JPH0473636B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of the Invention] The present invention relates to a semiconductor radiation detector that detects radiation including thermal neutron beams.

[Prior art and its problems]

As a typical example of a semiconductor radiation detector is shown in FIG. 8, an n region 2 is formed in a P-type high resistivity silicon plate 1 by phosphorus diffusion, and a reverse voltage is applied to this Pn junction. Radiation is detected by a current flowing between both electrodes on both sides (not shown) based on electron-hole pairs generated when radiation enters the depletion layer.

However, since neutron beams have no charge, they do not have any effect on the orbital electrons or the Coulomb field of the atomic nucleus other than nuclear reactions, and therefore no electron-hole pairs are generated. For this reason, a neutron beam is transmitted through a substance with a large neutron absorption cross section, and alpha rays are generated by a neutron transmutation reaction, thereby generating electron-hole pairs in the depletion layer. That is, conventionally, a Boral plate 3 containing boron, for example, is attached to the window portion where radiation enters the silicon plate 1 of the detector, and when the thermal neutron beam 4 is incident, the neutron absorption cross section in the boron is ¹⁰ B of the boron isotope ¹⁰ B, which is about 5 orders of magnitude larger
Using the (n, α) reaction, α rays 5 are generated and detected.

[Purpose of the invention]

An object of the present invention is thus to provide a semiconductor radiation detector that does not require a neutron transmutation reactant to be mounted on the front surface for thermal neutron beam detection.

[Key points of the invention]

This invention forms a coating made of boron on the surface of a semiconductor substrate or an electrode of a detection element, and ^10B of isotope ^10B present in the boron coating.
The object is to generate α rays using the (n, α) reaction and detect the α rays, thereby making it possible to detect neutron rays.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to the drawings. In each figure, parts common to those in FIG. 8 are given the same reference numerals. In Figures 1 to 7, 6 and 7 are electrodes formed on both sides of this detection element, and when radiation is incident on the semiconductor substrate 1, it interacts with the crystals in the depletion layer that are generated when a reverse bias voltage is applied. This is for extracting the electron-hole pairs as a pulse signal.

1 and 2 show the case of a detection element having a surface barrier type structure, for example, in P-type silicon, aluminum is vacuum-deposited as the barrier metal 6, and gold is vacuum-deposited as the ohmic contact electrode 7, respectively. A boron coating 8 is formed on at least one surface of said 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, α rays 5 are generated by a neutron transmutation reaction of ¹⁰ B+n→ ⁷ Li+α in the boron coating 8, and this α ray Therefore, electron-hole pairs are generated in the depletion layer and current flows, allowing thermal neutron beam detection. When a boron coating 8 is formed on each of the surfaces of both electrodes 6 and 7 as shown in FIG. 2, the alpha rays generated on the back surface are also detected, so the thermal neutron detection efficiency is lower than that shown in FIG. Even higher than the example.

3, 4, and 5 show the case of a Pn junction type radiation detection element, in which a boron coating 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 coating 8 . This P ⁺ layer is 10 ²¹ ~
Because it has an extremely high boron concentration of ¹⁰²² atoms/cm ³ , thermal neutron beams can be detected efficiently. Furthermore, in order to improve the detection efficiency of thermal neutron beams,
As shown in the figure, a boron coating 8 is also formed on the surfaces of the electrodes 6 and 7. As a result, the same effect as in FIG. 2 can be obtained.

6 and 7 show detection elements of surface barrier type and Pn junction type structures using a P-type silicon substrate,
A P ⁺ layer 10, ie, an ohmic contact layer, is formed directly below the boron film 8, and the boron film 8 is also formed on the electrode.

The above-mentioned boron coating is produced by placing the substrate to be coated in a vacuum container, heating it to a predetermined temperature, for example, 300°C, introducing diborane gas into the container, and generating a glow discharge in the container. decomposes gas,
Preferably, it is formed by depositing a boron coating on a substrate. The boron concentration at this time is 10 ²³
atoms/cm ³ or more, and the thickness of the boron coating is approximately 500
It is Å. The method for forming the boron film and the formation of a highly doped region on the surface of the semiconductor substrate by depositing the boron film are described in Patent Application No. 58-93218 and No. 58-93220 filed by the present applicant. Please refer to the book. Of course, this boron coating contains ¹¹ B and ¹⁰ B in a ratio of 4:1, so
¹⁰ The content of B is only 1/5. However, the boron concentration of the boron film formed in this way was 10 ²³
Since it is more than atom/cm ³ , for example, JP-A-57-
Compared to the ion implantation dose shown in Publication No. 85268, which forms a boron layer by mass-separating only ¹⁰ B, a film containing a higher concentration of boron can be easily formed, and therefore thermal neutron Line detection efficiency is increased.

Since the structure itself of the radiation detector according to the present invention is similar to that of conventional detectors, it is naturally possible to detect radiation other than thermal neutron beams. For example, in the case of r-rays,
In order to detect secondary electron beams due to the photoelectric effect and Compton effect, the output shows a continuous spectrum with respect to the pulse height as shown in curve 11 in Figure 5, so it can be clearly distinguished from the pulse height of a thermal neutron beam as shown in curve 12. can. Furthermore, if a polyethylene plate is placed in the entrance window, fast neutron beams can also be detected. That is, when a fast neutron beam is incident on a polyethylene plate, protons knocked out by elastic collisions enter the depletion layer and generate electron-hole pairs, so it can be detected like other radiation.

Even if the semiconductor substrate used here is a compound semiconductor such as GaAs or CdTe in addition to the silicon and germanium mentioned above, the formation temperature of the boron film is 300°C or less, so there is no loss of crystallinity. ,
It is effective as a radiation detector including neutron beams.

〔Effect of the invention〕

According to the present invention, thermal neutron beams can be detected without attaching a neutron transmutation reactant to the front surface of a radiation detection element as in the prior art. Moreover, since this boron coating is in close contact with the radiation detection element, the α rays generated by the ¹⁰ B (n, α) reaction with ¹⁰ B can efficiently penetrate into the semiconductor substrate, allowing thermal neutron radiation to penetrate into the semiconductor substrate. At the same time, the boron coating can be approximately 500 Å thick, making the dead layer width extremely thin. As a result, there is no problem in detecting α-rays, low-energy β-rays, and r-rays.

[Brief explanation of the drawing]

1 to 7 are cross-sectional views showing different embodiments of the present invention, FIG. 8 is a cross-sectional view showing an example of detecting a thermal neutron beam using a conventional semiconductor radiation detector, and FIG. 9 is a cross-sectional view showing an example of detecting a thermal neutron beam using a conventional semiconductor radiation detector. FIG. 3 is a diagram illustrating the output pulse height of a detector. 1...P-type silicon substrate, 4...thermal neutron beam,
5...α ray, 6, 7... Electrode, 8... Boron coating, 9... N-type silicon substrate, 10... P ⁺ region.

Claims (1)

[Claims] 1. A boron coating layer formed by glow discharge in an atmosphere containing diborane gas is provided on at least one of the surface of the semiconductor substrate and the surface of the electrode formed on the semiconductor substrate. Semiconductor radiation detector.