JPH0543196B2 - - Google Patents

Description

[Detailed description of the invention] [Industrial application field]

The present invention relates to a method for manufacturing a semiconductor radiation detector using a heterojunction formed between a high-purity single crystal semiconductor substrate and an amorphous semiconductor layer thereon.

[Conventional technology]

As a means of forming a depletion layer in a detector that detects radiation by carriers generated by the incidence of radiation into a depletion layer in a semiconductor, for example, a high purity single crystal silicon substrate and an amorphous silicon film deposited thereon are used. Semiconductor radiation detectors that utilize the heterojunction formed between the two have already been disclosed in JP-A-59-22716 and JP-A-60-47471. As shown in the structure of FIG. 2, this detector has an amorphous silicon layer 2 deposited on one surface and side surfaces of a single crystal silicon substrate 1, and metal electrodes 3 provided on both surfaces.
and 4 to spread a depletion layer 5 in the semiconductor single crystal 1, radiation is incident into this depletion layer to generate electron-hole pairs, and a signal is detected.

[Problem to be solved by the invention]

However, in the above-mentioned detector, especially when the silicon single crystal 1 and the amorphous silicon layer 2 have high specific resistance, the Schottky barrier that occurs at the interface between the metal electrodes 3 and 4 and the single crystal silicon and silicon Since a large voltage drop occurs, the voltage applied to the heterojunction between the original amorphous silicon and single crystal silicon is not sufficiently applied, and as a result, the depletion layer does not spread sufficiently into the crystalline silicon. was. Another drawback is that the shot key barrier portion is not desirable because it becomes a source of noise when a signal is extracted as a semiconductor radiation detector. FIG. 3 shows the energy distribution in the semiconductor radiation detector shown in FIG. 2, and the positions of each part are indicated by the symbols written in FIG. 2 below. Also E _F
represents Fermi level energy, C and B represent conduction bands, and V and B represent valence bands, respectively. In FIG. 3, Schottky barriers are generated at the joint 21 between the metal electrode 4 and the single crystal silicon 1 and at the joint 23 between the amorphous silicon 2 and the metal electrode 3, and the single crystal silicon 1 and the amorphous silicon 2 A heterojunction 22 exists at the interface. The Schottky barrier is caused by the energy difference between the work functions of a semiconductor and a metal, and it is a known technique that the Schottky barrier can be reduced by reducing this energy difference. In addition, in order to reduce this Schottky barrier, that is, to form an ohmic contact, there is a method of forming a p ⁺ layer on a p-type semiconductor substrate and forming a metal electrode thereon, or a method of forming an n ⁺ layer on an n-type semiconductor substrate. The method of forming a metal electrode on the metal electrode is a technique widely used in current semiconductor processes.
However, the currently used p ⁺ layer and n ⁺ layer formation technology, that is, ohmic contact formation technology, uses thermal diffusion methods at temperatures above 1000°C, and ion implantation methods that require post-processing at temperatures above 800°C. be. All of these methods involve high-temperature processes of 800°C or higher, which poses little problem with conventional low-resistance silicon, but they are not suitable processes for semiconductor radiation detectors that use high-purity silicon substrates. The reason for this is that exposing a high-purity silicon substrate to high temperatures causes thermal defects in the silicon substrate itself, resulting in a shortened lifetime and significant deterioration of the electrical characteristics of the device. The present invention has been made in view of the above points, and consists of depositing an amorphous semiconductor layer on one surface of a high-purity semiconductor single crystal, and depositing an amorphous semiconductor layer on each surface of the semiconductor single crystal and the amorphous semiconductor layer. Provided is a manufacturing method that prevents the formation of a Schottky barrier at the interface between the electrode and semiconductor of a previously applied semiconductor radiation detector having a metal electrode, and that does not cause thermal defects by exposing a single crystal semiconductor substrate to high temperatures. The purpose is to

[Means to solve the problem]

In order to achieve the above object, in the first invention of the present application, one main surface of a high purity single crystal semiconductor substrate of one conductivity type (for example, p-type) is provided with an opposite conductivity type (for example, weak n-type).
An amorphous semiconductor layer with high specific resistance is deposited using a mold), a film of an impurity metal such as aluminum is formed on the other main surface of the semiconductor substrate opposite to the one main surface, and a film of an impurity metal, such as aluminum, is deposited in an inert gas plasma. impurity metal is infiltrated into the semiconductor substrate from the other main surface to form a surface layer with the same conductivity type as the semiconductor substrate and high impurity concentration (p ⁺ type),
An electrode made of impurity metal (aluminum) is provided on this surface layer. Further, in the second invention of the present application, an amorphous semiconductor layer of a high specific resistance of an opposite conductivity type (for example, a weak n-type) is formed on one main surface of a high-purity single crystal semiconductor substrate of one conductivity type (for example, a p-type). A film of an impurity metal, such as gold containing antimony, is formed on this amorphous semiconductor layer, and the impurity is transferred from the surface of the amorphous semiconductor layer to this amorphous semiconductor layer in an inert gas plasma. Infiltrating a metal to form a (n ⁺ type) surface layer with the same conductivity type as the amorphous semiconductor layer and high impurity concentration, and providing an electrode made of impurity metal (gold-antimony) on this surface layer. shall be.

