JPH05283665A - Array type infrared sensor - Google Patents

Abstract

PURPOSE:To prevent influence of a distortion due to a thermal expansion difference by forming an insular structure in which all photodiodes for pixels are completely isolated on a silicon layer deposited on an insulating layer. CONSTITUTION:An insulating layer 2 and a silicon layer 3 are deposited on an entire silicon chip 1. Then, a GaAs buffer layer 4, a CdTe buffer layer 5, a p-type HgCdTe layer 6 and an n-type HgCdTe layer 7 are sequentially grown to form an HgCdTe photodiode having a p-n junction. Thereafter, in order to isolate the photodiodes to elements, a groove having a depth reaching the layer 4 is formed by etching. A width of the groove is set to 5mum, a pitch of the grooves is set to 30mum, and hence an insulator photodiode having a port of 25mum can be formed. The silicon and the HgCdTe have different thermal expansion coefficients, but an insular shape is formed, i.e., elements are isolated on the layer 3, and contact parts are small. Accordingly, influence of deterioration of characteristics of the element due to its distortion can be entirely eliminated even at an end of the chip.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an infrared sensor using a semiconductor having a narrow band gap.

[0002]

2. Description of the Related Art Generally, it is known that an infrared sensor using a semiconductor having a narrow band gap has high sensitivity. In particular, a detector having a configuration in which a single detection element is arranged in one dimension or two dimensions is very effective when used in an infrared imaging device.

"Advanced Infrared Detectors and Systems" (December 1983) is a comparatively excellent conventional array type infrared sensor.
There is a sensor called the loophole structure shown on page. This is because an HgCdTe layer is adhered on a signal processing chip including a silicon CCD, and a photodiode serving as an infrared detector formed on this HgCdTe layer and a charge signal injection layer in the signal processing chip are electrically connected through a through hole. Connected to each other. Such an infrared sensor is generally used at 77K, so 300K and 7K each time it is used.
A thermal cycle of 7K is required. Since the silicon chip for signal processing and the HgCdTe for infrared detection are bonded by an adhesive, they are always in a distorted state at the time of use due to different thermal expansion coefficients. This is because when the integration degree of the infrared array increases (for example, 512 × 512) and the chip size increases to about 10 mm □ or more, the characteristics of the HgCdTe photodiode are deteriorated at the chip end portion where a large amount of distortion is caused, and further the cause of destruction is also caused. It can be a big problem.

As a structure for avoiding the thermal expansion difference between this silicon and HgCdTe, "Journal of the Infrared Society of Japan, 1991" has been proposed.
, Vol. 1, p. 2 ", a monolithically integrated HgCdTe photodiode is proposed on a signal processing silicon chip. The cross-sectional structure is shown in FIG. , Selectively Ga in the part where the silicon surface is exposed without the readout circuit
After forming the As buffer layer 22 and the CdTe buffer layer 23, the p-HgCdTe layer 24 and the n-HgCdTe layer 2 are formed.
5 is epitaxially grown to form a photodiode.
After that, a surface protection film 26 is deposited, a pattern is formed, and
The -HgCdTe layer 25 and the charge signal injection layer 28 are connected to the electrode 27.
Wire with.

This structure has several tens of μm on a silicon chip.
Since the island-shaped HgCdTe photodiode of about φ is formed, HgCdTe due to the thermal expansion difference with silicon is formed.
The influence of strain on the photodiode is very small, and even if the chip size increases, there is almost no deterioration in the characteristics of the photodiode. Therefore, it can be said that the structure is suitable for high integration and large area monolithic arrays.

[0006]

However, the array type infrared sensor having such a structure has the following drawbacks.

The portion where the photodiode is present is only a portion on the silicon chip, and the other portion is occupied by a circuit and wiring for reading the signal from the charge signal injection layer 28. The ratio occupied by the light receiving portion, that is, the fill factor is about 30%. Part of the infrared light 29 incident from the upper part is incident on the photodiode and can be extracted as a signal, but the other part cannot be extracted as a signal. Therefore, when this is imaged, it is clear that an image with sufficient characteristics cannot be obtained due to a decrease in sensitivity, disappearance of a point light source (small target), and the like.

An object of the present invention is to provide an array type infrared sensor which eliminates these drawbacks.

[0009]

In the array type infrared sensor of the present invention, a silicon layer, a GaAs buffer layer, and a CdT are provided on a silicon chip having an output signal processing section through an insulating layer.
e buffer layers are sequentially stacked, an HgCdTe photodiode having a pn junction is formed on the CdTe buffer layer, and the HgCdTe photodiode is electrically separated corresponding to each pixel by a groove having a depth reaching the silicon layer. The HgCdTe photodiodes are electrically connected to the corresponding output signal processing portions of the silicon chip through the holes penetrating the insulating layer and the silicon layer.

[0010]

The array type infrared sensor of the present invention has an island structure in which all the photodiodes for each pixel are completely separated on the silicon layer deposited on the insulating layer. When stored, that is, when subjected to thermal cycles of 77K and 300K, signal processing silicon chip and HgCd
There is almost no effect of strain due to the difference in thermal expansion between Te and Te, and good diode characteristics can be obtained even at the edge portion of the chip.

