JPH0227776A - Semiconductor neutron beam detector - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention provides a method for reducing boron isotope g when a thermal neutron beam is incident
The present invention relates to a semiconductor neutron beam detection element that utilizes α rays generated by reaction with I*B.

[Conventional technology]

The principle of semiconductor radiation 4mm output element is that of pn junction and semiconductor
A diode structure is formed using either a metal Schittky junction or a heterojunction between a single crystal semiconductor and an amorphous semiconductor, and a reverse bias voltage is applied to the diode.
This spreads a depletion layer in the semiconductor, and electron-hole pairs generated by radiation that enters the depletion layer are counted and detected as current pulses.

Regarding radiation, X-stripes, α-rays, β-rays, and γ-rays directly generate electron-hole pairs within the semiconductor depletion layer, so radiation can be detected as they are. On the other hand, since neutron beams have no electric charge, they do not have any effect on the orbital electrons or the Coulomb field of the electron nucleus other than the nuclear reaction, so no electron-hole pairs are generated in the semiconductor depletion layer, and the neutron beam cannot be detected by the above method, so the neutron wA method is used to transmit neutron beams through a substance with a large neutron absorption cross section, and generate alpha rays through a neutron transmutation reaction. There is a method in which the α rays detect electron-hole pairs generated within the semiconductor depletion layer.

As a specific example, using boron isotope +03, which has a large scattering cross section for thermal neutron beams, α rays ( There are methods to detect 'Hθ) and 'Li nuclei.

Summer・B + n - DingLi + a ('1ie)
-m-...---111 Figure 2 shows the cross-section J# structure and detection principle of a thermal neutron cotton spearing element known from, for example, Japanese Unexamined Patent Publication Nos. 61-17477 using this method. ,n
A film is formed on the window portion of the surface protective film 24 covering the upper surface of the shaped silicon substrate 2I by plasma CVD, as is known from, for example, Japanese Patent Application Laid-open No. 59-218732 and Japanese Patent Application Laid-open No. 59-219462. A p'' layer 23 is formed under the boron coating 22, an electrode 25 is provided on the upper surface of the boron coating 22, and an 'IlP*2G is provided on the lower surface of the substrate 21.This element is reverse biased. When thermal neutron val is irradiated with -vl applied and a depletion Ji27 is generated, a negative reaction of neutron beam change i (formula 11) occurs between +aB contained in the boron film 22, and each other When the alpha rays 3 shown by the solid lines flying in the form of @ or the 'Ll results 4 shown by the broken lines reach the depletion 1127, electron-hole pairs are generated, and these are detected via an amplifier circuit and a counting circuit (not shown). Ru.

In order to increase the neutron sensitivity of this element, it is sufficient to increase the amount of 183 as shown by equation (1). 1. At OXl0j3 atoms/ci, the atomic density reaches a value almost equal to the boron concentration. Therefore, a highly sensitive neutron beam detection element can be obtained by forming a boron film thicker than the diborane gas containing concentrated "B" described in Japanese Patent Application No. 62-323240, which is another patent application filed by the present applicant. .

A method using concentrated 10B is, for example, by applying a solution containing concentrated IIB to a silicon wafer with a brush, heat-treating it to form a p-n junction, and using the reaction of equation (1) to generate thermal neutrons. The method of detecting is 11゜M, Man
American magazine by n and F, J, Jaaarek
IRETrans, “NS 9. No. 3 (1962
), page 200, ``Method of forming a pn junction by implanting B into the surface of a silicon substrate by ion implantation and then performing heat treatment'' by Rikitsuki, G., Gverdtstell and others, Soviet magazine Pr1b, Tekhl'ksp.

No, 3. (1979) on page 81.

[Invention tries to solve &! Title]

Forming a film containing a large amount of 1113 by the method described above,
In order to generate a large number of α rays according to the +11 formula and further increase sensitivity, it is necessary to increase the number of α rays or electron-hole pairs generated by reaching the 'Ll nuclear depletion layer.

The object of the present invention is not only to provide a means for generating a large amount of α-rays and 'Ll nuclei, but also to provide a means for generating α-rays and 'LiJAi
An object of the present invention is to provide a semiconductor neutron "41A" storage device which effectively utilizes neutrons to generate electron-hole pairs.

[Means to solve the problem]

In order to achieve the above object, the present invention provides a method for detecting neutron beams in which a boron coating containing concentrated isotope I@B is deposited on an n-type semiconductor substrate, and a p-type doped layer is present under the coating. In the element, the thickness of the boron coating is thinner than the range of alpha rays in the boron coating.

[Effect]

The range of alpha rays in a boron coating is about 4.4μ, and the range of Li nuclei is about 1.4μ, which is much shorter. The α rays and 'Ll nuclei are simply absorbed in the boron coating and do not reach the depletion layer. Therefore, if the thickness of the boron coating is made thinner than the range of the boron coating of the α rays, which is longer than that of the 7L1 nucleus, At least almost all of the α rays that travel toward the depletion layer contribute to the generation of electron-hole pairs, improving neutron sensitivity.

〔Example〕

Figure 1 shows the boron coating 1!22 shown in Figure 2. p' layer 23
and a partial enlarged view of the depletion layer 27, the boron coating 22 is d
It is assumed that the ++P'' layer 23 has a thickness of d.

On the other hand, the range of α12 in the boron coating is '+', and the range of 'Li spear 4 is 11.

