JPS6135384A - Neutron detector - Google Patents

Abstract

PURPOSE:To obtain a neutron detector with high detection accuracy by combining a semiconductor P-N junction or semiconductor metallic Schottky junction or crystal semiconductor-amorphous semiconductor hetero junction and a thin boron film contg. the isotope <10>B of boron at a high concn. CONSTITUTION:An aluminum electrode 6 as a barrier metal and a metallic electrode 7 as an ohmic contact are respectively deposited by vacuum evaporation on, for example, a P type silicon substrate 1. Then thin boron film 8 is formed on the surface of at least either of the electrodes 6 and 7. When thermal neutron rays 4 are made incident on the element having such surface barrier type construction while a reverse voltage is held impressed thereto, alpha rays 5 are generated by neutron nuclear transformation reaction during the passage of the rays 4 through the thin boron film 8. The alpha rays 5 intrude into the depletion layer formed in the substrate 1, thus forming electron-hole pairs and forming current pulses. The detection of the thermal neutron rays is made possible. The neutron detector having the simple construction, high stability and high detection sensitivity is thus obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical field to which the invention pertains] The present invention relates to a neutron detection device using a boron thin film.

[Prior art and its problems]

The principle of a semiconductor radiation detector is to form a diode structure using any method such as a PN junction, a semiconductor-metal junction, a toggle junction, or a crystalline semiconductor-amorphous semiconductor heterojunction, and then apply a reverse bias voltage to the diode. As a result, a depletion layer is expanded in the semiconductor, and the depletion layer is counted and detected as a current pulse in the form of electron-hole pairs generated by the radiation that has flown into the inverse layer.

Semiconductor materials include germanium (Ge) and silicon (S).
i), etc. Currently, Silikoshi (SL) is overwhelmingly used as a radiation dosimeter industrially because the material is easily available. Recently, high-purity, high-resistivity silicon has come to be used due to the demand for low-voltage operation.

Even with radiation, X-rays, α-rays, β-rays, and R-rays are directly M in the semiconductor depletion layer! It is possible to generate electron-hole pairs and detect radiation using conventional methods, but since neutron beams have no electric charge, other than nuclear reactions, there is no effect on the orbital electrons or the Kuhn field of the atomic nucleus. also has no effect, therefore within the semiconductor depletion layer.

No electron-hole pairs are produced and detection of the neutron beam is not possible with conventional methods. Therefore, as a neutron beam detection method, neutron beams are transmitted through a material with a large neutron absorption cross section, and α rays are generated by a neutron transmutation reaction, and the α rays generate electron-hole pairs within the semiconductor depletion layer. 1-1 There is a method to detect this and detect the neutron beam.

There is a method of detecting the alpha rays generated from boron when neutron scarlet is incident, using the sieve and α) reaction and following the reaction shown by the next Musketeer.

+oB(n,α) reaction: 10B+' n −+ L
i + He However, boron has an extremely high melting point of 2000'C or more, and it is difficult to easily form a single layer of boron. Even if a boron layer could be formed,
There was a problem in that the substrate itself, which should detect the alpha rays, would be destroyed or deteriorated due to the high temperature.

Particularly in semiconductor radiation detectors, there is a problem that thermal distortion occurs at high temperatures, resulting in deterioration of element characteristics. In particular, since semiconductors used in radiation detectors have high purity and high specific resistance, a low-temperature process is required in the manufacturing process.

It is said that thermal strain begins to occur in high-purity, high-resistivity silicon at temperatures above 400°C. Therefore.

High-temperature processes of 800° C. or higher that are commonly used in semiconductor processes are not suitable for semiconductor radiation detectors.

For example, a neutron detector combining a boron phosphide layer and a semiconductor PN junction is known, but this has the following problems.

■Because the thermal decomposition method is used to form the boron phosphide layer, 90%
Since the semiconductor substrate is exposed to a high temperature of 0° C., deterioration of semiconductor characteristics is unavoidable for the reasons mentioned above.

