CN102074610A - Beta-radiation detector based on field effect tube structure of silicon carbide metal semiconductor - Google Patents

Abstract

The invention discloses a beta ray radiation detector based on a silicon carbide metal semiconductor field effect transistor structure, which mainly solves the problems of poor radiation resistance and low energy conversion efficiency of the existing beta radiation detectors. The detector consists of an n-type substrate (8), a p-type buffer layer (7), an n-type channel (6) with a concentration of 3.5-4×10 ¹⁷ cm ^-3 , an n-type buffer layer (5 ) and ohmic contact layer (4), the source and drain electrodes (2) are deposited on the ohmic contact layer, and the translucent Schottky contact layer (1) is deposited on the n-type buffer layer, the Schottky contact layer consists of a high potential barrier Composed of Schottky metal Au/Ti/Pt, the depth of which is buried in the n-type buffer layer (5) is 0.06-0.08 μm, and the surface area other than the gate, source and drain is covered with a layer of _SiO2 passivation layer (3) . The invention has the characteristics of strong radiation resistance, high energy conversion efficiency and high detection efficiency, and can be used for detecting beta rays in nuclear energy.

Description

β Radiation Detector Based on Silicon Carbide Metal Semiconductor Field Effect Transistor Structure

technical field

The invention belongs to the field of microelectronics, and in particular relates to a beta radiation detector based on a silicon carbide metal semiconductor field effect tube structure, which can be used in the field of beta ray ionizing radiation detection.

technical background

Semiconductor radiation detector is a new type of advanced detector developed after gas detector and scintillator detector. The basic principle is to use semiconductor technology, such as evaporation, diffusion, ion implantation, etc., to make a thicker depletion layer or diffusion region on the semiconductor substrate under the working condition of reverse bias voltage, which is used to detect incident rays or charged particles. Existing semiconductor radiation detectors are all based on Si, GaAs materials such as diodes and PIN tubes, and are mainly used to detect alpha particles, beta rays and neutrons.

Semiconductor radiation detectors have high requirements on materials, and it is generally believed that they should have the following characteristics:

(1) Larger forbidden band width ensures that the detector has higher resistivity and lower leakage current when it is working;

(2) Good process performance, easy to produce crystals with high purity and good integrity, and have good mechanical and chemical properties at the same time, easy to carry out mechanical processing, and easy to make barrier contact or ohmic contact;

(3) Excellent physical properties, capable of high reverse bias, small reverse current, and small forward current; at the same time, the mobility-lifetime product of carriers in the material should be large to ensure that the detector has good energy resolution.

Traditional Si and GaAs junction field effect transistor devices are not suitable for nuclear radiation detection and other fields, because these devices have low thermal conductivity, low breakdown voltage, low power density, and poor radiation resistance. In order to meet the needs of high-performance and high-reliability semiconductor radiation detectors in the national defense and medical fields, it is necessary to develop radiation detectors based on new semiconductor materials.

SiC, a semiconductor material, has a wide band gap of 2.6 to 3.2eV, a high saturation electron drift velocity of 2.0×10 ⁷ cm·s ^-1 , a high breakdown electric field of 2.2MV·cm ^-1 and 3.4 to 4.9W·cm ^{-1 1} · s ^-1 high thermal conductivity and other properties, and has a low dielectric constant, these characteristics determine its great potential in high temperature, high frequency, high power semiconductor devices, radiation resistance, digital integrated circuits, etc. Application potential, especially the advantages of good radiation resistance and suitable for nuclear environment work, so based on SiC radiation-resistant semiconductor devices will have better application prospects in the field of radiation detection. For this reason, relevant researchers have also done research in this area. SiC-based metal-semiconductor field-effect transistors are field-effect transistors that use gold half-junctions instead of PN junctions. The metal-semiconductor contact process allows the channel of the metal-semiconductor field effect transistor to be made shorter, which is conducive to improving the switching speed and operating frequency of the device.

