminance difference for each pixel. Examples of the divided images thus obtained are shown as images G1, G2, G3, and G4 in FIG. 5, and small points in these divided images indicate that the surface roughness or the like in the apex portion 13 is a regular contrast difference. As background light (offset of differential output due to surface roughness, etc.), which is based on fine irregularities on the surface, for example, small irregularly reflected light generated according to processing roughness, scratches, foreign matter It is a comparatively small irregularly reflected light generated in a state where no etc. exist. On the other hand, if there are scratches, foreign matter, etc. on the surface, the diffusely reflected light from these is larger than the background light (difference output offset due to surface roughness etc.), and as large points D1, D2 as shown in images G2, G3 appear. That is, each point in the images G1 and G2 indicates irregular reflection from the apex portion 13, and the size of the point indicates the magnitude or intensity of the reflected light.

  In the inspection processing unit 70, the signal data In of the entire divided image is calculated by summing (integrating) the signal data of the entire divided image at each index position (step S3). This is performed at all index positions over the entire circumference of the apex section 13, and the signal values In at all positions are obtained. The results are shown in the bar graphs of FIGS. 4 and 5, and the horizontal axis in this bar graph indicates the index position (that is, the position corresponding to each index angle at the entire circumferential angle of 0 to 360 degrees), and is indicated on the vertical axis. The length of the bar represents the signal value In of the divided image at each index position. Note that FIG. 4 shows only the bar graph portion of FIG. 5 and shows the same graph.

  Here, as shown in the divided images G2 and G3 shown in FIG. 5, when the defects D1 and D2 exist, the reflected light from these defects is large, so that the signal value In at each index position is indicated by bars B and C. The value becomes larger. As described above, since a defect exists at an index position where the signal value In is large, for example, by searching for a location where the signal value In is equal to or greater than a predetermined threshold (threshold value) based on the signal value In, The presence can be detected.

  By the way, as described in the description section of the prior art, the magnitude of the offset of the differential output due to surface roughness or the like when the apex portion 13 of the wafer 10 is imaged by the imaging portion 30 is the surface state of the apex portion 13. It fluctuates depending on (for example, surface processing roughness). Even in the apex portion 13 of one wafer 10, it is difficult to obtain a uniform surface state over the entire circumference. For example, as shown in FIG. 5, the apex portion 13 in a region including the divided images G1 and G2 is used. And the surface state of the apex portion 13 in the region including the divided images G3 and G4 are often different. For example, in the case of this embodiment, the surface of the apex portion 13 in the region including the divided images G1 and G2 is rough and the offset of the differential output due to surface roughness is large, whereas the divided images G3 and G4 are displayed. The surface of the apex portion 13 in the included region is smooth, and the offset of the differential output due to surface roughness is small.

  In the inspection processing unit 70, as described above, the presence or absence of defects is inspected based on the height of each bar (the magnitude of the signal value In) in the bar graphs shown in FIGS. Since the value In includes a differential output offset due to surface roughness or the like, if the offset of the differential output due to surface roughness or the like differs depending on the index position as described above, the inspection result is affected by the influence. There is a problem of being accurate. Specifically, the offset of the differential output due to surface roughness or the like is large in the regions Z1 and Z2 including the images G1 and G2 in the graph of FIG. 5, whereas the surface roughness and the like are included in the region including the images G3 and G4. Since the offset of the difference output due to is small, the signal values for the images G1 and G4 in which no defect exists are indicated by the signal values A and D (signal value A)> (signal value D). Similarly, the signal values for the images G2 and G3 having the defects D1 and D2, respectively, in which substantially the same reflected light are generated, are represented by the signal values B and C (signal value B)> (signal value C). In addition, in this example, the relationship is (signal value A> signal value C).

  In such a case, for example, as shown in FIG. 5, when the presence / absence of a defect is determined based on whether or not the signal value In is larger than a first threshold value (threshold value) SH1, the position of the image G2 is determined. The presence of the defect D1 can be determined, but the defect D2 at the position of the image G3 cannot be determined. Therefore, if the second threshold SH2 smaller than the first threshold SH1 is determined so that the defect D2 at the position of the image G3 can also be determined, the defect D2 at the position of the image G3 can be determined, but the defect is not detected. An erroneous determination is made that a defect exists in the non-existing regions Z1 and Z2.

  Therefore, the flow will be described with reference to FIG. 3 again. In this inspection apparatus, the signal value In of the divided image at each index position is obtained over the entire circumference of the apex unit 13, and then the process proceeds from step S3 to step S4. Then, a moving average value of these signal values In is calculated. Specifically, with respect to the signal value In at each index position, a calculation for calculating an average value of a signal values (In-a to In + a) before and after the index value as a moving average value at the index position, Repeat for all index positions. The result is shown in FIG. 6, and it is possible to obtain a signal change characteristic corresponding to the offset of the differential output due to surface roughness or the like, although the signals of the defects D1 and D2 are included.

