JPS61187672A - Method and apparatus for inspecting flaw of close contact type image sensor - Google Patents

Abstract

PURPOSE:To inspect the presence of the flaw of an indivisual electrode pattern within a short time, by a bright signal generated when a photodiode is irradiated with light. CONSTITUTION:A probe 10 is contacted with the connection pad relating to the photodiode of one block in such a state that the phtotdiode 2 of a sensor substrate 1 is irradiated with light. MOSFET switches 8 are successively turned ON by th shift register 7 of a drive circuit 6. Subsequently, when the switches 8 are turned OFF at a certain time and a charge accumulation time arrives, the photodiode 2 is discharged by the sum of a photocurrent and the leak current of the photodiode 2, After a definite time, the switches 8 are again turned ON and the re-charging current flowed in the photodiode 2 is detected by a detection circuit 9 to obtain a bright current. The flaw of the indivisual electrode pattern of one block of the substrate 1 can be inspected by said bright current and this inspection is successively performed with respect to the indivisual electrode pattern at every block and the inspection of all of the indivisual electrode patterns of th sensor substrate 1 is performed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method and apparatus for inspecting bit defects in a dimensional image sensor for contact type document reading.

[Prior art and its problems]

Recently, in order to miniaturize document reading devices such as facsimile machines, the development of contact type image sensors has been actively promoted. This is a photoelectric conversion device that incorporates a long-dimensional image sensor with the same width as the original. Conventional CCD and M
A photoelectric conversion system with an OS-type IC image sensor requires a reduction lens system to project the original onto the image sensor, and in order to ensure the optical path length, a large space is required within the device, so it is necessary to miniaturize the device. However, it had some difficult drawbacks.

However, the above-mentioned contact type image sensor does not require this reduction lens system, and the image sensor and document are in close contact with each other.
Therefore, the device can be significantly downsized.

The photoelectric conversion section of the contact image sensor has a structure in which optical sensor elements each having a small light-receiving area are arranged in a line with at least the same width as the original. For example, in order to read an A4 size document at a density of 8 lines/mm, 1728 optical sensor elements must be arranged in a length of about 21 cm. For this purpose, hydrogenated amorphous silicon, which can form a uniform thin film over a large area, has high sensitivity to visible light, and can be formed at a relatively low temperature so that inexpensive glass substrates can be used, is used for contact image sensors. It is used as a photoelectric conversion material. Since a hydrogenated amorphous silicon film is a high-resistance, high-quality semiconductor thin film, a photodiode with extremely low leakage current can be formed by forming a sandwich structure with a blocking electrode (for example, S, Kaneko et al. al, IEDM, 328
(1982)), by using this photodiode as the above-mentioned optical sensor element, a contact type image sensor capable of high-speed reading can be realized.

By the way, in order to commercialize this image sensor,
Defect-free is an absolute requirement. If even one bit out of thousands of bits is defective, 1. The value of the image sensor will be lost.Therefore, defect inspection during the manufacturing process is important from the viewpoint of manufacturing cost.
Since the cost of the entire unit is large, it is necessary to inspect the sensor board for defects before mounting the drive IC on all products. Therefore, in order to inspect a large number of sensor substrates, it is important to establish a defect inspection method that can be evaluated in a short time and to develop a defect inspection apparatus.

One of the causes of defects in sensor substrates is disconnection of electrode wiring and short circuit between wirings. There are two types of wiring on the sensor substrate: common electrodes and individual electrodes. Generally, the common electrode has a large area, and defects such as disconnection hardly occur. However, the wiring width of individual electrodes becomes narrower as the reading density of the sensor becomes higher. For example, in the case of a reading density of 8 lines/mm, the wiring width is 50 μm, and at 16 lines/mm, it becomes 25 μm. With such thin wires, there is a possibility that wire breakage or short circuits may occur due to dust or poor etching during the photolithography process.

The conventional method for inspecting wiring defects has been visual inspection using a microscope. This visual inspection requires careful inspection of each individual electrode one by one and is very time consuming. Moreover, it was an incomplete inspection method as it sometimes overlooked defects.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to eliminate such drawbacks and provide a method and apparatus for inspecting individual electrode patterns for defects in a short time.

[Structure of the invention]

A defect inspection method for a contact image sensor according to the present invention includes: a photodiode of a contact image sensor in which a plurality of photodiodes are arranged in a line on the same substrate; a driving IC formed on a surface of the substrate of the contact image sensor; The present invention is characterized in that defects in the individual electrode patterns connecting the connection pads are detected by a bright signal when the photodiode is irradiated with light.

