JPH03261810A - Outer appearance inspection apparatus - Google Patents

Abstract

PURPOSE:To automatically select the optimum illuminating condition by illumi nating two optional areas of an object to be inspected by each of a plurality of illuminating means, calculating the ratio of video signals at each representa tive point corresponding to the illumination, and selecting and controlling a plurality of the illuminating means based on each signal ratio. CONSTITUTION:A representative point of each of a blank part in the periphery of an object 9 to be inspected and a part to be hatched is input as an indicating point A, B by an operator. The SN ratio is SNR1 and SNR2 from the relation of the intensity of the N, S signals of the indicating points A, B. A first, a second and a third illuminating devices 11, 12, 13 are controlled to be driven through control of a control circuit 6, so that the illuminating strength to the object 9 is gradually increased from zero. An image of the object 9 is input as a video signal by an image sensing device 2, and the value of the image is converted to a digital value by an A/D converter 3 and stored in an image memory 4. The SN ratio is calculated by an SNR calculating circuit 5 based on the image signal. The SN ratio is compared with an allowable SN ratio set beforehand by the control circuit 6, whereby the illuminating device 11 (or 12, 13) is determined to be the optimum one.

Description

[Detailed Description of the Invention] [Summary] The present invention relates to an appearance inspection device that inspects the form of an object to be inspected, and particularly to an appearance inspection device that automatically selects the optimum illumination for the object to be inspected. The purpose of the present invention is to provide an appearance inspection device that can automatically select a lighting device based on the value of each signal ratio of video signals representing two areas of the object to be inspected. a plurality of illumination means for illuminating according to a method; and an imaging means for capturing an image of the object to be inspected illuminated by the plurality of illumination means and outputting a video signal, and inspecting the object to be inspected based on the video signal. In the visual inspection apparatus, a signal ratio calculation means for calculating a signal ratio between a first video signal and a second video signal representing arbitrary two areas of the inspection object, and the calculated signal for each illumination. The illumination control means selectively combines and drives and controls a plurality of illumination means based on the ratio.

It is. Appearance inspection devices that perform these various measurements and inspections optically image the object to be inspected, and perform image processing on this imaged data using an image processing device to precisely measure and inspect the appearance of the object.

In this way, since visual inspection equipment optically images the form of the object to be inspected and inputs the image, the suitability of the illumination during image capture has a large effect on the image input state, and it is important to It is necessary to select a lighting method.

[Industrial application field]

The present invention relates to a visual inspection device for inspecting the form of an object to be inspected, and more particularly to a visual inspection device for automatically selecting the optimum illumination for the object to be inspected.

In recent years, industrial equipment has become more precise and requires high manufacturing precision. In particular, in the field of semiconductors, integrated circuits are becoming more highly integrated.
High-precision microfabrication is required.

Various techniques have been developed for precisely optically measuring and inspecting devices, elements, etc. produced by this miniaturization process. [Prior Art] Conventionally, there has been an appearance inspection apparatus of this type as shown in FIG. 8. FIG. 8 shows a block diagram of the configuration of a conventional apparatus, and in the same figure, the conventional visual inspection apparatus includes a plurality of illumination devices 11, 12, and 13 that illuminate the object 9 to be inspected using different illumination methods. , an imaging device 2 that captures an image of the inspection object 9 illuminated by the illumination device 11.12.13;
The video signal of the imaging device 2 is converted into analog/digital (A/
D) An A/D converter 3 for conversion, an image memory 4 for storing digital video signals output from the A/D converter 3, and image processing based on the video signals stored in the image memory 4. This configuration includes an image processing device 8 that performs.

Next, the operation of the conventional device will be explained based on the above configuration. First, an operator manually selects multiple lighting devices11.12.
．． The lighting device 11 that is considered to be optimal is selected from among the 13 lighting devices.

The selected illumination device 11 illuminates the inspection object 9, and the imaging device 2 obtains a video signal. .

This video signal is converted into a digital value video signal by an A/D converter 3, and this video signal is stored in an image memory 4 serving as a buffer memory. The stored image signals are sequentially read out to the image processing device 8 and subjected to image processing, and the appearance of the inspection object 9 is inspected based on this image processing data.

[Problem to be solved by the invention]

Since conventional visual inspection equipment was configured as described above, various lighting methods can be considered depending on the object to be inspected, and combinations of various lighting methods can also be considered, and it takes a lot of skill to select the optimal lighting. The problem with this method is that it requires a huge amount of testing time based on the many years of experience of a person or a lot of trial and error.

