JPH06307852A - Integrated afm sensor and its manufacture - Google Patents

Abstract

PURPOSE:To provide an integrated AFM sensor equipped with a high resolution and establish a method for manufacturing the sensor. CONSTITUTION:An integrated AFM sensor is composed of a cantilever supporting part 103 made of glass etc., a cantilever 101 made of silicon, etc., whose one end is supported by the supporting part 103, a resistance layer 104 of silicon with boron dispersed and sensing the displacement of the cantilever installed on the surface of the cantilever 101, a probe 102 made of silicon nitride installed at the rear surface of the free end of the cantilever 101, and an electrode 105 connected with the resistance layer 104.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an integrated AFM sensor used in an atomic force microscope and a manufacturing method thereof.

[0002]

2. Description of the Related Art Conventionally, a scanning tunneling microscope (STM: Scanni), which was invented by Binning and Rohrer, was used as an apparatus for observing a conductive sample with a resolution of atomic size order.
ng Tunneling Microscope), but in STM, the samples that can be observed are limited to conductive ones.

Therefore, an atomic force microscope is used as a microscope capable of observing an insulating sample, which has been difficult to measure with STM, with an accuracy of atomic size order while utilizing elemental technologies such as servo technology in STM. (AF
M) was proposed. This AFM is disclosed, for example, in Japanese Patent Laid-Open No. 62-
130302 (patent applicant: IBM, inventor: G. Binnig, title of invention: method and apparatus for forming an image of a sample surface).

The structure of the AFM is similar to that of the STM and is positioned as one of scanning probe microscopes.
In the AFM, a cantilever having a sharp protruding portion (probe portion) at its free end is arranged facing and close to the sample, and due to the interaction force acting between the atom at the tip of the probe and the sample atom, While measuring the function of the displacing cantilever electrically or optically, the sample is scanned in the XY directions, and the positional relationship between the cantilever and the probe part is relatively changed, thereby It is now possible to capture three-dimensional information such as irregularity information on the order of atomic size.

In the AFM, the displacement measuring sensor for measuring the displacement of the cantilever is generally provided separately from the cantilever. However, recently, an integrated AFM sensor with a function that can measure displacement on the cantilever itself has been developed by M.
Proposed by Tortonese et al. This integrated AFM
The sensor may be, for example, M. Tortonese, H. Yamada, RC.
Barrett and CF Quate: Transducers and Sensors'
91: Atomic forcemicroscopy using a piezoresistiv
e cantilever.

The piezoresistive effect is used as the measuring principle of this integrated AFM sensor. That is, when the tip of the cantilever is brought close to the measurement sample, the cantilever bends due to the interaction between the tip and the sample, causing distortion. A resistance layer is laminated on the cantilever portion, and its resistance value changes according to the strain of the cantilever portion. Therefore, if a constant voltage is applied to the resistance layer from the electrode part,
The current flowing through the resistance layer changes according to the amount of strain of the cantilever, and the amount of displacement of the cantilever can be known by detecting the change in the current.

Since such an integrated AFM sensor has an extremely simple structure and is small in size, it is expected that a so-called stand-alone AFM in which the cantilever side is moved can be formed. In the conventional AFM, since the sample is moved in the XY directions to change the relative positional relationship between the tip of the cantilever and the probe, the size of the sample is limited to about several cm at the maximum. There is an advantage that the limitation of the size of the sample can be removed.

Next, the integrated AFM sensor will be described with reference to the drawings. First, the manufacturing method will be described with reference to FIGS. Start wafer 50
As shown in FIG. 5A, a silicon wafer 501 on which a silicon layer 503 is provided via a silicon oxide separation layer 502, for example, a bonded wafer is prepared. Next, as shown in FIG. 5B, boron (B) is implanted into the extreme surface of the silicon layer 503 by ion implantation to form a piezoresistive layer 504, which is shown in FIG. After patterning in the shape of a cantilever, the surface is covered with a silicon oxide film 505. Then, a hole for bonding is formed on the fixed end side of the cantilever, and aluminum is sputtered to form the electrode 506. Furthermore, an etching mask layer is formed on the lower side of the silicon wafer 501.
Form 507. Then, as shown in FIG.
Using the etching mask layer 507 as a mask, the silicon wafer 501 is etched up to the separation layer 502 with a KOH aqueous solution. Finally, the separation layer 502 is removed with a hydrofluoric acid aqueous solution to form a cantilever beam portion 508, and the integrated AFM sensor shown in FIG. 6 is completed.