■Boron isotope 10B is found in nature at 10B:1
1 B≠l:4, but in addition to this, IOB
Even at higher concentrations, phosphorus is included in the boron phosphide layer using phosphine (PHs).

The concentration of 10B decreases. Therefore, neutron detection sensitivity decreases.

(2) Since the thickness of the prepared boron phosphide layer is more than 10 μm, the generated α-rays are reduced by self-absorption, and therefore the neutron detection sensitivity is reduced.

As described above, a neutron detection device that combines a boron phosphide layer and a semiconductor has problems.

In addition, neutron detectors that do not use semiconductors have a complicated structure, lack stability, have low detection sensitivity, and have poor counting characteristics.

[Purpose of the invention]

It is an object of the present invention to provide a neutron detection device having a simple structure, high stability, and high detection sensitivity.

[Key points of the invention]

In order to achieve this object, the present invention performs glow discharge using diborane gas (82H6) prepared by selectively concentrating boron isotope B when forming a boron thin film.
It is characterized by forming a boron thin film containing a high concentration of.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to the drawings. Hereinafter, in all of the Examples disclosed herein, the boron thin film shown is a boron thin film containing the aforementioned boron isotope B at a high concentration. 1 and 2 show the case of a detector having a surface barrier type structure. For example, in the case of P-type silicon, an aluminum electrode 6 as a barrier metal and a gold electrode 7 as an ohmic contact are vacuum-deposited, respectively.

A thin boron film [8] is formed on at least one surface of the electrodes 6 and 7. When a thermal neutron beam 4 is incident on an element with this surface barrier type structure with a reverse voltage applied, when the thermal neutron beam passes through the boron thin film 8, B-1-on-+
α rays 5 are generated by the neutron transmutation reaction Li + α, and the α rays enter the depletion layer formed in the silicon semiconductor 1 and generate electron-hole pairs, which become electric current (current). The neutron beam will be difficult to detect. When a boron thin film 8 is formed on each of the surfaces of both electrodes 6 and 7 as shown in FIG. 2, α rays generated on the back surface are also detected, so that the thermal neutron detection efficiency is the same as that of the embodiment shown in FIG. 1. It can be further enhanced.

3, 4, and 5 show the case of a pn junction type radiation detection element, in which a boron thin film 8 is selectively formed on an n-type silicon substrate 9. A boron interstitial layer, that is, a p+ layer 10, is formed on the n-type silicon substrate 9 directly under the boron thin film 8. This 1 layer is 1021~101022ato/1ytt
Since it has an extremely high boron concentration and contains a high concentration of IOB, thermal neutrons can be detected efficiently. It is formed by using a gas containing a high concentration of B as the diborane gas used for this high concentration of B.

In addition, in order to further increase the detection efficiency of thermal neutron beams, a fourth
As shown in the figure and FIG. 5, a boron thin film 8 is also formed on the surfaces of the electrodes 6 and 7. As a result, a neutron detection element with high detection efficiency can be obtained.

FIG. 6 is a structural sectional view of a surface barrier type detection element.

A P+ layer 10, that is, an ohmic contact layer, is formed directly under the boron thin film 8, and a boron thin film 8 is also formed on the electrode.
is formed.

FIG. 7 is a structural diagram of a heterojunction element in which amorphous silicon is formed on the surface of a single-crystal silicon semiconductor.

This is manufactured by depositing amorphous silicon on the surface of single crystal silicon by plasma CVD method, and then plasma CVD using dibory B2H6 gas containing high concentration of B.
A thin boron film layer is formed using a method.

This detection element uses the plasma CVD method and all element manufacturing processes are performed at a low temperature of 200°C or less, so there is almost no thermal deterioration of the high-purity silicon 9.
Even single crystal silicon with a resistivity of 10 kΩ-a or more is not thermally degraded.

For example, when calculating the sensitivity of silicon Ueno 1 with a surface area of loo&, at a neutron flux density of 100 nV, the counting rate A=Nδφ where N is the atomic density, δ is the scattering cross section, and φ is the flux density.