The document "Nuclear Instruments and Methods in Physics ResearchA 583(2007) 157-161" "Silicon carbide for UV, alpha, beta and X-ray detectors: Results and perspectives" introduced the SiC metal-semiconductor structure proposed by Italian Francesco Moscatelli The idea of a beta detector. This structure is a layer of p-type silicon carbide epitaxial on the silicon carbide semi-insulating substrate, and then a layer of n-type silicon carbide epitaxially on the p-type silicon carbide, the source and drain regions are formed by n+ high doping, and the gate is formed in the middle region. pole, as shown in Figure 3. However, there are high-density surface traps in this field-effect transistor based on the traditional SiC Schottky structure. In SiC materials, the acceptor surface traps trap electrons to form surface charges, so that part of the electric force line terminates on the surface charges. Due to the high electric field in the gate and drain regions Under the action, the electrons flowing from the source to the drain will be captured by surface traps when passing through the channel, thereby forming a depletion layer on the surface, making the effective channel thickness for current transmission thinner, thus affecting the metal semiconductor field effect transistor device. electrical properties. At the same time, when the β-ray reaches the surface of the detector, only part of the β-ray can enter the interior of the device due to the blocking of the thicker gate metal layer. Only beta particles entering the depletion region will contribute to the current output. Therefore, the thicker gate structure results in a large energy loss of incident particles and lower energy conversion efficiency.

Contents of the invention

The purpose of the present invention is to avoid the defects of the above-mentioned prior art, and utilize the unique advantages of SiC semiconductor materials to propose a silicon carbide metal semiconductor field-effect transistor-based β radiation detector and its manufacturing method, so as to weaken the traditional MESFET structure detector. The surface trap effect and the thicker gate structure lead to a large energy loss of the incident β particles, and the low energy conversion efficiency affects the performance of the device and improves the detection efficiency.

In order to achieve the above object, the β radiation detector based on the silicon carbide metal semiconductor field effect transistor structure proposed by the present invention includes an n-type substrate, a p-type buffer layer, an n-type channel, an n-type buffer layer and N+-doped ohmic contact layer on both sides, metal Ni is deposited on the ohmic contact layer as the source and drain, and a semi-transparent Schottky contact layer is deposited in the middle area of the n-type buffer layer and buried in the n-type buffer layer. The Schottky contact layer is composed of high-barrier Schottky metal Au/Ti/Pt, and the surface area other than the gate, source and drain is covered with a layer of _SiO2 passivation layer, and the concentration of the n-type channel is 3.5~ 4×10 ¹⁷ cm ^-3 , the depth at which the Schottky contact layer is buried in the n-type buffer layer is 0.06-0.08 μm.

In order to achieve the above object, the method for manufacturing a beta radiation detector based on a silicon carbide metal semiconductor field effect transistor structure provided by the present invention includes the following steps:

(1) Epitaxially layer a p-type epitaxial layer with a thickness of 0.15 μm and a doping concentration of 1.4×10 ¹⁵ cm ^-3 on an n-type 4H-SiC substrate;

(2) An n-type channel with a thickness of 0.26 μm and a doping concentration of 3.5 to 4×10 ¹⁷ cm ^-3 is epitaxially formed on the p-type buffer layer;

(3) Epitaxially layer an n-type buffer layer with a thickness of 0.1 μm and a doping concentration of 1.7×10 ¹⁷ cm ^-3 on the n-channel;

(4) On the n-type buffer layer, epitaxially layer a source-drain layer with a thickness of 0.15 μm and a doping concentration of 1×10 ¹⁹ cm ^-3 ;

(5) Dry oxygen oxidation on the epitaxial layer in the source and drain layer to form SiO _Passivation layer;

(6) _SiO2 is wet-etched on the surface of both sides of the passivation layer to form a source and drain region, and Ni is evaporated with an electron beam to form a 0.2 μm ohmic _contact metal source and drain in the source and drain region;

(7) Wet etch the middle area of the passivation layer, etch vertically to the surface of the n-type buffer layer to form the gate area of the radiation detector, and perform dry oxygen oxidation on the surface area other than the metal source and drain to form a layer A capping layer of _SiO2 ;

(8) In the middle area of 0.8 μm from the drain and 0.4 μm from the source, use wet etching to remove the SiO ₂ on the surface and the n-type buffer layer at a depth of 0.06-0.08 μm, and use electron beam evaporation in this etching area Deposit a semi-transparent high-barrier Schottky metal Ti or metal Pt or metal Au with a thickness of 100nm to form a Schottky metal gate.

