JP2981712B2 - Manufacturing method of semiconductor radiation 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 forming an electrode of a semiconductor radiation detector for detecting radiation based on a current flowing between electrodes. In particular, the present invention relates to the formation of an anode electrode used in medical and industrial nondestructive inspection devices and semiconductor radiation detectors that can be used for measuring environmental radiation.

[0002]

2. Description of the Related Art A semiconductor radiation detector measures a photocurrent generated in a semiconductor due to radiation with an electrode provided on the surface thereof. When a group II-VI compound semiconductor, particularly a compound semiconductor containing CdTe as a main component such as CdTe or CdZnTe, is used, it can operate at room temperature due to a wide band gap, and has a large atomic number of a constituent element. The absorption coefficient of X-ray and γ-ray is large, and high sensitivity can be obtained. Such a detector is used for a monitor of a radiation use facility, a spectrum survey meter, and the like. In addition, detectors can be miniaturized and arrayed, and arrayed detectors have begun to be applied to medical diagnostic equipment, industrial nondestructive inspection devices, and the like.

Conventionally, electrodes of a semiconductor radiation detector using CdTe include Pt formed by electroless plating,
Metal electrodes mainly containing Au or the like have been mainly used. (BTAMckee et al .; Nucl. Instr. And Method,
A272, p.825 (1988)) Further, it has been proposed to use In as an anode electrode in order to reduce dark current. (JP-A-3-248578, MRSquilantte et a
l.; Nucl. Instr. and Method, A283, p.323 (1989)) This makes it possible to increase the electric barrier to holes at the anode electrode and reduce the dark current, and to reduce the voltage applied to the detection element. (Bias voltage) can be increased, so that high carrier collection efficiency and high-speed operation can be achieved.

[0004] Such an In electrode capable of increasing the electrical barrier to holes at the anode electrode is composed of CdT.
The surface of a compound semiconductor such as e is polished, and a work-affected layer generated by the polishing is removed by etching to form a surface by a vacuum evaporation method. Thereafter, it is known that high energy resolution can be obtained even at a low applied voltage by heat-treating the In electrode. This is presumably because In is diffused into the compound semiconductor by the heat treatment and is less affected by the oxide film at the interface.

[0005]

However, according to the above-described manufacturing method, the dark current can be reduced by the heat treatment after the formation of the anode electrode, but the dark current value varies widely. In particular, when the applied voltage was increased, the characteristics of the detection element were unstable. An object of the present invention is to provide an electrode
Heat treated before forming homogenized oxide layer, production of semiconductor radiation detectors obtained a low dark current by increasing an electrical barrier for holes at the anode electrode stable
It provides a method .

[0006]

[MEANS FOR SOLVING THE PROBLEMS] To achieve the above object
Further, the present invention provides a method for manufacturing a semiconductor radiation detector in which an electrode is provided on a surface of a II-VI compound semiconductor, wherein the surface of the II-VI compound semiconductor is purified by etching before forming the electrode, and thereafter, , 100 to 25 on the surface
Heat treatment at 0 ° C. for 5 to 60 minutes
The generated surface oxide is homogenized, and the surface is treated in another way.
The electrode is formed without adding any. Also on
In the electrode forming process, first, the anode electrode is formed
Then, the anode electrode is heated at 150 ° C. to 250 ° C. for 1 minute to 20 minutes.
After the heat treatment for minutes, the cathode electrode is
May be formed. Further, the II-VI group compound
That the material semiconductor contains CdTe as a main component (for example, CdT
e, CdZnTe, etc.). Even better
Further, the formation of the electrode is performed by a method that does not oxidize the surface.
May be performed.

[0007]

The present inventor has studied the variation of the dark current value due to the heat treatment after the formation of the anode electrode. As a result, the thickness and composition of the oxide layer at the interface between the compound semiconductor and the electrode are not uniform. This is considered to be because the heat treatment temperature required for diffusing the elements constituting the electrode into the compound semiconductor is not the same. That is, there is variation in the oxide layer formed by etching the surface of the compound semiconductor, and even when heat treatment is performed after the electrodes are formed, detection characteristics such as dark current are not uniform due to the variation in the oxide layer. In particular, when the voltage applied between the electrodes is high, such a dark current variation becomes remarkable.

Therefore, it has been found that by performing a heat treatment before forming the electrode, the oxide layer can be made uniform and the variation in detection characteristics such as dark current can be reduced. Although the effect of the heat treatment is not clear, it is considered that the heat treatment removes an unstable oxide component in the oxide layer, thereby improving the uniformity. Therefore, according to the present invention, it is easy to manufacture a semiconductor radiation detector with uniform detection characteristics such as dark current and the like, and it is possible to manufacture at a high yield.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A manufacturing process of a CdTe radiation detector according to one embodiment of the present invention will be described below with reference to FIG.

As shown in FIG. 1A, a substrate 1 (15 mm square) made of a chlorine-doped high-resistance CdTe semiconductor single crystal is polished on both sides using alumina abrasive grains to a thickness of 2 mm. The affected layer by polishing is removed by etching using an etching solution such as a bromo-methanol solution. The thickness to be etched is 5 to 5
It is preferable to select an etchant that has a thickness of 50 μm, has no unevenness on the surface, and can form a surface oxide layer as uniform as possible.

