CN113990550A

CN113990550A - Planar Pin type beta irradiation battery with passivation layer surface field and preparation method thereof

Info

Publication number: CN113990550A
Application number: CN202111177392.5A
Authority: CN
Inventors: 郭辉; 钱驰文; 韩超; 袁飞霞; 张玉明; 袁昊
Original assignee: Xidian University
Current assignee: Xidian University
Priority date: 2021-10-09
Filing date: 2021-10-09
Publication date: 2022-01-28
Anticipated expiration: 2041-10-09
Also published as: CN113990550B

Abstract

The invention relates to a planar Pin type beta irradiation battery with a passivation layer surface field and a preparation method thereof, wherein the irradiation battery comprises a Pin unit and a radioisotope unit positioned on the Pin unit, the Pin unit comprises an N-type doped 4H-SiC substrate, an N-type doped 4H-SiC epitaxial layer, a P-type ion injection region, an N-type ohmic contact electrode, a first passivation layer, a second passivation layer and a P-type ohmic contact electrode, and the P-type ion injection region is positioned in the surface layer of the N-type doped 4H-SiC epitaxial layer to form a distributed P-type region; the first passivation layer is positioned on the N-type doped 4H-SiC epitaxial layer and covers the surface of the isolation table top; the second passivation layer is positioned on the first passivation layer at the isolation table-board; the P-type ohmic contact electrode is positioned on the P-type ion implantation area and is arranged at intervals with the first passivation layer. The irradiation cell reduces the energy deposition of beta rays in a P-type area, improves the short-circuit current Isc, the open-circuit voltage Voc and the fill factor FF, and achieves the purpose of improving the energy conversion efficiency of the beta irradiation cell.

Description

Planar Pin type beta irradiation battery with passivation layer surface field and preparation method thereof

Technical Field

The invention belongs to the technical field of microelectronics, and particularly relates to a planar Pin type beta irradiation battery with a passivation layer surface field and a preparation method thereof.

Background

The Micro nuclear battery or radioisotope battery has the advantages of small volume, light weight, long service life, easy integration, no influence of external environment on working and the like, can be used for solving the long-term power supply problem of aerospace deep space exploration, artificial cardiac pacemakers, portable mobile electronic products, implanted microsystems and the like, and is considered as one of ideal long-term energy sources for Micro-Electro-Mechanical systems (MEMS for short), sensors and other Micro-power applications.

Beta irradiation cell is a kind of utilization³H、⁶³Ni and¹⁴⁷a semiconductor isotope battery which outputs electric energy by the radiation volt effect of beta ray emitted by radioactive isotope such as Pm. In 1953, through Rappaport research, it is found that an electron-hole pair is generated in a silicon PN junction by utilizing beta-ray energy generated by isotope decay, a carrier collection process similar to a photovoltaic Effect is generated, and finally, the beta-ray energy is converted into electric energy to be output, and the phenomenon is called a radiation Ford Effect (beta-Voltaic Effect). In 1957, Elgin-Kidde first used β -Voltaic Effect for power supply, and successfully produced the first isotope microbattery (β -Voltaic Battery).

Since 2006, with the progress of the preparation of the wide bandgap semiconductor material SiC and the process technology, related reports of SiC-based isotope microbatteries have emerged. The silicon carbide has the characteristics of large forbidden band width, strong thermal stability, high thermal conductivity, large carrier saturation rate, excellent radiation resistance and the like, and the characteristics are favorable for improving the energy conversion efficiency and the stability of the output performance of the beta irradiation battery. In recent decades, the overall conversion efficiency of beta-irradiated cells has been increased from 0.2% to nearly 4% due to the use of wide bandgap semiconductor materials, with the energy conversion efficiency of silicon carbide PiN devices reaching 18.6%.

However, in the existing report, the energy conversion efficiency of the silicon carbide diode device under the ideal condition can reach 23.5%, which is much higher than the experimental result, and the reason is mainly that the energy deposition of the beta ray in the silicon carbide material is exponentially attenuated along with the incident depth, and a large number of electron-hole pairs generated by irradiation are located in the range of 1 μm on the surface of the device, which causes the surface recombination and the thickness of a P-type region dead layer of the silicon carbide PiN device to have a significant influence on the energy conversion efficiency.

Referring to fig. 1, fig. 1 is a schematic structural diagram of a conventional silicon carbide PiN-type beta irradiation cell provided in the prior art, the PiN nuclear cell sequentially includes, from top to bottom, a radioactive source 60, a P-type ohmic contact electrode 50, a P-type highly doped SiC layer 30, an intrinsic i layer 20, an N-type highly doped SiC substrate 10, and an N-type ohmic contact electrode 40; the surface recombination of the P-type highly doped SiC layer 30 reduces the collection efficiency of electron-hole pairs generated by beta rays in a semiconductor, thereby causing the reduction of short-circuit current Isc, and increases the saturation current of a Pin device, thereby causing the reduction of open-circuit voltage Voc and fill factor FF; the relatively thick P-type highly doped SiC layer 30 will increase the dead layer loss and further enhance the negative effects of surface recombination. And the maximum output power Pout of the beta irradiation cell is FF · Isc · Voc, so the thickness of the surface recombination and P-type region dead layer will limit the energy conversion efficiency of the silicon carbide PiN-type beta irradiation cell. In addition, in order to prevent the ohmic contact electrode from blocking incident ions, the P-type ohmic electrode is simply arranged at one corner of the device, so that irradiation charge carriers far away from the P-type ohmic electrode are compounded in the transportation process, and the energy conversion rate is reduced.

Disclosure of Invention

In order to solve the problems in the prior art, the invention provides a planar Pin type beta irradiation battery with a passivation layer surface field and a preparation method thereof. The technical problem to be solved by the invention is realized by the following technical scheme:

the embodiment of the invention provides a planar Pin type beta irradiation battery with a passivation layer surface field, which comprises a Pin unit and a radioisotope unit positioned on the Pin unit, wherein the Pin unit comprises an N type doped 4H-SiC substrate, an N type doped 4H-SiC epitaxial layer, a P type ion implantation area, an N type ohmic contact electrode, a first passivation layer, a second passivation layer and a P type ohmic contact electrode,

the N-type ohmic contact electrode, the N-type doped 4H-SiC substrate and the N-type doped 4H-SiC epitaxial layer are sequentially laminated, and an isolation table top is arranged on the outer peripheral side of the N-type doped 4H-SiC epitaxial layer;

the P-type ion implantation region is positioned in the surface layer of the N-type doped 4H-SiC epitaxial layer to form a distributed P-type region;

the first passivation layer is positioned on the N-type doped 4H-SiC epitaxial layer and covers the surface of the isolation table top;

the second passivation layer is located on the first passivation layer at the isolation mesa;

the P-type ohmic contact electrode is positioned on the P-type ion implantation area and arranged at intervals with the first passivation layer;

the radioisotope unit is located above the first passivation layer and the P-type ohmic contact electrode.

