Method for preparing super-large aspect ratio inclined AFM probe tip with controllable size and inclination angle

Abstract

The application provides a preparation method of an ultra-high aspect ratio inclined AFM probe tip with controllable size and inclination angle. The technical scheme utilizes the characteristics that the irradiation of a focused ion beam on a suspended micro-nano metal structure will make the micro-nano metal structure fold upwards, and the folding angle is related to the irradiation energy. A metal film is deposited on the top end of a cantilever beam, and different focused ion beam parameters are selected to irradiate the suspended part of the metal structure outside the cantilever beam, so as to prepare an ultra-high aspect ratio inclined AFM probe tip with a controllable inclination angle. As a novel manufacturing method of a high aspect ratio AFM probe, the application is controllable in consistency, suitable for various materials, and simple in method and suitable for mass production. As a core component of an atomic force microscope, the product has higher detection precision.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of micro-nano processing technology, and particularly relates to a preparation method of an ultra-large high aspect ratio inclined AFM probe tip with controllable size and inclination angle. BACKGROUND

[0002] Atomic force microscope (AFM) is a commonly used detection device, and its basic principle is to detect the sample surface topography by using the atomic interaction force between the probe tip and the sample surface. AFM can not only realize three-dimensional surface imaging with nanometer resolution, but also can work in complex environments such as atmosphere, liquid and low temperature, and can image active samples such as single cells and single molecules. According to the use purpose, the atomic force microscope probe is divided into contact probes, non-contact / tapping mode probes, conductive probes, magnetic probes, large aspect ratio probes and diamond-like atomic force microscope probes. The topography of the tip has a great influence on the detection accuracy. The sharper the tip, the higher the detection accuracy. Especially for the sample surface with large relief, narrow and deep grooves, the detection results of ordinary probes are easy to deviate from the actual sample topography, as shown in FIG. 1. Therefore, the aspect ratio of the probe is extremely important, and the research on the large aspect ratio probe has become a hot spot in the field of AFM probe research. Figure 1

[0003] The methods for preparing large aspect ratio probes mainly include carbon nanotube attachment method, focused ion beam etching method, focused ion beam deposition method, metal particle catalyst induced silicon nanowire growth method, etc. The carbon nanotube attachment method is to place the AFM probe in the carbon nanotube dispersion liquid, and use the electric field force to make the carbon nanotube attached to the AFM probe on the ordinary AFM probe. Since the size and direction of the carbon nanotube attached to the probe tip are random, the size and inclination angle of the obtained large aspect ratio tip cannot be accurately controlled. The focused ion beam etching method is to use a focused ion beam to bombard the tip of an ordinary probe to "sharpen" the tip. This method has high cost and long time consumption, and is not suitable for mass production. The focused ion beam deposition method is to use a focused ion beam to deposit a nanowire on the tip of an ordinary probe as a new tip. This method also has high cost and long time consumption, and is not suitable for mass production. The metal particle catalyst induced silicon nanowire growth method uses gold or other metal particles as catalysts attached to the silicon surface, and then uses chemical vapor deposition to grow silicon nanowires as probe tips. Due to the inherent shortcomings of chemical vapor deposition, the controllability of the size of the tip is not strong. SUMMARY

[0004] The present application aims at the technical defects of the prior art, and provides a preparation method of an ultra-large high aspect ratio inclined AFM probe tip with controllable size and inclination angle, so as to solve the technical problems of high cost and poor consistency of the conventional preparation process of the large aspect ratio AFM probe.

[0005] ​To achieve the above technical purposes, the present application adopts the following technical solutions:

[0006] The method for preparing the super-large high aspect ratio tilting AFM probe tip with controllable size and tilting angle comprises the following steps:

[0007] 1) spin-coat 200-400 nm PMMA photoresist on the surface of a cleaned SOI wafer, and bake at 180 DEG C for 1-2 minutes;

[0008] 2) expose the sample obtained in step 1) to an electron beam exposure machine, and the exposure dose is 500-1000 mJ / cm 2 ; after exposure, develop the sample in a developing solution for 30-50 seconds, and then fix the sample in a fixing solution for 30-50 seconds;

[0009] 3) directly deposit a 20-30 nm Cr or Ti metal film on the sample obtained in step 2) by using a thermal evaporation film coating device, an electron beam evaporation film coating device or a magnetron sputtering film coating device;

[0010] 4) immerse the sample obtained in step 3) in acetone, and soak at room temperature for 10-30 minutes (so that the photoresist naturally falls off, leaving a metal structure);

[0011] 5) etch the sample obtained in step 4) on both sides to prepare the AFM probe cantilever part and the base part (at this time, the metal structure part is in a suspended state);

[0012] 6) fold the metal nanowire structure by irradiating it with a focused ion beam.

