Preparation method of high-aspect-ratio double-layer diamond nanostructure

Abstract

The invention provides a preparation method of a high-aspect-ratio double-layer diamond nanostructure. The preparation method comprises the following steps: carrying out surface pretreatment on monocrystal diamond; coating a double-layer photoresist on the surface of the pretreated single crystal diamond, and forming a double-layer photoresist nano-structure pattern on the surface of the single crystal diamond through electron beam lithography in combination with wet etching; performing first metal deposition on the surface of the single crystal diamond, stripping the upper photoresist to expose the nanostructure pattern of the lower photoresist, performing second metal deposition on the surface of the single crystal diamond, and stripping the lower photoresist to obtain a pattern with a double-layer metal mask nanostructure; and carrying out two-step reactive ion etching and one-step wet etching between the two-step reactive ion etching on the surface of the monocrystal diamond by utilizing the double-layer metal mask to obtain the double-layer diamond nano-structure pattern with the target size. And the simple, efficient, repeatable and low-cost wafer-level manufacturing of the high-aspect-ratio double-layer single crystal diamond nano structure is realized.

Description

Technical Field

[0001] The invention relates to the technical field of quantum materials, and in particular to a method for preparing a high-aspect-ratio double-layer diamond nanostructure. Background Art

[0002] Single crystal diamond has excellent material properties, such as extremely high thermal conductivity, mechanical hardness, optical transparency in almost the entire wavelength range, and almost complete chemical inertness. NV (Nitrogen Vacancy) and SiV (Silicon Vacancy) in diamond have attracted extensive attention in the fields of quantum sensing and quantum information processing. However, the chemical inertness of diamond makes it difficult to achieve micro-nano processing by wet etching. In recent years, processing methods based on reactive ion etching, focused ion beam, ion beam etching and other technologies have been developed to achieve the processing of various diamond micro-nano structures.

[0003] In current research, the mask size required for nanopillar etching is usually determined during the photolithography process. It is particularly difficult to accurately change the mask shape through the reactive ion etching process, and due to the low etching rate and selectivity of single-crystal diamond, high-aspect-ratio diamond nanopillars with sharp tips are difficult to process in batches. In addition, existing research cannot accurately achieve high-aspect-ratio processing of double-layer single-crystal diamond structures with adjustable size.

[0004] Therefore, it is required to propose a new technical solution to achieve repeatable, controllable, and batch manufacturing of double-layer diamond nanostructures with high aspect ratio, and to solve the huge technical difficulties faced by the wafer-level process manufacturing of double-layer high-aspect ratio single-crystal diamond nanostructures with adjustable double-layer sizes. Summary of the invention

[0005] According to the current research status, in order to solve or at least partially solve the huge technical difficulties faced by the wafer-level process manufacturing of double-layer size-adjustable high-aspect ratio single-crystal diamond nanostructures in the related art, the present invention proposes a method for preparing a high-aspect ratio double-layer diamond nanostructure.

[0006] One object of the present invention is to achieve wafer-level manufacturing of double-layer size-adjustable high-aspect-ratio single-crystal diamond nanostructures.

[0007] A further object of the present invention is to increase the aspect ratio of single crystal diamond nanostructures and to achieve simple, efficient, repeatable and low-cost manufacturing of high aspect ratio double-layer diamond nanostructures.

[0008] In particular, the present invention provides a method for preparing a high aspect ratio double-layer diamond nanostructure, comprising:

[0009] Surface pretreatment of single crystal diamond;

[0010] Coating a double-layer photoresist on the surface of the pretreated single-crystal diamond, and forming a double-layer photoresist nanostructure pattern on the surface of the single-crystal diamond by electron beam lithography combined with wet etching;

[0011] Performing a first metal deposition on the surface of the single crystal diamond, stripping off the upper photoresist to expose the nanostructure pattern of the lower photoresist, performing a second metal deposition on the surface of the single crystal diamond, and stripping off the lower photoresist to obtain a pattern with a double-layer metal mask nanostructure;

[0012] The double-layer metal mask is used to perform two-step reactive ion etching on the surface of the single crystal diamond and one-step wet etching between the two-step reactive ion etching to obtain a double-layer diamond nanostructure pattern of a target size.

[0013] Optionally, the electron beam lithography operation includes:

[0014] According to a preset nanostructure pattern, the upper layer of photoresist is exposed by electron beam lithography equipment, and the upper layer of photoresist is developed to obtain a nanostructure pattern of the upper layer of photoresist;

[0015] The wet etching operation includes:

[0016] The lower layer of photoresist is wet-etched until the nanostructure pattern of the lower layer of photoresist reaches a predetermined size.

[0017] Optionally, the upper photoresist is polymethyl methacrylate, polymethyl methacrylate-methyl methacrylate copolymer, or acrylic copolymer, with a thickness of 100 to 200 nm; the lower photoresist is polydimethylglutarimide or phenolic resin, with a thickness of 200 to 500 nm;

[0018] The corrosive agent used for the wet etching is a weak alkaline corrosive agent, wherein the weak alkaline corrosive agent is a tetramethylammonium hydroxide solution with a concentration of 0.5-10 wt% or a 1-10 g / L sodium carbonate solution.

