JP2010071694A - Surface inspection apparatus, defect detecting method using the same, program, and recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface inspection apparatus detecting all kinds of defects such as thickness variation, a flaw, a projection, a foreign substance, color irregularity, and the like occurring on a photoreceptor surface, by adding a new processing flow to a conventional three-dimensional measurement method using a stripe pattern projection method and Fourier transformation, and to provide a defect detecting method using the surface inspection apparatus, a program and a recording medium. <P>SOLUTION: This surface inspection apparatus comprises a means for projecting a stripe pattern on an object, a means for imaging the surface of the object, a means for calculating three-dimensional shape data of the object by the Fourier transformation based on the image data of the object, a means for detecting a defect based on a high frequency component of the image data, and a means for detecting the defect based on a low frequency component. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a surface inspection apparatus for detecting defects such as irregularities on the surface of an object, foreign matter, scratches, or shading unevenness, a defect detection method using the same, a program, and a recording medium.

  Conventionally, a moire method or a heterodyne method is known in which a lattice pattern is projected onto an object and a three-dimensional shape is measured from a lattice image deformed according to the height distribution of each part of the object. However, such a method has a problem that it cannot be applied to objects other than the object having a smooth shape and connected to each part.

  In order to solve the above-mentioned problem, a three-dimensional shape measurement method that enables measurement of an instantaneous shape of a discontinuous object during movement or deformation has been disclosed (for example, Patent Document 1). Specifically, a two-dimensional lattice pattern in which a plurality of one-dimensional lattices having different periods and directions are superimposed is projected onto an object, and a two-dimensional lattice image deformed according to the three-dimensional shape of the object is captured. This is a technique for obtaining a measurement value by detecting a phase for each one-dimensional grating component from an image from a two-dimensional grating.

  In addition, there is a problem that the apparatus becomes complicated in order to measure a three-dimensional shape. In order to solve this problem, a measurement method using a Fourier transform method in which the phase distribution is measured three-dimensionally with an easy apparatus is also disclosed (for example, Patent Document 2).

  Here, with respect to the conventional three-dimensional measurement method using the Fourier transform method and the fringe pattern projection method described above, a diagram showing the fringe pattern projection method with reference to “three-dimensional shape measurement using the Fourier transform method” in Non-Patent Document 1. 6 will be described. As shown in FIG. 6, this method projects a fringe pattern obliquely to a target object from a projector located at a height L 1, and uses a camera located at a distance D 1 from a deformed grid image on the object surface. In this method, the amount of deviation of the stripe pattern due to the object shape is calculated as a phase from the obtained image. The deformed lattice image g (x, y) photographed by the camera is expressed as in the following formula (1) and FIG.

g (x, y) = a (x, y) + b (x, y) cos [2π (f _x0 x + f _y0 y) + φ (x, y)] Equation (1)

  Here, a (x, y) is the background, and b (x, y) is the amplitude distribution of the change in brightness of the stripes. fx0 and fy0 are carrier frequencies depending on the fringe interval of the projected fringe pattern, and φ (x, y) is a phase having information on the object shape. The phase φ (x, y) and the height h (x, y) of the object are related by the following equation (2).

  A method that removes unnecessary signals a (x, y) and b (x, y) from the deformed lattice image g (x, y) and extracts only the phase φ (x, y) having the object height information Is the Fourier transform method. When the transformed lattice image g (x, y) is Fourier transformed, the following equation (3) is obtained.

_{G (f x, f y)} = A (f x, f y) + C (f x -f x0, f y -f y0) + C * _{[- (f x + f x0)} , - (f y - f _y0 )] ... Equation (3)

  c (x, y) = (1/2) b (x, y) exp [iφ (x, y)] (4)

  Here, * indicates the complex, A (fx, fy) indicates a Fourier transform of a (x, y), and C (fx, fy) indicates the Fourier transform of the above equation (4).

