Fan-shaped silicon drift detector and its fabrication method

Abstract

This invention provides a fan-shaped silicon drift detector, comprising a substrate, an upper surface of which is a collecting surface, and a lower surface of which is an incident surface. At the center of the collecting surface is a collecting anode, and outwardly from the collecting anode are sequentially arranged a collecting surface floating cathode ring and an inner collecting surface pressure ring, all concentrically positioned. A fan-shaped unit is arranged around the inner collecting surface pressure ring, with surface electron discharge channels between the fan-shaped units. An annular protective anode is arranged outside the fan-shaped units. The incident surface includes an incident surface window, an incident surface cathode pressure ring, and an incident surface protection ring. The incident surface window is located inside the incident surface cathode pressure ring, and the incident surface protection ring is located outside the incident surface cathode pressure ring. This invention solves the problems of surface leakage current being collected by the anode and the inability to splice fan-shaped structures with different angles in existing technologies. This invention also provides a method for fabricating the fan-shaped silicon drift detector.

Description

Technical Field

[0001] This invention belongs to the field of radiation detection technology and relates to a sector-shaped silicon drift detector and its fabrication method. Background Technology

[0002] Silicon drift detectors were developed for atomic physics, nuclear physics, and elementary particle physics. Currently, silicon drift detectors are widely used in radiation source detection, high-energy physics particle trajectory detection, food safety testing, and many other fields. Traditional cylindrical silicon drift detector designs employ a single-sided spiral ring design, with the collecting anode located in the center of the spiral ring and the incident surface being a single cathode. Different operating bias voltages are applied to both the anode and incident surfaces, forming an electron collection channel pointing towards the anode. Leakage current in silicon drift detectors includes bulk leakage current and surface leakage current. Due to the properties of the silicon dioxide layer, electrons can be induced on its lower surface, existing at the interface between silicon dioxide and silicon. In traditional cylindrical silicon drift detector designs, both surface and bulk leakage currents are collected by the anode, with the surface leakage current contributing to additional adverse effects on the detector. Traditional cylindrical silicon drift detectors typically employ cylindrical, hexagonal, or square designs; fan-shaped structures with different angles are not feasible. Summary of the Invention

[0003] To achieve the above objectives, this invention provides a sector-shaped silicon drift detector and its fabrication method, which solves the problems in the prior art, such as surface leakage current being collected by the anode and the inability to splice together sector-shaped structures at different angles.

[0004] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is a fan-shaped silicon drift detector, including a substrate, the upper surface of which is a collecting surface and the lower surface of which is an incident surface; the center of the collecting surface is a collecting anode, and a collecting surface floating cathode ring and an inner collecting surface pressure ring are arranged sequentially outward from the collecting anode, the inner collecting surface pressure ring, the collecting anode, and the collecting surface floating cathode ring are concentric; a fan-shaped unit is arranged around the inner collecting surface pressure ring, and a surface electron discharge channel is provided between the fan-shaped units; an annular protective anode is arranged outside the fan-shaped unit; the incident surface includes an incident surface window, an incident surface cathode pressure ring, and an incident surface protection ring, the inside of the incident surface cathode pressure ring is the incident window, the outside of the incident surface cathode pressure ring is the incident surface protection ring, and the incident surface cathode pressure ring and the incident surface protection ring are concentric with the center of the incident surface.

[0005] Furthermore, the sector-shaped unit includes a collection surface protection ring and a collection surface outer ring cathode pressure ring. The collection surface protection ring is located at the outermost edge of the sector-shaped unit, and the collection surface outer ring cathode pressure ring is located inside the collection surface protection ring.

[0006] Furthermore, the sector unit also includes a pressure-distributing chain and a collection surface drift ring; the pressure-distributing chain and the collection surface drift ring are arranged alternately from the innermost side of the sector unit outwards; the length and width of the pressure-distributing chain increase sequentially from the inside to the outside; the two ends of the collection surface drift ring are correspondingly connected to the two ends of the pressure-distributing chain drift ring.

[0007] Furthermore, the width of the pressure-distributing chain in the innermost ring is 5 μm, and the width of the pressure-distributing chain in the outermost ring is 17 μm; the width of the drift ring on the collection surface is 55 μm.

[0008] Furthermore, the surfaces of the fan-shaped unit's collecting surface drift ring, the fan-shaped unit's collecting surface outer ring cathode pressure ring, the collecting surface inner ring pressure ring, the collecting surface floating cathode ring, and the incident surface cathode pressure ring are plated with aluminum layers; the spaces between the aluminum layers are filled with silicon dioxide layers.

