CN102931272A - Ultraviolet detector structure with gain and preparation method thereof - Google Patents

Abstract

The invention discloses a SiC-based ultraviolet detector with gain and a preparation method thereof. The ultraviolet detector comprises: a semi-insulating SiC substrate; a p-type buffer SiC epitaxial layer epitaxially grown on the semi-insulating SiC substrate; An n-type SiC epitaxial layer epitaxially grown on the p-type buffer SiC epitaxial layer; an n ⁺ -type SiC epitaxial layer epitaxially grown on the n-type SiC epitaxial layer; partially etching the n ⁺ -type SiC epitaxial layer to expose the n type SiC epitaxial layer, thereby forming a strip-shaped concave gate region on the surface of the n-type SiC epitaxial layer; source-drain region ohmic contacts formed on the n ⁺ -type SiC epitaxial layer that are not etched on both sides of the strip-shaped concave gate region a source and a drain; a transparent Schottky barrier gate formed on the strip-shaped concave gate region; and a passivation dielectric formed between the ohmic contact source, drain and the transparent Schottky barrier gate layer. The SiC ultraviolet detector structure proposed by the present invention can obtain higher gain without increasing bias voltage, and can avoid extra noise caused by avalanche.

Description

A kind of ultraviolet detector structure with gain and its preparation method

technical field

The invention relates to the technical field of semiconductor devices, in particular to a SiC-based ultraviolet detector structure with gain and a preparation method thereof.

Background technique

Ultraviolet detection technology is a newly developed technology in the past 50 years. It has extensive and important applications in military and civilian fields, so it has become a key topic of research and development at home and abroad. For the military, ultraviolet detectors have played an important role in the fields of ultraviolet confrontation and anti-anti-resistance technology, ultraviolet guidance and early warning systems, ultraviolet secure communication; for civil affairs, ultraviolet detectors can be used for flame detection, criminal investigation, astronomical observation, Medical care and other daily production, life and many other fields.

Wide bandgap semiconductor materials such as silicon carbide (SiC), gallium nitride (GaN), diamond (C), etc., can detect 200-380nm bands under strong visible and infrared background due to their wide bandgap. Ultraviolet light, which has the characteristics of high temperature resistance, high efficiency and high reliability, is an ideal material for preparing ultraviolet photodetectors. At present, GaN and SiC are relatively mature materials used to prepare ultraviolet detectors. Among them, the advantages of SiC material as a photodetector include: (1) SiC material itself has a substrate, and with the rapid development and application of SiC material in power devices, its material quality is relatively high, and its defect density is much lower than that of The defect density of GaN is beneficial to the preparation of large-area optoelectronic devices. (2) SiC is a compound semiconductor material on which high-quality SiO ₂ can be directly generated by thermal oxygen, and the SiO ₂ formed by thermal oxygen can be used as a passivation layer to reduce the leakage current on the surface of the device. (3) Due to the huge application prospects of SiC materials in power devices, the related preparation technology of SiC devices has developed rapidly. These factors provide a good basis for SiC as a material for the preparation of ultraviolet photodetectors.

At present, the research on SiC materials mainly focuses on 4H-SiC materials with wide band gaps. Common structures of SiC-based ultraviolet detectors include Schottky photodiodes, p-i-n photodiodes, metal-semiconductor-metal (MSM) photodetectors, and avalanche photodiodes (APDs). Among them, SiC photodetectors with Schottky, p-i-n and MSM structures have relatively simple fabrication processes and low working bias voltages, but they have no internal gain and have low responsivity to weak light signals, which cannot meet the requirements for weak ultraviolet light. The detection requirements of the signal make its application subject to certain restrictions.

Compared with detectors with other structures, the 4H-SiC ultraviolet APD device uses the avalanche multiplication mechanism to achieve internal gain and photocurrent amplification, with high sensitivity and fast response speed, and is suitable for the detection of weak ultraviolet signals. The APD ultraviolet detector of 4H-SiC material is characterized in that it can achieve high gain in operation, but it needs to increase the bias voltage when in use, which will bring higher noise to the device and reduce the signal noise of the device Ratio; and in order to improve the breakdown voltage of the device, it is often necessary to add a junction terminal design to the device structure, which increases the difficulty of the device's fabrication process.