The contact type image sensor defect inspection device of the present invention is capable of fixing a contact type image sensor in which a plurality of photodiodes are arranged in a line on the same substrate, and the contact type image sensor has a contact type image sensor having a width at least equal to or larger than the reading width of the contact type image sensor in the arrangement direction of the photodiodes. Is there any contact between the movable stage with a stroke and the driving IC formed on the substrate surface of the contact type image sensor? a probe card provided with a light source that irradiates the photodiode G through a plurality of rising probes and holes; a switching circuit that is attached to a supporting part that supports the probe card and sequentially scans the photodiode; a drive circuit having a detection circuit that detects a bright signal when the photodiode G is irradiated with light, and a probe of the probe card is brought into contact with the connection pad corresponding to one block of the photodiode, The present invention is characterized in that the bright signal is measured and the movable stage is moved to sequentially perform the measurement for each block of the photodiodes, thereby inspecting the individual electrodes of the contact type image sensor for defects.

[Effect]

The individual electrode wiring on the sensor board can be thought of as having the function of extracting the current flowing through the photodiode to a connection node with an external circuit. Therefore, the most reliable way to determine whether there is a defect in the individual electrode wiring is to determine whether the current flowing through the photodiode can be measured using the connection pad.

The current flowing through the photodiode includes a leakage current of the photodiode and a photocurrent generated by light irradiation. It is better to use photocurrent as a signal source for wiring inspection. This is because the photocurrent is three to four orders of magnitude larger than the leakage current, and the current value becomes a constant value by setting the intensity of the irradiated light to a constant value. On the other hand, the leakage current is very small and difficult to distinguish from a disconnection, and its magnitude varies depending on the characteristics of the photodiode, making it unsuitable as a signal source for defect inspection.

As a method for detecting photocurrent, there is a dynamic characteristic evaluation method in which a photodiode is driven in a charge accumulation mode and a bright signal is measured in defect inspection of the photodiode itself. The principle of the dynamic characteristic evaluation method will be explained using the drive circuit diagram shown in FIG. Third
In the figure, one electrode of the photodiode 23 is connected to a common electrode 24. The other electrode is individual electrode 2
5, and the individual electrodes are connected to pads 27 for connection with the driving IC 26. The connection node is connected to the output terminal 29 via the MOS FET switch 28 of the drive IC 26. Furthermore, the output terminal 29
is connected to a detection circuit (not shown). M.O.S.
The FET switches 28 are sequentially turned on by a shift register 30 within the driving IC 26. MOS at a certain time
When the FET switch 28 is turned off and the charge storage time begins, the photodiode 23 is discharged due to the sum of the photocurrent and the leakage current of the photodiode. For a certain period of time (
A bright signal is obtained by detecting the voltage drop across the photodiode 23 when the MOS FET switch 28 is turned on again after the charge accumulation time, or by detecting the recharging current flowing through the photodiode 23 after the switch is turned on.

Therefore, the measurement of the dynamic characteristics of the photodiode is completed in the charge accumulation time. Since the normal storage time is around 5ms,
Dynamic characterization method is a very fast defect inspection method.

The defect inspection method for individual electrode patterns of the present invention is intended to inspect defects in individual electrode patterns by detecting bright signals obtained in the above-described dynamic characteristic evaluation method. The output when there is a defect in the turn of the individual electrode will be explained with reference to FIG. Here, it is assumed that the bright signal is detected by a charge reading method that integrates the recharge current. A normal signal output waveform with no defects is similar to (A). If there is a disconnection at one point, the photodiode cannot be charged, and only the signal corresponding to the output of that bit becomes 0, as shown in (B).

In addition, if individual bridges are short-circuited, if the short-circuited bits are read first, the output of the node will flow with a charge force that recharges the two photodiodes, so the output signal will be doubled. The next bit to be read out has already been charged, so the output signal becomes O. Therefore,
When a defect inspection method using a bright signal is used, it is possible to distinguish and detect a wire break and a short circuit between wires based on the output signal.

〔Example〕

FIG. 1 is a diagram for explaining an embodiment of a defect inspection method for a contact type image sensor according to the present invention.

In FIG. 1, ``■'' is a contact type image sensor to be inspected, that is, a sensor substrate, and a plurality of photodiodes 2 are arranged in a line on the same substrate. The cathodes of these photodiodes are connected to a common electrode 3,
The anode is connected to individual electrodes 4. These individual electrodes are each connected to a pad 5 for connection to an external circuit.

