Nanotweezer and scanning probe microscope equipped with nanotweezer

A nanotweezer (1) according to the present invention includes: a supporting member (25); an observation probe (10) that projects out from the supporting member (25), and is used when observing a surface of a specimen; a movable arm (20) that is arranged next to the observation probe (10) projecting out from the supporting member (25), and makes closed or opened between the observation probe (10) and the movable arm (20) to hold or release the specimen held between the observation probe (10) and the movable arm (20); and a drive mechanism that drives the movable arm (20) so as to make closed or opened between the observation probe (10) and the movable arm (20), and the supporting member (25), the observation probe (10) and the movable arm (20) are each formed by processing a semiconductor wafer (30) through a photolithography process.

TECHNICAL FIELD

The present invention relates to a nanotweezer used to observe the surface of a specimen and hold a minuscule object and a scanning probe microscope equipped with the nanotweezer.

BACKGROUND ART

In a scanning probe microscope (SPM), a probe at a cantilever is positioned in the vicinity of specimen, over a very small distance down to the atomic-diameter order and the probe is then used to two-dimensionally scan the surface of the specimen. A force attributable to, for instance, the interaction of the specimen and the probe is detected through this process, and recessions, projections or the like present at the specimen surface are observed based upon the detected force. A nanotweezer holds a minuscule object in a nano order size as its front end is opened and closed. There are nanotweezers known in the related art that have both the observation function and the holding function described above (see, for instance, patent reference literature 1). In the device disclosed in the patent reference literature, two carbon nano tubes are fixed onto the front end of the cantilever of an atomic force microscope, one of the carbon nano tubes is used to observe a minuscule object and the minuscule specimen is grasped and released as the front ends of two carbon nano tubes are made to open/close with electrostatic force or the like.

DISCLOSURE OF THE INVENTION

Problems to be Solved by the Invention

However, in addition to the standard manufacturing steps followed while manufacturing nanotweezers in the related art, an additional, difficult manufacturing step for fixing the two carbon nano tubes to the front end of the cantilever must be performed to manufacture the nanotweezer disclosed in patent reference 1.

Means for Solving the Problems

A nanotweezer according to the 1st aspect of the present invention comprises: a supporting member; an observation probe that projects out from the supporting member, and is used when observing a surface of a specimen; a movable arm that is arranged next to the observation probe projecting out from the supporting member, and makes closed or opened between the observation probe and the movable arm to hold or release the specimen held between the observation probe and the movable arm; and a drive mechanism that drives the movable arm so as to make closed or opened between the observation probe and the movable arm, and the supporting member, the observation probe and the movable arm are each formed by processing a semiconductor wafer through a photolithography process.

A nanotweezer according to the 2nd aspect of the present invention comprises: a supporting member; an observation probe that extends from the supporting member along a specific direction, and includes a probe portion used in specimen surface observation and a first holding portion used to hold a specimen; a movable arm that extends from the supporting member along the specific direction, is arranged next to the observation probe, and includes a second holding portion facing to the first holding portion along the specific direction; and a drive mechanism that drives the movable arm along the direction in which the movable arm extends so as to hold the specimen between the first holding portion and the second holding portion, and the supporting member, the observation probe and the movable arm are each formed by processing a semiconductor wafer through a photolithography process.

It is acceptable that: the first holding portion is a projection projecting out from the observation probe toward the specimen surface and includes a first holding surface ranging perpendicular to the specific direction and the probe portion formed at a front end of the projection; and the second holding portion includes a second holding surface used to hold the specimen between the first holding surface and the second holding surface. And it is also acceptable that the first holding surface and the second holding surface are formed so as to range perpendicular to the specific direction.

It is acceptable that: the semiconductor wafer is an SOI wafer that includes an SiO2layer sandwiched between a pair of Si layers; the observation probe and the movable arm are formed side-by-side over a specific distance from each other at one of the pair of Si layers; and the first holding portion, the second holding portion and the probe portion are each formed so as to project out along a direction in which the observation probe and the movable arm are arranged side-by-side. And it is acceptable too that the first holding portion, the second holding portion and the probe portion are each formed so as to project out along a direction extending perpendicular to a direction in which the observation probe and the movable arm are arranged side-by-side.

Also, it is acceptable that: the observation probe is constituted with a beam of a horseshoe-shaped member with a slit space formed to extend along the specific direction; and the movable arm is arranged so as to be allowed to slide freely along the specific direction within the slit space.

Moreover, it is acceptable that the drive mechanism drives the movable arm through thermal deformation caused by heat generated with supplied electric power.

A scanning probe microscope according to the 3rd aspect of the present invention, comprises: any one of nanotweezers described above; a detection unit that detects a displacement attributable to an interaction between the observation probe and the specimen surface; a control unit that controls a drive operation of the drive mechanism; an arithmetic operation unit that determines through arithmetic operation a physical and/or chemical state at the specimen surface based upon the displacement detected by the detection unit; and a scanning means for engaging the observation probe in scanning movement relative to the specimen surface. There may be further provided a display unit that provides a visual display of results of the arithmetic operation executed by the arithmetic operation unit.

Also, it is acceptable that: the detection unit includes a light source that radiates light onto the observation probe and a light receiving unit that detects light reflected from the observation probe; and the arithmetic operation unit determines through arithmetic operation a surface contour of the specimen based upon a detection signal provided by the light receiving unit.

Furthermore, it is acceptable that: there is further provided an exciter unit that causes the observation probe to vibrate in a direction to the specimen with a resonance frequency selected for the observation probe in order to enable observation of the specimen in a tapping mode; and the movable arm is formed to have a resonance frequency set at a value different from the resonance frequency of the observation probe.

A method for manufacturing the nanotweezer described above according to the 4th aspect of the present invention, comprises: using the semiconductor wafer constituted with an SOI wafer; a step of forming two projecting strips to define basic shapes of the observation probe and the movable arm by partially removing one of silicon layers in the SOI wafer; a step of forming a pointed portion to come into close proximity to or contact with the specimen at a front end of a projecting strip to define a basic shape of the observation probe; and a step of forming the observation probe and the movable arm with the two projecting strips by partially removing another silicon layer and a silicon oxide layer in the SOI wafer and also forming the supporting member with a portion remaining unremoved.

A nanotweezer according to the 5th aspect of the present invention, comprises: a supporting member; a pair of arms that are arranged side-by-side extending from the supporting member with holding portions used to hold a specimen each formed at one of the pair of arms; a probe portion that is used for specimen surface observation and is formed at least one of the pair of arms; a force-applying mechanism that applies a force to the pair of arms so as to move the arms toward each other until the holding portions at the pair of arms come in contact with each other; and a drive mechanism that drives the pair of arms so as to move the pair of arms away from each other against the force applied by the force-applying mechanism.

It is acceptable that the supporting member, the pair of arms, the force-applying mechanism and the drive mechanism are each formed by processing a semiconductor wafer through a photolithography method.

It is also acceptable that: there is further provided a thermal actuator that functions both as the force-applying mechanism and the drive mechanism; and the thermal actuator is a member formed by doping the Si layer with boron and then annealing the Si layer doped with boron and includes an electrode to which electric power is supplied.

