JPH09260717A - Manufacture of photodiode - Google Patents

Abstract

PROBLEM TO BE SOLVED: To lessen leakage current of a diode, by forming and heat-treating a first and a second protective films and then removing the surface of an HgCdTe layer and the first and the second protective films, by etching. SOLUTION: The surface 12a of a p-type HgCdTe layer 12 grown on a CdZnTe substrate 11 is etched. Then, a first protective film, for example, a ZnS film, is formed. Next, B+ ions 14 are implanted into the p-type HgCdTe layer 12 through resist 15 to selectively form n-type regions 16. After that, the resist 15 is removed. Furthermore, a second protective film 17, for example, a ZnS film, is formed and heat-treated. Then, the first and the second protective films 13, 17 are removed by using hydrochloric acid, and then the entire surface of the HgCdTe layer is etched. After that, a third protective film 18, for example, a ZnS film, is selectively formed, and then a metal electrode 19 is selectively formed. A photodiode is thus manufactured.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a photodiode using HgCdTe.

[0002]

2. Description of the Related Art The bandgap Eg of Hg _1-x Cd _x Te changes from 0 to 1.6 eV depending on the value of the composition x, and when the composition x is around 0.2, the bandgap Eg is about 0.1 e.
V is effective for detecting infrared rays in the 10 μm band and is used as a photodiode. A conventional method of manufacturing a photodiode using HgCdTe will be described with reference to the schematic cross-sectional view of process steps shown in FIG.

For example, HgCd is formed on a CdZnTe substrate 21.
Te22 is used for liquid phase crystal growth, and then a p-type wafer that has been heat-treated in a mercury atmosphere to have an appropriate carrier concentration is used, and its surface 22a is etched with, for example, a Br methanol solution (FIG. 3A). ).

Thereafter, for example, B ⁺ ions 24 are implanted through the resist 23 under the conditions of 150 KeV and 1 × 10 ¹⁴ cm ^-2 to selectively form an n-type region 25 (FIG. 3B).
The resist 23 is removed. In this case, the ion is about 200n
Implanted to a depth of m.

Next, a protective film 26 and an electrode 27 are selectively formed to complete a photodiode sensitive to infrared rays (FIG. 3 (c)).

[0006]

A pn with a small leak current (dark current) is used to manufacture a highly sensitive photodiode.
It is important to make a bond. There are various causes of the leak current, but the leak current near the surface of HgCdTe is often the cause.

The commonly used p-type HgCdTe substrate has various electrically active impurities in addition to the p-type acceptor (generally called mercury vacancies), and the HgCdTe surface has Inevitably, there are crystal defects. Further, HgCdTe is thermally and chemically unstable such as being deteriorated by heating at about 150 ° C. and mechanically weak. For this reason, the various impurities described above diffuse and accumulate in the defects near the surface in various modes, resulting in an abnormal carrier concentration distribution near the surface.

Further, in the n-type layer formed by the ion implantation, a large amount of crystal defects are generated together with the implanted donors, so that the carrier concentration distribution becomes more complicated than that in the unimplanted region. For example, in the case of HgCdTe, the carrier concentration distribution is different from the ion implantation profile, and a donor, which is one of the crystal defects generated by ion implantation, is added and the ion arrival depth is about 2
The carrier concentration in the vicinity of the surface is often more than 10 times the ion implantation profile and deeper than 00 nm to 1 μm or more.

This is because some of the defects due to ion implantation reach as deep as carriers as deep as the implantation profile, and the various impurities accumulate in the defect layer due to ion implantation in various modes.

Abnormal carrier concentration distribution near the surface is Hg
In the case of CdTe, unlike a normal semiconductor, it is not a problem that the abnormal region disappears only by etching. After the removal by etching, the various impurities may be newly diffused and accumulated in the HgCdTe layer in various modes by, for example, a device manufacturing process, and an abnormal carrier concentration distribution may occur again near the surface.

In addition, this abnormal carrier concentration distribution is often different within and between wafers. This cause is H
This is because various electrically active impurities contained in gCdTe, particularly easily diffusible impurities, are diffused and accumulated in the vicinity of the surface due to interaction with crystal defects.

When the carrier concentration distribution abnormal layer is present on the surface of HgCdTe as described above, in a photodiode using a pn junction formed by implanting B ⁺ ions, a leak current near the surface is increased and infrared light is emitted. The S / N ratio with the current signal due to is decreased. Therefore, it becomes difficult to obtain uniform and highly sensitive characteristics.