[0019] Optionally, after coating the double-layer photoresist, the preparation method further comprises:

[0020] A conductive layer is coated on the surface of the upper photoresist, and the thickness of the conductive layer is 10-30 nm.

[0021] Optionally, the double-layer metal mask comprises a second metal mask deposited on the surface of the single crystal diamond and a first metal mask covering and surrounding the second metal mask;

[0022] The first metal deposition and the second metal deposition are carried out by electron beam evaporation or magnetron sputtering;

[0023] The material of the first metal mask layer is chromium or aluminum, and the thickness is 100 to 300 nm;

[0024] The material of the second metal mask layer is titanium or gold, and the thickness is 30-150 nm.

[0025] Optionally, the step of performing two-step reactive ion etching on the surface of the single crystal diamond using the double-layer metal mask and one-step wet etching between the two-step reactive ion etching to obtain a double-layer diamond nanostructure pattern of a target size includes:

[0026] Performing a first reactive ion etching on the surface of the single crystal diamond until a first designated etching height is reached;

[0027] performing wet etching using a wet etchant to remove the first metal mask, the wet etchant having a high selectivity ratio to the material of the first metal mask and the material of the second metal mask;

[0028] A second reactive ion etching is performed on the surface of the single crystal diamond until a second designated etching height is reached.

[0029] Optionally, the first reactive ion etching adopts inductively coupled plasma reactive ion etching, and the process parameters are: inductively coupled plasma power 400-800W, radio frequency power 50-200W, working pressure 3-15mTorr, oxygen flow rate 20-50sccm, etching time 5-30min, etching rate 150-200nm / min;

[0030] When the material of the first metal mask is chromium, the wet etchant is a mixed solution containing 5-10 vol% of 65-70% nitric acid, 30-50 g / L of cerium ammonium nitrate and deionized water; when the material of the first metal mask is aluminum, the wet etchant is a tetramethylammonium hydroxide solution with a concentration of 0.5-10 wt%; the etching rate of the wet etching is 5-20 nm / s;

[0031] The second reactive ion etching adopts inductively coupled plasma reactive ion etching, and the process parameters are: inductively coupled plasma power 400-800W, radio frequency power 50-200W, working pressure 3-15mTorr, oxygen flow rate 20-50sccm, etching time 5-10min, and etching rate 150-200nm / min.

[0032] Optionally, after completing the second reactive ion etching, the preparation method further comprises:

[0033] removing the second metal mask layer and cleaning the single crystal diamond with an acid solution;

[0034] Wherein, when the material of the second metal mask layer is titanium, the second metal mask layer is removed by using a buffered oxide etchant, and when the material of the second metal mask layer is gold, the second metal mask layer is removed by using aqua regia;

[0035] The acid solution is a mixture of concentrated sulfuric acid and concentrated nitric acid, and the volume ratio of concentrated sulfuric acid to concentrated nitric acid is 3:1;

[0036] The cleaning operation includes: placing the single crystal diamond in the acid solution and heating it at 150-200° C. for acid boiling.

[0037] Optionally, the surface pretreatment operation includes:

[0038] The single crystal diamond is subjected to double-sided mechanical fine polishing until the roughness Ra of the diamond surface is less than 1 nm;

[0039] Chemically treating the polished single crystal diamond to remove surface impurities;

[0040] The chemical treatment operation includes: placing the single crystal diamond in an acid solution and heating it at 150-200° C. for acid boiling, wherein the acid solution is a mixture of concentrated sulfuric acid and concentrated nitric acid, and the volume ratio of concentrated sulfuric acid to concentrated nitric acid is 3:1.

[0041] Optionally, before performing the electron beam lithography, the preparation method further comprises:

[0042] Cleaning the surface of the single crystal diamond;

[0043] The cleaning process includes:

[0044] Cleaning the single crystal diamond using piranha solution; and

[0045] The single crystal diamond is ultrasonically treated with acetone, isopropanol and deionized water in sequence.

[0046] The invention provides a method for preparing a high aspect ratio double-layer diamond nanostructure. The method comprises the following steps: firstly, a double-layer photoresist nanostructure pattern is formed on the surface of a pretreated single-crystal diamond by electron beam lithography of a double-layer photoresist combined with wet etching; then, the double-layer photoresist nanostructure pattern is used to sequentially perform a first metal deposition, an upper photoresist stripping, a second metal deposition and a lower photoresist stripping on the surface of the single-crystal diamond to obtain a double-layer metal mask nanostructure; finally, the double-layer metal mask is used to perform two-step reactive ion etching and one-step wet etching to obtain a double-layer nanostructure pattern of a target size, thereby realizing wafer-level process manufacturing of the double-layer single-crystal diamond nanostructure.

[0047] Furthermore, by controlling the size of the double-layer photoresist nanostructure pattern and then adjusting the size of the double-layer metal mask, the aspect ratio of the single-crystal diamond nanostructure can be improved, thereby achieving simple, efficient, repeatable and low-cost manufacturing of high-aspect-ratio double-layer diamond nanostructures.