[0009] Furthermore, the substrate is an N+ type high-resistivity silicon wafer with a thickness of 300–500 μm and a doping concentration of 4 × 10¹¹–2 × 10¹² cm⁻¹. -3 .

[0010] Furthermore, the collector surface drift ring, pressure dividing chain, collector surface protection ring, outer collector surface cathode pressure ring, inner collector surface pressure ring, collector surface floating cathode ring, incident surface window, incident surface protection ring, and incident surface cathode pressure ring are all P+ type ion doped with a doping concentration of 10¹⁶–10²⁰ cm⁻¹. -3 The thickness is 0.5um.

[0011] Furthermore, the collecting anode and the annular protective anode are doped with N+ type ions at a concentration of 10¹⁶–10²⁰ cm⁻¹. -3 The thickness is 0.5um.

[0012] This invention also provides a method for fabricating a sector-shaped silicon drift detector, comprising the following steps:

[0013] Step S1: A layer with a thickness of approximately [thickness missing] is formed on the upper and lower surfaces of an N+ type high-resistivity silicon wafer using a getter oxidation process. The silicon dioxide layer is used to transfer the designed detector pattern onto the silicon dioxide layer through a photolithography process;

[0014] Step S2: Using a double-sided etching process, etch the silicon dioxide layer in the areas containing the collecting surface drift ring, pressure dividing chain, collecting surface protection ring, collecting surface outer ring cathode pressure ring, collecting surface inner ring pressure ring, collecting surface floating cathode ring, incident surface window, incident surface protection ring, and incident surface cathode pressure ring to...

[0015] Step S3: P+ type ions are implanted into the etched area to form a collection surface drift ring, a pressure dividing chain, a collection surface protection ring, a collection surface outer ring cathode pressure ring, a collection surface inner ring pressure ring, a collection surface floating cathode ring, an incident surface window, an incident surface protection ring, and an incident surface cathode pressure ring.

[0016] Step S4: Using photolithography and etching processes, the silicon dioxide layer in the area where the collecting anode and the annular protective anode are located is etched to the bottom, and then N+ type ions are implanted to form the collecting anode and the annular protective anode;

[0017] Step S5: Activate the injected P+ and N+ ions using an oxidation furnace;

[0018] Step S6: Using photolithography and etching processes, the silicon dioxide layer in the areas where the collection surface drift ring, the outer ring cathode pressure ring, the inner ring pressure ring, the floating cathode ring, and the incident surface cathode pressure ring are located is etched to the bottom.

[0019] Step S7: An aluminum film is generated by magnetron sputtering. An aluminum layer is generated above the areas where the drift ring, outer ring cathode pressure ring, inner ring pressure ring, floating cathode ring, and incident cathode pressure ring are located by photolithography and aluminum etching.

[0020] Step S8: Repair the damage caused by the previous steps through annealing process, and form an aluminum-silicon alloy to form an ohmic contact.

[0021] The beneficial effects of this invention are:

[0022] 1. By designing a fan-shaped silicon drift detector and a grounded anode protection structure outside the detector's sensitive area, the surface leakage current flows out through the protective anode, reducing the detector's leakage current, lowering the detector's background noise, and ultimately improving the detector's energy resolution.

[0023] 2. By designing sector-shaped silicon drift detector units at different angles, detectors of different shapes can be spliced ​​together according to usage requirements while ensuring a good distribution of the electric field. Each sector-shaped unit operates independently. Attached Figure Description

[0024] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1This is a view of the drift detector collection surface when using a sector-shaped unit (θ = 45°) according to an embodiment of the present invention.

[0026] Figure 2 This is an incident plane diagram of a circular silicon drift detector with a sector unit (θ = 45°) according to an embodiment of the present invention.

[0027] Figure 3 This is a schematic diagram of the middle area of ​​the collection surface in an embodiment of the present invention.

[0028] Figure 4 This is a schematic diagram of the connection between the collection surface drift ring and the pressure dividing chain in an embodiment of the present invention.

[0029] Figure 5 This is a schematic diagram showing the positional relationship between the collecting anode, the floating cathode on the collecting surface, and the inner ring pressure ring of the collecting surface in an embodiment of the present invention.