Compared with the prior art, the present invention has the following advantages:

(1) The present invention utilizes the characteristics of strong radiation resistance of the silicon carbide structure, which can ensure that electronic equipment can still work normally under the radiation of nuclear radiation and cosmic rays, which is very beneficial for detecting β-rays;

(2) The β radiation detector of the present invention adopts a structure based on a buried trench buried gate silicon carbide metal-semiconductor field-effect transistor. Compared with a traditional metal-semiconductor field-effect transistor structure, due to the addition of an n-type buffer layer, the effective conduction channel can be made The channel is far away from the surface, which weakens the surface trap effect, thereby weakening the influence of the surface trap on the electrical performance of the device and improving the device performance;

(3) The n-type channel doping concentration of the present invention is 3.5-4×10 ¹⁷ cm ^-3 , which is higher than the n-type channel doping concentration of traditional metal semiconductor field effect transistors, which is conducive to improving the channel conduction current density; metal The gate is buried in the n-type buffer layer at a depth of 0.06-0.08 μm, which can reduce the surface trap effect compared with the metal gate not buried in the n-buffer layer. At the same time, as the buried depth increases, the thickness of the effective conductive channel decreases, and the drain The saturation current also decreases, thereby reducing the influence of the drain saturation current on the device.

(4) The present invention adopts a thin metal grid with a thickness of 100nm, which effectively reduces the blocking of low-energy incident particles by the metal grid, improves energy conversion efficiency, and has higher detection efficiency.

Description of drawings

Fig. 1 is a structural schematic diagram of a beta radiation detector of the present invention;

Fig. 2 is the main flow schematic diagram of making beta radiation detector of the present invention;

FIG. 3 is a schematic diagram of the structure of a conventional metal-semiconductor field effect transistor.

Detailed ways

Referring to Fig. 1, the β radiation detector based on the silicon carbide metal semiconductor field effect transistor structure of the present invention mainly includes an n-type substrate 8 with a thickness of 0.4 μm and a doping concentration of 1×10 ¹⁸ cm ^-3 from bottom to top On the substrate is a p-type buffer layer 7 with a thickness of 0.15 μm and a doping concentration of 1.4×10 ¹⁵ m ⁻³ ; on the p-type buffer layer 7 is a layer of 0.26 μm in thickness and a doping concentration of 3.5 to 4× 10 ¹⁷ cm ^-3 n-type channel 6; on the n-type channel 6 is an n-type buffer layer 5 with a doping concentration of 1.7×10 ¹⁷ cm ^-3 and a thickness of 0.1 μm; the surface of the n-type buffer layer 5 On both sides of the ohmic contact layer 4 with a doping concentration of 1×10 ¹⁹ cm ^-3 , metal Ni is deposited on the ohmic contact layer as the source and drain electrodes 2 , and a half layer with a thickness of 100 nm is deposited in the middle region of the n-type buffer layer Transparent Schottky contact layer 1, the Schottky contact layer is made of high barrier Schottky metal Au or Ti or Pt, which is embedded in the n-type buffer layer 5, and the depth of the embedded n-type buffer layer 5 is 0.06 ~0.08 μm; the surface area other than the gate and source/drain is covered with a passivation layer 3 of _SiO2 .

With reference to Fig. 2, the method for making the β radiation detector shown in Fig. 1 of the present invention is described in detail by the following examples:

Example 1

In the first step, an n-type 4H-SiC substrate with a thickness of 0.4 μm and a doping concentration of 1×10 ¹⁸ cm ^-3 is selected as the substrate 8. After cleaning, LPCVD is used for low-pressure hot-wall chemical vapor deposition. _{4H- _ _ _} ^{_ _} The p-type buffer layer 7 of SiC is shown in Fig. 2a.

