Preparation method of atomic-scale precision knife edge
By preparing the metal film on the SOI wafer and the lapse, etching and wet etching on the SOI wafers, forming a different knife mouth along the 110 crystal surface solves the inconsistency of the edge edge of the knife in the existing technology and the unable to achieve two -way cutting. The problem has realized the preparation of atomic -level precision, and has the advantages of high -precision cutting and large -scale production.
Patent Information
- Application Number
- CN202411522427.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-10-29
- Publication Date
- 2025-01-24
AI Technical Summary
The prior art is difficult to prepare atomic precision cutter with consistent edge sharpness, able to completely prevent electron beam transmission and having two-way cutting capabilities.
Using SOI wafers as raw materials, a conductive metal film is prepared on the wafer surface, and photolithography and etching are performed. Combined with wet etching technology, anisotropic etching is performed along the 110 crystal plane to form a knife edge with atomic level precision.
The prepared knife edge has consistent sharpness, can completely prevent electron beam transmission, and has high-precision two-way cutting capabilities, making it suitable for mass production and industrial applications.
Smart Images
Figure CN119361431A_ABST
Abstract
Description
Technical Field
[0001] The invention belongs to the field of electronic technology and relates to a method for preparing a knife edge with atomic-level precision. Background Art
[0002] For instruments that use electron beams, such as scanning electron microscopes, transmission electron microscopes, and electron beam lithography machines, the beam spot of the electron beam is often only a few hundred nanometers or even a few nanometers. The measurement of parameters such as the current density and shape of the beam spot requires a precise cutting method, that is, the sharpest blade needs to be formed. For example, two blades at a certain angle can unitize electron beam spots as small as a few nanometers. Combined with analysis software, Faraday cups and other measuring instruments, precise measurements of electron beam spots can be performed. Therefore, obtaining the sharpest blade is of great guiding significance for the evaluation of electron beam spots and the improvement of electron beam micro-nano processing capabilities.
[0003] Conventional knife edge preparation methods can use inductively coupled plasma etching (ICP), reactive ion etching (RIE) and other etching methods, but the knife edge prepared by these methods has a verticality of about 90±1°, and the edge sharpness is limited, and there is usually a certain fluctuation, that is, the sharpness of different areas of the knife edge is inconsistent, making it difficult to improve the cutting accuracy of the ion beam. Another common knife edge preparation method is the crystal splitting method, which uses semiconductor materials such as single crystal silicon or gallium arsenide as raw materials and prepares the knife edge by splitting along the crystal direction. However, this method has a certain degree of randomness and is easy to deviate from the preset split crystal direction. Its preparation process usually cannot directly process the cross-section area, so the flatness of the cross section cannot be ensured. In particular, this knife edge only has one sharp edge and can cut the electron beam in one direction, but it is not directly applicable to situations where the cross-sectional shape of the electron beam needs to be accurately measured. In addition, the material type and thickness of the blade are closely related to the electron beam energy. Taking a 50keV electron beam as an example, when the thickness of the blade is too thin, it cannot completely prevent the electron beam from transmitting, making it difficult to achieve precise measurement of the electron beam spot.
[0004] Therefore, obtaining a method for preparing a knife edge with atomic-level precision that has consistent sharpness in different edge areas, can completely prevent electron beam transmission and directly has two-way cutting capabilities is of great significance for improving electron beam micro-nano processing capabilities. Summary of the invention
[0005] The technical problem to be solved by the present invention is to provide a method for preparing a knife edge with atomic-level precision that has consistent sharpness in different edge areas, can completely prevent electron beam transmission and directly has two-way cutting capability in view of the deficiencies in the prior art.
[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is: A method for preparing a knife edge with atomic-level precision comprises the following steps: S1. Provide SOI wafer; S2, cleaning the surface of the SOI wafer; S3, calibrating the crystal orientation of the top silicon surface of the SOI wafer to determine the 111 crystal orientation of the top silicon; S4, preparing a conductive metal film on the front and back surfaces of the SOI wafer; S5, performing photolithography and etching on the front and back sides of the SOI wafer, so that the conductive metal films on the front and back sides of the SOI wafer form windows corresponding to the target patterns; S6, wet-etching the SOI wafer to form a target cross section; S7. Remove the silicon oxide layer of the SOI wafer and complete the preparation of the knife edge with atomic-level precision.