In one embodiment of the present invention, the doping concentration of the P-type ion implantation region is 1 × 10¹⁹～5×10¹⁹cm^-3The implantation depth is 0.2-0.5 μm, the width is 10-20 μm, and the distance between adjacent implantation regions in the P-type ion implantation region is 100-1000 μm.

In an embodiment of the invention, the P-type ohmic contact electrode includes a plurality of longitudinal rectangular strips and a plurality of transverse rectangular strips, the longitudinal rectangular strips are distributed in parallel, the transverse rectangular strips are distributed in parallel, and each transverse rectangular strip is connected with the longitudinal rectangular strips.

In one embodiment of the invention, a plurality of the longitudinal rectangular strips are distributed at equal intervals, and a plurality of the transverse rectangular strips are distributed at equal intervals and vertically equally divide the longitudinal rectangular strips.

In one embodiment of the present invention, the number of the longitudinal rectangular bars is greater than or equal to 5, and the number of the transverse rectangular bars is greater than or equal to 1; the width of the longitudinal rectangular strips and the width of the transverse rectangular strips are both 10-20 micrometers, and the distance between the longitudinal rectangular strips is 100-1000 micrometers.

In one embodiment of the invention, the P-type ohmic contact electrode comprises a plurality of circular rings and a plurality of rectangular strips, the circular rings are sequentially overlapped in the order of increasing radius, and each rectangular strip is connected with a plurality of circular rings.

In one embodiment of the invention, a plurality of the circular rings are concentric circles distributed at equal intervals, the ring interval is equal to the inner diameter of the central circular ring, and a plurality of the rectangular strips are distributed at equal angles.

In one embodiment of the invention, the number of said circular rings is greater than or equal to 5, the number of said rectangular bars is greater than or equal to 4; the width of the circular ring and the width of the rectangular strip are both 10-20 microns, and the ring spacing of the circular ring and the inner diameter of the central circular ring are both 100-1000 microns.

In one embodiment of the present invention, the radioisotope unit includes a radioisotope source layer over the number of first passivation layers and the P-type ohmic contact electrode.

Another embodiment of the present invention provides a method for preparing a planar PiN-type beta irradiation cell having a passivation layer surface field, comprising the steps of:

s1, epitaxially growing an N-type doped 4H-SiC epitaxial layer on the N-type doped 4H-SiC substrate;

s2, carrying out mesa etching on the N-type doped 4H-SiC epitaxial layer to form an isolation mesa;

s3, performing ion implantation in the surface layer of the N-type doped 4H-SiC epitaxial layer to form a distributed P-type ion implantation area;

s4, preparing a first passivation layer on the surface of the N-type doped 4H-SiC epitaxial layer and the surface of the isolation mesa;

s5, preparing a second passivation layer on the first passivation layer at the isolation mesa;

s6, preparing a P-type ohmic contact electrode on the P-type ion implantation area, and enabling the P-type ohmic contact electrode and the first passivation layer to be arranged at intervals;

s7, epitaxially growing an N-type ohmic contact electrode on the back surface of the N-type doped 4H-SiC substrate;

and S8, preparing a radioisotope unit above the first passivation layer and the P-type ohmic contact electrode.

Compared with the prior art, the invention has the beneficial effects that:

according to the irradiation cell, the distributed P-type ion injection region is formed in the surface layer of the N-type doped 4H-SiC epitaxial layer, the P-type ohmic contact electrode is prepared on the distributed P-type region, and meanwhile, the passivation layer treatment is carried out on the surface outside the P-type region, so that the surface of the N-type epitaxial layer covers the first passivation layer, the energy deposition of beta rays in the P-type region is reduced, the surface recombination effect of the device is weakened, the collection efficiency of the ohmic contact electrode on carriers generated by irradiation is improved, the recombination of the carriers generated by irradiation in the transportation process is reduced, the saturation current of the device is reduced, the short-circuit current Isc, the open-circuit voltage Voc and the filling factor FF are further improved, and the purpose of improving the energy conversion efficiency of the beta irradiation cell is achieved.

Drawings

Fig. 1 is a schematic structural diagram of a conventional silicon carbide PiN type beta irradiation cell provided in the prior art;

fig. 2 is a schematic structural diagram of a planar PiN-type beta irradiation cell with a passivation layer surface field according to an embodiment of the present invention;

fig. 3 is a schematic structural diagram of a gate-shaped P-type ohmic contact electrode according to an embodiment of the present invention;

fig. 4 is a schematic structural diagram of an annular P-type ohmic contact electrode according to an embodiment of the present invention;

fig. 5a to fig. 5j are schematic process diagrams of a method for manufacturing a planar PiN type beta irradiation cell with a passivation layer surface field according to an embodiment of the present invention.

Detailed Description

The present invention will be described in further detail with reference to specific examples, but the embodiments of the present invention are not limited thereto.

Example one

Referring to fig. 2, fig. 2 is a schematic structural diagram of a planar PiN-type beta irradiation cell with a passivation layer surface field according to an embodiment of the present invention. The PiN cell and a radioisotope cell located on the PiN cell.

The Pin unit comprises an N-type doped 4H-SiC substrate 1, an N-type doped 4H-SiC epitaxial layer 2, a P-type ion implantation region 3, an N-type ohmic contact electrode 4, a first passivation layer 5, a second passivation layer 6 and a P-type ohmic contact electrode 7.

Specifically, the shape of the PiN cell includes, but is not limited to, a square or a circle. When the Pin unit is square, the area of the table top is 0.5 multiplied by 0.5 cm-1.0 multiplied by 1.0 cm; when the Pin unit is circular, the area of the table top is phi 0.5 cm-phi 1.0 cm; the area size of the PiN cell is not limited to the above area and size.

