Diamond-based sunken electrode photoconductive switch and preparation method thereof

Abstract

The present application relates to a kind of diamond-based sunken electrode photoconductive switch and its preparation method, and the preparation method includes: growing diamond etching mask layer on the surface of insulating diamond substrate;Photoetching defines the electrode etching area of insulating diamond substrate on diamond etching mask layer, simultaneously defining alignment mark area;Remove the diamond etching mask layer of electrode etching area and alignment mark area;Etching insulating diamond substrate of electrode etching area and alignment mark area;After etching, insulating diamond substrate is carried out organic cleaning and RCA cleaning;After etching cleaning, insulating diamond substrate is carried out oxygen plasma treatment and forms surface oxygen terminal;Using photoetching overlaying process, electrode sputtering area is defined by alignment mark;Ohmic contact electrode sunk into electrode groove is made in electrode sputtering area.This method reduces the manufacturing cost and difficulty of diamond photoconductive switch, and improves the voltage withstand characteristic and conduction characteristic of device.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of semiconductor optoelectronic devices, and particularly relates to a diamond-based sunken electrode photoconductive switch and a preparation method thereof. BACKGROUND

[0002] With the rapid development of high-voltage, pulsed power and wide-bandgap semiconductor technology, there is an increasing demand for photoconductive switches with excellent high-voltage resistance, high-temperature resistance and radiation resistance. As a key component that can be controlled by optical signals, photoconductive switches can withstand high voltage and large current in a short time, and are widely used in high-performance fields such as pulsed power systems, ultrafast lasers, radars and communications.

[0003] Diamond is known as the "ultimate semiconductor" and has characteristics such as a large bandgap (5.47 eV), a high breakdown electric field (10 MV / cm), a low dielectric constant (5.7), a high thermal conductivity (>20 W / cm·K), and a high carrier mobility (μ e =2200 cm 2 / V·s, μ h =1600 cm 2 / V·s), which is very suitable for working under high voltage, high power and high frequency conditions. Photoconductive semiconductor switches (PCSS) are triggered by optical pulses and can control the conductivity of semiconductor materials, thereby controlling the turn-on and turn-off of the switch, and are often used in high-energy pulse generation, high-current density and radio frequency microwave applications.

[0004] However, the breakdown voltage of existing diamond photoconductive switches is much lower than the theoretical value, and the voltage resistance performance of the device still has a lot of room for improvement. The traditional photoconductive switch is prone to breakdown failure under a large electric field, which is specifically manifested in that the accumulation of charges around the electrode causes the electric field of the device to concentrate at the edge of the electrode, resulting in a too high peak electric field and current density around the electrode, thereby causing the device to have a shortened service life and a decreased overall reliability. Secondly, due to the small cross-sectional area of carrier transport caused by the electrode design, the turn-on characteristics of the diamond planar electrode photoconductive switch are often poor, mainly manifested in high turn-on resistance and low turn-on efficiency. Finally, the existing preparation scheme of the diamond photoconductive switch usually involves ion implantation, epitaxial growth and complex electrode preparation steps, resulting in high device manufacturing cost, complex manufacturing process, high processing difficulty and low economic benefit, which has become a factor restricting the popularization and application of high-performance diamond photoconductive switches. Therefore, how to develop a diamond photoconductive switch technical scheme with a simple preparation process and which can effectively reduce the peak electric field, current density and turn-on resistance of the device under high voltage conditions has become a key technical problem to be solved at present. SUMMARY

[0005] In order to solve the above problems existing in the prior art, the application provides a diamond-based sunken electrode photoconductive switch and a preparation method thereof.

[0006] The application provides a preparation method of a diamond-based sunken electrode photoconductive switch, including the following steps:

[0007] A diamond etching mask layer is grown on the surface of the cleaned insulating diamond substrate;

[0008] A photoetching is performed on the diamond etching mask layer to define an electrode etching area and an alignment mark area of the insulating diamond substrate;

[0009] The diamond etching mask layer of the electrode etching area and the alignment mark area is removed to form a diamond etching mask;

[0010] The insulating diamond substrate of the electrode etching area and the alignment mark area is etched through the diamond etching mask to form an electrode groove and an alignment mark;

[0011] The etched insulating diamond substrate is subjected to organic cleaning and RCA cleaning, so that the etched insulating diamond substrate has an electronic-grade clean surface;

[0012] The cleaned insulating diamond substrate is subjected to oxygen plasma treatment to form a surface oxygen terminal;

[0013] An electrode sputtering area is defined on the surface of the insulating diamond substrate through a photoetching overlaying process and the alignment mark, wherein the center of the electrode sputtering area coincides with the center of the electrode etching area;

[0014] An ohmic contact metal is made in the electrode sputtering area to form an ohmic contact electrode sunken into the electrode groove.

[0015] In an embodiment of the application, the insulating diamond substrate of the electrode etching area and the alignment mark area is etched through the diamond etching mask to form an electrode groove and an alignment mark, including:

[0016] An O-based dry etching process is adopted to etch the insulating diamond substrate of the electrode etching area and the alignment mark area through the diamond etching mask to form an electrode groove and an alignment mark.

[0017] In one embodiment of the present application, the conditions of the O-based dry etching process include: the reaction gas comprises O2, the O2 flow rate is 30-80 sccm, the reaction chamber pressure is 7 mTorr, the upper electrode power is 400-800 W, the lower electrode power is 60-200 W, and the etching depth is 0.2-3 μm.

[0018] In one embodiment of the present application, after the insulating diamond substrate is etched by the diamond etching mask to form the electrode recess and the alignment mark, the method further comprises the steps of:

[0019] removing the residual diamond etching mask on the surface of the insulating diamond substrate.

[0020] In one embodiment of the present application, the etched insulating diamond substrate is subjected to organic cleaning and RCA cleaning to make the etched insulating diamond have an electronic-grade clean surface, comprising:

[0021] placing the etched insulating diamond substrate into acetone and isopropyl alcohol solutions in sequence for ultrasonic cleaning;

[0022] placing the etched insulating diamond substrate into a mixed solution of H2O2 and concentrated H2SO4 for cleaning;

[0023] placing the etched insulating diamond substrate into a mixed solution of NH4OH, H2O2 and H2O for water bath heating cleaning, and flushing the mixed solution of NH4OH, H2O2 and H2O on the surface of the sample with ultrapure water;

[0024] placing the etched insulating diamond substrate into a mixed solution of HCl, H2O2 and H2O for water bath heating cleaning, and flushing the mixed solution of HCl, H2O2 and H2O on the surface of the sample with ultrapure water;

[0025] placing the etched insulating diamond substrate into a mixed solution of BOE and ultrapure water for cleaning, and flushing the mixed solution of BOE and ultrapure water on the surface of the sample with ultrapure water;

[0026] blowing dry the sample with nitrogen to obtain the insulating diamond substrate with an electronic-grade clean surface.

