Photoconductive switch capable of generating parasitic capacitance effect based on dislocation, preparation method and tuning method

Abstract

The invention discloses a photoconductive switch capable of generating a parasitic capacitance effect based on dislocation, a preparation method and a tuning method, and relates to the technical field of semiconductor devices. The preparation method comprises the following steps: preparing a silicon carbide substrate, performing dislocation analysis on the silicon carbide substrate to obtain substrate intervals with different dislocation densities, and partitioning the substrate intervals with different dislocation densities; preparing a composite metal layer on the silicon carbide substrate, and obtaining a positive silicon carbide wafer with a photoconductive switch electrode structure through photoetching, developing, stripping and other processes; and carrying out alloy treatment on the silicon carbide wafer without the non-electrode area to obtain a photoconductive switch, and then scribing the photoconductive switch to obtain a single discrete photoconductive semiconductor device. According to the invention, the substrate dislocation density of the photoconductive switch device is regulated and controlled, and the half-peak width and the frequency spectrum of the output signal of the photoconductive switch are tunable by utilizing the capacitance effect introduced by the dislocation defect.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of semiconductor devices, and in particular to a photoconductive switch based on dislocation-induced parasitic capacitance effect, a preparation method and a tuning method. BACKGROUND

[0002] The statements in this section merely provide background information related to the present application and do not necessarily constitute the prior art.

[0003] Photoconductive semiconductor switches have the advantages of high breakdown field, fast turn-on, long service life and low jitter, and have been widely used in the fields of microwave generation, pulse power systems and pulse radar. At present, higher performance requirements are put forward for the response speed, miniaturization, portability and adjustability of photoconductive semiconductor devices. As the third generation of semiconductor, the photoconductive switch prepared by silicon carbide has more superior performance and wider application environment than the first generation of semiconductor silicon and the second generation of semiconductor gallium arsenide. 4H-SiC material has the characteristics of wide band gap (~3eV), high dark state resistance (>10 8 Ω), high breakdown field (4MV / cm), high saturated electron drift velocity (2×10 7 cm / s) and high thermal conductivity (4.9W / cm·°C). These key parameters greatly improve the high resistivity and high thermal conductivity of the photoconductive switch.

[0004] 4H-SiC photoconductive semiconductor switches can be applied to microwave generation. In order to realize high-frequency microwave radiation output, the fast turn-on characteristic of 4H-SiC can be used to directly generate electromagnetic pulses. The rise time of the linear 4H-SiC photoconductive switch device output waveform depends on the rise time of the trigger laser, that is, by using an ultrafast picosecond laser trigger, a picosecond fast front edge electrical signal can be obtained. However, the current method of using an ultrafast laser trigger to realize a wide spectrum electromagnetic pulse has some limitations. First, the output spectrum parameters are usually fixed or difficult to be widely tuned. In addition, the price of the ultrafast picosecond laser is expensive, and the high-power ultrafast picosecond laser has a large volume, which is difficult to use portably.

[0005] In view of the current problems, some related research introduces a narrow-band high-power adjustable frequency radio frequency / microwave generation scheme of a high-power pulse cluster all-fiber laser system. For example, an electro-optic modulator (EOM) of an arbitrary waveform generator (AWG) can be used to modulate the trigger laser signal, and then the continuous adjustable pulse output waveform can be realized. However, in practical applications, the trigger laser mode of the modulated high frequency will lead to a too complex structure of the laser trigger system, and the laser light source needs a large device volume and is expensive. On the other hand, the high repetition frequency of the laser pulse is also more serious for the damage of the photoconductive switch, thereby reducing the service life of the photoconductive switch system.

[0006] In summary, the prior art optical guide switch has the defects of high cost, coordination difficulty and large damage to the device in the process of generating microwaves. SUMMARY

[0007] In view of the defects of the prior art, the purpose of the present application is to provide an optical guide switch based on dislocation generated parasitic capacitance effect, preparation and tuning method, by controlling the dislocation density of the substrate of the optical guide switch device, the capacitance effect introduced by the inherent microstructure such as dislocation defects is used to realize the tunable half peak width and spectrum of the output signal of the optical guide switch.