An N-type ohmic contact electrode 4, an N-type doped 4H-SiC substrate 1 and an N-type doped 4H-SiC epitaxial layer 2 are sequentially laminated. An isolation table top is formed at the peripheral side of the partial N-type doped 4H-SiC epitaxial layer 2; specifically, the side surface of part of the N-type doped 4H-SiC epitaxial layer 2 and the peripheral surface of the N-type doped 4H-SiC epitaxial layer 2 form an isolation mesa.

In a specific embodiment, the material of the N-type doped 4H-SiC substrate 1 is N-type highly doped 4H-SiC with a doping concentration of 5 x 10¹⁸cm^-3The thickness was 380. mu.m. The N-type doped 4H-SiC epitaxial layer 2 is made of N-type low-doped 4H-SiC with the doping concentration of 1 multiplied by 10¹⁴～1×10¹⁵cm^-3The thickness is 4.0-10.0 μm, and the doped ions are nitrogen ions. The material of the N-type ohmic contact electrode 4 includes but is not limited to Ni, and the thickness is 200 nm; ohmic contact is formed between the interface of the N-type ohmic contact electrode 4 and the N-type doped 4H-SiC substrate 1.

The P-type ion implantation region 3 is positioned in the surface layer of the N-type doped 4H-SiC epitaxial layer 2 to form a distributed P-type region; the distributed P-type region can be a grid-shaped distributed P-type region and a ring-shaped distributed P-type region. Specifically, the P-type ion implantation region 3 is formed by ion implantation of N-type doped 4H-SiC epitaxial layer 2 with a doping concentration of 1 × 10¹⁹～5×10¹⁹cm^-3The implantation depth is 0.2-0.5 μm, the width is 10-20 μm, and the implanted ions are aluminum ions; the distance between adjacent implanted regions in the distributed P-type ion implanted region 3 is 100-1000 μm.

The first passivation layer 5 is located in the N typeThe doped 4H-SiC epitaxial layer 2 is on and covers the surface of the isolation mesa, i.e., the surface and side surfaces of the N-type doped 4H-SiC epitaxial layer 2 between the P-type ion implantation regions 3 are the first passivation layer 5. In particular, the material of the first passivation layer 5 comprises SiO₂The thickness of the first passivation layer 5 is 30-50 nm, the width of the first passivation layer 5 between the P-type ion implantation regions 3, namely between the P-type ohmic contact electrodes 7, is equal to the distance between adjacent implantation regions in the distributed P-type ion implantation regions 3, and the width is 100-1000 μm.

The second passivation layer 6 is located on the first passivation layer 5 at the isolation mesa, i.e., the second passivation layer 6 is located on the outer side surface of the first passivation layer 5. Specifically, the thickness of the second passivation layer 6 is 0.2-0.5 μm, and the height of the side surface is 1 μm.

The P-type ohmic contact electrode 7 is positioned on the P-type ion implantation region 3 and is arranged at an interval with the first passivation layer 5. It can be understood that the P-type ohmic contact electrode 7 completely covers the P-type ion implantation region 3, and the other portion is the first passivation layer 5. The shape of the P-type ohmic contact electrode 7 is the same as that of the P-type ion implantation region 3, forming a distributed ohmic contact electrode. The material of the P-type ohmic contact electrode 7 includes, but is not limited to, one or more of Ti, Ni, and Al, for example, the material of the P-type ohmic contact electrode 7 is Ti, or Ni, or Al, or a combination of Ti and Ni, or a combination of Ti and Al, or a combination of Ni and Al, or a multilayer metal combining Ti, Ni, and Al; the thickness of the P-type ohmic contact electrode 7 is 50-150 nm, and the width is 10-20 μm; ohmic contact is formed between the P-type ohmic contact electrode 7 and the interface of the P-type ion implantation region 3.

The radioisotope unit is located over the first passivation layer 5 and the P-type ohmic contact electrode 7. Specifically, the radioisotope unit includes a radioisotope source layer 8, the radioisotope source layer 8 is located above the first passivation layer 5 and the P-type ohmic contact electrode 7, and the beta-emitting source material of the radioisotope source layer 8 includes Ni⁶³、Pm¹³⁷、H³But are not limited to these isotopes.

Referring to fig. 3, fig. 3 is a schematic structural diagram of a gate-shaped P-type ohmic contact electrode according to an embodiment of the invention.

In fig. 3, the P-type ohmic contact electrode 7 is a grid-shaped distributed electrode, and includes a plurality of longitudinal rectangular strips 71 and a plurality of transverse rectangular strips 72, the longitudinal rectangular strips 71 are distributed in parallel, the transverse rectangular strips 72 are distributed in parallel, and each transverse rectangular strip 72 is connected to each longitudinal rectangular strip 71. It is understood that the transverse rectangular strips 72 may be connected in the middle of the longitudinal rectangular strips 71, or may be connected at the ends of the longitudinal rectangular strips 71.

Further, the plurality of longitudinal rectangular bars 71 are equally spaced, and the plurality of transverse rectangular bars 72 are equally spaced and perpendicularly equally spaced to the longitudinal rectangular bars 71.

In one embodiment, the plurality of longitudinal rectangular strips 71 are distributed at equal intervals, the length of the longitudinal rectangular strips is the same as the longitudinal length of the Pin unit, the width of the longitudinal rectangular strips is 10-20 μm, and the number of the longitudinal rectangular strips is greater than or equal to 5; the distance h1 between the longitudinal rectangular strips 71, the distance between adjacent injection regions and the width of the first passivation layer 5 between the P-type ohmic contact electrodes 7 are all the same and are 100-1000 μm. The transverse rectangular strips 72 vertically equally divide the longitudinal rectangular strips 71, the length of the transverse rectangular strips is the same as the transverse length of the Pin unit, the width of the transverse rectangular strips is 10-20 mu m, and the number of the transverse rectangular strips is more than or equal to 1.

Referring to fig. 4, fig. 4 is a schematic structural diagram of a ring-shaped P-type ohmic contact electrode according to an embodiment of the invention.

