JP4535706B2 - Cantilever for scanning probe microscope and manufacturing method thereof - Google Patents

Description

  The present invention relates to a cantilever for a scanning probe microscope and a manufacturing method thereof.

  A scanning probe microscope (SPM) scans the surface of a sample with a cantilever probe close to the sample at an atomic diameter level, and scans the surface of the sample two-dimensionally. It is a device that detects light passing through an opening. SPM cantilevers are mainly manufactured from Si wafers by applying an IC manufacturing process. In this Si cantilever, the length direction and thickness direction of the lever portion are selected in parallel with the surface of the Si wafer, and the width direction of the lever portion is selected in the thickness direction of the silicon wafer. It is manufactured (see, for example, Patent Document 1).

JP 11-337563 A (second page, FIGS. 8 to 10)

  Since the SPM cantilever is often worn or contaminated by scanning the sample surface, a certain number of spares are usually prepared and replaced with new ones as necessary. In other words, since the cantilevers are treated as consumables, there must be no dimensional variation among the individual cantilevers, and it is desirable to produce as many cantilevers as possible from one semiconductor substrate from the viewpoint of cost reduction. ing. In the above prior art, since the length direction of the lever portion is selected to be parallel to the surface of the Si wafer, it is difficult to remove the material for arranging the cantilevers at a high density on the surface of the Si wafer, and it is difficult to reduce the manufacturing cost. .

(1) In the method of manufacturing a cantilever for a scanning probe microscope according to claim 1, a cantilever for a scanning probe microscope in which a probe portion is integrally formed at one end of a linear lever portion and a support portion is integrally formed at the other end is provided on a semiconductor substrate. A first step of forming a ridge line connected to the tip of the probe portion on the surface of the semiconductor substrate, and a second step of defining the length of the lever portion by etching in the thickness direction of the semiconductor substrate . and step, a third step of defining the thickness of the lever portion of the side surface of the lever portion exposed by the second step etching, by etching the tip of the lever portion exposed by the second step the probe a longitudinal section is parallel to the surface of the semiconductor substrate with the direction of the ridge, it has a a fourth step of three sides the shape of the probe portion in atomic dense surface is a triangular pyramid shape composed of, first 3 steps this performed with the fourth step The features.

(2) The invention of claim 2 is the method of manufacturing a cantilever for a scanning probe microscope according to claim 1, wherein the surface of the semiconductor substrate is selected as the (001) plane of the semiconductor material, and a triangular pyramidal probe portion These three surfaces are constituted by {111} surfaces .

(3) In the method for manufacturing a cantilever for a scanning probe microscope according to claim 1 or 2, an SOI wafer can be used as a semiconductor substrate. In this case, the length of the lever portion is preferably equal to the thickness of one Si layer of the SOI wafer.
(4) In the method for manufacturing a cantilever for a scanning probe microscope according to claim 1 or 2, a Si wafer can be used as a semiconductor substrate. In this case, the length of the lever portion is preferably equal to the depth obtained by removing the Si wafer in the thickness direction by the ICP-RIE method.
(5) The cantilever for a scanning probe microscope according to claim 7 is manufactured by the manufacturing method according to any one of claims 1 to 6.

  According to the present invention, a large number of cantilevers for a scanning probe microscope with no dimensional variation can be produced from a single semiconductor substrate.

Hereinafter, a cantilever for a scanning probe microscope according to the present invention (hereinafter referred to as an SPM cantilever) will be described with reference to FIGS.
FIG. 1 is a schematic configuration diagram schematically showing the configuration of the main part of the SPM to which the cantilever of the present embodiment is attached. The SPM cantilever 10 includes a lever 11, a probe 12, and a support 13, and is detachably held by a holder 14. That is, the holder 14 has a structure that holds the support 13 in a detachable manner, and supports the entire SPM cantilever 10. Examples of the attaching / detaching method include a method in which the support 13 is slid into the groove portion of the holder 14 and a method in which the support 13 is pressed by a leaf spring attached to the holder 14.
The lever 11 is, for example, a thin film having a length L = 150 μm, a thickness t = 2 μm, and a width 30 μm. The probe 12 is, for example, a triangular pyramid having a length d = 5 μm. The support 13 is a rectangular parallelepiped.

