KR102084975B1 - Micro-cantilever structure for an atomic force microscope and manufacturing method of the same - Google Patents

Abstract

The present invention relates to a micro-cantilever structure for scanning a sample surface in an atomic force microscope (AFM), and a manufacturing method thereof. The micro cantilever structure of the present invention includes: a body unit (100); a bending cantilever (110) which extends from the body unit (100) and has a tip (111) formed at the front end thereof and a groove (112) formed at the lower end surface thereof so as to be bent in a tilting direction by the weight thereof; a piezoresistive displacement sensor circuit unit (210) mounted in the bending cantilever (110) to detect displacement in the tilting direction; and a heat-driven circuit unit (220) mounted in the bending cantilever (110) to tilt the bending cantilever by Joule′s heat.

Description

Micro-cantilever structure for an atomic force microscope and manufacturing method of the same}

The present invention relates to a microcantilever structure for scanning a sample surface in an atomic force microscope (AFM) and a method of manufacturing the same.

Scanning tunneling microscopy (STM), developed by G. Bignning in 1981, informed us of the laws and shapes of nature in the microworld and the three-dimensional view of the structure of atoms that were considered dreams. Made it possible. Scanning tunneling microscopy, however, was able to analyze the surface at high resolution using a tungsten probe, but had the limitation that it could only be used in conductors among various samples (conductors, semiconductors, insulators). In order to improve the shortcomings of the scanning tunneling microscope, an atomic force microscope (AFM) was developed by G. Bignning in 1986, and has high resolution (~ 1nm lateral, <0.1nm vertical resolution), quantitative 3-D information. It has the advantage that it can be used in analysis, analysis of various materials (conductors, semiconductors, insulators) and in various environments (air, solution and vacuum). In atomic force microscopy, instead of tungsten needles, a micromachined tip was used as a small rod called an integrated silicon cantilever, and the tip of the cantilever had a tiny probe, shaping the surface to the atomic level. can do. Conventional atomic force microscopy is used to bend the cantilever bent by the attraction and repulsion between the atom at the tip of the probe and the atom at the sample surface by approaching the sample surface on the bottom surface while the laser is illuminated on the upper surface of the cantilever tip. The surface is shown at the atomic level by measuring the laser beam angle using a photodiode. However, the laser-based optical apparatus used to measure the displacement of the cantilever complicates atomic microscope construction and makes it difficult to miniaturize. In order to solve this problem, various silicon-based cantilevers have been developed that integrate displacement sensors inside the cantilever to reduce and simplify the atomic microscope, but show a problem that the cantilever manufacturing process is complicated and the manufacturing cost increases.

Publication No. 10-2011-0078439 (published Jul. 7, 2011)

The present invention is to improve the problems of the prior art, the driving means for adjusting the position of the self in the tilting direction and the sensing means for measuring the displacement of the cantilever integrally integrated in the cantilever can reduce the atomic microscope It is an object of the present invention to provide a microcantilever structure having a tip easily accessible to a surface and a method of fabricating the same.

Micro cantilever structure according to the present invention for achieving this object, the body portion; A bending cantilever extending from the body portion, a tip formed at a tip end, and a groove formed at a bottom end thereof, the bending cantilever being bent in a tilting direction by its own weight; A piezoresistive displacement sensor circuit unit mounted on the bending cantilever to detect displacement in a tilting direction; And a thermal driving circuit unit mounted on the bending cantilever to tilt the driving of the bending cantilever by a row of rows.

Preferably, the tip is formed to protrude in parallel with the bending cantilever, the groove is composed of a plurality of the perpendicular to the longitudinal direction of the bending cantilever, the piezoresistance displacement sensor circuit portion is a Wheatstone disposed on the body portion It further comprises a bridge circuit.