[0048] Furthermore, by adjusting the size of the double-layer metal mask and controlling the etching height of the two-step reactive ion etching, the size and morphology of the double-layer diamond nanostructure can be adjusted.

[0049] The above description is only an overview of the technical solution of the present invention. In order to more clearly understand the technical means of the present invention, it can be implemented according to the contents of the specification. In order to make the above and other purposes, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are listed below.

[0050] Based on the following detailed description of specific embodiments of the present invention in conjunction with the accompanying drawings, those skilled in the art will become more aware of the above and other objects, advantages and features of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Various other advantages and benefits will become apparent to those of ordinary skill in the art by reading the detailed description of the preferred embodiments below. The accompanying drawings are only for the purpose of illustrating the preferred embodiments and are not to be considered as limiting the present invention. Moreover, the same reference symbols are used throughout the accompanying drawings to represent the same components. In the accompanying drawings:

[0052] Figure 1 A schematic flow chart of a method for preparing a high aspect ratio double-layer diamond nanostructure according to an embodiment of the present invention is shown;

[0053] Figure 2 A schematic flow chart of a method for preparing a high aspect ratio double-layer diamond nanostructure according to another embodiment of the present invention is shown;

[0054] Figure 3a and Figure 3bAn optical microscope image and an electron microscope image of a method for characterizing the size of a nanostructure pattern of a lower layer of photoresist during a wet etching process according to an embodiment of the present invention;

[0055] Figure 4 A schematic diagram of the processing flow of a high aspect ratio double-layer diamond nanostructure according to an embodiment of the present invention;

[0056] Figure 5 This is an electron microscope image of a double-layer diamond nanorod waveguide prepared in one embodiment of the present invention (the shooting tilt angle is 45 degrees);

[0057] Figure 6 This is an electron microscope image of a high aspect ratio double-layer diamond nanorod with a sharp tip prepared in one embodiment of the present invention (the image was taken at a tilt angle of 45 degrees).

[0058] Figure 7 The electron microscope images of various double-layer metal mask nanostructures obtained according to some embodiments of the present invention are shown (the shooting tilt angle is 0 degrees);

[0059] Figures 8a to 8e Electron microscope images of double-layer diamond nanostructures of different sizes and morphologies prepared according to some embodiments of the present invention are shown (the shooting angle is 45 degrees). DETAILED DESCRIPTION

[0060] The exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although the exemplary embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided to enable a more thorough understanding of the present disclosure and to fully convey the scope of the present disclosure to those skilled in the art.

[0061] According to the current research status, in order to solve the huge technical difficulties faced by the wafer-level process manufacturing of double-layer high-aspect ratio single-crystal diamond nanostructures with adjustable double layers in the related technology, the present invention proposes a preparation method for a high-aspect ratio double-layer diamond nanostructure.

[0062] Figure 1 FIG. 2 is a schematic diagram showing a process of preparing a high aspect ratio double-layer diamond nanostructure according to an embodiment of the present invention. Figure 1 As shown, the processing method may at least include the following steps S102 to S108.

[0063] Step S102: performing surface pretreatment on the single crystal diamond;

[0064] Step S104: coating a double-layer photoresist on the surface of the pretreated single-crystal diamond, and forming a double-layer photoresist nanostructure pattern on the surface of the single-crystal diamond by electron beam lithography combined with wet etching;

[0065] Step S106: performing a first metal deposition on the surface of the single crystal diamond, stripping off the upper photoresist to expose the nanostructure pattern of the lower photoresist, performing a second metal deposition on the surface of the single crystal diamond, and stripping off the lower photoresist to obtain a pattern with a double-layer metal mask nanostructure;

[0066] Step S108: using a double-layer metal mask to perform two-step reactive ion etching and one-step wet etching between the two-step reactive ion etching on the surface of the single crystal diamond to obtain a double-layer diamond nanostructure pattern of a target size.

[0067] In this embodiment, a double-layer photoresist nanostructure pattern is first formed on the surface of the pretreated single-crystal diamond through an electron beam lithography process of a double-layer photoresist combined with wet etching; then, the double-layer photoresist nanostructure pattern is used to sequentially perform a first metal deposition, an upper photoresist stripping, a second metal deposition and a lower photoresist stripping on the surface of the single-crystal diamond to obtain a double-layer metal mask nanostructure; finally, the double-layer metal mask is used to perform two-step reactive ion etching and one-step wet etching to obtain a double-layer nanostructure pattern of a target size, thereby realizing wafer-level process manufacturing of a double-layer single-crystal diamond nanostructure.

[0068] In some embodiments, the surface pretreatment operation in step S102 may include: first, performing double-sided mechanical fine polishing on the single crystal diamond, specifically making the roughness Ra of the diamond surface less than 1 nm; then, chemically treating the polished single crystal diamond to remove surface impurities. Surface impurities include surface pollutants and metal impurities introduced during the polishing process.