[0007] The above preparation method is further improved, in step S1, the SOI wafer includes a single crystal top silicon layer along the 110 crystal direction, a silicon oxide layer and a single crystal silicon layer along the 100 crystal direction, which are sequentially arranged from top to bottom.
[0008] The above preparation method is further improved in that the thickness of the single crystal top silicon layer is greater than 21 μm.
[0009] The above preparation method is further improved in that the resistivity of the single crystal top silicon layer is less than 0.02Ω.cm.
[0010] The above preparation method is further improved in that the thickness of the silicon oxide layer is 100nm to 1μm.
[0011] The above preparation method is further improved in that the thickness of the single crystal silicon layer along the 100 crystal direction is 300 μm to 700 μm.
[0012] The above preparation method is further improved, in step S3, the 111 crystal orientation of the top silicon is determined by any of the following methods; Method 1: Use X-ray testing method to calibrate the crystal orientation and determine the 111 crystal orientation of the top silicon.
[0013] Method 2 includes the following steps: selecting a 111 crystal orientation edge, exposing a grating array distributed at a certain angle, wet etching the top silicon of the SOI wafer using potassium hydroxide, finding the one with the most symmetrical etched hole morphology in the grating array, and using its direction as the 111 crystal orientation of the top silicon.
[0014] The above preparation method is further improved, in step S4, a conductive metal film is prepared on the front and back surfaces of the SOI wafer by evaporation.
[0015] The above preparation method is further improved, in step S4, the thickness of the conductive metal film is 10nm to 100nm.
[0016] The above preparation method is further improved, in step S4, the thickness of the conductive metal film is 60nm to 100nm.
[0017] The above preparation method is further improved, in step S4, the material of the conductive metal film is one of iridium, tungsten, tantalum and gold, wherein the back coating needs to ensure the density of the metal, thereby ensuring that the wet etching will not affect the area outside the etching opening.
[0018] The above preparation method is further improved, in which in step S5, ion beam etching is used to etch the front and back sides of the SOI wafer.
[0019] The above preparation method is further improved in that in step S6, potassium hydroxide solution is used to wet etch the SOI wafer.
[0020] The above preparation method is further improved in that the mass fraction of the potassium hydroxide solution is 35% to 50%; and the temperature of the potassium hydroxide solution is 70° C. to 99° C.
[0021] The above preparation method is further improved, in step S7, a hydrofluoric acid diluent (BOE) is used to etch the silicon oxide layer of the SOI wafer to remove the silicon oxide layer of the SOI wafer.
[0022] The above-mentioned preparation method is further improved. In step S7, the opening shape of the top of the blade is a rectangle, a square or a boat-shaped hole; one of the sides of the top of the blade is parallel to the 111 crystal direction; the side length of the top of the blade is 1μm to 50μm; when the shape of the top of the blade is a boat-shaped hole, the internal angles are 125.5°, 109.5° and 125°; the top of the blade is formed with a side wall of 90±0.1°.
[0023] The above preparation method is further improved, in step S7, the bottom of the blade is centered on the opening at the top; the opening shape of the bottom of the blade is a square; the side length of the bottom of the blade is 100μm to 800μm.