The present invention solves the above-mentioned drawbacks, and an object of the present invention is to provide a method of manufacturing a photodiode using HgCdTe with a small leak current.

[0014]

In order to achieve the above object, the present invention provides a step of forming a first protective film on a substrate having a p-type HgCdTe layer, and a step of forming the first protective film on the substrate. A step of selectively implanting ions, a step of forming a second protective film on the first protective film, a step of heat-treating the substrate on which the second protective film is formed, A step of removing a second protective film and a surface portion of the substrate on which ions have been implanted; a step of selectively forming a third protective film on the substrate from which the surface portion has been removed; And a step of selectively forming an electrode metal.

Further, the first, second and third protective films are made of ZnS. Further, at least one of the first, second and third protective films is ZnS.

The first, second and third protective films are anodic sulfide films.

Further, at least one of the first, second and third protective films is an anodic sulfide film.

Further, the first protective film is formed with a thickness of 20 nm to 5 nm.
It is characterized by being formed to a thickness of 0 nm.

Further, the ion implantation is carried out by using B ⁺ ions of 30.
It is characterized in that the implantation is performed with an energy of KeV to 300 KeV.

Further, the second protective film is 50 nm to 5 nm.
It is characterized in that it is formed to a thickness of 00 nm.

The heat treatment is performed at 90 ° C. to 130 ° C.

The surface layer removal depth of the substrate is 5
It is characterized by being 0 nm to 200 nm.

Further, the third protective film is formed to have a thickness of 200 nm to 500 nm.

The action is p by selective ion implantation.
Before forming the n-junction, a first protective film is formed to diffuse and accumulate a part of various impurities, particularly impurities that are easily diffused, from HgCdTe in the vicinity of the surfaces of the first protective film and HgCdTe. In addition, HgC including them in a part of the ion implantation layer
HgCdT by removing with dTe surface area
The various impurities in e are removed.

The thickness of the first protective film is preferably about 1/10 to 1/2 of the depth of ion implantation. 1 /
When the thickness is less than 10, the effect of accumulating impurities is small, and 1
This is because if it exceeds / 2, the substantial amount of ion implantation is reduced.

Further, the effect of accumulating the impurities is further enhanced by forming a second protective film after ion implantation on the first protective film and performing heat treatment at 90 ° C. to 130 ° C.

The second protective film is preferably 50 nm to 500 nm. This is because if it is less than 50 nm, the effect of accumulating impurities is small, and if it exceeds 500 nm, the effect of accumulating impurities tends to be saturated.

If the treatment temperature is lower than 90 ° C., the heat treatment effect is small, and if it exceeds 130 ° C., HgCdTe is likely to be deteriorated. Therefore, the range of 90 to 130 ° C. is desirable.

The depth at which the HgCdTe surface is removed is preferably greater than the depth at which the implanted ions reach. This is because in the ion-implanted region, abnormalities in carrier concentration distribution are significant due to defects due to implantation and the effect of impurity accumulation.

Thus, according to the method of the present invention, HgCd
The abnormal carrier concentration distribution layer of the HgCdTe layer including the Te surface is eliminated, and a photodiode with a small leak current can be obtained.

[0031]

BEST MODE FOR CARRYING OUT THE INVENTION Manufacturing of a photodiode according to an embodiment of the present invention will be described below with reference to the drawings.
1 and 2 are schematic cross-sectional views for explaining the manufacturing process of the photodiode of the present invention in process order.

CdZnTe substrate 11 as shown in FIG.
P-type Hg with a carrier concentration of 1 × 10 ¹⁶ cm ^-3 grown on top
The surface 12a of the CdTe layer 12 is etched by Br methanol solution to about 2 μm.

Next, as shown in FIG. 1B, a ZnS film having a thickness of 20 nm is formed as the first protective film 13.

Next, as shown in FIG. 1C, B ⁺ ion 1
4, acceleration voltage 150 KeV, dose amount 1 × 10 ¹⁴ cm ^-2
40 μm × 40 μ through the resist 15 under the conditions of
It is implanted into an area of m to selectively form an n region 16. After that, the resist 15 is removed.

Further, as shown in FIG. 2A, a ZnS film, for example, having a thickness of 200 nm is formed as the second protective film 17, and 12
Heat treatment is performed at 0 ° C. for 1 hour.

Next, as shown in FIG. 2B, the first and second protective films 13 and 17 are removed with hydrochloric acid, and HgCd is added.
The entire surface of Te is etched with Br methanol solution to about 100 nm.