The HgCdTe photodiode has an SOI (Si) layer formed on an insulating layer formed on a signal processing silicon chip.
On Insulator) technology, a silicon layer is formed again, and a GaAs buffer layer and a CdTe buffer layer are formed. Therefore, it is possible to form the photodiode on the read circuit and the wiring portion formed on the signal processing silicon chip while electrically insulating the photodiode. As a result, the fill factor is increased, the sensitivity and the disappearance of minute targets in the image are eliminated, and the tracking of the point image is sufficiently possible.

[0012]

Embodiments of the present invention will now be described with reference to the drawings.

FIG. 1 is a perspective view showing an embodiment of the present invention, and FIG.
Is an enlarged view of one photodiode in the sectional view taken along line A-A '.

The structure of the array type infrared sensor of this embodiment will be described together with its manufacturing method. First, using a general SOI technique, the insulating layer 2 is deposited on the entire surface of 0.5 μm and the silicon layer 3 is deposited on the entire surface of 1 μm on the relatively flattened signal processing silicon chip 1. Here, SiO ₂ is used as the insulating layer 2,
It is formed by the CVD method including the silicon layer 3. Then M
The GaAs buffer layer 4 is 2 μm thick by using the BE method, and CdTe is
The buffer layer 5 is 5 μm, and the p-HgCdTe layer 6 is 10 μm.
m, n-HgCdTe layer 7 is sequentially grown to 2 μm, and pn
A HgCdTe photodiode with a junction is formed.
The silicon layer 3, the GaAs buffer layer 4, and the CdTe buffer layer 5 are relatively highly doped in order to improve electric conductivity. p-HgCdTe layer 6, n-HgC
The dTe layers 7 are 1 × 10 ¹⁶ cm ⁻³ and 2 × 10 ¹⁷ cm, respectively.
^-3 . Next, in order to separate the photodiode into each element, a groove having a depth reaching the silicon layer 4 is formed by etching. By setting the groove width to about 5 μm and the pitch to 30 μm, a 25 μm □ island-shaped photodiode array is formed. Further, the groove is arranged in accordance with the charge signal injection layer 10. Next, a part of the silicon layer 3 and the insulating layer 2 on the charge injection layer 10 is exposed on the etching surface. ZnS is vapor-deposited as the surface protection film 8, contact holes are opened on the n-HgCdTe layer 7 and the charge injection layer 10, and the electrode 9 is formed.
Wiring is done by. The electrodes of p-HgCdTe6 are all common to the silicon layer 3. 512 pixels
The chip size is × 512 and 20 mm × 20 mm.

Thus, the array type infrared sensor of the present invention shown in FIG. 1 is completed.

Next, the operation of the array type infrared sensor of this embodiment will be described.

The arrayed infrared sensor is cooled to 77K for operation. Since silicon and HgCdTe have different thermal expansion coefficients, the contraction rates of silicon and HgCdTe are also different, and distortion occurs in the contacting portions. However, in the configuration of this embodiment, Hg
The CdTe photodiode has an island shape, that is, each element is separated on the silicon layer 3, and the contact portion is 25 μm.
Since it is very small as □, there is no influence of the element characteristic deterioration due to the strain even at the edge portion of the chip.

When the incident infrared light 11 is incident from above, n
The infrared light 11 absorbed in the -HgCdTe layer 7 or the p-HgCdTe layer 6 generates carriers (electrons or holes) and is sent to the charge signal injection layer 10 and then output as a signal to the signal processing silicon chip 1 Is imaged and output by.

In the structure of the embodiment shown in FIG. 1, since the fill factor is about 70%, most of the incident infrared light 11 is effectively used, there is no problem such as the disappearance of minute targets in the image, and at the same time the sensitivity is high. Can be improved.

The array type infrared sensor shown in this embodiment has 5
Even if the degree of integration is increased as in the case of 12 × 512 pixels, the element characteristics are not deteriorated at the end portions, and a good image with high uniformity can be obtained.

This embodiment is merely an example, and the number of pixels, the thickness of each layer, the shape, the material, and the polarity are not limited to this.

[0022]

As described above, according to the present invention, it is possible to obtain an array type infrared detector which has a large fill factor and is hardly affected by the difference in thermal expansion and which is suitable for high integration and large area and large number of pixels.

[Brief description of drawings]

FIG. 1 is a perspective view of an array type infrared sensor that is an embodiment of the present invention.

FIG. 2 is a cross-sectional view taken along the line AA ′ of FIG.

FIG. 3 is a diagram for explaining a conventional example of an array type infrared sensor.

[Explanation of symbols]

 1,21 Signal processing silicon chip 2 Insulating layer 3 Silicon layer 4,22 GaAs buffer layer 5,23 CdTe buffer layer 6,24 p-HgCdTe layer 7,25 n-HgCdTe layer 8,26 Surface protective film 9,27 Electrode 10, 28 Charge signal injection layer 11, 29 Infrared light

Claims (1)

[Claims] 1. A silicon chip, a GaAs buffer layer, and a C layer on a silicon chip having an output signal processing section, with an insulating layer interposed therebetween.
dTe buffer layers are sequentially stacked, an HgCdTe photodiode having a pn junction is formed on the CdTe buffer layer, and the HgCdTe photodiode is electrically isolated by a groove having a depth reaching the silicon layer. And an output signal processing unit of the silicon chip to which each of the HgCdTe photodiodes corresponds,
An array type infrared sensor, which is electrically connected through a hole penetrating the insulating layer and the silicon layer.