  The SPM measures the surface of the sample S as follows. When the probe 12 is brought close to the surface of the sample S at the atomic diameter level, the tip of the lever 11 is displaced by the interaction between the tip of the probe 12 and the surface of the sample S. This amount of displacement is measured by, for example, an optical lever method. That is, the amount of displacement can be measured by making the laser light that has passed through the optical fiber 15 incident on the back surface of the lever 11 and detecting the incident position of the reflected light by the two-divided photodiode 16. When the probe 12 is two-dimensionally scanned along the surface of the sample S, a displacement distribution map corresponding to the interaction is obtained.

  FIG. 2A is a perspective view illustrating the structure of the SPM cantilever 10 according to the present embodiment. 2B is a side view seen from the X direction, and FIG. 2C is a front view seen from the Y direction. FIG. 3 is a partially enlarged view of the main part of FIG. In FIG. 2A and FIG. 3, the direction of the lever 11 is represented by orthogonal coordinates in which the length direction is the Z direction, the thickness direction is the Y direction, and the width direction is the X direction.

Hereinafter, the SPM cantilever 10 will be described in detail with reference to these drawings.
FIG. 2 shows three cantilevers in the process of making a large number of cantilevers from a single wafer. As shown in the drawing, by cutting along two planes 29 parallel to the YZ plane, three SPM cantilevers 10 having the same size and shape can be obtained. The SPM cantilever is integrally manufactured from an SOI (Silicon on Insulator) wafer 100. The SOI wafer 100 is obtained by forming a SiO ₂ layer on one of _two Si single crystal plates and bonding them together via the SiO ₂ layer.

The SPM cantilever 10 has a probe 12 formed at one end of the lever 11 and a support 13 provided at the other end of the lever 11. The lever 11 and the probe 12 are formed from the upper Si layer 20 (indicated by a two-dot chain line) of the SOI wafer 100, and the support 13 is formed from the SiO ₂ layer 30 and the lower Si layer 40. That, SPM cantilever 10, only connecting portion between the lever 11 and the support 13 is SiO _2, the other consists of all Si. The length of the lever 11 is equal to the thickness of the upper Si layer 20.

  FIG. 3 is a perspective view of the main part showing the structure of the lever 11 and the probe 12 in detail. The lever 11 has a substantially quadrangular prism shape with a length L, a thickness t, and a width w. When the surface of the upper Si layer 20 is a main surface (001) (indicated by hatching), the length direction of the lever 11 is the Z direction, that is, the <001> direction. As will be described later, the (001) plane has a higher etching rate than the other planes, and is suitable for deep etching. Since the length L of the lever 11 is equal to the thickness of the upper Si layer 20, if the thickness of the upper Si layer 20 is managed, the length of the lever 11 can be adjusted very accurately.

  The probe 12 is a triangular pyramid having a length d having a longitudinal direction in the Y direction. This triangular pyramid has a shape obtained by cutting a triangular prism by a plane connecting vertices A, B, and C, and the vertex A is the tip of the probe 12. When the surface of the upper Si layer 20 is taken as the main surface (001), the orientations of the two surfaces divided by the ridge line 12a of the probe 12 are both {111} planes and are triangles connecting the vertices A, B, and C. Is also the {111} plane. The {111} plane is an atomic dense plane, and the vertex A where the three {111} planes intersect has high microscopic strength and high chemical stability. Therefore, the probe 12 has high wear resistance and corrosion resistance.

Since the probe 12 has a shape surrounded by three {111} planes, it has excellent shape reproducibility and stability. The length d of the probe 12 is determined by the crystal structure of the upper Si layer 20 and the height h of the ridge line structure having the ridge line 12a. In the case of a Si single crystal, the relationship between the length d of the probe 12 and the height h of the ridge line structure is d = 0.71h. Therefore, if the height h of the ridge line structure is accurately manufactured, reproducibility and stability of the length d of the probe 12 can be expected.
At the lower end of the lever 11, a triangular prism protrusion 14 resulting from a manufacturing process described later is formed. Moreover, the part displayed with a virtual line (two-dot chain line) is a part from which the upper Si layer 20 has been removed by the manufacturing process.