Then, as shown in FIG. 2C, a third protective film 18, for example, ZnS is selectively formed to a thickness of 300 nm, and then a metal electrode 19 is selectively formed to manufacture a photodiode. To do.

As described above, according to the photodiode manufacturing method of the present invention, a pn junction with a small leak current can be formed, and a highly sensitive HgCdTe photodiode can be manufactured. Here, the leak current is represented by, for example, a current when a negative bias voltage of −50 mV is applied at a liquid nitrogen temperature.

In the photodiode manufactured by the conventional manufacturing method, the leak current is 5.0 μA on average and the standard deviation is 4.5 μA.
(100 in total). On the other hand, in the photodiode of the present invention, the leak current has an average of 0.2 μA and a standard deviation of 0.05 μA. That is, since the leak current was reduced to 1/25, the infrared detection sensitivity was increased 25 times, and the uniformity was also improved.

This is the formation of the first protective film before ion implantation,
This is because the abnormal carrier concentration distribution in the vicinity of the HgCdTe surface disappeared by forming the second protective film after the ion implantation, heat treatment, and etching the surface of the HgCdTe including the protective film.

Further, in the pn junction, there are many implantation damages,
This is because the surface layer in which the carrier concentration distribution abnormality of the ion-implanted layer in which the impurities are more diffused and accumulated is more remarkable is removed.

In the above embodiment, the first, second and third protective films were made of ZnS. However, similar results were obtained with other anodic sulfide films. The heat treatment condition was 120 ° C. for 1 hour, but similar results were obtained between 90 ° C. and 130 ° C. It was also found that the HgCdTe including the ion-implanted layer after the heat treatment can be etched to a depth of ion penetration to form a pn junction with excellent characteristics. This is because in the formation of a pn junction by ion implantation, a donor, which is a type of ion implantation defect, is formed up to the ion penetration depth or more.

[0043]

According to the present invention, H having a small leakage current is used.
A method of manufacturing a photodiode using gCdTe can be realized.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a photodiode of the present invention in the order of steps.

FIG. 2 is a sectional view showing a photodiode of the present invention in the order of steps.

FIG. 3 is a cross-sectional view showing a conventional photodiode in the order of steps.

[Explanation of symbols]

 11, 21 ... CdZnTe substrate 12, 22 ... HgCdTe layer 12a, 22a ... HgCdTe layer surface 13 ... First protective film 14, 24 ... Implanted ion 15 ... Resist 16, 25 ... Ion-implanted n-type layer 17 ... Second Protective film 18 ... Third protective film 19, 27 ... Metal electrode 23 ... Resist 26 ... Protective film

Claims (11)

[Claims] 1. A step of forming a first protective film on a substrate having a p-type HgCdTe layer; a step of selectively ion-implanting the first protective film onto the substrate; Forming a second protective film on the protective film, heat treating the substrate on which the second protective film is formed, the first and second protective films and the ion-implanted substrate. The step of removing a surface portion of the substrate, the step of selectively forming a third protective film on the substrate from which the surface portion has been removed, and the step of selectively forming an electrode metal on the substrate. And a method for manufacturing a photodiode. 2. The first, second and third protective films are Z
The method for manufacturing a photodiode according to claim 1, wherein the photodiode is nS. 3. The method of manufacturing a photodiode according to claim 1, wherein at least one of the first, second and third protective films is ZnS. 4. The method of manufacturing a photodiode according to claim 1, wherein the first, second and third protective films are anodic sulfide films. 5. The method of manufacturing a photodiode according to claim 1, wherein at least one of the first, second and third protective films is an anodic sulfide film. 6. The first protective film is 20 nm to 50 n
The method of manufacturing a photodiode according to claim 1, wherein the photodiode is formed to a thickness of m. 7. The ion implantation is 30 Ke of B ⁺ ions.
The method of manufacturing a photodiode according to claim 1, wherein the implantation is performed with an energy of V to 300 KeV. 8. The second protective film is 50 nm to 500 nm thick.
The method for manufacturing a photodiode according to claim 1, wherein the photodiode is formed to have a thickness of nm. 9. The method of manufacturing a photodiode according to claim 1, wherein the heat treatment is performed at 90 ° C. to 130 ° C. 10. The removal depth of the surface layer of the substrate is 50.
The method for manufacturing a photodiode according to claim 1, wherein the thickness is from 200 nm to 200 nm. 11. The third protective film is formed in a thickness of 200 nm to 5 nm.
The method for manufacturing a photodiode according to claim 1, wherein the photodiode is formed to a thickness of 00 nm.