JPH11132899A - Inspection method of solid-state imaging device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make the inspection method of a solid-state imaging device as simple as possible, and reduce the inspection time. SOLUTION: Let (n) be an odd natural number. In the respective vertical transfer parts 12 constituting a CCD, any one out of A field reading and B field reading is executed, and whether defective picture elements exist is judged from a picture element signal of one obtained image plane. The A field reading adds and reads the n-th picture element signal and the (n+1)th picture element signal, from a horizontal transfer part 13. The B field reading adds and reads the (n+1)th picture element signal and the (n+2)th picture element signal, from the horizontal transfer part 13.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a method of inspecting a solid-state imaging device using a charge coupled device (CCD), and more particularly, to an efficient inspection process and a shortened inspection time.

[0002]

2. Description of the Related Art Solid-state imaging devices using CCDs are widely used in electronic imaging equipment, mainly for consumer video cameras. In response to the demand for higher definition of images, the resolution of image sensors has been increasing, and CCs having more than 600,000 pixels have been developed.
D is also being used in popular video cameras for consumer use. A solid-state imaging device using a high-pixel CCD used in such home appliances is required to have high performance and quality, but is also strongly demanded to reduce costs. For this reason, with respect to inspection, it is required to simplify the inspection process without lowering the quality and shorten the inspection time.

FIG. 1 is a block diagram showing a schematic configuration of a conventional inspection apparatus. In response to a command from a computer 6 operated by the inspection program, the pulse generator 5 generates a predetermined drive pulse group and supplies the group to the solid-state imaging device (CCD) 1. The analog signal output from the solid-state imaging device 1 is A /
After being converted into a digital signal by the D converter 2 and subjected to predetermined processing such as signal addition and averaging of the same pixel by the signal processing circuit 3 as needed for the purpose of removing random noise, it is temporarily stored in the image memory 4. Is stored.

[0004] Based on the image data stored in the image memory 4, the computer 6 determines the quality of the CCD according to an inspection program. For example, assume that an output signal for one horizontal scanning period as shown in FIG. A signal change indicated by a smooth curve is a normal video signal, and a whisker-like portion where the level changes rapidly is a pixel defect portion.

[0005] In addition to the data corresponding to the signal of FIG.
2A, data subjected to a smoothing process for removing a rapid change from the data corresponding to the signal, that is, FIG.
Data corresponding to the signal shown in (b) is also calculated and stored. Further, the computer 6 calculates difference data between the data corresponding to the signal in FIG. 2A and the data corresponding to the signal in FIG. 2B, that is, the data corresponding to the signal illustrated in FIG. This difference data is also stored in the image memory 4.

[0006] The computer 6 regards the positive and negative peak values of the difference data obtained as described above as being non-defective if they are within a predetermined range, and is deemed to be defective if there is a portion exceeding the upper or lower limit. For example, in FIG. 2C, the portion indicated by A exceeds the upper limit value B, and this portion is determined to have a so-called white defect pixel defect. The portion indicated by c is below the lower limit value d, and this portion is determined to have a so-called black defect pixel defect. The monitor 7 is used for displaying the progress of the inspection, the inspection result, and the like.

[0007] In addition to the above-described defect for each pixel, the defect of the solid-state image sensor includes an area defect in which a certain range of pixels collectively has a defect, that is, a defect such as spot or shading. In addition, one of the vertical line or the horizontal line
There is also a line defect in which a book or a plurality of books are collectively defective.
Conventionally, a computer performs necessary image processing on data for each pixel in accordance with these inspection items, thereby shortening the inspection time.

[0008] The capture of data for each pixel of the CCD 1 is as follows.
Actually, it goes as follows. FIG. 3 shows a structure of a solid-state imaging device (CCD) to be inspected. This CCD is called an interline transfer CCD, in which a photoelectric conversion element 11 provided for each pixel and a vertical transfer section 12 adjacent thereto are provided alternately for each vertical line. A horizontal transfer unit 13 connected to one end of the transfer unit 12 and an output amplifier 14 connected to one end of the transfer unit 12 are provided. For the sake of simplicity, FIG. 3 illustrates a CCD having 4 pixels in the horizontal direction and 9 pixels in the vertical direction, for a total of 36 pixels.

