JP2738328B2 - Infrared detecting element and method of manufacturing the same - 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 infrared detecting element, and more particularly to a method for manufacturing a photoconductive infrared detecting element using HgCdTe crystal.

[0002]

2. Description of the Related Art A photoconductive infrared detecting element using a HgCdTe crystal has a high sensitivity and a high response, and furthermore, the wavelength of infrared light to be detected is arbitrarily set by changing the composition ratio of Hg and Cd. It can be used in a wide range of applications. In this infrared detecting element, minority carriers in the HgCdTe crystal are excited by the incident infrared light, and the resistance of the HgCdTe crystal changes in response to the excitation, thereby detecting infrared light.

[0003] A photoconductive infrared detector is shown in FIG.
(E) An element having a structure shown in (e), a substrate 3 having excellent insulating properties and flatness, an infrared light receiving section 1 fixed on the substrate 3, and the infrared light for measuring an output voltage by applying a bias. It comprises an electrode 5 provided at both ends of the light receiving section 1 and an infrared anti-reflection film 6 formed on the infrared light receiving section 1.

Conventionally, this infrared detecting element has been manufactured by the following procedure.

[0005] n-type Hg _1-x Cd _{x serving as} infrared light receiving section 1
A Te (0.2 <x <0.3) crystal is bonded to the sapphire substrate 3 with the epoxy adhesive 2 (FIG. 2).
(A)). At this time, the anodic oxide film 4 is formed on the back surface of the HgCdTe crystal, that is, the bonding surface, and then the sapphire substrate 3 is bonded.

After the adhesive 2 is cured, the HgCdTe crystal 1 is thinned to a thickness of about 10 μm by polishing and wet etching, and an anodic oxide film 4 is formed on the HgCdTe crystal surface.
Is formed (FIG. 2B). The anodic oxide film 4 of the HgCdTe crystal is 0.1 M KOH-90%
Using an aqueous solution of ethylene glycol, P
The HgCdTe crystal is connected as the working electrode 10 to the cathode 9 such as t, and is formed by applying a constant voltage from the DC power supply 11 (FIG. 4).

After the anodic oxide film 4 is formed, the anodic oxide films 4 at both ends of the infrared light receiving section 1 are removed by ion beam etching, and then the electrode film 5 is formed by vacuum evaporation (FIG. 2).
(C)) Further, an infrared anti-reflection film 6 is formed on the infrared receiving section 1 (FIG. 2 (e)). As the electrode material,
Au / Cr, Al, In or the like is used, and ZnS is generally used as the antireflection film material.

[0008]

An anodized film 4 is formed on an infrared light receiving portion 1 of a photoconductive infrared detecting element using HgCdTe crystal. The anodic oxide film 4 has a positive fixed charge and functions to confine the minority carriers excited by the incidence of infrared rays in the infrared light receiving section 1. As a result, the recombination of the minority carriers on the surface of the infrared light receiving section 1 is suppressed, so that the sensitivity of the infrared detection element can be increased. Therefore, the characteristics of the infrared detecting element depend on the characteristics and the state of formation of the anodic oxide film 4.

When the anodic oxide film 4 is formed by the above-described conventional manufacturing method, the oxide film 4a obtained at a formation voltage of 14V exhibits the best characteristics as fixed charges. However, since the anodic oxide film 4a is inferior in chemical resistance, the anodic oxide film 4a immediately dissolves during the production of the infrared detecting element, particularly in the photolithography step for forming the anti-reflection film 6, when it comes into contact with a strongly alkaline developer (see FIG. 2 (d)). As a result, there is a problem that the rate at which minority carriers recombine on the surface of the infrared light receiving section 1 increases, and the sensitivity characteristics of the infrared detection element deteriorate significantly.

On the other hand, when anodizing treatment is performed at a formation voltage of 26 V or more, an anodized film having a two-layer structure is obtained (FIG. 3).
(B)). In this case, a first-layer oxide film 4b is formed on the outermost surface of the infrared receiving section 1, and a second-layer oxide film 4c that is hardly soluble in the developer is formed therein. Therefore, when the surface of the infrared ray receiving section 1 comes into contact with the developing solution in the photolithography process, the first oxide film 4b is immediately dissolved, but the second oxide film 4c remains without being affected by the developing solution at all. (FIG. 3D). This is because the first oxide film 4b has almost the same composition as the oxide film 4a formed at the formation voltage of 14V, and Hg-Cd-
This is because the second oxide film 4c, which is a Te-O-based compound, is a Cd-Te-O-based compound having an extremely low Hg content, whereas the second oxide film 4c is a Hd-containing compound. The difference in the composition of these oxide films appears as an effect of chemical resistance, but on the other hand, the characteristics of the infrared light receiving portion as fixed charges are reversed, and the oxide film 4c of the second layer is formed.
Has almost no function as a fixed charge. Therefore, when the anodic oxide film of the infrared light receiving section 1 is formed at a chemical conversion voltage of 26 V, the characteristics of the infrared detecting element can be improved even if the second oxide film 4c remains even if the first oxide film 4b is dissolved. Is deteriorated.

[0011]

SUMMARY OF THE INVENTION An object of the present invention is to provide a photoconductive infrared detecting element in which an anodic oxide film 4 having excellent chemical resistance and having a sufficient function as a fixed charge is formed on the surface of an infrared receiving section 1. To provide. For this purpose, when the anodic oxide film 4 is formed, a CdTe film 7 is formed on the surface of the HgCdTe crystal 1 in advance, and then the HgCdTe crystal 1 and the CdTe film 7 are anodized simultaneously.