Next, in the method of manufacturing a micro-cantilever structure according to the present invention, forming a concave-convex pattern corresponding to the groove on the substrate, coating SU-8 on the upper portion of the microcantilever structure, and removing a portion thereof to planarize the body portion and the bending cantilever. Forming a base pattern corresponding to the structure; A photolithography process is performed on the base pattern through an AZ-based photoresist to form a wiring pattern on which the piezoresistive displacement sensor circuit part and the thermal driving circuit part are to be formed, and a metal layer is deposited on the wiring pattern. A second step of manufacturing a conductive pattern for the piezoresistive displacement sensor circuit portion and the thermal drive circuit portion through a lift-off process; Coating a SU-8 on the substrate so as to cover the conductive pattern, and removing a portion thereof to integrally form an upper pattern on the base pattern; And a fourth step of separating the substrate from the micro-cantilever assembly manufactured in the third step.

Preferably, after the substrate is oxidized in the first step, the base pattern is formed, and in the fourth step, the oxide film is removed to separate the substrate from the microcantilever structure.

The micro-cantilever structure according to the present invention includes a bending cantilever extending from the body portion and having a tip formed at the tip and a groove formed at the bottom surface thereof, the bending cantilever being bent in the tilting direction due to its own weight, and the displacement in the tilting direction mounted on the bending cantilever. A piezoresistive displacement sensor circuit unit for detecting a and a thermal drive circuit unit for tilting the bending cantilever by a row of columns mounted on a bending cantilever can reduce the atomic microscope and facilitate tip access to the sample surface. Do.

In addition, the micro-cantilever structure of the present invention, the piezoresistive displacement sensor circuit portion has an uneven structure and the Wheatstone bridge circuit can be accurately measured the resistance change can be precise displacement measurement in the tilting direction.

In addition, the manufacturing method of such a micro cantilever structure has an advantage that can be easily manufactured through a batch process using a micro machining process.

1 is a perspective configuration diagram of a micro cantilever structure according to an embodiment of the present invention;
2 is a cross-sectional configuration diagram of a micro cantilever structure according to an embodiment of the present invention;
Figure 3 (a) (b) (c) is a view showing the operation example of the micro cantilever structure and the prior art cantilever according to an embodiment of the present invention,
4 is an enlarged plan view of a part of a micro cantilever structure according to an embodiment of the present invention;
Figure 5 (a) to (l) is a view briefly showing the manufacturing process of the micro cantilever structure according to an embodiment of the present invention.

Specific structural or functional descriptions presented in the embodiments of the present invention are only illustrated for the purpose of describing the embodiments according to the inventive concept, and the embodiments according to the inventive concept may be implemented in various forms. In addition, it is not to be construed as limited to the embodiments described herein, it should be understood to include all modifications, equivalents, and substitutes included in the spirit and scope of the present invention.

Meanwhile, terms such as first and / or second in the present invention may be used to describe various components, but the components are not limited to the terms. The above terms are for the purpose of distinguishing one component from other components only, for example, within the scope not departing from the scope of rights according to the concept of the present invention, the first component may be named as the second component, Similarly, the second component may also be referred to as the first component.

When a component is referred to as being "connected" or "connected" to another component, it is to be understood that the component may be directly connected or connected to that other component, but other components may be present in between. something to do. On the other hand, when a component is said to be "directly connected" or "directly contacted" to another component, it should be understood that no other component exists in the middle. Other expressions for describing relationships between components, such as "between" and "immediately between" or "adjacent to" and "directly adjacent to", should likewise be interpreted.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. The terms "comprises" or "having" herein are intended to indicate that there is a feature, number, step, action, component, part, or combination thereof that is implemented, and that one or more other features or numbers, It is to be understood that it does not exclude in advance the possibility of the presence or addition of steps, actions, components, parts or combinations thereof.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a perspective configuration diagram of a micro cantilever structure according to an embodiment of the present invention, Figure 2 is a cross-sectional configuration diagram of a micro cantilever structure according to an embodiment of the present invention.

1 and 2, the micro-cantilever structure according to an embodiment of the present invention, the body portion 100; A bending cantilever (110) extending from the body portion (100) and having a tip (111) formed at its tip and bending in a tilting direction (Z-axis direction) by its own weight; A piezoresistive displacement sensor circuit part mounted on the bending cantilever 110 and a thermal drive circuit part mounted on the bending cantilever 110 are included.