The photoelectric conversion element 11 is composed of a photodiode or the like, and the signal charge corresponding to the luminance obtained here is transferred to a vertical transfer unit 12, and the vertical transfer unit 12 directs the signal charges to the horizontal transfer unit 13 one scanning line at a time. Transferred. Each vertical transfer unit 12
The signal charges for one scanning line transferred to the horizontal transfer unit 13 from the end of the signal are sequentially transferred to the output amplifier 14, and a standard image signal is output from the output amplifier 14.

The transfer of signal charges from the photoelectric conversion elements 11 to the vertical transfer units 12, the transfer of charges in the respective vertical transfer units 12, the transfer of charges from the vertical transfer units 12 to the horizontal transfer units 13, and the transfer of signal charges in the horizontal transfer units 13. Are controlled by a group of driving pulses supplied from the pulse generator to the CCD.
There are various driving methods such as two-phase driving, three-phase driving, and four-phase driving depending on the number of driving pulse signals to be added.

As a driving method of such a CCD, a driving method called field accumulation is generally used. As shown by the solid line in FIG. 3, in the odd field (A field), each vertical transfer unit 12
The pixel signals A11 to A14 are generated by adding the first to third pixel signals and the second pixel signal, and the pixel signals A21 to A2 are added by adding the third and fourth pixel signals.
For example, 16 pixel signals A11 to A44 of the A field are generated. On the other hand, in the even field (B field), as shown by the broken line in FIG.
The 16th pixel signal B11 of the B field is shifted by one by shifting the combination of the odd-numbered and even-numbered pixels, for example, by adding the third pixel signal and the third pixel signal.
B44 is generated.

In the conventional inspection method, data is taken in for each pixel of the CCD by using the above driving method as it is. That is, by obtaining an output signal as shown in FIG. 4A and performing A / D conversion with a clock signal as shown in FIG. 4B, a time-series pixel signal as shown in FIG. Get the data. This pixel signal data is stored in the image memory as described above. If data per pixel is composed of m bytes, the A field and the B field require a total capacity of 32 × m bytes. In addition, the above-described smoothing process is generally performed by a method of including a plurality of pixel data output before and after one pixel data to be smoothed. Since data cannot be overwritten, 2 × 32 × m bytes are used. A minimum capacity is required for inspection of pixel defects.

[0013]

SUMMARY OF THE INVENTION An object of the present invention is to reduce the inspection time by simplifying the above-described CCD inspection method as much as possible. Based on the following analysis. First, C
In the CD inspection time, the time for reading out the pixel data of the CCD and storing it in the image memory is dominant, and it is necessary to reduce this time in order to reduce the inspection time.

Further, regarding the inspection of the pixel defect, the above-mentioned A
Field read data and B field read data have redundancy. That is, assuming that there are two defects a and b in FIG. 3, as shown in FIGS. 4A and 4C, the data including the defects are A21 and A3.
4, B21, and B34. By eliminating this redundancy, it is conceivable to reduce the time for reading out pixel data and storing it in the image memory.

In the area defect inspection, since the data for each pixel is not finally required, it is conceivable to reduce the number of data by collecting the pixel data at the stage of reading the pixel data and storing it in the image memory. .

[0016]

In order to achieve the purpose of shortening the inspection time and the like based on the above analysis, the first inspection method of the present invention, when n is an odd natural number,
In each of the vertical transfer units constituting the CCD, an A-field readout is performed in which the nth pixel signal and the (n + 1) th pixel signal are added and read from the horizontal transfer unit, and the (n + 1) th pixel signal and the (n + 2) th pixel signal are read out from the horizontal transfer unit. It is characterized in that only one of the B field reading and the pixel signal reading which is added and read is executed, and the presence or absence of a defective pixel is determined from the obtained pixel signals for one screen.

That is, the inspection method that conventionally performs both the A-field reading and the B-field reading following the driving method in a product is stopped, and only one of the data is read and stored in the image memory. As a result, the time required for storing the pixel data is reduced to half that of the related art. The time required for the subsequent image processing and the required memory capacity are also reduced.