[0008] In order to achieve the above purpose, the present application is realized by the following technical scheme: The first aspect of the present application provides a preparation method of an optical guide switch based on dislocation generated parasitic capacitance effect, comprising the following steps: Preparation of silicon carbide substrate, dislocation analysis is carried out on the silicon carbide substrate to obtain different dislocation density substrate intervals, and the different dislocation density substrate intervals are partitioned; Preparation of composite metal layer on the silicon carbide substrate, formation of local photoresist protection area in the silicon carbide electrode area, and obtaining of positive silicon carbide wafer with optical guide switch electrode structure by photoetching and stripping in turn; The silicon carbide wafer without electrode area is subjected to alloying treatment to obtain an optical guide switch, and then the optical guide switch is subjected to dicing to obtain a single discrete optical guide semiconductor device. The second aspect of the present application provides an optical guide switch made of the preparation method of the optical guide switch based on dislocation generated parasitic capacitance effect according to the first aspect.

[0009] The third aspect of the present application provides a tuning method of an optical guide switch based on dislocation generated parasitic capacitance effect, comprising the following steps: Outputting microwave signal by the optical guide switch according to the second aspect; Controlling the dislocation density of the substrate of the optical guide switch, and changing the frequency characteristics of the output signal by the capacitance effect generated by the dislocation defects.

[0010] The above one or more technical solutions have the following beneficial effects: The present application discloses an optical guide switch based on dislocation generated parasitic capacitance effect, preparation and tuning method, by controlling the dislocation density of the substrate of the optical guide switch device, the capacitance effect introduced by the inherent microstructure such as dislocation defects is used to realize the tunable half peak width and spectrum of the output signal of the optical guide switch. The capacitance value of the parasitic capacitance can be controlled by changing the dislocation density, distribution or external bias.

[0011] The photoconductive switch of the application comprises a vanadium-doped silicon carbide substrate, a Ni metal layer, a pair of ohmic contact electrodes, and a preparation process comprising the steps of cleaning, uniform coating, photolithography, etching, metal layer plating, peeling, slicing, thinning, packaging, etc. The upper surface of the silicon carbide substrate is provided with electrodes on both sides; the electrodes and the silicon carbide substrate form ohmic contact through the setting of Ni metal. The application triggers the silicon carbide impurity level through the centimeter-level absorption depth of visible light, avoiding the problem of low yield caused by stress during the device thinning process.

[0012] The application optimizes the dislocation density of the substrate, and realizes the generation of picosecond-level electrical output triggered by nanosecond-level light without picosecond-level laser triggering through the photoconductive switch device generated by the parasitic capacitance effect of the high dislocation density substrate, greatly reducing the system volume and cost.

[0013] The advantages of the additional aspects of the application will be partially given in the following description, partially become obvious from the following description, or be known through the practice of the application. BRIEF DESCRIPTION OF DRAWINGS

[0014] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor on the basis of these drawings.

[0015] Figure 1 The preparation method flow chart of the photoconductive switch in the first embodiment of the application; Figure 2 The dislocation interval diagram of the photoconductive semiconductor device substrate in the first embodiment of the application, wherein (a) is a physical diagram of the silicon carbide substrate required by the photoconductive switch, and (b) is a dislocation density analysis result diagram of the silicon carbide substrate by a dislocation analyzer; Figure 3 The comparative diagram of the photoconductive semiconductor device in the first embodiment of the application at different dislocation densities of the substrate, and the corresponding output waveform diagram and frequency spectrum diagram, wherein (a) from top to bottom is the corresponding physical diagram, output current waveform and amplitude diagram when the dislocation density of the substrate is less than 3.0×10 3 cm -2 ; (b) from top to bottom is the corresponding physical diagram, output current waveform and amplitude diagram when the dislocation density of the substrate is 9.0×10 3 ~1.5×10 4 cm -2 ; (c) from top to bottom is the corresponding physical diagram, output current waveform and amplitude diagram when the dislocation density of the substrate is greater than 1.5×10 4 cm -2 . DETAILED DESCRIPTION

