JPH07169988A - Semiconductor radioactive rays detector - Google Patents

Abstract

PURPOSE:To prevent a window electrode from being corroded in the case of discriminating and measuring various alpha species involved in dust in a nitric acid vapor or alpha species in a uranium nitrate solution. CONSTITUTION:A depletion layer 6 is formed with a hetero junction of a semiconductor substrate 1 and an amorphous carbon film 2, and a window electrode 3 on the amorphous carbon film 2 is formed with a graphic film or an amorphous carbon film into which boron is doped, whereby there may be eliminated the use of a corrosive metal window electrode. Further surroundings of the window electrode 3 and an Al pad 5 to which a lead wire is connected are coated with the amorphous carbon film 7 for protection.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to various α contained in dust in vapor of nitric acid in a working environment such as a nuclear facility.
The present invention relates to a semiconductor radiation detection element for discriminating and measuring nuclides.

[0002]

2. Description of the Related Art A radiation detecting element using a semiconductor is disclosed in Japanese Patent Publication No. 61-61707. In this silicon semiconductor radiation detecting element, gold containing antimony is used for the window electrode on which radiation enters. The window electrode is a gold electrode containing 0.5 to 2% of antimony. After depositing such gold on a p-type silicon substrate, sintering or alloying heat treatment is applied to the antimony contained in the gold in the silicon substrate. To form a donor and form a pn junction. This pn
When a reverse bias voltage is applied to the junction, the depletion layer grows and the α-ray incident from the window electrode side can be detected. Since the main component of the electrode that becomes the entrance window of this radiation detection element is gold, it has corrosion resistance to the uranium nitrate solution, and the window electrode is not corroded even if it is directly immersed in this solution, and is included in the solution. It is possible to measure the α ray.

The semiconductor radiation detecting element disclosed in Japanese Patent Application Laid-Open No. 3-96284 has the same purpose. It is an element in which a heterojunction is formed at the interface between the first amorphous silicon thin film and the single crystal silicon substrate. Further, a second amorphous silicon thin film is grown on and around the window electrode surface to improve the corrosion resistance. This element is also α
Detect lines. The semiconductor radiation detecting element described in Japanese Patent Application No. 203991 of 1993 also uses a hydrogenated amorphous carbon film instead of the above amorphous silicon film for the same purpose as the above two elements. It is an element with increased corrosion resistance.

All of these elements can detect α rays contained in dust in the vapor of nitric acid.

[0005]

[Problems to be Solved by the Invention]
The radiation detecting elements disclosed in JP-A-61-61707 and JP-A-3-96284 are all α-rays that emit energy close to each other, for example, ^{24 1} Am (5.426 MeV) and ²⁴² Cm (5.796
It was difficult to separate and detect MeV). Japanese Patent Office Sho 61
In the element disclosed in the -61707 publication, since α rays transmitted through the window electrode containing gold as a main component are detected in the depletion layer,
There is a problem that α rays are attenuated in the metal and the resolution deteriorates. Therefore, if the thickness of the gold vapor deposition film is reduced in order to reduce the attenuation of α rays, gold is dispersed in particles during the heat treatment during alloying, and a uniform pn junction layer cannot be obtained. Therefore, it is difficult to discriminate and detect the α-rays that emit energy close to each other because the energy resolution is lowered.

The radiation detecting element disclosed in Japanese Unexamined Patent Publication No. 3-96284 has a smaller decrease in the attenuation rate of α rays until reaching the depletion layer and an improved resolution as compared with the element using the pn junction described above. Even with the element, it is difficult to separate and detect the α rays having the above-mentioned energy close to each other. The reason is,
The thickness of the first amorphous silicon layer is 0.5 to 1 μm, the thickness of the second amorphous silicon layer is 1 μm or more, and α rays are oblique to the amorphous silicon layer and the metal layer of the electrode. When incident on, the attenuation rate is large. Therefore, in addition to the α rays incident in the direction perpendicular to the window electrode surface, the α rays whose energy has been attenuated in this way are added, so that the resolution is lowered.

Another element described in Japanese Patent Application No. 203991 of 1993 is an improvement of the above two elements, in which a second hydrogenated amorphous carbon film is formed on the surface of the window electrode. It is an element with improved chemical resistance. That is, as shown in FIG. 2, a hydrogenated amorphous carbon film is formed on the p-type silicon substrate 1.
21 is deposited, an Al electrode 31 is provided thereon, and a second hydrogenated amorphous carbon film 22 is coated thereon. The lead wire 51 is connected to the Al electrode 31, and the lead wire 52 is connected to the Al electrode 4 attached to the back surface of the substrate 1.
The first amorphous carbon film 21 is provided between the lead wires 51 and 52.
The depletion layer 6 is grown by applying a reverse bias voltage of the heterojunction between the silicon substrate 1 and the silicon substrate 1. However, even in this method, since the thickness of the second amorphous carbon film 22 is set to about 0.2 μm to protect the Al electrode 31, the energy resolution may decrease.

