JPH06112515A - Semiconductor radiation detector and its manufacture - Google Patents

Abstract

PURPOSE:To obtain such a structure that can connect the surface of an anode electrode without deteriorating the characteristics of a detecting element by constituting a conductive part which connects the anode electrode to external wiring of such a material that does not lower the height of the electric barrier of the anode electrode against holes. CONSTITUTION:The title detector has a compound semiconductor 1 which is sensitive to radiation, cathode electrode 2 formed on one main surface of the semiconductor 1, anode electrode 3 formed on the other main surface of the semiconductor 1 facing the main surface on which the electrode 2 is formed, and conductive part 6 which connects the electrode 3 to external wiring 5. The part 6 is constituted of such a material that does not lower the height of the electric barrier of the electrode 3 against holes. For example, a cathode electrode 2 made of Pt and anode electrode 3 made of In are formed on a substrate 1 made of a CdTe semiconductor single crystal and the electrode 3 is connected to wiring 5 made of an Ag/Pd film through an In-Sn alloy 6.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure for connecting an anode electrode of a semiconductor radiation detector and a manufacturing method thereof.

[0002]

2. Description of the Related Art A semiconductor radiation detector measures a photocurrent generated in a semiconductor due to radiation by an electrode provided on its surface. When a compound semiconductor such as CdTe or HgI ₂ is used, it can operate at room temperature because of its wide bandgap, and has a large absorption coefficient for X-rays and γ-rays because of its large atomic number of constituent elements, resulting in high sensitivity. can get. Such detectors are used for monitors of radiation facilities, spectrum survey meters, and the like.
Further, the detectors can be downsized and arrayed, and the arrayed detectors are beginning to be applied to medical diagnostic equipment, industrial nondestructive inspection devices, and the like.

Conventionally, as electrodes of a semiconductor radiation detector using CdTe, Pt formed by electroless plating,
A metal electrode containing Au or the like as a main component has been mainly used. Recently, the present inventor has increased the withstand voltage of a detection element, and in order to improve response speed, detection efficiency, and energy resolution
It has been proposed to use a metal that has a high electric barrier against holes for the anode electrode. Such an anode electrode exhibits a barrier height of more than 0.5 eV, and the In, G
It is composed of a metal such as a and Al. The height of the barrier of the metal electrode of Pt, Au, or the like, which has been conventionally used by electroless plating, is 0.5 eV or less.

In a semiconductor radiation detector using CdTe, the crystal structure that causes the semiconductor portion to be in a high temperature state of 250 ° C. or higher is deteriorated and the detection characteristics are deteriorated. It used a conductive adhesive called silver epoxy that can be used. Such a conductive adhesive obtains conductivity by dispersing conductive particles such as fine silver particles in an insulating adhesive such as an epoxy resin.

[0005]

However, when a metal showing a high electric barrier against holes is used for the anode electrode,
It has been found that when a conductive adhesive such as silver epoxy is used for fixing to a substrate such as a wiring board via the electrode surface, dark current increases and characteristics such as detection efficiency and energy resolution deteriorate.

An object of the present invention is to provide a structure and a connecting method capable of connecting the anode electrode surface without deteriorating the characteristics of the detecting element.

[0007]

The inventor of the present invention has studied in detail the deterioration of the characteristics of such a detecting element.
It has been found that the metal component contained in the conductive adhesive such as silver epoxy diffuses into the metal layer forming the anode electrode, which lowers the electrical barrier against holes and deteriorates.

The present invention is based on such knowledge, and the structure of the semiconductor radiation detector according to the present invention is (a)
A compound semiconductor sensitive to radiation, (b) a cathode electrode provided on one main surface of the compound semiconductor, and (c) an anode provided on another main surface of the compound semiconductor facing the one main surface. An electrode; and (d) a conductive portion that connects the anode electrode to an external wiring, and (e) the conductive portion is made of a material that does not lower the height of an electrical barrier against holes in the anode electrode. . As a compound semiconductor, C
It is desirable to use a crystalline material containing dTe or CdTe as a main component (for example, CdZnTe). The conductive portion may be a material having conductivity by dispersing metal particles in a metal layer or an insulator. As a material that lowers the height of the electrical barrier against holes in the anode electrode, A
Elements such as g, Au, Cu, P and Sb may be mentioned.

The method of manufacturing a semiconductor radiation detector according to the present invention comprises (a) a step of forming a cathode electrode on one main surface of a compound semiconductor sensitive to radiation, and (b) an anode electrode for holes. Softening a material capable of obtaining a high electric barrier, and connecting it to the other main surface of the compound semiconductor facing the one main surface. The anode electrode may be formed in advance before the step of connecting. Although it may be melted when it is softened, it is preferably heated to a temperature below the temperature at which the compound semiconductor deteriorates.

[0010]

According to the present invention, since the anode electrode is connected to the external wiring by the metal made of the material that does not lower the height of the electric barrier against holes in the anode electrode, Connection can be performed while maintaining a high electrical barrier, and carrier injection can be prevented. In addition, since the anode electrode is connected by softening the material that does not lower the height of the electric barrier against holes in the anode electrode, the anode electrode can be surely connected while maintaining a high electric barrier against holes. it can.