  Next, the manufacturing process of the SPM cantilever 10 according to the present invention will be described in detail with reference to FIGS. The manufacturing process proceeds in order from process (a) to (l) as shown in the partial perspective views of FIGS.

First, referring to FIG.
In step (a), an SOI wafer 100 is prepared. The SOI wafer 100 has a three-layer structure of an upper Si layer 20 having a thickness of 150 μm, an SiO ₂ layer 30 having a thickness of 1 μm, and a lower Si layer 40 having a thickness of 500 μm. The crystal orientation of the upper Si layer 20 is (001) in the XY plane, (110) in the ZX plane, and <110> in the Y direction. Hereinafter, for convenience of explanation, the surface of the SOI wafer 100 is divided into two parallel to <110>, which are defined as planes P1 and P2.

  In the step (b), a silicon nitride (SiN) layer 21 is formed on the upper Si layer 20 on the surface P2 by sputtering.

  In the step (c), anisotropic etching is performed on the surface of the surface P1 where the upper Si layer 20 is exposed using an aqueous KOH solution using the SiN layer 21 as a mask. At this time, a {111} plane is formed at the boundary with the SiN layer 21.

  In step (d), an oxide film 22 having a thickness of 200 nm is formed by local oxidation on the etching surface of the upper Si layer 20 on the surface P1. The oxidation method is steam oxidation using steam generated by reacting oxygen gas and hydrogen gas at a high temperature.

Reference is now made to FIG.
In step (e), the SiN layer 21 on the surface P2 is removed by RIE using the oxide film 22 on the surface P1 as a mask. That is, etching is performed at an etching rate of 12 nm / min using CF ₄ as a process gas.

  In the step (f), anisotropic etching is performed using a KOH aqueous solution on the surface of the upper Si layer 20 where the surface P2 is exposed.

  In the step (g), the oxide film 22 on the surface P1 is removed with a 50% hydrofluoric acid aqueous solution. On the surface of the upper Si layer 20, a linear protrusion (nanowire) 23 having a triangular cross section is formed at the boundary between the surfaces P1 and P2.

  In the step (h), a patterned thick film resist 24 is formed at the center of the nanowire 23. When viewed from the Z direction, the pattern shape of the thick film resist 24 is a rectangular shape with a narrow central portion and is symmetric with respect to the line segment 25. The thick film resist 24 is formed by applying a resist to the entire surface P1, P2 by a spin coater, baking at 110 ° C. on a hot plate, developing after ultraviolet exposure.

Next, referring to FIG.
In step (i), the columnar structure 26 is formed by deeply etching the upper Si layer 20 by ICP-RIE (inductively coupled plasma-reactive ion etching) using the patterned thick film resist 24 as a mask. The columnar structure 26 is a prototype of the lever 11 manufactured in a later process. Since the etching action by ICP-RIE is stopped by the SiO ₂ layer 30, the etching depth, in other words, the height of the columnar structure 26 is equal to 150 μm which is the thickness of the upper Si layer 20. After the etching, the surface of the SiO ₂ layer 30 is exposed.

ICP-RIE etches a sample under a relatively low pressure of 0.05 to 1 Pa using a chemical reaction between ions of a process gas in a high-density plasma and the sample surface. High etching processing is possible. As the process gas, an oxidizing gas such as CCl ₂ F ₂ or CF ₄ is used. In the case of Si, the main surface (001) has a higher etching rate than the {111} surface, and is thus removed preferentially.

  In step (j), the thick film resist 24 used as a mask is removed by RIE, that is, ashing using oxygen gas, a remover dedicated to resist, or a sulfuric acid / hydrogen peroxide solution (sulfuric acid: hydrogen peroxide = 3: 1). Thereafter, an oxide film having a thickness of 0.5 μm is formed on the entire surface of the columnar structure 26 to produce a columnar structure 27 covered with the oxide film.