The substrate 1 is heat-treated in a vacuum at 200 ° C. for 20 minutes in a resistance heating furnace. Thereby, the surface oxide layer generated by the etching becomes uniform. This heat treatment is 10
The reaction may be performed at 0 ° C. to 250 ° C. for 5 minutes to 60 minutes. Below this range, there is no homogenizing effect, and above this range, the separation and decomposition of the substrate compound components are undesirable. The atmosphere for the heat treatment may be air or an inert atmosphere such as N _2, and only one surface of the substrate 1 may be heat-treated by an infrared lamp or the like.

As shown in FIG. 1B, indium (I) having a thickness of 150 nm is formed on one surface of the substrate 1 by a vacuum evaporation method.
n) A metal layer is formed as the anode electrode 2. As a metal constituting the anode electrode 2, a metal element having a high electric barrier to holes, such as gallium (Ga) or aluminum (Al), can be used. As a forming method, it is preferable to use a forming method such as a vacuum evaporation method that hardly generates an oxide at the interface with the substrate 1, and a plating method or the like is not preferable because an oxide or the like is newly formed at the interface.
After the formation of the anode electrode 2, a heat treatment (150 ° C.
２５０250 ° C., 1 minute to 20 minutes).

Then, as shown in FIG. 1C, the other main surface of the substrate 1 facing the anode electrode 2 is immersed in an aqueous solution of chloroplatinic acid (hexachloroplatinic (IV) acid, 2 g / l). The cathode electrode 3 made of platinum (Pt) having a thickness of 100 nm is formed by an electroless plating method. As the cathode electrode 3, gold (Au) or the like can be used.
As a forming method, it is desirable to use an electroless plating method such as a displacement plating method since a leak current can be reduced. Note that when the cathode electrode 3 is heat-treated, the electrical barrier against electrons may be reduced, so the anode electrode 2 is formed first.

Thereafter, as shown in FIG. 1D, the substrate 1 including the anode electrode 2 and the cathode electrode 3 is cut into a 2 mm square by a dicing saw to complete the radiation detecting element 4. This radiation detecting element 4 was evaluated by the radiation measuring circuit shown in FIG. This evaluation circuit includes a bias power supply 5
, A bias voltage up to 1000 V is applied to the radiation detecting element 4, and a current flowing in proportion to the incident X-ray dose is measured by the ammeter 6.

The current when the radiation detecting element 4 was not irradiated with X-rays was measured as a dark current. The results are shown in FIG. Also, the results of measurement of the radiation detecting element manufactured in the same manner as in the example except that the heat treatment before the formation of the anode electrode after the etching of the substrate 1 is not performed are also shown by using ● as a comparative example. As is clear from this figure, the dark current is smaller in this embodiment than in the comparative example, and the applied voltage is 100 V or more (the electric field in the semiconductor is 50 V / mm or more).
In particular, the dark current has decreased. In addition, when X-rays were incident on both the examples and comparative examples, the current increased in proportion to the dose. Further, a radiation detection element was repeatedly manufactured and evaluated in the same manner as in the example, and almost the same detection characteristics were stably obtained. As described above, according to this embodiment, the dark current can be reduced and the radiation can be increased to a high S / N ratio.
It can be seen that a CdTe radiation detector that can be measured by the ratio can be manufactured with good reproducibility.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view for explaining a manufacturing process of a CdTe radiation detector according to the present embodiment.

FIG. 2 is a radiation measurement circuit using a CdTe radiation detector.

FIG. 3 is a characteristic diagram showing dark current according to an example and a comparative example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate (semiconductor) 2 Anode electrode 3 Cathode electrode 4 Radiation detection element 5 Bias power supply 6 Ammeter

Claims (4)

(57) [Claims] 1. A method of manufacturing a semiconductor radiation detector in which an electrode is provided on a surface of a group II-VI compound semiconductor, wherein the surface of the group II-VI compound semiconductor is purified by etching before forming the electrode , and thereafter, 5 minutes to 60 minutes at 100 ° C to 250 ° C on the surface
Oxidation caused by the above-mentioned etching after heat treatment
Homogenize the material and without any other treatment on the surface
A method for manufacturing a semiconductor radiation detector, comprising forming an electrode . (2) In the electrode forming process, first,
A cathode electrode is formed on the anode electrode at 150 ° C. to 250 ° C.
After a heat treatment for 1 to 20 minutes at
2. The method according to claim 1, wherein the step is performed without any processing.
Of manufacturing a semiconductor radiation detector. 3. A process according to claim 1 or claim 2 wherein the Group II-VI compound semiconductor is characterized in that a main component CdTe
The method of manufacturing a semiconductor radiation detector according to. Formation of claim 4 wherein said electrodes, claims 1, characterized in that it is performed by a method which does not oxidize the surface
Item 4. A method for manufacturing a semiconductor radiation detector according to Item 3 .