  It can be seen that the function C (fx, fy) including the object shape information is separated from the unnecessary signal A (fx, fy) by the carrier frequencies fx0 and fy0. The absolute value of each term of this spectrum G (fx, fy) is illustrated in the frequency space as shown in FIG. In the above equation (3), as shown in FIG. 9, by extracting only C (fx-fx0, fy-fy0) and shifting in the direction of the origin by the carrier frequency fx0, fy0, C (fx, fy) becomes Is obtained (see FIG. 10). Since the complex amplitude c (x, y) is obtained by inverse Fourier transform of this spectrum, the phase φ (x, y) is calculated by the arc tangent of the imaginary part and the real part (formula (5)).

φ (x, y) = tan ⁻¹ [Im [c (x, y)] / Re [c (x, y)]] (5)

Finally, if the phase φ (x, y) is converted into the height h (x, y) from the relationship of the above equation (2), the three-dimensional shape of the target surface can be measured.
Japanese Patent No. 3388684 JP-A-11-230833 "Three-dimensional shape measurement using Fourier transform method", University of Electro-Communications 2007 ETL No.6 Koichi Otohttp: //www.ils.uec.ac.jp/AtractiveGI/ETL_2007/prog_6/ETL6.pdf

  Here, consider a case where the above-described measurement method is applied to the surface inspection of an object such as an OPC (Organic PhotoConductor) drum. The OPC drum as shown in FIG. 11 has a structure in which layers such as a UC (UnderCoat) layer, a CG (Charge Generation) layer, and a CT (Charge Transfer) layer are formed on a metal substrate. As defect types that occur, film thickness unevenness (FIG. 11: a) and scratches (FIG. 11: b), protrusions (FIG. 11: c), foreign matter (FIG. 11: d) mixed in the CT layer, There is color unevenness (FIG. 11: e) due to uneven application of the CG layer.

  A defect such as the film thickness unevenness in FIG. 11A can be measured by the above-described fringe pattern projection method and Fourier transform method if a carrier frequency slightly higher than the spatial frequency of the film thickness unevenness is set. However, the scratches in FIG. 11b, the protrusions in c, and the foreign matter in d are small in size and suddenly change in shape, so that the spatial frequency becomes too high, and C (fx-fx0, fy-fy0) in FIG. Since it will be removed in the process of taking out only, it cannot be detected. Further, the color unevenness e in FIG. 11 is lower than the carrier frequency on the image, and is included in a (x, y) and b (x, y) of the above equation (1). However, these signals are removed as unnecessary signals in the Fourier transform method, and as a result, color unevenness cannot be detected.

  That is, when an OPC drum surface inspection is performed by applying a three-dimensional measurement method using a fringe pattern projection method and a Fourier transform method, it is possible to detect film thickness unevenness, but other scratches, protrusions, foreign matter, and color unevenness. There has been a problem that defects such as these cannot be detected.

  The present invention has been made in view of such circumstances, and a film thickness generated on the surface of an object by adding a new processing flow to the conventional three-dimensional measurement method by the fringe pattern projection method and the Fourier transform method. It is an object of the present invention to provide a surface inspection apparatus for detecting all kinds of defects such as unevenness, scratches, protrusions, foreign matter and color unevenness, a defect detection method using the same, a program, and a recording medium.

  The surface inspection apparatus according to the present invention includes a fringe pattern projecting unit that projects a fringe pattern onto an object, an image capturing unit that captures an image of the surface of the object, and image data of the object obtained by the fringe pattern projecting unit and the image capturing unit. A three-dimensional shape calculation means for calculating three-dimensional shape data of the object by Fourier transform method, and a high-frequency defect detection means for detecting a defect based on a high-frequency component of the image data of the object. .

  The surface inspection apparatus of the present invention further includes a low-frequency defect detection unit that performs defect detection based on a low-frequency component of image data of an object.

  The surface inspection apparatus of the present invention is characterized by detecting defects such as scratches, protrusions, foreign matter contamination, and color unevenness.

  The defect detection method of the present invention includes a fringe pattern projecting step for projecting a fringe pattern onto an object, an imaging step for imaging the surface of the object, and the image data of the object obtained by the fringe pattern projecting step and the imaging step. 3D shape calculation step for calculating the 3D shape data of the object by the Fourier transform method, and removing the high frequency component higher than the carrier frequency of the image data of the object without removing it, and detecting the defect based on the high frequency component And a high-frequency defect detection step.