  In the step (k), dicing is performed on the line segment 25 at right angles to the main surface (001). The columnar structure 27 is completely separated by dicing to form two columnar structures 28 having the same size and shape, but the lower Si layer 40 leaves the connection portion 41 without being completely separated. In FIG. 6 (d), the cut surface where the Si layer is exposed by dicing is indicated by hatching in one columnar structure 28 divided into two by dicing. This cut surface is the (110) plane.

  In step (l), anisotropic etching is performed on the (110) plane, which is a cut plane by dicing, using an aqueous KOH solution. The thickness t of the lever 11 is determined by the etching conditions of this anisotropic etching. For example, when an aqueous KOH solution of 70 ° C. and 30 wt% is used, the etching rate of the (110) plane of Si is about 0.8 μm / min. Therefore, the thickness t of the lever 11 can be adjusted by the etching time. In actual work, etching was performed while measuring the thickness of the lever 11 using a length measuring microscope, and finally t = 2 μm ± 0.2 μm was adjusted.

  On the other hand, the probe 12 is also formed by anisotropic etching using a KOH aqueous solution. As described above, the shape of the probe 12 is a triangular pyramid determined by the three {111} planes of a Si single crystal. Even if there are some errors in the etching conditions for anisotropic etching, the probe 12 always has the same shape. The needle 12 can be made. In the present embodiment, the height h of the nanowire 23 formed in the step (g) is formed at a desired height, and the length d of the probe 12 determined by the formula d = 0.71 h is 5 μm ± 0. Adjusted to 2 μm.

  After the step (l), the SPM cantilever 10 is completed by slicing the plane 29 at right angles to the main surface (001). The SPM cantilever 10 is attached to the SPM apparatus of FIG. When attaching, the probe 12 side may be slightly inclined so as to approach the sample S so that the projection 14 of the triangular prism formed at the lower end of the lever 11 does not contact the sample S.

Although a series of manufacturing processes for one SPM cantilever has been described above, the actual manufacturing process is a so-called batch process performed in units of SOI wafers.
FIG. 7 is a top view showing the arrangement of a plurality of columnar structures 27 on one SOI wafer 100. FIG. 7 is shown as a diagram corresponding to steps (i) to (k) described above. In FIG. 7, the line segment 25 in FIGS. 6A and 6B is represented as a cut surface 25 parallel to the X direction, and the plane 29 in FIG. 6E is a cut surface 29 parallel to the Y direction. It is expressed as For the columnar structure 27, the width and thickness of the lever 11 and the length of the probe 12 are represented by w, t, and d, respectively.

  In the present embodiment, the length direction of the lever 11 is the Z direction and depends only on the thickness of the upper Si layer 20, so that the lever 11 having an accurate length can be manufactured. Moreover, since the probe 12 is a triangular pyramid determined by three {111} of Si single crystal, the probe 12 having excellent reproducibility and stability can be obtained. Furthermore, since a large number of columnar structures 27 can be arranged at high density on one SOI wafer 100 and the material can be taken, more SPM cantilevers 10 can be produced from one SOI wafer 100, As a result, material waste is hardly generated. This leads to significant manufacturing cost reduction, especially in batch processing.

  Hereinafter, modified examples will be described. FIG. 8 is a partial cross-sectional view for explaining a modification of the SPM cantilever according to the present embodiment. In the step (g) of FIG. 5 described above, the nanowire 23 is formed at the boundary portion between the planes P1 and P2, and this cross-sectional shape is an isosceles triangle shown in FIG. The cross-sectional shape of the nanowire 23a shown in FIG. 8B is a right triangle whose surface P2 side is perpendicular to the main surface (001), and the cross-sectional shape of the nanowire 23b shown in FIG. The two slopes are curved surfaces, both of which can be applied to the present invention.

  In the case of FIG. 8B, instead of steps (d) to (f), a resist layer is formed on the surface P1, and the surface P2 is etched by ICP-RIE. In the case of FIG. 8C, instead of steps (b) to (f), a strip-shaped resist layer 31 is formed in the boundary region between the surfaces P1 and P2 in step (a), and isotropic etching is performed. To do. In any of the modifications, the manufacturing process is simplified as compared with the present embodiment.