[0016] It should be noted that the following detailed description is exemplary in nature and is intended to provide further description of the application. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

[0017] It is also important to note that the terms used herein are not intended to limit the particular embodiments of the present application to the preferred embodiments described. Rather, the terms are used only to describe specific embodiments of the present application. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and / or "comprising," when used in this specification, specify the presence of stated features, steps, operations, elements, and / or components, but do not preclude the presence or addition of one or more other features, steps, operations, elements, components, and / or groups thereof. The technical solutions in the embodiments of the present application will be apparently and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0018] Term explanation: High-density dislocation substrate refers to a single crystal or polycrystalline substrate of a semiconductor material, which is grown or processed by a specific process (such as hetero-epitaxy, ion implantation, annealing, etc.) to make the dislocation density in the lattice significantly higher than that of a conventional semiconductor substrate. The material of the substrate can include but is not limited to silicon carbide (SiC), gallium nitride (GaN), gallium arsenide (GaAs), silicon (Si) or other III-V, II-VI compound semiconductors.

[0019] Parasitic capacitance refers to the capacitance effect introduced by the inherent microstructure such as dislocation defects, grain boundaries or stress concentration areas in the high-density dislocation substrate. The capacitance is distributed in the active area of the device, and its value can be regulated by changing the dislocation density, distribution or applied bias, rather than the lumped capacitance formed by the traditional metal-insulator-metal (MIM) structure.

[0020] Spectrum tunable refers to the ability to continuously or discretely change the frequency characteristics of the output microwave signal, including but not limited to the center frequency, frequency range and spectrum shape, by changing the dislocation density parameter of the substrate used in the light guiding microwave device.

[0021] Embodiment one: The embodiment one of the present application provides a preparation method of a light guiding switch based on parasitic capacitance effect generated by dislocations, like Figure 1As shown, the preparation process includes Si surface KOH etching, laser etching division, Si surface grinding and polishing, device preparation, and sampling according to the mark area. The parasitic capacitance effect is mainly regulated by changing the dislocation density, distribution, or applied bias, and the output signal half-peak width and spectrum of the photoconductive switch are tuned by using the inherent microstructure such as dislocation defects to introduce the capacitance effect.

[0022] The photoconductive switch device includes a silicon carbide substrate, a Ni metal layer, and a pair of ohmic contact electrodes. The two sides of the upper surface of the silicon carbide substrate are respectively provided with electrodes, and the electrodes and the silicon carbide substrate form ohmic contact through the Ni metal layer. The embodiment triggers the silicon carbide impurity level by using centimeter-level absorption depth visible light, increases the photoelectric current modulation depth, and avoids the problem of low yield caused by stress during the device thinning process.

[0023] Specifically, the following steps are included: Step 1: preparing a silicon carbide substrate, performing dislocation analysis on the silicon carbide substrate to obtain different dislocation density substrate intervals, and partitioning different dislocation density substrate intervals.

[0024] In a specific embodiment, the actual drawing of the silicon carbide substrate required by the photoconductive switch is as shown in Figure 2 (a), Figure 2 (b) is a dislocation density analysis result graph of the silicon carbide substrate by a dislocation analyzer, which divides the dislocation density into three partitions, including a low dislocation area substrate 1 (<3.0x10 3 cm -2 ), a medium dislocation area substrate 2 (9.0x10 3 ~1.5x10 4 cm -2 ), and a high dislocation area substrate 3 (>1.5x10 4 cm -2 ). The front surface of the silicon carbide substrate is a silicon (Si) surface, and the back surface is a carbon (C) surface. The dislocation analysis of the front surface of the silicon carbide substrate is performed by a KOH etching process to obtain different dislocation density substrate intervals, and then a laser etching process is used to partition different dislocation density areas on the back surface of the silicon carbide substrate.

