JP3114410B2 - Image sensor test method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for testing variations in light detection sensitivities of a plurality of optical sensors in order to check the image detection accuracy of an image sensor.

[0002]

2. Description of the Related Art In an image sensor as a CCD device or a photodiode array, a large number of optical sensors can be integrated in a small chip by using an integrated circuit technology. There is an increasing demand for heightening. For example, in an image sensor for an autofocus camera, high precision that can convert the light intensity received by each optical sensor into digital data of 4 bits or more is required. In order to satisfy such requirements, the light detection characteristics of the optical sensors in the image sensor must be uniform in accordance with the required level of image detection accuracy. A test needs to be performed, and a sufficiently uniform light flux needs to be incident on the image sensor for this test.

FIG. 2 shows an example of a conventional method suitable for applying the uniform test light beam to an image sensor. As shown in the drawing, the test light Lt is generated by, for example, a pair of light sources 30, reflected by a diffusion plate 60, converted into a diffusive light flux, and then incident on the image sensor 10. As the light source 30, an incandescent lamp 31 such as a halogen bulb emitting light with a wide wavelength distribution suitable for a test is used, and is combined with the reflector 32 so as to spread the luminous flux given to the diffuser 60 as much as possible. As the diffusion plate 60, a matte white paint is used. In this conventional method, the distance between the light source 30 and the diffusion plate 60, and the distance between the diffusion plate 60 and the image sensor 10 are made as large as possible, and the diffusion or scattering of the diffusion plate 60 with respect to light is increased, so that a substantially uniform light suitable for testing is obtained. A diffusive luminous flux of the test light Lt having an appropriate intensity distribution can be given to the image sensor 10.

In the conventional example shown in FIG. 3, a diffusion box 50 is used instead of the diffusion plate 60 shown in FIG. The light source 30 includes an incandescent lamp 31 and a reflector 32 in a case 33, and the diffusion box 50 is a case.
A diffusion coating 52 is provided on the inner surface of 51, and an entrance window 53 for receiving a light beam from the light source 30 and a window 54 for emitting the light beam of the test light Lt are provided on the image sensor 10, and a light diffusing milky white glass or the like is further provided on the emission window 54. A certain window material 55 is attached. In this conventional method, the test light Lt from the light source 30 is repeatedly reflected on the inner surface of the diffusion box 60 to form a diffusive light flux, and the diffusivity is further enhanced by the window material 55 to test the uniform light intensity distribution on the image sensor 10. Light Lt can be given. A measuring device is connected to the image sensor 10 receiving the test light Lt according to the conventional method shown in FIGS. 2 and 3, and a variation in detection sensitivity is tested by measuring a light detection signal value of each light sensor.

[0005]

However, recently, the demand for improving the image detection accuracy of the image sensor has been increasing more and more, and accordingly, the light intensity received by each optical sensor of the image sensor is, for example, 8-bit accuracy. In order to improve the sensitivity of the optical sensor, it is necessary to suppress the variation in the detection sensitivity of the optical sensor to 0.4% or less. It is necessary to equalize the error within a smaller error range of, for example, 0.1% or less. However, the conventional method described with reference to FIGS. 2 and 3 has a problem that it is very difficult to make the test light uniform within an error range of 1% or less.

That is, in the conventional method shown in FIG. 2, it is difficult to obtain a good light diffusing property of the diffusion plate 60, and the intensity distribution of the test light Lt received by the image sensor 10 is easily changed depending on the position where the light source 30 is placed. Even if the positions of the light sources 30 are variously changed using the pair of light sources 30, it is difficult to make the intensity distribution uniform. Further, if the diffusion plate 60 is separated from the image sensor 10 and the light source 30 by 3 to several meters, the problem is considerably reduced, but the use efficiency of the test light Lt is remarkably reduced and the test under high light intensity becomes difficult. In addition, the test equipment including the light projecting system becomes very large. Also, the conventional method shown in FIG.
It is difficult to enhance the performance of converting Lt into a diffusive light flux, and when the incandescent lamp 31 is used as the light source 30 as described above, when the image sensor 10 is tested at a low light intensity contrary to FIG. There is a problem that the uniformity of the test light Lt is particularly likely to decrease.

Under these circumstances, an object of the present invention is to provide a light intensity distribution of a test light so that even when the image detection accuracy of an image sensor is enhanced, the variation in the light detection sensitivity of the optical sensor can be tested with a correspondingly high accuracy. Is to equalize.