[0027] In one embodiment of the present application, in the mixed solution of H2O2 and concentrated H2SO4, the H2O2 is 30% H2O2 by mass fraction, and the volume ratio of H2O2 to concentrated H2SO4 is 1:2-1:4;

[0028] In the mixed solution of NH4OH, H2O2 and H2O, the volume ratio of NH4OH, H2O2 and H2O is 1:1:5;

[0029] The volume ratio of HCl, H2O2 and H2O in the mixed solution of HCl, H2O2 and H2O is 1:1:6.

[0030] The volume ratio of BOE and ultrapure water in the mixed solution of BOE and ultrapure water is 2:3, and the BOE solution comprises a 49% HF solution and a 40% NH4F solution in a volume ratio of 1:6.

[0031] In an embodiment of the present application, the material of the insulating diamond substrate comprises single crystal or polycrystalline diamond, and the dark state resistance is greater than or equal to 10 13 Ω.

[0032] The material of the diamond etching mask layer comprises a dielectric material or a metal material, the dielectric material comprises any one of silicon nitride and silicon dioxide, and the metal material comprises any one of aluminum, titanium and gold, and the thickness of the diamond etching mask layer is 200-400 nm.

[0033] The shape of the alignment mark comprises a cross pattern.

[0034] The area of the electrode sputtering region is greater than the area of the electrode etching region.

[0035] The thickness of the ohmic contact electrode is greater than the depth of the electrode groove.

[0036] The material of the ohmic contact electrode comprises Ti / Pt / Au laminated metal, Ti / Au laminated metal, Ti / Al laminated metal, Ti / Pt / Au / Ti laminated metal, Ti / Au / Ti / Au / Ti laminated metal or Ti / Pt / Au / Ti / Pt / Au / Ti laminated metal, wherein the thickness of the contact layer metal Ti in each laminated metal is 5-50 nm.

[0037] In an embodiment of the present application, the shapes of the electrode groove and the ohmic contact electrode both comprise a rectangle or a rounded rectangle.

[0038] Another embodiment of the present application provides a diamond-based sunken electrode photoconductive switch prepared by the preparation method described in the above embodiment, comprising an insulating diamond substrate, a first ohmic contact electrode, a second ohmic contact electrode, a first alignment mark and a second alignment mark, wherein,

[0039] The first electrode groove and the second electrode groove are arranged in the insulating diamond substrate.

[0040] The first ohmic contact electrode and the second ohmic contact electrode are arranged in the first electrode groove and the second electrode groove, respectively.

[0041] The first alignment mark and the second alignment mark are arranged on the insulating diamond substrate and located at opposite corners of the first and second ohmic contact electrode forming regions.

[0042] Compared with the prior art, the present application has the following advantages:

[0043] 1、The preparation method comprises electrode etching region definition, insulating diamond substrate etching, RCA cleaning of the insulating diamond substrate, electrode sputtering region definition and ohmic contact electrode preparation, and has the advantages of simple preparation process, simple structure design, avoidance of complex electrode shape and material epitaxy, ion implantation and other complex processes, reduction of device manufacturing cost and difficulty, improvement of device preparation efficiency and economic benefit, realization of large-scale manufacturing, easiness of mass production and popularization, and meeting of large-scale high-voltage and high-frequency application requirements.

[0044] 2、The ohmic contact electrode is sunk into the electrode groove, so that the ohmic contact electrode is sunk into the insulating diamond substrate to form a sunk electrode structure, which has the following advantages: first, the longitudinal distribution of current density is more uniform, instead of being concentrated on the device surface region, the uniformity of the electric field is significantly improved, local electric field concentration is avoided, the peak electric field strength is reduced, the electric field concentration at the electrode edge can be effectively reduced, the voltage withstand characteristic of the device is improved, and the service life of the device is prolonged; second, the sunk electrode structure can reduce the on-resistance by increasing the cross-sectional area of the conductive channel, and the on efficiency and current carrying capacity of the device are improved, so that the on characteristic of the switch is improved; third, the sunk electrode structure optimizes the current path, makes the current density more uniform, reduces local overheating phenomenon, reduces power loss, and improves the working efficiency and reliability of the device. BRIEF DESCRIPTION OF DRAWINGS

[0045] Figure 1 A flowchart of a preparation method of a diamond-based sunk electrode photoconductive switch is provided for the embodiment of the present application.

[0046] Figures 2a-2b A front view and a top view of a diamond-based sunk electrode photoconductive switch are provided for the embodiment of the present application.

[0047] Figure 3 A structure diagram of another diamond-based sunk electrode photoconductive switch is provided for the embodiment of the present application.

[0048] Figure 4 A peak electric field simulation result graph is provided for the embodiment of the present application.

[0049] Figure 5 A current density simulation result graph is provided for the embodiment of the present application.

[0050] Figures 6a-6jA schematic diagram of a preparation process of a method for preparing a diamond-based sunken electrode photoconductive switch provided by an embodiment of the present invention;

[0051] Figure 7 A characterization diagram of the diamond etching morphology provided by an embodiment of the present invention;

[0052] Figure 8 A comparison of the photoelectric response curves of the sunken electrode device provided by an embodiment of the present invention and the traditional planar electrode device. DETAILED DESCRIPTION

[0053] The present invention will be further described in detail below with reference to specific examples, but the embodiments of the present invention are not limited thereto.

[0054] Example 1

[0055] See Figure 1 , Figure 1 A schematic flow chart of a method for preparing a diamond-based sunken electrode photoconductive switch according to an embodiment of the present invention. The method comprises the following steps:

[0056] S1. Growing a diamond etching mask layer on the surface of the cleaned insulating diamond substrate.

[0057] Specifically, the insulating diamond substrate is firstly ultrasonically cleaned with acetone and isopropyl alcohol. The material of the insulating diamond substrate includes single crystal or polycrystalline diamond, and the dark state resistance is ≥10 13 Ω.