The second step is to use low-pressure hot-wall chemical vapor deposition method LPCVD, under the conditions of epitaxial temperature of 1570 ° C, pressure of 100 mbar, and growth gas of C ₃ H ₈ , SiH ₄ and H ₂ , on the p-type buffer layer 7 An epitaxial layer of n-type channel 6 with a thickness of 0.26 μm and a doping concentration of 3.5×10 ¹⁷ cm ^-3 , as shown in Figure 2b;

The third step is to use the low-pressure hot-wall chemical vapor deposition method LPCVD, under the conditions of the epitaxial temperature of 1570 ° C, the pressure of 100 mbar, and the growth gas of C ₃ H ₈ , SiH ₄ and H ₂ , epitaxial layer on the n-channel An n-type buffer layer 5 with a thickness of 0.1 μm and a doping concentration of 1.7×10 ¹⁷ cm ^-3 , as shown in Figure 2c;

In step 4, epitaxially epitaxial a layer of silicon carbide with a thickness of 0.15 μm on the n-type buffer layer 5 and doped with ion implantation to form an n-type ohmic contact layer 4 with a doping concentration of 1×10 ¹⁹ cm ^-3 , as shown in As shown in Figure 2d;

In step 5, at a temperature of 1100±50° C., perform dry oxygen oxidation on the epitaxial substrate in step 4 for two hours to form a _SiO2 passivation layer 3, as shown in FIG. 2e;

The 6th step, on SiO ₂ passivation layer 3 adopts wet method to etch away its surface SiO ₂ on both sides regions Form the source and drain region, use electron beam to evaporate Ni in this source and drain region as the ohmic contact metal of source and drain, at 1000 Rapid annealing at high temperature in a nitrogen atmosphere at ℃ for 10 minutes to form ohmic contact metal source and drain electrodes 2 with a thickness of 0.2 μm, as shown in Figure 2f;

Step 7: Wet etch the gate region of the radiation detector in the middle region of the passivation layer, that is, use a buffered HF acid with a concentration of 5% to etch for 10 seconds, and etch the middle region of the _SiO2 passivation layer 3 to the surface of the n-type buffer layer 5, and carry out dry oxygen oxidation to the area other than the metal source and drain electrodes 2 to form a passivation layer 3 of _SiO2 , as shown in Figure 2g;

Step 8: In the middle area 0.4 μm away from the source and 0.8 μm away from the drain, use a wet method to etch away the SiO ₂ on the surface, and continue to etch down to the n-type buffer layer 5 at a depth of 0.06 μm, and then On the etched buffer layer 5, a translucent high-barrier Schottky metal Ti with a thickness of 100nm was deposited by electron beam evaporation, and rapidly annealed at a high temperature of 1000°C for 10 minutes in a nitrogen atmosphere to form a Schottky metal gate 1, as shown in the figure 2h shown.

Example 2

In the first step, an n-type 4H-SiC substrate with a substrate thickness of 0.4 μm and a doping concentration of 1×10 ¹⁸ cm ^-3 is selected as the substrate (8). After cleaning, C ₃ H ₈ , SiH ₄ and H ₂ , Where H ₂ is the carrier gas, a p-type buffer layer 7 of 4H-SiC with a thickness of 0.15 μm and a doping concentration of 1.4×10 ¹⁵ cm ^-3 is grown on the epitaxial surface, as shown in Figure 2a;

The second step is to use the low-pressure hot-wall chemical vapor deposition method LPCVD, under the conditions of the epitaxial temperature of 1570 ° C, the pressure of 100 mbar, and the growth gas of C ₃ H ₈ , SiH ₄ and H ₂ , on the p-type buffer layer. A layer of n-type channel 6 with a doping concentration of 3.7×10 ¹⁷ cm ^-3 and a thickness of 0.26 μm, as shown in Figure 2b;

The third step is to use low-pressure hot-wall chemical vapor deposition method LPCVD, under the conditions of epitaxial temperature of 1570 ° C, pressure of 100 mbar, and growth gas of C ₃ H ₈ , SiH ₄ and H ₂ , epitaxial layer on the n-channel An n-type buffer layer 5 with a doping concentration of 1.7×10 ¹⁷ cm ^-3 and a thickness of 0.1 μm, as shown in Figure 2c;