A method for manufacturing a nanotweezer according to the 6th aspect of the present invention, comprises: using the semiconductor wafer constituted with an SOI wafer that includes an SiO2layer sandwiched between a pair of Si layers; a first step of forming the pair of arms, the force-applying mechanism and the drive mechanism by etching one of the Si layers in the SOI wafer; a second step of doping boron onto the Si layer constituting the force-applying mechanism; and a third step of creating at the force-applying mechanism contraction stress to be used to drive the pair of arms along a closing direction by annealing the Si layer doped with boron.

It is acceptable that: in the first step, the pair of arms are formed side-by-side over a specific distance from each other; and in the third step, the pair of arms are set in a closed state by creating the contraction stress at the force-applying mechanism.

A scanning probe microscope, according to the 7th aspect of the present invention, comprises: the nanotweezer described above; a detection unit that detects a displacement attributable to an interaction between the arms and the specimen surface; a control unit that controls a drive operation of the drive mechanism; an arithmetic operation unit that determines through arithmetic operation a physical and/or chemical state at the specimen surface based upon the displacement detected by the detection unit; and a scanning means for engaging a front end of the arm in scanning movement relative to the specimen surface.

There may be provided a display unit that provides a visual display of results of the arithmetic operation executed by the arithmetic operation unit.

Effect of the Invention

According to the present invention, the elements constituting the nanotweezer, such as the supporting member, the observation probe, the movable arm and the holding arm, are formed through photolithography by using a semiconductor wafer as a base material and, as a result, a high level of dimensional accuracy is achieved to enable accurate observation of the specimen while firmly holding the specimen. In addition, compared to a nanotweezer in the related art that includes carbon nano tubes fixed therein, the nanotweezer according to the present invention can be manufactured at lower cost. Furthermore, since the specimen is held with two holding portions by linearly moving the holding portion of the movable arm toward the holding portion of the observation probe, a firm hold is achieved with ease.

BEST MODE FOR CARRYING OUT THE INVENTION

The following is an explanation of the embodiments of the present invention, given in reference to the drawings.

First Embodiment

FIG. 1schematically shows the structure adopted in an atomic force microscope system (hereafter referred to as an AFM system) embodying the scanning probe microscope according to the present invention as the first embodiment thereof.FIG. 2shows the essential structural elements constituting a nanotweezer (a nano pincette)1installed in the AFM system100inFIG. 1(a pair of nanotweezers is referred to as a nanotweezer), with (a) showing an observation probe10and a movable arm20and (b) showing the probe portion of the observation probe10.

As shown inFIG. 1, the AFM system100comprises the nanotweezer1, a laser light source2, a two-element split photodiode3, an arithmetic operation unit4, an exciter unit5and a power supply unit6. The nanotweezer1, which includes the observation probe10and the movable arm20formed so as to constitute an integrated unit together with a supporting member25, is formed by processing an SOI wafer through photolithography, as detailed later.

The observation probe10includes a lever11extending along the X direction in the figure and a probe portion12extending from the front end of the lever11along the X direction. The movable arm20arranged or disposed next to the observation probe10includes a lever21extending along the X direction and a holding portion22extending from the front end of the lever21along the X direction. The probe portion12and the holding portion22extending substantially parallel to each other are set over a distance d from each other. Drive levers23and24, provided as integrated parts of the supporting member25, function as a thermal actuator that drives the movable arm20. Ends of the drive levers23and24are connected to the movable arm20, thereby forming a link mechanism. Power is supplied from the power supply unit6to the drive levers23and24functioning as a thermal actuator.

The supporting member25is detachably held by a holder (not shown) located at the AFM system100. It is to be noted that only part of supporting member25is shown inFIG. 1. Although not shown, the AFM system100includes a three-dimensional stage to which the holder used to hold the supporting member25is fixed. As the three-dimensional stage is driven, the entire nanotweezer1can be displaced along directions in three dimensions. The supporting member25may be attached to the holder, by adopting any of various methods, e.g., sliding and fitting the supporting member25into a groove or a recess formed at the holder or clamping the supporting member25with a plate spring disposed at the holder.

A detection signal provided by the two-element split photo diode3is input to the arithmetic operation unit4. Based upon the detection signal input thereto, the arithmetic operation unit4calculates the amplitude of the observation probe10and determines the contour of the surface of a specimen S through arithmetic operation. The arithmetic operation results are indicated at a monitor7. The exciter unit5includes a piezoelectric element (not shown) that induces resonance at the observation probe10by vibrating the entire nanotweezer1and a drive circuit engaged in drive of the piezoelectric element.

As shown inFIG. 2, the YZ sections of the lever11at the observation probe10and the lever21at the movable arm20are rectangular, the levers11and21assume lengths measured along the X direction equal to each other and thicknesses measured along the Z direction equal to each other, and the lever11assumes a greater width taken along the Y direction compared to the width of the lever21. In addition, the probe portion12of the observation probe10and the holding portion22of the movable arm20assume dimensions equal to each other along their lengths measured in the X direction, their widths measured in the Y direction and their heights measured in the Z direction. The probe portion12and the holding portion22each assume a wedge shape tapering off along the −Z-direction, and they both have a right-angle triangle section taken along the YZ plane. The sections of the probe portion12and the holding portion22, disposed over the distance d, are symmetrical relative to the Z axis. Surfaces12aand22a(hereafter referred to as perpendicular surfaces) of the probe portion12and the holding portion22, facing opposite each other, range parallel to each other. A ridgeline12c, at which the perpendicular surface12aand a sloping surface12bof the probe portion12connect with each other, and a ridgeline22cat which the perpendicular surface22aand a sloping surface22bof the holding portion22connect with each other, extend parallel to the X axis, and the probe portion and the holding portion function as the sharp ends (blade ends) that approach or contact the specimen S.

The method adopted when observing the specimen is now explained in reference toFIGS. 1 and 2. In the embodiment, the contour of the surface of the specimen S is determined through measurement by driving the piezoelectric element (not shown) disposed at the exciter unit5, thereby inducing a flexural vibration of the observation probe10along the direction (the Z direction) indicated by the arrow V inFIG. 2and, at the same time, scanning the nanotweezer1along the XY direction. This method is generally referred to as a tapping mode. During the observation process, the probe portion12of the observation probe10is moved very close to the specimen surface so as to position it over a very small distance down to the atomic diameter order, and the specimen surface is scanned two-dimensionally while inducing vibration at the observation probe along the Z direction. As the specimen surface with recessions and projections is scanned and thus the distance between the front end of probe portion12and the specimen S (the average distance between the front end of the vibrating probe portion12and the specimen S) changes, the amplitude at the lever11also changes due to the change occurring in the interaction between the specimen surface and the probe portion12. The extent of the change in the amplitude is measured through an optical lever measurement method which utilizes the laser light source2and the two-element split photodiode.

In the optical lever measurement method, laser light L1originating from the laser light source2is directed onto the upper surface of the lever11, and reflected light L2from the upper surface of the lever11is received at the two-element split photodiode3functioning as a light receiving unit. The two-element split photodiode3outputs a detection signal corresponding to the light reception position to the arithmetic operation unit4. Based upon the detection signal provided by the two-element split photodiode3, the arithmetic operation unit4calculates the extent of change having occurred in the amplitude of the lever11and also determines through arithmetic operation the contours at the surface of the specimen S based upon the extent in the amplitude change. The surface contour thus determined is then displayed at the monitor7.

