JP2697674B2 - Manufacturing method of photoconductive infrared detecting element - 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 a photoconductive infrared detector.

[0002]

2. Description of the Related Art Heretofore, this type of photoconductive infrared detecting element has a photoelectric conversion of an infrared ray incident on a light receiving region provided in a semiconductor crystal such as a HgCdTe crystal to generate a carrier. Is detected by electrodes provided at both ends of the semiconductor crystal.

[0003] In order to improve the sensitivity of this type of photoconductive infrared detecting element, it is necessary to suppress the recombination of carriers generated by photoelectric conversion before reaching the electrodes. The rate of carrier recombination is determined mainly by the properties of the semiconductor crystal, such as carrier concentration and carrier mobility, inside the semiconductor crystal, but the carrier recombination occurs on the surface and side walls of the semiconductor crystal due to strain generated during polishing and processing. Bonding is promoted. Therefore, the sensitivity of the photoconductive infrared detection element depends on the carrier recombination speed around the light receiving region (front surface, back surface, and side wall) provided in the semiconductor crystal, that is, the carrier lifetime.

Therefore, in order to suppress recombination of carriers around the semiconductor crystal, a film having a positive fixed charge called an anodic oxide film is usually formed on the front and back surfaces of the semiconductor crystal to separate electrons and holes. , To improve carrier life. Hereinafter, a conventional method of manufacturing this type of photoconductive infrared detecting element will be described with reference to FIGS. This type of photoconductive infrared detector is generally manufactured by the following procedure. (1) After polishing and etching one surface of a semiconductor crystal (HgCdTe crystal) 4, an anodic oxide film 3 is formed on the etched surface (see FIG. 6). (2) The surface (back surface) on which the anodic oxide film 3 is formed is bonded to a support substrate 1 such as sapphire with an epoxy adhesive 2 (see FIG. 6). (3) The exposed surface (surface) of the semiconductor crystal (HgCdTe crystal) 4 is polished and etched to form an anodic oxide film 8 (see FIG. 7). (4) Electrodes 5 of Au / Cr, for example, at both ends of semiconductor crystal 4
Is formed (see FIG. 8). (5) The semiconductor crystal 4 and the electrode 5 are processed into a device shape by using ion milling or sputtering (see FIG. 9).

In the photoconductive infrared detecting element manufactured by the above-described method, the anodic oxide film is formed on the front surface and the back surface of the light receiving region, but the side wall of the light receiving region remains processed in the above step (5). In this state, the processed surface is exposed, so that no anodic oxide film is formed, and recombination of carriers is promoted on the side wall of the light receiving region. The effect of the recombination of carriers on the side wall of the light receiving region becomes more noticeable as the shape (particularly, width) of the element becomes smaller.

[0006]

The above problem can be solved by forming an anodic oxide film also on the side wall of the light receiving region. For this purpose, it is necessary to perform anodic oxidation after the processing step (5). There is. However, after the step (5), a metal film serving as an electrode is formed in a portion other than the light receiving region of the semiconductor crystal. Depending on the type of metal, the dissolution of the electrode or the oxygen foaming reaction occurs actively, and a sufficient current is not supplied to the semiconductor crystal side. Therefore, there is a problem that a good anodic oxide film cannot be formed on the semiconductor crystal.

In order to avoid the above-mentioned problem, it is necessary to select a metal having such a property that the electrode dissolution or oxygen generation reaction does not occur in the anodic oxidation solution and the anodic oxidation reaction proceeds as the metal film to be the electrode. Further, since the infrared detection element needs to be electrically connected to the package through a metal film serving as an electrode, the metal film must be capable of easily performing wire bonding.

