JPH07202246A - Semiconductor radiation detector - Google Patents

Abstract

PURPOSE:To prevent decrease in resolution due to an increased attenuation of a radioactive ray obliquely incident in a radiation detector using a semiconductor substrate and a hetero-junction between amorphous carbon films on the substrate. CONSTITUTION:Amorphous carbon in which attenuation of radioactive ray and particularly an alpha-ray is low has excellent chemical resistance. The carbon is used for a protective layer 4. Further, an entire thickness of a layer for forming a radiation incident window is formed 1.6mum or less, thereby obtaining resolution of 2% or less required for an alpha-ray detector. When a thickness of a barrier layer 2 is made 2-500nm, a uniform and complete junction structure can be formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor radiation detecting element utilizing electron-hole pairs generated by the incidence of radiation on a depletion layer in a semiconductor body.

[0002]

2. Description of the Related Art Among the radiation detecting elements of this type using a semiconductor, the element disclosed in Japanese Patent Publication No. 61-61707 discloses a silicon semiconductor radiation detecting element containing gold containing antimony in a window electrode on which the radiation is incident. Is used. The window electrode contains 0.5 to 2% of antimony. After depositing this gold on a p-type silicon substrate, alloying heat treatment is performed to convert the antimony contained in gold into a donor in the silicon substrate.
Form a pn junction. When a reverse bias voltage is applied to this pn junction, the depletion layer grows and the α ray incident from the window electrode side can be detected.

Japanese Patent Laid-Open No. 3-96284 also discloses an element in which a heterojunction is formed at the interface between a first amorphous silicon thin film and a single crystal silicon substrate for the same purpose as the above element, and further on the surface of the window electrode. A device is disclosed in which a second amorphous silicon is grown around it to increase the corrosion resistance. This element also detects α rays in the same manner as the above-mentioned element. The device described in Japanese Patent Application No. 5-203991 also has the same purpose as the above two devices, in that a second amorphous carbon film is grown on and around the surface of the window electrode to improve corrosion resistance. Is an element that has increased.

[0004]

However, the radiation detecting elements disclosed in Japanese Patent Publication No. 61-61707 and Japanese Patent Application Laid-Open No. 3-96284 are all α-rays, for example, ²⁴¹ Am (5. 426Me
It was difficult to detect V) and ²⁴² Cm (5.796 MeV) separately.

In the radiation detecting element disclosed in Japanese Patent Publication No. 61-61707, since α rays transmitted through the window electrode containing gold as a main component are detected by the depletion layer, the α rays are attenuated in the metal electrode and the resolution is improved. There was a problem that was worse. Therefore, if the thickness of the vapor deposited gold film is reduced in order to reduce the attenuation of α rays, gold is dispersed in a granular form during the heat treatment during alloying, resulting in a uniform p
No n-junction can 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.

In the radiation detecting element disclosed in Japanese Patent Laid-Open No. 3-96284, the attenuation rate of α rays until reaching the depletion layer is smaller than that of the above element, and the resolution is improved.
Even with this element, it is difficult to separate and detect the α rays having the above-mentioned energy close to each other. The reason is that, as shown in that publication, the thickness of the first amorphous silicon layer is about 1 μm and the thickness of the second amorphous silicon layer is 1 μm or more. When α-rays are obliquely incident on the layers and the metal layers of the electrodes, the attenuation rate is large.
Therefore, in addition to the α rays incident in the direction perpendicular to the window electrode, the α rays whose energy has been attenuated in this way are added, so that the resolution is lowered.

The object of the invention is to solve the above-mentioned drawbacks,
By suppressing the amount of α-rays absorbed by electrodes etc. before reaching the depletion layer, the resolution is improved and a uniform junction is formed.
Another object of the present invention is to provide a semiconductor detection element having a structure excellent in corrosion resistance.