During the observation conducted in the tapping mode described above, it is necessary to induce resonance at the observation probe10by vibrating the entire supporting member25along the Z direction via the piezoelectric element. Accordingly, the width of the lever11at the observation probe10is set larger than the width of the lever21at the movable arm20, as explained earlier, so as to ensure that the resonance frequency of the vibration along the thickness of the vibration probe10is higher than the resonance frequency of the movable arm20. As the exciter unit5vibrates the entire supporting member25with the resonance frequency set for the observation probe10, the observation probe10alone resonates and vibrates along the Z direction.

FIG. 3provides a diagram of the resonance frequency at the observation probe10, with the amplitude indicated along the vertical axis and the frequency indicated along the horizontal axis. V1inFIG. 3indicates the vibration curve of the observation probe10and V2inFIG. 3indicates the vibration curve of the movable arm20. When the frequency of the vibration induced via the exciter unit5is f1, a resonance occurs in the observation probe10and the amplitude peaks. This frequency f1is the resonance frequency of the observation probe10. The resonance frequency of the movable arm20is f2and the vibration peak manifests at the frequency f2. Once the frequency exceeds f2, the amplitude rapidly decreases and the amplitude k of the movable arm20at the frequency f1is much smaller than the amplitude at the observation probe10. By setting the widths of the levers11and21so that the resonance frequency f1of the observation probe10is higher than the resonance frequency f2of the movable arm20, it is possible to cause the observation probe10alone to vibrate.

Alternatively, the desirable resonance frequencies may be selected by adjusting the thicknesses of the levers11and21instead of selecting the desirable resonance frequencies through the adjustment of the widths of the levers11and21. In this case, the lever11of the observation probe10should assume a greater thickness than the thickness of the lever21at the movable arm20. Since the resonance frequency is represented by the value obtained by cubing the corresponding thickness, the resonance frequency can be adjusted to a significant extent simply by slightly altering the thickness.

Next, in reference toFIGS. 1 and 4, the thermal actuator that drives the movable arm20is explained.FIG. 4presents a schematic enlargement of the observation probe10, the movable arm20, the drive levers23and24and the power supply unit6inFIG. 1. The thermal actuator is constituted with the drive levers23and24and the power supply unit6. A beam portion23aof the drive lever23and a beam portion24aof the drive lever24are both connected to the movable arm20. While the beam portions23aand24aassume thicknesses equal to each other measured along the Z direction, the width, measured along the X direction of the beam portion24a, is set smaller than the width of the beam portion23a. The power supply unit6includes two variable power sources6aand6bconnected in series, with the negative pole of the variable power source6aconnected to the drive lever23and the positive pole of the variable power source6bconnected to the drive lever24. The potential at the connecting point at which the variable power source6aand the variable power source6bare connected and the potential at the movable arm20are both set to the ground potential.

As described earlier, the width of the beam portion24ameasured along the X direction is set smaller than that of the beam portion23aand thus, the resistance value at the beam portion24awith a smaller sectional area is greater than the resistance value at the beam portion23a. For this reason, as power is supplied from the power supply unit6to the beam portions23aand24a, a greater quantity of Joule heat is generated at the beam portion24athan at the beam portion23aand the beam portion24athermally expands to a greater extent than the beam portion23a. As a result, the movable arm20is caused to flex along an H direction extending parallel to the Y axis via the drive levers23and24with the fulcrum assumed at a narrow portion20awhere the width of the movable arm20becomes narrow. The extent of flexure of the movable arm20is adjusted through feedback control of the voltage applied from the power supply unit6to the beam portions23aand24a. It is to be noted that the voltage at the variable power sources6aand6bare adjusted so as to set the potential over an area21aof the movable arm20at ground level.

By adjusting the potential at the area21aof the movable arm22to ground level as described above, the potentials at both the observation probe20and the movable arm10can also be controlled at ground level, preventing the application of any unnecessary voltage to the specimen S being held.

The specimen is grasped and held with the nanotweezer1equipped with such a thermal actuator mechanism through the following operation. First, the specimen S to be held by the nanotweezer1is located by three-dimensionally displacing the nanotweezer1along the surface of the specimen and observing the contour of the specimen surface with the observation probe10. Once the specimen S is detected, the nanotweezer1is moved so that the specimen S is positioned between the probe portion12and the holding portion22. After stopping the tapping operation of the observation probe10, the drive levers23and24are driven and the movable arm20is flexed along the H direction in the figure so as to move the holding portion22closer to the probe portion12until the specimen S becomes clamped between the holding portion22and the probe portion12. During this process, the movable arm20alone is caused to flex by the drive levers23and24, while the observation probe10remains stationary.

To explain the holding procedure in more specific terms, the perpendicular surface12a(seeFIG. 2(b)) of the probe portion12at the observation probe10is first set in contact with the specimen S. Next, the movable arm20is flexed so as to move the perpendicular surface22a(seeFIG. 2(b)) of the holding portion22closer to the specimen S and the variable power sources6aand6bare adjusted so as to set the perpendicular surface22ain contact with the specimen S with an optimal level of pressure. As a result, the specimen S is by the nanotweezer1.

Since the perpendicular surfaces12aand22aare formed so as to range parallel to each other and face opposite each other, the specimen S is firmly held between the parallel surfaces12aand22a. Once the specimen S is held, the specimen S can be made to move three-dimensionally by driving the three-dimensional stage. In addition, the specimen S currently held can be released simply by reducing the voltage applied from the power supply unit6to zero and thus resetting the distance between the holding portion22and the probe portion12to the initial distance d. Through this operation, the specimen S can be held and, at the same time, observed via the nanotweezer1equipped with the observation probe10and the movable arm20.

Next, a method that may be adopted when manufacturing the nanotweezer1achieved in the embodiment is explained. The nanotweezer1is manufactured as an integrated unit constituted with an SOI (silicone on insulator) wafer. An SOI wafer is manufactured by pasting together two Si single-crystal plates so as to sandwich an SiO2layer formed at one of the Si single-crystal plates. As shown inFIG. 1, the supporting member25includes an upper Si layer31, an SiO2layer32and a lower Si layer33constituting the SOI wafer. Except for the electrodes and the like used to connect with the power supply unit6, the observation probe10, the movable arm20and the drive levers23and24are all constituted with the upper Si layer31. While the thicknesses of the layers31,32and33constituting the SOI wafer used in the embodiment are 6 um, 1 um and 300 um respectively, the present invention is not limited to this dimensional combination.

FIGS. 5˜14show the manufacturing steps (processes) through which the nanotweezer1achieved in the embodiment is manufactured as steps a through h are executed in sequence.FIGS. 5(a1) and5(a2) illustrate step a, with (a1) presenting a perspective and (a2) presenting a sectional view. In step a, a silicon nitride (SiN) film34is formed over a 50 nm thickness atop the upper Si layer31of an SOI wafer30constituted with the upper Si layer31, the SiO2layer32and the lower Si layer33. It is to be noted that the upper Si layer31of the SOI wafer30is formed so as to set the basal plane (001) of the Si single-crystal at the surface of the upper Si layer31.

InFIGS. 5(b1) and5(b2), step b is illustrated with (b1) presenting a perspective and (b2) presenting a sectional view taken along I-I. In step b, the SiN film34is partially etched and removed with C2F6through RIE executed by using a mask A shown inFIG. 6, until the upper Si layer31becomes partially exposed (over unhatched areas A1and A2). The area A1from which the SiN film34is removed through etching is substantially an area where the front end of the observation probe10and the front end of the movable arm20are to be formed. Over the area A2, the base end sides of the observation probe10and the movable arm20and the drive levers23and24are formed. The direction along which the observation probe10and the movable arm20are to extend, i.e., the direction along which the narrow strip A extends, should be aligned with the <110> direction of the upper Si layer31.