In fig. 4, the P-type ohmic contact electrode 7 is an annularly distributed electrode, and includes a plurality of circular rings 73 and a plurality of rectangular strips 74, the circular rings 73 are sequentially nested according to a sequence of radii from small to large, and each rectangular strip 74 is connected to the circular rings 73. Further, the rings 73 are concentric circles distributed at equal intervals, and the ring interval is equal to the inner diameter of the central ring 73; the two rectangular strips 74 are distributed at equal angles, that is, the included angles between two adjacent rectangular strips 74 are equal, and the rectangular strips 74 are distributed uniformly along the circumference of the ring 73.

In a specific embodiment, the plurality of circular rings 73 are concentric circles, the width of the circular rings 73 is 10 μm to 20 μm, the plurality of circular rings 73 are distributed at equal intervals, the interval between the circular rings is equal to the inner diameter of the central circular ring 73, and the number of the circular rings 73 is greater than or equal to 5; the ring spacing h2, the distance between the inner diameter h3 of the central ring 73 and the adjacent injection regions and the width of the first passivation layer 5 positioned between the P-type ohmic contact electrodes 7 are all the same and are 100-1000 μm. The rings are connected by a plurality of rectangular strips 74, and a plurality of two rectangular strips 74 are distributed at equal angles, for example, when the number of rectangular strips 74 is equal to 4, the included angle between two adjacent rectangular strips 74 is 90 °.

The shape of the P-type ohmic contact electrode 7 is not limited to the above-described gate distributed electrode and ring-shaped distributed electrode, as long as it satisfies the conditions of the distributed electrode.

Compared with the conventional silicon carbide Pin type beta irradiation cell, the embodiment obtains the distributed P type region by performing ion implantation on the N type doped 4H-SiC epitaxial layer, covers the ohmic contact electrode only above the distributed P type region, and passivates the surface of the N type epitaxial layer outside the distributed P type region to cover the surface of the N type epitaxial layer with SiO₂A first passivation layer. This has the following advantages: 1. the distributed P-type region is obtained by performing ion implantation treatment on the N-type epitaxial layer, compared with a process method of performing P-type epitaxy on the surface of the N-type epitaxial layer and obtaining the distributed P-type region by performing groove etching on the P-type epitaxial layer, the surface damage of the N-type epitaxial layer caused by surface etching is avoided, the composite action of the surface of the N-type region is reduced, meanwhile, a planar device obtained by the ion implantation process is beneficial to the transverse expansion of a depletion region electric field generated by the distributed P-type region in the N-type epitaxial layer, and therefore the collection efficiency of carriers is improved, and the saturation current is reduced. 2. The distributed P-type region and the ohmic contact electrodes above the distributed P-type region reduce the P-type dead zone on the surface of the device and the coverage area of the corresponding metal electrodes, so that the energy loss of beta rays caused by the ohmic contact electrodes and the P-type dead zone is reduced, the recombination of carriers in the P-type dead zone and a metal contact interface is reduced, meanwhile, the average transport distance in the carrier collection process is reduced through the pattern design of the distributed P-type region and the corresponding ohmic contact electrodes above the distributed P-type region, the recombination loss of the carriers in the transport process is reduced, and the carrier collection efficiency is improved. 3. Since the collection efficiency of the P-type region to carriers is much lower than that of the depletion region, the conventional silicon carbide PiN-type beta irradiation cell mainly uses the depletion region formed by a PN junction as a part of the sensitive region to collect carriers generated by beta ray irradiation, and thus,the incident beta rays must traverse the P-type dead bed region, causing significant particle energy loss; in the embodiment, the distributed P-type region is formed only in the ion implantation region by ion implantation treatment, and is formed by SiO₂The fixed negative charges on the interface of the first passivation layer and the silicon carbide of the N-type epitaxial layer replace a P-type region to generate a surface depletion region of the N-type epitaxial layer and a surface P-type inversion layer of the N-type epitaxial layer, so that the beta rays can deposit energy in the depletion layer without penetrating through the P-type dead layer region, and the collection efficiency of carriers is improved. SiO of surface of N-type epitaxial layer₂The first passivation layer improves the interface characteristic, reduces the surface recombination effect of the device, simultaneously, the depletion region electric field on the surface of the N-type epitaxial layer extracts electrons generated by beta rays, and a P-type inversion layer is formed on the surface, so that the recombination effect on the surface of the device is further reduced, the carrier recombination loss is reduced, and the saturation current of the device is reduced. The short-circuit current Isc can be improved by the two

points

2 and 3, the short-circuit current Isc, the open-circuit voltage Voc and the fill factor FF are simultaneously improved by the two

points

1 and 4, and finally the energy conversion efficiency of the beta irradiation battery is improved.

To sum up, in the irradiation cell of the embodiment, the distributed P-type ion implantation region is formed in the surface layer of the N-type doped 4H-SiC epitaxial layer, the P-type ohmic contact electrode is prepared on the distributed P-type region, and meanwhile, the passivation layer treatment is performed on the surface outside the P-type region, so that the first passivation layer covers the surface of the N-type epitaxial layer, the energy deposition of beta rays in the P-type region is reduced, the surface recombination effect of the device is weakened, the collection efficiency of the ohmic contact electrode on carriers generated by irradiation is improved, the recombination of the carriers generated by irradiation in the transportation process is reduced, the saturation current of the device is reduced, the short-circuit current Isc, the open-circuit voltage Voc and the fill factor FF are improved, and the purpose of improving the energy conversion efficiency of the beta irradiation cell is achieved.

Example two

On the basis of the first embodiment, please refer to fig. 5a to 5j, and fig. 5a to 5j are schematic process diagrams of a method for manufacturing a planar PiN-type β -cell with a passivation layer surface field according to an embodiment of the present invention, the method includes:

s1, epitaxially growing an N-type doped 4H-SiC epitaxial layer 2 on the N-type doped 4H-SiC substrate 1, please refer to FIG. 5a and FIG. 5 b.

Firstly, cleaning an N-type doped 4H-SiC substrate 1 sample wafer to remove surface pollutants.

Then, a layer of doping concentration of 1 multiplied by 10 is epitaxially grown on the surface of the cleaned N-type highly doped 4H-SiC substrate 1 sample wafer by using a chemical vapor deposition CVD method¹⁴～1×10¹⁵cm^-3And N-type low-doped 4H-SiC with the thickness of 4.0-10.0 μm to form the N-type doped 4H-SiC epitaxial layer 2.

And S2, carrying out mesa etching on the N-type doped 4H-SiC epitaxial layer 2 to form an isolation mesa, as shown in FIG. 5 c.