Contents of the invention

(1) Technical problems to be solved

In view of this, the main purpose of the present invention is to provide an ultraviolet photodetector and its preparation method, so as to realize optical gain without high bias voltage and avoid relatively high avalanche noise in the device.

(2) Technical solution

To achieve the above object, the present invention provides a SiC-based ultraviolet detector with gain, which includes: a semi-insulating SiC substrate; a p-type buffer SiC epitaxial layer grown epitaxially on the semi-insulating SiC substrate ; an n-type SiC epitaxial layer epitaxially grown on the p-type buffer SiC epitaxial layer; an n ⁺ -type SiC epitaxial layer epitaxially grown on the n-type SiC epitaxial layer; partially etching the n ⁺ -type SiC epitaxial layer to expose the The n-type SiC epitaxial layer thus forms a strip-shaped concave gate region on the surface of the n-type SiC epitaxial layer; the source-drain region ohms formed on the n ⁺ -type SiC epitaxial layer that is not etched on both sides of the strip-shaped concave gate region contact source and drain; a transparent Schottky barrier gate formed on the strip-shaped recessed gate region; and a passivation formed between the ohmic contacts source, drain and transparent Schottky barrier gate medium layer.

In the above solution, the thickness of the semi-insulating SiC substrate is 300-400 nm; the thickness of the p-type buffer SiC epitaxial layer is 0.5-2 μm; the thickness of the n-type SiC epitaxial layer is 0.2-0.4 μm; the n ⁺ type The thickness of the SiC epitaxial layer is 0.1-0.2 μm.

In the above solution, the p-type buffer SiC epitaxial layer has a doping concentration of 1×10 ¹⁵ to 5×10 ¹⁵ cm ^-3 ; the n-type SiC epitaxial layer has a doping concentration of 1×10 ¹⁷ to 3.5×10 ¹⁷ cm ^-3 ; the doping concentration of the n ⁺ -type SiC epitaxial layer is greater than 1×10 ¹⁹ cm ^-3 .

To achieve the above object, the present invention also provides a method for preparing a SiC-based ultraviolet detector with gain, the method comprising:

Step 10, sequentially growing a p-type buffer SiC epitaxial layer, an n-type SiC epitaxial layer and an n ⁺ -type SiC epitaxial layer on the semi-insulating SiC substrate;

Step 20, using the ICP etching process of SiC to isolate the device;

Step 30, using the ICP etching process of SiC, partially etching the n ⁺ -type SiC epitaxial layer to expose the n-type SiC epitaxial layer, thereby forming a strip-shaped concave gate region on the surface of the n-type SiC epitaxial layer;

Step 40, forming an ohmic contact source and drain of the source and drain regions on the n ⁺ -type SiC epitaxial layer that has not been etched on both sides of the strip-shaped recessed gate region;

Step 50, depositing a passivation layer SiN on the surface of the device by PECVD;

Step 60, preparing a transparent Schottky metal gate on the surface of the concave gate region of the n-type SiC epitaxial layer;

Step 70, thickening the device electrodes.

In the above scheme, the step 10 includes:

Step 101. Using CVD to epitaxially grow a p-type buffer SiC epitaxial layer on the front side of a semi-insulating SiC substrate with a thickness of 300-400 nm. The doping concentration of the p-type buffer SiC epitaxial layer is 1×10 ¹⁵ to 5×10 ¹⁵ cm ^-3 , the thickness is 0.5～2μm;

Step 102, growing an n-type SiC epitaxial layer on the p-type buffer SiC epitaxial layer, the doping concentration of the n-type SiC epitaxial layer is 1×10 ¹⁷ to 3.5×10 ¹⁷ cm ⁻³ , and the thickness is 0.2 to 0.4 μm;

Step 103 , growing an n ⁺ -type SiC epitaxial layer on the n-type SiC epitaxial layer, the doping of the n ⁺ -type SiC epitaxial layer is greater than 1×10 ¹⁹ cm ^-3 , and the thickness is 0.1-0.2 μm.

In the above scheme, the step 20 includes:

Step 201, using positive resist 9920 photoresist to make an etching mask layer with a thickness of 2 μm;

Step 202, using an ICP etching machine to etch the SiC epitaxial layer to the p-type SiC epitaxial layer.