[0058] Then, a diamond etch mask layer is grown on the cleaned surface of the insulating diamond substrate. The diamond etch mask layer uses an etch mask with a high etch selectivity ratio. Its material includes a dielectric material or a metal material. The dielectric material includes any one of silicon nitride and silicon dioxide, and the metal material includes any one of aluminum, titanium, and gold. The thickness is 200 to 400 nm. Preferably, a silicon nitride film with a thickness of 200 to 400 nm is grown using a plasma enhanced chemical vapor deposition (PECVD) process as the diamond etch mask layer.

[0059] S2. Photolithographically define the electrode etching area of ​​the insulating diamond substrate on the diamond etching mask layer, and simultaneously define the alignment mark area.

[0060] Specifically, the diamond etching mask layer is coated and spun, and then the sample after coating and spun is placed in a photolithography machine for exposure. The exposed sample is placed in a developer to remove the photoresist in the electrode etching area and the alignment mark area, thereby forming an electrode etching area and an alignment mark area.

[0061] Specifically, the shape of the electrode etching region can be a rectangle, or a rounded rectangle, and the rounded corner can be a circle or an ellipse. For example, the four corners of the rectangular region are each formed with a 1 / 4 circular arc chamfer. The shape of the alignment mark region can be a cross pattern. The shapes of the electrode etching region and the alignment mark are formed by a mask plate.

[0062] For example, the number of electrode etching regions and the number of alignment marks are both two, and the two electrode etching regions are arranged at intervals. The two alignment marks are arranged at diagonal positions of the two electrode etching regions.

[0063] S3, removing the diamond etching mask layer of the electrode etching region and the alignment mark region to form a diamond etching mask.

[0064] Specifically, when the diamond etching mask layer is silicon nitride, the silicon nitride film of the electrode etching region and the alignment mark region is removed by using a F-based dry etching process, and the etching is stopped on the surface of the diamond substrate to form the diamond etching mask.

[0065] S4, etching the insulating diamond substrate of the electrode etching region and the alignment mark region through the diamond etching mask to form electrode grooves and alignment marks.

[0066] Specifically, the insulating diamond substrate of the electrode etching region and the alignment mark region is etched through the diamond etching mask by using an O-based dry etching process to form the electrode grooves and the alignment marks. The conditions of the O-based dry etching process include: the reaction gas includes O2, the flow rate of O2 is 30-80sccm, one or more of Ar and CF4 can be added as auxiliary gas, the flow rate of the auxiliary gas is 0-15sccm, the reaction chamber pressure is 7mTorr, the upper electrode power is 400-800W, the lower electrode power is 60-200W, the etching depth is 0.2-3μm, and the etching time is determined by the etching depth. Preferably, the reaction gas is O2, the flow rate of O2 is 40sccm, the reaction chamber pressure is 7mTorr, the upper electrode power is 500W, and the lower electrode power is 80W.

[0067] It can be understood that the shape of the electrode groove can be a rectangle or a rounded rectangle. The shape of the alignment mark can be a cross pattern.

[0068] For example, the number of electrode grooves and the number of alignment marks are both two, and the two electrode grooves are arranged at intervals. The two alignment marks are arranged at diagonal positions of the two electrode grooves.

[0069] S5, performing organic cleaning and RCA cleaning on the etched insulating diamond substrate to make the etched insulating diamond substrate have an electronic grade clean surface.

[0070] Specifically, the etched insulating diamond substrate is sequentially placed in acetone, isopropyl alcohol solution and ultrasonically cleaned; the etched insulating diamond substrate is placed in a mixed solution of H2O2 and concentrated H2SO4 and cleaned; the etched insulating diamond substrate is placed in a mixed solution of NH4OH, H2O2 and H2O and cleaned by water bath heating, and the mixed solution of NH4OH, H2O2 and H2O on the surface of the sample is washed away by ultrapure water; the etched insulating diamond substrate is placed in a mixed solution of HCl, H2O2 and H2O and cleaned by water bath heating, and the mixed solution of HCl, H2O2 and H2O on the surface of the sample is washed away by ultrapure water; the etched insulating diamond substrate is placed in a mixed solution of BOE and ultrapure water and cleaned, and the mixed solution of BOE and ultrapure water on the surface of the sample is washed away by ultrapure water; the sample is dried by nitrogen to obtain an insulating diamond substrate with an electronic grade clean surface.

[0071] In the mixed solution of H2O2 and concentrated H2SO4, the mass fraction of H2O2 is 30%, the volume ratio of H2O2 to concentrated H2SO4 is 1:2-1:4, and preferably 1:3. In the mixed solution of NH4OH, H2O2 and H2O, the volume ratio of NH4OH to H2O2 to H2O is 1:1:5. In the mixed solution of HCl, H2O2 and H2O, the volume ratio of HCl to H2O2 to H2O is 1:1:6. In the mixed solution of BOE and ultrapure water, the volume ratio of BOE to ultrapure water is 2:3, and the BOE solution includes a 49% HF solution and a 40% NH4F solution in a volume ratio of 1:6.

[0072] The present embodiment uses a mild cleaning solution for the surface of the diamond substrate, and some cleaning steps are combined with ultrasonic cleaning technology to avoid surface damage and ensure the physical properties and functions of the diamond substrate. By combining various solutions and ratios in the organic cleaning and RCA cleaning processes, an electronic grade clean substrate surface is obtained to ensure the bonding quality with metals. In addition, the diamond substrate cleaning process is compatible with the silicon-based cleaning process, which is conducive to popularization and application on existing silicon-based production lines and reduces the cost of equipment modification.

[0073] S6, performing oxygen plasma treatment on the cleaned insulating diamond substrate to form a surface oxygen termination.

[0074] Specifically, after the insulating diamond substrate is cleaned to an electronic grade, the diamond substrate is treated by oxygen plasma to form a diamond surface oxygen termination, which reduces device leakage and further improves the withstand voltage performance. For example, the conditions for oxygen plasma treatment are as follows: the oxygen flow is 50 sccm, the power is set to 80 W, and the treatment is performed for 30 s after ignition.

[0075] S7, using a photolithography overlay process, aligning the electrode sputtering region and the electrode etching region by the alignment mark to define the electrode sputtering region on the surface of the insulating diamond substrate, wherein the center of the electrode sputtering region coincides with the center of the electrode etching region.