In the integrated AFM sensor thus manufactured, a DC voltage of several volts or less is applied between the two electrodes 506 at the time of measurement to bring the tip of the cantilever 508 close to the sample. When the interaction between the tip of the cantilever 508 and the atoms on the sample surface acts, the cantilever 508 is displaced. Since the resistance value of the piezoresistive layer 504 changes according to this, the displacement of the cantilever 508 is obtained as a current signal flowing between the two electrodes 506.

[0010]

However, in the above-mentioned conventional integrated type AFM sensor, in reality, the probe which is indispensable for performing high resolution AFM measurement has not been manufactured, and the probe at the tip of the lever is not actually manufactured. The development of an integrated AFM sensor with a needle has been awaited. Further, in the conventional fabrication of the integrated AFM sensor proposed by M. Tortonese et al., The support portion holding the cantilever portion is also fabricated using one silicon wafer as a start wafer, and the thickness and length of each portion are However, the controllability is not always good. For example, the thickness of the silicon wafer is 525μm ± 4mm for the 4 inch diameter wafer which is the most widely available on the market.
It is about 20 μm and has variations. M. Tortone
se et al. processed the silicon wafer from the surface into a U-shape and then etched the silicon wafer from the bottom to form a cantilever. At this time, the cantilever length was about the thickness variation. The variability of was inevitable.

The present invention has been made to solve the above problems in the conventional integrated AFM sensor, and provides a high resolution integrated AFM sensor which is easy to manufacture and has good controllability, and a manufacturing method thereof. The purpose is to

[0012]

SUMMARY OF THE INVENTION In order to solve the above problems, the present invention provides a support portion of a cantilever, a cantilever arranged so as to extend from the support, and the cantilever. A displacement detecting portion for detecting the displacement of the cantilever provided on the surface of the cantilever, and a silicon provided on the back end which is a free end of the cantilever and is opposite to the supporting portion with respect to the cantilever. An integrated AFM sensor is configured with a probe portion made of a compound.

Since the integrated type AFM sensor having such a structure is provided with the probe portion made of a silicon compound,
It becomes possible to perform high resolution AFM measurement.

Further, the manufacturing method according to the present invention comprises the steps of forming a replica hole for the probe portion on the surface of the substrate by etching, and thermally oxidizing the substrate to form an oxide film inside the replica hole. A step of depositing a base material of the probe portion on a substrate including the replica hole, a step of etching the base material into a predetermined shape, and an impurity diffusion layer for displacement detection in a predetermined region on the surface of the substrate. , A step of covering the surface of the substrate on which the impurity diffusion layer is formed with a protective film, a step of forming a cantilever pattern on the surface of the substrate, and a part of the protective film being opened to diffuse impurities. A step of exposing a part of the layer, a step of forming an Al electrode pattern on the protective film opening, a step of joining a cantilever support member to the substrate surface, and a cantilevered surface layer of the substrate. Leaving the beam thickness The back surface is intended to produce an integrated AFM sensor in the step of etching away.

In such a manufacturing method, since the supporting member of the cantilever is formed by bonding to the surface of the substrate, the processing can be performed only from the surface of the substrate, so that the manufacturing is simplified. Further, the length of the cantilever depends only on the alignment accuracy at the time of joining the support members and is not affected by the substrate thickness error, so that the controllability is improved. Further, by forming the probe portion with the base material deposited in the replica hole, the probe portion with a sharp tip can be easily formed, and the high resolution integrated type A
The FM sensor can be easily manufactured.

[0016]

EXAMPLES Next, examples will be described. 1A and 1B are views showing an embodiment of an integrated AFM sensor according to the present invention. FIG. 1A is a perspective view thereof, and FIG. 1B is a cross sectional view thereof. The integrated AFM sensor 100 of this embodiment includes a resistance layer 104 for measuring the displacement of the cantilever portion, a cantilever portion 101, a probe portion 102, a supporting portion 103, and an electrode portion 105. . The resistance layer 104 for measuring the displacement of the cantilever portion 101 is made of, for example, silicon in which boron or the like is diffused, the probe portion 102 is made of, for example, silicon nitride, and the cantilever portion 101 is made of silicon. The part 103 is made of glass.