  The defect detection method of the present invention further includes a low-frequency defect detection step that leaves a low-frequency component lower than the carrier frequency of the image data of the object without being removed and performs defect detection based on the low-frequency component. Features.

  The program of the present invention uses a Fourier transform method to project a fringe pattern on an object, an image of the surface of the object, a process of projecting, and image data of the object obtained by the process of imaging. A process for calculating the three-dimensional shape data of the object, a process for performing defect detection based on the high frequency component of the image data of the object, and a process for performing defect detection based on the low frequency component of the image data of the object. Let the computer run.

  According to the present invention, it is possible to detect all types of defects such as film thickness unevenness, scratches, protrusions, foreign matter, and color unevenness generated on the surface of an object.

  Hereinafter, examples of embodiments of the present invention will be described in detail with reference to the drawings. In the present embodiment, an OPC drum will be described as an example of the object.

  First, as the configuration of the optical system of the surface inspection apparatus according to the present embodiment, the same configuration as in FIG. 6 can be applied, and a pattern is projected onto the OPC drum surface from a pattern projector (Projector) that projects the pattern. Then, the deformed lattice image g ′ (x, y) is captured by the camera. More specifically, a fringe pattern is obliquely projected onto the target object from a projector at a height L, and a deformed grid image on the object surface is photographed with a camera at a distance D. From the obtained image, the shift amount of the stripe pattern due to the object shape is calculated as a phase. The configuration of the optical system is not limited to this.

  Here, assuming that the spatial frequency of the color unevenness generated on the OPC drum is fxc, fyc, the spatial frequency of the film thickness unevenness fxl, fyl, scratches, protrusions, and the spatial frequency of the foreign matter is fxd, fyd, the following formula (6) It becomes a relationship like this.

f _xc , f _yc <f _xl , f _yl <f _xd , f _yd (6)

  Here, the carrier frequencies fx0 and fy0 are set so that the following equation (7) is satisfied. It may be several times the spatial frequency of the smallest film thickness unevenness that occurs.

f _xc , f _yc <f _xl , f _yl <f _x0 , f _y0 <f _xd , f _yd (7)

  When there are various defects having the above relationship, the deformed lattice image obtained by the camera is as shown in the following equation (8) and FIG.

g ′ (x, y) = a (x, y) + b (x, y) cos [2π (f _x0 x + f _y0 y) + φ (x, y)] + d (x, y)・ Formula (8)

  Color unevenness information is included in a (x, y) and b (x, y) together with illumination unevenness. Height information due to film thickness unevenness is included in the phase φ (x, y). The last d (x, y) includes information on defects having a high spatial frequency such as scratches, protrusions, and foreign matters. Next, when the transformed lattice image g ′ (x, y) is Fourier-transformed, the following equation (9) is obtained.

G '(f _x , f _y ) = A (f _x , f _y ) + C (f _x -f _x0 , f _y -f _y0 ) + C ^* (-(f _x + f _x0 ),-(f _y -f _y0 )] + D (f _x , f _y ) (9)

  Here, D (fx, fy) represents the Fourier transform of d (x, y). The absolute value of each term of the spectrum G ′ (fx, fy) is illustrated in the frequency space as shown in FIG. Compared with FIG. 8 described above, high frequency components due to scratches, protrusions, and foreign matter are added.

  Thereafter, in the three-dimensional shape calculation device, C (fx-fx0, fy-fy0) is taken out, moved to the origin, and then subjected to inverse Fourier transform to obtain the complex amplitude c (x, y), and the phase φ (x , Y) is calculated and converted into a height h (x, y), and a change in shape due to film thickness unevenness is measured.

(Embodiment 1)
FIG. 3 shows an example of the processing method of the surface inspection apparatus according to the present embodiment. In the present embodiment, an example of defect detection processing by the surface inspection apparatus will be described with reference to FIG.