Now, near the surface of the boron coating 22, a thermal neutron beam 101i"B 5
If d,>j, d,>7. Then, all the α rays 3 and 'LiA' 4 are absorbed within the 1!22 and do not reach the depletion layer 27, so they do not contribute to neutron sensitivity.
When the thermal neutron beam 12 reacts with l0BS at a position deeper than the surface, α rays 31, 32. 'Ll nucleus 41, 3 out of 42
2, only the α rays heading towards the depletion layer 27 reach the depletion layer and contribute to the neutron sensitivity. Also, thermal neutron beam 13.14
If 1085 reacts near the interface with the boron coating 227 and the semiconductor substrate 2, as in
I 4144:! , 43.3417) like 1jf
: Excluding those that go to the coating side, they contribute to neutron sensitivity with a probability of approximately 1/2.

As can be seen from the above explanation, the thickness d+ of boron '#IB 22 is the range j! ,,j, If it is thicker, even if the thermal neutron beam of X111 like 15-19 reacts with 1.B5 in the boron removal film 22,
As shown in 6.37, some substances are absorbed during the membrane rupture.
The coating 22 and the semiconductor substrate 2 contribute to neutron sensitivity.
Thermal neutron beam 17 that reacted with 1135 near the interface with 1
Neutron sensitivity decreases because it is limited to α rays 3 and 'Ll rays 4 generated at 19.

These facts will be explained below using formulas.

+11 d , ≦2. In the case of 1.
(pieces/cd・S), α generated in the film
The number of lines and 'Li spears that reach the depletion layer is i o
(1-e-'''嘗), where N is the number of 1113 in the boron removal film and σ is the scattering cross section of +63.

(2) When 1×≦d,≦11, the number of α-rays generated in the boron-extracted film and reaching the depletion layer is Io
(1e−””), but the number of 'Ll kernels is I
o ((1-a ″””)-(1-e-”L ′.

-l sergeant))] becomes.

In the case of +31 d, ≧l, the number of α rays and 'Ll nuclei generated in the boron-extracted film by reaction with thermal neutron beams and reaching the depletion layer is Io, respectively.
((1e-Mt't) (1, -5t(4°!・)
)] and ■. ((1-8-”～)-(1-e-H#j
4B meeting))].

The song M61 in Figure 3 is l t -4, 44, 1g -1,
Assuming 4m, the above +11. (This shows the results calculated from the values of 21 and +31. The horizontal axis shows the thickness of the boron-free film, and the vertical axis shows the relative ratio of thermal neutron sensitivity.

Although the thermal neutron relative sensitivity increases as d increases, its slope changes depending on the conditions (1), (2), and (3) above.
Curve 62 shows the relative ratio of measurement results obtained when neutron beam detection elements formed with boron-free films of various thicknesses were irradiated with the standard neutron beam B aSλG through a polyethylene moderator with a thickness of 40 mm. . The reason why the curve 62 does not match the curve 61 is that the generated α rays and 'Ll nuclei reach the depletion layer with a certain probability, and in addition to the dead layer of the p° layer 23, the α rays and 'Ll nuclei generated inside the boron-free M422 'The boron depletion film becomes an insensitive layer for the Ll nucleus, and after passing through these dead layers, it reaches the depletion layer, so the maximum output pulse height becomes small, and in order to remove the rHIA component mixed in, a certain amount of This is done by counting only the output pulse heights that exceed the magnitude.

From Figure 3, the relationship between the thickness d of the film and the thermal neutron sensitivity is clarified for the side T including IOB, and the maximum thermal neutron sensitivity is the thickness d of the film from which the boron is removed. It has been found that this can be obtained when the range is thinner than the α-ray range of 11.

〔Effect of the invention〕

According to the present invention, based on the fact that thermal neutron sensitivity decreases when the thickness of the boron-free film containing IOB exceeds the range of alpha rays in the boron-free film, the thickness of the boron-free film is reduced. By making the thickness thinner than the range of α rays, a detection element with high neutron sensitivity can be obtained. Therefore, since there is no need to form an unnecessary thick film unlike in the past, the manufacturing process is shortened and costs can be reduced. In addition, the optimum thickness of the boron removal film based on the present invention can of course be similarly applied to the case of coating the inner wall of a proportional counter tube for neutron detection using gas. When combined with a moderator for neutron beams such as paraffin in a predetermined shape, it is now possible to easily obtain a lightweight and compact dosimeter for personal use with high sensitivity for controlling neutron radiation exposure, which was previously impossible. Ta.

[Brief explanation of the drawing]

Figure 1 shows a thermal neutron beam and an IOB in an embodiment of the present invention.
Fig. 2 is a cross-sectional view of a detection element according to an embodiment of the present invention, and Fig. 3 shows the relationship between boron removal film thickness and thermal neutron mi degree. It is a line diagram. 10-19: Thermal neutron beam, 21: N-type silicon & plate, 2
2: Boron removal film, 23: p'' layer, 25, 26: electrode, 2
7: Depletion layer, 3: α ray, 4: Full Li nucleus, 5: l11B.

Claims (1)

[Claims] 1) In a device in which a boron film containing concentrated isotope ^1^0B is deposited on an n-type semiconductor substrate and a p-type doped layer is formed below the boron film, the thickness of the boron film is α. A semiconductor neutron beam detection element characterized by being thinner than the range of a beam in a boron coating.