[0069] Specifically, the chemical treatment operation includes: placing the polished single crystal diamond in an acid solution, heating and boiling the acid at 150-200° C. Optionally, the acid solution is a mixture of concentrated sulfuric acid and concentrated nitric acid, and the volume ratio of concentrated sulfuric acid to concentrated nitric acid is 3:1. The concentrated sulfuric acid can be a commonly used concentrated sulfuric acid with a mass fraction of 98%. The concentrated nitric acid can be a commonly used concentrated nitric acid with a mass fraction of about 65%.

[0070] After surface pretreatment, a clean, finely polished, and highly flat single crystal diamond substrate is obtained.

[0071] Figure 2 A schematic flow chart of a method for preparing a high aspect ratio double-layer diamond nanostructure according to another embodiment of the present invention is shown.

[0072] See also Figure 2As shown, in some embodiments, step S104 may include:

[0073] Step S1041: coating a double layer of photoresist on the surface of the pre-treated single crystal diamond, thereby forming a lower layer of photoresist and an upper layer of photoresist stacked on the surface of the single crystal diamond;

[0074] Step S1042 (electron beam lithography step): according to a preset nanostructure pattern, the upper layer of photoresist is exposed by electron beam lithography equipment, and the upper layer of photoresist is developed to obtain a nanostructure pattern of the upper layer of photoresist; and

[0075] Step S1043 (wet etching step): wet etching the lower layer of photoresist until the nanostructure pattern of the lower layer of photoresist reaches a predetermined size.

[0076] In some embodiments, in step S1041 , a double layer of photoresist is coated on one side of the pre-treated single crystal diamond by a spin coating process.

[0077] In some specific embodiments, the upper photoresist layer may be made of polymethyl methacrylate (PMMA, such as PMMA495A5), polymethyl methacrylate-methyl methacrylate copolymer (PMMA-MAA), or acrylic copolymer (such as PMMA-N), etc. The thickness of the upper photoresist layer may be in the range of 100 to 200 nm, such as 120 nm, 150 nm, 180 nm, etc.

[0078] The lower photoresist layer may be made of phenolic resin (eg, LOR1A), or polydimethylglutarimide (PMGI), etc. The thickness of the lower photoresist layer may be in the range of 200-500 nm, such as 200 nm, 250 nm, 350 nm, 450 nm, 500 nm, etc.

[0079] In some optional embodiments, after coating the double-layer photoresist, the preparation method of the present invention may further include: coating a conductive layer on the surface of the upper photoresist to suppress the charging effect during the electron beam exposure process. The thickness of the conductive layer may be in the range of 10 to 30 nm, such as 10 nm, 20 nm, 30 nm, etc. The material of the conductive layer may be, for example, Eltra92.

[0080] In some optional embodiments, before performing electron beam lithography, the preparation method of the present invention may further include: cleaning the surface of the single crystal diamond.

[0081] Specifically, the cleaning process includes: first, using piranha solution to clean the single crystal diamond, specifically, the cleaning time can be about 30 minutes, to remove organic matter on the surface of the single crystal diamond; then, using acetone, isopropanol and deionized water to ultrasonically treat the single crystal diamond, specifically, the ultrasonic treatment time of each can be 5-10 minutes. Afterwards, the surface of the single crystal diamond can also be blown dry with nitrogen.

[0082] The electron beam exposure of the upper layer of photoresist in step S1042 can be performed by conventional exposure operation. In a specific embodiment, the exposure energy of the electron beam exposure is 100 kV, and the exposure dose is 800-1500 μc·cm -2 .

[0083] The development process may adopt conventional development operations, for example, a mixed solution of methyl isobutyl ketone (MIBK) and isopropyl alcohol (IPA) in a ratio of 1:3 is used as a developer for development process, and the development time is 50 seconds.

[0084] After the development is completed, the film can be rinsed in an isopropyl alcohol solution and blown dry with nitrogen gas to obtain the desired upper photoresist nanostructure pattern.

[0085] In some specific embodiments, the nanostructure pattern of the upper photoresist is a nanopore structure pattern. The pore size of the nanopore is in the range of 30 to 150 nm, such as 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, 110 nm, 120 nm, 130 nm, 140 nm, etc. The period of the nanopore is in the range of 2 to 5 μm, such as 2 μm, 3 μm, 4 μm.

[0086] In some embodiments, the etchant used for wet etching in step S1043 is a weak alkaline etchant. In a specific embodiment, the weak alkaline etchant is a mixed solution of tetramethylammonium hydroxide (TMAH) and deionized water, and its concentration is 0.5-10wt%, such as 1.2wt%, 2.2wt%, 4wt%, 5wt%, 6wt%, etc. In another specific embodiment, the weak alkaline etchant is a sodium carbonate solution, and its concentration is 1-10g / L.

[0087] The specific size of the pattern of the lower photoresist is related to the design of the upper photoresist pattern and the processing time of the wet etching. In actual operation, the pattern of the lower photoresist can be observed by an electron microscope or an optical microscope to determine whether the wet etching of the lower photoresist has reached the end point (i.e., whether the nanostructure pattern of the lower photoresist has reached a predetermined size). The predetermined size of the lower photoresist pattern is related to the size of the large-size part in the double-layer nanostructure to be prepared, and can be specifically set according to actual needs.