[0013] Preferably, the SOI wafer in step 1) is composed of a device Si layer, an insulating SiO2 layer and a substrate Si layer, wherein the thicknesses of the device Si layer, the insulating SiO2 layer and the substrate Si layer are 1-5 microns, 0.5-2 microns and 350-500 microns, respectively.

[0014] Preferably, step 3) is replaced by step 3a) as follows: first deposit a 3-5 nm Cr or Ti adhesion layer on the sample obtained in step 2) by using a thermal evaporation film coating device, an electron beam evaporation film coating device or a magnetron sputtering film coating device, and then deposit a 20-30 nm metal film.

[0015] Preferably, the metal of the metal film is selected from one or several of the following components: W, Pt and Au.

[0016] Preferably, step 4) is implemented by using a liftoff process.

[0017] As preferred, in step 5), the front and back surfaces of the sample are etched respectively by using photolithography and deep silicon etching Bosch process (Bosch process will have tens of nanometers of lateral etching, so the silicon under the metal nanowire structure will be etched away).

[0018] As preferred, in step 6), the AFM probe tip in vertical state or different tilt angles is obtained by adjusting the ion beam irradiation parameters.

[0019] As preferred, in step 1), the SOI wafer is cleaned by RCA standard process, and the surface is clean and free of impurities under ultraviolet lamp inspection.

[0020] As preferred, in step 1), the spin coating conditions are: the front rotation speed is 500 r / min, the time is 5 s, and the rear rotation speed is 4000 r / min, the time is 40 s.

[0021] As preferred, in step 2), the acceleration voltage of the electron beam exposure machine is 100 KeV, and the beam current is 100 pA.

[0022] The application provides a preparation method of an ultra-large high aspect ratio tilt AFM probe tip with controllable size and tilt angle. The technical scheme utilizes the characteristics that the irradiation of a focused ion beam on a suspended micro-nano metal structure will make the micro-nano metal structure fold upwards, and the folding angle is related to the irradiation energy, deposits a metal film on the top end of a cantilever beam, irradiates the suspended part of the metal structure outside the cantilever beam by selecting different focused ion beam parameters, and prepares an ultra-large high aspect ratio tilt AFM probe tip with a controllable tilt angle. As a brand-new high aspect ratio AFM probe manufacturing method, the application is controllable in consistency, suitable for various materials, and simple and suitable for mass production. As a core component of an atomic force microscope, the product has higher detection precision. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 is a difference map measured by different types of probes;

[0024] Figure 2 is a flowchart of the method of the application;

[0025] Figure 3 is Figure 2 in which 2e is a top view of the metal nanowire structure;

[0026] in which:

[0027] 1, SOI silicon wafer 2, photoresist 3, metal film 4, probe base

[0028] 5, probe cantilever beam 6, probe tip. DETAILED DESCRIPTION

[0029] The specific embodiments of the present application will be described in detail below. In order to avoid excessive unnecessary details, the known structures or functions will not be described in detail in the following examples. The approximate language used in the following examples can be used for quantitative expression, indicating that the amount can be allowed to have certain changes without changing the basic function. Unless defined, the technical and scientific terms used in the following examples have the same meaning as generally understood by those skilled in the art to which the present application belongs.

[0030] Example 1

[0031] A method for preparing a super-large aspect ratio inclined AFM probe tip with controllable size and inclination angle, comprising the following steps:

[0032] 1. A double-side polished SOI wafer is selected as the raw material, which is composed of a device silicon layer, a silicon dioxide layer, and a substrate silicon layer with thicknesses of 2.5 microns, 0.5 microns, and 350 microns, respectively. (As shown in Figure 2 a)

[0033] 2. The sample is cleaned by RCA standard process to achieve a clean surface without impurities under ultraviolet lamp inspection.