[0076] Specifically, in order to facilitate the subsequent production of the ohmic electrode, the step uses a double-layer glue process, first coating and spinning the release glue on the insulating diamond substrate, then coating and spinning the photoresist again on the release glue, then placing the sample with completed coating and spinning into a photoetching machine for exposure, using the alignment mark to ensure that the electrode sputtering region and the electrode etching region are aligned during the exposure process, then placing the sample after exposure into a developing solution to remove the photoresist in the electrode sputtering region, and finally placing the sample into an oxygen plasma glue removal machine for primer film processing to ensure that there is no residual photoresist in the electrode sputtering region.

[0077] Specifically, the electrode sputtering region should be able to contain the electrode etching region through the alignment mark, i.e. the area of the electrode sputtering region is larger than the area of the electrode etching region, so as to ensure the gap-filling effect of the sputtered metal. For example, the geometric size of the electrode etching region is 4mm x 8mm, and the geometric size of the electrode sputtering region is 4.1mm x 8.1mm, and the centers of the two are located at the same position.

[0078] Specifically, the two alignment marks are used to realize photolithography overlay, i.e. the pattern is on both masks in the two times of photolithography, and is transferred to the insulating diamond substrate together with the chamfered rectangular pattern. The alignment mark on the mask is aligned with the pattern of the first photolithography on the substrate during the second photolithography to realize accurate overlay, and the final purpose is to ensure that the electrode sputtering region contains the electrode etching region.

[0079] S8, producing an ohmic contact metal in the electrode sputtering region to form an ohmic contact electrode sunken into the electrode groove.

[0080] Specifically, a magnetron sputtering or evaporation process is used to deposit the ohmic contact metal in the electrode sputtering region, and the sample with completed metal deposition is peeled off to remove the ohmic contact metal, photoresist and release glue outside the electrode sputtering region, and finally the device is cleaned to form an ohmic contact electrode sunken into the electrode groove.

[0081] Specifically, the thickness of the ohmic contact electrode is greater than the depth of the electrode groove to ensure the interface contact between the electrode and the insulating diamond substrate and the good conductive contact between the electrode and the external circuit. The shape of the ohmic contact electrode can be rectangular or chamfered rectangular.

[0082] Materials with excellent conductivity and stability are selected as electrode materials to improve the reliability and conductivity of electrodes in high voltage applications. Exemplary, the material of ohmic contact electrode includes Ti / Pt / Au stacked metal, Ti / Au stacked metal, Ti / Al stacked metal, Ti / Pt / Au / Ti stacked metal, Ti / Au / Ti / Au / Ti stacked metal or Ti / Pt / Au / Ti / Pt / Au / Ti stacked metal, wherein the thickness of Ti as the contact layer metal in each stacked metal is 5-50 nm.

[0083] The bottom layer metal of the electrode is required to be Ti, and the outermost layer needs to be a metal with good conductivity, and the metal layer combination is preferably Ti / Pt / Au. Ti as the contact layer metal forms a low potential barrier in contact with the diamond surface, and can form a good ohmic contact with the diamond substrate; Pt as the buffer layer metal prevents Ti from intermelting with the outermost Au at high temperature; the thickest Au as the outermost layer is used as the conductive layer metal to prevent the oxidation of the lower metal and at the same time as the conductive layer to connect with the external circuit. Therefore, the material of the ohmic contact electrode is preferably Ti / Pt / Au stacked metal, and the thickness of Ti / Pt / Au is 10 / 50 / 500 nm.

[0084] In a specific embodiment, between steps S4 and S5, there can also be a step of removing the residual diamond etching mask on the surface of the insulating diamond substrate.

[0085] Specifically, after forming the electrode recess and the alignment mark, if the diamond etching mask material is selected as silicon nitride, the residual silicon nitride can be continuously retained as a passivation layer to further enhance the voltage resistance performance of the device, or the residual silicon nitride mask can be removed, i.e., after forming the electrode recess and the alignment mark, the diamond etching mask is removed first, and then the insulating diamond substrate is subjected to organic cleaning and RCA cleaning.

[0086] The preparation method of the embodiment includes electrode etching region definition, insulating diamond substrate etching, RCA cleaning of the insulating diamond substrate, electrode sputtering region definition and ohmic contact electrode preparation, and the preparation process is simple and easy to implement, the structure design is simple, the complex electrode shape and the complex processes such as material epitaxy and ion implantation are avoided, the manufacturing cost and difficulty of the device are reduced, the device preparation efficiency and economic benefit are improved, the large-scale manufacturing can be realized, the mass production and popularization are easier, and the demand of large-scale high voltage and high frequency equipment is met.

[0087] In this embodiment, the ohmic contact electrode is sunk into the electrode groove, thereby sinking the ohmic contact electrode into the insulating diamond substrate to form a sunken electrode structure. First, the depth distribution of the current density is made more uniform, rather than concentrated in the surface area of ​​the device, which significantly improves the uniformity of the electric field, avoids local electric field concentration, and reduces the peak electric field strength. It can effectively reduce the electric field concentration at the electrode, improve the voltage resistance of the device, and thus extend the service life of the device; second, the sunken electrode structure can reduce the on-resistance by increasing the cross-sectional area of ​​the conductive channel. From the perspective of electrical transport, the sunken electrode provides more carrier drift channels, improves the current carrying capacity of the device, and improves the conduction efficiency and current carrying capacity of the device, thereby improving the conduction characteristics of the switch; third, the sunken electrode structure optimizes the current path, makes the current density more uniform, reduces local overheating, and reduces power loss, thereby improving the working efficiency and reliability of the device.

[0088] Example 2

[0089] On the basis of the first embodiment, this embodiment provides a diamond-based sunken electrode photoconductive switch, which is prepared by the preparation method of the first embodiment.

[0090] See Figures 2a-2b , Figures 2a-2b The front view and top view of a diamond-based sunken electrode photoconductive switch provided by an embodiment of the present invention are as follows: Figure 2a For the main view, Figure 2b The photoconductive switch comprises an insulating diamond substrate 1, a first ohmic contact electrode 4, a second ohmic contact electrode 5, a first alignment mark 6, and a second alignment mark 7. The insulating diamond substrate 1 is provided with a first electrode groove 2 and a second electrode groove 3, with the first ohmic contact electrode 4 and the second ohmic contact electrode 5 disposed in the first electrode groove 2 and the second electrode groove 3, respectively. The first alignment mark 6 and the second alignment mark 7 are disposed on the insulating diamond substrate 1 and are located at opposite corners of the regions where the first ohmic contact electrode 4 and the second ohmic contact electrode 5 are formed.