[0088] Figure 3a and Figure 3b The optical microscope image and the electron microscope image of the method for characterizing the size of the nanostructure pattern of the lower photoresist during the wet etching process according to one embodiment of the present invention are shown. In a specific embodiment, Figure 3a As shown, the end point of etching to the bottom layer can be determined by using the dark field mode of a commercial optical microscope. Figure 3b As shown, the specific size of the etching can be determined according to the electron microscope (as shown by the long double arrow line), and then the etching time can be determined.

[0089] In some embodiments, the double-layer metal mask obtained in step S106 includes a second metal mask deposited on the surface of the single crystal diamond and a first metal mask covering and surrounding the second metal mask.

[0090] In some embodiments, the first metal mask and the second metal mask may be formed into a self-aligned double-layer metal mask stack structure.

[0091] In some embodiments, the first metal deposition and the second metal deposition may be performed by electron beam evaporation or magnetron sputtering.

[0092] The first metal mask and the second metal mask may use a high selectivity hard mask material.

[0093] In some specific embodiments, the material of the first metal mask layer may be chromium (Cr) or aluminum (Al). The thickness of the first metal mask layer may be within 100-300 nm, such as 120 nm, 150 nm, 180 nm, 200 nm, 220 nm, 250 nm, 300 nm, etc.

[0094] The material of the second metal mask layer can be titanium (Ti) or gold (Au). The thickness of the second metal mask layer can be in the range of 30 to 150 nm, such as 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, 110 nm, 120 nm, 130 nm, 140 nm, etc.

[0095] In step S106 above, after the first metal deposition is completed, the upper photoresist is stripped until the excess metal and photoresist of the upper pattern are completely removed. In some embodiments, the stripping of the upper photoresist is performed using a first specific liquid. The first specific liquid may be, for example, acetone or anisole.

[0096] After stripping the upper photoresist layer, isopropyl alcohol can be used to rinse the surface of the single crystal diamond until the undercut produced by the wet etching of the lower layer is completely exposed.

[0097] After the second metal deposition is completed, the lower photoresist is stripped to remove the metal layer not attached to the single crystal diamond substrate, and finally a double-layer self-aligned metal mask stack pattern is obtained. In some embodiments, the stripping of the lower photoresist is performed using a second specific liquid. The second specific liquid can be, for example, N,N-dimethyl sulfoxide (DMSO).

[0098] Continue to see Figure 2 As shown, in some embodiments, step S108 may include:

[0099] Step S1081: performing a first reactive ion etching on the surface of the single crystal diamond until a first designated etching height is reached;

[0100] Step S1082: performing wet etching using a wet etchant to remove the first metal mask layer, wherein the wet etchant has a high selectivity ratio to the material of the first metal mask layer and the material of the second metal mask layer;

[0101] Step S1083: performing a second reactive ion etching on the surface of the single crystal diamond until a second designated etching height is reached.

[0102] Those skilled in the art will understand that the etching height refers to the distance from the etching start surface to the etching stop surface.

[0103] During the execution of step S108 , a scanning electron microscope may be used to monitor the progress of etching to determine whether the required etching height is met.

[0104] In some embodiments, the first reactive ion etching adopts inductively coupled plasma reactive ion etching (ICP-RIE). Specifically, the process parameters of the first reactive ion etching are: inductively coupled plasma power 400-800W, radio frequency power 50-200W, working pressure 3-15mTorr, oxygen flow rate 20-50sccm, etching time 5-30min, etching rate 150-200nm / min.

[0105] In step S1082, wet etching is performed using a wet etchant having a high selectivity ratio for the material of the first metal mask layer and the material of the second metal mask layer, so that the first metal mask layer can be removed without damaging the second metal mask layer.

[0106] In some embodiments, when the material of the first metal mask is chromium, a mixed solution containing 5-10 vol% of 65-70% nitric acid, 30-50 g / L of ammonium cerium nitrate and deionized water is used in step S1082 to selectively remove the mask.

[0107] In some other embodiments, when the material of the first metal mask layer is aluminum, a tetramethylammonium hydroxide solution with a concentration of 0.5-10 wt % is used as a wet etchant in step S1082.

[0108] Specifically, the etching rate of the first metal mask layer may be in the range of 5 to 20 nm / s, for example, 5 nm / s, 10 nm / s, or 15 nm / s.

[0109] After wet etching to remove the first metal mask layer, the etched single crystal diamond can be fully rinsed with deionized water and blown dry with nitrogen.

[0110] In some embodiments, the second reactive ion etching uses inductively coupled plasma reactive ion etching, and the process parameters are: inductively coupled plasma power 400-800W, RF power 50-200W, working pressure 3-15mTorr, oxygen flow rate 20-50sccm, etching time 5-10min, and etching rate 150-200nm / min.