Although an SOI wafer is used in this embodiment mode, a single crystal Si wafer can also be used. In the case of using a Si wafer, since there is no SiO ₂ layer 30 having a function of stopping the etching action of ICP-RIE in the above-described step (i), it is necessary to control the conditions of ICP-RIE. In order to obtain an etching depth of 150 μm with respect to the {100} surface of the Si wafer, for example, a (SF ₆ + C ₄ F ₈ ) mixed gas is used as a reaction gas, and a process is performed for about 50 minutes at a high frequency output of 600 W. . Since the Si wafer is cheaper than the SOI wafer, and only the process (i) is changed, all other processes are the same as those in the present embodiment, so that the manufacturing cost can be further reduced. .

It is a schematic block diagram which shows typically the structure of the principal part of SPM which attached the cantilever which concerns on embodiment of this invention. FIG. 2A is a perspective view showing the structure of the SPM cantilever according to the present embodiment, and FIG. 2B is a side view of the SPM cantilever in FIG. FIG. 2C is a front view of the SPM cantilever in FIG. 2A viewed from the Y direction. FIG. 3 is a partially enlarged view of FIG. It is a fragmentary perspective view for demonstrating the manufacturing process (ad) of the cantilever for SPM which concerns on embodiment of this invention. It is a fragmentary perspective view for demonstrating the manufacturing process (eh) of the cantilever for SPM which concerns on embodiment of this invention. It is a fragmentary perspective view for demonstrating the manufacturing process (i-1) of the cantilever for SPM which concerns on embodiment of this invention. It is a wafer top view for demonstrating arrangement | positioning of the several cantilever for SPM which concerns on embodiment of this invention. It is a fragmentary sectional view for explaining a modification of an embodiment of the invention.

Explanation of symbols

10: Cantilever for SPM 11: Lever 12: Probe 13: Support 14: Holder 20: Upper Si layer 30: SiO ₂ layer 30: Lower Si layer 25: Line segment (cut surface)
26, 27, 28: Columnar structure 29: Plane (cut surface)
100: SOI wafer

Claims (7)

A method of producing a cantilever for a scanning probe microscope, in which a probe part is integrally formed at one end of a linear lever part and a support part is integrally formed at the other end, from a semiconductor substrate,
A first step of forming a ridge line connected to the tip of the probe portion on the surface of the semiconductor substrate;
A second step of defining the length of the lever portion by etching in the thickness direction of the semiconductor substrate;
A third step of defining the thickness of the lever portion side of the lever portion exposed by the second step by etching,
The tip of the lever portion exposed in the second step is etched so that the longitudinal direction of the probe portion is the direction of the ridgeline and parallel to the surface of the semiconductor substrate, and the shape of the probe portion is atomically dense. possess a fourth step of three surfaces in face to triangular pyramid shape composed of,
The method of manufacturing a cantilever for a scanning probe microscope, wherein the third step is performed together with the fourth step . In the manufacturing method of the cantilever for scanning probe microscopes of Claim 1,
A method for manufacturing a cantilever for a scanning probe microscope, wherein the surface of the semiconductor substrate is selected as the (001) plane of the semiconductor material, and the three faces of the triangular pyramid-shaped probe portion are constituted by {111} planes . In the manufacturing method of the cantilever for scanning probe microscopes of Claim 1 or 2,
The method of manufacturing a cantilever for a scanning probe microscope, wherein the semiconductor substrate is an SOI wafer. In the manufacturing method of the cantilever for scanning probe microscopes of Claim 3,
The method of manufacturing a cantilever for a scanning probe microscope, wherein the length of the lever portion is equal to the thickness of one Si layer of the SOI wafer. In the manufacturing method of the cantilever for scanning probe microscopes of Claim 1 or 2,
The method of manufacturing a cantilever for a scanning probe microscope, wherein the semiconductor substrate is a Si wafer. In the manufacturing method of the cantilever for scanning probe microscopes of Claim 5,
A length of the lever portion is equal to a depth obtained by removing the Si wafer in the thickness direction by an ICP-RIE method, and a method for manufacturing a cantilever for a scanning probe microscope. A cantilever for a scanning probe microscope produced by the production method according to claim 1.

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