The present invention has been made to solve the above-mentioned problems, and automatically selects an illumination device with an optimal illumination method according to the object to be inspected based on the value of each signal ratio of video signals representing two regions of the object to be inspected. The object is to provide an appearance inspection device that can be selectively combined.

[Means to solve the problem]

FIG. 1 is a diagram explaining the principle of the present invention.

A plurality of illumination means for illuminating an object to be inspected using various illumination methods, and an imaging means for capturing an image of the object to be inspected illuminated by each of the plurality of illumination means and outputting a video signal,
In a visual inspection apparatus that inspects an object to be inspected based on the video signal, signal ratio calculation calculates a signal ratio between a first video signal and a second video signal representing arbitrary two areas of the object to be inspected. and an illumination control means that selectively combines and drives and controls a plurality of illumination means based on the calculated signal ratio for each illumination.

[Effect]

In the present invention, a plurality of illumination means illuminate two arbitrary points on the object to be inspected, and a signal ratio calculation means calculates the signal ratio of each video signal of the two points corresponding to each illumination. By selectively combining and controlling the drive of a plurality of illumination means based on each signal ratio, it is possible to select a combination of illumination means that provides the necessary signal ratio when performing a visual inspection based on the video signal of the object to be inspected. Automatically selects and determines the optimal lighting conditions for the target object.

〔Example〕

(a) Description of an Embodiment A visual inspection apparatus according to an embodiment of the present invention will be described below with reference to the block diagram of the embodiment shown in FIG.

In the same figure, the visual inspection apparatus according to the present embodiment has a first, second, and third lighting device 11, 12, and the like, as in the conventional device.
．． 13, comprises an imaging device 2, an A/D converter 3, an image memory 4, and an image processing device 8, and in addition to the configuration, each of the I, 2, and 3 images stored in the image memory 2 SNR calculation circuit 5 that calculates each SN ratio of the first and second video signals (N signal, S signal) of point A and point B of the inspection object 9 when illuminated by the illumination devices 11, 12, and 13 respectively. and one construction of each of the above-mentioned first, second, and third lighting devices, ↑2.13
Control to output a control signal for driving and controlling each of the above, and to select each of the first, second, and third lighting devices 11, 12, and 3 based on the calculated SN ratio and output a control signal. The configuration includes a circuit 6 and lighting drive circuits 71, 72, and 73 that drive and control each of the first, second, and third lighting devices ↓1.12.13 based on the control signal.

In the imaging optical system formed by the first, second, and third illumination devices 1, 12, 3, and the imaging device 2, the first illumination device 11 provides a bright field and a bright field for the inspection object 9. The second illumination device 12 performs dark field illumination (dark field illumination) on the object 9 to be inspected, and the third illumination device illuminates the object 9 to be inspected. Each is configured to provide illumination (backlighting).

Next, the operation of the apparatus of this embodiment based on the above configuration will be explained based on FIGS. 3 to 6. This figure 3 (A), (
B) and (C) are a plan view and a video signal intensity distribution diagram of the target pattern part and peripheral part of the inspection object, and Fig. 4 (A)
, (B), and (C) are relationship diagrams between illumination intensity and video signals, FIG. 5 is a diagram of drive combinations of the first, second, and third lighting devices, and FIG. 6 is an operation flowchart.

First, as shown in FIG. 3(A), each representative point of an arbitrary peripheral area (blank area in FIG. 3(A)) and target pattern area (hatched area in FIG. 3(A)) on the inspection object 9 is manipulated. The operator points to indicated point A (peripheral area) and indicated point B (target pattern area).
(Step 1). Here, the SN ratio is determined as follows from the strength relationship of the N signal and S signal at the indicated points A and B. If the value is smaller due to the strength of the video signal N at the designated point A or the video signal S at the designated point B on the inspection object 9, this SN ratio is called the SNR.
, (=Sn/N,).

Also, the video signal N of the designated point A on the inspection object 9 has a value m greater than the intensity of the video signal S of the designated point B.
m, this SN ratio is set to 5NR2 (=N, , /S).

Based on the control operation of the control circuit 6, the first, second and third
The illumination devices 11, 12, and 13 are driven and controlled in the order of combination numbers 1 and 2.3 shown in FIG. Step 2).