[0024] Compared with the prior art, the advantages of the present invention are: (1) In view of the defects of existing knife edge preparation methods, such as limited edge sharpness, inconsistent sharpness of different areas of the knife edge, inability to ensure the flatness of the cross section, and difficulty in directly forming knife edge combinations in different directions, the present invention provides a knife edge preparation method with atomic-level precision. Using SOI wafer as raw material, a conductive metal film is first prepared on the surface of the SOI wafer. On the one hand, during the knife edge preparation process, the presence of the conductive metal film can ensure that wet etching does not affect the area outside the etching opening, which is beneficial to maintaining the stability of the support structure. On the other hand, the conductive metal film on the knife edge surface is beneficial to enhancing the conductivity of the upper and lower surfaces of the knife edge and preventing charge accumulation. On this basis, the single crystal silicon in the SOI wafer is anisotropically wet etched. During the wet etching process, the solution is etched along 11 The etching speed of the 0 surface is more than 600 times that of the 111 surface, so that etching can be performed accurately along the crystal plane, etching one atom thick laterally and more than 600 atoms thick longitudinally. Therefore, the side wall of the blade has atomic-level precision. By etching the top 110 silicon hole, two non-parallel edges will be formed, which are perpendicular to the bottom surface. Since the selectivity of wet etching along the crystal direction is extremely high, two sharp blades with a certain angle and excellent verticality are obtained, and a side wall of 90±0.1° can be formed on the top, making the blade have higher precision and able to achieve precise cutting of the electron beam spot. At the same time, in the wet etching process, the etching stability is higher, and the direction of the pattern opening is determined. One etching can have two non-parallel sections, which can cut the electron beam in two directions. In addition, an inverted pyramid is formed by etching the bottom silicon, and a square window is obtained by cutting the lower surface of silicon oxide with the inverted pyramid. Silicon oxide is selectively etched by the action of hydrofluoric acid dilution (BOE) to form a through-hole structure from the top silicon hole to the bottom silicon hole. The edge of the through-hole is determined by the top silicon etching edge, ensuring that the electron beam spot is cut by two knife edges with angles to each other and vertical edges. In addition, the unetched part of the bottom silicon plays a supporting role in the overall structure. The edge of the knife edge prepared by the preparation method of the present invention has the same sharpness in different areas, and a side wall of 90±0.1° is formed on the top, with good verticality, which can completely prevent the transmission of the electron beam, and can achieve high-precision cutting in two directions. At the same time, it has the advantage of multiple pieces output in one round of process, which is suitable for large-scale production and convenient for industrial application. It is of great significance for the evaluation of electron beam spot and electron beam micro-nano processing capabilities.
[0025] (2) In the present invention, by optimizing the thickness of the single crystal top silicon layer in the SOI wafer to be greater than 21 μm and the resistivity of the single crystal top silicon layer to be less than 0.02 Ω.cm, the knife edge can play a role in blocking the electron beam and completely prevent the electron beam from penetrating.
[0026] (3) In the present invention, by optimizing the thickness of the conductive metal film to be 10 nm to 100 nm, particularly 60 nm to 100 nm, the conductive metal film can be ensured to have good compactness while also avoiding adverse effects on the intensity distribution of the electron beam spot. BRIEF DESCRIPTION OF THE DRAWINGS
[0027] In order to make the purpose, technical solution and advantages of the embodiments of the present invention more clear, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention.
[0028] Figure 1 This is a flow chart of the process for preparing a knife edge with atomic-level precision in Example 1 of the present invention.
[0029] Figure 2 This is a top view of the bottom of the knife edge with atomic-level precision in Example 1 of the present invention.
[0030] Figure 3 Schematic diagram of the structure of the top of the knife edge with atomic level precision in Example 1 of the present invention. DETAILED DESCRIPTION
[0031] The present invention is further described below in conjunction with the accompanying drawings and specific preferred embodiments, but the protection scope of the present invention is not limited thereby.
[0032] Embodiment 1: A method for preparing a knife edge with atomic-level precision, the schematic diagram of the preparation process is as follows Figure 1 As shown, the following steps are included: S1. Provide an SOI wafer, wherein the SOI wafer includes a single crystal top silicon layer along a 110 crystal direction, a silicon oxide layer, and a single crystal silicon layer along a 100 crystal direction, which are arranged in sequence from top to bottom, wherein the single crystal top silicon layer has a thickness of 22 μm, a resistivity of the single crystal top silicon layer of 0.01 Ω.cm, a thickness of the silicon oxide layer of 800 nm, and a thickness of the single crystal silicon layer along the 100 crystal direction of 500 μm.
[0033] S2. Clean the surface of the SOI wafer to remove surface impurities.