[0025] Specifically, the silicon surface of the entire silicon carbide substrate is analyzed by a dislocation analyzer using a KOH etching process. The KOH etching process uses a KOH molten liquid. The temperature of the KOH etching process is 400-600℃, and preferably, the temperature of the KOH etching process is 480℃, and the etching time is 20 minutes.

[0026] Specifically, the laser etching process is used to etch the carbon surface of the substrate to distinguish the different dislocation densities of the entire silicon carbide substrate. The laser etching process selects an etching depth of 1-7 μm, and the laser wavelength of the laser etching process is 355 nm, 532 nm, and 1064 nm. Preferably, the laser etching uses 355 nm laser etching, and the etching depth is 3 μm, which is sufficient to see the etching line from the front surface of the substrate.

[0027] Step 2: A composite metal layer is prepared on the silicon carbide substrate, a local photoresist protection area is formed in the silicon carbide electrode area, and a positive silicon carbide wafer with a photoconductive switch electrode structure is obtained by photoetching and stripping in sequence.

[0028] In a specific embodiment, a thinning area is obtained by grinding and polishing the front surface of the silicon carbide substrate. A Ni metal layer is deposited on the silicon carbide substrate by electron beam evaporation technology. A composite metal layer structure is evaporated on the silicon carbide substrate by electron beam evaporation or magnetron sputtering method equipment. A photoresist mask is prepared to protect the electrode area by photoetching and developing process, and a whole silicon carbide wafer with a photoconductive switch electrode structure is obtained by stripping with acetone or ethanol.

[0029] Specifically, the overall thinning area of the silicon surface of the silicon carbide substrate is obtained by grinding and polishing. The front surface of the silicon carbide substrate is thinned by grinding and polishing. Diamond powder is used for grinding, and the thinning thickness is 80 μm. Al2O3 polishing liquid is used for polishing, and the polishing depth is 1 μm. The roughness is reduced to below 0.2 nm.

[0030] Specifically, the Ni layer is evaporated on the silicon carbide substrate with a thickness of 100-400 nm. Preferably, a 200 nm thick Ni metal layer is deposited on the silicon surface area of the silicon carbide substrate by electron beam evaporation technology.

[0031] Specifically, a composite metal layer is evaporated on the silicon carbide substrate by electron beam evaporation equipment. The composite metal layer is a Ti, Pt, Au composite metal layer or a Ti, Al, Ti, Au composite metal layer. The thickness of the Ti, Pt, Au composite metal layer is 100 nm, 50 nm, and 700 nm. The thickness of the Ti, Al, Ti, Au composite metal layer is 100 nm, 50 nm, 100 nm, and 700 nm. Preferably, the electrode is a Ti, Pt, Au composite metal layer with a thickness of 100 nm, 50 nm, and 700 nm.

[0032] Specifically, the photoresist is spin-coated, and a local photoresist protection area is formed in the silicon carbide electrode area by photoetching. Preferably, the photoresist is a positive photoresist. The electrode pattern of the photoconductive switch is prepared by photoetching and developing process, and the non-electrode area is removed by cleaning and stripping.