[0091] Specifically, the material of the insulating diamond substrate 1 includes single crystal or polycrystalline diamond, and its dark state resistance is ≥10 13 The depth of the first electrode groove 2 and the second electrode groove 3 is 0.2-3 μm.

[0092] Specifically, the height of the first ohmic contact electrode 4 is greater than the depth of the first electrode groove 2, and the height of the second ohmic contact electrode 5 is greater than the depth of the second electrode groove 3, so as to ensure the interface contact of the electrode and the insulating diamond substrate 1 and the good conductive contact of the electrode and the external circuit. In addition, the width of the high part of the first ohmic contact electrode 4 is greater than the width of the first electrode groove 2, and the width of the high part of the second ohmic contact electrode 5 is greater than the width of the second electrode groove 3, that is, the rectangular pattern of the ohmic contact electrodes 4 and 5 is slightly larger than the rectangular electrode pattern of the electrode grooves 2 and 3, so as to ensure that the ohmic contact electrode can contain the electrode groove.

[0093] Specifically, the electrode grooves 2 and 3 and the ohmic contact electrodes 4 and 5 are all rounded rectangular patterns. The rounding of the electrode can homogenize the electric field.

[0094] Specifically, the first alignment mark 6 and the second alignment mark 7 are two sets of cross patterns and are distributed at the diagonal of the ohmic contact electrodes 4 and 5.

[0095] Please refer to Figure 3 , Figure 3 Another structure diagram of a diamond-based sunken electrode photoconductive switch provided by the embodiment of the present application is shown. The diamond-based sunken electrode photoconductive switch comprises an insulating diamond substrate 1, a first ohmic contact electrode 4, a second ohmic contact electrode 5, a first alignment mark 6, a second alignment mark 7 and a diamond etching mask 8. The insulating diamond substrate 1 is provided with a first electrode groove 2 and a second electrode groove 3 in the middle; the first ohmic contact electrode 4 and the second ohmic contact electrode 5 are arranged in the first electrode groove 2 and the second electrode groove 3 respectively; the first alignment mark 6 and the second alignment mark 7 are arranged on the insulating diamond substrate 1 and located at the diagonal of the area formed by the first ohmic contact electrode 4 and the second ohmic contact electrode 5; the diamond etching mask 8 serves as a passivation layer and covers the surface of the insulating diamond substrate 1 except the first ohmic contact electrode 4 and the second ohmic contact electrode 5, and the first ohmic contact electrode 4 and the second ohmic contact electrode 5 extend to the side surface of the diamond etching mask 8.

[0096] The embodiment designs a diamond-based sunken electrode photoconductive switch. Compared with a planar electrode device, the device electric field distribution is optimized, the side wall electrode conductive path is increased, and the electrical transport characteristics are improved, so as to reduce the peak electric field strength and the on-resistance of the device, solve the problems of electric field concentration and poor on-state characteristics caused by the limitations of the traditional planar electrode design, and realize a diamond photoconductive switch with high withstand voltage and low on-resistance.

[0097] Embodiment three

[0098] On the basis of the embodiment one, the preparation method of the diamond-based sunken electrode photoconductive switch is further illustrated by the following examples.

[0099] Example 1

[0100] This example takes a device structure of Figures 2a-2b , which selects an insulating polycrystalline diamond substrate 1 with a size of 1 cm square and a thickness of 0.6 mm, the substrate surface has a high-quality first electrode groove 2 and a second electrode groove 3 with a depth of 400 nm, a first ohmic contact electrode 4 and a second ohmic contact electrode 5 are respectively filled in the first electrode groove 2 and the second electrode groove 3, the first ohmic contact electrode 4 and the second ohmic contact electrode 5 have a geometric size of 4 mm (width) x 8 mm (height) and are left-right symmetrical, the distance between them is 1 mm, the composition and thickness of the electrode is a Ti / Pt / Au metal layer of 10 / 50 / 500 nm, and the four corners are chamfered with a circular arc to homogenize the electric field. The diamond substrate 1 is provided with cross pattern alignment marks 6, 7 at the opposite corners, for realizing photoetching overlay alignment.

[0101] Before device preparation, the influence of the sunken electrode on the peak electric field and current density distribution of the device is analyzed by using Silvaco TCAD software, the direct current voltage of single-point testing is set to 3 kV, the contact between the electrode and the substrate is ohmic contact, and the excitation light source wavelength is 532 nm.

[0102] Please refer to Figure 4 , Figure 4 , which is the peak electric field simulation result graph provided by the embodiment of the present application. As shown in (a) of Figure 4 , two tangent lines are placed when analyzing the electric field distribution, which are located on the upper and lower surfaces of the electrode (the contact surfaces of the electrode and air and diamond substrate), corresponding to the positions of the switch surface and the internal position prone to breakdown; the simulation gives the influence of etching depth on the peak electric field intensity of the planar electrode device, and the peak electric field-etching depth change curves of the device in dark state and on state are shown in (b) and (c) of Figure 4 , wherein Figure 4 , the point with an etching depth of 0 in (b) and (c) represents a traditional planar device without etching process. Compared with the traditional planar device, the peak electric field intensity of the upper and lower surfaces of the sunken electrode device is obviously decreased, and with the increase of the sinking depth of the electrode, the peak electric field intensity has a tendency to continue to decrease.

[0103] On the other hand, the sinking of the electrode region makes the longitudinal distribution of the electron current density more uniform, rather than concentrated in the surface region of the device. Please refer to Figure 5 , Figure 5 , which is the current density simulation result graph provided by the embodiment of the present application, Figure 5The photo-generated carriers are mainly distributed between the two electrodes, and the charge accumulation effect in the region around the electrode leads to the occurrence of local high current density. Compared with the planar electrode device, the electron current in the sunken electrode device is still concentrated in the inside region of the anode, but its value is significantly reduced, which shows that the structure effectively alleviates the phenomenon of excessively high current density caused by charge accumulation around the electrode. From the perspective of electrical transport, the sunken electrode provides more carrier drift channels, improves the carrier capacity of the device, and thus can reduce the on-resistance of the device.