The object of the present invention is to eliminate the above-mentioned drawbacks, to make α-rays less likely to be absorbed by the window electrode before reaching the depletion layer, thereby improving the resolution, and even when contacting with dust containing nitric acid. Another object of the present invention is to provide a semiconductor radiation detection element having a window electrode capable of withstanding the temperature.

[0009]

In order to achieve the above-mentioned object, the semiconductor radiation detecting element of the present invention has a structure in which a heterojunction is formed on a front surface of a semiconductor substrate having a counter electrode on the back surface thereof. It is assumed that a crystalline carbon film is deposited and a window electrode made of a graphite film is provided on the amorphous carbon film. Alternatively, an amorphous carbon film is deposited on the surface of a semiconductor substrate having a counter electrode provided on the back surface, and a window electrode made of a metallic amorphous carbon film is provided on the amorphous carbon film. I shall. In that case, it is effective that the metallic amorphous carbon film is an amorphous carbon film doped with boron. In each case, the surface of the amorphous carbon film forming the heterojunction exposed around the window electrode or the portion where the lead wire for output extraction was connected to the window electrode was covered with the protective film. It is also effective that the protective film is an amorphous carbon film.

[0010]

Function A heterojunction is formed at the interface between the amorphous carbon film and the semiconductor substrate. Graphite or metallic amorphous carbon that forms the window electrode on it is a substance with a small atomic number that has corrosion resistance to dust containing nitric acid,
Since the window electrode can be formed on the silicon substrate with a thin film thickness, the radiation, especially α rays, is less attenuated. Therefore, almost the entire range of α rays is attenuated in the depletion layer. Since the depletion layer spreads on the semiconductor substrate by applying a reverse bias voltage, depending on the voltage applied to the semiconductor substrate having a predetermined resistance,
By making the thickness of the depletion layer about the same as or thicker than the range of α rays, almost the entire range of α rays within the depletion layer, that is, almost all energy can be converted into electric energy, and the resolution is improves.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will be described below with reference to FIG. 1 in which the same parts as those in FIG. Example 1 In the device, a hydrogenated amorphous carbon film 2 and a window electrode 3 are sequentially laminated on a semiconductor substrate 1. An Al electrode 4 is provided on the back surface of the silicon substrate 1 so as to face the window electrode 3. The lead wire 51 is connected to the window electrode 3 via the aluminum pad 5, and the lead wire 52 is connected to the Al electrode 4. The periphery of the window electrode 3 and the top of the Al pad 5 are protected by the amorphous carbon film 7.

Such a semiconductor device is manufactured as follows. First, after forming a first hydrogenated amorphous carbon (aC: H) film 2 having a thickness of, for example, 0.1 μm or less on a p-type Si substrate 1 having a resistivity of 1 kΩ · cm or more, This a
A graphite film having a thickness of, for example, 0.3 μm is formed as a window electrode 3 on the C: H film 2 through a mask by a sputtering method, and Al is vapor-deposited on the entire back surface of the substrate 1 to a thickness of 1 μm. To form the Al electrode 4. Then, at least one Al pad 5 having a thickness of 1 μm or more is formed on the outer peripheral portion of the window electrode 3 by a vapor deposition method through a metal mask, and the lead wire 51 is connected. a-
A C: H film 7 is formed to cover the exposed surface of the amorphous carbon film 2 around the window electrode 3.

In this detection element, a heterojunction is formed at the interface between the first aC: H film 2 and the semiconductor substrate 1, and when a reverse bias voltage is applied between the window electrode 3 and the back Al electrode 4,
The depletion layer 6 spreads just below and laterally of the window electrode 3, and when α rays pass through this portion, electron-hole pairs are generated and detected as a current pulse. An example of film forming conditions for the graphite film 3 is as follows.

Film forming method: Sputtering method Target: Graphite gas: Ar Gas flow rate: 5 SCCM Pressure: 0.6 Pa Power: DC 450 V, 110 mA The resistivity of the obtained graphite film is 1 to 3 × 10 ⁻¹ Ω · cm.
Is. The film forming conditions for the aC: H films 2 and 7 are as follows.

Film formation: plasma CVD method Film formation temperature: 200 ° C. Source gas: ethyl alcohol (temperature 20 ° C.) Gas pressure during glow discharge: 27 Pa Discharge voltage: DC 450 V Distance between electrodes: 50 mm Obtained aC : The H film has a resistivity of 2 to 5 × 10 ¹⁰ Ω · cm. Example 2 The device structure is the same as that of FIG. 1, but an aC: H film having a thickness of, for example, 0.2 μm is formed instead of the graphite film for the window electrode 3, and then plasma CVD is performed on the film.
It is doped with boron by the method and metallized to have a resistivity of 1 to 5 × 10 ⁻¹ Ω · cm. The difference from the detection element of Example 1 is that thermal neutrons can be detected in addition to the above α rays. In this case, the aC: H film 2, 7
The film forming conditions are the same as in Example 1. The boron doping conditions are as follows.