[0008]

SUMMARY OF THE INVENTION In the present invention, an object of the present invention is to test a variation in light detection sensitivity of a plurality of optical sensors of an image sensor, and arrange test light generated by a light source into small lenses in a plane. To the collective lens body
The light beam of the test light is supplied from the collective lens body to the light diffusion box through the entrance window, and the test light emitted from the light diffusion exit window is projected on the image sensor to test the light detection sensitivity of each optical sensor. Achieved by

It is advantageous to give the test light generated by the light source to the collective lens body via the optical fiber in order to reduce the size of the light projecting device, and to further reduce the test light from the optical fiber. Applying the light to the collective lens via the light guide is advantageous in improving the uniformity of the light intensity distribution of the test light to be applied to the image sensor. In order to improve the uniformity, it is advantageous to make the position of the focal point of the small lens of the lens assembly substantially coincide with the entrance window of the light diffusion box. It is preferable to attach a light-diffusing window material such as milky white glass to the light-diffusing exit window of the diffusion box as in the related art. When the test light given to the image sensor has a wavelength distribution in a desired range, it is most reasonable to attach a wavelength-selective filter to the entrance window of the diffusion box.

[0010]

The use of a diffusion box in the method of the present invention is similar to that of the prior art shown in FIG. 3, but the test light is transmitted through a collective lens body in which the small lenses described in the preceding paragraph are arranged in a plane at the entrance window. To solve the problem. This collective lens unit divides the test light beam received by it into small lenses and focuses them on the focal point or focal plane. Therefore, it plays a role of dispersing the luminous flux of the test light almost uniformly within the area of the entrance window of the diffusion box. Therefore, in the method of the present invention, the test light is given in the area of the entrance window of the diffusion box with a more uniform distribution than before, and the test light is diffused from the light diffusion exit window while sufficiently exhibiting the ability to diffuse the light to the diffusion box. Can be taken out and projected on the image sensor with a more uniform light intensity distribution than by the conventional method.

[0011]

An embodiment of the present invention will be described below with reference to FIG. The image sensor 10 to be tested shown in the lower left part of the figure is a semiconductor chip 11 in which a plurality of photosensors, for example, photodiodes, are mounted on a lead frame 12 and housed in a transparent package 13, At the time of the test, the lead 14 is inserted into the wiring board 15 and mounted as shown in the figure, and then connected to the measuring device 20 via the connector 16 and the connection wire 47. Light source for test light Lt shown in lower right of figure
Reference numeral 30 denotes a case in which a daylight-colored incandescent lamp 31 such as a halogen bulb and a reflector 32 are accommodated in a case 33, similarly to the conventional example of FIG.

In principle, the test light Lt emitted from the light source 30 may be directly applied to the collective lens body 40 shown in the center of the figure. However, in the illustrated embodiment, the test light Lt is transmitted through the optical fiber 34 and the optical conductor 42. The test light Lt is transmitted to the condenser lens body 40. Optical fiber
Numeral 34 denotes a normal type in which a number of glass fibers are bundled and covered with a sheath 35, and one end of the light source 30 attached to the case 33 by the connector 36 receives the test light Lt. Collective lens body 40
For example, a number of small hemispherical projections are distributed in the lower surface of the figure of a circular glass block to form small lenses.
A case 41 is housed in a case 43 together with a light guide 42 which is, for example, a rod-shaped optical glass. The case 43 is fixed with a lock nut 44 after screwing the lower end thereof into the case 51 of the light diffusion box 50 while adjusting the mounting position, and the other end of the optical fiber 34 is connected to the upper end thereof via a connector 37. It is attached.

The diffusion box 50 may be the same as that used in the conventional method shown in FIG. 3. The case 51 is provided with a white, preferably uneven, diffusible coating 52 on the inner surface thereof to receive the test light Lt received from the entrance window 53. It is good to take out the test light Lt through the window material 55 such as diffusible milky white glass attached to the exit window 54 while confining while reflecting on the inner surface, but in this embodiment, the test light Lt is suitable for testing the image sensor 10 with the test light Lt. Provided with wavelength selectivity to provide a wavelength distribution, for example, so-called N
An optical filter 56, which is a D filter, is attached to the entrance window 53, through which the test light Lt is taken. It is preferable that the optical filter 56 be different in light transmittance so that the image filter 10 can be tested by switching the intensity level of the test light Lt.