There are usually several thousand photodiodes 2 in one device,
They are arranged in a line over a length of 20 cm or more, and therefore there are several thousand individual electrodes 4, and it is not practical to test such a large number of individual electrodes together in terms of the testing equipment. Therefore, in this embodiment, the photodiode array is divided into blocks of several tens to hundreds of photodiodes, and measurements are made for each block.

In FIG. 1, 6 is a drive circuit, which includes a shift register 7 and MOSs that are sequentially turned on by this shift register.
It includes an FET switch 8 and a detection circuit 9.

The detection circuit 9 is a circuit that detects the integral value of the recharging current flowing through the photodiode 2 of the sensor board 1. The drive circuit 6 is connected to the connection pad 5 to which the individual electrode 4 of the sensor substrate 1 to be inspected is connected, for example, via a probe lO.

To inspect the individual electrode patterns of the sensor substrate 1 for defects, with the photodiodes 2 of the sensor substrate 1 irradiated with light, a probe 10 is attached to the connection pads associated with one block of photodiodes as shown in FIG. contact. Then, by the shift register 7 of the drive circuit 6, the MOS FE
Turn on the T switches 8 one after another. MOS F at a certain time
When the ET switch 8 is turned off and the charge accumulation time begins, the photodiode 2 is discharged due to the sum of the photocurrent and the leakage current of the photodiode. A bright signal is obtained by detecting the recharging current flowing into the photodiode 2 by the detection circuit 9 after the MOS FET switch 8 is turned on again after a certain period of time (charge accumulation time).

As described above, defects in the individual electrode patterns associated with the blocks of the sensor substrate 1 can be inspected using this bright signal. By sequentially performing the above inspection on the individual electrode patterns of each block, all the individual electrode patterns of the sensor substrate 1 can be inspected.

In this embodiment, the detection circuit 9 adopts a charge reading method that detects the integral value of the recharging current flowing through the photodiode, but it may also be a voltage reading method that detects the voltage drop in the photodiode due to discharge. good.

Next, a defect inspection apparatus using the contact image sensor defect inspection method of the present invention will be described in detail. FIG. 2 is a perspective view showing an embodiment of the defect inspection device. This defect inspection device is equipped with a movable stage 11 on which a sensor substrate 1 to be inspected can be fixed, and this movable stage 11 is fixed on a drive base 12 that moves this movable stage in a uniaxial direction. This drive stand is fixed on a drive stand 13 that moves the drive stand 12 in a direction perpendicular to the -axis direction. These drive bases 12.13
The movable stage 11 can be moved in two orthogonal directions. A probe card support part 14 is fixed to a stationary part of the drive base 13 so as to project above the movable stage 11.

A probe card 15 is attached to the probe card support section 14, and the distance between this probe card and the sensor substrate 1 fixed on the movable stage 11 is maintained at about 2 mm. A plurality of probes 16 that can come into contact with connection pads on the sensor substrate 1 are provided on the surface of the movable stage 11 of the probe card 15 . These probes are arranged so as to match the arrangement direction of the connection pads, and the adjustment holes 1 provided in the probe card 15
It is located near 7.

Further, in the probe card support section 14 near the probe card 15, a drive circuit 1 including a shift register, a switching FBT, and a detection circuit described in FIG.
8 is fixed. The detection circuit may be of a voltage reading type that detects the voltage drop across the photodiode due to discharge, or of a charge reading type that detects the integral value of the recharging current flowing through the photodiode. Using this detection circuit, as will be described later, in order to test one block of several dozen photodiodes at a time, switching FETs are sequentially turned on by a shift register to obtain a scanner function. The drive circuit 18 connects the probe 16 with the wiring 19.
It is connected to the. By shortening the wiring 19 in this manner, the wiring capacitance can be reduced and resistance to noise can be increased.

Further, there is an advantage that the number of wires connected to the data processing system outside the shield box, which will be described later, is reduced.

A hole 20 is provided in the probe card 15, and a light source 21 is attached to the probe card 15 so as to be located above the hole. This light source 21 is for irradiating the photodiodes of the sensor board 1 with light, and as mentioned above, since the distance between the probe card 15 and the sensor board 1 is approximately 2 mmL, it is not possible to provide a light source between them. It is arranged on the probe card 15.

Light from the light source 21 passes through the hole 20 and is irradiated onto the photodiode of the sensor substrate 1 . Note that since the hydrogenated amorphous silicon diode, which is a photodiode, has high sensitivity over the entire visible light range, there is no particular restriction on the wavelength, and therefore, an LED, a fluorescent lamp, or the like can be used as the light source 21.

All the components described above are housed in the shield box 22 to prevent external noise from affecting the inspection.

