JPH07114271B2 - Infrared solid-state imaging device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an infrared solid-state imaging device, and in particular, it has an infrared detector arranged one-dimensionally or two-dimensionally on a main surface of a semiconductor substrate. The present invention relates to an infrared solid-state imaging device.

[Prior Art] An infrared solid-state imaging device in which an infrared detection device array and a signal reading device such as a charge transfer device are integrated on the same semiconductor substrate has been vigorously developed. In particular, in an infrared solid-state imaging device having a silicon Schottky junction as an infrared detection unit, an infrared solid-state imaging device having a number of pixels that can be practically used is being developed.

FIG. 4 is a diagram showing an example of an optical system of a conventional infrared solid-state imaging device.

In the figure, 1 is an infrared lens, 2 is a cold shield for blocking excess light of infrared light that has passed through the infrared lens 1, and for preventing excess heat from flowing in, 3
Is an infrared solid-state imaging device for forming an image of infrared light that has passed through the infrared lens 1. As will be described later, the infrared solid-state imaging device 3 is composed of a semiconductor substrate, and has three types of infrared detectors 4a, 4b, 4c formed on its main surface. The infrared solid-state imaging device 3 is generally cooled to a low temperature before use. The cold shield 2 is also cooled to a low temperature to prevent heat from flowing into the infrared solid-state imaging device 3 and excessive infrared light from entering.

[Problems to be Solved by the Invention] Now, the openings of the cold shield 2 are the infrared detectors 4a, 4b,
It is desirable that the size is the minimum size that does not obstruct the viewing angle (5a, 5b, 5c) required for detection by 4c. On the other hand, the distance between the cold shield 2 and the infrared solid-state imaging device 3 cannot be set very large due to the restriction of the cooling capacity. Therefore, there is a non-negligible difference in the angle of view of the opening of the cold shield 2 between the infrared detector 4b at the center and the infrared detectors 4a and 4c at the ends of the infrared solid-state imaging device 3. In addition, since the amount of incident light from the infrared lens 1 and the intensity of radiated light from parts other than the infrared lens 1 are different, the output of the infrared detector 4b at the center is different from that of the other infrared detectors 4a. , 4c is larger than. As a result, infrared detectors 4a, 4
There was a problem that the outputs of b and 4c were not uniform. Note that, in FIG. 2, an infrared filter arranged between the cold shield 2 and the infrared solid-state imaging device 3 is omitted in order to prevent the drawing from becoming complicated.

Next, the problem will be described in more detail using an enlarged view of the infrared solid-state imaging device 3.

FIG. 5 is an enlarged view of the infrared solid-state imaging device 3 shown in FIG. The infrared solid-state imaging device 3 is composed of a semiconductor substrate such as a silicon semiconductor substrate 7. On the main surface of the silicon semiconductor substrate 7, three-dimensionally arranged 3
Infrared detectors 4a, 4b, 4c of various types are formed in an array. Three types of infrared filters 6a, 6b, 6c are arranged on the back surface side of the semiconductor substrate 7 so that the infrared detectors 4a, 4b, 4c have different spectral sensitivities. Since the semiconductor substrate 7 made of silicon or the like is transparent to infrared light, as shown in the figure, infrared light is generally incident from the back surface direction of the semiconductor substrate 7. The infrared light incident on the infrared detectors 4a, 4b, 4c must always pass through the infrared filters 6a, 6b, 6c, so the viewing angles of the infrared detectors 4a, 4b, 4c are 5a, 5a, respectively. Five
It is desirable that the angle is less than or equal to the corners indicated by b and 5c. But,
As long as the configuration as shown in FIG. 4 is taken, it is difficult to realize it, and the above-mentioned problem of uneven output is brought about. Further, in the configuration shown in FIG. 5, the infrared filters 6a, 6b,
Stray light 8 due to irregular reflection at the end face of 6c is detected by infrared detectors 4a, 4b,
It is not possible to prevent it from entering 4c. Note that this stray light may be generated even if an infrared filter is not used, if there is an object that causes some kind of reflection action between the cold shield 2 and the infrared solid-state imaging device 3.

The present invention has been made to solve the above problems, and it is possible to limit the field of view of the infrared detector to the necessary minimum, and to eliminate the effects of uneven output and stray light. , An infrared solid-state imaging device is provided.

[Means for Solving the Problems] The present invention includes an infrared detector arranged on a main surface of a semiconductor substrate in a one-dimensional or two-dimensional manner, and infrared light incident from the back surface side of the semiconductor substrate. The present invention relates to a solid-state imaging device. Then, in a semiconductor substrate around the infrared detector that does not include at least the infrared detector, infrared light is placed at a position where the viewing angle of the infrared detector can be limited to a viewing angle determined by an optical system or less. A feature is that a diffusion layer having a high impurity concentration for absorption is provided.

[Operation] Since a diffusion layer having a high impurity concentration is provided in the semiconductor substrate around the infrared detector, and the infrared light absorption function of the diffusion layer makes it possible to limit the viewing angle of the infrared detector. The unevenness of the amount of incident light between the infrared detectors is eliminated. Further, it is possible to prevent unnecessary light such as stray light from entering the infrared detector.