Therefore, the electrode surfaces can be connected without deteriorating the characteristics of the semiconductor radiation detector, and the deterioration of the characteristics due to environmental changes can be reduced.

[0012]

EXAMPLE A manufacturing process of a CdTe radiation detector which is an example of the present invention will be described below with reference to FIGS.

As shown in FIG. 1, the chlorine doped high resistance C
Substrate 1 made of dTe semiconductor single crystal (thickness: 2 mm, width:
After polishing and etching both facing main surfaces of a 2 mm cube, platinum (P
t, thickness: 100 nm) to form the cathode electrode 2. An anode electrode 3 made of indium (In, thickness: 150 nm) is formed on the other main surface of the substrate 1 facing the cathode electrode 2 by a vacuum vapor deposition method.

As shown in FIG. 2, a wiring 5 made of an Ag / Pd film is formed on an alumina substrate 4 (base) having a thickness of 2 mm. On this wiring 5, the In—Sn alloy 6 (atomic composition ratio 1: 1) is heated to its melting point of 125 ° C. or higher, and the anode electrode 3 is brought into close contact and cooled to room temperature for electrical connection. Mechanically fix (die attach). The cathode electrode 2 is connected to the gold wire 7 with a conductive adhesive (silver epoxy) and is connected to the measurement circuit (not shown) together with the anode electrode 3. The anode electrode 3 side is connected to the wiring 5 in order to use the radiation incident surface as the cathode electrode 2 side. This is because the mobility of electrons in CdTe semiconductors is about 10 times that of holes.
This is because the efficiency of collecting carriers can be increased (especially for radiation of 200 KeV or less) by using the cathode electrode 2 side as the incident surface.

A positive potential from the measuring circuit to the anode electrode 3 side,
FIG. 3 shows a change in dark current due to a bias voltage when a negative potential bias is applied to the cathode electrode 2 side. As is clear from the figure, even when the bias voltage was 500 V, the dark current was about 5 nA, which was a sufficiently low value.

In the above embodiments, the In--Sn alloy 6 is used for connection, but the temperature at which the height of the electrical barrier against holes is not lowered at the anode electrode and the temperature at which the CdTe semiconductor single crystal deteriorates is maintained. Or a metal or alloy having a softening temperature of 250 ° C. or less (for example, In, In—Ga,
In-Cd) may be used. In addition, the connection may be performed by electrical connection, and an insulating adhesive such as an epoxy resin may be used for mechanical fixing. It is also possible to use a conductive adhesive in which metal particles that do not reduce the height of the electrical barrier against holes in the anode electrode such as In and Al are dispersed in an insulating adhesive such as an epoxy resin.

[0017]

[Comparative Example] Similar to the example, after forming the cathode electrode 2 and the anode electrode 3 on the substrate 1, electrical connection and mechanical fixing to the wiring 5 on the alumina substrate 4 were performed by using a conductive adhesive (silver). Epoxy). Further, the cathode electrode 2 is
Gold wire 7 with a conductive adhesive (silver epoxy) in which silver particles are dispersed.
And the anode electrode 3 as well as a measuring circuit (not shown). The dark current in this case is shown in FIG. 3 together with the case of the embodiment. As is clear from the figure, in the case of the comparative example, the bias current is 500 V and the dark current is 10 n.
It is about A, which is much larger than that of the comparative example.

[Brief description of drawings]

FIG. 1 is a sectional view for explaining an electrode forming process of a CdTe radiation detector according to the present invention.

FIG. 2 is a cross-sectional view illustrating a step of fixing a CdTe radiation detector according to the present invention to a substrate.

FIG. 3 is a CdT according to an example of the present invention and a comparative example.
It is a characteristic view which shows the change of the dark current by the bias voltage of e radiation detector.

[Explanation of symbols]

 1 Substrate (Semiconductor) 2 Cathode Electrode 3 Anode Electrode 4 Alumina Substrate (Base) 5 Wiring 6 In-Sn Alloy 7 Gold Wire

Claims (3)

[Claims] 1. A compound semiconductor sensitive to radiation, (b) a cathode electrode provided on one main surface of the compound semiconductor, and (c) another compound semiconductor facing the one main surface. And (d) a conductive portion connecting the anode electrode to an external wiring, and (e) the conductive portion increases a height of an electric barrier against holes in the anode electrode. A semiconductor radiation detector characterized by being made of a material that does not degrade. 2. The anode electrode is made of a material showing a high electric barrier against holes, and the cathode electrode is made of a material showing a low electric barrier against holes. The semiconductor radiation detector according to claim 1. 3. A step of (a) forming a cathode electrode on one main surface of a compound semiconductor sensitive to radiation, and (b) softening a material capable of obtaining a high electric barrier against holes as an anode electrode, Connecting the other main surface of the compound semiconductor facing the one main surface.