[0034] 3. Before use, the sample is spin-coated with a layer of PMMA photoresist with a thickness of 200 nanometers at a spin speed of 500 r / min for 5 s and then at a spin speed of 4000 r / min for 40 s. The sample is placed on a hot plate and heated at 180°C for 1 min. (As shown in Figure 2 b)

[0035] 4. The photoresist is patterned using electron beam with an acceleration voltage of 100 KeV, a beam current of 100 pA, and a dose of 900 mJ / cm 2 .

[0036] 5. The sample is developed in MIBK 1:3 IPA at room temperature for 40 s, then fixed in IPA solution for 30 s, and taken out to dry. A long groove pattern with a triangular tip with a length of 5 microns and a width of 20 nanometers is obtained. (As shown in Figure 2 c)

[0037] 6. A 5-nanometer Cr+15-nanometer W metal thin film is evaporated on the sample using a thermal evaporation coating equipment. (As shown in Figure 2 d)

[0038] 7. The sample is immersed in acetone solution at room temperature for 10 min, and the photoresist is naturally stripped, leaving the metal structure. (As shown in Figure 2 e and Figure 3 f)

[0039] 8. First, coat the front surface of the sample with 10 microns of AZ4620 photoresist as a protective layer, then coat the back surface of the sample with 10 microns of AZ4620 photoresist, using a coating speed of 500 r / min for 10 s and 2000 r / min for 40 s, and then place the sample on a hot plate at 100°C for 3 min to bake the sample.

[0040] 9. Perform photolithography on the sample using 405 nm light, with an exposure dose of 1000 mJ / cm 2 .

[0041] 10. Develop using AZ positive photoresist developer, at room temperature for 5 min, then rinse with deionized water and dry.

[0042] 11. Dry etch the back surface to the middle silicon oxide layer of the SOI wafer, and remove the residual photoresist.

[0043] 12. Coat the front surface of the sample with 1.6 microns of AZ5214 photoresist, using a coating speed of 500 r / min for 5 s and 2000 r / min for 40 s, and then place the sample on a hot plate at 100°C for 1 min to bake the sample.

[0044] 13. Perform photolithography on the sample using 405 nm light, with an exposure dose of 100 mJ / cm 2 .

[0045] 14. Develop using AZ positive photoresist developer, at room temperature for 3 min, then rinse with deionized water and dry.

[0046] 15. Dry etch the back surface to the middle silicon oxide layer of the SOI wafer.

[0047] 16. Soak in BOE solution for 5 min to obtain the probe substrate and cantilever structure. (as shown in Figure 2 g)

[0048] 17. Scan the metal overhang with a focused ion beam to fold it upwards. Use a gallium ion source, with an acceleration voltage of 30 kV and a beam current of 150 pA. Obtain a metal probe that is vertical at an angle of 80° to the horizontal direction, and the probe preparation is complete. (as shown in Figure 2 j)

[0049] The core of the present application is to use ion beams of different energies to irradiate the overhanging metal nanowire structure to obtain a large aspect ratio needle tip with different angles. For those skilled in the art, various corresponding changes and adjustments of the parameters in each step can be made according to the scheme of the present application, and these changes and adjustments should not be excluded from the protection scope of the present application.

[0050] Example 2

[0051] The application discloses a preparation method of an ultra-large high-width-ratio tilting AFM probe tip with controllable size and tilting angle.

[0052] 1. After cleaning the SOI wafer, spin-coat 200-400 nm PMMA photoresist on the SOI wafer, and bake at 180 DEG C for 1-2 minutes. The SOI wafer is composed of a device Si layer, an insulating SiO2 layer and a substrate Si layer, and the thicknesses of the device Si layer, the SiO2 layer and the substrate Si layer are 1-5 microns, 0.5-2 microns and 350-500 microns respectively.

[0053] 2. Expose the sample with spin-coated photoresist to an electron beam exposure machine, and the exposure dose is 500-1000 mJ / cm 2 . After exposure, develop the sample in a developing solution for 30-50 seconds, and then fix the sample in a fixing solution for 30-50 seconds.