When each of the first, second, and third lighting devices 1 and 2.13 is driven, an image of the inspection object 9 is input as a video signal by the imaging device 2, and the video signal is sent to the A/
The D converter 3 converts it into a digital value and stores it in the image memory 4 as a digital video signal. Based on each of the stored image signals, the SNR calculation circuit 5 calculates the SN
Calculate the ratio (step 3).

The calculated SN ratios are compared with an allowable SN ratio value "3" set in advance by the control circuit 6 (step 4). This allowable SN ratio value "3" is a value specified in advance based on the image processing accuracy of the image processing device 8 and the like.

According to the comparison result of the control circuit 6, if the calculated SN ratio is equal to or higher than the allowable SN ratio value "3", the lighting device 11 (or 12.13) having the SN ratio is determined as the optimal lighting device. This happens (Step 5).

Further, according to the comparison result of the control circuit 6, if all the calculated SN ratios are below the allowable SN ratio value "3",
The first, second, and third lighting devices 11.12.13 are each combined, and the combined lighting devices 11.12.13 are controlled by the control device 6 via the lighting drive circuit 71.72.73. Drive (step 41). The illumination device combination operation of the control device 6 in step 41 is performed as follows based on the magnitude relationship of the video signal S and the video signal N of each SN ratio.

The relationship diagram between the illumination intensity and the video signal in the first illumination device 11 is shown in FIG. 4(A), the relationship diagram in the second illumination device 12 is shown in FIG. A relationship diagram is shown in FIG. 4(C). In each of the above figures, the video signal N (
or N), the nm signal level is a, and the indicated point B (see Figure 3 (A))
The signal level n of the video signal S (or S )
Let m be b. Based on the magnitude relationship of each signal level a and b, (SNR) and (SN
R2) is calculated as follows.

Figure 4 (A); from a > b 1 (SNR2)
, <3...■ Figure 4 (B); from a2<b2 (SNR1) 2<3...■ Figure 4 (C); from a>b3 (SNR2) 3< 3...■ From the relationship of ■, ■, and ■ above, those in which a and b have the same magnitude relationship (same 5NR2) are ■ and ■, so the first and third lighting devices 11.13 are combined to Driving and controlling each third lighting device 11.13 (step 41)
. In addition, in this drive control, the illumination intensity of each of the I and 3 illumination devices 1 and 13 is changed and adjusted so that the following equation is satisfied.

(SNR2)=(SNR2)1+(SNR2)3=(b
+b3)/(al10a3)≧3...■ The SNR calculation circuit 5 calculates the SN ratio when each of the adjusted first and third lighting devices 11.13 is driven (step 42). The control circuit 6 performs a comparison calculation to determine whether the calculated SN ratio is greater than or equal to the allowable SN ratio value "3" (step 43). That is, a comparison operation is performed to determine whether the formula (2) holds true.

Based on the above comparison calculation result, the calculated SN ratio is the allowable SN
If the ratio value is "3" or more, the combination of the first and third lighting devices 11.13 is determined as the optimal lighting device (
Step 5).

Based on the above comparison calculation result, the calculated SN ratio is the allowable SN
If the ratio value is less than "3", the control circuit 6 determines whether there is another combination (any of combination numbers 4 to 7 in FIG. 4) (step 431). If the control circuit 6 determines that other combinations are present,
The process returns to step 41 and the operations from steps 4 to 43 are repeated again.

On the other hand, in step 431, the other combinations are "none".
If it is determined that this is the case, the highest value of all the S/N ratios calculated so far is selected (step 432).

The combination of lighting devices having the selected highest value of the S/N ratio is determined as the optimal lighting device (step 5).

(b) Description of other embodiments In the above embodiments, each of the first, second, and third illumination devices 11, 12, and 13 was configured to perform bright field illumination, dark field illumination, and transmitted illumination. In addition to these illumination methods, various illumination devices such as polarized illumination, interference illumination, critical illumination, and Keller illumination may also be used. In the above embodiment, the illumination means is composed of three types of first, second, and third illumination devices 11, 12, and 13, but it can also be composed of any plurality of types of illumination devices.