[Effect]

With the above technical means of the first invention, the Schottky barrier at the interface between the semiconductor substrate and the metal electrode is reduced without causing thermal defects in the semiconductor substrate, and the contact between the semiconductor substrate and the metal electrode approaches ohmic contact. Further, by the above technical means of the second invention, the Schottky barrier at the interface between the amorphous semiconductor layer and the metal electrode is reduced without causing thermal defects in the semiconductor substrate, and the contact between the amorphous semiconductor layer and the metal electrode is made ohmic. approach contact.

【Example】

FIGS. 1a to 1e show most of the steps in the embodiment of the first invention of the present application. An undoped amorphous silicon layer 2 exhibiting weak n-type is deposited from monosilane gas by a known plasma CVD method on the upper surface of a p-type high-purity silicon single crystal substrate 1 with a specific resistance of 10 kΩcm or more as shown in FIG. 1a.b . Next, aluminum is deposited on the surface of the amorphous silicon layer 2 as a metal electrode 3c. Incidentally, the step c of providing the metal electrode 3 may be carried out after the low-temperature plasma treatment step explained later with reference to FIG. 4, and the process can proceed from the step b to the step d described below. Next, the substrate 1 is turned upside down (d), and an aluminum film 6 with a thickness of 0.01 to 0.1 μm is formed on the upper surface by vacuum evaporation (e). The device 10 that has undergone these steps is placed in the reaction tank 11 of the apparatus shown in FIG. 4, and the lower electrode plate 12 is placed with the aluminum film 6 facing upward.
Place it on top. The apparatus shown in FIG. 4 is also equipped with an upper electrode plate 13, a DC voltage power source 14, an exhaust system 15, a displacement adjustment valve 16, a vacuum gauge 17, a heater 18 for heating the lower electrode plate, and a heater power source 19. An inert gas cylinder 31 is connected to the tank 11 via a pressure reducing valve 32, a gas flow rate regulator 33, and a gas flow meter 34. Using the apparatus shown in FIG. 4, plasma is generated under the following conditions to cause aluminum to penetrate from the aluminum film 6 into the silicon single crystal. (1) Substrate (lower electrode plate) temperature: 300℃ (2) Degree of vacuum: 0.1 to 0.5 Torr (3) Applied voltage: DC 400 to 1000V (4) Inert gas used: Argon The process of aluminum penetration is explained below. . First, the lower electrode plate 12 on which the element 10 shown in FIG. 1e is mounted is heated to 300° C. using the motor 18. In this state, using the exhaust system 15,
After creating a high vacuum of 10 ^-7 Torr or less, the argon pressure in the reaction tank 11 is maintained at 0.1 to 0.5 Torr using the exhaust volume adjustment valve 16 and the gas flow rate adjustment valve 33.
Here, using the power supply 14 between the electrode plates 12 and 13,
Apply a DC voltage of 400 to 1000V. This causes a glow discharge between the electrodes in the reaction tank, and as a result, a Kurkus dark region with an extremely strong electric field is formed above the lower electrode plate. FIG. 5 is an enlarged view of the vicinity of the element 10 in FIG. 4. Here, the ionized argon 35 is accelerated toward the cathode electrode 12 and collides with the aluminum 6, causing the silicon single crystal 1
Aluminum penetrates into the p ⁺ layer 6 because aluminum, which is a group element, acts as an acceptor.
It is thought that it forms 1. It is also fully conceivable that the argon ions 35 colliding with the surface of the aluminum film 6 act to repel aluminum from the aluminum film 6. After forming the p ⁺ layer 61 in this manner, aluminum is again deposited on the surface of the p ⁺ layer by vacuum evaporation to form the electrode 4. In the semiconductor radiation detector obtained in this way, only the Schottky barrier at the interface between the electrode 4 and the silicon substrate 1 has been reduced, but most of the applied voltage is still Since the voltage can be applied to the junction, it is not only possible to sufficiently expand the depletion layer in the crystalline silicon, but also to suppress the noise that was previously generated by the Schottky barrier, making it possible to improve the performance of semiconductors with direct metal electrodes. Compared to the radiation detection group, the gamma-ray and beta-ray detection efficiencies were improved by 15% and 12%, respectively. Next, as an embodiment of the second invention of the present application, a structure in which the Schottky barrier shown at 23 in FIG. 3, that is, the Schottky barrier between the amorphous silicon and the metal electrode is reduced, will be described. In Figure 6, the deposition ratio is 10kΩcm or more in the same process as in Figure 1.
After depositing an undoped amorphous silicon layer 2 on a p-type single crystal substrate 1, antimony 1 to
A film 7 of gold containing 10% is vacuum deposited. Next, gold containing antimony is infiltrated into the amorphous silicon layer 2 by argon plasma using the apparatus shown in FIG. 4 in the same manner as in the above embodiment.
As a result, the amorphous silicon surface layer becomes an n ⁺ layer due to the addition of antimony, a metal-n ⁺ layer-weak n-type amorphous silicon junction is formed, and the Schottky barrier is reduced. After this, further gold-antimony film 7
Electrode 3 is formed by depositing gold on top of the electrode. However, the gold-antimony film may be made thicker and used as it is as one electrode. In the semiconductor radiation detector thus fabricated, only the Schottky barrier at the interface between the electrode 3 and the amorphous silicon layer 2 was reduced, but the aluminum electrode was still provided directly on the amorphous silicon layer. γ
The detection efficiency of rays and β rays was improved by 5% and 7%, respectively. In this embodiment, the amorphous silicon layer 2 is formed of undoped amorphous silicon, but if the n-type is strengthened by doping with an appropriate impurity,
Alternatively, even when a p-type amorphous silicon layer is deposited on an n-type silicon single crystal, the present invention can form an n ^{+ layer or a p+ layer} , respectively, using a low-temperature plasma process.
It is also effective to form the layer on an amorphous silicon surface layer.