[0054] 3. Directly deposit a 20-30 nm Cr or Ti metal film on the sample by using a thermal evaporation, electron beam evaporation or magnetron sputtering device, or first deposit a 3-5 nm Cr or Ti adhesion layer, and then deposit a 20-30 nm W, Pt or Au metal film.

[0055] 4. By using a liftoff process, immerse the sample after exposure and development in acetone, and soak at room temperature for 10-30 minutes, so that the photoresist naturally falls off, and the metal structure is left.

[0056] 5. By using photoetching and deep silicon etching Bosch process, etch the front and back surfaces of the sample to prepare the AFM probe cantilever part and the base part, and at this time, the metal structure part is in a suspended state. (Since this step is not the core step of the application, it is not described in detail. It should be noted that the Bosch process will have a lateral etching of tens of nanometers, so the silicon under the metal nanowire structure will be etched away.)

[0057] 6. Fold the metal nanowire structure by using focused ion beam irradiation, and by adjusting the ion beam irradiation parameters, the AFM probe tip in a vertical state or with different tilting angles is obtained.

[0058] The embodiments of the application are described in detail above, but the content described is only the preferred embodiments of the application, and is not used to limit the application. Any modification, equivalent replacement and improvement made within the application scope of the application should be included in the protection scope of the application.

Claims

1. A method for preparing a super-high aspect ratio tilting AFM probe tip with controllable size and tilting angle, characterized by comprising the following steps: In 1) spin-coating 200-400 nm PMMA photoresist on a clean SOI wafer surface, baking at 180°C for 1-2 minutes; 2) exposing the sample obtained in step 1) with an electron beam exposure machine, the exposure dose being 500-1000 mJ / cm2; after exposure, developing the sample in a developing solution for 30-50 seconds, and then fixing it in a fixing solution for 30-50 seconds to obtain a long groove pattern with a triangular tip; 3) directly depositing a 20-30 nm Cr or Ti metal film on the sample obtained in step 2) using a thermal evaporation film deposition device, an electron beam evaporation film deposition device or a magnetron sputtering film deposition device; 4) immersing the sample obtained in step 3) in acetone, and soaking it at room temperature for 10-30 minutes; 5) etching the sample to prepare the AFM probe cantilever part and the base part on the front and back surfaces of the sample obtained in step 4) respectively; 6) irradiating the metal nanowire structure with a focused ion beam to fold it. The SOI wafer in step 1) is composed of a device Si layer, an insulating SiO2 layer and a substrate Si layer, wherein the thicknesses of the device Si layer, the insulating SiO2 layer and the substrate Si layer are 1-5 microns, 0.5-2 microns and 350-500 microns respectively. Step 3) is replaced by step 3a) as follows: depositing a 3-5 nm Cr or Ti adhesion layer on the sample obtained in step 2) using a thermal evaporation film deposition device, an electron beam evaporation film deposition device or a magnetron sputtering film deposition device, and then depositing a 20-30 nm metal film. The metal of the metal film is selected from one or several of the following components: W, Pt, Au. Step 4) is implemented by using a liftoff process. In step 5), the front and back surfaces of the sample are etched by photolithography and deep silicon etching Bosch process respectively. In step 6), the AFM probe tip in a vertical state or with different tilting angles is obtained by adjusting the ion beam irradiation parameters.

2. The method of claim 1, wherein the method is characterized by: In step 1), the SOI wafer is cleaned by RCA standard process to achieve a clean surface without impurities under ultraviolet lamp inspection.

3. The method of claim 1, wherein the method further comprises: In step 1), the spin-coating conditions are: pre-rotation speed 500 r / min for 5 seconds, and post-rotation speed 4000 r / min for 40 seconds.

4. The method of claim 3, wherein the method further comprises: In step 2), the accelerating voltage of the electron beam exposure machine is 100 KeV, and the beam current is 100 pA.

5. The method of claim 1, wherein the method further comprises: ​ 6. The method of claim 1, wherein the method is further characterized by: ​ 7. The method of claim 1, wherein the method is further characterized by: ​ 8. The method of claim 1, wherein the method is further characterized by: ​ 9. The method of claim 1, wherein the method is further characterized by: ​ 10. The method of claim 1, wherein the method is further characterized by: ​

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