In the above scheme, the n ⁺ -type SiC epitaxial layer is etched using an ICP etching machine as described in step 202. The etching process conditions are: RF: 50W, LF: 300W, CHF ₃ : 20 sccm, C ₂ H ₄ : 3 sccm, pressure : 10mTorr, etching time is about 6 minutes.

In the above scheme, the step 30 includes:

Step 301, using positive resist 9920 photoresist to make an etching mask layer with a thickness of 2 μm;

Step 302 , using an ICP etching machine to etch the n ⁺ -type SiC epitaxial layer until the n-type SiC epitaxial layer is exposed, and forming strip-shaped concave gate regions on the surface of the n-type SiC epitaxial layer.

In the above solution, the n ⁺ -type SiC epitaxial layer is etched by an ICP etching machine in step 302, and the etching process conditions are: RF: 50W, LF: 300W, CHF ₃ : 20 sccm, C ₂ H ₄ : 3 sccm, pressure : 10 mTorr, etching time 40 seconds to 80 seconds.

In the above scheme, the step 40 includes:

Step 401, spin coating photoresist on the surface of the device, and form source and drain region ohmic contact patterns by photolithography;

Step 402, using magnetron sputtering technology to grow Ni metal, stripping to form source and drain region metal;

Step 403, performing rapid thermal annealing on the source and drain region metals in a vacuum environment or an inert gas atmosphere within a temperature range of 900° C. to 1000° C. to form ohmic contact sources and drains for the source and drain regions on the n ⁺ type SiC layer pole.

In the above scheme, the step 60 includes:

Step 601, spin-coat photoresist on the device surface, form a Schottky metal gate pattern by photolithography, and use ICP etching technology to open a SiN window;

Step 602 , growing transparent Ni metal by electron beam evaporation, and forming a Schottky metal grid in the concave grid region of the n-type SiC epitaxial layer after stripping.

In the above scheme, the step 70 includes:

Step 701, spin coating photoresist on the surface of the device, form an electrode thickening pattern by photolithography, and open a SiN window by using ICP etching technology;

Step 702 , using electron beam evaporation to grow Ti/Al, and after peeling off, complete device electrode thickening.

(3) Beneficial effects

As can be seen from the foregoing technical solutions, the present invention has the following beneficial effects:

1. In the SiC-based ultraviolet detector structure provided by the present invention, when the ultraviolet light is irradiated at the Schottky junction, the photogenerated electron-hole pairs formed due to the action of light move under the action of the electric field of the Schottky junction, The photo-generated voltage is formed, and the conductance between the source and the drain is modulated, so as to realize the detection and amplification of the ultraviolet light signal. Therefore, the ultraviolet detector structure provided by the present invention can realize signal gain without increasing the bias voltage, and can avoid relatively high avalanche noise in devices with an APD structure.

2. The preparation method based on the SiC ultraviolet light detector provided by the present invention can make full use of the mature process foundation of SiC materials in MESFET power devices, and reduce the difficulty of the preparation process of the device of the present invention.

Description of drawings

1 is a schematic structural view of a SiC-based ultraviolet detector with gain according to an embodiment of the present invention;

FIG. 2 is a flowchart of a method for fabricating a SiC-based ultraviolet detector with gain according to an embodiment of the present invention.

Detailed ways

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be described in further detail below in conjunction with specific embodiments and with reference to the accompanying drawings.

As shown in Figure 1, Figure 1 is a schematic structural view of a UV detector with gain based on SiC according to an embodiment of the present invention, the UV detector includes: a semi-insulating SiC substrate; epitaxial growth on the semi-insulating SiC substrate The p-type buffer SiC epitaxial layer; the n-type SiC epitaxial layer epitaxially grown on the p-type buffer SiC epitaxial layer; the n + type SiC epitaxial layer epitaxially grown on the n-type SiC epitaxial layer; the ^{n +} type SiC epitaxial layer is partially etched type SiC epitaxial layer to expose the n-type SiC epitaxial layer to form a strip-shaped recessed gate region on the surface of the n-type SiC epitaxial layer; the n ⁺ -type SiC epitaxial layer that is not etched on both sides of the strip-shaped recessed gate region The source and drain regions formed on the ohmic contact source and drain; the transparent Schottky barrier gate formed on the strip-shaped concave gate region; and the ohmic contact source, drain and transparent Schottky barrier gate The passivation dielectric layer formed between the poles.

