JP3024389B2 - Silicon 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 silicon radiation detecting element using a heterojunction of amorphous silicon and crystalline silicon.

[0002]

2. Description of the Related Art γ-rays, α-rays, β-rays, and X-rays are directly applied to a depletion layer generated by applying a voltage to a semiconductor junction.
Alternatively, as a radiation detection element that extracts a change in current caused by a change in conductivity caused by the incidence of a secondary electron beam generated thereby as an electric signal, in addition to one using a pn junction for generating a depletion layer, silicon
(Hereinafter referred to as a-Si) and a heterojunction between crystalline silicon (hereinafter referred to as c-Si) are described in Proc.
Sensor Synposium, Tsukuba (Institute of Electrical
Engineers of Japan, Tokyo.1984) p.105 by Yabe et al. FIG. 2 shows the structure of such a radiation detecting element, in which an a-Si film 2 is formed on a p-type c-Si substrate 1, an upper electrode 3 is provided on the surface of the a-Si film 2, and a back surface of the substrate 1 is provided. The lower electrode 4 is formed of Al. Then, a reverse bias in which the electrode 3 is positive and the electrode 4 is negative is applied to the hetero junction to generate a depletion layer.

[0003]

The detection element shown in FIG. 2 is an excellent device in which the a-Si film 2 as a functional film also serves as a passivation film.
In order to respond to a weak signal with high sensitivity as in the case of line detection, it is necessary to reduce the leakage current by increasing the applied voltage to prevent recombination. For that purpose, the passivation film is required to have low dark conductivity. On the other hand, high light conductivity is desirable from the viewpoint of the response to radiation. For that purpose, it is necessary to increase the light-dark conductivity ratio, but there is a problem that it is difficult to realize it with the conventional structure of FIG.

An object of the present invention is to solve this problem and to provide a silicon radiation detecting element having good responsiveness to radiation and having a small surface leakage current.

[0005]

In order to achieve the above object, a silicon radiation detecting element of the present invention comprises a first conductive type c-Si substrate, a lower layer having a second conductive type and a low impurity concentration. The upper layer is covered with a two-layered a-Si film which is doped with impurities and is almost neutral, and has a back surface of the c-Si substrate and an upper layer a-Si film.
It is assumed that an electrode is provided in contact with each surface of the film. It is effective that the c-Si substrate is p-type, the lower a-Si film is non-doped and n-type, and the upper a-Si film is doped with boron. Further, it is effective to form each a-Si film using an electron cyclotron resonance (ECR) plasma CVD apparatus.

[0006]

The lower a-Si contacting the c-Si substrate of the first conductivity type.
The film has a low impurity concentration, for example, a non-doped second conductivity type, and functions as a functional film having high light conductivity forming a heterojunction, while the upper a-Si film is doped with impurities and is almost neutral. Therefore, the dark conductivity is minimized, the resistance is increased, and the leakage current is reduced. Although the electrode is in contact with the upper a-Si film, the effect of the thinner thickness on the functionality of the lower a-Si film can be neglected. Further, since the upper a-Si film serving as the passivation film is made of the same material as the lower a-Si film, no stress is generated therebetween and there is no possibility of film peeling.

[0007]

FIG. 1 shows a silicon radiation detecting element according to an embodiment of the present invention, and the same parts as those in FIG. 2 are denoted by the same reference numerals. The substrate 1 has a thickness of 0.5 mm and a resistivity of 10 kΩ.
Using a p-type c-Si plate of cm or more, boron was first introduced from the back surface side to form ap ⁺ layer 11, and then Al was deposited to form an electrode 4 which makes ohmic contact. Next, using a parallel plate type high frequency plasma CVD apparatus, a mixed gas of SiH ₄ and H ₂ was introduced to form a lower a-Si film 21 on the surface of the c-Si substrate 1.
A film was formed to a thickness of μm. This film is undoped, but n
And forms a heterojunction with the p-type c-Si substrate 1. Next, diborane (B) was added to the raw material gas SiH _4.
By mixing ₂ H ₆ ), a boron-doped upper a-Si film 22 was formed to a thickness of 1000 ° in the same CVD apparatus. The a-Si film 22 covers the upper surface and side surfaces of the a-Si film 21 and functions as a protective film. Thereafter, the upper electrode 3 was formed on the a-Si film 22 by Al evaporation.

In another embodiment, an ECR plasma CVD apparatus was used for forming the a-Si films 21 and 22. This apparatus comprises a plasma chamber having a magnetic field generating mechanism around it and a reaction chamber containing a substrate. H ₂ , helium or argon is introduced as a plasma gas into the plasma chamber, and SiH is introduced into the reaction chamber.
Introduce ₄ . Then, the plasma generated in the plasma chamber is extracted, SiH ₄ is decomposed in the reaction chamber, and a-Si
Although a film is formed, B ₂ H ₆ may be mixed into either the plasma gas or SiH ₄ when forming the upper a-Si film 22. When the same CVD apparatus is used repeatedly, B ₂ H ₆ used for forming the previous upper layer a-Si film 22 remains on the apparatus wall surface or the gap between the apparatuses and forms the next lower layer a-Si film 21 when forming. In order to avoid mixing with the reaction gas, the lower the film forming pressure, the better. For that purpose, it is most reasonable to use an ECR plasma CVD apparatus.

[0009]

According to the present invention, an applied voltage can be increased by forming an a-Si film having a small dark conductivity, which is desirable as a passivation film, separately from an a-Si film serving as a heterojunction functional film. Has been obtained, and a highly sensitive and highly reliable radiation element, for example, an α-ray detecting element has been obtained. In this device, SiO, Si is used as a passivation film.
Compared to the case where an insulating film of another material such as N is used, a-
There is an advantage that no stress is generated between the Si film and the Si film, and the influence on the functional film is small. In addition, since both films can be formed continuously using the same apparatus, productivity is good.

[Brief description of the drawings]

FIG. 1 is a sectional view of a silicon radiation detecting element according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view of a conventional silicon radiation detecting element.

[Explanation of symbols]

 Reference Signs List 1 c-Si substrate 21 lower a-Si film 22 upper a-Si film 3 electrode 4 electrode

Claims (3)

(57) [Claims] 1. A two-layer amorphous silicon film having a lower conductivity type of a second conductivity type, a low impurity concentration, and an impurity-doped and substantially neutral layer is formed on a first conductivity type crystalline silicon substrate. A silicon radiation detecting element, wherein electrodes are provided to be in contact with the back surface of the crystalline silicon substrate and the surface of the upper amorphous silicon film. 2. The silicon radiation detecting element according to claim 1, wherein the crystalline silicon substrate is p-type, the lower amorphous silicon film is non-doped and n-type, and the upper amorphous silicon film is doped with boron. 3. The silicon radiation detecting element according to claim 1, wherein each amorphous silicon film is formed using an electron cyclotron resonance plasma CVD apparatus.