[0111] Continue to see Figure 2 In some embodiments, after the second reactive ion etching is completed, the preparation method of the present invention may further include:

[0112] Step S110: removing the second metal mask layer and cleaning the single crystal diamond with an acid solution, thereby completing the final cleaning process of the single crystal diamond after etching.

[0113] In some embodiments, when the material of the second metal mask is titanium, a buffered oxide etchant (BOE) is used to remove the second metal mask. Those skilled in the art will recognize that the buffered oxide etchant is composed of 49% HF aqueous solution and 40% NH 4 The F aqueous solutions were mixed in a volume ratio of 1:6.

[0114] In some other embodiments, when the material of the second metal mask is gold, the second metal mask is removed by using aqua regia, which is a mixture of concentrated hydrochloric acid and concentrated nitric acid in a volume ratio of 3:1.

[0115] In some embodiments, the acid solution used for cleaning is a mixture of concentrated sulfuric acid and concentrated nitric acid, and the volume ratio of concentrated sulfuric acid to concentrated nitric acid is 3: 1. The concentrated sulfuric acid can be a commonly used concentrated sulfuric acid with a mass fraction of 98%. The concentrated nitric acid can be a commonly used concentrated nitric acid with a mass fraction of about 65%.

[0116] The cleaning operation specifically includes: placing the single crystal diamond in an acid solution and heating it at 150-200° C. to remove the residual metal mask, and finally obtaining a single crystal diamond structure with a double-layer nanostructure pattern on the surface.

[0117] The embodiments of the present invention can improve the aspect ratio of the single crystal diamond nanostructure by controlling the pattern size of the double-layer photoresist nanostructure and then adjusting the size of the double-layer metal mask, thereby achieving simple, efficient, repeatable and low-cost manufacturing of high aspect ratio double-layer diamond nanostructures.

[0118] The embodiment of the present invention also achieves adjustable size and morphology of the double-layer diamond nanostructure by adjusting the size of the double-layer metal mask and controlling the etching height of the two-step reactive ion etching.

[0119] Figure 4 FIG. 1 is a schematic diagram of the processing flow of a high aspect ratio double-layer diamond nanostructure (specifically a double-layer nanocolumn) in one embodiment of the present invention. Figure 4 , the preparation method of the high aspect ratio double-layer diamond nanostructure of the present invention is specifically described through a specific embodiment.

[0120] Figure 4 Step (a) shows the formation of a double-layer photoresist layer on a single-crystal diamond substrate. Before forming the double-layer photoresist, the single-crystal diamond is first mechanically polished on both sides. The roughness requirement of the polished diamond surface is Ra<1nm. After polishing, a mixture of concentrated sulfuric acid and concentrated nitric acid (volume ratio 3:1) is used to heat and boil (150-200°C). The mass fraction of concentrated sulfuric acid used is 98%, and the mass fraction of concentrated nitric acid is 65%, until the surface pollutants and metal impurities introduced during the polishing process are completely removed, and a clean and finely polished single-crystal diamond substrate is obtained. Then, the double-sided finely polished single-crystal diamond is used as a substrate and cleaned with piranha solution for 30 minutes to remove organic matter on the surface. Subsequently, acetone, isopropanol and deionized water are used for ultrasonic treatment for 5-10 minutes, and the surface of the single-crystal diamond is blown dry with nitrogen.

[0121] This embodiment uses polymethyl methacrylate (PMMA, 495A5) and phenolic resin (LOR1A) as a double-layer photoresist system. First, by optimizing the spin coating process, a photoresist layer is formed on a single crystal diamond substrate, wherein PMMA (495A5) is used as an upper photoresist with a thickness of 120nm, and LOR1A is used as a lower photoresist with a thickness of 350nm. In addition, a 20nm thick conductive layer is spin-coated on the surface of the photoresist to suppress the charging effect during the electron beam exposure process.

[0122] Step (b) shows the electron beam lithography process. The upper layer of photoresist is exposed using an electron beam lithography device to write the designed nanostructure pattern, define the nanopore structure pattern with different sizes and periods (aperture range: 30-150nm, period range: 2-4μm), and use a mixed solution of methyl isobutyl ketone (MIBK) and isopropyl alcohol (IPA) in a ratio of 1:3 as a developer for development. After development, rinse in IPA solution and use N 2 The gas is blown dry to obtain the desired nanostructure upper layer photoresist pattern.

[0123] Step (c) shows the wet etching process for the lower photoresist. The lower photoresist is etched using a 2.2wt% tetramethylammonium hydroxide (TMAH) solution. During the etching process, the pattern of the lower photoresist is observed through an electron microscope or an optical microscope to determine the end point of the etching, and finally the desired lower photoresist pattern is obtained.

