A method for doping micro-nanostructure fixed-point defects and NV color center sensor

Abstract

The present invention provides a method for doping micro-nano structure fixed-point defects based on a self-alignment process, comprising: S1, forming a sacrificial layer and a photoresist layer on the surface of a crystal substrate in sequence; S2, photoetching a mask hole in the photoresist layer according to a micro-nano pattern; S3, isotropically etching the sacrificial layer through the mask hole, and enlarging the mask hole pattern to the sacrificial layer; S4, performing ion implantation doping on the exposed crystal surface below the mask hole; S5, removing the photoresist layer, and depositing a mask material; S6, removing the sacrificial layer, and transferring the micro-nano enlarged pattern in the sacrificial layer to a mask material pattern; S7, etching the exposed crystal surface, removing the surface mask material, and annealing to form a specific defect. The method provided by the present invention is based on a self-alignment process, does not require alignment operations, has high precision and a simple process, and does not have alignment errors.

Description

Technical Field

[0001] The present invention relates to the fields of micro-nano processing technology and quantum information technology, and in particular to a method and application of micro-nano structure fixed-point defect doping based on a self-alignment process. Background Art

[0002] Solid-state quantum systems are widely used and studied in the field of quantum information because of their integration and deviceization. Point defects in solids usually have good spin properties and optical properties because they are protected by solid materials. Therefore, they have become a hot spot for research and application in solid-state quantum computing, quantum precision measurement and other fields, such as nitrogen-vacancy color centers (NV) in diamond, silicon-vacancy color centers (SiV), nickel-nitrogen color centers (NE8), and point defects in silicon carbide. Among them, the NV color center in diamond has become one of the main solid-state systems studied in the field of quantum information due to its superior spin coherence time at room temperature, optical initialization readout means, and mature microwave control methods. Especially in the field of microscopic magnetic measurement, NV color centers as single-spin quantum sensors have demonstrated outstanding advantages such as nanospatial resolution, single-spin detection sensitivity, loose working conditions, non-destructiveness, and no need for magnetic shielding.

[0003] Optical defects such as NV color centers usually emit weak light. Limited by the high refractive index of the crystal material itself (such as diamond (n=2.4), silicon carbide (n=2.6), etc.), most of the fluorescence emitted by point defects is totally reflected at the interface, and it is necessary to prepare micro-nano structures to improve the optical fluorescence collection efficiency. For example, micro-nano optical structures such as solid immersion lenses [Applied Physics Letters, 2010, 97(24): 241901, Journal of Applied Physics, 2015, 118(14): 144501], nanopillar waveguides [Nano letters, 2015, 15(1): 165-169], ultra-thin diamond "bull's eyes" [Nanoletters, 2015, 15(3): 1493-1497] and parabolic surfaces [Nano letters, 2018, 18(5): 2787-2793] are prepared.

[0004] The effect of improving the optical fluorescence collection efficiency is closely related to the spatial position of defects in micro-nano optical structures. Usually, the defect positioning accuracy in the center of the structure must reach 50nm to achieve a strong effect. The traditional method of doping through maskless ion implantation is difficult to control the spatial position of defects in the structure. Usually, less than 10% of optical structures achieve the expected enhancement effect.

[0005] The spatial position uncertainty caused by process defects is the key factor restricting the optical structure effect and yield rate. In order to improve the yield rate of micro-nano optical structures, it is necessary to align the micro-nano structure and defect doping to achieve point-defect doping of the micro-nano structure.

[0006] The existing technical solutions mainly include:

[0007] 1. Electron beam lithography, alignment using electron beam imaging [Nano Lett. 2010, 10, 3168-3172]

[0008] 2. AFM tip is prepared by combining a small hole mask and using AFM imaging to achieve alignment [Applied Physics A, 2008, 91(4): 567-571, Patent: US7126139B2].

[0009] 3. Focused ion beam implantation, using ion beam imaging to achieve alignment [Nature Communications, 2017, 8(1): 1-7, Physica Status Solidi(a), 2013, 210(10): 2055-2059]

[0010] These methods all have complicated alignment processes, and there may be alignment errors in the alignment process. The equipment process requirements are high and the cost is expensive. Summary of the invention

[0011] 1. Technical issues to be resolved

[0012] In response to the above problems, the present invention provides a method and application of point-defect doping of micro-nano structures based on a self-aligned process, which is used to at least partially solve the technical problems that traditional maskless defect doping processes are difficult to control the spatial position of defects in micro-nano structures.