It is to be noted that the mask A shown inFIG. 6also covers the supporting member25, and that the portion of the mask above line R1-R1inFIG. 6is relevant to the illustrations presented inFIG. 1andFIG. 5(b1). Accordingly, the following explanation is provided with regard to the area above line R1-R1.

In step c shown inFIGS. 5(c1) and5(c2), an oxide film35is formed over a thickness of 0.1 um at the surface of the upper Si layer31over the areas A1and A2. The exposed surface of the upper Si layer31is oxidized through steam oxidation with steam generated by inducing a reaction of an oxygen gas and a hydrogen gas at high temperature.

FIGS. 7(a) and7(b) illustrate step d. In step d, an etching process is executed through ICP-RIE, (inductively coupled plasma-reactive ion etching) by using a mask B shown inFIG. 9. As shown inFIG. 9, the mask B includes a front end shielding area B1to shield the area A1inFIG. 7(c1). A slit SL1, extending along the up/down direction in the figure (along the <110> direction of the upper Si layer31), is formed at the front end shielding area B1. In addition, slits SL2and SL3are used when forming the drive levers23and24. It is to be noted that the portion of the mask B above line R2-R2inFIG. 9corresponds to the portion shown inFIGS. 7(a) and7(b).

The dotted lines inFIG. 7(a) indicate the mask B disposed atop the wafer30, having undergone the processing shown inFIG. 5(c1). The area that is not covered with the mask B inFIG. 7(a) is etched through ICP-RIE until the SiO2layer32becomes exposed. Since this etching process executed through ICP-RIE stops at the SiO2layer32, the observation probe10and the movable arm20with a uniform thickness can be formed with a high level of accuracy.

FIG. 7(b) shows the wafer30having undergone the etching process. By etching the area over the slit SL1at the mask B, a slit groove40extending along the <110> direction has been formed. The two side surfaces of the slit groove40range perpendicular to the surface of the SiN film34and the depth of the slit groove40is equal to the sum of the thicknesses of the SiN film34and the upper Si layer31. The two side surfaces of the slit groove40eventually become the perpendicular surface12aof the probe portion12and the perpendicular surface22aof the holding portion22(seeFIG. 2)in the finished nanotweezer product1.

FIG. 8presents sectional views of the wafer30taken before and after the etching process, with (a) presenting sectional views taken along II-II inFIGS. 7and (b) presenting sectional views taken along I-I inFIG. 7. Over the areas not covered with the mask B, the silicon nitride (SiN) film34, the oxide film35and the Si layer31are etched. As a result, the upper surface of the SiO2layer32and the side surfaces of the Si layer become exposed in the etched areas.

FIG. 10illustrates step e with a sectional view similar to those taken along I-I inFIG. 7, presented in (a) and a sectional view similar to those taken along II-II that inFIG. 7presented in (b). In step e, an oxide film36is formed for purposes of surface protection at the side surfaces of the upper Si layer31having become exposed through the etching process executed in step d. The oxide film is formed through steam oxidation as in step c.

FIG. 11illustrates step f, with a sectional view taken along I-I similar to that inFIG. 10(a) presented in (a) and a sectional view taken along II-II similar to that inFIG. 10(b) presented in (b). In step f, the SiN film34is removed through etching in an RIE process executed by using C2F6. As a result, the upper surface of the upper Si layer31becomes exposed as shown inFIGS. 11(a) and11(b). While this RIE process is executed without using a mask, the pressure of the C2F6gas is raised so as to achieve etching conditions under which the SiN film34is removed at an etching rate higher than the etching rate corresponding to the oxide films35and36and thus, the SiN film34alone is removed. This means that the oxide film35atop the upper Si layer31and the oxide film36at the side surfaces of the upper Si layer31remain unetched.FIG. 12is a perspective of the processed wafer30with the oxide films35and36indicated as the areas hatched with dots.

InFIG. 13, step g is illustrated in (a1) and (a2) and step h is illustrated in (b1).FIG. 13(a2) is a sectional view taken along III-III inFIG. 13(a1). In step g, the upper Si layer31is an isotropically etched by using a 30% KOH aqueous solution. Since the upper surface of the upper Si layer31is exposed only over the areas where the oxide films35and36are not present, as shown inFIG. 11, the upper Si layer31is anisotropically etched starting at the exposed upper surface areas and sloping surfaces11b,21b,12band22bare formed. As explained earlier, the basal plane (001) of the single-crystal Si is set at the surface of the upper Si layer31and thus, the {111} plane of the single-crystal Si is set at the sloping surfaces12band22bformed through anisotropic etching.

It is to be noted that the thickness of the lever11at the observation probe10can be set greater than the thickness of the lever21at the movable arm20so as to achieve the desired resonance frequencies, as explained earlier, by protecting the area except for the area to be taken up by the lever21with a resist and thermally oxidizing or etching the area corresponding to the lever21to a predetermined depth.

Next, an ICP-RIE process is executed along the thickness-wise direction by using a mask C shown inFIG. 14(a) so as to remove through etching the upper Si layer31remaining over the area around the area where the basic shapes of the observation probe10and the movable arm20have been formed until the surface of the SiO2layer31becomes exposed. Then, the oxide films35and36are removed through etching. Through the etching process executed by using the mask C as described above, the lengths of the probe portion12and the holding portion22can be adjusted. In addition, since end surfaces12eand22eset in line with each other range perpendicular to the direction along which the probe portion12and the holding portion22extend, the specimen S can be held with even greater firmness.

In step h shown inFIG. 13(b1), any unnecessary portion of the lower Si layer33is removed through etching in an ICP-RIE process executed by using a mask D shown inFIG. 14(b) starting at the rear surface of the SOI wafer30. This etching process stops at the SiO2layer32. Then, as any unnecessary SiO2layer32is removed with a hydrofluoric acid solution, the nanotweezer1achieving the intended shape is formed. It is to be noted that the portion removed through step h is indicated by the two-point chain line inFIG. 13(b1). It is also to be noted that the area above line R3-R3inFIG. 14showing the masks C and D correspond to the portion processed as shown inFIG. 13.

Through the steps described above, the nanotweezer1, which includes the observation probe10and the movable arm20formed as an integrated unit together with the supporting member25and extending along the same direction, is completed. The drive levers23and24, too, are formed through a similar method while forming the observation probe10and the movable arm20.

While the sequence of the manufacturing procedures for manufacturing a single nanotweezer1is explained above, the actual manufacturing process is executed in units of individual SOI wafers, i.e., the actual manufacturing process is executed through batch processing. Through such batch processing executed by adopting a photolithography method, numerous nanotweezers1are manufactured in a batch from a single SOI wafer, which allows a great reduction in the manufacturing cost.

By mounting the nanotweezer1achieved in the embodiment as described above in an AFM system, the following advantages are achieved.

