JPH0740165Y2 - Defect inspection equipment - Google Patents

Description

[Detailed Description of the Device] Purpose of the device; (Industrial field of application) This device has a periodic pattern such as shadow mask, color filter for CCD / LCD, projection screen, VDT filter, photomask for IC. The present invention relates to a defect inspection device for inspecting defects and unevenness generated in the manufacturing process of industrial products.

(Prior Art) Usually, when an image pickup signal obtained by irradiating an object to be inspected is used as inspection information, an intensity difference of an irradiation distribution appears in an illumination unit that configures the image pickup setting, or a photoelectric surface of an image pickup apparatus appears. There was a sensitivity distribution, and these remained as a problem of shading. Further, even if such shading and a slight difference in resolution distribution are involved in the detection sensitivity, it is extremely difficult to perform inspection at a uniform inspection level over the entire imaging region. As a result, there remains a problem of uneven sensitivity in that the inspection level becomes excessively high or low depending on the area of the object to be inspected.

(Problems to be Solved by the Invention) In order to solve such a problem, a method of adjusting the position of the illumination lamp to make the illuminance distribution uniform is performed. However, even if shading with a large cycle can be corrected, it is difficult to adjust to a partial change in sensitivity, and the adjustment is time-consuming. This is because, for example, when an image is picked up by the image pickup tube, the distribution of the shading, the resolution of the subject area, and the like acts synergistically as a function of showing a direction of decreasing the sensitivity with respect to the detection sensitivity at the four corners of the screen. The present invention has been made in view of such circumstances, and an object of the present invention is to provide a nonuniform detection sensitivity distribution due to the illumination of the inspection apparatus or the imaging lens, which causes the difference in brightness of the projected illuminance of the imaging light source and the imaging. To provide a defect inspection apparatus capable of performing inspection with uniform detection sensitivity by adding a correction circuit in consideration of a result of detection processing based on a curvature degree or the like of an image section (or an image section) to the inspection apparatus and performing correction. It is in.

The present invention relates to a defect inspection apparatus, and the above object of the present invention is to obtain an image pickup device for picking up an image of an illuminated object to be inspected, and to obtain the same from the image pickup apparatus. A uniform modulation shading correction circuit that amplifies the detection level of the peripheral part of the captured image signal rather than the central part, and an image processing device that collates the captured image signal corrected by the modulation shading correction circuit with a constant threshold distribution are provided. The inspection is performed by the detection sensitivity, and further, a superimposition shading correction circuit is added to control so that the detection level of the peripheral portion of the image pickup signal does not exceed the A / D conversion level to the image processing apparatus, or the screen is small. The image processing apparatus is provided with a frame memory that stores a threshold distribution that has been subjected to detection processing under predetermined imaging conditions for each area, and the threshold distribution is used as an imaging signal. It is achieved as to match the processed results.

(Operation) This invention corrects the non-uniform detection sensitivity of the defect inspection apparatus. The modulation shading correction circuit works so that the image processing apparatus amplifies the detection level of the peripheral portion rather than the central portion before the image processing device processes the image pickup signal, so that the detection can be performed with a constant threshold and uniform sensitivity. At this time, it is the superimposition shading circuit that operates so that the detection level in the peripheral portion does not exceed the input level of A / D conversion. This superimposition shading correction circuit has a role of a control circuit for the modulation shading correction circuit. However, the normal function of illuminance correction is neglected in this invention because it is canceled in the later calculation. In addition, the frame memory stores a threshold distribution serving as an inspection condition, reads pixel data into image data, and includes a predetermined threshold determined for each small area of a segmented screen.

(Example) The example of this invention is shown below.

One example of a defect inspection method for an industrial product having a periodic pattern is one in which there is an abnormality in the opening area of the shadow mask pattern as shown in FIG. 2 of JP-A-61-256237 by the present applicant. The inspection and the shadow mask are disclosed as an inspection when the light is not evenly transmitted and the transmitted light is uneven when the whole is irradiated with light. In this invention, an apparatus for supplementing such a defect inspection method is shown. I shall.

