JPH04318979A - Array type infrared ray sensor and manufacture thereof - Google Patents

Abstract

PURPOSE:To obtain a sensor which simultaneously satisfies high sensitivity due to a reduction in a dark current and high resolution due to multiple pixels in an array type infrared ray sensor. CONSTITUTION:An n<+> type HgCdTe ion implanted region 4 is formed on a p-type HgCdTe layer 2 by ion implanting, pixels are separated by mesa etching, and an n<-> type HgCdTe diffused region 3 is formed by heat treating. Since a p-n junction position of a photodiode 5 is moved to a region which is not damaged by the ion implantation, a dark current due to a recombination caused by a crystal defect is very small, and a high sensitivity photodiode is obtained. Further, since a mesa type structure is formed and lateral diffusion of the p-n junction by heat treating is suppressed, a pitch between the photodiodes can be reduced, and an array type infrared ray sensor having high resolution is obtained.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an array type infrared detector using a semiconductor having a relatively narrow forbidden band width and a method for manufacturing the same.

0002

2. Description of the Related Art In general, it is known that infrared detectors using semiconductors with a relatively narrow forbidden band have high sensitivity. In particular, a detector having a configuration in which single detection elements are arranged in one or two dimensions is very effective when used in an infrared imaging device.

0003

[Problems to be Solved by the Invention] As for the configuration of the conventional array type infrared detector, for example,
S.P.I.E” (Vol. 443, December 1983)
As shown on page 0), a hybrid structure is known in which a narrow bandgap semiconductor is used in the infrared detector section and this is connected to a signal processing section such as a silicon CCD (charge coupled device). .

FIG. 3 is a sectional view showing an example of a conventional array type infrared detector. In the same figure, the configuration of the conventional array type infrared detector is as follows: CdTe substrate 11, Hg0.8Cd0
．． 2Te layer 12, this Hg0.8Cd0.2Te layer 12
A photodiode 13 serving as an infrared detection section is formed on the top.
, an indium column 14, a signal processing chip 15 including a silicon CCD, and a charge signal injection layer 16 to the signal processing section, and infrared light 10 enters from the bottom side in the figure. In this configuration, a photodiode 13 serving as an infrared detection section is formed by ion implantation in a Hg0.8Cd0.2Te layer 12 epitaxially grown on a CdTe substrate 11, and an electric signal output from the photodiode is transferred to an indium column 14. , and is input to the signal processing chip 15 through the charge signal injection layer 16. As a result, output signals generated by the incident infrared light 10 in each infrared detection section in the array are read out to the outside through the signal processing chip 15 and output as an infrared image. In this case, infrared rays with a maximum wavelength of about 10 μm can be detected.

However, such an array type infrared detector has the following drawbacks in its structure and manufacturing process.

In the prior art, photodiodes are formed by selective ion implantation. Although the ion implantation method is excellent in terms of carrier concentration control, etc., the drawback is that many crystal defects are generated near the formed pn junction. This is a big problem especially when using a very brittle semiconductor such as HgCdTe. Figure 3
The infrared light 10 incident on the photodiode is absorbed by the HgCdTe 12 and generates electron/hole pairs, which diffuse and reach the pn junction and become the output of each photodiode. In infrared detectors, those with a small dark current exhibit good characteristics in terms of sensitivity, but in the process of photoelectric conversion, if there are many crystal defects at the p-n junction interface, the dark current due to recombination increases. As a detector, one with sufficient characteristics cannot be obtained. Therefore, a photodiode having a pn junction formed only by ion implantation cannot achieve a sufficiently low dark current.

[0007] As a method of suppressing this dark current, heat treatment after implantation can be considered. When heat treatment is performed under certain conditions, the p-n junction position becomes 3 times smaller than the position immediately after ion implantation.
It spreads ~4 μm deep. As a result, the pn junction moves to a region that has received little damage from ion implantation, resulting in a photodiode with low dark current. In conventional 32 x 32 or 64 x 64 array type infrared detectors, the photodiode pitch and light receiving diameter are typically 50 μm and 30 μm, respectively, but the number of pixels will be increased in order to achieve higher resolution in the future. 128×128,256
When increasing to ×256, the pitch and receiving diameter are 1/3 of the conventional one.
It is necessary to reduce the amount to ~1/4. That is, the pitch is 15
μm, and the receiving diameter is required to be 10 μm or less. If the number of pixels is increased in the conventional structure and heat treatment is performed after ion implantation to improve the characteristics of the photodiode, the p-n
Since the junction interface expands, each photodiode is electrically connected, making it impossible to maintain independence between pixels. Therefore, the function as an array type infrared detector cannot be obtained.