In the second inspection method according to the present invention, when n is an odd natural number, the nth pixel signal and the (n + 1) th pixel signal from the horizontal transfer section in each vertical transfer section constituting the CCD are provided. A field read, which is performed by adding the following, and the (n + 1) th pixel signal and n
B field readout which is performed by adding the + 2th pixel signal and reading out is performed, and one of odd or even data is taken in from the pixel signal for one screen obtained by the A field readout, and the B field readout is performed. It is characterized in that the other data of the odd number or the even number is fetched from the pixel signals for one screen obtained by reading, and the presence or absence of a defective pixel is determined from the fetched data.

That is, the pixel data read out from the CCD is both the A field and the B field as in the prior art. For example, by reducing the clock frequency of the A / D conversion to half, the data stored in the image memory becomes the A field. And thin the full data of the B field by half. When only the odd-numbered A-field data is stored, only the even-numbered B-field data is stored, so that all the pixel data are included by complementing each other. This reduces the required capacity of the image memory and shortens the processing time of the stored data. To that extent, the computer can execute other processing, so that the inspection time can be reduced as a whole.

In a third inspection method according to the present invention, in each of the vertical transfer units constituting the CCD, three or more consecutive pixel signals are added and read, and defective pixel signals are obtained from the obtained pixel signals for one screen. Is determined. As a result, area defects and line defects can be efficiently inspected while realizing a reduction in memory capacity and an inspection time. In other words, when the same defect is present over a plurality of pixels, the defect can be sufficiently detected by comparison with the reference level even when a plurality of pixel data are collectively (added) and taken in. Furthermore, by adding a plurality of continuous pixel signals also in the horizontal transfer unit, it is possible to further reduce the memory capacity and the inspection time. The addition of pixel data in the vertical transfer unit and the horizontal transfer unit can be easily performed by controlling the driving pulse waveform of the CCD, and the addition method itself is known.

In each inspection method according to the present invention,
It is preferable that, on an image memory that stores pixel signal data, an area size allocated to data of one screen is variable according to an inspection item. The number of pixel data required for the inspection of the area defect and the line defect is smaller than that of the inspection of the pixel defect by adding and taking in a plurality of pixel data as described above. Therefore, the area size allocated to data for one screen is not fixed, but is made variable according to the inspection item, so that the image memory can be used efficiently and the required overall capacity can be reduced.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an inspection method according to the present invention will be described below focusing on differences from the above-described conventional inspection method.

(Embodiment 1) In the inspection method according to Embodiment 1 of the present invention, the solid-state imaging device (CCD) 1 shown in FIG.
Are only the signals in the A field, as shown in FIGS. That is, in each of the vertical transfer units 12 in FIG. 5, the first pixel signal and the second pixel signal are added from the horizontal transfer unit 13 to obtain the pixel signal A1.
1 to A14, and the third pixel signal and the fourth pixel signal are added to generate pixel signals A21 to A24.
To A44. Successive ones shown in FIG.
The six pixel signals A11 to A44 are subjected to A / D conversion processing by the A / D converter 3 using clock signals as shown in FIG. 6B, and become time-series digital signals.
Time-series pixel signal data as shown in (c) is obtained. This pixel data is stored in the image memory 4 as in the conventional example.

In this way, the number of pixel data per screen required in the conventional example is reduced by half from 32 to 16 and the memory capacity required for storage is reduced. Then, the time required for storing the pixel data and the subsequent data processing is reduced, which contributes to shortening the inspection time. Even in this case,
Assuming that there are two pixel defects a and b in FIG. 5, as shown in FIGS. 6A and 6B, data including a pixel defect always appears as A21 and A34.