[0124] Steps (d) to (f) show the process of forming a double-layer metal mask. This embodiment uses hard masks of two different materials. Titanium (Ti) and chromium (Cr), which are highly selective hard mask materials suitable for diamond reactive ion etching (RIE) processes, are used as two mask materials. Specifically, 80nm of Ti is deposited by electron beam evaporation to form a second layer of metal mask, acetone or anisole is used to strip the upper layer of photoresist, and isopropanol is used to rinse until the undercut produced by the second layer of wet etching is completely exposed. Continue to use electron beam evaporation 150nm Cr to form a second layer of metal mask. Finally, N,N-dimethyl sulfoxide is used to strip the lower layer of photoresist to remove the metal layer not attached to the substrate, and finally a double-layer self-aligned metal mask structure is obtained.

[0125] Steps (g) to (i) show the process flow of two-step reactive ion etching (RIE) and one-step wet etching to construct a dual-diameter nanopillar structure. First, an Oxford Plasma 100 inductively coupled plasma (ICP) etching device is used to perform the first step of etching the large-diameter nanopillars (i.e., the first reactive ion etching). The etching process parameters are an inductively coupled plasma power of 600 W, a radio frequency power of 150 W, a working pressure of 5 mTorr, an oxygen flow rate of 30 sccm, an etching time of about 15 min, an etching rate of about 200 nm / min, and a first designated etching height of h1. After the etching is completed, nitric acid (HNO 3 ) and cerium ammonium nitrate (Ce(NO 3 ) 4 ) mixed solution to selectively remove the mask (i.e., only the Cr mask) at a removal rate of about 5 nm / s, followed by thorough rinsing in deionized water and nitrogen (N 2) and dried. On this basis, the second step of etching of small diameter nanocolumns (i.e., the second reactive ion etching) is carried out, and the etching process parameters are inductively coupled plasma power 600W, RF power 100W, working pressure 6mTorr, oxygen flow rate 25sccm, etching time about 6min, etching rate about 180nm / min, and the second specified etching height h2. After etching, the Ti mask is removed with BOE (buffered oxide etchant) solution, and a mixture of concentrated sulfuric acid and concentrated nitric acid (volume ratio 3:1) is heated and boiled (150-200°C) for cleaning to remove residues.

[0126] Figure 5 This is an electron microscope image of a double-layer diamond nanorod waveguide prepared in one embodiment of the present invention (photographed at a tilt angle of 45 degrees). Figure 6 This is an electron microscope image of a high aspect ratio double-layer diamond nanorod with a sharp tip prepared in one embodiment of the present invention (taken at a tilt angle of 45 degrees). Figure 5 and Figure 6 It can be seen that high-quality double-layer diamond nanorods with a high aspect ratio are obtained through the preparation method of the embodiment of the present invention.

[0127] Of course, in other embodiments of the present invention, the double-layer photoresist can be processed by designing nanostructure patterns of other different sizes and shapes to obtain double-layer metal mask nanostructures of other different sizes and shapes, and further obtain double-layer diamond nanostructures of other different sizes and morphologies.

[0128] Figure 7 Schematically showing electron microscope images of various double-layer metal mask nanostructures obtained according to some embodiments of the present invention (the shooting tilt angle is 0 degree). Figures 8a to 8e Schematically showing electron microscope images of double-layer diamond nanostructures of different sizes and morphologies prepared according to some embodiments of the present invention (the shooting tilt angle is 45 degrees).

[0129] Depend on Figure 7 and Figures 8a to 8e It can be seen that the preparation method of the present invention has the feasibility of controlling various double-layer diamond nanostructures and the flexibility of processing. Figure 8c and Figure 8d This indicates that the technical solution provided by the present invention can achieve universal applicability to different nanostructures.

[0130] In the description provided herein, a large number of specific details are described. However, it is understood that embodiments of the present invention can be practiced without these specific details. In some instances, well-known methods, structures and techniques are not shown in detail so as not to obscure the understanding of this description.

[0131] At this point, those skilled in the art should recognize that, although multiple exemplary embodiments of the present invention have been shown and described in detail herein, many other variations or modifications that conform to the principles of the present invention can still be directly determined or derived based on the content disclosed in the present invention without departing from the spirit and scope of the present invention. Therefore, the scope of the present invention should be understood and recognized as covering all these other variations or modifications.

Claims

1. A method for preparing a high aspect ratio double-layer diamond nanostructure, comprising: Surface pretreatment of single crystal diamond; Coating a double-layer photoresist on the surface of the pretreated single-crystal diamond, and forming a double-layer photoresist nanostructure pattern on the surface of the single-crystal diamond by electron beam lithography combined with wet etching; Performing a first metal deposition on the surface of the single crystal diamond, stripping off the upper photoresist to expose the nanostructure pattern of the lower photoresist, performing a second metal deposition on the surface of the single crystal diamond, and stripping off the lower photoresist to obtain a pattern with a double-layer metal mask nanostructure; The double-layer metal mask is used to perform two-step reactive ion etching on the surface of the single crystal diamond and one-step wet etching between the two-step reactive ion etching to obtain a double-layer diamond nanostructure pattern of a target size.

2. The method for preparing a high aspect ratio double-layer diamond nanostructure according to claim 1, wherein: The electron beam lithography operation includes: According to a preset nanostructure pattern, the upper layer of photoresist is exposed by electron beam lithography equipment, and the upper layer of photoresist is developed to obtain a nanostructure pattern of the upper layer of photoresist; The wet etching operation includes: The lower layer of photoresist is wet-etched until the nanostructure pattern of the lower layer of photoresist reaches a predetermined size.