[0104] Based on the influence of the above sunken electrode structure on the performance of the device, please refer to Figures 6a-6j , Figures 6a-6j The preparation process diagram of a preparation method of a diamond-based sunken electrode photoconductive switch provided by the embodiment of the present application, the preparation method comprising the steps of:

[0105] S1, growing a diamond etching mask layer 8 on the surface of the cleaned insulating diamond substrate 1. Specifically, it comprises:

[0106] S11, performing surface ultrasonic cleaning on the insulating diamond substrate 1, as shown in Figure 6a .

[0107] First, put the sample into the acetone solution and ultrasonically clean it for 3 minutes to remove the particles and organic matter and other contaminants on the surface of the substrate. Then, put the sample into the isopropyl alcohol solution and ultrasonically clean it for 3 minutes to remove the residual acetone and a small amount of organic contamination. Finally, rinse the sample with ultrapure water (DIW) and dry it with nitrogen.

[0108] S12, growing silicon nitride (Si3N4) on the insulating diamond substrate 1 as a diamond etching mask layer 8, as shown in Figure 6b .

[0109] Specifically, a 200nm-thick Si3N4 mask layer 8 is grown on the insulating diamond substrate 1 by plasma enhanced chemical vapor deposition (PECVD) process, and the process conditions for growth are as follows: NH3 and SiH4 are used as reaction gases, the substrate temperature is 250℃, the reaction chamber pressure is 600mTorr, and the RF power is 22W.

[0110] S2, photoetching to define the electrode etching area of the insulating diamond substrate on the diamond etching mask layer 8, as shown in Figure 6c , and defining the alignment mark area at the same time.

[0111] Specifically, first, the sample is placed on a hot plate at 200°C for 5 minutes; then, glue is applied and spun on the Si3N4 mask layer 8 on the diamond substrate 1, with a spinning speed of 3000 rpm, a photoresist 9 thickness of 800 nm, and the sample is placed on a hot plate at 90°C for 1 minute, after which the sample with the applied and spun glue is placed in a photoetching machine for exposure. Then, the sample is placed on a hot plate at 110°C for 1 minute; subsequently, the sample after exposure is placed in a developing solution to remove the photoresist in the electrode etching area, and it is rinsed with ultrapure water and dried with nitrogen. Finally, the sample is placed on a hot plate at 100°C for 1 minute. During the exposure and development of the photoresist, the electrode etching area and the alignment mark area are simultaneously formed.

[0112] S3, removing the diamond etching mask layer in the electrode etching area and the alignment mark area to form a diamond etching mask, as shown in Figure 6d .

[0113] Specifically, the Si3N4 mask layer 8 on the diamond substrate 1 is etched using a dry etching process with a reaction gas of 15 sccm CF4 and 15 sccm O2, a reaction chamber pressure of 3 Pa, an upper electrode power of 60 W, and a lower electrode power of 15 W, with an etching depth of 200 nm. Then the sample is sequentially placed in acetone solution and isopropyl alcohol solution for ultrasonic cleaning for 3 minutes to remove the residual photoresist 9 on the surface of the sample. Finally, the sample is rinsed with ultrapure water (DIW) and dried with nitrogen.

[0114] S4, etching the insulating diamond substrate in the electrode etching area and the alignment mark area through the diamond etching mask to form the first electrode groove 2 and the second electrode groove 3, the first alignment mark 6 and the second alignment mark 7, as shown in Figure 6e .

[0115] Specifically, the electrode etching area and the alignment mark area on the diamond substrate 1 are etched using a dry etching process with a reaction gas of 40 sccm O2, a reaction chamber pressure of 7 mTorr, an upper electrode power of 500 W, a lower electrode power of 80 W, and a tray bottom temperature of -5°C, with an etching depth of 400 nm, forming a pair of high-quality first electrode groove 2 and second electrode groove 3, and cross-shaped first alignment mark 6 and second alignment mark 7.

[0116] The improvement of the light guide switch electrical performance by the sunken electrode is determined by the high-quality diamond electrode groove, therefore, after forming the electrode groove, the etching selectivity and the diamond etching sidewall and topography are characterized by atomic force microscopy (AFM), and due to the limited scanning area of the instrument, the first alignment mark 6 and the second alignment mark 7 are taken as examples, and the characterization results are shown in Figure 7 , Figure 7A diamond etching morphology characterization map is provided for the embodiment of the present application. As shown in Figure 7 It can be seen that the etching selectivity ratio of diamond to silicon nitride is greater than 20:1, and the etched diamond sidewall is relatively steep, and the root mean square roughness of the etched diamond surface is about 1 nm, which indicates that a high-quality groove with steep sidewall and smooth surface can be obtained by the etching process.

[0117] Then, the sample is immersed in a BOE solution (49% HF:40% NH4F=1:6, volume ratio):ultra-pure water=2:3 solution for 2h to ensure that there is no Si3N4 mask residue on the diamond substrate 1, so as to remove the residual diamond etching mask 8 on the surface of the insulating diamond substrate 1, as shown in Figure 6f .

[0118] Finally, the sample is rinsed with ultra-pure water (DIW) and dried with nitrogen.

[0119] S5, organic cleaning and RCA cleaning are performed on the etched insulating diamond substrate, so that the etched insulating diamond substrate has an electronic grade clean surface. Specifically, the steps include:

[0120] S51, the sample is ultrasonically cleaned in an acetone solution for 5min to remove organic contaminants such as particles and grease on the surface of the substrate.

[0121] S52, the sample is ultrasonically cleaned in an isopropyl alcohol solution for 5min to further remove the surface organic contaminants and residual acetone; then, the sample is rinsed in ultra-pure water for 3min to remove the organic solution.

[0122] S53, the sample is cleaned in a 30% H2O2:concentrated H2SO4=1:3=100ml:300ml mixed solution for 5min to dissolve and remove the residual organic matter on the surface of the substrate.

[0123] S54, the sample is placed in an SC-1 solution (NH4OH:H2O2:H2O=1:1:5=60ml:60ml:300ml) and cleaned in an 80°C water bath for 10min to remove surface organic matter and metal ions; then, the sample is rinsed with ultra-pure water (DIW) for 3min to remove the SC-1 solution.