In FIG. 5, although the pixel data corresponding to the uppermost horizontal scanning line is not taken in, the actual CCD having more than 600,000 pixels has a pixel defect in one peripheral line. This is not a practical problem. Further, instead of taking in the pixel signal only in the A field, a pixel signal in only the B field may be taken in.
That is, in each vertical transfer unit 12 in FIG. 3, the second pixel signal and the third pixel signal from the horizontal transfer unit 13 are added, the fourth pixel signal and the fifth pixel signal are added, and so on. The combination of the odd and even numbers to be added may be shifted by one to generate 16 pixel signals of the B field and store the corresponding 16 pixel data in the image memory.

(Embodiment 2) In the inspection method according to Embodiment 2 of the present invention, the pixel signal output from the solid-state imaging device (CCD) 1 is, as shown in FIG.
All pixel signals in the A field and the B field. However, the A / D converter 2 thins out every other continuous pixel signal output from the CCD 1 and converts it into a digital value. This is performed by reducing the frequency of the clock pulse given to the A / D converter 2 to half as shown in FIG. However, the clock pulse timing is set such that odd-numbered pixel data is obtained for the A field and even-numbered pixel data is obtained for the B field.

As a result, as shown in FIG. 7C, eight pieces of pixel data for the A field and eight pieces of pixel data for the B field are obtained. Then, since the pixel data thinned out in the B field is taken in so as to complement the pixel data thinned out in the A field, if there is a defective pixel in the CCD, it must be detected from any of the stored pixel data. Is done. For example, if there are two pixel defects at a and b as shown in FIG. 3 or 5, data including pixel defects are represented by A21 and B24 as can be seen from FIGS. 7A and 7B. Appear.

As described above, according to the present embodiment, it is possible to halve the pixel data per screen to be stored in the pixel memory while reliably detecting the pixel defect. As a result, it is possible to reduce the image memory and the inspection time by shortening the time required for processing the stored pixel data. Note that, contrary to the above-described A / D conversion timing, the timing may be set so that even-numbered pixel data of the A field and odd-numbered pixel data of the B field are obtained.

(Embodiment 3) An inspection method according to Embodiment 3 of the present invention will be described with reference to FIGS. As shown in FIG. 8, in the present embodiment, four consecutive pixel signals are added in a vertical transfer unit 12 of a solid-state imaging device (CCD), and two consecutive pixel signals are also added in a horizontal transfer unit 13. Is added. That is, 32 pixel signals excluding the four pixels corresponding to the top one scanning line are added in the vertical direction to form eight pixel signals A11 to A14 and A21 to A21.
24, and are further combined into four pixel signals by horizontal addition. As described in the first embodiment, even if data of four pixels corresponding to one scanning line at the top is not taken in, there is no practical problem with a CCD having more than 600,000 pixels. Also, as described above, such addition processing can be easily realized by controlling the drive pulse given to the CCD.

By the addition processing as described above, four continuous pixel signals as shown in FIG. 9A are obtained from the CCD 1, and A / D conversion is performed at the timing of the clock pulse shown in FIG. 9B. By performing the processing, pixel data as shown in FIG. 9C is obtained. Since the signals of 32 pixels are combined into 4 pixel data and stored in the image memory,
The required capacity of the image memory is reduced, and the time required for processing the image data and, consequently, the overall inspection time are reduced.

In FIG. 8, assuming that there are two pixel defects a and b, as in the conventional example and the above-described embodiment, the pixel data of FIG. 9 shows A11 + A12 and A2
The value of 3 + A24 is affected. However, since eight pixel signals are added and converted into one pixel data, if only one of the pixels has a small defect, the change in the value of the pixel data after the above-described addition is obtained. That is, the difference from the normal value may be relatively small. In this case, it is difficult to detect a pixel defect depending on a method of comparing this value with a reference value.

However, in the case of an area defect or a line defect in which the same defect extends over a plurality of adjacent pixels, a change in the value of the pixel data after addition becomes large.
Defects can be detected without any problem by a method of comparing with a reference value. Note that the number of pixel signals to be added is an example, and is not limited to this. Also, 1 is obtained by adding only in the vertical direction without performing addition in the horizontal direction.
The number of pixel data per screen may be reduced.

