JP2817435B2 - Manufacturing method of array type infrared detector - 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 manufacturing an array type infrared detector using a semiconductor having a relatively narrow band gap.

[0002]

2. Description of the Related Art It is generally known that an infrared detector using a semiconductor having a relatively narrow forbidden band has high sensitivity. In particular, a detector having a configuration in which single detection elements are arranged one-dimensionally or two-dimensionally is very effective when used in an infrared imaging device.

[0003]

As a configuration of a conventional array type infrared detector, for example, a magazine "SPII.
S.P.I.E. "(Vol. 443, 1983 Dec. 12)
As shown in page 0), a hybrid structure is known in which a semiconductor having a narrow band gap is used for an infrared detector and connected to a signal processing unit 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 figure, the configuration of a conventional array type infrared detector is a CdTe substrate 11, Hg _0.8 Cd _0.2 T
e layer 12, a photodiode 13 serving as an infrared detector formed on the Hg _0.8 Cd _0.2 Te layer 12, a indium column 14, a signal processing chip 15 including a silicon CCD,
It has a charge signal injection layer 16 to the signal processing section, and the infrared light 10 enters from the lower side in the figure. In this configuration, H grown epitaxially on the CdTe substrate 11 is used.
A photodiode 13 serving as an infrared detecting unit is formed in the g _0.8 Cd _0.2 Te layer 12 by an ion implantation method, and an electric signal output from the photodiode is output to the indium pillar 1.
4, the signal processing chip 15 through the charge signal injection layer 16
Is to be entered. As a result, an output signal generated at each infrared detector in the array by the incident infrared light 10 is read out to the outside through the signal processing chip 15 and output as an infrared image. In this case, infrared rays having a maximum wavelength of about 10 μm can be detected.

[0005] However, such an array type infrared detector has the following disadvantages in its structure and manufacturing process.

In the conventional example, the formation of the photodiode is performed by selective ion implantation.
The ion implantation method is excellent in terms of carrier concentration control and the like, but has a drawback in that many crystal defects occur near the formed pn junction. This is a significant problem especially when using a very brittle semiconductor such as HgCdTe. FIG.
Is incident on HgCdTe12 to generate an electron-hole pair, and this electron-hole diffuses and becomes an output of each photodiode when reaching the pn junction. In the infrared detector, those having a small dark current show good characteristics such as sensitivity, but in the process of this photoelectric conversion, if there are many crystal defects at the pn junction interface, the dark current due to recombination increases, As a detector, one having sufficient characteristics cannot be obtained. Therefore, a photodiode having a pn junction formed only by ion implantation cannot achieve a sufficiently low dark current.

As a method of suppressing the dark current, a heat treatment after implantation can be considered. When heat treatment is performed under certain conditions, the pn junction position is extended to a depth of 3 to 4 μm as compared with the position immediately after ion implantation. As a result, the pn junction moves to a region that is hardly damaged by ion implantation, so that a photodiode with a small dark current can be obtained.
In a conventional array type infrared detector of about 32 × 32 or 64 × 64, the pitch and the light receiving diameter of the photodiode are typically 50 μm and 30 μm, respectively. 128 × 128,256
When increasing to × 256, the pitch and the light receiving diameter are reduced to 1/3 of the conventional values.
It is necessary to reduce to １ ／. That is, the pitch is 15
μm and a light receiving diameter of 10 μm or less are required. In the structure of the conventional example, when the number of pixels is increased and a heat treatment after ion implantation is performed to further improve the characteristics of the photodiode, pn
Since the junction interface expands, the photodiodes are electrically connected and the independence between pixels cannot be maintained. Therefore, the function as an array type infrared detector cannot be obtained.

[0008] In addition to those described above as examples of conventional array type infrared detectors, "Advanced Infrared Detectors and Systems" (Dec. 1983)
Page). This is Hg _0.8 C
Silicon C through a through-hole d _0.2 Te becomes infrared detecting part formed on the layer photodiode is formed therein
It is configured to be electrically connected to a signal processing chip including a CD. Even in this case, the photodiode is formed by ion implantation, and the improvement of the photodiode characteristics and the reduction of the pitch due to the number of pixels cannot be simultaneously satisfied by the heat treatment after the implantation, as in the above-described conventional example.

As described above, it is difficult to increase the number of pixels to increase the resolution and to improve the photodiode characteristics at the same time with the conventional structure and manufacturing method.

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

[0011]

According to the present invention, there is provided a method of manufacturing an array type infrared detector according to the present invention.
Is applied to the entire surface of a compound semiconductor with a relatively narrow bandgap.
A layer having conductivity opposite to that of the compound semiconductor by ion implantation.
Forming a pn junction so as to correspond to each pixel.
Separating by etching, the etching step
Performing a heat treatment after the step.

The arrangement formed in such a manufacturing method
The row-type infrared detector is a compound semiconductor with a relatively narrow bandgap.
The photodiodes arranged and arranged on the body are mesa-shaped
Having a structure, wherein each of the photodiodes is
A pn junction formed by heat treatment;
Junction is deep enough compared to the average projected range of the ion implantation
And between the pn junction and the average projected range.
The impurity concentration is lower than the impurity concentration within the average projected range.
At least one order of magnitude smaller, and conductive
Photodiodes use a silicon chip for signal processing and electrical
Are connected to each other.