[0013] (II) Technical solution

[0014] On one hand, the present invention provides a method for doping micro-nano structures with fixed-point defects based on a self-aligned process, comprising: S1, sequentially forming a sacrificial layer and a photoresist layer on the surface of a crystal substrate; S2, photolithographically etching a mask hole in the photoresist layer according to a micro-nano pattern; S3, isotropically etching the sacrificial layer through the mask hole to enlarge the micro-nano pattern to the sacrificial layer; S4, performing ion implantation doping on the exposed crystal surface below the mask hole; S5, removing the photoresist layer and depositing a mask material; S6, removing the sacrificial layer, and transferring the enlarged micro-nano pattern in the sacrificial layer to a mask material pattern; S7, etching the exposed crystal surface, removing the surface mask material and annealing to form a specific defect.

[0015] Furthermore, the sacrificial layer and the photoresist layer in S1 form a double-layer thin film structure, and the formation method includes coating and vapor deposition.

[0016] Furthermore, the sacrificial layer material in S1 includes PMGI (polydimethylglutarimide), SiO2, and S1N.

[0017] Furthermore, the mask hole in S2 is a scaled-down pattern of the micro-nano pattern, and the mask hole is located directly above the center of the underlying structure pattern.

[0018] Furthermore, the type of ions implanted in S4 is related to the type of doping defects, and the ion penetration depth cannot exceed the thickness of the photoresist layer.

[0019] Furthermore, the deposition of the mask material in S5 adopts a coating process, including evaporation coating and sputtering coating.

[0020] Furthermore, the sacrificial layer is removed in S6 by dissolving and stripping.

[0021] Furthermore, in S7, the exposed crystal surface is etched using a dry etching process, including plasma etching, reactive ion etching, and inductively coupled plasma etching.

[0022] Furthermore, in S7 , the surface mask material is removed by using a dry etching process or a wet etching process.

[0023] Another aspect of the present invention provides an NV color center sensor, in which the NV color center is prepared by the method as described above.

[0024] (III) Beneficial effects

[0025] The embodiment of the present invention provides a method and application of point-defect doping in micro-nano structures based on a self-alignment process, which realizes point-defect doping in micro-nano structures, effectively improves the accuracy of the position of defects in the micro-nano structures; eliminates the influence of spatial position uncertainty on the optical structure effect and yield; and obtains a high-quality NV color center sensor prepared by using this method. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 A flow chart schematically shows a method for point-defect doping of a micro-nanostructure based on a self-aligned process according to an embodiment of the present invention;

[0027] Figure 2 A schematic diagram of point defect doping of a micro-nano structure based on a self-aligned process according to an embodiment of the present invention is shown;

[0028] Reference numerals

[0029] 1-PMMA;

[0030] 2-PMGI;

[0031] 3- Diamond sample;

[0032] 4- Lattice defects;

[0033] 5-Metal mask;

[0034] 6-NV color center. DETAILED DESCRIPTION

[0035] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with specific embodiments and with reference to the accompanying drawings.

[0036] The first embodiment of the present invention provides a method for doping micro-nanostructure fixed-point defects based on a self-aligned process, see Figure 1 , including: S1, forming a sacrificial layer and a photoresist layer on the surface of a crystal substrate in sequence; S2, photolithography a mask hole in the photoresist layer according to the micro-nano pattern; S3, isotropically etching the sacrificial layer through the mask hole to enlarge the micro-nano pattern to the sacrificial layer; S4, ion implantation doping the exposed crystal surface below the mask hole; S5, removing the photoresist layer and depositing a mask material; S6, removing the sacrificial layer, and transferring the enlarged micro-nano pattern in the sacrificial layer to a mask material pattern; S7, etching the exposed crystal surface, removing the surface mask material and annealing to form specific defects.

[0037] A crystal substrate is provided, and a double-layer thin film structure is formed on the surface. The lower structure is a sacrificial layer that can be isotropically corroded, and the top structure is a photoresist. A mask hole is prepared on the top resist structure according to the shape of the micro-nano structure through a photolithography process. The lower structure is isotropically etched through the mask hole using an etching solution. The mask hole pattern is enlarged to the lower structure to achieve the patterning of the lower structure. The top structure is used as a mask to dope the exposed crystal surface below the mask hole through ion implantation. The top photoresist is removed, and the mask material is deposited through a coating process. The lower structure material is removed by dissolution and stripping to achieve the transfer of the lower structure pattern to the mask material pattern. The mask material pattern is used as an anti-etching mask, and the exposed crystal surface is etched by a dry etching process to form a micro-nano structure. The remaining mask material on the surface is then removed and annealed to form specific defects.

[0038] On the basis of the above embodiment, the sacrificial layer and the photoresist layer in S1 form a double-layer thin film structure, and the formation method includes coating and vapor deposition.

[0039] The photoresist layer is used to prepare mask holes for ion implantation through S2 photolithography, the sacrificial layer is used for S3 isotropic etching to form a pattern, and is coated through S5 and removed through S6 to form an etching mask.