3. The method for preparing a high aspect ratio double-layer diamond nanostructure according to claim 2, wherein: The upper photoresist is polymethyl methacrylate, polymethyl methacrylate-methyl methacrylate copolymer, or acrylic copolymer, and has a thickness of 100 to 200 nm; the lower photoresist is polydimethylglutarimide or phenolic resin, and has a thickness of 200 to 500 nm; The corrosive agent used in the wet etching is a weak alkaline corrosive agent, wherein the weak alkaline corrosive agent is a tetramethylammonium hydroxide solution with a concentration of 0.5-10 wt% or a sodium carbonate solution with a concentration of 1-10 g / L.

4. The method for preparing a high aspect ratio double-layer diamond nanostructure according to claim 1, wherein: After coating the double-layer photoresist, the preparation method further comprises: A conductive layer is coated on the surface of the upper photoresist, and the thickness of the conductive layer is 10-30 nm.

5. The method for preparing a high aspect ratio double-layer diamond nanostructure according to claim 1, wherein: The double-layer metal mask comprises a second metal mask deposited on the surface of the single crystal diamond and a first metal mask covering and surrounding the second metal mask; The first metal deposition and the second metal deposition are carried out by electron beam evaporation or magnetron sputtering; The material of the first metal mask layer is chromium or aluminum, and the thickness is 100 to 300 nm; The material of the second metal mask layer is titanium or gold, and the thickness is 30-150 nm.

6. The method for preparing a high aspect ratio double-layer diamond nanostructure according to claim 5, wherein: The step of performing two-step reactive ion etching on the surface of the single crystal diamond using the double-layer metal mask and one-step wet etching between the two-step reactive ion etching to obtain a double-layer diamond nanostructure pattern of a target size comprises: Performing a first reactive ion etching on the surface of the single crystal diamond until a first designated etching height is reached; performing wet etching using a wet etchant to remove the first metal mask, the wet etchant having a high selectivity ratio to the material of the first metal mask and the material of the second metal mask; A second reactive ion etching is performed on the surface of the single crystal diamond until a second designated etching height is reached.

7. The method for preparing a high aspect ratio double-layer diamond nanostructure according to claim 6, wherein: The first reactive ion etching adopts inductively coupled plasma reactive ion etching, and the process parameters are: inductively coupled plasma power 400-800W, radio frequency power 50-200W, working pressure 3-15mTorr, oxygen flow rate 20-50sccm, etching time 5-30min, etching rate 150-200nm / min; When the material of the first metal mask is chromium, the wet etchant is a mixed solution containing 5-10 vol% of 65-70% nitric acid, 30-50 g / L of cerium ammonium nitrate and deionized water; when the material of the first metal mask is aluminum, the wet etchant is a tetramethylammonium hydroxide solution with a concentration of 0.5-10 wt%; the etching rate of the wet etching is 5-20 nm / s; The second reactive ion etching adopts inductively coupled plasma reactive ion etching, and the process parameters are: inductively coupled plasma power 400-800W, radio frequency power 50-200W, working pressure 3-15mTorr, oxygen flow rate 20-50sccm, etching time 5-10min, and etching rate 150-200nm / min.

8. The method for preparing a high aspect ratio double-layer diamond nanostructure according to claim 6, wherein: After completing the second reactive ion etching, the preparation method further comprises: removing the second metal mask layer and cleaning the single crystal diamond with an acid solution; Wherein, when the material of the second metal mask layer is titanium, the second metal mask layer is removed by using a buffered oxide etchant, and when the material of the second metal mask layer is gold, the second metal mask layer is removed by using aqua regia; The acid solution is a mixture of concentrated sulfuric acid and concentrated nitric acid, and the volume ratio of concentrated sulfuric acid to concentrated nitric acid is 3:1; The cleaning operation includes: placing the single crystal diamond in the acid solution and heating it at 150-200° C. for acid boiling.

9. The method for preparing a high aspect ratio double-layer diamond nanostructure according to claim 1, wherein: The surface pretreatment operation includes: The single crystal diamond is subjected to double-sided mechanical fine polishing until the roughness Ra of the diamond surface is less than 1 nm; Chemically treating the polished single crystal diamond to remove surface impurities; The chemical treatment operation includes: placing the single crystal diamond in an acid solution and heating it at 150-200° C. for acid boiling, wherein the acid solution is a mixture of concentrated sulfuric acid and concentrated nitric acid, and the volume ratio of concentrated sulfuric acid to concentrated nitric acid is 3:

1.

10. The method for preparing a high aspect ratio double-layer diamond nanostructure according to claim 1, wherein: Before performing the electron beam lithography, the preparation method further comprises: Cleaning the surface of the single crystal diamond; The cleaning process includes: Cleaning the single crystal diamond using piranha solution; and The single crystal diamond is ultrasonically treated with acetone, isopropanol and deionized water in sequence.

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