Next, a first embodiment of a method of manufacturing the integrated AFM sensor having such a structure will be described with reference to FIGS.
It will be described based on the manufacturing process chart shown in FIG. First, as a starting substrate 200, as shown in FIG.
0) silicon wafer 201 on the surface of silicon oxide film 202
After forming, the n-type silicon wafer 203 having the same plane orientation (100) is bonded, that is, a so-called bonded SOI (Silicon On Insulator) substrate is used. Here, the silicon wafer 203 forms a cantilever, and its thickness is set according to the required characteristics of the lever. For example, its thickness is about 2 μm.

Next, as shown in FIG. 2B, a mask pattern 204 is formed on the surface of the substrate where the replica hole for forming the probe portion is to be formed, and the silicon wafer 20 is formed.
For example, RIE (Reactive Ion E
The replica hole 205 is formed by etching the start substrate 200 by using the tching method. Then, as shown in FIG. 2C, the inside of the replica hole 205 is oxidized at a temperature not higher than the glass transition temperature of silicon oxide, for example, 950 ° C. to form a sharpened oxide film 206. By this step, the tip of the replica hole 205 can be further sharpened, and a probe with a sharper tip can be formed. Next, for example, a silicon nitride film 20 is used as a material for forming the probe.
7 is deposited on the substrate surface, a mask pattern is formed in the replica hole portion, and then the silicon nitride film 207 is etched to expose the substrate surface except the replica hole portion.

As shown in FIG. 2D, a mask pattern is formed at a predetermined position on the surface of the substrate and doped with p-type impurities such as boron. And diffused by heat treatment,
The surface sheet resistance of the boron diffusion layer is, for example, 150 Ω /
By setting it to about sq., the resistance layer 208 for measuring the strain of the cantilever is formed. Next, as shown in FIG. 2E, a cantilever forming mask pattern is formed so as to cover the strain measuring resistance layer 208 formed on the substrate,
The silicon wafer 203 is etched by the RIE method or the like. Next, as shown in FIG. 2F, after a thin oxide film 209 is formed on the surface of the substrate, the strain measuring resistance layer 208 is formed.
A contact hole is formed in the place where the upper electrode is to be formed, and the electrode 210 is made of, for example, Al.

Then, as shown in FIG. 2G, a Pyrex glass (Corning # 77) having a groove on one side in advance was formed.
40) is anodically bonded to form the support portion 211. After that, as shown in FIG. 2H, the surface of the substrate is protected by a polyimide film or the like, the silicon wafer 201 is removed by etching with an aqueous solution of potassium hydroxide, and finally the silicon oxide film 202 is removed with an aqueous solution of hydrofluoric acid. After removing
The integrated AFM sensor 212 according to the present invention can be obtained by removing the polyimide film.

Since the integrated AFM sensor thus formed uses the bonded SOI substrate as the start substrate 200, when the base silicon wafer 201 is removed by etching, the intermediate silicon oxide film 202 is surely etched. Since it stops, the cantilever beam pattern is not damaged and the thickness can be surely controlled.

In this embodiment, the n-type silicon substrate is used as the substrate for forming the cantilever. However, it is also possible to use the p-type substrate and the resistance layer for strain measurement. By appropriately selecting the diffusion layer forming impurities and the orientation of the cantilever, the integrated AFM sensor can be formed by the same steps as in this embodiment.

Next, the second embodiment of the method of manufacturing the integrated AFM sensor according to the present invention will be described with reference to FIGS.
An explanation will be given using (H). In this embodiment, as the starting substrate 300, as shown in FIG. 3A, a p-type silicon wafer 301 having a plane orientation (100) and an n-type epitaxial layer 303 formed thereon is used. Here, the epitaxial layer 303 forms a cantilever, and its thickness is set according to the required characteristics of the lever. Next, as shown in FIG. 3B, a mask pattern
After forming the replica hole 305 using the 304 so as to penetrate to the silicon wafer 301, the glass substrate to be the supporting portion 311 as shown in FIG. 3G is formed by the same method as in the first embodiment. Up to joining.