[0040] The coating process forms a film structure by spin coating or spray coating, and is commonly used for materials such as photoresist, PMGI, and spin-coated SiO2 layers; vapor deposition forms a film structure by physical vapor deposition or chemical vapor deposition, and is commonly used for SiO2 and SiN materials. Photoresist materials include ultraviolet photoresist and electronic photoresist.

[0041] Based on the above embodiment, the sacrificial layer material in S1 includes PMGI, SiO2, and SiN.

[0042] The sacrificial layer is preferably PMGI, which has the characteristics that the S3 process can be isotropically etched by tetramethylammonium hydroxide (TMAH) solution, and the process has little effect on the upper photoresist structure. In addition, when acetone is used to remove the photoresist layer in the S5 process, it will not dissolve in acetone. In the S6 process, the mask material pattern is obtained by using the reagent N-methylpyrrolidone (NMP) for removal.

[0043] The sacrificial layer can also be SiO2 or SiN sacrificial layer. Their characteristics are that the S3 process can be isotropically etched by BOE (buffered oxide etchant) or hydrofluoric acid solution, and the process has little effect on the upper photoresist structure. And when acetone is used to remove the photoresist layer in the S5 process, it will not dissolve in acetone. In the S6 process, the mask material pattern is obtained by using the reagent BOE (buffered oxide etchant) or hydrofluoric acid solution.

[0044] On the basis of the above embodiment, the mask hole in S2 is a pattern that is proportionally reduced from the micro-nano pattern, and the mask hole is located directly above the center of the underlying structure pattern.

[0045] The mask hole is used not only as an isotropic etching mask for the sacrificial layer in the S3 process, but also as a mask hole for ion implantation in the S4 process. The mask hole is prepared on the top layer glue structure according to the shape of the micro-nano structure by a photolithography process, and the photolithography process can be an electron beam lithography process or an ultraviolet lithography process.

[0046] On the basis of the above embodiment, the type of ions implanted in S4 is related to the type of doping defects, and the ion penetration depth cannot exceed the thickness of the photoresist layer.

[0047] Depending on the type of doping defect, the type of injected ions is different, for example, nitrogen-containing ions are injected when doping NV color centers, and silicon-containing ions are injected when doping SiV color centers.

[0048] The ion penetration depth cannot exceed the thickness of the photoresist layer because after exceeding the thickness of the photoresist layer, the photolithography will not be able to block the ion implantation into the crystal, and therefore the position of the implanted ions cannot be controlled.

[0049] On the basis of the above embodiment, the deposition of the mask material in S5 adopts a coating process, including evaporation coating and sputtering coating.

[0050] The mask material can be metal, metal oxide, non-metal, non-metal oxide. The evaporation coating process includes thermal evaporation coating and electron beam evaporation coating, which has the advantages of low energy and good mask edge after peeling; the sputtering coating process has the advantages of high film density and small particle size.

[0051] On the basis of the above embodiment, the sacrificial layer is removed in S6 by dissolving and peeling.

[0052] The reagents used in the dissolution and stripping process are determined according to the type of the underlying structure material. For example, the reagent N-methylpyrrolidone (NMP) is used for the dissolution and stripping of the underlying structure PMGI, and the reagent containing hydrofluoric acid is used for the dissolution and stripping of the underlying structure SiO2 and SiN.

[0053] On the basis of the above embodiment, in S7, the exposed crystal surface is etched using a dry etching process, including plasma etching, reactive ion etching, and inductively coupled plasma etching.

[0054] The dry etching process includes ion beam etching, reactive plasma etching, inductively coupled plasma etching, etc., and by adjusting the etching power, gas ratio, etching pressure, etching temperature, etching time and other conditions, the etching depth and the inclination angle of the etching side wall are controlled to form a specific micro-nano structure.

[0055] Based on the above embodiment, the surface mask material is removed in S7 by using a dry etching process or a wet etching process.

[0056] The mask material can be removed by dry etching or wet etching. The dry etching process requires the use of plasma etching equipment and has the advantages of simple operation, stable process and high precision. The wet etching process has the advantage of low cost.

[0057] A second embodiment of the present invention provides an NV color center sensor, in which the NV color center is prepared by the aforementioned method.

[0058] See also Figure 2 The present invention provides a method for achieving fixed-point doping in micro-nano structures, which can be used for fixed-point doping of point defects in diamond, silicon carbide, and h-BN micro-nano structures. The following takes the fixed-point doping of the nitrogen vacancy color center at the center of the end face of a diamond nanocolumn waveguide as an example to provide a specific implementation plan:

[0059] A double-layer thin film structure is formed on the surface of a diamond substrate 3, and a PMGI sacrificial layer 2 and an electron beam photoresist PMMA photoresist layer 1, namely S1, are formed by a spin coating process;

[0060] Electron beam lithography is performed on the electron beam photoresist PMMA to prepare a mask hole, the mask hole is circular in shape, and the diameter is smaller than the diameter of the nanocolumn waveguide, that is, S2;

[0061] The etching solution cannot damage the top layer of the double-layer thin film structure. In this step, tetramethylammonium hydroxide (TMAH) solution is used for isotropic etching. The lower structure is patterned into the shape of the final micro-nano structure. The mask hole in the substrate plane is located directly above the center of the lower structure pattern. In this embodiment, the lower structure pattern is circular, and the mask hole is located in the center, that is, S3.