(1) Since the observation probe10and the movable arm20are formed as an integrated unit from an SOI wafer through photolithography, the nanotweezer can be manufactured at low manufacturing cost. In addition, since a high level of dimensional accuracy is assured, the specimen S can be held firmly with the observation probe10and the movable arm20.
(2) Since the widths or the thicknesses of the levers11and21are set so as to ensure that the resonance frequency f1at the observation probe10is higher than the resonance frequency f2at the movable arm20, the observation probe10alone must be moved into close proximity to the specimen S and be made to vibrate assuming that the resonance frequency at which the observation probe10is excited in the tapping mode is set as the resonance frequencies of the observation probe. Thus, the presence of the movable arm20disposed next to the observation probe does not hinder the observation operation.
(3) Since the movable arm20is driven via a thermal actuator, no voltage is applied to the movable arm20and, as a result, even an electrically conductive specimen or a biological specimen can be held firmly with ease.
(4) When driving the movable arm20via the thermal actuator, the voltage is controlled through feedback control so as to set the potentials at the movable arm20and the observation probe10substantially equal to the ground potential. Consequently, application of any undesirable potential to the specimen S to be held is prevented.

Second Embodiment

FIG. 15schematically shows the overall structure adopted in the AFM system achieved in the second embodiment. It is to be noted that the same reference numerals are assigned to components identical to those in the first embodiment so as to preclude the necessity for a repeated explanation thereof. The movable arm20is driven by a drive mechanism300along an M direction (X direction). The drive mechanism300includes a pair of electrodes301, a pair of thermal deformation portions302, a pair of lever portions303, a pair of linking portions304and a pair of beam portions305. As in the first embodiment, the supporting member25of the nanotweezer1is detachably held by the holder (not shown) that can be three-dimensionally displaced via a 3-D stage (not shown).

The electrodes301are each connected to one of the thermal deformation portions302, and the front ends of the thermal deformation portions302are set in contact with the corresponding lever portion303. The lever portions303, in turn, are connected to a beam portions305via the corresponding linking portions304, and the beam portions305are connected to the base of the movable arm20. The pair of electrodes301are connected to the power supply unit6, and thus, power can be supplied from the power supply unit6to the thermal deformation portions302via the electrodes301. As power is applied to the thermal deformation portions302, the thermal deformation portions302become thermally expanded along the lengthwise direction due to the Joule heat, causing the movable arm20to move linearly along the +X direction. Accordingly, by adjusting the power supplied to the drive mechanism300functioning as the thermal expansion actuator, i.e., by adjusting the value of the electrical current supplied to the thermal deformation portions32, the movable arm20can be engaged in reciprocal motion M along the X direction.

In the first embodiment explained earlier, the observation probe10and the movable arm20are set side-by-side along the Y direction and the movable arm20is driven along the Y direction via the thermal actuator. In the second embodiment, however, the observation probe10and the movable arm20are set side-by-side, one above the other along the Z direction and the movable arm20is made to move so as to slide along the X direction via the drive mechanism300.

InFIG. 16, the positional relationship between the observation probe10and the movable arm20is shown in (a) and the front ends of the observation probe and the movable arm are shown in an enlargement in (b). It is to be noted that the drive mechanism300is shown in a simplified schematic illustration inFIG. 16. The observation probe10includes a lever11extending along the X direction, a holding portion12present at the front end of the lever11and projecting out along the Z direction and a probe portion13present at the front end of the holding portion12. This observation probe10is formed as an integrated part of the supporting member25of the nanotweezer1. The movable arm20, too, includes a lever21extending along the X direction and a holding portion22located at the front end of the lever21and projecting out along the Z direction. The drive mechanism300is linked at the base of the movable arm20.

The extent to which the lever11projects out beyond the supporting member25is set greater than the extent to which the lever21projects out beyond the supporting member25. In addition, the width of the lever11measured along the Y direction and the width of the lever21measured along to the Y direction are equal to each other and the levers are set side-by-side along the Z direction over a predetermined distance from each other.

As shown in the enlargement presented inFIG. 16(b), the holding portion12and the holding portion22are disposed along the X direction, and the holding portions12and22include flat surfaces that face opposite each other. These surfaces12aand22afacing opposite each other range perpendicular to the X axis and parallel to each other. The distance d between the opposite surfaces12aand22acan be adjusted by displacing the movable arm20along the M direction.

The probe portion13and a front end22bof the holding portion22are both pointed and the line connecting the probe portion13with the front end22bof the holding portion22extends substantially parallel to the X axis. Thus, when the opposite surfaces12aand22aare placed in contact with each other by linearly displacing the movable arm20, the probe portion13and the front end22bof the holding portion22become aligned.

In reference toFIG. 17, the observation operation executed by using the nanotweezer1to observe a specimen surface and the holding operation executed by using the nanotweezer1to hold the specimen are explained. The observation operation is explained first. In the second embodiment the specimen surface is also observed in a tapping mode similar to that adopted in the first embodiment. The supporting member25of the nanotweezer1is caused to vibrate along the Z direction by the exciter unit25to induce resonance at the observation probe10in the second embodiment as well.

The holder (not shown) holding the nanotweezer1is three-dimensionally displaced until the nanotweezer1is set close to the specimen surface P with a tilt of a predetermined angle of inclination relative to the specimen surface P, as shown inFIG. 17(a). When executing the observation operation, the drive mechanism300is not engaged and the distance d between the holding portion12of the observation probe10and the holding portion22of the movable arm20is set to the maximum distance d0. Then, the probe portion13of the observation probe10is positioned in the vicinity of the specimen surface P over a very small distance in the atomic-diameter order and the specimen surface is observed through a method similar to that adopted in the first embodiment. The specific observation method is not described in detail here.

When observing the specimen surface P or a miniscule specimen S in the tapping mode by using the observation probe10, the probe portion13of the observation probe10, vibrating with a greater amplitude than the front end22bof the movable arm20needs to be positioned in the vicinity of the specimen surface P or the miniscule specimen S. Accordingly, the nanotweezer in the second embodiment is designed so that the resonance frequency of the vibration of the lever11along the thickness-wise direction is higher than the resonance frequency of the vibration of the lever21as in the first embodiment by setting the thickness of the lever11at the observation probe10greater than the thickness of the lever21at the movable arm20. As the supporting member25of the nanotweezer1is caused to vibrate at the selected resonance frequency via the exciter unit5, the lever11alone resonates and vibrates to a significant extent along the Z direction. As a result, AFM observation via the observation probe10is enabled without the movable arm20ever getting in the way of the observation.

Once the nanotweezer1is moved to a position at which the miniscule specimen S is positioned between the holding portions12and22, as shown inFIG. 17(b), the drive mechanism300is engaged in operation to grasp and hold the miniscule specimen S. Prior to the holding operation, the vibrating operation by the exciter unit5is stopped. The nanotweezer1is moved toward the miniscule specimen S while maintaining the distance d at d0. As an electrical current is supplied to the thermal deformation portions302at the drive mechanism300, the thermal deformation portions302become thermally expanded due to Joule heat generated thereat and the extent of their displacement along the +X direction attributable to thermal expansion is increased by the lever portions303. Then, the beam portions305and the movable arm20are driven along the +X direction via the linking portions304.

Through the operation described above, the miniscule specimen S becomes clamped between the holding portion22and the holding portion12, and the miniscule specimen S thus becomes held between the surfaces12aand22aranging parallel to each other. During this operation, by adjusting the value of the electrical current supplied to the thermal deformation portions302, the miniscule specimen S, can be held with an optimal level of holding force. The distance d between the holding portion12and the holding portion22holding the specimen between them equals d1(d1<d0) which matches the size of the miniscule specimen.