[0033] Specifically, the whole silicon carbide wafer with photoconductive switch electrode structure is obtained by stripping with acetone or ethanol. First, the wafer is soaked in acetone for ultrasonic stripping for more than 10 minutes until the non-electrode area is stripped completely. Then, the wafer is soaked in ethanol again for ultrasonic cleaning for 10 minutes. Finally, the wafer is rinsed and dried. Step 3: The silicon carbide wafer without non-electrode area is subjected to alloying treatment to obtain a photoconductive switch. Then, the photoconductive switch is scribed to obtain a single discrete photoconductive semiconductor device. In a specific embodiment, the silicon carbide wafer is placed in an alloying furnace in a nitrogen atmosphere for alloying treatment. The purpose is to increase the adhesion of the material and the metal to form an ohmic contact of Ni and Si. Then, the photoconductive semiconductor device is scribed by laser or mechanical scribing to obtain a single discrete photoconductive semiconductor device. The switch is classified by laser scribing on the back of the silicon carbide substrate with different dislocation densities.

[0034] Specifically, the temperature of the alloying furnace is 800-1100°C, and the treatment time is 1-3 min. Preferably, the temperature of the alloying furnace is 950°C, and the treatment time is 2 min. The alloying furnace annealing treatment increases the adhesion of the material and the metal and forms an ohmic contact.

[0035] For the prepared spectrum-tunable silicon carbide photoconductive switch device, the dislocation density is changed, and the substrate dislocation density is divided into low, medium and high three types, which are <3.0×10 3 cm -2 , 9.0×10 3 ~1.5×10 4 cm -2 and >1.5×10 4 cm -2 .

[0036] This embodiment triggers the silicon carbide impurity level by centimeter-level absorption depth of visible light, without device thinning, and improves the yield. Different dislocation density substrates are used to control the parasitic capacitance parameters to effectively adjust the output waveform of the photoconductive switch. As shown in (a) of Figure 3 , when the substrate dislocation density is <3.0×10 3 cm -2 , the output current waveform presents a single peak form, the pulse width is 20 ns, and the center frequency is 50 MHz; as shown in (b) of Figure 3 , when the dislocation density increases to 9.0×10 3 ~1.5×10 4 cm -2 , the output waveform of the photoconductive switch appears a half-conduction half-oscillation characteristic, and the center frequency contains multiple frequency points of 50 MHz, 1.2 GHz and 2.1 GHz; as shown in (c) of Figure 3(c) in the figure, when the dislocation density > 1.5 x 10 4 cm -2 , the light guide switch output waveform presents full oscillation characteristics, the pulse width is 0.5 ns, and the center frequency is 2.1 GHz. The application can control the parasitic capacitance parameter by different dislocation densities of the substrate, and then affect the output waveform of the light guide switch, that is, the radiation frequency, aiming to meet the needs of adjustable, ultrafast and other application scenarios, and facilitate miniaturization and practical popularization.

[0037] Embodiment two: The embodiment two of the application provides a light guide switch, which is prepared by the preparation method of the light guide switch based on the parasitic capacitance effect of dislocation.

[0038] Embodiment three: The embodiment three of the application provides a tuning method of a light guide switch based on a parasitic capacitance effect of dislocation, which comprises the following steps: The light guide switch outputs a microwave signal.

[0039] The dislocation density of the substrate of the light guide switch is regulated, and the capacitance effect of the dislocation defect is used to change the frequency characteristics of the output signal.

[0040] The steps and method of the above embodiment two and three correspond to the embodiment one, and the specific embodiment can refer to the related description part of the embodiment one.

[0041] The above description is only a specific embodiment of the application, but the protection scope of the application is not limited to this, any skilled person in the technical field can easily think of changes or replacements within the technical range disclosed by the application, which should be covered in the protection scope of the application. Therefore, the protection scope of the application should be subject to the protection scope of the claims.

Claims

1. A method for fabricating a photoconductive switch based on the parasitic capacitance effect generated by dislocations, characterized in that, Includes the following steps: A silicon carbide substrate is prepared, and dislocation analysis is performed on the silicon carbide substrate to obtain substrate regions with different dislocation densities. The substrate regions with different dislocation densities are then divided into zones. A composite metal layer is prepared on a silicon carbide substrate, a local photoresist protection area is formed in the silicon carbide electrode area, and a positive silicon carbide wafer with a photoconductive switch electrode structure is obtained by photolithography and lift-off in sequence. The silicon carbide wafer with the non-electrode region removed is alloyed to obtain a photoconductive switch. The photoconductive switch is then diced to obtain a single discrete photoconductive semiconductor device.