[0008] In addition to the above-mentioned conventional array type infrared detector, there is a detector shown in "Advanced InfraRed Detectors and Systems" (1983, p. 12). This is Hg0.8C
A configuration is adopted in which a photodiode serving as an infrared detection section formed on the d0.2Te layer is electrically connected to a signal processing chip including a silicon CCD through a through hole formed therein. Even in this case, the photodiode is formed by ion implantation, and as described in the previous example, it is not possible to simultaneously improve the photodiode characteristics by heat treatment after implantation and reduce the pitch due to the large number of pixels.

As explained above, it is difficult to increase the number of pixels in order to increase the resolution and simultaneously improve the photodiode characteristics using the conventional structure and manufacturing method.

An object of the present invention is to provide an array type infrared detector and a method for manufacturing the same which eliminates these drawbacks.

[0011]

[Means for Solving the Problems] In order to achieve the above object, in the array type infrared detector according to the present invention, the photodiodes formed in an array on a compound semiconductor having a relatively narrow forbidden band width are mesa-type. Each photodiode has a p-type structure formed by heat treatment after ion implantation.
The p-n junction is located at a position sufficiently deep compared to the average projected range of the ion implantation, and the impurity concentration between the p-n junction and the average projected range is equal to the average projected range. at least one order of magnitude lower than the impurity concentration within
The photodiodes are of the same conductivity type, and each photodiode is electrically connected to a silicon chip for signal processing.

The method for manufacturing an array type infrared detector according to the present invention further includes the step of forming a layer having conductivity opposite to that of the compound semiconductor by ion implantation on the entire surface of the compound semiconductor having a relatively narrow forbidden band width. , a step of separating p-n junctions by etching so as to correspond to each pixel, and a step of performing heat treatment after the etching step.

[0013]

[Operation] The array type infrared detector manufactured by the manufacturing method of the present invention has a structure in which the photodiode forming each pixel has a p-n junction interface diffused by heat treatment after ion implantation. Each photodiode has a p-n junction in a region that has not been damaged by ion implantation, so the recrystallization current at the p-n junction caused by crystal defects is very small. Since the impurity concentration is low, the tunnel current can be suppressed to a small level regardless of the impurity concentration on the substrate side, and it exhibits excellent characteristics as a photodiode. The electrical isolation of each photodiode is
This is done by forming a mesa structure after ion implantation, and therefore, the diffusion of the pn junction interface by subsequent heat treatment is limited to only the lateral direction. Therefore, it is possible to sufficiently reduce the pitch of the arrayed photodiodes while maintaining electrical isolation between each pixel, that is, it is possible to increase the number of arrayed photodiodes per unit area.

As described above, in the structure and manufacturing method of the present invention, since the dark current of each photodiode is small, it is possible to increase the number of pixels with high temperature resolution and high sensitivity. A vessel is obtained.

[0015]

Embodiments Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a sectional view showing an embodiment of the present invention. Here, p-Hg is used as a narrow bandgap compound semiconductor.
The case where a 0.8Cd0.2Te layer is used is shown. Figure 2
FIG. 2 is a diagram for explaining the manufacturing method of the present invention. First, the manufacturing method of the present invention will be explained using FIG. 2.

As shown in FIG. 2(a), a CdTe substrate 1
About 15 μm of p-Hg0.
An n+-Hg0.8Cd0.2Te ion implantation region 4 is formed by implanting boron ions into the 8Cd0.2Te layer 2.
form. The depth is approximately 1.5 μm. At this time p-
Hg0.8Cd0.2Te layer 2 and n+-Hg0.8Cd
There is a lot of damage caused by ion implantation near the pn junction at the interface of the 0.2Te ion implantation region 4.

Next, as shown in FIG. 2(b), a photodiode is formed by arranging mesas two-dimensionally to correspond to each pixel using a reactive ion beam etching method.
A surface protective film 6 is deposited. The depth of the mesa at this time is n
+-Hg0.8Cd0.2Te ion implantation region 4 was deeper than 4 μm. The diameter of each photodiode is 10 μm, the pitch is 15 μm, and 25
6×256 photodiodes are integrated. As the surface protection film 6, zinc sulfide was used.