As metals satisfying these conditions, In,
There are metals such as Ti and Al. Among them, In and Al are described below in JP-A-61-251167. According to this, when In is used as the metal film to be an electrode, the current of anodic oxidation mainly flows to the In electrode side because the oxide film of In is conductive, and it takes an extremely long time to anodize the HgCdTe layer, Dissolution of the photoresist film formed on the electrode surface causes contamination. Therefore, the upper part of the In electrode is covered with an insulating film of Al to prevent the In from coming into contact with the anodic oxide solution. Although the composition of the anodizing liquid not disclosed in this application specification, 0.1M KOH-90% ethylene glycol + 10% H ₂ O solution is used as the anodizing solution of normal HgCdTe crystals. In this electrolyte, 5 μA / mm ² was applied to both the HgCdTe crystal and the In electrode.
When a direct current of a certain level is supplied, the reaction at the In electrode is predominantly performed as described in the above specification, but the chemical reaction in the electrolytic solution is only the state of the electrolytic solution (composition, pH, liquid temperature, etc.). However, it also changes depending on the conditions of the applied current. Therefore, it is possible to form a good anodic oxide film on the HgCdTe crystal by performing anodic oxidation under conditions that suppress the dissolution of In and the oxygen generation reaction.

[0009] Further, the specification states that the surface of In is coated with Al. However, unlike a metal such as Al, the deposited film of In has a remarkable unevenness on the surface.
It is difficult to completely cover In even if an Al film having a thickness of about a degree is formed, so that HgCdT
It is difficult to form a good anodic oxide film on the e layer,
Further, if the Al film is too thick, there is a problem that a problem occurs in wire bonding.

An object of the present invention is to provide a method for manufacturing a photoconductive infrared detecting element which can solve the above-mentioned problems and can prevent a decrease in sensitivity due to recombination of carriers on the side of the element. It is.

[0011]

According to the present invention, a step of forming a metal film serving as an electrode on a HgCdTe crystal fixed to a support substrate, and processing the HgCdTe crystal and the metal film by ion milling or sputtering. The process of
In the method for manufacturing a photoconductive infrared detecting element having a step of forming an anodic oxide film on an exposed portion of the HgCdTe crystal, the metal film is made of In / Ti, and the HgC
A method for producing a photoconductive infrared detecting element, characterized in that a pulse-like voltage is applied to a dTe crystal and the metal film in an electrolytic solution composed of KOH to form an anodic oxide film on the surface and side walls of the HgCdTe crystal. can get.

Further, according to the present invention, the metal film is formed of I
n, whereby a method for producing a photoconductive infrared detecting element, wherein n is obtained.

Further, according to the present invention, as the electrolyte,
Using a 0.01-0.1 M KOH-90% ethylene glycol + 10% H ₂ O solution, the applied pulse has a peak / peak voltage of 10 to 15 V and a repetition frequency of 5
A method for manufacturing a photoconductive infrared detecting element, characterized in that the photoconductive infrared detecting element has a duty ratio of 00 to 2 kHz and a duty ratio of 5 to 20%.

[0014]

A pulse is applied under the above-described conditions to generate HgCdTe.
When the crystal and the In or In / Ti electrode are simultaneously anodized, a current is supplied to both the HgCdTe crystal and the electrode at the rising state of the pulse, and an anodic oxide film is formed on both of them. After that, the reaction of the electrode becomes dominant and the anodizing current is consumed only by the electrode. When the pulse is at a low level, that is, at the same potential as the electrolyte, the positive reaction stops and the OH ^- ions diffuse into the vicinity of the HgCdTe crystal and the electrode.
By repeating this operation, the thickness of the anodic oxide film on the HgCdTe crystal side gradually increases, and the formation of the anodic oxide film having a predetermined thickness is completed in about 10 minutes from the application of the pulse.

[0015]

An embodiment of the present invention will be described below with reference to the drawings. 1 to 4 are a plan view and a sectional view showing a manufacturing process of a photoconductive infrared detecting element according to an embodiment of the present invention. FIG. FIG. 6 is a diagram showing a change over time of an applied pulse and an anodizing current in FIG.