Specifically, mesa etching is carried out on the N-type doped 4H-SiC epitaxial layer 2 by utilizing an Inductively Coupled Plasma (ICP) etching method, the etching depth is 1 mu m, so that part of the N-type doped 4H-SiC epitaxial layer 2 forms a mesa, and mesa isolation of the device is formed.

And S3, performing ion implantation in the surface layer of the N-type doped 4H-SiC epitaxial layer 2 to form a distributed P-type ion implantation region 3, as shown in FIG. 5 d.

Specifically, a silicon dioxide ion implantation mask layer is deposited on the surface of a sample, glue is coated on the silicon dioxide ion implantation mask layer, a barrier layer with a distributed P-type area pattern is formed through photoetching, an ion implantation window is opened by etching silicon dioxide through an acid wet method, and an ion implantation method is adopted to form a doping concentration of 1 x 10 on the upper portion of an N-type doped 4H-SiC epitaxial layer 2¹⁹～5×10¹⁹cm^-3And a P-type ion implantation area with the depth of 0.2-0.5 mu m, and carrying out high-temperature thermal annealing at 1700 ℃ under the protection of the surface carbon film, thereby forming a distributed P-type ion implantation area 3.

S4, preparing a first passivation layer 5 on the surface of the N-type doped 4H-SiC epitaxial layer 2 and the surface of the isolation mesa, and please refer to FIG. 5 e.

Specifically, sacrificial oxidation is carried out on a sample subjected to ion implantation, an acid wet method is used for corroding silicon dioxide to remove a surface sacrificial oxide layer, the sample is cleaned, then high-temperature thermal oxidation is carried out on the sample, a dense SiO2 passivation thin layer with the thickness of 30-50 nm is formed, and a first passivation layer 5 is formed.

S5, a second passivation layer 6 is prepared on the first passivation layer 5 at the isolation mesa, see fig. 5 f.

In particular, in dense SiO₂Coating glue on the passivation thin layer, photoetching to form a barrier layer with a sensitive region pattern, and coating the barrier layer on the dense SiO₂Carrying out CVD deposition on the surface of the passivation thin layer to passivate the sample wafer, and carrying out CVD deposition on the surface of the passivation thin layer to form a thin film on the surface of the thin film₂Passivating the surface of the thin layer to form SiO with the thickness of 0.2-0.5 mu m₂Passivation layer, forming a second passivation layer 6.

And S6, preparing the P-type ohmic contact electrode 7 on the P-type ion implantation area 3, so that the P-type ohmic contact electrode 7 and the first passivation layer 5 are arranged at intervals.

First, glue is coated on the first passivation layer 5, a barrier layer with a distributed P-type region pattern is formed by photolithography, and a window of the first passivation layer 5 is opened as a P-type ohmic contact electrode region 7' by etching silicon dioxide with an acid wet method, as shown in fig. 5 g.

Then, coating glue on the front surface of the sample wafer, photoetching to form a metal deposition window on the surface of the distributed P-type region, cleaning the windowed sample wafer, depositing P-type ohmic contact electrode metal which is Ti or Ni or Al or multilayer metal containing Ti or Ni or Al by magnetron sputtering, and then stripping the photoresist to form a P-type ohmic contact electrode 7, please refer to fig. 5 h.

And S7, epitaxially growing an N-type ohmic contact electrode 4 on the back surface of the N-type doped 4H-SiC substrate 1, as shown in FIG. 5 i.

And gluing and protecting the front surface of the sample wafer, forming an N-type ohmic contact electrode 4 on the back surface of the sample wafer through magnetron sputtering deposition, wherein the N-type ohmic contact electrode 4 is made of Ni and has the thickness of 200 nm.

S8, a radioisotope unit is prepared on the first passivation layer 5 and the P-type ohmic contact electrode 7, as shown in fig. 5 j.

Specifically, a radioisotope source layer 8 is formed on the upper surface of the sample piece by using a deposition or smearing method, and the planar silicon carbide Pin type beta irradiation battery with the distributed P type region and the passivation layer surface field is obtained.

Please refer to embodiment one for the device structure manufactured by the above manufacturing method, which is not described in detail in this embodiment.

In the irradiation cell prepared by the embodiment, the distributed P-type ion injection region is formed in the surface layer of the N-type doped 4H-SiC epitaxial layer, the P-type ohmic contact electrode is prepared on the distributed P-type region, and meanwhile, the passivation layer treatment is performed on the surface outside the P-type region, so that the surface of the N-type epitaxial layer covers the first passivation layer, the energy deposition of beta rays in the P-type region is reduced, the surface recombination effect of the device is weakened, the collection efficiency of the ohmic contact electrode on carriers generated by irradiation is improved, the recombination of the carriers generated by irradiation in the transportation process is reduced, the saturation current of the device is reduced, the short-circuit current Isc, the open-circuit voltage Voc and the fill factor FF are further improved, and the purpose of improving the energy conversion efficiency of the beta irradiation cell is achieved.

EXAMPLE III

On the basis of the second embodiment, please refer to fig. 5a to 5j, the preparation method of the present embodiment will be described with reference to fig. 5a to 5j, taking the preparation of a planar silicon carbide PiN-type β -irradiation cell with a grid-shaped distributed P-type region and a passivation layer surface field as an example, wherein the area of the cell is 0.7cm × 0.7cm, the pitch of the P-type implanted regions is 300 μm, the number of electrodes of the longitudinal rectangular strips 71 is 22, and the number of electrodes of the transverse rectangular strips 72 is 1.

And S1, epitaxially growing an N-type doped 4H-SiC epitaxial layer 2 on the N-type doped 4H-SiC substrate 1.

First, a sample of the N-doped 4H-SiC substrate 1 was cleaned using a standard RAC to remove surface contaminants, see FIG. 5 a.

Specifically, the doping concentration is firstly adjusted to 5X 10 at 25 DEG C¹⁸cm^-3The N-type highly doped 4H-SiC substrate 1 sample with the thickness of 380 mu m is prepared on the H₂SO₄:H₂O₂Soaking the sample in the reagent (4:1) for 10min to remove organic and metal contamination on the surface of the sample; then removing organic and metal contamination on the surface of the sample wafer H at 85 DEG C₂O:NH₄OH:H₂O₂Soaking the reagent in the ratio of (5:1:1) for 10min to remove impurity particles; then, the sample piece with the impurity particles removed is placed in H at 85 DEG C₂O:HCl:H₂O₂Soaking in the reagent (5:1:1) for 10min to remove metal and re-separatingSeed contamination; finally, the sample wafer from which the metal and heavy ion contamination has been removed is placed in H at 25 deg.C₂Soaking in HF (10:1) for 10min to remove the natural oxide layer on the surface.