[0012]

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

N-type Hg _1-x Cd _{x serving as} infrared light receiving section 1
Te (0.2 <x <0.3) is bonded to the sapphire substrate 3 with the epoxy adhesive 2 (FIG. 1A).
At this time, an anodic oxide film 4 is formed in advance on the back surface of the infrared light receiving unit and then adhered to the substrate 3. However, the anodic oxide film 4 on the back surface may be dissolved by contact with a chemical or the like in a later manufacturing process. Therefore, it is formed at a formation voltage of 14 V by a conventional anodic oxide film forming method.

After the adhesive 2 is cured, the HgCdTe crystal 1 is thinned to a thickness of about 10 μm by polishing and wet etching.
A 0A CdTe film 7 is formed (FIG. 1B). This time, the MBE method was used, but any method such as a vacuum evaporation method and a sputtering method may be used.

Next, an anodic oxide film 4 is formed on the surface of the infrared light receiving section 1 (FIG. 1C). The method of forming the anodic oxide film 4 is the same as the conventional method shown in FIG. 4, using 0.1 M KOH-90% ethylene glycol aqueous solution as the electrolytic solution 8, Pt as the cathode 9 in the electrolytic solution 8, and HgCdT having a CdTe film 7 formed on the surface as a working electrode 10
It is formed by connecting the e-crystals 1.

After the formation of the anodic oxide film 4, to obtain an ohmic contact, the oxide film on both ends of the infrared light receiving portion is removed by ion beam etching, and then the electrode 5 is formed by a vacuum deposition method (FIG. 1 (d)). Then, an antireflection film 6 is formed on the surface of the infrared light receiving section 1 (FIG. 1F). As the electrode material, Cr 500 angstroms (hereinafter abbreviated as A) and Au5000A were sequentially laminated, and ZnS was used as an antireflection film material.

In the step of forming the anodic oxide film 4,
A current density of 5 μA / mm ² and a formation voltage of 20 V were applied to the working electrode. It is known that the thickness of the anodic oxide film 4 depends on the formation voltage.
All the CdTe films 7 of A become oxide films 4d. Cd
After the anodization of the Te film 7 is completed, the HgCdTe crystal 1 is subsequently anodized, and an oxide film 4c of about 450 A is formed on the HgCdTe surface, and the process is completed.

As described above, by the anodic oxide film forming step,
An anodized film having a two-layer structure is formed on the surface of the infrared light receiving unit 1, and this is an oxide film having a structure different from that conventionally obtained. That is, the outermost surface of the infrared ray receiving section 1 is made of a CdTe film anodic oxide film 4d, and a Cd-Te-O-based compound having excellent chemical resistance is formed therein.
Hg-Cd-T as anodized film 4e of CdTe crystal
An e-O-based compound is formed. Therefore, even if the infrared receiving section 1 comes into contact with the developing solution during the manufacturing process of the infrared detecting element, the surface of the infrared receiving section is hardly soluble in Cd-T
Since the Hg-Cd-Te-O-based compound 4e, which functions as a fixed charge, is not broken due to being covered with the e-O-based compound 4d, the characteristics of the infrared detecting element are not degraded.

[0019]

As described above, in the method for manufacturing an infrared detecting element of the present invention, an anodic oxide film having excellent chemical resistance and sufficient function as a fixed charge is formed on the surface of an infrared detecting section. And an infrared detecting element having excellent characteristics can be manufactured.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a manufacturing process of an infrared detecting element of the present invention.

FIG. 2 is a cross-sectional view of a manufacturing process of a conventional infrared detecting element.

FIG. 3 is a cross-sectional view of a manufacturing process of a conventional infrared detecting element.

FIG. 4 is a schematic view of a method for forming an anodized film.

[Explanation of symbols]

1 Infrared ray receiving section (Hg _1-x Cd _x Te, 0.2 <x <
0.3) 2 Epoxy adhesive 3 Sapphire substrate 4 Anodized film 4a Anodized film of HgCdTe formed at formation voltage of 14V 4b First layer of anodized film of HgCdTe formed at formation voltage of 26V 4c Formed at formation voltage of 26V Second layer of anodic oxide film of HgCdTe 4d Anodized film of CdTe 4e Anodized film of HgCdTe 5 Electrode 6 Antireflection film 7 CdTe film 8 Electrolyte for forming anodized film (0.1 M KOH-9
0% ethylene glycol aqueous solution) 9 Cathode 10 Working electrode 11 DC power supply

Claims (2)

(57) [Claims] 1. Hg _1-x Cd _x Te (0.2 <x <0.
3) An infrared detecting element having electrodes on both ends of an infrared ray receiving section and having an anodic oxide film on the surface of the infrared ray receiving section, wherein the anodic oxide film is formed of the infrared ray receiving section.
A Hg _1-x Cd _x Te anodic oxide film in contact with
Infrared radiation characterized by having a laminated structure with an extreme oxide film
Detection element. 2. Hg _1-x Cd _x Te (0.2 <x <0.
Electrodes are provided at both ends of the infrared light receiving unit using 3)
An infrared detector with an anodized film formed on the surface of the infrared receiver
In the method for manufacturing a light emitting element,
After coating with a dTe film, the CdTe film and the Hg
By anodizing a part of the surface of _1-x Cd _x Te
To form an anodized film
Production method of output element.