First, as shown in FIG. 1, for example, HgCdT
After polishing and etching one surface (back surface) of e-crystal 4,
0.1M KOH-90% ethylene glycol + 10%
An anodic oxide film 3 is formed in an H ₂ O solution. At this time, since the material other than HgCdTe is not mixed in the anodic oxidation, the plating current may be DC or pulse.
When anodic oxidation is performed by supplying a DC current of A / mm ² until the potential becomes 14 V, an anodic oxide film 3 having a thickness of about 700 A is formed. After the formation of the anodic oxide film 3, the support substrate 1 made of, for example, sapphire is bonded to the surface with an epoxy adhesive 2.

Next, after polishing and etching the HgCdTe crystal 4 to a thickness of about 10 μm, a resist pattern is formed on a portion of the HgCdTe crystal 4 which becomes the light receiving region 6 as shown in FIG. Is deposited by 1-2 μm or In (1-2 μm) / Ti (several 100 A). After the deposition, the sample is immersed in an organic solvent such as acetone to dissolve the resist pattern, and at the same time, the deposited film on the light receiving region 6 is lifted off to form the electrode 5.

Next, as shown in FIG. 3, after forming a resist pattern for processing the HgCdTe crystal 4 and the electrode 5 into a final shape, the HgCdTe crystal 4 and the electrode 5 are formed using an HgCdTe crystal using an ion milling apparatus.
The dTe crystal 4 and the electrode 5 are etched. After the etching, the resist pattern is removed, and the HgCdTe crystal 4 and the electrode 5 are immersed in the anodic oxidizing solution together with the counter electrode in a mixed state. At this time, the anodic oxidation solution is used in an amount of 0.01 to 0.1.
1M KOH-90% ethylene glycol + 10% H ₂
Using an O solution, the HgCdTe crystal 4 and the electrode 5 side are +,
The connection is made so that the counter electrode becomes negative, and a pulse voltage as shown in FIG. 5 is applied. The pulse conditions are set such that the low level is the same potential as the electrolytic solution, the high level is 14 V, the pulse repetition frequency is 2 kHz, and the duty ratio is 20%. Here, the peak / peak voltage of the pulse affects the reaction of the electrode 5 in the anodic oxidation solution. For example, if the voltage is too high, the electrode 5 is dissolved and oxygen is generated, and if the voltage is too low, HgCdTe is generated.
An anodized film having a predetermined thickness cannot be formed on crystal 4. The pulse frequency and duty ratio are HgCd
The current to be distributed to the Te crystal 4 side is determined. For example, if the frequency is small and the duty ratio is large, the DC component of the pulse increases, and the current selectively flows to the electrode 5 side, and the distribution to the HgCdTe crystal 4 side decreases. Therefore, when these parameters and the above-mentioned materials and solutions are used, the peak / peak voltage of the pulse is 10 to 15 V, and the pulse repetition frequency is 500.
The appropriate range is ２2 kHz and the duty ratio is 5-20%.

Next, the anodic oxidation reaction between the HgCdTe crystal 4 and the electrode 5 when a pulse is applied will be discussed with reference to FIG. First, in the rising state of the pulse,
Since voltage is instantaneously applied to the sample, the anodic oxidation reaction
HgCdTe crystal 4 and electrode 5
Current is supplied to both of them, the anodic oxidation reaction proceeds, and HgC
An insulating oxide film is formed on the dTe crystal 4 and a conductive oxide film is formed on the electrode 5. However, with the passage of time, the potential of the reaction is as high as when a direct current is applied, that is, the reaction on the side of the HgCdTe crystal 4 on which the insulating oxide film is formed becomes difficult to occur, so that the current drops to a certain level, Thereafter, the reaction proceeds only with the electrode 5. Next, when the pulse is at a low level, that is, at the same potential as the electrolytic solution, the positive reaction is stopped and OH ^- ions are diffused to the vicinity of the HgCdTe crystal 4 and the electrode 5. By repeating this operation, the thickness of the anodic oxide film on the HgCdTe crystal 4 side gradually increases, and as shown in FIG. Formed on the side wall and surface of the substrate. Next, a protective film such as ZnS is formed on a portion other than the bonding pad of the electrode 5 to complete the infrared detecting element.