In the fourth step, epitaxially epitaxial a layer of silicon carbide with a thickness of 0.15 μm on the n-type buffer layer, and highly doped this region by ion implantation to form an ohmic contact 4 with a doping concentration of 1×10 ¹⁹ cm ^-3 , as shown in Figure 2d shown;

In the fifth step, at a temperature of 1100±50°C, dry oxygen oxidation is performed on the substrate after the epitaxy in the fourth step for two hours to form a _SiO2 passivation layer, as shown in Figure 2e;

The sixth step is to wet-etch away the surface SiO ₂ on both sides of the SiO ₂ passivation layer to form a source and drain region, and use electron beam to evaporate Ni in the source and drain region as the ohmic contact metal of the source and drain, in a nitrogen atmosphere of 1000 Rapid annealing at a high temperature of ℃ for 10 minutes to form a metal source and drain with a thickness of 0.2 μm ohmic contact, as shown in Figure 2f;

In the seventh step, the gate region of the radiation detector is etched out by wet etching in the middle region of the passivation layer. A buffered HF acid with a concentration of 5% is selected for etching for 10 seconds, and the middle area of the SiO ₂ passivation layer 3 is etched to the surface of the n-type buffer layer. And dry oxygen oxidation is performed on the area other than the metal source and drain electrodes 2 to form a covering layer of SiO ₂ , as shown in FIG. 2g;

In the eighth step, in the middle area 0.4 μm away from the source and 0.8 μm away from the drain, use a wet method to etch away the SiO ₂ on the surface, and continue to etch down to the n-type buffer layer 5 at a depth of 0.07 μm, and then On the etched buffer layer 5, a translucent high-barrier Schottky metal Pt with a thickness of 100 nm is deposited by electron beam evaporation, and the Schottky metal gate 1 is formed by rapid annealing at a high temperature of 1000°C in a nitrogen atmosphere for 10 minutes, as shown in Figure 2h shown.

Example 3

In step A, select an n-type 4H-SiC substrate with a substrate thickness of 0.4 μm and a doping concentration of 1×10 ¹⁸ cm ^-3 as the substrate (8), after cleaning, use a low-pressure hot-wall chemical vapor deposition method LPCVD, the epitaxial temperature is 1570°C, the pressure is 100mbar; the growth gas is C ₃ H ₈ , SiH ₄ and H ₂ , where H ₂ is the carrier gas, the growth thickness on the epitaxial surface is 0.15 μm, and the doping concentration is 1.4×10 ¹⁵ cm ^-3 p-type buffer layer 7 of 4H-SiC, as shown in Figure 5a;

Step B, using low-pressure hot-wall chemical vapor deposition method LPCVD, epitaxy on the p-type buffer layer under the conditions of epitaxy temperature of 1570°C, pressure of 100mbar, and growth gas of C ₃ H ₈ , SiH ₄ and H ₂ A layer of n-type channel 6 with a doping concentration of 4.0×10 ¹⁷ cm ^-3 and a thickness of 0.26 μm, as shown in Figure 5b;

Step C, use low-pressure hot-wall chemical vapor deposition method LPCVD, under the conditions of epitaxy temperature 1570℃, pressure 100mbar, growth gas C ₃ H ₈ , SiH ₄ and H ₂ , epitaxial layer on the n-channel An n-type buffer layer 5 with a doping concentration of 1.7×10 ¹⁷ cm ^-3 and a thickness of 0.1 μm, as shown in Figure 5c;

In step D, a layer of silicon carbide with a thickness of 0.15 μm is epitaxially grown on the n-type buffer layer, and this region is highly doped by ion implantation to form an ohmic contact 4 with a doping concentration of 1×10 ¹⁹ cm ^-3 , as shown in Figure 5d ;

Step E, at a temperature of 1100±50°C, perform dry oxygen oxidation on the epitaxial substrate in step D for two hours to form a _SiO2 passivation layer, as shown in Figure 5e;

In step F, use wet etching to remove the surface _SiO on both sides of the passivation layer to form a source and drain region, and use electron beam evaporation of Ni in the source and drain region as the ohmic contact metal of the source and drain, in a nitrogen atmosphere of ₁₀₀₀ Rapid annealing at a high temperature of ℃ for 10 minutes to form a metal source and drain with a thickness of 0.2 μm ohmic contact, as shown in Figure 2f;