A=2.0xlOx 1500xlOx 3814xl
Atomic density of O"10B Thickness of B thin film Scattering cross section of B xlOx 10 φ Surface area = IQcps Therefore, a highly sensitive neutron detector can be easily formed. Also, if this boron thin film is formed in multiple layers, of course the sensitivity will be It gets better than this.

Here, the conditions for manufacturing this device are shown below.

Resilicon single crystal: resistivity 10 Ω or more (40φ)
Amorphous silicon: Monosilane [SiH4 (10%H2
(base)] or by C plasma CVD method.

・Plasma CVD method Substrate temperature 200℃ pressure
Force IQ, QTorr Applied voltage 700 ■ Reholon thin film Nijibora y CB2H6 (1000ppm
) (2 base)] or by C plasma CVD method.

・Plasma CVD method Substrate temperature 200℃ pressure
Force: 2.0 Torr Applied voltage: 560 V The structure itself of the radiation detector according to the present invention is similar to that of conventional detectors.Of course, radiation other than thermal neutrons can also be detected. For example, in this semiconductor detector, the vector is shown.

As mentioned above, when neutrons enter this detector and pass through the boron thin film, they react with the boron isotope B (n.α) to generate α rays of 2.30 MeV.

Therefore, the spectrum shown at 12 in FIG. 7 is shown. As shown in FIG. 8, normally detectable r-rays and α-rays caused by thermal neutron beams can be clearly distinguished.

Furthermore, if a moderator such as polyethylene is placed on the neutron beam entrance window of this detector, fast neutron beams can also be detected. That is, when a fast neutron beam is incident on the moderator, protons ejected by elastic collisions enter the depletion layer formed within the detector to generate electron-hole pairs, so that it can be detected in the same way as other radiation.

In the embodiments disclosed here, silicon was used for the semiconductor substrate, but of course germanium and compound semiconductors were used.
Even if aAs or CdTe is used, this detector can sufficiently detect the neutron beam. The reason for this is that the aforementioned boron thin film is formed by the plasma CVD method using glow discharge, but the temperature applied to the semiconductor substrate is 300'C or less, so the boron thin film is formed without causing thermal distortion to the semiconductor substrate. This is because it produces a good radiation detector.

〔Effect of the invention〕

According to the present invention, thermal neutron beams can be detected without attaching a neutron transmutation material to the front surface of a radiation detection element as in the prior art. Moreover, since this boron thin film is in close contact with the radiation detection element, it causes a B(n, α] reaction with the boron isotope B, and since the boron thin film itself is thin at around 1500 A, self-absorption of α rays is also low. Because the generated alpha rays efficiently penetrate into the semiconductor substrate,
The detection efficiency of thermal neutron beams is increased, and at the same time, the thickness of the boron thin film is 500 to 1600 A, and the width of the dead layer is extremely thin. As a result, there is no particular problem in detecting α-rays, β-rays, and R-rays.

[Brief explanation of drawings]

Figures 1 and 2 are cross-sectional views of a surface barrier type radiation detector, Figures 3, 4, and 5 are cross-sectional views of a pn junction type radiation detector, and Figure 6 is a cross-sectional view of a surface barrier type radiation detector. FIG. 7 is a cross-sectional view of a heterojunction radiation detector, and FIG. 8 is a spectrum of count rate versus pulse height when neutron beams are measured using the semiconductor radiation detector according to the present invention. 1...p-type silicon substrate, 4...neutron beam, 5...
・α rays, 6 and 7... Electrode, 8... Boron thin film, 9
...n-type silicon substrate, 10...P region, 11.
...r-ray spectrum, 12...α-ray spectrum,
...Amorphous silicon. ;71(2) f'z flash

Claims (1)

[Claims] 1) A neutron characterized by a combination of a semiconductor PN junction, a semiconductor-metal Schottky junction, or a crystalline semiconductor-amorphous semiconductor heterojunction, and a boron thin film containing a high concentration of the boron isotope ^1^0B. Detection device.