[0020]

As described above, in the method of manufacturing the photoconductive infrared detecting element of the present invention, in the anodizing step, the peak / peak voltage is 10 to 15 V, the repetition frequency is 500 to 2 kHz, and the duty ratio is 5 When a pulse is applied to both the HgCdTe crystal 4 and the electrode 5 made of In or In / Ti under the condition of ２０20%, a voltage is instantaneously applied in a rising state of the pulse, and a current is applied to the HgCdTe crystal 4 simultaneously with the electrode 5. Since it is supplied, if the anodic oxidation is performed for a predetermined time, the light receiving region 6 of the HgCdTe crystal 4
An anodic oxide film having a predetermined thickness can be formed on the front surface 8 and the side surface 7. Therefore, it is possible to prevent a decrease in sensitivity due to the recombination of carriers on the side surface of the device, which is a problem in the conventional device.

[Brief description of the drawings]

FIG. 1A is a process drawing for explaining a method of manufacturing a photoconductive infrared device according to the present invention, and FIG.
3 is a sectional view taken along line AA ′ of FIG.

FIG. 2 (a) is a process diagram for explaining a method of manufacturing a photoconductive infrared device according to the present invention, and (b) is a diagram showing (a).
3 is a sectional view taken along line AA ′ of FIG.

FIG. 3 (a) is a process diagram for explaining a method of manufacturing a photoconductive infrared device according to the present invention, and (b) is a diagram showing (a).
3 is a sectional view taken along line AA ′ of FIG.

FIG. 4 is a cross-sectional view showing the structure of the photoconductive infrared device after the steps shown in FIGS. 1 to 3 are completed.

FIG. 5 is a diagram showing a temporal change of an applied pulse and an anodic oxidation current at the time of forming an anodic oxide film.

FIG. 6A is a process diagram for explaining a conventional method for manufacturing a photoconductive infrared device, and FIG. 6B is a process diagram of A- in FIG.
It is A 'line sectional drawing.

FIG. 7 is a process chart for explaining a conventional method of manufacturing a photoconductive infrared device.

FIG. 8A is a process drawing for explaining a conventional method for manufacturing a photoconductive infrared device, and FIG.
It is A 'line sectional drawing.

FIG. 9 (a) is a process diagram for explaining a conventional method of manufacturing a photoconductive infrared device, and FIG. 9 (b) is a process diagram of FIG.
It is A 'line sectional drawing.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Support substrate 2 Adhesive 3,7,8 Anodized film 4 HgCdTe crystal 5 Electrode 6 Light receiving area

Claims (3)

(57) [Claims] A step of forming a metal film serving as an electrode on the HgCdTe crystal fixed to a supporting substrate;
In a method of manufacturing a photoconductive infrared detecting element, the method includes a step of processing a Te crystal and the metal film by ion milling or sputtering, and a step of forming an anodic oxide film on an exposed portion of the HgCdTe crystal. In /
Ti, and KOH is added to the HgCdTe crystal and the metal film.
A pulse-like voltage is applied in the electrolytic solution consisting of
A method for manufacturing a photoconductive infrared detecting element, comprising forming an anodic oxide film on the surface and side walls of a CdTe crystal. 2. The method according to claim 1, wherein the metal film is In. 3. An electrolytic solution comprising 0.01 to 0.1 MK.
OH-90% ethylene glycol + 10% H ₂ O solution, and a peak / peak voltage of 10
3. The method for manufacturing a photoconductive infrared detecting element according to claim 1, wherein the repetition frequency is 500 to 2 kHz and the duty ratio is 5 to 20%.