[0013]

The array type infrared detector manufactured by the manufacturing method of the present invention has a structure in which the photodiode serving as each pixel has a pn junction interface diffused by a heat treatment after ion implantation. Since each photodiode has a pn junction in a region that has not been damaged by ion implantation, the recrystallization current at the pn junction caused by crystal defects is very small. Since the impurity concentration is low, the tunnel current can be kept low irrespective of the level of the impurity concentration on the substrate side, and the photodiode exhibits excellent characteristics. The electrical isolation of each photodiode is
This is performed by forming a mesa structure after ion implantation. Therefore, with respect to diffusion at the pn junction interface by the subsequent heat treatment, the spread only in the lateral direction is limited. Therefore, it is possible to sufficiently reduce the pitch of the photodiodes arranged while taking electrical separation between the pixels, that is, to increase the number of photodiodes arranged per unit area.

As described above, according to the manufacturing method of the present invention, since the dark current of each photodiode is small, the temperature resolution is high, the sensitivity is high, the number of pixels can be sufficiently increased, and a high-resolution array type infrared detector is provided. Is obtained.

[0015]

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 compound semiconductor having a narrow band gap.
_The case where a _0.8 Cd _0.2 Te layer is used will be described. FIG. 2 is a diagram for explaining the manufacturing method of the present invention. First, the manufacturing method of the present invention will be described with reference to FIG.

As shown in FIG. 2A, the CdTe substrate 1
Approximately 15 μm p-Hg _0.8 epitaxially grown thereon
An n ⁺ -Hg _0.8 Cd _0.2 Te ion-implanted region 4 is formed in the Cd _0.2 Te layer 2 by ion implantation of boron ions. The depth is about 1.5 μm. At this time, p-Hg _0.8
Numerous damages due to ion implantation exist near the pn junction at the interface between the Cd _0.2 Te layer 2 and the n ⁺ -Hg _0.8 Cd _0.2 Te ion implantation region 4.

Next, as shown in FIG. 2B, the mesas are two-dimensionally arranged so as to correspond to each pixel by a reactive ion beam etching method to form a photodiode.
A surface protection film 6 is deposited. The depth of the mesa at this time is n
^The thickness was set to 4 μm so as to be deeper than the ⁺ −Hg _0.8 Cd _0.2 Te ion-implanted region 4. Each photodiode has a diameter of 10μ
m, pitch is 15 μm, 256 × 2 in 5 mm square
56 photodiodes are integrated. As the surface protective film 6, zinc sulfide was used.

Next, as shown in FIG. 2C, heat treatment is performed at 150 ° C. for one hour in a nitrogen atmosphere. As a result, n ⁺ -H
The n ⁻ −Hg _0.8 Cd _0.2 Te diffusion region 3 having a relatively lower carrier concentration than the g _0.8 Cd _0.2 Te ion implantation region 4 expands, and the pn junction moves to a deeper position where there is no influence of the ion implantation damage. I do. This is HgCdTe
In the case of (1), the diffusion of Hg atoms in the interstitial is considered to be the main cause. Under the above conditions, the diffusion width is 3.5 to 4.0 μm. As shown in FIG. 2C, since a mesa is formed, this diffusion mainly spreads only in the depth direction, and the spread in the lateral direction occurs only in a portion deeper than the mesa.
Very small, 1.5 μm. Therefore, even if the pitch of each photodiode is reduced to 15 μm as described above, there is no problem that the pixels are coupled by heat treatment when the structure and the manufacturing method of the present invention are used. 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 described with reference to FIG.

The incident infrared light 10 enters from the lower side in the figure.
The infrared light 10 passing through the CdTe substrate 1 and absorbed by the p-Hg _0.8 Cd _0.2 Te layer 2 generates carriers (electrons or holes). In this case, the minority carrier electrons fall within the diffusion length of the photodiode. When the number reaches 5, the charge is injected into the charge signal injection layer 8 through the indium column 7 and is output as an output signal by the signal processing chip 9.

Among the infrared detectors, those having a small dark current show good characteristics such as sensitivity. In the structure of the present invention, the pn junction is formed by heat treatment and is located in a region not damaged by ion implantation. Therefore, during the photoelectric conversion process, recombination caused by crystal defects existing at the pn junction interface occurs. Very low dark current. Furthermore, since the n ⁻ -Hg _0.8 Cd _0.2 Te diffusion region 3 having a relatively low carrier concentration is present, the dark current due to the tunnel current can be sufficiently suppressed regardless of the impurity concentration of the CdTe substrate 1. A low dark current can be achieved, and an infrared detector with excellent characteristics can be obtained.

In this embodiment, the case where a p-Hg _0.8 Cd _0.2 Te layer is used as a compound semiconductor having a narrow band gap is shown, but the material, polarity and composition are not limited to this.

[0024]

As described in detail above, the present invention
According to the fabrication method, since the dark current of each photodiode is small, the temperature resolution is high, the sensitivity is high, the number of pixels can be sufficiently increased, and a high-resolution array type infrared detector can be provided.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an arrayed infrared detector formed by a manufacturing method of the present invention.

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

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

[Explanation of symbols]

1,11 CdTe substrate 2,12 p-Hg _0.8 Cd _0.2 Te layer 3 n ^-- Hg _0.8 Cd _0.2 Te diffusion region 4 n ⁺ -Hg _0.8 Cd _0.2 Te ion implantation region 5,13 Photodiode 6 Surface protective film 7,14 Indium pillar 8,16 Charge signal injection layer 9,15 Signal processing chip 10 Infrared light

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H01L 31/08

Claims (1)

(57) [Claims] A step of forming a layer having conductivity opposite to that of the compound semiconductor by ion implantation over the entire surface of the compound semiconductor having a relatively narrow forbidden band;
A method for manufacturing an arrayed infrared detector, comprising: a step of separating an n-junction by etching; and a step of performing a heat treatment after the etching step.