[Embodiment] An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a sectional view of an embodiment of the present invention. Note that this figure is the same as FIG. 5 in that it is an enlarged view of a part of the optical system of the infrared solid-state imaging device shown in FIG. Therefore, although a cold shield and the like are not shown, they are present. Three types of infrared detectors 4a, 4b, 4c are formed in a one-dimensional array on the main surface of a semiconductor substrate, for example, a silicon semiconductor substrate 7. Three types of infrared filters 6a, 6b, 6c are attached to the back surface of the semiconductor substrate 7 so that the infrared detectors 4a, 4b, 4c have different spectral sensitivities. The infrared light from the optical system passes through the infrared filters 6a, 6b, 6c and forms an image on the infrared detectors 4a, 4b, 4c.

The point different from the conventional infrared solid-state imaging device shown in FIG. 5 is the front surface side of the semiconductor substrate 7, and the infrared detectors 4a, 4b,
The diffusion layer 9 having a high impurity concentration is formed in the peripheral portion of 4c. The diffusing layer 9 exhibits an infrared light absorbing action and works to limit the viewing angle of the infrared detectors 4a, 4b, 4c. This impurity may be n-type P, As, Sb or p-type B, Al, Ga. These impurity layers can be formed by, for example, diffusion or ion implantation.

Next, the function of the diffusion layer 9 having a high impurity concentration will be described.

Since such a diffusion layer has an infrared light absorbing function, infrared light incident on the impurity diffusion layer 9 is absorbed and cannot be transmitted. Therefore, the viewing angles of the infrared detectors 4a, 4b, and 4c are limited to the angles indicated by 5a, 5b, and 5c, respectively, and the three types of infrared detectors 4a, 4b, and 4c each have a surface 6a ′ of the infrared filter. , 6b ′, 6
Only c'is seen, and the infrared light 8 scattered by the end face of the infrared filter is absorbed by the impurity diffusion layer 9 and does not enter the infrared detectors 4a, 4b, 4c.

Also, the impurity diffusion layer 9 eliminates the difference in the amount of incident light due to the difference in optical position between the infrared detector 4b on the central axis of the optical system and the infrared detectors 4a and 4c deviating from the infrared detector 4b. Will be able to. These effects cannot be achieved by the conventional infrared solid-state imaging device using only the cold shield.

In addition, in the above-mentioned embodiment, the case where the impurity diffusion layer is provided on the surface side of the semiconductor substrate on which the infrared detector is formed has been described, but the present invention is not limited to this.

FIG. 2 shows another embodiment of the present invention and is shown in a sectional view. An impurity diffusion layer 9 is provided on the back surface side of the semiconductor substrate 7 on which the infrared detector 4 is formed. With such a configuration, the same effect as that of the above-described embodiment can be realized.

FIG. 3 shows another embodiment of the present invention.
It is represented in cross section. An impurity diffusion layer 9 is buried in a portion located between the front surface side and the back surface side of the semiconductor substrate 7. With such a configuration, the same effect as that of the above-described embodiment can be realized.

Further, it goes without saying that the same effect can be realized even if the impurity diffusion layers are formed by combining the aspects of the embodiments shown in FIGS. 1, 2, and 3.

In the above embodiment, the case where three types of one-dimensional infrared detector arrays are formed on the same semiconductor substrate has been described, but the semiconductor substrate 7 is thinner and the infrared detector pixel pitch is larger than that of the optical system. In this case, the same effect as that of the embodiment is achieved even with a two-dimensional infrared detector array.

In addition, although the infrared solid-state imaging device provided with the infrared filter has been described in the above embodiment, the present invention is not limited to this, and even when the infrared filter is not provided, the same effect as that of the embodiment can be obtained. To be realized.

Furthermore, although the semiconductor substrate is used as the semiconductor substrate in the above embodiments, the present invention is not limited to this.
Other types may be used.

[Effects of the Invention] As described above, according to the present invention, a diffusion layer having a high impurity concentration is provided in a semiconductor substrate around an infrared detector, and the infrared absorption function of the diffusion layer causes the infrared rays to be absorbed. Since the detector's viewing angle is limited, problems such as uneven output due to the difference in the optical position of the infrared detector and stray light from the infrared filter entering the infrared detector Can be eliminated. As a result, the optical performance of the infrared solid-state imaging device is improved.

[Brief description of drawings]

FIG. 1 is a sectional view of an infrared solid-state imaging device according to an embodiment of the present invention, FIG. 2 is a sectional view of an infrared solid-state imaging device according to another embodiment of the present invention, and FIG. 3 is still another embodiment of the present invention. 4 is a sectional view of an infrared solid-state imaging device according to the embodiment of the present invention, FIG. 4 is a diagram showing an example of an optical system of a conventional infrared solid-state imaging device, and FIG. 5 is an enlarged sectional view of a conventional infrared solid-state imaging device. . In the figure, 3 is an infrared solid-state imaging device, 4a, 4b, 4c are infrared detectors, 7 is a silicon semiconductor substrate, and 9 is a diffusion layer having a high impurity concentration. In each drawing, the same reference numerals indicate the same or corresponding parts.

Claims (2)

[Claims] 1. An infrared solid-state image pickup device, comprising an infrared detector arranged in a one-dimensional or two-dimensional array on a main surface of a semiconductor substrate, wherein infrared light is incident from a rear surface side of the semiconductor substrate. In the semiconductor substrate around the infrared detector that does not include a detector, at a position where the viewing angle of the infrared detector can be limited to a viewing angle determined by an optical system or less, a high impurity concentration of infrared light is absorbed. An infrared solid-state imaging device having a diffusion layer. 2. The high impurity concentration diffusion layer is obtained by diffusing or ion-implanting impurities from the front surface or the back surface of a semiconductor substrate on which the infrared detector is formed. The infrared solid-state imaging device according to item 1.