Next, as shown in FIG. 2(c), heat treatment is performed at 150° C. for 1 hour in a nitrogen atmosphere. As a result, n+-H
The n--Hg0.8Cd0.2Te diffusion region 3, which has a relatively lower carrier concentration than the g0.8Cd0.2Te ion implantation region 4, expands, and the p-n junction moves to a deeper position where it is not affected by damage caused by ion implantation. do. this is,
In the case of HgCdTe, the main cause is thought to be the diffusion of Hg atoms in the interstitials, and under the above conditions the diffusion width is 3.5 to 4.0.
It is μm. As shown in FIG. 2(c), since a mesa is formed, this diffusion mainly spreads only in the depth direction, and the lateral spread occurs only in a part deeper than the mesa, which is 1 to 1. Very small at 5 μm. Therefore, as mentioned above, even if the pitch of each photodiode is reduced to 15 μm,
If the structure and manufacturing method of the present invention are used, there is no problem of coupling between pixels due to heat treatment. Finally, it is electrically connected to the signal processing chip via the indium pillar 7. The final structure is shown in FIG.

Next, the operation of the array type infrared detector of the present invention will be explained using FIG.

Incident infrared light 10 enters from the bottom side in the figure. Passing through the CdTe substrate 1, p-Hg0.8Cd0.2Te
The infrared light 10 absorbed by the layer 2 generates carriers (electrons or holes), and in this case, the minority carrier electrons are
When it reaches the photodiode 5 within the diffusion length, it is sent to the charge signal injection layer 8 via the indium column 7, and is outputted as an output signal by the signal processing chip 9.

[0022] In infrared detectors, those with less dark current exhibit better characteristics in terms of sensitivity and the like. In the structure of the present invention, the p-n junction is formed by heat treatment and is located in an area that is not damaged by ion implantation. Dark current is very low. Furthermore, due to the presence of the n--Hg0.8Cd0.2Te diffusion region 3 with a relatively low carrier concentration, the dark current due to tunnel current can be suppressed to a sufficiently low level regardless of the impurity concentration of the CdTe substrate 1, so that each photodiode is sufficiently This makes it possible to achieve low dark current and obtain an infrared detector with excellent characteristics.

In this embodiment, a p-Hg0.8Cd0.2Te layer is used as a narrow bandgap compound semiconductor, but the material, polarity, and composition are not limited thereto.

[0024]

Effects of the Invention As explained in detail above, in the structure and manufacturing method of the present invention, the dark current of each photodiode is small, so it is possible to achieve high temperature resolution, high sensitivity, and a sufficient number of pixels. A high-resolution array-type infrared detector can be provided.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an array type infrared detector according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view showing the manufacturing method of the present invention in order of steps.

FIG. 3 is a sectional view for explaining a conventional example.

[Explanation of symbols]

1,11 CdTe substrate 2,12 p-Hg0.8Cd0.2Te layer 3 n
--Hg0.8Cd0.2Te diffusion region 4 n+-H
g0.8Cd0.2Te ion implantation region 5, 13 Photodiode 6 Surface protection film 7, 14 Indium column 8, 16 Charge signal injection layer 9, 15 Signal processing chip 10 Infrared light

Claims (2)

[Claims] 1. Photodiodes arranged and formed on a compound semiconductor having a relatively narrow forbidden band width have a mesa-type structure, and each of the photodiodes has a p-n structure formed by heat treatment after ion implantation. the p-n junction is located at a position sufficiently deep compared to the average projected range of the ion implantation, and the impurity concentration between the p-n junction and the average projected range is equal to the average projected range. An array-type infrared detector, characterized in that the impurity concentration is at least one order of magnitude lower than the impurity concentration within 100 degrees, and is of the same conductivity type, and each of the photodiodes is electrically connected to a silicon chip for signal processing. 2. A step of forming a layer having conductivity opposite to that of the compound semiconductor on the entire surface of a compound semiconductor having a relatively narrow forbidden band width, and etching a p-n junction corresponding to each pixel. A method for manufacturing an array-type infrared detector, comprising the steps of separating, and performing heat treatment after the etching step.