Wherein, the Schottky barrier gate is formed in the strip-shaped concave gate region on the n-type SiC epitaxial layer, the source and drain are respectively formed on the n ⁺ type SiC epitaxial layer, and each electrode A passivation medium layer is further provided between them. When ultraviolet light is radiated on the surface of the Schottky junction of the device, the photogenerated electron-hole pairs formed due to the action of light will move under the action of the electric field in the Schottky junction to form a photogenerated voltage, and its effect is equivalent to that in the gate A bias voltage is applied to the Schottky junction of the electrode, thereby modulating the conductance between the source and drain electrodes, and completing the detection and amplification of the ultraviolet light signal.

The thickness of the semi-insulating SiC substrate is 300-400 nm; the thickness of the p-type buffer SiC epitaxial layer is 0.5-2 μm; the thickness of the n-type SiC epitaxial layer is 0.2-0.4 μm; the thickness of the n ⁺ type SiC epitaxial layer is 0.1 to 0.2 μm. The p-type buffer SiC epitaxial layer has a doping concentration of 1×10 ¹⁵ to 5×10 ¹⁵ cm ^-3 ; the n-type SiC epitaxial layer has a doping concentration of 1×10 ¹⁷ to 3.5×10 ¹⁷ cm ^-3 ; The doping concentration of the n ⁺ -type SiC epitaxial layer is greater than 1×10 ¹⁹ cm ^-3 .

FIG. 2 is a flow chart of a method for fabricating a SiC-based ultraviolet detector with gain according to an embodiment of the present invention. This method can make the SiC ultraviolet detector shown in Figure 1, including the following steps:

Step 10, sequentially growing a p-type buffer SiC epitaxial layer, an n-type SiC epitaxial layer and an n ⁺ -type SiC epitaxial layer on the semi-insulating SiC substrate; the steps are as follows:

Step 101. Using CVD to epitaxially grow a p-type buffer SiC epitaxial layer on the front side of a semi-insulating SiC substrate with a thickness of 300-400 nm. The doping concentration of the p-type buffer SiC epitaxial layer is 1×10 ¹⁵ to 5×10 ¹⁵ cm ^-3 , the thickness is 0.5～2μm;

Step 102, growing an n-type SiC epitaxial layer on the p-type buffer SiC epitaxial layer, the doping concentration of the n-type SiC epitaxial layer is 1×10 ¹⁷ to 3.5×10 ¹⁷ cm ⁻³ , and the thickness is 0.2 to 0.4 μm;

Step 103 , growing an n ⁺ -type SiC epitaxial layer on the n-type SiC epitaxial layer, the doping of the n ⁺ -type SiC epitaxial layer is greater than 1×10 ¹⁹ cm ^-3 , and the thickness is 0.1-0.2 μm.

Step 20, using the ICP etching process of SiC to isolate the device; the details of this step are as follows:

Step 201, using positive resist 9920 photoresist to make an etching mask layer. Thickness 2μm;

Step 202, using an ICP etching machine to etch the SiC epitaxial layer to the p-type SiC epitaxial layer. The etching process conditions are: RF: 50W, LF: 300W, CHF ₃ : 20 sccm, C ₂ H ₄ : 3 sccm, pressure: 10 mTorr, and the etching time is about 6 minutes.

Step 30. Using the ICP etching process of SiC, partially etch the n ⁺ -type SiC epitaxial layer to expose the n-type SiC epitaxial layer, thereby forming a strip-shaped concave gate region on the surface of the n-type SiC epitaxial layer; the step is as follows :

Step 301, using positive resist 9920 photoresist to make an etching mask layer with a thickness of 2 μm;

Step 302, using an ICP etching machine to etch the n ⁺ type SiC epitaxial layer, the etching process conditions are: RF: 50W, LF: 300W, CHF ₃ : 20sccm, C ₂ H ₄ : 3sccm, pressure: 10mTorr, etching time 40 seconds to 80 seconds, until the n-type SiC epitaxial layer is exposed, and strip-shaped concave gate regions are formed on the surface of the n-type SiC epitaxial layer.