[0124] S55, the sample is placed in an SC-2 solution (HCl:H2O2:H2O=1:1:6=50ml:50ml:300ml) and cleaned in an 80°C water bath for 10min to remove surface alkali metal cations and other cations; then, the sample is rinsed with ultra-pure water (DIW) for 3min to remove the SC-2 solution.

[0125] S56, the sample is placed in a solution of BOE:DIW=2:3=160ml:240ml for 15 seconds, and then the substrate surface is rinsed with ultrapure water (DIW) for 3 minutes.

[0126] S57, the diamond substrate 1 is dried using nitrogen gas to obtain an electronically clean surface.

[0127] S6, the cleaned insulating diamond substrate is subjected to oxygen plasma treatment to form a surface oxygen termination to reduce device leakage, as shown in Figure 6g

[0128] Specifically, the sample is placed in an oxygen plasma stripping machine, the oxygen flow is set to 50sccm, the power is set to 80W, and the treatment time is set to 30s to form an oxygen termination on the surface of the diamond substrate 1.

[0129] S7, using a photolithography overlay process, the electrode sputtering area is aligned with the electrode etching area by aligning the marks, and the electrode sputtering area is defined on the surface of the insulating diamond substrate, wherein the center of the electrode sputtering area coincides with the center of the electrode etching area, as shown in Figure 6h

[0130] First, the overlay uses a double-layer resist process, and the sample is baked on a hot plate at 200°C for 5 minutes before coating. The peeling resist 10 is coated on the diamond substrate 1 and spun, the spinning speed is 2000 revolutions / min, the thickness of the photoresist 10 is 0.35μm, and the sample is baked on a hot plate at 200°C for 5 minutes. The peeling resist 10 is coated and spun again, the spinning speed is 5000 revolutions / min, the photoresist 11 is formed, the thickness of the photoresist 11 is about 2.8μm, the width of the photoresist 11 in the double-layer resist formed is slightly larger than the width of the peeling resist 10, and the sample is baked on a hot plate at 100°C for 2 minutes. The sample after coating and spinning is placed in a photoetching machine for exposure; this step uses cross alignment marks 6, 7 to ensure that the electrode sputtering area is aligned with the electrode etching area in step S3. Subsequently, the sample after exposure is placed in a developing solution to remove the photoresist in the electrode etching area, and it is rinsed with ultrapure water and dried with nitrogen. Finally, the sample is placed in an oxygen plasma stripping machine for primer treatment, the oxygen flow is set to 100sccm, the power is set to 200W, and the treatment time is set to 5 minutes to remove the residual photoresist in the electrode sputtering area.

[0131] S8, an ohmic contact metal is made in the electrode sputtering area by a magnetron sputtering process to form a first ohmic contact electrode 4 and a second ohmic contact electrode 5 that sink into the electrode groove.

[0132] First, the sample is placed in a magnetron sputtering machine, and the vacuum degree of the reaction chamber is adjusted to 2×10 -6 ​​After Torr, the sample surface is sputtered with a three-layer metal layer composed of Ti, Pt and Au in turn from bottom to top, and the Ti / Pt / Au metal layer has a thickness of 10 / 50 / 500 nm, as shown in FIG. 2. Then, the sample with completed metal sputtering is peeled off to remove the photoresist and metal outside the electrode sputtering area, i.e., the stripping glue 10, the photoresist 11 and the metal 12 thereon, to form the first ohmic contact electrode 4 and the second ohmic contact electrode 5, as shown in FIG. 3. Figure 6i Figure 6j Then, the sunken device with completed electrode preparation is cleaned, rinsed with ultrapure water (DIW) and dried with nitrogen, and the device is completed, and the structure of the prepared device is shown in FIG. 4 and FIG. 5. Figure 2a 2b

[0133] The photoelectric response of the sunken electrode device of the embodiment and the conventional planar electrode device is tested, and the test results are shown in FIG. 6 and FIG. 7. Figure 8 Figure 8 FIG. 6 and FIG. 7 are a comparison diagram of photoelectric response curves of the sunken electrode device and the conventional planar electrode device provided by the embodiment. Figure 8 In the embodiment, under the same test conditions (laser energy is 1 mJ / pulse, and power supply voltage is 200 V), the output signal photoelectric response curve of the high-speed oscilloscope load resistor is drawn. The results show that while ensuring the ultrafast response speed (the half-height width of the response curve is about 0.3 ns), the sunken electrode device generates a higher peak photocurrent, which can effectively improve the conduction characteristics of the device (the conduction resistance decreases by about 30%).

[0134] Example 2

[0135] The difference between Example 1 and Example 2 is that the polycrystalline diamond substrate 1 of Example 1 is replaced by a single crystal diamond, and the remaining steps are the same. The diamond-based sunken electrode photoconductive switch is prepared by preparing a high-quality electrode groove, and the voltage withstand performance of the prepared sunken device is significantly improved.

[0136] Example 3

[0137] The difference between Example 1 and Example 3 is that after the step S4 of forming the first electrode groove 2 and the second electrode groove 3, the first alignment mark 6 and the second alignment mark 7, the diamond etching mask 8 is retained as a dielectric passivation layer to further enhance the voltage withstand performance of the device. The structure of the device prepared in Example 3 is shown in FIG. 8. Figure 3

[0138] The embodiment is directed to the preparation process of the photoconductive switch of the diamond substrate, which includes the systematic combination of the electronic grade cleaning of the diamond substrate, the oxygen plasma surface treatment, the high-quality groove etching of the diamond and the electrode pattern etching process, so as to realize the diamond-based photoconductive switch with high voltage withstand, fast response and low conduction resistance. ​​​​​

[0139] The embodiment provides a simple, efficient and easy-to-promote preparation method of a diamond-based sunken electrode photoconductive switch, which comprises a systematic combination of processes such as electronic-grade cleaning of a diamond substrate, surface oxygen terminal reconstruction, high-quality groove etching of the diamond substrate and preparation of an ohmic metal layer. The preparation method avoids complex processes such as ion implantation and epitaxial growth, and can prepare a diamond photoconductive switch with high withstand voltage and low on-resistance without the premise of preparing a complex electrode pattern, improves device preparation efficiency and economic benefits, makes the diamond photoconductive switch more easy to mass-produce and promote, and expands the high-voltage high-frequency application scenarios of the diamond photoconductive switch.