  As shown in FIG. 3, the surface inspection apparatus according to this embodiment includes a high-frequency defect detection apparatus in addition to the three-dimensional shape calculation apparatus. A processing method in the high-frequency defect detection apparatus will be described. First, only high frequency components are extracted from the spectrum G ′ (fx, fy), and inverse Fourier transform is performed. As a result, the brightness change due to the pattern and background light disappears from the original modified lattice image g ′ (x, y), and only the brightness change due to defects with high spatial frequency such as scratches, protrusions, and foreign matters remains. After that, it is converted into a binary image by threshold processing, and noise is removed by morphological processing such as isolated point removal, expansion, and contraction, and then recognized as one lump by labeling processing. For each label, defect feature amounts such as the number of pixels and length are calculated, and pass / fail is determined based on the size of the feature amount.

  According to this embodiment, in the three-dimensional measurement method using the fringe pattern projection method and the Fourier transform method, by using a high frequency component higher than the carrier frequency that has been removed in the past, defects having a high spatial frequency such as scratches, protrusions, and foreign matters are deformed in the same manner. It is possible to detect from the lattice image.

(Embodiment 2)
FIG. 4 shows an example of a processing method of the surface inspection apparatus according to the present embodiment. In the present embodiment, an example of defect detection processing by the surface inspection apparatus will be described with reference to FIG.

  As shown in FIG. 4, the surface inspection apparatus according to the present embodiment includes a low-frequency defect detection apparatus in addition to the three-dimensional shape calculation apparatus. A processing method in the low-frequency defect detection apparatus will be described. First, only a low frequency component is extracted from the spectrum G ′ (fx, fy), and inverse Fourier transform is performed. As a result, light and dark changes due to patterns and light and dark changes due to defects with high spatial frequency such as scratches, protrusions, and foreign objects are removed from the original modified lattice image g ′ (x, y), and low-frequency light and dark due to uneven color illumination. Only changes remain. Changes in brightness due to uneven illumination are separated by shading correction. As a shading correction method, a method of generating illumination unevenness data generated from an image obtained by capturing a non-defective image, a white reference plate, or the like and subtracting it from the image to be inspected can be considered. After the shading correction, the image is divided into appropriate rectangular areas, the standard deviation of the image data is calculated in each rectangular area, and the quality is determined based on the size.

  According to this embodiment, in the three-dimensional measurement method using the fringe pattern projection method and the Fourier transform method, by using a low frequency component lower than the carrier frequency that has been removed in the past, defects having a low spatial frequency such as color unevenness can be displayed in the same deformed grid image It becomes possible to detect from.

(Embodiment 3)
FIG. 5 shows an example of the processing method of the surface inspection apparatus according to the present embodiment. In the present embodiment, an example of defect detection processing by the surface inspection apparatus will be described with reference to FIG.

  As shown in FIG. 5, the surface detection device according to the present embodiment includes a high-frequency defect detection device and a low-frequency defect detection device in addition to the three-dimensional shape calculation device.

  The processing method in each arithmetic unit is the same as described above. That is, the high-frequency defect detection apparatus extracts only high-frequency components from the spectrum G ′ (fx, fy) and performs inverse Fourier transform. After that, it is converted into a binary image by threshold processing, and noise is removed by morphological processing such as isolated point removal, expansion, and contraction, and then recognized as one lump by labeling processing. For each label, defect feature amounts such as the number of pixels and length are calculated, and pass / fail is determined based on the size of the feature amount.

  In the low frequency defect detection apparatus, only the low frequency component is extracted from the spectrum G ′ (fx, fy), and inverse Fourier transform is performed. Changes in brightness due to uneven illumination are separated by shading correction. After the shading correction, the image is divided into appropriate rectangular areas, the standard deviation of the image data is calculated in each rectangular area, and the quality is determined based on the size.

  According to the present embodiment, the three-dimensional measuring device using the fringe pattern projection method and the Fourier transform method includes a high-frequency defect detection device and a low-frequency defect detection device in addition to the three-dimensional shape calculation device. By using the component, it is possible to detect a defect having a high spatial frequency such as a scratch, a protrusion, or a foreign substance and a defect having a low spatial frequency such as color unevenness from the same deformed grid image.