【Effect of the invention】

As explained above, the electrodes provided on the single crystal semiconductor and the amorphous semiconductor of the radiation detector that utilize the electric signal generated by the incidence of radiation into the depletion layer based on the heterojunction of the single crystal semiconductor and the amorphous semiconductor. In order to reduce the Schottky barrier at the interface and bring it closer to ohmic contact, metal is infiltrated into the single crystal semiconductor substrate or amorphous semiconductor layer using the energy of plasma generated at low temperature. By forming a highly concentrated impurity layer on the surface of each semiconductor layer, we can avoid the negative effects of high-temperature processing on high-purity semiconductor single crystals.
The detection efficiency of semiconductor radiation detectors can be improved at low cost with short processing time and simple equipment.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing a part of the process of an embodiment of the first invention of the present application, FIG. 2 is a sectional view of a semiconductor radiation detector which is the object of the present invention, and FIG. 3 is an energy level diagram thereof. 4 is a configuration explanatory diagram of an example of a plasma generator used in the low-temperature plasma treatment process of the first and second inventions of the present application, FIG. 5 is an enlarged sectional view of a part of the apparatus of FIG. 4, and FIG. FIG. 2 is a cross-sectional view sequentially showing a part of the steps of the second embodiment of the invention. 1: p-type single crystal silicon plate, 2: amorphous silicon layer, 3, 4: metal electrode, 6: aluminum film,
61: p ⁺ layer, 7: gold-antimony film, 10: element, 11: reaction tank, 12, 13: electrode plate, 15:
Exhaust system, 31: Inert gas cylinder.

Claims (1)

[Claims] 1. An amorphous semiconductor layer of an opposite conductivity type and high specific resistance is deposited on one main surface of a high-purity single crystal semiconductor substrate of one conductivity type, and the semiconductor substrate faces the one main surface. A film of an impurity metal is formed on the other main surface of the semiconductor substrate, and the impurity metal is allowed to enter the semiconductor substrate from the other main surface in an inert gas plasma to form a surface having the same conductivity type as the semiconductor substrate and having a high impurity concentration. forming a layer, and providing an electrode made of the impurity metal on this surface layer;
A method for manufacturing a semiconductor radiation detector, characterized in that: 2. The method for manufacturing a semiconductor radiation detector according to claim 1, wherein the high purity single crystal semiconductor plate is a p-type silicon substrate and the impurity metal is aluminum. 3. Depositing an amorphous semiconductor layer of opposite conductivity type and high specific resistance on one main surface of a high purity single crystal semiconductor substrate of one conductivity type, and forming an impurity metal film on this amorphous semiconductor layer, Intruding the impurity metal from the surface of the amorphous semiconductor layer into the amorphous semiconductor layer in an inert gas plasma to form a surface layer having the same conductivity type as the amorphous semiconductor layer and having a high impurity concentration; A method for manufacturing a semiconductor radiation detector, characterized in that an electrode made of the impurity metal is provided on this surface layer. 4. Manufacturing a semiconductor radiation detector according to claim 3, wherein the amorphous semiconductor layer is a weak n-type amorphous silicon layer, and the impurity metal is gold containing antimony. Method.