JP2659617B2 - Infrared solid-state imaging device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an infrared solid-state imaging device, and more particularly to an infrared solid-state imaging device having an infrared detector arranged one-dimensionally or two-dimensionally on a main surface of a semiconductor substrate. The present invention relates to an imaging device.

[Prior Art] In recent years, an infrared detector array including a plurality of infrared detectors (hereinafter, also referred to as infrared detectors) and a signal reading device such as a charge transfer device are integrated on the same semiconductor substrate.
The development of infrared solid-state imaging devices has been energetically advanced. In particular, an infrared solid-state imaging device using a silicon Schottky junction as an infrared detection unit is being developed with a number of pixels that can withstand practical use.

As a general infrared solid-state imaging device using this type of silicon Schottky junction for an infrared photodetector, here,
A so-called charge sweeping device (CSD: Charge Sweep Device) is used for a vertical charge transfer means in the solid-state imaging device.
A conventional example adopting the above will be described with reference to FIGS. 4, 5 and 6. FIG.

FIG. 4 shows the photodetector and CS in the infrared solid-state imaging device.
FIG. 5 is a layout diagram showing the layout of D and the like, and FIG.
It is a figure which shows the structure of a V line cross section typically. This CS
Regarding the infrared solid-state imaging device using the D method, for example, a publicly known document (“ISSCC: IEEE International Solid-State
Circuits Conference-Digest of Technical Paper 198
February 110, p. 110 "). FIG. 6 schematically shows the configuration of the output signal.

In the figure, 41 is a photodetector formed of a silicon Schottky junction, 42 is a vertical CSD for vertically transferring signal charges accumulated in the photodetector 41, and 43 is a horizontal direction for transferring signal charges transferred from the vertical CSD42. The horizontal CCD to be transferred is 44
An output unit for outputting the signal charges from the CD 43 to the outside as a video signal.

1 is a P-type silicon semiconductor substrate; 2 is a Schottky junction with the main surface of the substrate 1; and a photoelectric conversion layer composed of a metal electrode made of a metal such as gold-palladium or a metal silicide such as palladium silicide; Reference numeral 3 denotes n ⁻ for alleviating electric field concentration around the photoelectric conversion layer 2 and preventing dark current.
N ^- type guard ring composed of a mold region, 4 is a field insulating film made of a silicon oxide film for element isolation and insulation,
Reference numerals 5 and 6 denote an interlayer insulating film made of a silicon oxide film, and reference numeral 7 denotes an interlayer insulating film formed on the photoelectric conversion layer 2 via the interlayer insulating film 6 so as to reflect infrared light from the back side of the substrate 1 that has passed through the photoelectric conversion layer 2. This is an Al reflection film for re-entering the photoelectric conversion layer 2.

Reference numeral 60 denotes a video signal read from the output unit 44, reference numeral 61 denotes an optical signal component included in the video signal 60, and reference numeral 62 denotes a dark current component included in the video signal 60.

 Next, the operation will be described with reference to these figures.

The infrared light incident from the back surface of the P-type silicon semiconductor substrate 1 reaches the photoelectric conversion layer 2 of the Schottky junction, where it is photoelectrically converted to generate optical signal charges, and the optical signal charges are accumulated in the Schottky junction. . The accumulated optical signal charges are read out to the vertical CCDs 42, and then transferred in the vertical direction and sent to the horizontal CCDs 43. This optical signal charge is then transferred to the horizontal CCD.
The video signal is transferred in the horizontal direction by 43 and read out from the output unit 44 as a video signal. Thus, a video signal corresponding to the amount of infrared light incident on the photodetector 41 is obtained.

Here, the aluminum reflective film 7 is provided to reflect infrared light which has not been absorbed by the photoelectric conversion layer 2 and has passed through the layer 2 and makes the infrared light re-enter the photoelectric conversion layer 2. It works to improve the detection sensitivity. Further, the interlayer insulating film 6 is formed to have a predetermined thickness so that the reflected light from the aluminum reflecting film 7 can be efficiently incident on the photoelectric conversion layer 2. I have. In the photoelectric conversion layer 2 formed by the Schottky junction, a light component having energy equal to or higher than the barrier height of the Schottky barrier can be detected. For example, platinum silicide (PtSi)
And a P-type silicon can detect a light component having a wavelength of about 5 μm or less.

[Problems to be solved by the invention]

However, a video signal 60 obtained by a conventional infrared solid-state imaging device includes an optical signal component 61 due to incident infrared light and a dark current component 62 not due to incident infrared light. For example, when the absolute temperature of an object is measured using the infrared solid-state imaging device, the dark current component greatly affects the measurement, and a large error occurs in the measurement result.