  The program for the CPU to execute the processes shown in FIGS. 3 to 5 constitutes a program according to the present invention. As a computer-readable recording medium for recording the program, a semiconductor storage unit, an optical and / or magnetic storage unit, or the like can be used. By using such a program and recording medium in a system having a configuration different from that of each of the above-described embodiments and causing the CPU to execute the program, substantially the same effects as those of the present invention can be obtained.

  Although specifically described above based on the preferred embodiment, the present invention is not limited to the above-described surface inspection apparatus, defect detection method, program and recording medium using the same, and does not depart from the gist of the invention. Needless to say, various changes can be made.

  The present invention can also be applied to a defect inspection method and apparatus for optical discs and photosensitive drums.

It is a figure which shows the example of a deformation | transformation lattice image obtained by the optical system of the surface inspection apparatus which concerns on this embodiment. It is a figure which shows the absolute value of each term of spectrum G '(fx, fy) in frequency space. It is a figure which shows the example of a processing method of the surface inspection apparatus which concerns on this embodiment. It is a figure which shows the example of a processing method of the surface inspection apparatus which concerns on this embodiment. It is a figure which shows the example of a processing method of the surface inspection apparatus which concerns on this embodiment. It is a figure which shows the conventional fringe pattern projection method. It is a figure which shows the deformation | transformation lattice image image | photographed with the optical system of the prior art. It is the figure which showed the absolute value of each term of spectrum G (fx, fy) of the prior art in the frequency space. It is the figure which showed the absolute value at the time of taking out only C (fx-fx0, fy-fy0) of a prior art in frequency space. It is the figure which showed the absolute value of C (fx, fy) of the prior art in the frequency space. It is a figure which shows the defect which generate | occur | produces in an OPC drum.

Claims (11)

A fringe pattern projection means for projecting a fringe pattern onto the object;
Imaging means for imaging the surface of the object;
Three-dimensional shape calculation means for calculating the three-dimensional shape data of the object by Fourier transform from the image data of the object obtained by the fringe pattern projection means and the imaging means;
A surface inspection apparatus comprising: high-frequency defect detection means that performs defect detection based on a high-frequency component of image data of the object.   The surface inspection apparatus according to claim 1, further comprising a low-frequency defect detection unit that performs defect detection based on a low-frequency component of image data of the object.   The surface inspection apparatus according to claim 1, wherein the high-frequency defect detection unit detects defects such as scratches, protrusions, and foreign matters.   The surface inspection apparatus according to any one of claims 1 to 3, wherein the low-frequency defect detection means detects a color unevenness defect. A fringe pattern projecting step for projecting a fringe pattern onto the object;
An imaging step of imaging the surface of the object;
A three-dimensional shape calculation step of calculating three-dimensional shape data of the object by Fourier transform from the image data of the object obtained by the fringe pattern projecting step and the imaging step;
A defect detection method comprising: a high-frequency defect detection step that leaves a high-frequency component higher than a carrier frequency of image data of the object without being removed and performs defect detection based on the high-frequency component.   The low frequency defect detection step of leaving a low frequency component lower than the carrier frequency of the image data of the object without removing it and performing defect detection based on the low frequency component is further provided. Defect detection method   The defect detection method according to claim 5, wherein the high-frequency defect detection step detects defects such as scratches, protrusions, and foreign matters.   The surface inspection apparatus according to claim 5, wherein the low-frequency defect detection step detects a color unevenness defect. Projecting a fringe pattern on the object;
Processing to image the surface of the object;
A process of calculating the three-dimensional shape data of the object by Fourier transform from the image data of the object obtained by the process of projecting and the process of imaging;
A program that causes a computer to execute a defect detection process based on a high-frequency component of image data of the object.   The program according to claim 9, further causing the computer to execute a process of detecting a defect based on a low frequency component of the image data of the object.   The computer-readable recording medium which recorded the program of Claim 9 or 10.

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