Subsequently, by three-dimensionally moving a holder holding the nanotweezer1via the 3-D stage (not shown), the miniscule specimen S can also be three-dimensionally displaced, as shown inFIG. 17(c). The nanotweezer1achieved in the embodiment, which also includes the observation probe10and the movable arm20, can be utilized to observe the specimen surface P or the miniscule specimen S and to hold the miniscule specimen S. In addition, since the miniscule specimen S can be held firmly while holding the opposite surfaces12aand22aof the holding portion12and22parallel to each other, the miniscule specimen S can be held with greater firmness compared to a miniscule specimen held with a nanotweezer in the related art that opens/closes as the holding portions move in a circular arc path. For this reason, the nanotweezer1achieved in the embodiment is ideal when a miniscule object with spherical surfaces, such as a cylindrical carbon nano tube or a spherical fullerene needs to be held. It is to be noted that the hold on the miniscule specimen S by the nanotweezer1can be released simply by lowering the voltage applied from the power supply unit6or resetting the voltage to zero so as to increase the distance d between the holding portion22and the holding portion12.

Next, the manufacturing process through which the nanotweezer1achieved in the second embodiment is manufactured is explained. In the explanation, nine steps (processes), a through i are described in sequence.FIGS. 18(a1) and18(a2) illustrate step a, with (a1) presenting a plan view and (a2) presenting a sectional view. In step a, and SOI wafer400is prepared. The SOI wafer400used in the embodiment includes an upper Si layer401with a thickness of 50 um, an SiO2layer402with a thickness of 1 um and a lower Si layer403with a thickness of 400 um. The upper Si layer401is formed so that the basal plane (001) of single-crystal Si is set at the surface thereof, with the direction (100) extending to the left and the right in the figure.

FIGS. 18(b1) and18(b2) illustrate step b, with (b1) presenting a plan view and (b2) presenting a sectional view. In step b, the surface of the upper Si layer401is oxidized through steam oxidation (wet oxidation) by using steam generated through a high-temperature reaction of oxygen gas and hydrogen gas and an oxide film404is formed over the entire surface of the upper Si layer401over a thickness of 0.3 um.

FIGS. 18(c1),18(c2) and18(c3) illustrate step c with (c1) presenting a plan view, (c2) presenting a sectional view and (c3) presenting a plan view of a mask MA used in step c. The mask MA is a resist mask formed through photolithography. In step c, BHF etching is executed by using the mask MA so as to remove part of the oxide film404.

FIGS. 19(a1) and19(a2) illustrate step d with (a1) presenting a plan view and (a2) presenting a sectional view. In step d, a silicon nitride film (an Si3N4film or an SiN film) is formed through LP CVD over a thickness of 0.05 um atop the oxide film404and the exposed upper Si layer401.

FIGS. 19(b1),19(b2) and19(b3) illustrate step e with (b1) presenting a plan view, (b2) presenting a sectional view taken along IA-IA and (b3) presenting a plan view of a mask MB used in step e. In step e, upon forming the mask MB, the SiN film405is etched through RIE and then, the oxide film404having become exposed by etching the SiN film405, is removed by through a BHF etching process. Subsequently, the portion of the upper Si layer401having become exposed through the BHF etching process, is etched by executing ICP-RIE (inductively coupled plasma-reactive ion etching). The ICP-RIE process advances substantially perpendicular in the thickness-wise direction and stops at the SiO2layer402. As a result, a groove B11with a depth of 50 um, which is equal to the thickness of the upper Si layer401, is formed as shown inFIG. 19(b2). It is to be noted that the groove B11is formed through an etching process starting at anon-shielding portion B12of the mask B.

FIGS. 19(c1) and19(c2) illustrate step f, with (c1) presenting a plan view and (c2) presenting a sectional view taken along IA-IA. In step f, the exposed surface of the upper Si layer401is oxidized through steam oxidation and an oxide film406is formed over a thickness of 0.3 um. This oxide film406functions as a protective film to prevent the inner walls and the like of the groove B11from becoming etched during the subsequent anisotropic etching process to be detailed later.

FIGS. 20(a1) and20(a2) illustrate step g, with (a1) presenting a plan view and (a2) presenting a sectional view taken along IA-IA. In step g, the SiN film405is removed through RIE. As a result, the upper Si layer401becomes exposed over an area A10where the SiN film405has been previously present.FIGS. 20(b1) and20(b2) illustrate step h, with (b1) presenting a plan view and (b2) presenting a sectional view taken along IA-IA. In step h, the upper Si layer401present in the area A10is anisotropically etched by using a TMAH (tetra-methyl ammonium hydroxide) solution. The oxide films404and406, which are not readily etched with TMAH, function as stopper layers during the anisotropic etching process. Through this anisotropic etching process, three triangular cones all constituted with the upper Si layer401and having sloping surfaces C1, C2and C3are formed. The sloping surfaces C1, C2and C3are (111) planes with a low etching rate. It is to be noted that a KOH solution instead of the TMAH solution may be used in step h.

FIGS. 20(c1),20(c2) and20(c3) illustrate step i with (c1) presenting a plan view, (c2) presenting a sectional view taken along IA-IA and (c3) presenting a plan view of a mask MC used in step i. In step i, any unnecessary portion of the lower Si layer403is removed through an etching process executed by using the mask MC shown inFIG. 20(c3) and starting at the rear surface of the SOI wafer400, i.e., on the side where the lower Si layer403is present and the remaining SiO2layer402is also removed. The lower Si layer403present over an area A12covered with a shielding portion A13of the mask MC remains unetched to eventually form the supporting member25, as shown inFIG. 20(c2). In addition, through the etching process executed on the SiO2layer402as described above, the SiO2layer402present between the Si layer401and the lower Si layer403over the area corresponding to the movable arm20and the areas ranging from the thermal deformation portions through the beam portions at the drive mechanism300is etched and lifted off the supporting member25, and thus, displacement attributable to thermal deformation is enabled.

While the manufacturing method described above imposes restrictions with regard to the widths of the observation probe10and the movable arm20in conformance to the thickness (e.g., 50 um, as in the explanation provided above) of the upper Si layer401, the dimensions of the observation probe and the movable arm along the lengthwise direction and the thickness-wise direction can be set freely through photolithography. In other words, the lengths and the thicknesses of the observation probe10and the movable arm20can be set with ease to optimal values ideal for achieving the required resonance frequencies for vibrations in the tapping mode. In addition, the distance d between the holding portion12and the holding portion22can also be set freely.

While the sequence of manufacturing procedures for manufacturing a single nanotweezer1is explained above, the actual manufacturing process is executed in units of individual SOI wafers, i.e., the actual manufacturing process is executed through batch processing. Through such batch processing executed by adopting a photolithography method, numerous nanotweezers1are manufactured in a batch from a single SOI wafer, which allows a great reduction in manufacturing cost.

By mounting the nanotweezer1achieved in the embodiment as described above in an AFM system, the following advantages are achieved.