If the infrared solid-state imaging device is not sufficiently cooled, the dark current component 62 included in the video signal 60 increases, the S / N ratio decreases, and the dark current component 6 decreases.
In order to make 2 smaller, the infrared solid-state imaging device must be sufficiently cooled.

Therefore, since it is impossible to directly monitor the dark current with the conventional infrared solid-state imaging device, the resistance value of the sheet resistance formed on the surface of the imaging device is monitored to control the temperature, and the dark current is reduced. However, accurate temperature measurement was difficult, and the S / N ratio was not preferable.

The present invention has been made to solve the above problems, and can directly detect the dark current of an infrared detector, thereby improving the S / N ratio and accurately measuring the temperature of an object. It is an object of the present invention to obtain an infrared solid-state imaging device capable of performing the above.

[Means for solving the problem]

An infrared solid-state imaging device according to the present invention is configured such that a high impurity concentration diffusion layer that absorbs incident infrared light is formed on a predetermined portion of a silicon semiconductor substrate on which a plurality of infrared detectors are mounted. Are optical black portions which are shielded from light by the diffusion layer.

[Action]

In the present invention, a diffusion layer having a high impurity concentration is provided in a silicon semiconductor substrate immediately below a photoelectric conversion layer of an infrared detector, and the infrared detector is shielded from light by an infrared absorption function of the diffusion layer. With this configuration, the output of the infrared detector of the optical black portion can be read as a dark current signal.

For this reason, an accurate optical signal component can be obtained by subtracting the dark current component from the video signal of the infrared detector other than the optical black part, thereby enabling accurate measurement of the temperature of the object and cooling. It is possible to solve the problem that the dark current increases at the time of shortage and the S / N ratio deteriorates.

Further, since the dark current can be directly measured, the temperature of the infrared solid-state imaging device can be easily controlled.

〔Example〕

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

FIG. 1 is a diagram showing an arrangement of each functional unit in an infrared solid-state imaging device according to one embodiment of the present invention, and FIG. 2 is a diagram II in FIG.
FIG. 3 is a diagram showing a cross-sectional structure taken along the line II, and FIG. 3 is a diagram schematically showing a configuration of an output signal of the infrared solid-state imaging device.

In FIG. 1, reference numeral 11 denotes a photodetector arranged in a light-shielded region and formed of a silicon Schottky junction, 14 denotes a photodetector arranged in a non-light-shielded region and formed of a silicon Schottky junction,
Is a vertical CSD that transfers the signal charges accumulated in each photodetector in the vertical direction, 15 is a horizontal CCD that transfers the signal charges transferred from the vertical CSD 12 in the horizontal direction, and 16 is a signal charge from the horizontal CCD 15. This is an output unit that outputs to the outside as a video signal.

13 is a photodetector 1 arranged in the light-shielding area.
1, an optical black part that has a vertical CCD 12 and a horizontal CCD 15 and outputs only a dark current component as a video signal,
Adjacent to the normal infrared detector area. Here, a predetermined number of photodetectors 11 in the optical black section 13 may be provided as needed.

In FIG. 2, reference numerals 1 to 8 denote the same components as those in FIG. 5, and reference numeral 9 denotes a semiconductor substrate 1 directly below the photoelectric conversion layer 2 of the infrared detector 11 with a slight distance from the layer. This is a diffusion layer with a high impurity concentration formed. The diffusion layer 9 absorbs infrared light from the back side of the substrate and acts on the photoelectric conversion layer 2 so as to block incident infrared light. Here, the impurity of the diffusion layer 9 may be n-type P, As, Sb or P-type B, Al, Ga.

Note that these impurity diffusion layers can be formed by, for example, high energy ion implantation or a method described below.

FIG. 9 is a diagram showing a method of forming the impurity diffusion layer. In the figure, reference numeral 91 denotes a Si layer formed on the P-Si substrate 1 by epitaxial growth.

As a specific manufacturing method, first, as shown in FIG. 9A, an impurity diffusion layer 9 is selectively formed on the P-Si substrate 1 by diffusion. Next, as shown in FIG.
As shown in FIG. 7, the Si layer 91 is epitaxially grown. Thus, the impurity layer 9 embedded in the Si substrate can be formed.

3, reference numeral 30 denotes a video signal output from the output unit 16, reference numeral 31 denotes an optical signal component corresponding to the incident infrared light included in the video signal 30, and reference numeral 32 denotes an incident infrared light included in the video signal 30. 33 is a dark current component generated independently of the optical
This is an output signal read from the shielded infrared detector 11 of the black section 13, which is a dark current component contained in the video signal 30.
It is equivalent to 32.

 Next, the operation will be described with reference to these drawings.

In FIG. 1, operations of a normal infrared detector portion and a charge transfer portion other than the optical black portion 13 are the same as those of the conventional infrared solid-state imaging device.

Next, the operation of the optical black portion will be described.