Body portion 100 has a rectangular (rectangle) structure having a predetermined thickness, the bending cantilever (110) having a tip (111) formed at the front end extending in a direction perpendicular to one edge is provided to support the bending cantilever (110). Preferably, the body portion 100 may be a material having excellent thermal expansion, and may be used as PDMS (Poly di-methyl siloxane) or SU-8. More preferably, the body portion 100 in the present invention is used SU-8, SU-8 is inexpensive compared to silicon (Si wafer) and the coefficient of thermal expansion is large, it is possible to drive a large displacement even at low driving temperature, The manufacturing process is easy and simple.

A plurality of ports 101 formed therethrough may be formed on the upper surface of the body part 100, and each port 101 may be in electrical contact with a piezoresistive displacement sensor circuit part and a thermal driving circuit part disposed inside the body part 100. Terminals are provided for.

The bending cantilever 110 has a strip shape having a narrow width extending from the body portion 100, and a pointed tip 111 is formed at a free end supported by the body portion 100 and capable of tilting. Preferably, the tip 111 protrudes on the same plane as the bending cantilever 110.

Preferably, as illustrated in FIG. 2, the bending cantilever 110 has a plurality of grooves 112 formed at a bottom surface thereof, and preferably, the groove 112 has a length of the bending cantilever 110. It is formed in a direction perpendicular to the direction (y-axis direction) (x-axis direction), and the bending cantilever 110 is bent by a predetermined angle (θ) in the tilting direction (Z-axis direction) by its own weight. The bending cantilever 110 is bent downward with respect to the body part 100 by its own weight (bending state), and the bending degree of the bending cantilever 110 is formed at the lower end of the fixed end of the bending cantilever 110. The width or number of grooves 112 may be appropriately determined.

Figure 3 (a) (b) (c) is a view showing the operation example of the micro cantilever structure and the conventional cantilever according to an embodiment of the present invention, (a) shows an embodiment according to the present invention (b) and (c) show cantilevers of the prior art.

As illustrated in (a) of FIG. 3, in the present invention, the tip 111 protruding from the free end of the bending cantilever 110 is formed to protrude on the same plane, and the bending cantilever 110 is formed of the body portion 100. It is arranged with an angle of inclination relative to the tip, so that the tip 111 can be easily accessed to the sample surface 1 during the scanning process.

On the other hand, as shown in the cantilever 10 of the prior art in Fig. 3 (b) (c), the tip (11a) (11b) which is formed to protrude perpendicularly to the bottom of the cantilever 10 is substantially a tip ( Due to alignment errors between the 11a) 11b and the cantilever 10, it is difficult to produce the tips 11a and 11b at the exact positions of the ends of the cantilever 10. Figure 3 (c) shows a case in which the tip (11b) is not exactly located at the end of the cantilever 10 of the prior art, in this case, in the scanning process is not a tip (11b) on the sample surface (1) The tip of the cantilever 10 is in contact and cannot accurately shape the sample surface 1.

4 is a partially enlarged plan view of the microcantilever structure according to the embodiment of the present invention.

Referring to FIG. 4, the bending cantilever 110 includes a piezoresistive displacement sensor circuit 210 that detects displacement in a tilting direction, and a thermal drive for tilting driving of the bending cantilever 110 by joule heat. And a circuit unit 220.

The piezoresistive displacement sensor circuit unit 210 is disposed at a fixed end of the bending cantilever 110 in a concave-convex structure so that a large change in the sensor resistance is generated during the tilting driving of the bending cantilever 110. The circuit unit 210 may be formed of the Wheatstone bridge circuits R1, R2, R3, and R4 disposed in the body part 100, thereby accurately measuring displacement of the bending cantilever 110.

The thermal drive circuit unit 220 is disposed in the body portion 100 and is connected to the terminals 221a and 222a and the conductive lines 221 and 222 to supply power through the terminals 221a and 222a.

Preferably, the thermal drive circuit unit 220 is formed in a section substantially adjacent to the groove 111 (see FIG. 1) formed on the bottom surface of the bending cantilever 110, and is formed by a row of heat applied to the thermal drive circuit unit 220. The driving in the tilting direction is performed by thermal expansion of the bending cantilever 110, which is a SU-8 material having a low spring constant.