[0140] The above is a further detailed description of the present application in combination with specific preferred embodiments, and the specific implementation of the present application cannot be limited to these descriptions. For ordinary skilled persons in the technical field to which the present application belongs, a number of simple deductions or substitutions can be made without departing from the concept of the present application, and all of them shall be regarded as falling within the protection scope of the present application.

Claims

1. A method for preparing a diamond-based sunken electrode photoconductive switch, characterized in that: Including steps: growing a diamond etching mask layer on the surface of the cleaned insulating diamond substrate; Photolithographically defining an electrode etching region of the insulating diamond substrate on the diamond etching mask layer, and simultaneously defining an alignment mark region; removing the diamond etching mask layer in the electrode etching area and the alignment mark area to form a diamond etching mask; Etching the insulating diamond substrate in the electrode etching area and the alignment mark area through the diamond etching mask to form electrode grooves and alignment marks; Performing organic cleaning and RCA cleaning on the etched insulating diamond substrate so that the etched insulating diamond substrate has an electronic grade clean surface; performing oxygen plasma treatment on the cleaned insulating diamond substrate to form surface oxygen terminations; Using a photolithography overlay process, the electrode sputtering region is aligned with the electrode etching region through the alignment mark, and the electrode sputtering region is defined on the surface of the insulating diamond substrate, wherein the center of the electrode sputtering region coincides with the center of the electrode etching region; An ohmic contact metal is fabricated in the electrode sputtering region to form an ohmic contact electrode sunk into the electrode groove.

2. The method for preparing a diamond-based sunken electrode photoconductive switch according to claim 1, characterized in that: Etching the insulating diamond substrate in the electrode etching area and the alignment mark area through the diamond etching mask to form an electrode groove and an alignment mark, comprising: An O-based dry etching process is adopted to etch the insulating diamond substrate in the electrode etching area and the alignment mark area through the diamond etching mask to form electrode grooves and alignment marks.

3. The method for preparing a diamond-based sunken electrode photoconductive switch according to claim 2, wherein: The conditions of the O-based dry etching process include: the reaction gas includes O2, the O2 flow rate is 30-80sccm, the reaction chamber pressure is 7mTorr, the upper electrode power is 400-800W, the lower electrode power is 60-200W, and the etching depth is 0.2-3μm.

4. The method for preparing a diamond-based sunken electrode photoconductive switch according to claim 1, wherein: After etching the insulating diamond substrate of the electrode etching area and the alignment mark area through the diamond etching mask to form the electrode groove and the alignment mark, the process further includes the following steps: The diamond etching mask remaining on the surface of the insulating diamond substrate is removed.

5. The method for preparing a diamond-based sunken electrode photoconductive switch according to claim 1, wherein: The insulating diamond substrate after etching is subjected to organic cleaning and RCA cleaning, so that the insulating diamond after etching has an electronic grade clean surface, including: The etched insulating diamond substrate was placed in acetone and isopropyl alcohol solutions for ultrasonic cleaning in turn; The etched insulating diamond substrate is placed in a mixed solution of H2O2 and concentrated H2SO4 for cleaning; The etched insulating diamond substrate was placed in a mixed solution of NH4OH, H2O2 and H2O for heating and cleaning in a water bath, and the mixed solution of NH4OH, H2O2 and H2O on the sample surface was rinsed off with ultrapure water; The etched insulating diamond substrate was placed in a mixed solution of HCl, H2O2 and H2O for heating and cleaning in a water bath, and the mixed solution of HCl, H2O2 and H2O on the sample surface was rinsed off with ultrapure water; The etched insulating diamond substrate was placed in a mixed solution of BOE and ultrapure water for cleaning, and the mixed solution of BOE and ultrapure water on the sample surface was rinsed off with ultrapure water; The sample was blown dry with nitrogen to obtain an insulating diamond substrate with an electronic grade clean surface.

6. The method for preparing a diamond-based sunken electrode photoconductive switch according to claim 5, characterized in that: In the mixed solution of H2O2 and concentrated H2SO4, H2O2 has a mass fraction of 30%, and the volume ratio of H2O2 to concentrated H2SO4 is 1:2 to 1:4; In the mixed solution of NH4OH, H2O2 and H2O, the volume ratio of NH4OH, H2O2 and H2O is 1:1:5; In the mixed solution of HCl, H2O2 and H2O, the volume ratio of HCl, H2O2 and H2O is 1:1:6; In the mixed solution of BOE and ultrapure water, the volume ratio of BOE to ultrapure water is 2:3, and the BOE solution includes 49% HF solution and 40% NH4F solution in a volume ratio of 1:

6.

7. The method for preparing a diamond-based sunken electrode photoconductive switch according to claim 1, wherein: The material of the insulating diamond substrate includes single crystal or polycrystalline diamond, and the dark state resistance is ≥10 13 Ω; The material of the diamond etching mask layer includes a dielectric material or a metal material, the dielectric material includes any one of silicon nitride and silicon dioxide, the metal material includes any one of aluminum, titanium, and gold, and the thickness of the diamond etching mask layer is 200 to 400 nm; The shape of the alignment mark includes a cross figure; The area of ​​the electrode sputtering region is larger than the area of ​​the electrode etching region; The thickness of the ohmic contact electrode is greater than the depth of the electrode groove; The material of the ohmic contact electrode includes Ti / Pt / Au stacked metal, Ti / Au stacked metal, Ti / Al stacked metal, Ti / Pt / Au / Ti stacked metal, Ti / Au / Ti / Au / Ti stacked metal or Ti / Pt / Au / Ti / Pt / Au / Ti stacked metal, wherein the thickness of the contact layer metal Ti in each stacked metal is 5-50nm.

8. The method for preparing a diamond-based sunken electrode photoconductive switch according to claim 1, wherein: The electrode groove and the ohmic contact electrode both have a rectangular shape or a rounded rectangular shape.

9. A diamond-based sunken electrode photoconductive switch, characterized in that: The method according to any one of claims 1 to 8 comprises: an insulating diamond substrate, a first ohmic contact electrode, a second ohmic contact electrode, a first alignment mark and a second alignment mark, wherein: The insulating diamond substrate is provided with a first electrode groove and a second electrode groove at intervals; The first ohmic contact electrode and the second ohmic contact electrode are respectively disposed in the first electrode groove and the second electrode groove; The first alignment mark and the second alignment mark are provided on the insulating diamond substrate and are located at opposite corners of regions where the first ohmic contact electrode and the second ohmic contact electrode are formed.

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