Then, an N-type doped 4H-SiC epitaxial layer 2 is epitaxially grown, see fig. 5 b.

Specifically, an N-type 4H-SiC low-doped epitaxial layer 2 is grown on a cleaned N-type high-doped 4H-SiC substrate 1 sample wafer in an unintentional doping epitaxial mode by using a low-pressure chemical vapor deposition LPCVD method. The process conditions are as follows: the epitaxy temperature is 1580 deg.C, the pressure is 100mbar, and the reaction gas is propane (C)₃H₈) And Silane (SiH)₄) C/Si is 1, the carrier gas is pure hydrogen, and the obtained nitrogen doping concentration is 7 multiplied by 10¹⁴cm^-3And an N-type 4H-SiC low-doped epitaxial layer 2 with the thickness of 9 mu m.

Firstly, standard RCA cleaning is carried out on a sample wafer after epitaxial growth is completed; after the cleaning of the sample wafer is finished, the doping concentration of nitrogen is 7 multiplied by 10¹⁴cm^-3Depositing a Ni film with the thickness of 200nm on the N-type doped 4H-SiC epitaxial layer 2 through magnetron sputtering to serve as an etching mask layer, and patterning the Ni film by using a photoetching plate to form a pattern required by etching; then, etching part of the N-type doped 4H-SiC epitaxial layer 2 on the upper surface of the sample wafer by utilizing Inductively Coupled Plasma (ICP), wherein the etching depth is 1 mu m, and H is used at the temperature of 25 DEG C₂SO₄:H₂O₂(4:1) soaking the etched sample wafer for 10min by using the reagent to remove the Ni mask layer so as to form the mesa isolation of the device.

Firstly, standard RCA cleaning is carried out on a sample wafer subjected to mesa etching; then, depositing silicon dioxide with the thickness of 3 microns on the surface of the sample wafer by using a Chemical Vapor Deposition (CVD) method to be used as an ion implantation mask layer; then, photoresist is coated on the silicon dioxide ion implantation mask layer in a spinning mode, a blocking layer with a distributed P-type area pattern is formed in a photoetching mode, and buffering is conducted through the blocking layer with the concentration of 5%Etching silicon dioxide by using an HF solution BHF acid wet method to open an ion injection window; then, ion implantation is carried out on the N-type doped 4H-SiC epitaxial layer 2 to form a grid-shaped distributed P-type ion implantation region 3 with the doping concentration of 1.5 multiplied by 10¹⁹cm^-3The implantation depth is 0.3 μm, the width is 16 μm, the spacing is 300 μm, and the ion implantation parameters are as follows: p-type implanted impurities are monovalent aluminum ions, the energy of the aluminum ions is less than or equal to 350KeV, and the implantation temperature is 400 ℃; and finally, removing the silicon dioxide ion implantation mask layer on the sample wafer subjected to ion implantation by adopting 5% buffered HF solution BHF acid wet etching, then carrying out Physical Vapor Deposition (PVD) deposition of a carbon film protective layer on the surface of the sample wafer, and carrying out high-temperature thermal annealing for 20 minutes at the temperature of 1700 ℃.

Firstly, standard RCA cleaning is carried out on a sample wafer after ion implantation; then, carrying out wet oxygen oxidation on the surface of the sample piece for 2 hours at the temperature of 1150 +/-50 ℃ to form a sacrificial oxide layer; then, removing the sacrificial oxide layer on the sample wafer subjected to sacrificial oxidation by adopting a 10% HF solution DHF acid wet etching method; then, standard RCA cleaning is carried out on the sample wafer with the sacrificial oxide layer removed; finally, the surface of the sample piece after ion implantation is subjected to dry oxygen oxidation for 3 hours at the temperature of 1150 +/-50 ℃ to form dense SiO with the thickness of 30nm₂The thin layer is passivated and then annealed in a nitrogen atmosphere at a temperature of 1150 + -50 deg.c for 1 hour to form a first passivation layer 5.

Firstly, spin-coating a photoresist on the first passivation layer 5; then, patterning the photoresist by using a photoetching plate to form a barrier layer with a sensitive area pattern; finally, a 300nm thick SiO layer was deposited on the first passivation layer 5 using PECVD at a temperature of 250 deg.C₂And then rapid thermal annealing is performed at a temperature of 1000 ± 50 ℃ for 5 minutes in a pure argon atmosphere to form the second passivation layer 6.

First, the first passivation layer 5 is etched to form P-type ohmic contact electrode regions 7', see fig. 5 g. Specifically, photoresist is spin-coated on the first passivation layer 5, and is patterned by using a photomask to form a barrier layer with a distributed P-type region pattern required by corrosion windowing, then a 5% buffered HF solution BHF acid wet etching silicon dioxide is used to open a window of the first passivation layer 5, and the windowing region is used as a P-type ohmic contact electrode region.

Then, a sensitive-gate-like distributed P-type ohmic contact electrode 7 is formed, see fig. 5 h. Specifically, firstly, spin-coating a photoresist on the front surface of a sample wafer; then, patterning the photoresist by using a photoetching plate to form a metal deposition window on the surface of the distributed P-type area; cleaning the surface of the windowed sample wafer by a wet method and a dry method, and depositing Ti/Al double-layer metal with the thickness of 30nm/70nm through magnetron sputtering to form contact metal of a P-type ohmic contact electrode; finally, the photoresist is stripped, and grid-shaped distributed P-type ohmic contact electrodes 7 with the electrode width (namely the width of the longitudinal rectangular strips and the width of the transverse rectangular strips) being 16 microns, the electrode spacing of the longitudinal rectangular strips being 300 microns, the number of the electrodes of the longitudinal rectangular strips 71 being 22, and the number of the electrodes of the transverse rectangular strips 72 being 1 are formed.