2. The method for fabricating a photoconductive switch based on the parasitic capacitance effect generated by dislocations as described in claim 1, characterized in that, The front side of a silicon carbide substrate is a silicon surface, and the back side is a carbon surface. Silicon carbide substrates include low dislocation region substrates, medium dislocation region substrates, and high dislocation region substrates.

3. The method for fabricating a photoconductive switch based on the parasitic capacitance effect generated by dislocations as described in claim 1, characterized in that, The specific steps for performing dislocation analysis on a silicon carbide substrate to obtain substrate regions with different dislocation densities, and then dividing these regions into zones, are as follows: Dislocation analysis was performed on the front side of a silicon carbide substrate using a KOH etching process to obtain substrate ranges with different dislocation densities. Then, laser etching was used to partition regions with different dislocation densities on the back side of the silicon carbide substrate.

4. The method for fabricating a photoconductive switch based on the parasitic capacitance effect generated by dislocation as described in claim 3, characterized in that, The KOH etching process uses molten KOH at a temperature of 400-600℃.

5. The method for fabricating a photoconductive switch based on the parasitic capacitance effect generated by dislocations as described in claim 3, characterized in that, Laser etching was used to partition regions with different dislocation densities on the back side of a silicon carbide substrate. The etching depth was selected from 1 to 7 μm, and the laser wavelengths were 355 nm, 532 nm, and 1064 nm, respectively.

6. The method for fabricating a photoconductive switch based on the parasitic capacitance effect generated by dislocations as described in claim 1, characterized in that, The specific steps for fabricating a composite metal layer on a silicon carbide substrate and obtaining a positive silicon carbide wafer with a photoconductive switch electrode structure by photolithography and lift-off are as follows: The thinned area is obtained by secondary processing of the front side of the silicon carbide substrate through grinding and polishing. Ni metal layer deposited on silicon carbide substrate using electron beam evaporation technology; Composite metal layer structures are deposited on silicon carbide substrates by electron beam evaporation or magnetron sputtering. By employing photolithography replication process, a local photoresist protection area is formed in the silicon carbide electrode area; A monolithic silicon carbide wafer with a photoconductive switch electrode structure is obtained by stripping with acetone or ethanol.

7. The method for fabricating a photoconductive switch based on the parasitic capacitance effect generated by dislocations as described in claim 1, characterized in that, The composite metal layer is a Ti, Pt, Au composite metal layer or a Ti, Al, Ti, Au composite metal layer. The thickness of the Ti, Pt, Au composite metal layer is 100 nm, 50 nm and 700 nm, and the thickness of the Ti, Al, Ti and Au composite metal layer is 100 nm, 50 nm, 100 nm and 700 nm.

8. The method for fabricating a photoconductive switch based on the parasitic capacitance effect generated by dislocations as described in claim 1, characterized in that, The specific steps for forming a localized photoresist protection area in the silicon carbide electrode region are as follows: Spin-coating photoresist utilizes photolithography to form a localized photoresist protection area in the silicon carbide electrode region; The electrode pattern of the photoconductive switch is prepared by photolithography and development, and then the non-electrode areas are removed by cleaning and stripping.

9. A photoconductive switch, characterized in that, It is made by the method of fabrication of photoconductive switch based on dislocation-induced parasitic capacitance effect as described in any one of claims 1-8.

10. A tuning method for a photoconductive switch based on the parasitic capacitance effect generated by dislocations, characterized in that, Includes the following steps: The photoconductive switch described in claim 9 is used to output a microwave signal; The dislocation density of the substrate of the photoconductive switch is controlled, and the frequency characteristics of the output signal are changed by utilizing the capacitance effect generated by the dislocation defects.

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