The embodiments described above can be implemented in combination. That is, as described above,
In the inspection of D, it is necessary to execute various inspection items such as a defect for each pixel, a defect having an area, a defect such as shading, and a line defect that becomes defective in a line shape. It is desirable to implement the method of the embodiment in which the inspection time can be reduced as much as possible, thereby reducing the overall inspection time. At this time, since the number of pixel data for one screen differs according to the embodiment, it is preferable that the area size of the image memory allocated to the data for one screen is not fixed, but is variable according to the inspection item. For example, it is possible to secure a large area for inspection of pixel defects that require fine inspection accuracy, and to use a small memory area for inspection of area defects. As a result, the required capacity of the entire memory can be reduced, and the data processing time including reading, writing, and transferring between memories can be reduced.

[0034]

As described above, according to the method for inspecting a solid-state image sensor of the present invention, it is possible to shorten the inspection time and reduce the required image memory capacity while maintaining the conventional inspection accuracy. it can.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a schematic configuration of a conventional inspection apparatus.

FIG. 2 is a waveform chart showing an output signal and the like from a solid-state imaging device in one scanning period for explaining a pixel defect detection method;

FIG. 3 is a diagram showing a simplified structure of a solid-state imaging device to be inspected;

FIG. 4 is a diagram showing an output signal of a solid-state imaging device, an A / D conversion pulse, and obtained pixel data in a conventional inspection method in a time-series manner.

FIG. 5 is a diagram showing a simplified structure of a solid-state imaging device for explaining an inspection method according to the first embodiment of the present invention;

FIG. 6 is a diagram schematically showing an output signal of a solid-state imaging device, an A / D conversion pulse, and obtained pixel data in a time series according to the inspection method of the first embodiment.

FIG. 7 is a diagram schematically showing an output signal of a solid-state image sensor, an A / D conversion pulse, and obtained pixel data in a time series according to the inspection method of the second embodiment.

FIG. 8 is a diagram showing a simplified structure of a solid-state imaging device for explaining an inspection method according to a third embodiment of the present invention;

FIG. 9 is a diagram showing an output signal of a solid-state imaging device, an A / D conversion pulse, and obtained pixel data in a time series in the inspection method according to the third embodiment.

[Explanation of symbols]

 Reference Signs List 1 solid-state imaging device (CCD) 2 A / D converter 3 signal processing circuit 4 image memory 5 pulse generator 6 computer 7 monitor

Claims (5)

[Claims] 1. A method for inspecting a solid-state imaging device using a CCD, wherein, when n is an odd natural number, an nth pixel signal from a horizontal transfer unit and n + 1 Only one of A field readout, which reads out by adding the nth pixel signal, and B field readout, which reads out by adding the (n + 1) th pixel signal and the (n + 2) th pixel signal from the horizontal transfer unit, are executed. A method of inspecting a solid-state imaging device, wherein the presence or absence of a defective pixel is determined from the obtained pixel signals for one screen. 2. A method for inspecting a solid-state imaging device using a CCD, wherein, when n is an odd natural number, an n-th pixel signal from a horizontal transfer unit and n + 1 in each vertical transfer unit constituting the CCD. A field readout by adding and reading out the Ath pixel signal and B field readout by adding and adding the (n + 1) th pixel signal and the (n + 2) th pixel signal from the horizontal transfer unit are executed. Either odd-numbered or even-numbered data is fetched from the obtained one-screen pixel signal, and odd-numbered or even-numbered other data is fetched and fetched from the one-screen pixel signal obtained by B-field reading. A method for inspecting a solid-state imaging device, comprising: determining presence or absence of a defective pixel from the data obtained. 3. A method for inspecting a solid-state imaging device using a CCD, wherein at each vertical transfer unit constituting the CCD, three or more consecutive pixel signals are added and read out.
A method for inspecting a solid-state imaging device, comprising determining presence or absence of a defective pixel from pixel signals of a screen. 4. The inspection method for a solid-state imaging device according to claim 3, wherein, in addition to the addition of the pixel signals in the vertical transfer unit, a plurality of continuous pixel signals are also added in the horizontal transfer unit. 5. An image memory for storing pixel signal data, wherein an area size allocated to data of one screen is variable according to an inspection item. Inspection method for solid-state imaging device.