(1) Since the observation probe10and the movable arm20are formed as an integrated unit from an SOI wafer through photolithography, the nanotweezer can be manufactured at low manufacturing cost. In addition, since a high level of dimensional accuracy is assured, the specimen S can be held firmly by the observation probe10and the movable arm20.
(2) Since the miniscule specimen S is grasped and held between the two holding portions by linearly sliding the holding portion22of the movable arm20toward the holding portion12of the observation probe10, the holding operation can be executed with ease.
(3) Since the movable arm20is driven via a thermal actuator, no voltage is applied to the movable arm20and, as a result, even an electrically conductive specimen or a biological specimen can be held firmly with ease.
(4) Since the thicknesses of the levers11and21are set so as to ensure that the resonance frequency at the observation probe10is higher than the resonance frequency at the movable arm20, the observation probe10alone must be moved in close proximity to the specimen surface P and be made to vibrate, and thus, the observation operation is not hindered by the movable arm20.

Third Embodiment

FIG. 21presents schematic plan views, showing the structure adopted in the nanotweezer achieved in the third embodiment, withFIG. 21(a) showing a drive mechanism80thereof in a non-driving state,FIG. 21(b) showing the drive mechanism80in a driving state andFIG. 21(c) showing the nanotweezer inFIGS. 21(a) and21(b) in a partial enlargement. As shown inFIG. 21(a), a nanotweezer51comprises an observation probe60, a movable arm70, a supporting member75and the drive mechanism80. The observation probe60, which constitutes an integrated unit together with the supporting member75, includes a U-shaped (horseshoe-shaped) lever61extending along the X direction, a holding portion62projecting out along the Z direction in the vicinity of the front end of the lever61and a probe portion63disposed at the front end of the holding portion62.

The probe portion63is located at the front end of the holding portion62. The movable arm70is slidably disposed within a U-shaped space formed by the lever61. At the front end of a lever71of the movable arm70, extending along the X direction, a holding portion72projecting out along the Z direction is formed. The lever61and the lever71are positioned on a single plane, the thicknesses of the lever61and the lever71measured along the Z direction are equal to each other and the heights assumed by the probe portion63and the holding portion72along the Z direction are also equal to each other.

FIG. 22schematically illustrates the essential structural elements of the nanotweezer51achieved in the third embodiment. A surface62aof the holding portion62and a surface72aof the holding portion72, facing opposite each other, range parallel to each other. In addition, the probe portion63and a front end72bof the holding portion72are each pointed, and the line connecting the probe portion63with the front end72bof the holding portion72extends substantially parallel to the sliding direction M along which the lever71slides. The nanotweezer51holds a miniscule specimen between these opposite surfaces62aand72a, and AFM observation of a specimen surface is conducted by using the probe portion63.

The base of the movable arm70is linked to the drive mechanism80and the movable arm70is thus driven to slide along the M direction via the drive mechanism80. Since the drive mechanism80adopts a structure similar to that of the drive mechanism300in the second embodiment, a detailed explanation of the drive mechanism80is omitted. In addition, as is the nanotweezer1achieved in the first embodiment, the nanotweezer51in the third embodiment is installed in the AFM system100shown inFIG. 15to be used in AFM observation of a specimen surface and also to hold a miniscule specimen.

FIG. 23illustrates the observation operation executed by using the nanotweezer51. As shown inFIGS. 23(a1) and23(a2), the nanotweezer51is moved into close proximity to a specimen surface P at a tilt with a predetermined angle of inclination relative to the specimen surface. At this time, the distance d between the holding portion62of the observation probe60and the holding portion72of the movable arm70is maintained at the maximum distance do. It is to be noted that L1is light originating from the laser light source2, which is radiated onto the upper surface of the observation probe60. Light L2reflected off the upper surface of the observation probe60enters the two-element split photodiode3.

Then, as shown inFIGS. 23(b1) and23(b2), the probe portion63is positioned very close to the specimen surface P over a distance in the atomic-diameter order while maintaining the distance d between the opposite surfaces62aand72aat d0and the specimen surface is observed in the tapping mode. In the nanotweezer51achieved in the third embodiment, the lever61alone is made to resonate and vibrate with a large amplitude by setting the width of the lever61at the observation probe60greater than the width of the lever71at the movable arm70.

FIGS. 23(c1) and23(c2) illustrate the holding operation executed by using the nanotweezer51to hold a miniscule specimen S. As is the nanotweezer31achieved in the second embodiment, the nanotweezer51is also moved so as to position the miniscule specimens S between the holding portion72and the holding portion62maintaining the distance d0from each other. Then, the movable arm70is made to slide along the +X direction until the miniscule specimen S is clamped between the holding portion72and the holding portion62. In this embodiment the opposite surfaces62aand72aholding the miniscule specimen S between them also range parallel to each other and thus, the miniscule specimen S can be held with a high level of firmness.

Next, the manufacturing process through which the nanotweezer51is manufactured is explained.FIGS. 24(a1) through24(a3) illustrate step a, with (a1) presenting a plan view, (a2) presenting a sectional view taken along IIA-IIA and (a3) showing a mask ME used in step a. An SOI wafer90constituted with an upper Si layer91(with a thickness of 10 um), an SiO2layer92(with a thickness of 1 μm) and a lower Si layer93(with a thickness of 400 um) is first prepared and a silicon nitride film (an Si3N4film or an SiN film)94is formed over a thickness of 0.05 μm through LP CVD ratio the upper Si layer91.

Subsequently, an RIE process is executed by using the mask ME shown inFIG. 24(a3) to remove the SiN film94present or an area D1corresponding to an opening D2in the mask ME, and then, the upper Si layer91is also etched along the thickness-wise direction through ICP-RIE. Since the ICP-RIE process stops at the SiO2layer92, a groove D1with a depth of 10 μm, which is equal to the thickness of the upper Si layer91, is formed, as shown inFIG. 24(a2). In step b shown inFIGS. 24(b1) and24(b2), an oxide film95with a thickness of 0.3 μm is formed through steam oxidation over the exposed portions (the inner walls of the groove D1) of the upper Si layer91.

FIGS. 25(a1) through25(a3) illustrates step c, with (a1) presenting a plan view, (a2) presenting a sectional view taken along IIA-IIA and (a3) showing a mask MF. In step c shown inFIGS. 25(a1) and25(a2), the SiN film94present in an area E1to the left of the line IIA-IIA is removed through etching over an area F1by using the mask MF shown inFIG. 24(a3) until the upper Si layer91becomes exposed. The area F1corresponds to a non-shielding portion F2of the mask MF.

FIGS. 25(b1) and25(b2) illustrate step d, with (b1) presenting a plan view and (b2) presenting a sectional view taken along IIA-IIA. In step d, the upper Si layer91in the area F1is anisotropically etched by using a KOH solution. This etching process is stopped at, for instance, a time point at which the etching depth has become equal to 5 μm, half the fitness of the upper Si layer91, so as to form two triangular cones on the two sides of the groove D1, which have sloping surfaces G1and G2and assume a height of 5 μm. The sloping surfaces G1and G2are each positioned on the (111) plane of the Si crystal and the etching rate at the (111) plane is lower than that at the (001) plane ranging parallel to the substrate surface. It is to be noted that a TMAH solution, instead of the KOH solution, may be used in step d.

FIGS. 26(a1) and26(a2) illustrate step e, with (a1) presenting a plan view and (a2) presenting a sectional view taken along IIA-IIA. In step e, an oxide film96is formed over the exposed surface (the area F1) of the upper Si layer91.FIGS. 26(b1) and26(b2) illustrate step f, with (b1) presenting a plan view and (b2) presenting a sectional view taken along IIA-IIA. In step f, all the remaining SiN film94is removed through RIE. Thus, the upper Si layer91also becomes exposed over an area E2to the right of line IIA-IIA.

