JPH0447992B2 - - Google Patents

Description

[Detailed description of the invention] [Technical field to which the invention pertains]

The present invention relates to a method for manufacturing 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. 2, an n region 22 is formed in a p-type high resistivity silicon plate 21 by phosphorus diffusion, and a reverse voltage is applied to this p-n 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 resulting 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, and electron-hole pairs are generated in the depletion layer by the alpha rays. For this reason, conventionally,
A Boral plate 23 containing, for example, boron is attached to the window portion where radiation enters the silicon plate 21 of the detector, and when the thermal neutron beam 11 is incident, the neutron absorption cross section in boron is approximately five orders of magnitude larger. Isotope of boron
A method was used to generate and detect alpha rays 12 using the ¹⁰ B(n,α) reaction of ¹⁰ B. However, alpha rays are easily absorbed by materials; for example, the range of alpha rays with an energy of 5.5 MeV is about 4 cm in air and about 30 μm in silicon. For this reason, alpha rays generated by the neutron transmutation reactant are transmitted to the air space between the reactant and the radiation detection element, and to the electrodes of the detection element.
Detection efficiency is poor because it is easily absorbed in insensitive regions such as p-n junction regions. In order to eliminate this runner-up, the inventors of the present invention have proposed patent application No. 59-96110.
In the radiation detector filed in No. 158414, a boron film produced by plasma CVD from diborane with ¹⁰ B, for example, is provided on a semiconductor substrate on which a depletion layer is formed, and ¹⁰ B
(n, α) reaction was used. However, when using a p-type semiconductor substrate, in order to efficiently detect the alpha rays 12 generated in the boron coating 2 formed between the back electrode 6 and the p ⁺ ohmic contact layer 24 as shown in FIG. It is necessary to apply a high reverse bias voltage between the back electrode 6 and the front electrode 5 until the depletion layer 7 reaches the ohmic contact layer 24. On the other hand, in the case of an n-type semiconductor substrate, since a boron film can be provided on the surface side of the pn junction, the α rays generated in the boron film reach the depletion layer region extremely efficiently and are detected, resulting in a high reverse bias. No voltage required. However, since this boron coating is conductive, it is necessary to remove the coating that adheres to unnecessary areas, but boron coating has extremely strong chemical resistance and can be selectively removed from unnecessary areas around the semiconductor substrate. This was difficult and required a lot of man-hours.

[Purpose of the invention]

The present invention provides a method for manufacturing a semiconductor radiation detector in which a boron film that does not require selective removal is formed on the p-region side surface of an n-type semiconductor substrate having a p-n junction, while eliminating the above-mentioned drawbacks. The purpose is to

[Key points of the invention]

In the present invention, a boron film is selectively deposited on one side of an n-type semiconductor substrate through a mask, and then heated to form a p-type boron penetration region under the boron film. To achieve the above objectives.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to the drawings. The same reference numerals are given to parts common to each figure, including the already explained FIGS. 2 and 3. FIG. 1 shows the process and operating principle of an embodiment of the present invention, in which a mask 13 is placed on the surface of an n-type silicon substrate 1.
After forming the boron film 2 through the silicon substrate, the silicon substrate is inserted into an electric furnace for heat treatment,
C. for 10 to 20 minutes in dry nitrogen to further electrically activate the boron 3 that has penetrated into the silicon substrate, forming a p ⁺ region 4. (a and b
figure). Next, an electrode 5 is applied to the surface of the boron coating 2 through a mask 14 having a diameter of 100 to 120 μm smaller than that of the mask 13, for example, by vacuum evaporation of aluminum.
In addition, an electrode 6 is formed on the back surface of the silicon substrate 1 (FIG. c). The device manufacturing conditions are as follows. (1) Substrate: Silicon single crystal, n-type, resistivity 10kΩ
cm or more (2) Boron coating: Diborane [B ₂ H ₆ (1000ppmH ₂
Manufactured by D, C plasma CVD method using [base)]. (3) Plasma CVD method Substrate temperature: 200℃ Pressure: 2.0Torr Applied voltage: 560V As shown in Figure 1 d, reverse voltage -
When thermal neutron beam 11 is incident with V _E applied,
α rays 12 are generated in the boron coating 2 by a neutron transmutation reaction of ¹⁰ B+n→ ⁷ Li+α, and the α rays generate electron-hole pairs in the depletion layer 7, which are detected through the amplifier circuit 15. . Particularly in this case, since the thickness of the boron atomic layer penetrating directly under the boron coating 2, that is, the p ⁺ layer 4, is about 0.1 μm, the width of the insensitive layer to radiation is extremely thin, and the detection efficiency of thermal neutrons is high. FIG. 4 shows another embodiment of the present invention, and the difference from FIG. 3 is that after a thermal oxide film or CVD oxide film 8 is deposited on the surface of an n-type silicon substrate 1
Figure), window 9 is opened in the photoetching process (Figure b),
This is the point where a boron coating 2 was formed on this window through a mask 13 (Figures c and d). Figure 4e shows the same process as Figure 1c, but the result is Figure 4f.
Since the oxide film 8 is present as a surface protective film as shown in FIG. 2, there is an advantage that a highly reliable detector can be obtained. 5 and 6 show a modification of the embodiment shown in FIGS. 1 and 4, in which a boron coating 2 is formed not only on the front surface of the n-type silicon substrate 1 but also on the back surface. . As a result, alpha rays 1 generated on the back side
2 is also detected, so the detection sensitivity is further increased than in the embodiments shown in FIGS. 3 and 4. Since the structure 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 neutrons. For example, in the case of γ-rays, since secondary electron beams due to the photoelectric effect and Compton effect are detected, the output shows a continuous spectrum with respect to the pulse height as shown by curve 71 in FIG.
It can be clearly distinguished from the pulse height of the thermal neutron beam shown in . 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 that it can be detected in the same way as other radiation.

[Effects of the Invention] According to the present invention, in order to selectively form a boron film on an n-type semiconductor substrate through a mask, a boron film with strong chemical resistance is once formed on the entire surface of one side of the substrate. The manufacturing process can be significantly shortened compared to conventional methods in which unnecessary parts are then removed using methods such as chemical etching or sputtering. Furthermore, in the present invention, boron enters from the boron film deposited on the n-type semiconductor substrate, and a pn junction is created directly under the boron film, thereby forming a depletion layer. can be made extremely thin. As a result, α rays generated by ^{the 10} B(n, α) reaction, that is, thermal neutron beams, can be efficiently detected.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view sequentially showing the steps and operating principle of an embodiment of the present invention, FIGS. 2 and 3 are cross-sectional views showing the operating principle of a conventional semiconductor radiation detector, and FIG. 4 is a cross-sectional view showing the operating principle of a conventional semiconductor radiation detector. 5 and 6 are cross-sectional views of the detectors obtained by two different embodiments, and FIG. 7 is the output of the detector according to the present invention. FIG. 3 is a diagram showing pulse heights. 1: n-type silicon substrate, 2: boron coating, 4:
P ⁺ region, 5, 6: electrode, 7: depletion layer, 11: neutron beam, 12: α ray.

Claims (1)

[Claims] 1. Semiconductor radiation characterized by selectively depositing a boron film on one surface of an n-type semiconductor substrate through a mask, and then heating to form a p-type boron penetration region under the boron film. Detector manufacturing method.