JP3390931B2 - Inspection method for colored pattern defects - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for inspecting the appearance of a color filter or the like used for a liquid crystal display or the like.
In particular, the present invention relates to a method for detecting a minute white defect. Colored unit patterns with certain optical properties and shapes
Alternatively, samples (industrial products) or unit patterns regularly and repeatedly arranged in two-dimensional directions are repeatedly arranged while gradually changing the optical properties, shapes, and arrangement pitches in one-dimensional and two-dimensional directions. The present invention relates to a method for inspecting a defect generated in a sample (industrial product). Hereinafter, a region in which a colored unit pattern having a certain optical property and shape is regularly and repeatedly arranged in a one-dimensional direction or a two-dimensional direction is referred to as a periodic pattern region, and the optical property, shape and A region that is repeatedly arranged while the arrangement pitch in the one-dimensional direction and the two-dimensional direction gradually changes is referred to as a substantially periodic pattern region. 2. Description of the Related Art Conventionally, a defect inspection of a sample (industrial product) having a periodic pattern area or a substantially periodic pattern area has been performed by a microscope photographing apparatus capable of resolving a pattern arrangement unit and a defect shape. A first method of examining a video signal and performing pattern recognition, capturing a pattern having no defect in the same manner as the pattern to be inspected, and comparing the signals obtained from both patterns to detect a defect, Alternatively, for products having a periodic aperture, an optical Fourier transform using a diffraction image of the light due to the periodic aperture when irradiating coherent light, a third method of detecting defects by a spatial filtering method, and the like have been proposed. ing. However, in any of the methods, the inspection for the minute white defect is as follows.
If automatic detection is difficult and the resolution of the imaging means is increased by increasing the detection magnification, etc., there is a problem that the inspection tact increases, and in order to shorten the inspection tact, there is a problem that the apparatus cost increases. . In particular, in the case of a sample (industrial product) having a halftone periodic colored pattern region or a substantially periodic colored pattern region such as an LCD color filter, it is difficult, and it is difficult for human eyes to directly transmit the light by using a microscope. A method of observing a defect is generally used, and high-sensitivity automatic defect detection in inspection of a minute white defect has been desired. [0003] The inspection method of the present invention comprises:
Under such circumstances, a method for automatically detecting, with high sensitivity, a minute white defect in a sample (industrial product) having a periodic colored pattern region or a substantially periodic colored pattern region, such as an LCD color filter, is to be provided. Things. A colored pattern defect inspection method according to the present invention transmits a dark field light and a bright field light simultaneously to a sample having a periodic colored pattern area or a substantially periodic colored pattern area. Illumination, the transmitted light of the sample is detected by the imaging means, an image signal is obtained, a signal obtained by performing an enhancement process on the obtained image signal is obtained, and this signal is binarized at a predetermined slice level. By performing a slicing process, masking is performed on portions other than the defective portion, and only the defective portion is detected. Here, the bright-field light is illumination light whose optical axis coincides with the optical axis of the light-receiving unit of the imaging means, and dark-field light is illumination light whose optical axis is the light of the light-receiving part of the imaging means. It does not match the axis. Here, an example will be given as the emphasis processing.
First, an image is picked up by the image pickup means a plurality of times at the same portion of the sample, an image signal is obtained, and the obtained image signals for the plurality of times are integrated and averaged. This is because the light transmittance distribution as shown in FIG. 4A is obtained for a portion including a defective portion, but the video signal from the image pickup device has the pattern illumination unevenness and the image pickup surface as shown in FIG. A signal that responds to a signal that includes a gradual signal change (shading) due to uneven sensitivity, random noise generated in a video signal circuit, and a local change in the signal due to dust or the like attached to an optical system. In the same place, an image signal is obtained a plurality of times by the imaging means, an image signal is obtained, and the obtained image signal is integrated and averaged for a plurality of times, whereby the number of additions is reduced as shown in (c). If N, the ratio of random noise is 1 / ^N1 / ² . Here, A1,
B1, A2, and B2 indicate defective portions, and C indicates a local change of a signal due to dust or the like attached to the optical system. Next, by slightly shifting the position to be imaged and similarly integrating and averaging, a signal (d) obtained by slightly displacing the signal (c) can be obtained. When the difference signal is obtained, the signal becomes as shown in (e), and a signal component that does not change due to a gradual signal change (shading) or a movement of the imaging position is removed. Here, only the signal component due to the change in light transmittance and the reduced random noise component remain, and when this signal (e) is further subjected to a subtraction or differentiation process of the neighborhood average value, as shown in FIG. It can be seen that the gradual signal change (shading) component is also removed, and as a result, the obtained signal (f) is locally changed only in a portion corresponding to the defective portion, and is emphasized. In the binarization by the slice processing, the signal (f) is processed at a predetermined slice level SL, and only the defective portion is determined and binarized. It should be noted that the type of defect (white defect, black defect) can be identified by the order of signal inversion at the defective portion in FIG. [0005] White and black defects can be detected by such an emphasizing process and a slicing process, but the S / N by the illumination of the signal itself obtained by the imaging means is limited. Is 30 μm, it has conventionally been considered difficult to detect minute white defects and black defects of 5 μmφ or less as defects, but the pattern defect inspection method of the present invention uses transmitted light dark field illumination. Thereby, S by the illumination of the signal itself obtained by the imaging means