Firstly, a photoresist is coated on the front surface of a sample wafer in a spinning mode. Then, the surface of the sample wafer is cleaned by a wet method and a dry method. Then, Ni metal with the thickness of 200nm is deposited on the lower surface of the sample wafer through magnetron sputtering, and an N-type ohmic contact electrode 4 is formed. And finally, carrying out rapid thermal annealing at the temperature of 1000 ℃ for 3 minutes in a pure argon atmosphere, and simultaneously forming an ohmic contact interface of the N-type ohmic contact electrode 4 and the P-type ohmic contact electrode 7.

Specifically, a beta radioactive source is placed on the upper surface of the sample piece by using a deposition or smearing method to form a radioactive isotope source layer 8, and the planar silicon carbide Pin type beta irradiation battery with a grid-shaped distributed P-type region and a passivation layer surface field is obtained.

Example four

On the basis of the second embodiment, please refer to fig. 5a to 5j, the method for manufacturing a planar sic PiN-type β -cell with a ring-shaped P-type region and a passivation layer surface field is described in this embodiment, wherein the area of the cell is Φ 0.8cm, the pitch of the P-type implanted regions is 900 μm, the number of ring electrodes is 8, and the number of rectangular bars 74 is 4.

Specifically, the doping concentration is firstly adjusted to 5X 10 at 25 DEG C¹⁸cm^-3The N-type highly doped 4H-SiC substrate 1 sample with the thickness of 380 mu m is prepared on the H₂SO₄:H₂O₂Soaking the sample in the reagent (4:1) for 10min to remove organic and metal contamination on the surface of the sample; then removing organic and metal contamination on the surface of the sample wafer H at 85 DEG C₂O:NH₄OH:H₂O₂Soaking the reagent in the ratio of (5:1:1) for 10min to remove impurity particles; then, the sample piece with the impurity particles removed is placed in H at 85 DEG C₂O:HCl:H₂O₂Soaking the reagent in the ratio of (5:1:1) for 10min to remove metal and heavy ion contamination; finally, the sample wafer from which the metal and heavy ion contamination has been removed is placed in H at 25 deg.C₂Soaking in HF (10:1) for 10min to remove the natural oxide layer on the surface.

Specifically, an N-type low-doped 4H-SiC epitaxial layer 2 is grown on a cleaned N-type high-doped 4H-SiC substrate 1 sample wafer in an unintentional doping epitaxial growth mode by using a low-pressure chemical vapor deposition LPCVD method. The process conditions are as follows: the epitaxy temperature is 1580 deg.C, the pressure is 100mbar, and the reaction gas is propane (C)₃H₈) And Silane (SiH)₄) C/Si is 1.5, the carrier gas is pure hydrogen,the obtained nitrogen doping concentration is 1 × 10¹⁴cm^-3And an N-type low-doped 4H-SiC epitaxial layer 2 with the thickness of 10 mu m.

Firstly, standard RCA cleaning is carried out on a sample wafer after epitaxial growth is completed; after the cleaning of the sample wafer is finished, the doping concentration of nitrogen is 1 multiplied by 10¹⁴cm^-3Depositing a Ni film with the thickness of 200nm on the N-type doped 4H-SiC epitaxial layer 2 through magnetron sputtering to serve as an etching mask layer, and patterning the Ni film by using a photoetching plate to form a pattern required by etching; then, etching part of the N-type doped 4H-SiC epitaxial layer 2 on the upper surface of the sample wafer by utilizing Inductively Coupled Plasma (ICP), wherein the etching depth is 1 mu m, and H is used at the temperature of 25 DEG C₂SO₄:H₂O₂(4:1) soaking the etched sample wafer for 10min by using the reagent to remove the Ni mask layer so as to form the mesa isolation of the device.

Firstly, standard RCA cleaning is carried out on a sample wafer subjected to mesa etching; then, depositing silicon dioxide with the thickness of 3 microns on the surface of the sample wafer by using a Chemical Vapor Deposition (CVD) method to be used as an ion implantation mask layer; then, spin-coating photoresist on the silicon dioxide ion implantation mask layer, photoetching to form a barrier layer with a distributed P-type region pattern, and etching the silicon dioxide by using a 5% buffered HF solution BHF acid wet method to open an ion implantation window; then, ion implantation is carried out on the N-type doped 4H-SiC epitaxial layer 2 to form an annular distributed P-type ion implantation area 3 with the doping concentration of 3 multiplied by 10¹⁹cm^-3The implantation depth is 0.25 μm, the width is 12 μm, the spacing is 900 μm, and the ion implantation parameters are as follows: p-type implanted impurities are monovalent aluminum ions, the energy of the aluminum ions is less than or equal to 350KeV, and the implantation temperature is 400 ℃; finally, removing the silicon dioxide ion implantation mask layer on the sample wafer subjected to ion implantation by adopting 5% buffered HF solution BHF acid wet etching, then carrying out Physical Vapor Deposition (PVD) deposition of a carbon film protective layer on the surface of the sample wafer, and carrying out high temperature of 20 minutes at 1700 DEG CAnd (6) thermal annealing.

Firstly, standard RCA cleaning is carried out on a sample wafer after ion implantation; then, carrying out wet oxygen oxidation on the surface of the sample piece for 2 hours at the temperature of 1150 +/-50 ℃ to form a sacrificial oxide layer; then, removing the sacrificial oxide layer on the sample wafer subjected to sacrificial oxidation by adopting a 10% HF solution DHF acid wet etching method; then, standard RCA cleaning is carried out on the sample wafer with the sacrificial oxide layer removed; finally, the surface of the sample piece after ion implantation is subjected to dry oxygen oxidation for 4 hours at the temperature of 1150 +/-50 ℃ to form dense SiO with the thickness of 40nm₂The thin layer is passivated and then annealed in a nitrogen atmosphere at a temperature of 1150 + -50 deg.c for 1 hour to form a first passivation layer 5.

Firstly, spin-coating a photoresist on the first passivation layer 5; then, patterning the photoresist by using a photoetching plate to form a barrier layer with a sensitive area pattern; finally, a 400nm thick SiO layer was deposited on the first passivation layer 5 using PECVD at a temperature of 250 deg.C₂And then rapid thermal annealing is performed at a temperature of 1000 ± 50 ℃ for 5 minutes in a pure argon atmosphere to form the second passivation layer 6.