  Therefore, the process proceeds to step S5, and the moving average value of FIG. 6 having a signal characteristic substantially corresponding to the offset of the difference output due to surface roughness or the like is subtracted from the detection value shown in FIG. A correction signal value In ′ from which the influence of the offset of the differential output due to roughness or the like is removed is calculated. The calculation result is shown in FIG. 7 (note that the correction signal value that is a negative value as a result of the subtraction is expressed as zero), and the correction signal value at the index position of the image in which the defects D1 and D2 exist. Appears significantly larger. Since the moving average value is a calculated value including the signal values of the defects D1 and D2, a slight signal value appears in the regions Z1 and Z2 due to the influence thereof. However, as shown in FIG. The signal value A due to the offset of the differential output does not become larger than the signal value C at the position having the defect. For example, if the magnitude of the correction signal value is determined based on the third threshold value SH3 shown in FIG. The index position having the defects D1 and D2 can be reliably detected (step S6).

  The inspection apparatus according to the preferred embodiment of the present invention has been described above, but the present invention is not limited to the above embodiment, and can be applied to various forms. For example, in the above-described embodiment, the apex portion 13 is imaged over the entire circumference of the wafer 10, but the present invention is not limited to this, and a desired angular position range in the apex portion 13 is controlled by the operation control of the control unit 50. Only the image may be taken. Thereby, the presence or absence of a defect can be inspected only for a desired angular position range in the apex portion 13.

  In the above-described embodiment, the imaging unit 30 images the apex portion 13 of the wafer 10, but is not limited to this. For example, as shown by a one-dot chain line in FIG. 2, the upper bevel of the wafer 10. The portion 11 may be imaged, and the lower bevel portion 12 of the wafer 10 may be imaged as indicated by a two-dot chain line in FIG. In this way, it is possible to inspect for defects in the upper bevel portion 11 and the lower bevel portion 12 as well as the apex portion 13 of the wafer 10. Furthermore, it is possible to inspect not only the outer peripheral end portion of the wafer 10 or the vicinity of the outer peripheral end portion, but, for example, a glass substrate. It is effective to apply the form.

  It should be noted that not only the fluctuation of the offset of the differential output due to the roughness of the surface, but also when the color of the surface changes gently, it is detected as an image difference signal and becomes an offset, that is, a background signal, causing defects due to inaccuracy However, according to the above-described defect detection method, this offset component can be canceled, and the defect detection accuracy such as scratches can be increased.

  In the above-described embodiment, an amplification type solid-state imaging device such as a CCD or a CMOS can be used as the image sensor. However, the image sensor may be a two-dimensional sensor or a one-dimensional sensor.

It is a schematic block diagram of the surface inspection apparatus which concerns on this invention. It is a side view which shows the outer periphery edge part vicinity of a wafer. It is a flowchart which shows the content of the inspection process by the said surface inspection apparatus. It is a bar graph which shows the detection signal value for every index position over the perimeter of the apex part of a wafer. It is explanatory drawing which shows the example of the division | segmentation image in the predetermined index position in the bar graph shown in FIG. 4 corresponding to the said bar graph. It is a bar graph which shows the moving average value of the signal value of FIG. It is a bar graph which shows the result of subtracting the moving average value of FIG. 6 from the detected value of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Inspection apparatus 10 Wafer (test object) 13 Apex part 20 Wafer support part (rotation holding part) 30 Imaging part 40 Image processing part 50 Control part 60 Interface part 70 Inspection processing part

Claims (5)

Imaging the surface of the test object while relatively moving an imaging device capable of imaging the surface of the test object with respect to the test object; and
Extracted from the captured image of the surface of the test object is an inspection signal value corresponding to a predetermined inspection item for each of a plurality of regions obtained by dividing the surface of the test object into a plurality of parts along the relative movement direction. And steps to
Calculating a moving average value of the inspection signal values in the relative movement direction for each of the plurality of regions;
Subtracting the moving average value from the inspection signal value for each of the plurality of areas to obtain a corrected inspection signal value;
A surface inspection method comprising: inspecting the predetermined inspection item based on the corrected inspection signal value.   The moving average value is calculated by calculating an average value of the inspection signal values in a predetermined number of regions before and after the corresponding region in each of the plurality of regions as a moving average value of the corresponding region. Item 6. The surface inspection method according to Item 1.   The surface inspection method according to claim 1, wherein the test object is a disk-shaped semiconductor wafer, and the outer peripheral end of the semiconductor wafer is imaged by the imaging device while rotating the semiconductor wafer. A holding device for holding the test object;
An imaging device capable of imaging the surface of the test object held by the holding device;
A relative movement device for moving the test object held by the holding device relative to the imaging device;
A control device that performs imaging control by the imaging device and relative movement control of the test object by the relative movement device;
An inspection processing device that inspects a surface defect from a captured image of the surface of the object imaged by the imaging device;
The control device causes the imaging device to divide the surface of the test object into a plurality of divided areas while causing the relative movement device to move the test object relative to the imaging device,
The inspection processing device extracts an inspection signal value corresponding to a predetermined inspection item in an image for each of a plurality of divided regions imaged by the imaging device, and calculates a moving average value of the inspection signal value for each of the plurality of divided regions. The corrected inspection signal value is obtained by subtracting the moving average value from the inspection signal value for each of the plurality of areas, and the inspection for the predetermined inspection item is performed based on the corrected inspection signal value. Surface inspection apparatus characterized by being made.   The test object is a disk-shaped semiconductor wafer, and the relative movement device is configured to rotate the semiconductor wafer held by the holding device to move relative to the imaging device. The surface inspection apparatus according to claim 4.

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