Since the diffusion layer 9 having a high impurity concentration in the infrared detector 11 has a function of absorbing infrared light, all the infrared light incident from the back side of the substrate 1 is absorbed by the impurity diffusion layer 9 and It cannot be transmitted. Therefore, only signal charges due to dark current are accumulated in the photoelectric conversion layer 2 of the optical black portion 13. This signal charge is read out to the vertical CSD 12, transferred in the vertical direction, further transferred in the horizontal direction by the horizontal CCD 15, and read out as a dark current signal 33 from the output unit 16.

Then, the dark current signal 33 read from the output unit 16 is temporarily stored in, for example, an image memory or the like, and then the dark current signal is obtained from the video signal 30 obtained by each photodetector 14 other than the optical black unit 13. By subtracting 33, an optical signal corresponding to the incident infrared light can be obtained as a video signal.

As described above, in the present embodiment, the impurity diffusion layer 9 is formed in a part of the semiconductor substrate 1 on which the plurality of infrared detectors 11 are mounted, and the part of the infrared Since the optical black section 13 shielded from incident infrared light is provided, the output of the optical black section 13 can be detected as a dark current component of the infrared detector. As a result, the dark current component 32 can be subtracted from the output video signal 30, so that the measurement error of the optical signal caused by the dark current signal component and the problem of S / N deterioration due to insufficient cooling can be solved. The temperature of the object can be accurately measured.

Further, by monitoring the dark current signal obtained from the output unit 16, the temperature of the infrared solid-state imaging device can be easily controlled.

In the above embodiment, the case where the impurity diffusion layer 9 is provided immediately below the photoelectric conversion layer 2, that is, in the middle part of the silicon substrate, has been described. The value may be changed according to the F value of the optical system provided on the front surface of the imaging device, that is, the value obtained by dividing the focal length of the lens by the aperture diameter. That is, for example, a photodetector
When the incident angle θ10 of the infrared light incident on 11 is large (the F value is small), as shown in FIG.
Should be brought closer to the photoelectric conversion layer 2. Conversely, when the incident angle θ10 of infrared light is small (the F value is large), the impurity diffusion layer 9 is provided on the lower surface side of the silicon substrate away from the photoelectric conversion layer 2 as shown in FIG. Is also good.

Further, in the above-described embodiment, an example is shown in which the optical black section 13 is provided behind the normal infrared detector portion when viewed from the output section 16, but this is reversed as shown in FIG. It may be located in front of the infrared detector.

Further, in the above embodiment, the case where the semiconductor substrate is a silicon substrate has been described, but the present invention is not limited to this, and the semiconductor substrate may be of another type.

〔The invention's effect〕

As described above, according to the present invention, a diffusion layer having a high impurity concentration is formed inside a semiconductor substrate on which a plurality of infrared detectors are mounted, and a part of the infrared detectors As we constituted optical black part shaded by action,
The output of the infrared detector in the optical black section can be detected as a dark current component of the infrared detector, thereby causing an error in temperature measurement due to the dark current or an insufficient cooling when the cooling is insufficient.
A high-performance infrared solid-state imaging device capable of preventing S / N ratio deterioration and easily controlling the temperature of the device can be obtained.

[Brief description of the drawings]

FIG. 1 is a view showing the arrangement of each part of an infrared solid-state imaging device according to an embodiment of the present invention, FIG. 2 is a view showing a structure taken along the line II-II of FIG. 1, and FIG. FIG. 4 is a schematic diagram for explaining a video signal obtained by the solid-state imaging device, FIG. 4 is a diagram showing an arrangement of each part of the conventional infrared solid-state imaging device, and FIG. FIG. 6 is a schematic diagram for explaining a video signal obtained by a conventional infrared solid-state imaging device, and FIGS. 7A and 7B are infrared solid-state images according to another embodiment of the present invention. FIG. 8 is a diagram showing a cross-sectional structure of an imaging device, FIG. 8 is a diagram showing an arrangement of an optical black portion of an infrared solid-state imaging device according to still another embodiment of the present invention, and FIG. FIG. 4 is a diagram illustrating a method of manufacturing an impurity diffusion layer that forms an optical black portion. In the figure, 1 is a silicon semiconductor substrate, 2 is a photoelectric conversion layer, 9 is a diffusion layer having a high impurity level, 11 is a light-shielded infrared detector, and 13 is an optical black portion. In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (1)

(57) [Claims] 1. An infrared solid-state imaging device having a structure in which a plurality of infrared detectors are arranged on a surface of a semiconductor substrate, and detecting an incident infrared light and outputting a video signal. An infrared solid having an impurity diffusion layer formed in a region for absorbing the incident infrared light, and having an optical black portion for outputting a signal current of an infrared detector shielded by the impurity diffusion layer; Imaging device.