/ N is improved to enable detection of minute white defects of 5 μmφ or less. Here, a white defect refers to a pinhole or a missing pattern in a colored pattern portion, and a black defect refers to an extra colored portion or a light-shielding portion other than a predetermined pattern in the colored pattern portion. Since the optical axis of the dark-field light does not coincide with the optical axis of the light-receiving unit of the imaging means, light from the dark-field illumination of the light-receiving unit is transmitted to the light-receiving unit through the aperture of the periodic pattern or the substantially periodic pattern. Since it is not incident, almost only the diffracted light of the defect is detected, so that S
/ N is large. The S / N is improved by the combined use of the transmitted dark-field illumination because the S / N of the signal from the transmitted light from the illumination obtained by the imaging means is S ₁ / N _{1 in} the case of the transmitted dark-field illumination. , in the case of a transmission bright field illumination, S ₂
/ N ₂ , S ₁ / N ₁ > S ₂ / N ₂ , and (S ₁ + S ₂ ) / (N ₁ + N ₂ )> S ₂ / N _2. in the case of single use field illumination is _{S 1 / N 1> S 2} / N 2, of course. According to the method for inspecting a defect of a colored pattern according to the present invention, the dark field light is used for the transmitted illumination means, so that the imaging means can capture an image of the sample (industrial product) by the imaging means.
/ N is improved, and as a result, it is possible to detect a minute white defect. By performing signal processing such as enhancement processing and slicing processing on the obtained signal, it is possible to detect a minute white defect by automation. I have. A first embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram for implementing the detection method of Example 1, in which an LCD color filter is used as a test sample.
1 shows an apparatus for automatically inspecting for defects using a CCD line sensor. 1 is an imaging camera using a CCD line sensor, 2 is an LCD color filter, 3, 3a and 3b are light sources, and 4 is an image processing device. The LCD color filter of the test sample has a pattern in which red, green, and blue colored pattern portions are periodically arranged in a stripe shape.
At a predetermined position of the color pattern portion, a white defect of a predetermined size is provided with a plurality of test color patterns produced. When all of the sample and the imaging device such as the imaging camera 1 are kept stationary, the imaging camera 1
More than two CCD line sensors are arranged in a straight line, and the image of the color filter 2 is formed on the light receiving surface of the CCD line sensor by a lens, and only an image on a straight line of the color filter is taken. However, Example 1
Moves the imaging camera 1 in a direction orthogonal to the linear CCD line sensor to capture an image of the entire surface of the sample. The light source 3 illuminates the color filter of the entire field of view of the imaging camera 1 with transmitted bright-field illumination, and the light sources 3a and 3b illuminate the color filter of the entire field of view of the imaging camera 1 with transmitted dark-field illumination. When the transmitted dark-field light is illuminated on the fine pinhole portion of the colored portion of the sample, the diffracted light forms an image on the CCD line sensor. And finer white defects could be detected. Table 1 shows the results of the comparison and the red coloring pattern. In the case of conventional transmitted bright-field illumination, at a resolution of a CCD camera of 30 μm, a defect detection rate of a defect smaller than 5 μmφ is 0%, a defect detection rate of 5 μmφ to 8 μmφ is 0%, and a defect detection rate of 8 μmφ or more is 50%
On the other hand, when the transmission dark-field illumination and the transmission bright-field illumination of Example 1 were used together, the size defect detection rate of less than 5 μmφ 50
%, 5μmφ to 8μmφ size defect detection rate 90%, 8μ
It can be seen that the defect detection rate was 100% at mφ size or more, and the white defect detection rate was significantly improved. In addition, regarding the black defect having a size of 1 μmφ or less,
And the defect having a size of 15 μmφ or more can be detected using dark-field illumination for both white defect and black defect.
No difference was seen when not used. Almost the same results were obtained for the pattern portions other than red. Hereinafter, another inspection method different from the first embodiment will be described below. Embodiment 2 will be described with reference to FIG. In the case where the LCD color filter 22 is automatically inspected by the imaging camera 21 using the CCD area sensor, the whole or a part of the LCD color filter 22 is photographed by the imaging camera 21 at one time. 23 and 23a are light sources, and 24 is an image processing device. The light source 23 illuminates the color filter portion of the entire field of view of the imaging camera 21 with transmitted bright field illumination. The light source 23a is a ring fiber light source and illuminates the color filter portion of the entire field of view of the imaging camera 1 with transmitted dark field illumination. With the above-described configuration, the defect detection method of the present invention is an automated, highly efficient method for detecting a sample having a colored periodic pattern area or a colored substantially periodic pattern area. The present invention provides a method for detecting a white defect having high sensitivity, and in particular, it is possible to provide a method for detecting a defect which is effective for detecting a minute white defect.

[Brief description of the drawings] FIG. 1 is a schematic view of an apparatus according to a first embodiment of the present invention. FIG. 2 is a schematic view of an apparatus according to a second embodiment of the present invention. FIG. 3 is a diagram for explaining an emphasis process according to the present invention; [Explanation of symbols] 1, 21 imaging device 2,22 LCD color filter 3, 23 bright field light source 3a, 3b, 23a Dark field light source 4, 24 image processing device

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-62-201335 (JP, A) JP-A-6-208017 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01N 21/84-21/958 G01M 11/00-11/08

Claims (1)

(57) [Claim 1] A white defect observed by transmitting illumination to a sample having a periodic colored pattern region or a substantially periodic colored pattern region is imaged by an imaging unit and obtained. In the automatic inspection method for detecting a white defect by applying an emphasis process to an image signal, a defect inspection method for a colored pattern is characterized in that bright-field light and dark-field light are simultaneously used for a transmitted illumination unit.