[0030] In the figure, 1. collecting surface, 2. sector-shaped unit, 3. annular protective anode, 4. outer ring cathode pressure ring of collecting surface, 5. collecting surface protection ring, 6. surface electron removal channel, 7. incident surface, 8. incident surface window, 9. incident surface cathode pressure ring, 10. incident surface protection ring, 11. pressure dividing chain, 12. collecting surface drift ring, 13. inner ring pressure ring of collecting surface, 14. collecting anode, 15. collecting surface floating cathode ring. Detailed Implementation

[0031] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0032] The sector-shaped silicon drift detector unit of the present invention can be designed with different angles θ. Each unit can independently realize the function of a silicon drift detector through autonomous voltage division, or they can be assembled into other shapes. In this embodiment, a unit structure with a central angle θ = 45° will be used for illustration.

[0033] like Figures 1-5As shown, a sector-shaped silicon drift detector includes a substrate, with the upper surface of the substrate being a collection surface 1 and the lower surface of the substrate being an incident surface 7. The center of the collection surface 1 is a collection anode 14, and a collection surface floating cathode ring 15 and a collection surface inner ring pressure ring 13 are arranged outward from the collection anode 14. The collection surface inner ring pressure ring 13, the collection anode 14, and the collection surface floating cathode ring 15 are concentric. The arrangement of the collection surface floating cathode ring 15 can optimize the electric field distribution between the collection anode 14 and the collection surface inner ring pressure ring 13. Eight sector-shaped units 2 are arranged in a ring around the collection surface inner ring pressure ring 13, and surface electron discharge channels 6 are provided between the sector-shaped units 2. The incident surface 7 includes an incident surface window 8, an incident surface cathode pressure ring 9, and an incident surface protection ring 10. The incident surface window is inside the incident surface cathode pressure ring 9, and the incident surface protection ring 10 is outside the incident surface cathode pressure ring 9. The incident surface cathode pressure ring 9 and the incident surface protection ring 10 are concentric with the center of the incident surface 7. When the detector is working, photons or high-energy particles enter through the incident surface window 8. The incident surface pressure cathode 9 provides the working voltage to the incident surface of the detector, and the potential V of the entire incident surface is... B The same everywhere.

[0034] The sector-shaped unit 2 includes a collecting surface protection ring 5 and a collecting surface outer ring cathode pressure ring 4. The collecting surface protection ring 5 is located at the outermost edge of the sector-shaped unit 2, and the collecting surface outer ring cathode pressure ring 4 is located inside the collecting surface protection ring 5. The collecting surface outer ring cathode pressure ring 4 is used to provide the detector operating voltage V. OUT This causes the detector to operate in a fully depleted state, with the working voltage V applied to the inner ring pressure ring 13 of the collection surface. E1 V-shaped formation on the detector surface OUT -V E1 The potential gradient, together with the incident cathode pressure ring 9, forms a drift channel from the outer end of the detector to the collecting anode 14. The design of the collecting surface protection ring 5 can effectively balance the high electric field region at the edge of the detector, preventing breakdown and damage to the detector structure.

[0035] like Figures 3-4 As shown, the sector unit 2 also includes a pressure-distributing chain 11 and a collection surface drift ring 12. The pressure-distributing chain 11 and the collection surface drift ring 12 are arranged in a staggered pattern from the innermost side outwards of the sector unit 2. To ensure a good electric field distribution between the cathode collection surface drift rings 12, the length and width of the pressure-distributing chain 11 between the cathode drift rings 12 are designed to vary: the width of the pressure-distributing chain 11 is smaller towards the innermost ring. In this embodiment, the width of the pressure-distributing chain 11 of the innermost ring is 5 μm, and the width of the pressure-distributing chain 11 of the outermost ring reaches 17 μm. Figure 4As shown, in this embodiment, the collecting surface drift ring 12 is connected to the corner of the pressure dividing chain 11, that is, the two ends of the collecting surface drift ring 12 are connected to the two ends of the drift ring of the pressure dividing chain 11 respectively. The potential at the connection point of the pressure dividing chain 11 can be measured. In this embodiment, the width of the collecting surface drift ring 12 is 55μm. The inner ring of the pressure dividing chain 11 is pressurized with V. E1 The outermost ring is pressurized with V OUT The voltage divider chain 11 has a change in potential gradient. In this embodiment, the potential gradient between the drift electrodes is designed to keep the potential difference between adjacent rings equal.

[0036] Furthermore, an annular protective anode 3 is provided on the outside of the sector unit 2. The annular protective anode 3 can collect surface electrons and discharge them through grounding, thereby reducing the leakage current of the detector and improving the energy resolution performance of the detector.

[0037] Furthermore, the surfaces of the collecting surface drift ring 12, the collecting surface outer ring cathode pressure ring 4, the collecting surface inner ring pressure ring 13, the collecting surface floating cathode ring 15, and the incident surface cathode pressure ring 9 are plated with aluminum layers; and silicon dioxide layers are filled between the aluminum layers.