Then, a sensitive-gate-like distributed P-type ohmic contact electrode 7 is formed, see fig. 5 h. Specifically, firstly, spin-coating a photoresist on the front surface of a sample wafer; then, patterning the photoresist by using a photoetching plate to form a metal deposition window on the surface of the distributed P-type area; cleaning the surface of the windowed sample wafer by a wet method and a dry method, and depositing Ni metal with the thickness of 120nm through magnetron sputtering to form contact metal of a P-type ohmic contact electrode; and finally, stripping the photoresist to form the annular distributed P-type ohmic contact electrodes 7 with the electrode widths of 12 microns, namely the widths of the circular rings and the rectangular strips, wherein the inter-ring distance of the electrodes is 900 microns, the number of the circular ring electrodes is 8, and the number of the rectangular strips 74 is 4.

The foregoing is a more detailed description of the invention in connection with specific preferred embodiments and it is not intended that the invention be limited to these specific details. For those skilled in the art to which the invention pertains, several simple deductions or substitutions can be made without departing from the spirit of the invention, and all shall be considered as belonging to the protection scope of the invention.

Claims

1. A planar PiN type beta irradiation battery with a passivation layer surface field is characterized by comprising a PiN unit and a radioisotope unit positioned on the PiN unit, wherein the PiN unit comprises an N type doped 4H-SiC substrate (1), an N type doped 4H-SiC epitaxial layer (2), a P type ion implantation region (3), an N type ohmic contact electrode (4), a first passivation layer (5), a second passivation layer (6) and a P type ohmic contact electrode (7),

the N-type ohmic contact electrode (4), the N-type doped 4H-SiC substrate (1) and the N-type doped 4H-SiC epitaxial layer (2) are sequentially stacked, and an isolation table top is arranged on the outer peripheral side of the N-type doped 4H-SiC epitaxial layer (2);

the P-type ion implantation region (3) is positioned in the surface layer of the N-type doped 4H-SiC epitaxial layer (2) to form a distributed P-type region;

the first passivation layer (5) is positioned on the N-type doped 4H-SiC epitaxial layer (2) and covers the surface of the isolation mesa;

the second passivation layer (6) is located on the first passivation layer (5) at the isolation mesa;

the P-type ohmic contact electrode (7) is positioned on the P-type ion implantation area (3) and arranged at intervals with the first passivation layer (5);

the radioisotope unit is located above the first passivation layer (5) and the P-type ohmic contact electrode (7).

2. Planar PiN type beta irradiation cell with passivation layer surface field according to claim 1, characterized in that the doping concentration of the P-type ion implantation region (3) is 1 x 10¹⁹～5×10¹⁹cm^-3The implantation depth is 0.2-0.5 μm, the width is 10-20 μm, and the distance between adjacent implantation regions in the P-type ion implantation region (3) is 100-1000 μm.

3. The planar PiN type beta irradiation cell with passivation layer surface field according to claim 1, characterized in that said P-type ohmic contact electrode (7) comprises a number of longitudinal rectangular strips (71) and a number of transverse rectangular strips (72), a number of said longitudinal rectangular strips (71) being distributed in parallel, a number of said transverse rectangular strips (72) being distributed in parallel and each of said transverse rectangular strips (72) connecting a number of said longitudinal rectangular strips (71).

4. The planar PiN type beta irradiation cell with surface field of passivation layer according to claim 3, characterized in that several of said longitudinal rectangular strips (71) are equally spaced, several of said transverse rectangular strips (72) are equally spaced and perpendicularly equally spaced said longitudinal rectangular strips (71).

5. -the planar PiN type β radiation cell with surface field of passivation layer according to claim 3, characterized in that the number of longitudinal rectangular strips (71) is greater than or equal to 5, the number of transverse rectangular strips (72) is greater than or equal to 1; the width of the longitudinal rectangular strips (71) and the width of the transverse rectangular strips (72) are both 10-20 micrometers, and the distance between the longitudinal rectangular strips (71) is 100-1000 micrometers.

6. The planar PiN type beta irradiation cell with passivation layer surface field according to claim 1, wherein said P type ohmic contact electrode (7) comprises a plurality of circular rings (73) and a plurality of rectangular strips (74), wherein said plurality of circular rings (73) are sequentially nested in order of radius from small to large, and each of said rectangular strips (74) is connected with a plurality of circular rings (73).

7. The planar PiN type beta irradiation cell with surface field of passivation layer according to claim 6, characterized in that several of said circular rings (73) are concentric circles distributed with equal distance, the distance between the rings is equal to the inner diameter of the central circular ring (73), and several of said rectangular strips (74) are distributed with equal angle.

8. The planar PiN type beta irradiation cell with passivation layer surface field according to claim 6, characterized in that the number of said circular rings (73) is greater than or equal to 5, the number of said rectangular bars (74) is greater than or equal to 4; the width of the circular ring (73) and the width of the rectangular strip (74) are both 10-20 microns, and the ring spacing of the circular ring (73) and the inner diameter of the central circular ring (73) are both 100-1000 microns.

9. Planar PiN type beta irradiation cell with passivation layer surface field according to claim 1, characterized in that the radioisotope unit comprises a radioisotope source layer (8), said radioisotope source layer (8) being located above said number of first passivation layers (5) and said P-type ohmic contact electrode (7).

10. A method for preparing a planar Pin type beta irradiation battery with a passivation layer surface field is characterized by comprising the following steps:

s1, epitaxially growing an N-type doped 4H-SiC epitaxial layer (2) on the N-type doped 4H-SiC substrate (1);

s2, carrying out mesa etching on the N-type doped 4H-SiC epitaxial layer (2) to form an isolation mesa;

s3, performing ion implantation in the surface layer of the N-type doped 4H-SiC epitaxial layer (2) to form a distributed P-type ion implantation region (3);

s4, preparing a first passivation layer (5) on the surface of the N-type doped 4H-SiC epitaxial layer (2) and the surface of the isolation mesa;

s5, preparing a second passivation layer (6) on the first passivation layer (5) at the isolation mesa;

s6, preparing a P-type ohmic contact electrode (7) on the P-type ion implantation area (3) so that the P-type ohmic contact electrode (7) and the first passivation layer (5) are arranged at intervals;

s7, epitaxially growing an N-type ohmic contact electrode (4) on the back surface of the N-type doped 4H-SiC substrate (1);

s8, preparing a radioisotope unit above the first passivation layer (5) and the P-type ohmic contact electrode (7).