The thermal drive circuit unit 220 adjusts the amount of heat generated by the power applied through the terminals 221a and 222a during the scanning process, thereby controlling displacement in the tilting direction, thereby maintaining a constant distance between the tip 111 and the sample surface. I can keep it.

Preferably, the piezoresistive displacement sensor circuit 210 and the thermal drive circuit 220 may be mounted inside the bending cantilever 110 and may be provided by depositing a conductive pattern such as Au.

Meanwhile, in order to prevent the heat generated during the operation of the thermal drive circuit unit 220 from affecting the piezoresistive displacement sensor circuit 210, a distance between the piezoresistive displacement sensor circuit 210 and the thermal drive circuit 220 is fixed. It is disposed apart from the above, in this case by pressing the position of the groove 112 with the thermal drive circuit unit 220 with respect to the piezoresistive displacement sensor circuit portion 210 disposed at the fixed end of the bending cantilever 110 by dropping the position from the fixed end A sufficient separation distance between the resistance displacement sensor circuit unit 210 and the thermal drive circuit unit 220 may be secured.

Such a microcantilever structure according to the present invention can be manufactured through a micromachining process, and the process will be described in detail below.

5 (a) to (l) is a view briefly showing the manufacturing process of the micro cantilever structure according to an embodiment of the present invention.

Referring to FIG. 5, in the method of manufacturing a microcantilever structure according to the present invention, a concave-convex pattern 21 corresponding to a groove is formed on a substrate 20, a SU-8 is coated on the upper portion thereof, and a portion thereof is removed. A first step of forming a base pattern 51 corresponding to the planar structure of the portion and the bending cantilever; A photolithography process is performed on the base pattern 51 through an AZ-based photoresist to form a wiring pattern on which the piezoresistive displacement sensor circuit part and the thermal driving circuit part are to be formed, and to deposit a metal layer on the wiring pattern. A second step of manufacturing a conductive pattern 60 for the piezoresistive displacement sensor circuit part and the thermal drive circuit part through a lift-off process; A third step of coating SU-8 on the substrate 20 so as to cover the conductive pattern 60 and removing a portion thereof to integrally form an upper pattern on the base pattern 51; And a fourth step of separating the substrate from the micro-cantilever assembly manufactured in the third step.

The first step is a process of forming a base pattern 51 corresponding to the planar structure of the body portion and the grip portion on the substrate 20.

Specifically, an oxide film (SiO ₂ ) 30 is formed to a thickness of 100 nm on the silicon (Si) 100 substrate 20 using an oxidation furnace (a) (b), followed by a spin coater. Coating the AZ5214 PR, patterning the coated PR through a photolithography process, and then etching the 100 nm thick oxide film (SiO ₂ ) using a BHF (6: 1) solution to pattern the oxide film (SiO ₂ ), The substrate 30 patterned with the oxide film SiO ₂ is placed in TMAH to etch silicon to form an uneven pattern 31 for forming grooves formed on the lower surface of the bending cantilever (c). Next, an oxide film (SiO ₂ ) 40 having a thickness of 300 nm is formed by using an oxide furnace on the substrate 20 obtained by etching the oxide film SiO ₂ using a BHF (6: 1) solution (d) ( e). Subsequently, SU-8 2002 (50) is coated to a thickness of 3 μm (f), and the coated SU-8 2007 (30) is formed through a photolithography process using a mask aligner to form a base pattern 51 (g). Meanwhile, in the present embodiment, the mask used in the photolithography process was L-edit program, and the mask was manufactured using the micro PG equipment.

The second step is to fabricate the conductive pattern 60 for the piezoresistive displacement sensor circuit and the thermal drive circuit on the base pattern 51. After coating AZ5214 on the base pattern 51 with a thickness of 2 μm, A photolithography process forms a wiring pattern for forming the piezoresistive displacement sensor circuit portion and the thermal drive circuit portion, and then deposits Cr (5 nm) / Au (200 nm) using an E-beam and lifts off the wiring pattern. The conductive pattern 60 is formed through a lift-off process (h).

The third step is a process of integrally forming a body pattern of SU-8 on the base pattern 51, specifically, the SU-8 2007 again on the oxide film 40 to cover the conductive pattern 60. 50 is coated with a thickness of 2 μm (i), and then the cantilever assembly is manufactured by integrally forming the upper pattern 71 on the base pattern 51 through the photolithography process (j).