FIG. 1 is a block diagram of the detection unit of the defect inspection apparatus of this invention. The inspected object 1 obtains a predetermined imaging condition by means of an illumination lamp 2 for irradiating it and a TV camera 3 provided for imaging. The image pickup signal from the TV camera 3 is sent from the modulation shading correction circuit 5 to the image processing device 6 via the superposition shading correction circuit 4. With this configuration, the TV camera 3 captures an image of the device under test 1, and the image capturing signal obtained from this is corrected. Second
Figures (A) to (C) and (A ') to (C') show screens related to the operation of the correction process (A), (B), (C).
(A '), and the actual detection sensitivity to a certain threshold condition of the detection system of the defect inspection apparatus are compared (A'),
(B ') and (C') are screen diagrams corresponding to the respective actions of the correction processing. For example, when the image pickup signal from the TV camera 3 is not corrected, the central portion of the DUT 1 is usually brighter than the peripheral portion due to the irradiation distribution of the illumination lamp 2 as shown in FIG. 2, and the image pickup lens is not affected by shading and resolution. Since the detection sensitivity is involved due to the presence of a distribution or the like, the state of signal change due to defects or the like exhibits a mountain-shaped distribution. Therefore, the peripheral defect Q1 and the central defect
Even if Q2 is the same level of defects, a difference occurs between the detection levels that exceeds the detection allowable range, and as shown in Fig. 2 (A '), it is centered with respect to a certain threshold (dotted line area in the same figure). Part defects
In some cases, Q2 is detected and peripheral defect Q1 is not detected. Therefore, the superimposed shading correction circuit 4 is provided to reduce the signal level in the peripheral portion. FIG. 2 (B) shows the operation of the superimposition shading correction circuit. In the present invention, however, the signal level of the peripheral part is A / D converted in the image processing device 6 with respect to the modulation shading correction circuit 5 to be sent next. The above-mentioned image processing device 6 has the same number of frame integration / subtraction for correcting the illuminance distribution as is commonly used. It is canceled by the calculation of the number of times and does not work. That is, it is not necessary when the signal level of the peripheral portion is within the input level range of A / D conversion. Even when this correction is applied, it does not contribute to the correction of the detection sensitivity with respect to a certain threshold as shown in FIG. 2 (B ').

The following function of the modulation shading correction circuit 5 acts as a virtual data correction process, and is shown in FIG. 2 (C). The modulation / shading correction circuit 5 applies a predetermined amplification factor to the imaging detection level to raise the detection level of the peripheral portion and suppress the detection level of the central portion, thereby, for example, the defect Q1 in the peripheral portion and the central portion. The defect Q2 is also detected with a constant threshold value, which is shown in FIG. 2 (C ').

In this way, the image pickup signal from the TV camera 3 is corrected so as to obtain a uniform detection sensitivity before being subjected to the image pickup process and the detection process by the A / D conversion and frame integration / subtraction in the image processing device 6. Is done.

(Modification) There is another method for coping with the case where the modulation shading correction circuit 5 in the above-mentioned embodiment cannot completely correct the shading. As shown in FIG. 3B, the image processing apparatus 6 is provided with a frame memory capable of deciding a threshold value based on a predetermined image pickup condition in advance for each small area of the divided screen. By doing so, it becomes possible to change the threshold value within the screen as shown in FIG. 3A, and it is considered that the defect Q1 in the peripheral portion and the defect Q2 in the central portion are similar in the inspection processing, and depending on the threshold value determination. A desired detection sensitivity can also be obtained. Note that the determination of the threshold value determined in the embodiment and the modification is only for the purpose of legend and is not particularly limited.

As described above, according to the present invention, in the defect inspection apparatus for industrial products having a periodic pattern, the problem of non-uniform detection sensitivity due to the illumination, the imaging lens, etc. is solved by the means using the correction circuit. We have realized a defect inspection system that is extremely rational. Since the detection data presented by the defect inspection device for precision products is highly reliable and accurate, the defect inspection device with uniform detection sensitivity achieved by the present invention has a great significance and can be set to a desired detection sensitivity. Can provide a highly practical defect inspection apparatus.

[Brief description of drawings]

FIG. 1 is a main configuration diagram showing an embodiment of the present invention, FIG. 2 is a screen view of image processing showing a detection result, and FIG. 3 is a screen view for explaining another embodiment. 1 ... Inspected object, 2 ... Illumination lamp, 3 ... TV camera,
4 ... Superimposition shading correction circuit, 5 ... Modulation shading correction circuit, 6 ... Image processing device.

Claims (3)

[Scope of utility model registration request] 1. An image pickup device for picking up an image of an illuminated object, a modulation shading correction circuit for amplifying a detection level of a peripheral portion of an image pickup signal obtained from the image pickup device, and a modulation shading. An image processing apparatus for collating an image pickup signal corrected by a correction circuit with a constant threshold distribution, and inspecting with uniform detection sensitivity. 2. The defect inspection apparatus according to claim 1, further comprising a superposition shading correction circuit for controlling so that a detection level of a peripheral portion of the image pickup signal does not exceed an A / D conversion level to the image processing apparatus. 3. The image processing apparatus is provided with a frame memory that stores a threshold distribution for a result of detection processing under a predetermined imaging condition for each small area, and the detection processing result is collated with the threshold distribution. The defect inspection apparatus according to claim 1 or 2.