In addition, in the above embodiment, the lighting device combination control operation of the control circuit 6 (steps 41 to 43 in FIG. 6) is controlled at the instruction point A.
-B signal levels aSb are combined depending on the magnitude relationship, but the control operation of the control circuit 6 can be configured as shown in FIG. In the figure, the control circuit 6 combines all of the lighting devices 11, 12, and 13 (combination numbers 4 to 8 in FIG. 5), and sequentially drives the combined lighting devices (step 410). When the combined lighting devices are driven, the SNR calculation circuit 5 calculates the SN ratio for each (step 420).
The control circuit 6 performs a comparison calculation to determine whether the N ratio value is equal to or greater than "3" (step 430). The above SN ratio is the allowable SN ratio value "3"
” or more, the combination is determined as the optimal lighting device (step 5) in the same way as in the previous example, but if the allowable SN ratio value is “3” or less, the highest SN ratio of all the SN ratios calculated so far is determined. A value of the SN ratio is selected (step 432), and the combination of lighting devices with the highest value of the SN ratio is determined as the optimal lighting device (step 5).

In addition, in the above embodiment, two single pointing points A1B are indicated on the peripheral part of the inspection object 9 and the target pattern part, respectively, but if the materials of the peripheral part or the target pattern part are different, It is also possible to specify a plurality of arbitrary locations as instruction points.

Furthermore, in the above embodiment, the illumination intensity of each illumination device for the inspection object 9 is gradually changed strongly from zero within a predetermined range (step 2 in FIG. 6), but the irradiation angle is also changed at a predetermined angle. It is also possible to have a configuration that allows

〔Effect of the invention〕

As explained above, in the present invention, each of two arbitrary regions of the object to be inspected is illuminated by a plurality of illumination means, and the signal ratio calculation means calculates the signal ratio of each video signal of the representative point corresponding to each illumination. By selecting and controlling the drive of a plurality of illumination means based on each signal ratio, a combination of illumination means that provides the signal ratio required when performing an external appearance inspection based on the video signal of the inspection object can be determined. You will be able to choose,
This has the effect that the optimal illumination conditions for the object to be inspected can be automatically selected and determined.

[Brief explanation of drawings]

Fig. 1 is a diagram explaining the principle of the present invention, Fig. 2 is a block diagram of an embodiment of the present invention, and Fig. 3 (A
) is a plan view of the target pattern and surrounding area of the object to be inspected, and Fig. 3 (B) and (C) are the indicated point A in Fig. 3 (A).
, B, each video signal intensity distribution diagram; FIGS. 4(A), (B), and (C) are relationship diagrams between illumination intensity and video signal in the case of each of the first, second, and third lighting devices; FIG. 5 is a diagram of a combination of the first, second, and third lighting devices; FIG. 6 is an operation flowchart of an embodiment of the present invention; FIG. 7 is a main part of another embodiment of the present invention. Operation Flow Chart FIG. 8 shows a block diagram of the configuration of a conventional visual inspection device. 2... Imaging device 3... A/D converter 4... Image memory 5... SNR calculation circuit 6... Control circuit 8... Image processing device 9... Inspection object 11.12 .13. (1st, 2nd, 3rd each) Lighting device 71.72.73...Lighting drive circuit Book 4 DoB month f > Principle ttF March diagram Chame-tei - Sharo's Ichigo "Sel P1 Block structure 8th 2nd day W November strong liquid [Wl employment strength [Wl relationship diagram between Terumou strong pass and video signal Ke5
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Claims (1)

[Claims] 1. A plurality of illumination means for illuminating an object to be inspected using various illumination methods, and an imaging means for capturing an image of the object to be inspected illuminated by each of the plurality of illumination means and outputting a video signal. In a visual inspection apparatus that inspects an object to be inspected based on the video signal, a signal ratio between a first video signal and a second video signal representing arbitrary two areas of the object to be inspected is calculated. An external appearance inspection apparatus comprising: a signal ratio calculation means for calculating a signal ratio; and a lighting control means for selectively combining and driving and controlling a plurality of lighting means based on the calculated signal ratio for each lighting. 2. The visual inspection apparatus according to claim 1, wherein the plurality of illumination means illuminate the object to be inspected by changing the illumination intensity. 3. The lighting control means determines the magnitude of the signal level of the first video signal and the second video signal when the signal ratios for each lighting calculated by the signal ratio calculation means are all below a predetermined value. 2. The external appearance inspection apparatus according to claim 1, wherein a plurality of illumination means corresponding to signal ratios for each illumination having the same relationship are selected and combined, and the combined plurality of illumination means are driven and controlled.