Thereafter, the silicon wafer 301 is removed by etching with a potassium hydroxide aqueous solution or the like. At this time, etching is performed with a positive potential applied to the epitaxial layer 303 and a negative potential applied to the silicon wafer 301 (electricity). Chemical etching). By taking this method,
When the silicon wafer 301 is gradually etched and the n-type epitaxial layer 303 is exposed, a silicon oxide film is formed on the interface, so that the etching automatically stops. As a result, as shown in FIG. 3H, the integrated type A
The FM sensor 312 is obtained. It should be noted that FIG.
In (H), members that are the same as or correspond to the members shown in FIGS. 2A to 2H of the first embodiment are shown with the corresponding symbols in the 300s in place of the symbols in the 200s. ing.

FIGS. 4A to 4H are manufacturing process diagrams showing a third embodiment of the method of manufacturing the integrated AFM sensor of the present invention. In this embodiment, as the start substrate 400, as shown in FIG. 4A, a silicon wafer 403 having a plane orientation (111) bonded to the surface of a silicon wafer 401 having a plane orientation (100) is used. To do. Next, a replica hole 405 for forming the probe is formed on the silicon wafer 40.
After forming so as to penetrate up to 1, the integrated AFM sensor 412 of the present invention is obtained as shown in FIG. 4H by the same steps as in the first embodiment. In addition, this FIG.
Also in (A) to (H), the members equivalent to or corresponding to the members shown in (A) to (H) of FIG. 2 of the first embodiment correspond to those in the 400 series instead of the reference numerals in the 200 series. It is shown with reference numerals.

According to the manufacturing method shown in this embodiment, the silicon wafer 40 having the plane orientation (100) is used as the starting substrate.
Since the substrate 400 in which the silicon wafer 403 having the plane orientation (111) is bonded is used, the etching can be reliably stopped at the interface of the silicon wafer 403 when the base silicon wafer 401 is removed by etching. it can. This is because, for example, when an aqueous solution of potassium hydroxide is used as the etching solution, the etching rate of the (111) plane is reduced to about 1/400 of that of the (100) plane.

Next, a fourth embodiment of the method of manufacturing the integrated AFM sensor of the present invention will be described. This embodiment can be applied to each of the first to third embodiments, but the difference from the first to third embodiments is that after the probe material is deposited in the replica hole, Instead of forming a resist pattern only around the probe part using the photomask of
After applying the resist, the entire surface of the substrate is exposed and developed to leave the resist only inside the replica hole. Since the resist film thickness of the replica hole becomes considerably thicker than the surface of the substrate, it is possible to leave the resist only inside the replica hole by appropriately selecting the irradiation exposure energy when exposing the entire surface of the substrate. This allows
Since the step of aligning the photomask with the substrate is omitted, the manufacturing becomes very simple.

Next, a fifth embodiment of the manufacturing method according to the present invention will be described. In each of the above-mentioned first to fourth embodiments, the replica hole is formed, and the cantilever pattern is formed after depositing the probe material in the replica hole portion. However, in this embodiment, the replica hole The formation and the cantilever pattern are performed simultaneously. As a result, the probe and the cantilever are formed in a self-aligned manner, so that non-uniformity due to a positioning error is eliminated. In addition, the photolithography process for forming the cantilever can be omitted, so that the manufacturing is very simple.

Next, a sixth embodiment of the manufacturing method according to the present invention will be described. In this embodiment, in the method of manufacturing the integrated AFM sensor according to each of the above-mentioned embodiments, after removing the protective polyimide film in the final step, the surface of the cantilever opposite to the supporting portion bonding surface, that is, the probe The step of forming a conductive film on the formed surface and the probe portion by vapor deposition or sputtering is added. Thus, if the electrode wiring for measuring the tunnel current is connected to the conductive film,
Not only AFM measurement but also STM measurement can be performed at the same time. When a conductive film is formed on the probe for STM measurement, if the conductive film is also formed on the electrode for the displacement measurement resistance layer of the cantilever, the electrode for displacement measurement is generally formed. Since there are a plurality of them, they are short-circuited with each other.
One of the features of the method of manufacturing an integrated AFM sensor of the present invention is that electrodes for the displacement measuring resistance layers of the probe portion and the cantilever are respectively formed on different surfaces of the cantilever. Therefore, it is extremely easy to form the conductive film only on the surface of the cantilever on the side of the probe portion different from the side of the displacement measuring electrode.

[0030]

As described above with reference to the embodiments, according to the present invention, since the probe portion is provided, it is possible to perform high resolution AFM measurement. Further, according to the manufacturing method of the present invention, since the supporting member of the cantilever is provided by bonding to the substrate surface, the processing can be performed only by processing from a simple surface and the length of the cantilever can be reduced. The controllability can be improved. Further, since the probe part is formed of the base material deposited in the replica hole, the high-performance probe part can be easily formed.