In the light projecting apparatus of this embodiment configured as described above, the test light Lt from the light source 30 passes through the optical fiber 34 and has a rod-shaped light guide in the form of a light beam having a certain divergence angle.
Enter 40. The light guide 40 transmits the obliquely traveling component in the light beam of the test light Lt while totally reflecting it on its peripheral surface, and gives the light beam having a uniform light intensity distribution to the collective lens body 40. The collective lens body 40 converges this light beam on the focal points or focal planes distributed according to the arrangement for each of the small lenses 41 so that the test light Lt is uniformly dispersed within the light beam area, and then the diffusion box 50
Give to. The diffusion box 50 is connected to the optical filter 56 of the entrance window 53.
The test light Lt converted into a wavelength distribution suitable for the test is confined inside while being reflected by the inner coating 52 and emitted from the emission window 54 as a diffusive light flux Ld. After being further strengthened by the translucent window material 55, the light is projected onto the image sensor 10 as a light beam of the test light Lt.

As described above, according to the present invention, the luminous flux of the test light Lt generated by the light source 30 is converted into a luminous flux having a uniform light intensity distribution by the collective lens body 40 in which the small lenses 41 are arranged in a compound eye of a dragonfly. Since the light is applied to the diffusion box 50, the light intensity distribution of the diffusible light flux of the test light Lt applied to the image sensor 10 can be made more uniform than before. According to the experimental results of the embodiment of FIG. 1, the brightness converted to the brightness of the test light Lt given to the image sensor 10 is a so-called luminescence value LV of 6, or 4.5 Cd /
In the case of cm ² , the variation in the light intensity received by a large number of optical sensors is within 4 × 10 ⁻³ Cd / cm ² . This is the same as the conventional method.
%, It can be understood that the uniformity of the test light Lt is improved by about one digit according to the present invention.

In this experimental result, when the collective lens body 40 is adjusted so that the focal point of the small lens 41 coincides with the position of the entrance window 53 of the diffusion box 50, in the example of FIG. The test light Lt has the best uniformity. When testing the image sensor 10 receiving the test light Lt from the light emitting device adjusted in this way, the maximum value, the minimum value, and the average value of the light detection signal values of the respective light sensors are measured by the measuring device 20 of FIG. This makes it possible to determine the quality of the image sensor 10 by measuring the variation in the photodetection sensitivity of the plurality of optical sensors. Further, the image sensor 10 can be tested by switching the intensity level of the test light Lt by replacing the optical filter 56.

[0017]

As described above, according to the method of the present invention, when testing the variation in the photodetection sensitivity of a plurality of photosensors of an image sensor, the luminous flux of the test light generated from the light source is applied to a small lens in a plane. After being given to the arrayed lens elements and converted to a light beam with a uniform light intensity distribution, it is given to the light diffusion box from its entrance window, and the test light taken out from the light diffusion exit window of this light diffusion box is sent to the image sensor. By projecting light and testing the photodetection sensitivity of the photosensor, the variation in the intensity distribution of the test light received by the photosensor of the image sensor is reduced from about 1% to 0.1% of the conventional level, and the photodetection sensitivity of the photosensor is reduced. Can be tested more accurately than before. The method of the present invention is suitable for testing a high-precision image sensor capable of converting the light intensity received by the optical sensor into digital data with an accuracy of 4 bits or more, and particularly for an accurate and practical image sensor having an image detection accuracy of about 8 bits. It is the first time that testing is possible.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view including an image sensor and a light projecting device showing an embodiment of a method for testing an image sensor according to the present invention.

FIG. 2 is an arrangement diagram of an image sensor, a light source, and a diffusion plate, showing an example of a conventional image sensor test method.

FIG. 3 is a sectional view of a light source and a diffusion box showing another example of a conventional test method.

[Explanation of symbols]

 10 Image sensor 20 Measuring device 30 Light source 34 Optical fiber for transmitting test light 40 Collective lens body 41 Small lens 42 Light guide 50 Light diffusion box 53 Light diffusion box entrance window 54 Light diffusion box exit window 55 Exit window window material 56 Optical filter Ld Diffusive light beam Lt Test light or its light beam

Continuation of front page (56) References JP-A-2-90645 (JP, A) JP-A-6-34487 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H01L 21 / 66 H01L 27/14 G01M 11/00

Claims (3)

(57) [Claims] 1. A method for testing a variation in photodetection sensitivity of a plurality of optical sensors of an image sensor, wherein test light generated by a light source is provided to a collective lens body in which small lenses are arranged in a plane. The luminous flux of the test light from the body is given to the light diffusion box from the entrance window, and the test light extracted from the light diffusion exit window is projected on the image sensor to test the light detection sensitivity of the optical sensor. A method for testing an image sensor, comprising: 2. The method according to claim 1, wherein the test light generated by the light source is supplied to the collective lens body via an optical fiber. 3. The method according to claim 1, wherein the focus of each small lens of the lens assembly is made to substantially coincide with the entrance window of the light diffusion box.