[0008]

In order to achieve the above object, the present invention provides a barrier layer made of amorphous carbon, a metal electrode layer, and a protective layer in this order on one surface of a semiconductor substrate of the first conductivity type. The back surface electrode layer is laminated and has an ohmic contact on the other surface, and the semiconductor substrate is a depletion layer that spreads from the junction between the semiconductor substrate and the barrier layer into the semiconductor substrate by the voltage applied between the metal electrode layer and the back surface electrode layer. In a semiconductor radiation detection element that detects radiation based on electron-hole pairs generated by radiation incident from one surface side, the total thickness of the barrier layer, the metal electrode layer and the protective layer is 1.6 μm or less. To do. It is effective that the thickness of the barrier layer is 2 to 500 nm. It is preferable that the semiconductor substrate be made of p-type silicon, the protective layer be made of amorphous carbon that is substantially the same in quality as the barrier layer, and that the metal electrode layer be made of aluminum.

[0009]

Since amorphous carbon is a substance having a small atomic number and can be formed thin on a silicon substrate, the attenuation of radiation, especially α rays is small. Even when amorphous carbon is used for the protective layer, by setting the total thickness of the layer forming the window to 1.6 μm or less, almost all incident α rays are attenuated in the depletion layer, That is, most of the energy of incident α-rays is converted into electric energy, and an α-ray detection element with excellent resolution can be obtained.

Further, the barrier layer has a thickness of 2 to 500 n.
By setting m, a uniform and complete joint structure can be obtained. That is, the depletion layer can be sufficiently expanded to improve the energy conversion efficiency. By forming the protective layer and the barrier layer with substantially the same amorphous carbon, it is possible to improve the product resistance and share the film forming apparatus.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view showing a semiconductor radiation detecting element according to an embodiment of the present invention. In the figure, high resistivity p-type Si
A barrier layer 2 made of amorphous carbon, an electrode layer 3 made of Al, and a protective layer 4 made of amorphous carbon are formed on a substrate 1.
Are stacked in this order. On the other hand, the back surface electrode layer 5 made of Al is provided on the back surface of the silicon substrate 1. Also,
Lead wires 6 and 7 are connected to the electrode 3 and the back surface electrode 5, respectively, and a reverse bias voltage for a junction between the Si substrate 1 and the barrier layer 2 is supplied from a power source 9 via the lead wires 6 and 7. Is applied. Note that Si
Although there is a p-type high impurity concentration layer for obtaining an ohmic connection between the substrate 1 and the back surface electrode layer 5, the illustration thereof is omitted.

Such a semiconductor radiation detecting element is manufactured, for example, as follows. First, the resistivity is 10k
Amorphous carbon is deposited over the entire surface to a thickness of 10 nm on a p-type Si substrate 1 having a resistance of about Ωcm to form a barrier layer 2. The electrode layer 3 is vapor-deposited only on the central portion on this using a mask. on the other hand,
An Al back electrode layer 5 is formed on the entire back surface. After that, an amorphous carbon film is formed to a thickness of 300 nm to form the protective film 4.

In the semiconductor radiation detecting element thus manufactured, a so-called heterojunction is formed at the interface between the barrier layer 2 and the Si substrate 1, and when a reverse bias voltage is applied between the electrode layer 31 and the back electrode layer 5, the electrode layer 2 is formed. The depletion layer 8 spreads just below
Since electron-hole pairs are generated when α rays pass through this portion, it is possible to detect this as a current pulse.

The conditions for forming the amorphous carbon film are as follows. Film forming method: ECR plasma CVD method Source gas: Methane gas pressure: 0.6 Pa Substrate heating temperature: 100 ° C. Such a semiconductor device having a barrier layer thickness of 2 to 500 n
It was produced by changing the range of m. Table 1 is a summary of the values of the leak currents when a reverse bias of 60 V is applied to these devices.

[0015]

[Table 1] If the thickness of the barrier layer 2 is less than 2 nm, perfect bonding cannot be performed, the leak current is unstable, and reproducibility is low.
The characteristics of the Si / Al Schottky junction were as high as 0 ^-5 A / cm ² or more. On the other hand, when the film thickness is 500 nm, the rectification ratio is about 10: 1 (at 60 V), and it has been found that the rectification ratio is extremely reduced when the film thickness exceeds this. From the above results, it was revealed that the bonding characteristics were incomplete unless the thickness of the barrier layer 2 was in the range of 2 to 500 nm.