Step 40, forming the ohmic contact source and drain of the source and drain regions on the n ⁺ -type SiC epitaxial layer that has not been etched on both sides of the strip-shaped concave gate region; this step is specifically as follows:

Step 401, spin coating photoresist on the surface of the device, and form source and drain region ohmic contact patterns by photolithography;

Step 402, using magnetron sputtering technology to grow Ni metal, stripping to form source and drain region metal;

Step 403, within the temperature range of 900°C to 1000°C, perform rapid thermal annealing on the metal of the source and drain regions in a vacuum environment or an inert gas atmosphere to form ohmic contact sources and drains of the source and drain regions on the n ⁺ type SiC layer pole.

Step 50, depositing a passivation layer SiN on the surface of the device by PECVD;

Step 60, preparing a transparent Schottky metal grid on the surface of the concave grid region of the n-type SiC epitaxial layer; the steps are as follows:

Step 601, spin-coat photoresist on the device surface, form a Schottky metal gate pattern by photolithography, and use ICP etching technology to open a SiN window;

Step 602 , growing transparent Ni metal by electron beam evaporation, and forming a Schottky metal grid in the concave grid region of the n-type SiC epitaxial layer after stripping.

Step 70, thickening the device electrodes. The steps are as follows:

Step 701, spin coating photoresist on the surface of the device, form an electrode thickening pattern by photolithography, and open a SiN window by using ICP etching technology;

Step 702 , using electron beam evaporation to grow Ti/Al, and after peeling off, complete device electrode thickening.

The specific embodiments described above have further described the purpose, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above descriptions are only specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims (12)