[0034] S3, calibrate the crystal orientation of the top silicon surface of the SOI wafer to determine the 111 crystal orientation of the top silicon, specifically: A 111 crystal direction edge is roughly selected on the top silicon surface of the SOI wafer, and a grating array distributed at a certain angle is exposed. Potassium hydroxide is used to wet-etch the top silicon of the SOI wafer, and the one with the most symmetrical etched hole morphology in the grating array is found, and this direction is taken as the actual 111 crystal direction of the top silicon. In another embodiment, the crystal direction calibration can also be performed by X-ray testing.
[0035] S4. Prepare a conductive metal film on the front and back surfaces of the SOI wafer. Specifically, prepare the conductive metal film on the front and back surfaces of the SOI wafer by evaporation. The thickness of the conductive metal film is 100 nm, and the material of the conductive metal film is gold.
[0036] S5. Photolithography and etching are performed on the front and back sides of the SOI wafer to form windows corresponding to the target pattern on the conductive metal films on the front and back sides of the SOI wafer, specifically: S5-1. Place the mask pattern on the front side of the SOI wafer, prepare a mask on the front side of the SOI wafer to form a target mask pattern, perform photolithography on the mask, form a window to be etched on the front surface of the SOI wafer, and then etch the conductive metal film on the front side of the SOI wafer by ion beam etching (IBE) to carve out a window corresponding to the designed pattern (target pattern) in the conductive metal film.
[0037] S5-2. Place the mask pattern on the back side of the SOI wafer, prepare a mask on the back side of the SOI wafer to form a target mask pattern, photolithograph the mask to form a window to be etched on the back surface of the SOI wafer, and then etch the conductive metal film on the back side of the SOI wafer by ion beam etching (IBE) to carve a window corresponding to the designed pattern (target pattern) in the conductive metal film.
[0038] S6. Wet-etch the SOI wafer using a potassium hydroxide solution with a mass fraction of 40% and a temperature of 80° C. to remove the top silicon layer and the bottom silicon layer of the SOI wafer, and form target cross sections on both sides of the SOI wafer.
[0039] S7, using hydrofluoric acid dilution (BOE) to etch the silicon oxide layer of the SOI wafer, remove the silicon oxide layer of the SOI wafer, and obtain two sidewall vertical blade edges and a through-hole area at a certain angle. The method of the present invention can obtain dozens to dozens of blade edges through one round of process flow according to the size of the dicing.
[0040] like Figure 2 and Figure 3 As shown, the top opening of the knife edge prepared in this embodiment is a boat-shaped hole, one of the sides of the top of the knife edge is parallel to the 111 crystal direction, the side length of the top of the knife edge is 33 μm, the internal angles of the boat-shaped hole are 125.5°, 109.5° and 125°, and the top of the knife edge is formed with a side wall of 90±0.1°. Figure 2 As shown, the bottom of the blade is centered on the opening at the top, the opening shape of the bottom of the blade is a square, and the side length of the bottom of the blade is 430 μm.
[0041] After testing, in the preparation method of this embodiment, a vertical section can be formed in a specific direction on the upper surface of the SOI wafer by wet etching, as shown in FIG. Figure 3As shown in the figure, the four bold edges correspond to the vertical sections formed in the direction of the 111 crystal plane during the wet etching process of the 110 crystal orientation silicon single crystal, that is, the two cutting edges of the knife edge, and at the same time, an inverted trapezoidal opening is formed on the lower surface of the SOI wafer. The top of the prepared knife edge forms a side wall of 90±0.1° with atomic-level precision. In addition, the thickness of the knife edge is greater than 21um, that is, one side of the knife edge can completely cut off the electron beam, which can effectively prevent the electron beam from transmitting.
[0042] It can be seen from the above results that, compared with the conventional method, the blade prepared by the preparation method of the present invention has the same sharpness in different edge areas, and a side wall of 90±0.1° is formed on the top, which can completely prevent the transmission of the electron beam, can directly achieve high-precision cutting in two directions, and has the advantage of outputting multiple pieces in one round of process. It also has the advantages of simple process, easy operation, low cost, etc. It is suitable for large-scale production and convenient for industrial application. It is of great significance for the evaluation of electron beam spot and electron beam micro-nano processing capabilities.