[0038] Furthermore, the substrate of the fan-shaped silicon drift detector is an N+ type high-resistivity silicon wafer with a thickness of 300–500 μm and a doping concentration of 4 × 10¹¹–2 × 10¹² cm⁻¹. -3 The following components are incorporated into the substrate: a drift ring 12 on the collecting surface, a pressure dividing chain 11, a protective ring 5 on the collecting surface, an outer ring cathode pressure ring 4 on the collecting surface, an inner ring pressure ring 13 on the collecting surface, a floating cathode ring 15 on the collecting surface, an incident window 8, an incident protection ring 10, and an incident cathode pressure ring 9. These components are doped into the substrate using a P+ type ion implantation process, with a doping concentration of 10¹⁶–10²⁰ cm⁻¹. -3 The thickness is 0.5 μm, significantly higher than that of the high-resistivity silicon substrate. The collecting anode 14 and the annular protective anode 3 were doped into the substrate using N+ type ion implantation, with a doping concentration of 10¹⁶–10²⁰ cm⁻¹. -3 It is much higher than that of a high-resistivity silicon substrate, with a thickness of 0.5um.

[0039] Specific preparation method:

[0040] Step S1: A layer of approximately [thickness missing] is formed on the upper and lower surfaces of an N+ type high-resistivity silicon wafer (substrate) using a getter oxidation process. The silicon dioxide layer is used to transfer the designed detector pattern onto the silicon dioxide layer through a photolithography process;

[0041] Step S2: Using a double-sided etching process, etch the silicon dioxide layer in the areas containing the following components: the drift ring 12, the pressure dividing chain 11, the protection ring 5, the outer ring cathode pressure ring 4, the inner ring pressure ring 13, the floating cathode ring 15, the incident window 8, the incident protection ring 10, and the incident cathode pressure ring 9.

[0042] Step S3: P+ type ions are implanted into the etched area to form a collection surface drift ring 12, a pressure dividing chain 11, a collection surface protection ring 5, a collection surface outer ring cathode pressure ring 4, a collection surface inner ring pressure ring 13, a collection surface floating cathode ring 15, an incident surface window 8, an incident surface protection ring 10, and an incident surface cathode pressure ring 9.

[0043] Step S4: Through photolithography and etching processes, the silicon dioxide layer in the area where the collecting anode 14 and the annular protective anode 3 are located is etched to the bottom, and then N+ type ions are implanted to form the collecting anode 14 and the annular protective anode 3;

[0044] Step S5: Activate the injected P+ and N+ ions using an oxidation furnace;

[0045] Step S6: Using photolithography and etching processes, the silicon dioxide layer in the areas where the collection surface drift ring 12, the outer ring cathode pressure ring 4, the inner ring pressure ring 13, the floating cathode ring 15, and the incident surface cathode pressure ring 9 are located is etched to the bottom.

[0046] Step S7: An aluminum film is generated by magnetron sputtering. An aluminum layer is generated above the areas where the drift ring 12, outer ring cathode pressure ring 4, inner ring pressure ring 13, floating cathode ring 15, and incident cathode pressure ring 9 are located by photolithography and aluminum etching.

[0047] Step S8: Repair the damage caused by the previous steps through annealing process, and form an aluminum-silicon alloy to form an ohmic contact.

[0048] The various embodiments in this specification are described in a related manner. The same or similar parts between the various embodiments can be referred to each other. Each embodiment focuses on describing the differences from other embodiments.

[0049] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention are included within the scope of protection of the present invention.

Claims

1. A sector-shaped silicon drift detector, characterized in that, The substrate includes an upper surface as a collecting surface (1) and a lower surface as an incident surface (7). The collecting surface (1) has a collecting anode (14) at its center. A collecting surface floating cathode ring (15) and a collecting surface inner ring pressurizing ring (13) are arranged sequentially outwards from the collecting anode (14). The collecting surface inner ring pressurizing ring (13), collecting anode (14), and collecting surface floating cathode ring (15) are concentric. A fan-shaped unit (2) is arranged around the collecting surface inner ring pressurizing ring (13). A surface electron discharge channel (6) is provided between the fan-shaped units (2); an annular protective anode (3) is provided on the outside of the fan-shaped units (2); the incident surface (7) includes an incident surface window (8), an incident surface cathode pressure ring (9) and an incident surface protection ring (10). The inside of the incident surface cathode pressure ring (9) is the incident window, and the outside of the incident surface cathode pressure ring (9) is the incident surface protection ring (10). The incident surface cathode pressure ring (9) and the incident surface protection ring (10) are concentric with the center of the incident surface (7). The sector unit (2) includes a collection surface protection ring (5) and a collection surface outer ring cathode pressure ring (4). The collection surface protection ring (5) is located at the outermost edge of the sector unit (2), and the collection surface outer ring cathode pressure ring (4) is located inside the collection surface protection ring (5). The sector unit (2) also includes a pressure-distributing chain (11) and a collection surface drift ring (12); the pressure-distributing chain (11) and the collection surface drift ring (12) are arranged alternately from the innermost side to the outermost side of the sector unit (2); the length and width of the pressure-distributing chain (11) increase sequentially from the inside to the outside; the two ends of the collection surface drift ring (12) are connected to the two ends of the drift ring of the pressure-distributing chain (11); The substrate is an N+ type high-resistivity silicon wafer with a thickness of 300~500μm and a doping concentration of 4×10¹¹~2×10¹²cm⁻¹. -3 .