1. A kind of ultraviolet detector with gain based on SiC, it is characterized in that, this ultraviolet detector comprises: Semi-insulating SiC substrate; A p-type buffer SiC epitaxial layer epitaxially grown on the semi-insulating SiC substrate; An n-type SiC epitaxial layer epitaxially grown on the p-type buffer SiC epitaxial layer; An n + -type SiC epitaxial layer epitaxially grown on the n ^- type SiC epitaxial layer; Partially etching the n ⁺ -type SiC epitaxial layer to expose the n-type SiC epitaxial layer so as to form a strip-shaped concave gate region on the surface of the n-type SiC epitaxial layer; The source and drain regions formed on the unetched n ⁺ -type SiC epitaxial layer on both sides of the strip-shaped concave gate region are in ohmic contact with the source and drain; a transparent Schottky barrier gate formed on the strip-shaped concave gate region; and A passivation dielectric layer formed between the ohmic contacts source, drain and transparent Schottky barrier gate. 2. The ultraviolet detector with gain based on SiC according to claim 1, characterized in that, the thickness of the semi-insulating SiC substrate is 300-400 nm; the thickness of the p-type buffer SiC epitaxial layer is 0.5-2 μm; The thickness of the n-type SiC epitaxial layer is 0.2-0.4 μm; the thickness of the n ⁺ -type SiC epitaxial layer is 0.1-0.2 μm. 3. The SiC-based ultraviolet detector with gain according to claim 1, characterized in that the p-type buffer SiC epitaxial layer has a doping concentration of 1×10 ¹⁵ to 5×10 ¹⁵ cm ^-3 ; The n-type SiC epitaxial layer has a doping concentration of 1×10 ¹⁷ to 3.5×10 ¹⁷ cm ^-3 ; the n ⁺ type SiC epitaxial layer has a doping concentration greater than 1×10 ¹⁹ cm ^-3 . 4. A method for preparing an ultraviolet detector with gain based on SiC, characterized in that the method comprises: Step 10, sequentially growing a p-type buffer SiC epitaxial layer, an n-type SiC epitaxial layer and an n ⁺ -type SiC epitaxial layer on the semi-insulating SiC substrate; Step 20, using the ICP etching process of SiC to isolate the device; Step 30, using the ICP etching process of SiC, partially etching the n ⁺ -type SiC epitaxial layer to expose the n-type SiC epitaxial layer, thereby forming a strip-shaped concave gate region on the surface of the n-type SiC epitaxial layer; Step 40, forming an ohmic contact source and drain of the source and drain regions on the n ⁺ -type SiC epitaxial layer that has not been etched on both sides of the strip-shaped recessed gate region; Step 50, depositing a passivation layer SiN on the surface of the device by PECVD; Step 60, preparing a transparent Schottky metal gate on the surface of the concave gate region of the n-type SiC epitaxial layer; Step 70, thickening the device electrodes. 5. the preparation method of the ultraviolet detector with gain based on SiC according to claim 4, is characterized in that, described step 10 comprises: Step 101. Using CVD to epitaxially grow a p-type buffer SiC epitaxial layer on the front side of a semi-insulating SiC substrate with a thickness of 300-400 nm. The doping concentration of the p-type buffer SiC epitaxial layer is 1×10 ¹⁵ to 5×10 ¹⁵ cm ^-3 , the thickness is 0.5～2μm; Step 102, growing an n-type SiC epitaxial layer on the p-type buffer SiC epitaxial layer, the doping concentration of the n-type SiC epitaxial layer is 1×10 ¹⁷ to 3.5×10 ¹⁷ cm ⁻³ , and the thickness is 0.2 to 0.4 μm; Step 103 , growing an n ⁺ -type SiC epitaxial layer on the n-type SiC epitaxial layer, the doping of the n ⁺ -type SiC epitaxial layer is greater than 1×10 ¹⁹ cm ^-3 , and the thickness is 0.1-0.2 μm. 6. the preparation method of the ultraviolet detector with gain based on SiC according to claim 4, is characterized in that, described step 20 comprises: Step 201, using positive resist 9920 photoresist to make an etching mask layer with a thickness of 2 μm; Step 202, using an ICP etching machine to etch the SiC epitaxial layer to the p-type SiC epitaxial layer. 7. The method for preparing an ultraviolet detector with gain based on SiC according to claim 6, characterized in that, the SiC epitaxial layer is etched using an ICP etching machine as described in step 202, and the etching process conditions are: RF: 50W, LF: 300W, CHF ₃ : 20 sccm, C ₂ H ₄ : 3 sccm, pressure: 10 mTorr, etching time 6 minutes. 8. the preparation method of the ultraviolet detector with gain based on SiC according to claim 4, is characterized in that, described step 30 comprises: Step 301, using positive resist 9920 photoresist to make an etching mask layer with a thickness of 2 μm; Step 302 , using an ICP etching machine to etch the n ⁺ -type SiC epitaxial layer until the n-type SiC epitaxial layer is exposed, and forming strip-shaped concave gate regions on the surface of the n-type SiC epitaxial layer. 9. The method for preparing a SiC-based ultraviolet detector with gain according to claim 8, wherein, in step 302, an ICP etching machine is used to etch the n ⁺ type SiC epitaxial layer, and the etching process condition is : RF: 50W, LF: 300W, CHF ₃ : 20 sccm, C ₂ H ₄ : 3 sccm, pressure: 10 mTorr, etching time 40 seconds to 80 seconds. 10. the preparation method of the ultraviolet detector with gain based on SiC according to claim 4, is characterized in that, described step 40 comprises: Step 401, spin coating photoresist on the surface of the device, and form source and drain region ohmic contact patterns by photolithography; Step 402, using magnetron sputtering technology to grow Ni metal, stripping to form source and drain region metal; Step 403, performing rapid thermal annealing on the source and drain region metals in a vacuum environment or an inert gas atmosphere within a temperature range of 900° C. to 1000° C. to form ohmic contact sources and drains for the source and drain regions on the n ⁺ type SiC layer pole. 11. the preparation method of the ultraviolet detector with gain based on SiC according to claim 4, is characterized in that, described step 60 comprises: Step 601, spin-coat photoresist on the device surface, form a Schottky metal gate pattern by photolithography, and use ICP etching technology to open a SiN window; Step 602 , growing transparent Ni metal by electron beam evaporation, and forming a Schottky metal grid in the concave grid region of the n-type SiC epitaxial layer after stripping. 12. The method for preparing a SiC-based ultraviolet detector with gain according to claim 4, wherein the step 70 comprises: Step 701, spin coating photoresist on the surface of the device, form an electrode thickening pattern by photolithography, and open a SiN window by using ICP etching technology; Step 702 , using electron beam evaporation to grow Ti/Al, and after peeling off, complete device electrode thickening.

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