In step G, the gate area of the radiation detector is etched out by wet etching in the middle area of the passivation layer. A buffered HF acid with a concentration of 5% is selected for etching for 10 seconds, and the middle area of the SiO ₂ passivation layer 3 is etched to the surface of the n-type buffer layer. And dry oxygen oxidation is performed on the area other than the metal source and drain electrodes 2 to form a covering layer of SiO ₂ , as shown in FIG. 2g;

In step H, in the middle area 0.4 μm away from the source and 0.8 μm away from the drain, use wet etching to remove the SiO ₂ on the surface, and continue to etch downward to the n-type buffer layer 5 at a depth of 0.08 μm, and then On the etched buffer layer 5, use electron beam evaporation to deposit semi-transparent high-barrier Schottky metal Au with a thickness of 100nm, and rapidly anneal for 10min at a high temperature of 1000°C in a nitrogen atmosphere to form a Schottky metal gate 1, as shown in Figure 2h shown.

Claims (3)

1. A beta radiation detector based on a silicon carbide metal semiconductor field effect transistor structure, comprising an n-type substrate (8), a p-type buffer layer (7), an n-type channel (6), n-type from bottom to top type buffer layer (5) and n+ doped ohmic contact layer (4) on both sides, metal Ni is deposited on the ohmic contact layer as the source and drain electrodes (2), and the middle area of the n-type buffer layer is deposited with semi-transparent Schott The base contact layer (1) is buried in the n-type buffer layer (5). The Schottky contact layer is composed of high barrier Schottky metal Au/Ti/Pt, and the surface area other than the gate, source and drain Covered with a SiO ₂ passivation layer (3), characterized in that the concentration of the n-type channel is 3.5 to 4×10 ¹⁷ cm ^-3 , the Schottky contact layer (1) is buried in the n-type buffer layer (5) The depth is 0.06-0.08 μm. 2. The β radiation detector according to claim 1, characterized in that the Schottky contact layer (1) adopts Schottky metal Ti or Pt or Au with a thickness of 100 nm. 3. A method for manufacturing a beta radiation detector based on a silicon carbide metal semiconductor field effect transistor structure, comprising the steps of: 1) Epitaxially layer a p-type epitaxial layer (7) with a thickness of 0.15 μm and a doping concentration of 1.4×10 ¹⁵ cm ^-3 on the n-type 4H-SiC substrate (8); 2) An n-type channel (6) with a thickness of 0.26 μm and a doping concentration of 3.5-4×10 ¹⁷ cm ⁻³ is epitaxially formed on the p-type buffer layer (7); 3) Epitaxially layer an n-type buffer layer (5) with a thickness of 0.1 μm and a doping concentration of 1.7×10 ¹⁷ cm ⁻³ on the n channel (6); 4) On the n-type buffer layer (5), epitaxially layer a source-drain layer (4) with a thickness of 0.15 μm and a doping concentration of 1×10 ¹⁹ cm ⁻³ ; 5) dry oxygen oxidation on the epitaxial layer in the source and drain layer (4), forming SiO ₂ passivation layer (3); 6) Wet etch the SiO _{2 on the surface of the SiO 2 passivation} layer on both sides to form the source and drain regions, evaporate Ni with electron beams, and form a 0.2 μm ohmic contact metal source and drain in the source and drain regions (2) ; 7) Wet etching the middle area of the passivation layer, vertically etching to the surface of the n-type buffer layer, forming the gate area of the radiation detector, performing dry oxygen oxidation on the surface area other than the metal source and drain to form a layer of SiO ₂ overlays; 8) In the middle area 0.8 μm away from the drain electrode and 0.4 μm away from the source electrode, use a wet method to etch away the SiO ₂ on the surface, and continue to etch downward to the n-type buffer layer (5) at a depth of 0.06-0.08 μm, Then electron beam evaporation is used to deposit semi-transparent high-barrier Schottky metal Ti or metal Pt or metal Au with a thickness of 100 nm on the etched buffer layer 5 to form a Schottky metal gate (1).

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