JP2689946B2 - Manufacturing method of infrared detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a semiconductor having a narrow band gap,
In particular, the present invention relates to a method for manufacturing an infrared detector using a compound semiconductor containing Hg.

[0002]

2. Description of the Related Art It is generally known that an infrared detector using a semiconductor having a narrow band gap has high sensitivity. In particular, the photovoltaic element having a pn junction in the detecting portion, that is, the photodiode is very effective because it can be applied to an array type infrared detector having a configuration in which single elements are two-dimensionally arrayed. A typical example thereof is an infrared detector using HgCdTe semiconductor crystal.

In the case of HgCdTe crystal, it is relatively difficult to control the carrier polarity and carrier concentration in the crystal during growth, and generally, the amount of Hg in the HgCdTe crystal is controlled by heat treatment in an Hg atmosphere after the growth. I was doing it. Therefore, the device has been produced through the steps of forming a pn junction by ion implantation, forming a surface protective film, and forming an electrode after the step of controlling the carrier concentration.

By the way, the characteristics of the infrared detector using HgCdTe are very sensitive to the type of the surface protective film and the forming method. Regarding the type of film, a CdTe film, which is excellent in surface characteristics and adhesion strength, has been widely used in recent years and has become the mainstream. There are various MBE methods, vapor deposition methods, etc. regarding the forming method, but it is considered that the surface state before the film formation controls the characteristics.

[0005]

In the above-described method for manufacturing an infrared detector, the carrier concentration of the HgCdTe crystal is controlled by heat treatment in an Hg atmosphere after growth, and the surface of the HgCdTe crystal is exposed. ,
The protective film had to be formed in the subsequent process. In the step of forming the protective film, surface treatment such as etching is performed immediately before forming the film, but since the HgCdTe crystal is exposed to the atmosphere even temporarily, it is difficult to sufficiently solve the influence of the surface oxide film. It was This has been considered to be the cause of variation and deterioration of element characteristics.

An object of the present invention is to solve the above problems and to provide a method of manufacturing an infrared detector comprising a photodiode having good surface characteristics.

[0007]

The present invention is a method for manufacturing an infrared detector having at least an HgCdTe layer which serves as an infrared detecting portion and a CdTe layer which serves as a surface protective layer on a substrate, and at least the HgCdTe layer is epitaxially grown. After that, a step of continuously epitaxially growing the CdTe layer for several atomic layers and a step of controlling the carrier concentration of the HgCdTe layer by performing a heat treatment in an Hg atmosphere after that are included.

[0008]

In the method of manufacturing an infrared detector according to the present invention, the CdTe layer that serves as a surface protective film is formed of HgCdT that serves as an infrared detecting section.
Since the epitaxial layer is continuously epitaxially grown at the same time as the e layer, the interface with the CdTe layer, which is the surface of the HgCdTe layer, is in a very clean state without any oxide film or impurities that affect the surface inversion or the surface level. Further, the thickness of the CdTe layer is about 1000 angstrom (hereinafter abbreviated as A) to about 5000 A, whereas it is several atomic layers. Therefore, the heat treatment in the Hg atmosphere causes HgCdTe to grow.
It is also possible to sufficiently control the amount of Hg in the crystal, that is, the carrier concentration.

Here, the lattice constant of CdTe varies depending on the plane, but is 6 to 7 A. Further, the thickness of the CdTe layer in which the effect of the present invention can be confirmed is about 20 atomic layers. Therefore,
If the thickness of the CdTe layer is about 6 to 150 A, the effect of the present invention can be obtained.

[0010]

EXAMPLE A method for manufacturing an infrared detector of the present invention will be specifically described with reference to FIG.

In the crystal growth step shown in FIG. 1 (a),
CdTe buffer layer 2 of 5 μm, H on GaAs substrate 1
gCdTe layer 3 is 10 μm, CdTe protective film 4 is 50 A
Continuously grows by the MBE method. At this time HgCd
As a matter of course, the interface between the Te layer 3 and the CdTe protective film 4 does not have an oxide film, and the interface state due to impurities is small, which is a very normal state. On the other hand, the HgCdTe layer 3 is H
This is a state in which g holes and Hg between lattices are mixed, and the polarity and carrier concentration are not at desired values.

Next, as shown in FIG. 1 (b), the carrier concentration in the HgCdTe layer 3 is controlled by heat treatment in an Hg atmosphere. Since the CdTe protective film 4 is very thin, Hg can be sufficiently taken in and out through the film. Here, the temperature of the region of Sample 5 was set to 315 ° C., and heat treatment was performed for 12 hours to obtain a p-type carrier concentration of 2 × 10 ¹⁶ cm ⁻³ .

Thereafter, as shown in FIG. 1 (c), Cd for insulating the wiring electrodes and the like and for preventing Hg removal from the surface.
After forming the Te insulating film 6, the CdTe insulating film 6 and the like in the portion where the photodiode is formed are partially removed, and a normal process such as pn junction formation by ion implantation and electrode formation is performed to manufacture an infrared detector. .

As described above, according to the method of manufacturing the infrared detector of the present invention, it is possible to perform different processes in which the surface of the HgCdTe layer 3, particularly the portion near the pn junction, is exposed to the atmosphere even once. Therefore, it is possible to obtain an element having excellent surface characteristics without the influence of characteristic deterioration due to the surface oxide film or the like.

In the above description, the crystal growth method,
The substrate material, the film thickness of each layer, the heat treatment conditions, and the steps after FIG. 1C are merely examples, and ZnS or the like may be used instead of the CdTe insulating film 6, and the buffer layer 2 or the like is necessary depending on the properties of the substrate. It may be formed according to Further, there is no problem even if the ion implantation step is introduced before the insulating film forming step.

[0016]

As described above, according to the method of manufacturing an infrared detector of the present invention, it is possible to provide a photodiode having excellent surface characteristics, and to sufficiently contribute to the high performance of the infrared detector. Can be done.

[Brief description of the drawings]

FIG. 1 is a diagram showing a method for manufacturing an infrared detector according to the present invention.

[Explanation of symbols]

 1 GaAs substrate 2 CdTe buffer layer 3 HgCdTe layer 4 CdTe protective film 5 Sample 6 CdTe insulating film

Claims (3)

(57) [Claims] 1. An H which serves as at least an infrared detecting portion on a substrate.
A method for manufacturing an infrared detector having a gCdTe layer and a CdTe layer serving as a surface protective layer, comprising at least the above HgC.
After epitaxially growing the dTe layer, the CdTe
A method for manufacturing an infrared detector, comprising: a step of continuously epitaxially growing a layer for several atomic layers; and a step of controlling the carrier concentration of the HgCdTe layer by subsequently performing heat treatment in an Hg atmosphere. 2. After heat treatment in an Hg atmosphere,
The method for manufacturing an infrared detector according to claim 1, further comprising a step of forming an insulating film on the CdTe layer. 3. The method for manufacturing an infrared detector according to claim 1, wherein the thickness of the CdTe layer is 6 angstroms or more and 150 angstroms or less.