Doping method: Plasma CVD method Film forming temperature: 200 ° C. Source gas: Diborane (B ₂ diluted to 1000 ppm with hydrogen)
H ₆ ) Gas pressure during glow discharge: 27 Pa Discharge voltage: DC 900 V Discharge time: 10 to 15 minutes Distance between electrodes: 50 mm In the device of this example, the window electrode 3 is also formed of an aC: H film. Therefore, after laminating the aC: H film on the entire surface of the aC: H film 2 on the semiconductor substrate, boron is doped only in the central portion using a mask to form a window electrode, An undoped aC: H film in the peripheral portion may be used as an insulating protective film. In that case, a resin or the like is separately used to protect the Al pad 5. Furthermore, this element is
As disclosed in Japanese Patent Publication No. 7, lead wires 51, 52 can be used even when used by being immersed in radioactive waste liquid which is a nitric acid solution, by enclosing it in a chemical-resistant protective case made of, for example, fluororesin. Can be sufficiently protected.

FIG. 3 is an evaluation of the energy resolution of the detection element of Example 1, and as radioactive substances, ²³⁹ Pu (average energy: 5.148 MeV), ²⁴¹ Am (same: 5.426 MeV),
^This is a spectrum obtained when the element was irradiated with a standard α-ray source emitting ²⁴⁴ Cm (5.796 MeV). Peak 81,
82 and 83 correspond to α rays from ²³⁹ Pu, ²⁴¹ Am and ²⁴⁴ Cm, respectively, and the energy resolution (half-width) is about 55 keV. The detection element having an energy resolution of this order is, for example, Pu (energy: about 5.
16 MeV) and Rn-Th (same: about 6.29 MeV) can be detected separately. In the devices disclosed in the above-mentioned Japanese Patent Publication No. 61-61707 and Japanese Unexamined Patent Publication No. 3-96284, the gold antimony alloy layer, the amorphous silicon layer, and the window electrode layer which are insensitive layers to radiation are thicker than those of the device of the present invention. Therefore, the peaks 81, 82, and 83 are often not separable, and are not suitable for the above-mentioned α-ray discrimination detection.

The depletion layer is sufficiently expanded by the reverse bias voltage applied to the device. For example, a reverse bias voltage of 20 V produces a depletion layer having a thickness of about 100 μm.
In this depletion layer, α rays generate electron-hole pairs and are absorbed. The range of the α ray is about 30 to 35 μm in the silicon substrate. Further, since the mean free path of electron-hole pairs in the silicon substrate is large, it is effectively converted into a current and detected as a pulse without self-annihilation, and as a result, high-resolution α-ray detection becomes possible.

[0019]

According to the present invention, a metal film having low chemical resistance
Instead of, graphite film or boron-doped amorphous
Chemical resistance by applying a high quality carbon film as a window electrode
It has become possible to obtain an α-ray detection element having excellent properties. Shi
Even if a-C: H film is not formed on the window electrode made of Al
And the thickness of the layer on the heterojunction compared to prior art devices.
Can be thin. Therefore, if the α-ray passes through the window electrode,
But its attenuation rate is small, so its energy resolution is high.
An α ray detection element is obtained. As a result, for example, nuclear facilities
Promptly even when Pu is included in the dust in the working environment of
Highly safe work environment as it can be detected separately from Rn-Tn
Has come to be obtained. In addition, it is easy to corrode Al
Long-term confidence for at least several years because no metal is used
Reliability is improved, and air is used to form an amorphous silicon film.
Monosilane (SiH _Four) Do not use gas
Therefore, the safety at the time of device manufacturing is improved and the man-hours are simplified.
There is also the effect of In addition, heterojunction forming film, window
AC: H film can be applied to all electrodes and protective films
It is possible to consolidate film forming equipment and film forming technology.
It

[Brief description of drawings]

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

FIG. 2 is a sectional view of an example of a conventional semiconductor radiation device.

²³⁹ to the semiconductor device of an embodiment of the present invention; FIG Pu, ²⁴¹
Α-ray spectrum obtained when irradiated with Am, ²⁴⁴ Cm standard α-ray source

[Explanation of symbols]

 1 Semiconductor Substrate 2, 7 Amorphous Carbon Film 3 Window Electrode 4 Al Electrode 5 Al Pad 6 Depletion Layer

Claims (6)

[Claims] 1. An amorphous carbon film for forming a heterojunction with a semiconductor substrate having a counter electrode provided on the back surface of the semiconductor substrate, and a window made of a graphite film on the amorphous carbon film. A semiconductor radiation detecting element, characterized in that electrodes are provided. 2. An amorphous carbon film, which forms a heterojunction with the semiconductor substrate, is adhered to the surface of a semiconductor substrate having a counter electrode provided on the back surface, and the amorphous carbon film is coated with a metallic material. A semiconductor radiation detecting element comprising a window electrode made of an amorphous carbon film. 3. The semiconductor radiation detecting element according to claim 2, wherein the metallic amorphous carbon film is a boron-doped amorphous carbon film. 4. The semiconductor radiation detecting element according to claim 1, wherein the surface of the amorphous carbon film forming the heterojunction exposed around the window electrode is covered with a protective film. 5. The semiconductor radiation detecting element according to claim 1, wherein a portion of the window electrode to which the lead wire for outputting the output is connected is covered with a protective film. 6. The protective film is an amorphous carbon film.
Alternatively, the semiconductor radiation detection element according to the item 5.