[0043] The above embodiments are only preferred implementations of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions under the concept of the present invention belong to the protection scope of the present invention. It should be pointed out that for ordinary technicians in this technical field, improvements and modifications without departing from the principle of the present invention should also be regarded as the protection scope of the present invention.
Claims
1. A method for preparing a knife edge with atomic level precision, characterized in that: The following steps are involved: S1. Provide SOI wafer; S2, cleaning the surface of the SOI wafer; S3, calibrating the crystal orientation of the top silicon surface of the SOI wafer to determine the 111 crystal orientation of the top silicon; S4, preparing a conductive metal film on the front and back surfaces of the SOI wafer; S5, performing photolithography and etching on the front and back sides of the SOI wafer, so that the conductive metal films on the front and back sides of the SOI wafer form windows corresponding to the target patterns; S6, wet-etching the SOI wafer to form a target cross section; S7. Remove the silicon oxide layer of the SOI wafer and complete the preparation of the knife edge with atomic-level precision.
2. The preparation method according to claim 1, characterized in that: In step S1, the SOI wafer includes a single crystal top silicon layer, a silicon oxide layer and a single crystal silicon layer along the 100 crystal direction, which are arranged in sequence from top to bottom; the thickness of the single crystal top silicon layer is greater than 21 μm; the resistivity of the single crystal top silicon layer is less than 0.02 Ω.cm; the thickness of the silicon oxide layer is 100 nm to 1 μm; the thickness of the single crystal silicon layer along the 100 crystal direction is 300 μm to 700 μm.
3. The preparation method according to claim 2, characterized in that: In step S3, the 111 crystal orientation of the top silicon is determined by any of the following methods; Method 1: Use X-ray testing to calibrate the crystal orientation and determine the 111 crystal orientation of the top silicon. Method 2 includes the following steps: selecting a 111 crystal orientation edge, exposing a grating array distributed at a certain angle, wet etching the top silicon of the SOI wafer using potassium hydroxide, finding the one with the most symmetrical etched hole morphology in the grating array, and using its direction as the 111 crystal orientation of the top silicon.
4. The preparation method according to any one of claims 1 to 3, characterized in that In step S4, a conductive metal film is prepared on the front and back surfaces of the SOI wafer by evaporation; the thickness of the conductive metal film is 10nm to 100nm; the material of the conductive metal film is one of iridium, tungsten, tantalum and gold.
5. The preparation method according to claim 4, characterized in that: In step S4, the thickness of the conductive metal film is 60 nm to 100 nm.
6. The preparation method according to any one of claims 1 to 3, characterized in that: In step S5, the front and back sides of the SOI wafer are etched by ion beam etching.
7. The preparation method according to any one of claims 1 to 3, characterized in that In step S6, a potassium hydroxide solution is used to wet-etch the SOI wafer; the mass fraction of the potassium hydroxide solution is 35% to 50%; and the temperature of the potassium hydroxide solution is 70° C. to 99° C.
8. The preparation method according to any one of claims 1 to 3, characterized in that In step S7, a hydrofluoric acid dilution solution is used to etch the silicon oxide layer of the SOI wafer to remove the silicon oxide layer of the SOI wafer.
9. The preparation method according to any one of claims 1 to 3, characterized in that: In step S7, the opening shape of the top of the blade is a rectangle, a square or a boat-shaped hole; one of the sides of the top of the blade is parallel to the 111 crystal direction; the side length of the top of the blade is 1μm to 50μm; when the shape of the top of the blade is a boat-shaped hole, the internal angles are 125.5°, 109.5° and 125°; the top of the blade is formed with a side wall of 90±0.1°.
10. The preparation method according to claim 9, characterized in that: In step S7, the bottom of the blade is centered on the opening at the top; the opening shape of the bottom of the blade is a square; and the side length of the bottom of the blade is 100 μm to 800 μm.