Next, the resolution of the α-ray detecting element will be considered. Fig. 2 shows Si of 6.3 MeV α rays (eg Rn).
The range in the substrate 1 is plotted against the incident angle. However, the range in the dead layer (corresponding to the barrier layer, the electrode layer, and the protective layer in the device of the example of the present invention) having a film thickness of d μm is subtracted. This is because the electron-hole pairs generated in the dead layer on the incident side of Si cannot be extracted to the outside by recombination. As shown in FIG. 2, it can be seen that the range reduction rate at which the film thickness of the dead layer increases is large.

Although various usage states of the α-ray detecting element can be considered, it is generally convenient to place the radiation source at a distance approximately the same as the size of the detecting element in view of the balance between detection sensitivity and resolution. Therefore, the incident angle is in the range of 0 to 45 degrees. On the other hand α
The resolution (full width at half maximum) of the line detection element is required to be 120 KeV, which is about 2% with respect to the central energy. The range in the insensitive layer at normal incidence (0 degree) is dμm, and the range in the insensitive layer at 45 degree incidence is cos 45 ° × d = 2 ^1/2 × dμ
The range in m and Si is 33 μm. Therefore, the dispersion (that is, resolution) of the number of electron-hole pairs generated in Si is
It can be calculated by (2 ^1/2 −1) × d / 33. It is calculated that d must be less than 1.6 μm for this to be less than 2%. That is, in the device according to the present invention, the total film thickness of the barrier layer 2, the metal electrode layer 3, and the protective layer 4 must be 1.6 μm or less. When the protective layer is formed of an organic resin or the like, radiation is attenuated so much that the total film thickness must be further reduced.

Although the method of forming amorphous carbon on the p-type Si substrate by the ECR-CVD method has been described in the above-mentioned embodiment, the constitution and manufacturing method of each element do not prevent appropriate modification. Absent. The gist of the present invention is that the total thickness of the barrier layer made of amorphous carbon, the metal electrode layer and the protective layer is 1.
The thickness is 6 μm or less, and the thickness of the barrier layer is 2 to 500 nm.

[0019]

According to the present invention, by setting the total film thickness of the barrier layer, the metal electrode and the protective layer to 1.6 μm or less, the energy resolution of 2% which is a practical value can be achieved. Further, by setting the thickness of the barrier layer to 2 to 500 nm, a uniform and complete junction structure can be obtained. Furthermore, by using amorphous carbon as the material of the protective layer, α with excellent chemical resistance can be obtained.
This can be achieved by a simple process because the line detecting element is provided and the barrier layer and the protective layer are formed of substantially the same amorphous carbon.

[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 diagram showing the relationship between the range of α-rays and the incident angle in the substrate with the thickness of the dead layer on the Si substrate as a parameter.

[Explanation of symbols]

 1 p-type Si substrate 2 barrier layer 3 electrode layer 4 protective layer 5 back electrode layer 8 depletion layer 9 reverse bias power supply

Claims (5)

[Claims] 1. A barrier layer made of amorphous carbon, a metal electrode layer, and a protective layer are sequentially laminated on one surface of a semiconductor substrate of the first conductivity type, and a back electrode layer in ohmic contact is deposited on the other surface. Based on the electron-hole pairs generated by the radiation incident from one side of the semiconductor substrate on the depletion layer spreading from the junction between the semiconductor substrate and the barrier layer to the semiconductor substrate by the voltage applied between the metal electrode layer and the back electrode layer. A semiconductor radiation detection element for detecting radiation, wherein the total thickness of the barrier layer, the metal electrode layer and the protective layer is 1.6 μm or less. 2. The semiconductor radiation detecting element according to claim 1, wherein the barrier layer has a thickness of 2 to 500 nm. 3. The semiconductor radiation detecting element according to claim 1, wherein the semiconductor substrate is made of p-type silicon. 4. The semiconductor radiation detecting element according to claim 1, 2 or 3, wherein the protective layer is made of amorphous carbon having substantially the same quality as that of the barrier layer. 5. The semiconductor radiation detecting element according to claim 1, wherein the metal electrode layer is made of aluminum.