[Brief description of drawings]

FIG. 1 is a perspective view and a cross-sectional view showing an embodiment of an integrated AFM sensor according to the present invention.

FIG. 2 is a manufacturing process diagram for explaining the first embodiment of the method of manufacturing the integrated AFM sensor according to the present invention.

FIG. 3 is a manufacturing process diagram for explaining the second embodiment of the method of manufacturing the integrated AFM sensor according to the present invention.

FIG. 4 is a manufacturing process diagram for explaining the third embodiment of the method of manufacturing the integrated AFM sensor according to the present invention.

FIG. 5 is a manufacturing process diagram for describing a manufacturing method of a conventional integrated AFM sensor.

6 is a top view of the integrated AFM sensor obtained by the manufacturing method shown in FIG.

[Explanation of symbols]

 100 Integrated AFM sensor 101 Cantilever 102 102 Probe 103 Support 104 Resistive layer 105 Electrode 200, 300, 400 Start substrate 201 Silicon wafer 202 Silicon oxide film 203 Silicon wafer 204 Mask pattern 205 Replica hole 206 Sharp oxidation Film 207 Silicon nitride film 208 Resistive layer 209 Oxide film 210 Electrode 211 Support part 212 Integrated AFM sensor

Claims (12)

[Claims] 1. A support portion for a cantilever, a cantilever arranged so as to extend from the support, and a displacement detector provided on the surface of the cantilever for detecting the displacement of the cantilever. An integrated type, comprising a free end of the cantilever and a probe portion made of a silicon compound provided on a back surface opposite to the supporting portion with respect to the cantilever. AFM sensor. 2. The integrated AFM sensor according to claim 1, wherein the silicon compound forming the probe portion is silicon nitride. 3. The integrated type according to claim 1, wherein the support portion of the cantilever is configured by joining a member different from the cantilever to the cantilever. AFM sensor. 4. The integrated AFM sensor according to claim 3, wherein the support portion of the cantilever is made of glass that is anodically bonded to the cantilever. 5. The integrated AFM sensor according to claim 1, wherein the cantilever is made of silicon. 6. The displacement detection unit of the cantilever comprises a piezoresistive layer whose resistance value changes according to strain, according to any one of claims 1 to 5. Integrated AFM sensor. 7. The integrated AFM sensor according to claim 1, further comprising a conductive film on the back surface of the cantilever and the surface of the probe portion. 8. A step of forming a replica hole for a probe portion on a surface of a substrate by etching, a step of thermally oxidizing the substrate to form an oxide film inside the replica hole, and a substrate including the replica hole A step of depositing a base material of the probe portion on the top, a step of etching the base material into a predetermined shape, a step of forming an impurity diffusion layer for displacement detection in a predetermined region on the substrate surface, Covering the surface of the substrate on which the impurity diffusion layer is formed with a protective film; forming a cantilever pattern on the surface of the substrate; and opening a part of the protective film to expose a part of the impurity diffusion layer. A step, a step of forming an Al electrode pattern on the protective film opening, a step of joining a cantilever support member to the substrate surface, leaving the surface layer of the substrate by the thickness of the cantilever. Process for removing the backside of the substrate by etching Manufacturing method of an integrated AFM sensor characterized by comprising a. 9. The substrate having an oxide film interposed between the substrates 2
9. A bonded substrate formed by bonding silicon substrates having a plane orientation (100) is used.
A method for manufacturing the integrated AFM sensor described. 10. A laminated substrate in which an n-type silicon epitaxial layer is formed on a p-type silicon substrate having a plane orientation (100) is used as the substrate, and the p-type silicon substrate and the 9. The method of manufacturing an integrated AFM sensor according to claim 8, wherein the p-type silicon substrate is removed by etching while applying a potential difference to the n-type silicon epitaxial layer. 11. The bonded substrate in which a silicon substrate having a plane orientation (100) and a silicon substrate having a plane orientation (111) are bonded together is used as the substrate.
A method for manufacturing the integrated AFM sensor described. 12. The integrated mold A according to claim 8, wherein the step of forming the replica hole for the probe portion and the step of forming a cantilever beam are performed at the same time.
Manufacturing method of FM sensor.