In general, one device usually includes several thousand photodiodes, and they are arranged in a line over a distance of 20 cm or more. In this way, the contact image sensor is a long device,
Basically, it is sufficient to set up as many probes as there are photodiodes and connect them to the detection circuit, but this is not practical due to problems such as the wiring density and accuracy of the probe card and the large number of lead lines from the probe card. Therefore, the photodiode array is divided into blocks of several tens to hundreds of photodiodes, and measurements are taken for each block. In order to measure from one end of the sensor board 1 to the other, it is necessary to move the sensor board 1 at least by the length of the photodiode array. The stroke must be the width of the sensor's reading.

In order to inspect the individual electrode patterns of the sensor substrate 1 for defects using the apparatus of this embodiment, the movable stage 11 is moved by the drive stands 12 and 13 and positioned at one end of the sensor substrate 1 relative to the probe card 15. At this time, the probe 16 of the probe card 15 is brought into contact with the connection pad corresponding to one block of photodiodes. One block of individual electrode patterns is inspected for defects as explained in FIG. When the measurement of one block is completed, the probe card 15 is separated from the sensor board 1, the stage 11 is moved, and the probe 16 is brought into contact with the connecting band of the next block again at the next measurement position to perform an inspection. By repeating such measurements, the contact image sensor can be inspected for defects in a short time.

For example, if a 550 nm LED is used as the light source, the illuminance on the sensor surface is 300 lux, and the detection method is a charge reading method that obtains the output by integrating the recharge current, the output waveform will be When you observe
A bright signal of about 1■ was obtained.

When the broken bit was measured, an output of 30 mV, which was thought to be the switching noise of the MOS FET, was obtained. Therefore, wiring defects such as disconnections could be easily detected using the bright signal.

Next, the time required to measure one sensor board using this inspection device will be described. The number of sensor elements is A
In the case of 4 sizes and 8 lines/llll11, there are 1728 elements, and if the drive circuit used in the experiment has a 64-bit shift register, 64 bits can be measured in one measurement. Therefore, to measure all bits, it is sufficient to repeat the measurement 27 times. Including the time required to move the probe, one measurement (64 bits) was completed within 10 seconds, and one sensor board (1728 bits) could be inspected in about 5 minutes. This time is a sufficiently practical value.

〔Effect of the invention〕

As explained above, according to the present invention, defects in individual electrode wiring can be detected by irradiating the sensor with light and measuring bright signals of dynamic characteristics, and the time required to measure one board is short. (This makes it possible to realize a practical high-speed inspection method and device for contact type image sensors.

[Brief explanation of drawings]

FIG. 1 is a diagram for explaining an embodiment of a defect inspection method for a contact type image sensor according to the present invention, and FIG. 2 is a perspective view of an embodiment of a defect inspection apparatus for a contact type image sensor according to the present invention. Figure 3 is a diagram for explaining the dynamic evaluation method for measuring bright signals, and Figure 4 is a waveform diagram of bright signals in normal and defective cases. l...Sensor board 2...Photodiode 3...Common electrode 4...Individual electrode 5...Connection pad 6.18...・Drive circuit 7...Shift register 8...MOS FET 9...Detection circuit 10.16...Probe 11...Movable stage 12.13... Drive base 14...Probe card support section 15...Probe card 19...Wiring 20...Light source hole 21...Light source

Claims (2)

[Claims] (1) The photodiode of a contact type image sensor in which a plurality of photodiodes are arranged in a row on the same substrate, and the driving I formed on the substrate surface of the contact type image sensor.
A defect inspection method for a contact type image sensor, characterized in that a defect in an individual electrode pattern connecting a contact pad with a contact pad is detected by a bright signal when the photodiode is irradiated with light. (2) a movable stage capable of fixing a contact type image sensor in which a plurality of photodiodes are arranged in a row on the same substrate, and having a stroke in the arrangement direction of the photodiodes that is at least larger than the reading width of the contact type image sensor; A probe card that is provided with a light source that irradiates light to the photodiode through a plurality of probes and holes that can contact pads for connection with a driving IC formed on the surface of a substrate of an image sensor; and a probe card that supports this probe card. a drive circuit that is attached to a support and has a switching circuit that sequentially scans the photodiodes and a detection circuit that detects a bright signal when the photodiodes are irradiated with light; The probe of the probe card is brought into contact with the pad to measure the bright signal, and the movable stage is moved to sequentially perform the measurement for each block of the photodiode, whereby the individual electrodes of the contact image sensor are measured. A defect inspection device for a contact image sensor, which is characterized by inspecting pattern defects.