Preferably, the cantilever assembly completed in the third step may be a process of forming a body pattern 72 on the upper portion of the body portion. As described above, the body pattern 72 is additionally formed to increase the thickness of the body portion, thereby easily operating the cantilever assembly. The manufacturing process of the body pattern 72 may be performed by coating SU-8 2100 with a thickness of 200 μm so as to cover the cantilever assembly on which the upper pattern 71 is formed (k).

In the fourth step, the cantilever assembly is separated from the substrate. The cantilever assembly bonded to the oxide film 40 on the substrate is removed from the substrate by removing the oxide film 40 having a thickness of 300 nm using a BHF (6: 1) solution. Separation can result in the final micro cantilever structure (i). On the other hand, the micro-cantilever structure separated from the substrate is a state in which the bending cantilever 110 with respect to the body portion 100 is formed at a predetermined angle (θ) in the tilting direction.

In the micro cantilever structure according to the present invention configured as described above, the tip is protruded in a direction parallel to the bending cantilever, and the bending cantilever is bent so as to have an inclination in the tilting direction with respect to the body portion, so that the tip is easily accessible to the sample surface. .

In addition, a piezoresistive displacement sensor circuit for detecting displacement in the tilting direction of the bending cantilever and a thermal drive circuit unit for driving in the tilting direction are integrated in the bending cantilever, so that the displacement of the cantilever can be accurately measured and Real-time response to rapid step changes in the sample surface is possible. In addition, the piezoresistive displacement sensor circuit portion and the thermal drive circuit portion are mounted inside the bending cantilever and can be used in various environments, so that they can be applied to research fields for 3D surface analysis.

The present invention described above is not limited to the above-described embodiments and the accompanying drawings, and various substitutions, modifications, and changes can be made without departing from the technical spirit of the present invention. It will be evident to those who have knowledge of.

100: body 111: tip
112: groove 110: bending cantilever
210: piezoresistive displacement sensor circuit portion 220: thermal drive circuit portion

Claims (6)

As a micro cantilever structure for an atomic microscope,
A body portion;
A bending cantilever extending from the body portion, a tip protruding at the tip end, and a groove formed at the bottom surface thereof, the bending cantilever being bent in a tilting direction by its own weight;
A piezoresistive displacement sensor circuit unit mounted on the bending cantilever to detect displacement in a tilting direction;
A microcantilever structure for an atomic force microscope including a thermal drive circuit for tilting the bending cantilever by a row of wires mounted on the bending cantilever. The microcantilever structure of claim 1, wherein the tip protrudes alongside the bending cantilever. The micro-cantilever structure for an atomic microscope according to claim 1, wherein the groove is composed of a plurality of grooves at right angles to the longitudinal direction of the bending cantilever. The microcantilever structure of claim 1, wherein the piezoresistive displacement sensor circuit further comprises a Wheatstone bridge circuit disposed on the body portion. In the method for producing a micro-cantilever structure for an atomic microscope according to claim 1,
Forming a base pattern corresponding to the planar structure of the body portion and the bending cantilever by forming a concave-convex pattern corresponding to the groove on the substrate, coating SU-8 on an upper portion thereof, and removing a portion thereof;
A photolithography process is performed on the base pattern through an AZ-based photoresist to form a wiring pattern on which the piezoresistive displacement sensor circuit part and the thermal driving circuit part are to be formed, and a metal layer is deposited on the wiring pattern. A second step of manufacturing a conductive pattern for the piezoresistive displacement sensor circuit part and the thermal drive circuit part through a lift-off process;
Coating a SU-8 on the substrate so as to cover the conductive pattern and removing a portion thereof to integrally form an upper pattern on the base pattern;
Method of manufacturing a micro-cantilever structure for an atomic microscope comprising a fourth step of separating the substrate and the micro-cantilever assembly manufactured in the third step. The microcantilever structure of claim 5, wherein the base pattern is formed after the substrate is oxidized in the first step, and the substrate and the microcantilever structure are separated by removing the oxide film in the fourth step. How to make.

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