[0062] The position of the doped defect plane is controlled by the ion implantation direction. In this embodiment, the ion implantation direction is perpendicular to the substrate surface, and the position of the lattice defect 4 will be located at the center of the lower layer pattern; the ion implantation ion type is nitrogen-containing group ions, namely S4;

[0063] Acetone is used to dissolve the top photoresist PMMA without damaging the lower structure PMGI sacrificial layer 2; the mask material 5 uses metal Ti, and the evaporation coating process is preferred, that is, S5;

[0064] Using reagent N-methylpyrrolidone (NMP) to dissolve and peel off the PMGI sacrificial layer 2 of the lower structure, i.e. S6;

[0065] Through inductively coupled plasma etching, a diamond nanocolumn waveguide structure with high fluorescence collection efficiency is formed; BOE solution wet etching is used to remove Ti metal 5; annealing is performed in a 600-1200°C vacuum environment to form an NV color center 6, which is located at the center of the end face of the nanocolumn waveguide, namely S7.

[0066] The above embodiments complete the self-aligned point-doping of micro-nano structures. Finally, a NV color center sensor can be obtained through the embodiments, which is characterized in that the NV color centers are all located in the center of the end face of the diamond nanocolumn waveguide structure, and can achieve the expected optimal fluorescence collection efficiency with a high yield. The working principle of the NV color center sensor is to convert external magnetic, electrical, temperature and other information into information on the fluorescence intensity of the NV color center for reading. The NV color center sensor obtained in this embodiment has a higher fluorescence signal collection efficiency and therefore has better detection sensitivity.

[0067] It should be noted that the sensor obtained by this patent can be combined with scanning microscopy imaging technology to form a scanning NV color center sensor. For example, it can replace the nanocolumn waveguide structure manufacturing method in patent CN202010100070.X to improve the yield of the sensor.

[0068] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for doping micro-nanostructure fixed-point defects based on a self-aligned process, comprising: S1, forming a sacrificial layer and a photoresist layer in sequence on the surface of a crystal substrate; S2, photolithography a mask hole in the photoresist layer according to the micro-nano pattern; S3, isotropically etching the sacrificial layer through the mask hole to enlarge the micro-nano pattern to the sacrificial layer; S4, performing ion implantation doping on the exposed crystal surface below the mask hole; S5, removing the photoresist layer and depositing a mask material; S6, removing the sacrificial layer, and transferring the micro-nano magnified pattern in the sacrificial layer to a mask material pattern; S7, etching the exposed crystal surface to remove the mask material on the surface and annealing to form specific defects.

2. The method for doping micro-nanostructure fixed-point defects based on a self-aligned process according to claim 1, characterized in that: The sacrificial layer and the photoresist layer in S1 form a double-layer thin film structure, and the formation method includes coating and vapor deposition.

3. The method for doping micro-nanostructure fixed-point defects based on a self-aligned process according to claim 1, characterized in that: The sacrificial layer material in S1 includes PMGI, SiO2, and SiN.

4. The method for doping micro-nanostructure fixed-point defects based on a self-aligned process according to claim 1, characterized in that: The mask hole in S2 is a scaled-down pattern of the micro-nano pattern, and the mask hole is located just above the center of the underlying structure pattern.

5. The method for doping micro-nanostructure fixed-point defects based on self-aligned process according to claim 1, characterized in that: The type of ions implanted in S4 is related to the type of doping defects, and the ion penetration depth cannot exceed the thickness of the photoresist layer.

6. The method for doping micro-nanostructure fixed-point defects based on a self-aligned process according to claim 1, characterized in that: The deposition of the mask material in S5 adopts a coating process, including evaporation coating and sputtering coating.

7. The method for doping micro-nanostructure fixed-point defects based on a self-aligned process according to claim 1, characterized in that: The sacrificial layer is removed in S6 by dissolving and stripping.

8. The method for doping micro-nanostructure fixed-point defects based on a self-aligned process according to claim 1, characterized in that: In S7, the exposed crystal surface is etched using a dry etching process, including plasma etching, reactive ion etching, and inductively coupled plasma etching.

9. The method for doping micro-nanostructure fixed-point defects based on a self-aligned process according to claim 1, characterized in that: In S7, the mask material on the surface is removed by dry etching or wet etching process.

10. An NV color center sensor, characterized in that: The NV color center in the NV color center sensor is prepared by the method according to any one of claims 1-9.

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