2. The sector-shaped silicon drift detector according to claim 1, characterized in that, The width of the innermost pressure-dividing chain (11) is 5 μm, and the width of the outermost pressure-dividing chain (11) is 17 μm; the width of the collection surface drift ring (12) is 55 μm.

3. A sector-shaped silicon drift detector according to claim 1, characterized in that, The surfaces of the collection surface drift ring (12), the collection surface outer ring cathode pressure ring (4), the collection surface inner ring pressure ring (13), the collection surface floating cathode ring (15), and the incident surface cathode pressure ring (9) of the fan-shaped unit (2) are plated with aluminum layers; a silicon dioxide layer is filled between the aluminum layers.

4. A sector-shaped silicon drift detector according to claim 1, characterized in that, The collection surface drift ring (12), pressure dividing chain (11), collection surface protection ring (5), outer ring cathode pressure ring (4), inner ring pressure ring (13), floating cathode ring (15), incident surface window (8), incident surface protection ring (10), and incident surface cathode pressure ring (9) are all P+ type ion doped with a doping concentration of 10¹⁶~10²⁰ cm⁻¹. -3 The thickness is 0.5um.

5. A sector-shaped silicon drift detector according to claim 1, characterized in that, The collecting anode (14) and the annular protective anode (3) are obtained by N+ type ion doping with a doping concentration of 10¹⁶~10²⁰ cm⁻¹. -3 The thickness is 0.5um.

6. A method for fabricating a sector-shaped silicon drift detector as described in any one of claims 1-5, characterized in that, Includes the following steps: Step S1: A silicon dioxide layer with a thickness of 4000~6000Å is generated on the upper and lower surfaces of the N+ type high resistivity silicon wafer by a getter oxidation process, and the designed detector pattern is transferred onto the silicon dioxide layer by a photolithography process. Step S2: The silicon dioxide layer in the area containing the collection surface drift ring (12), pressure dividing chain (11), collection surface protection ring (5), collection surface outer ring cathode pressure ring (4), collection surface inner ring pressure ring (13), collection surface floating cathode ring (15), incident surface window (8), incident surface protection ring (10) and incident surface cathode pressure ring (9) is etched to 1000 Å using a double-sided etching process. Step S3: P+ type ions are implanted into the etched area to form a collection surface drift ring (12), a pressure dividing chain (11), a collection surface protection ring (5), a collection surface outer ring cathode pressure ring (4), a collection surface inner ring pressure ring (13), a collection surface floating cathode ring (15), an incident surface window (8), an incident surface protection ring (10), and an incident surface cathode pressure ring (9). Step S4: Through photolithography and etching processes, the silicon dioxide layer in the area where the collecting anode (14) and the annular protective anode (3) are located is etched to the bottom, and then N+ type ions are implanted to form the collecting anode (14) and the annular protective anode (3). Step S5: Activate the injected P+ and N+ ions using an oxidation furnace; Step S6: Through photolithography and etching processes, the silicon dioxide layer in the area where the collection surface drift ring (12), the outer ring cathode pressure ring (4), the inner ring pressure ring (13), the floating cathode ring (15), and the incident surface cathode pressure ring (9) are located is etched to the bottom. Step S7: An aluminum film is generated by magnetron sputtering. An aluminum layer is generated above the areas where the drift ring (12), outer ring cathode pressure ring (4), inner ring pressure ring (13), floating cathode ring (15), and incident cathode pressure ring (9) are located by photolithography and aluminum etching. Step S8: Repair the damage caused by the previous steps through annealing process, and form an aluminum-silicon alloy to form an ohmic contact.

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