FIGS. 27(a1) and27(a2) illustrate step g, with (a1) presenting a plan view and (a2) presenting a sectional view taken along IIA-IIA. In step g, a process similar to that executed in step d inFIGS. 27(b1) and27(b2) is executed to anisotropically edge the upper Si layer91over the area E2. The anisotropic etching of the area E2also stops as soon as the etching depth reaches 5 μm. Thus, two more triangular cones are formed along the line IIA-IIA, which have sloping surfaces G3and G4. The sloping surfaces G3and G4are also each set on the (111) plane, as are the sloping surfaces G1and G2.

FIGS. 27(b1) and27(b2) illustrate step h, with (b1) presenting a plan view and (b2) presenting a sectional view taken along IIA-IIA. In step h, the oxide film96having been formed in order to protect the area F1is removed through etching. The combination triangular cone constituted with the triangular cone that includes the sloping surface G1and the triangular cone that includes the sloping surface G3eventually forms the holding portion62and the probe portion63, whereas the combination triangular cone constituted with the triangular cone that includes the sloping surface G2and the triangular cone that includes the sloping surface G4eventually forms the holding portion72. Since the area D1assumes a rectangular shape, the surfaces of the holding portion62and the holding portion72facing opposite each other range parallel to each other.

FIGS. 28(a1) through28(a3) illustrate step i, with (a1) presenting a plan view, (a2) presenting a sectional view taken along IIIA-IIIA and (a3) showing a mask MG. In addition,FIGS. 28(b1) through28(b3) illustrate step j, with (b1) presenting a plan view and (b2) and (b3) respectively presenting a plan view and a perspective of the observation probe60and the movable arm70having been formed. It is to be noted that the illustrations presented inFIGS. 28(a1),28(a3),28(b1) and28(b3) assume ranges greater than those assumed inFIGS. 24 through 27.

In step i shown inFIGS. 28(a1) and28(a2), an ICP-RIE process is executed by using the mask MG to define the outlines of the observation probe60and the movable arm70. Through this etching process, part of the outline of the supporting member75is also formed. As shown inFIG. 28(a1), the basic shapes of the observation probe60and the movable arm70are formed with the upper Si layer91as the upper Si layer91present at the boundary between the observation probe60and the movable arm70and the surrounding area around the observation probe and the movable arm is removed. It is obvious that over the areas where the upper Si layer91is removed, the SiO2layer92is exposed.

In step j shown inFIGS. 28(b1) and28(b2), an ICP-RIE process is executed by using a mask MH so as to separate the observation probe60and the movable arm70from each other and define the outline of the supporting member75. In step j, any unnecessary portions of the lower Si layer93and the SiO2layer92are removed from the rear surface of the SOI wafer90, i.e., from the side where the lower Si layer93is present. Through this procedure, the formation of the nanotweezer51which includes the observation probe60and the movable arm70, extending along a single direction and constituting an integrated unit together with the supporting member75, is completed. In addition, the drive mechanism80is also concurrently formed through a similar method while forming the observation probe60and the movable arm70. The drive mechanism80is also constituted with the upper Si layer91as are the observation probe60and the movable arm70.

The manufacturing method described above allows the dimensions of the observation probe60and the movable arm70, measured along the lengthwise direction (X direction), the widthwise direction (Y direction) and the thickness-wise direction (Z direction), to be selected freely through photolithography. The lengths and the widths are determined in correspondence to the mask dimensions, and the width of the lever61at the observation probe60can easily be set to a value optimal for achieving the required resonance frequency of the vibration in the tapping mode. In addition, the distance d (=maximum distance d0) between the holding portion62and the holding portion72can also be set freely. The thicknesses of the leavers61and71, the combined height of the holding portion62and the probe portion63and the height of the holding portion72, which are all determined in correspondence to the extent to which the upper Si layer91is etched, should be controlled during the manufacturing process.

By installing the nanotweezer51in the third embodiment in an AFM system, advantages similar to those of the nanotweezer in the second embodiment are realized. It is to be noted that better accuracy is assured by adjusting the width of the lever61at the observation probe60rather than the thickness of the lever61when selecting optimal dimensions for achieving the resonant frequency of vibration in the tapping mode, as explained earlier.

Fourth Embodiment

FIG. 29illustrates the fourth embodiment, with (a) presenting a plan view of a nanotweezer1taken on the specimen surface side and (b) and (c) each presenting an enlargement illustrating the structure assumed that a front end R of the nanotweezer1. Arms201and202are formed at the supporting member25. Reference numerals203and204indicate drive units that drive the arms201and202to open/close along the direction indicated by the arrows in the figure. The drive units203and204are thermal expansion actuators that are caused to expand by Joule heat and are engaged in operation by power supplied from a power source209. Reference numerals205and206indicate electrodes of the drive units203and204respectively, and the power source209is connected to the electrodes205and206.

The structure shown inFIG. 29(b) or the structure shown inFIG. 29(c) may be adopted in the front end area R at the arms201and202. It is to be noted thatFIGS. 29(b) and29(c) each show the arms in an open state so as to illustrate the structure of the front end more clearly. The structure illustrated inFIG. 29(b) is similar to that adopted in the nanotweezer achieved in the first embodiment explained earlier, and includes holding portions201aand202awith a right-angle triangle section formed therein. The front end structure illustrated inFIG. 29(c) is similar to that of the nanotweezer achieved in the third embodiment and includes projections201band202b, assuming the shape of an angular cone or a pyramid formed on the flat surfaces of the arms201and202toward the specimen.

FIG. 30illustrates the holding operation executed by using the arms201and202to hold the specimen S. While the power source209is in an OFF state, the arms201and202are closed, as shown inFIG. 29(a). In the embodiment, boron is doped over the silicon layers at the drive units203and204, and thus; when the power source209is in an OFF state, stress is applied along the direction indicated by the arrows pointing upward and downward inFIG. 29so as to cause the drive units203and204to contract.

In order to grasp and hold the specimen S, the nanotweezer1, still in the closed state, is moved to the vicinity of the specimen S. Next, the power source209is turned on to apply a voltage to the electrodes205and206. In response, an electrical current flows through a path indicated as; electrode205→drive unit203→arm201→arm202→drive unit204→electrode206. Much Joule heat is generated at the drive unit203and204with a smaller sectional area, and thus, the drive units203and204are caused to thermally expand along the direction indicated by the arrows inFIG. 30(a) (along the vertical direction in the figure). As a result, the arm201is displaced to the right and the arm202is displaced to the left, setting the arms201and202in an open state.

Once the arms201and202are set in the open state as shown inFIG. 30(a), the nanotweezer1is moved so as to position the specimen S between the arms201and202. When the arms201and202are in the open state, no electrical current flows, since the arm201and the arm202are no longer in contact with each other. As a result, the temperature at the drive units203and204decreases, setting off the natural tendency for the drive units203and204having become expanded, to resume the initial state. As the temperature becomes lower, the arms201and202move along the closing direction until they close on the specimen S as shown inFIG. 30(b). Then, the stress occurring as the drive units203and204try to contract generates the holding force with which the specimen S is grasped and held. It is to be noted that the power source209is turned off if the arms201and202enter an open state and that the specimen S is grasped and held in the power OFF state.

When the nanotweezer1is used as an observation probe in an AFM system, the arms are closed, as illustrated inFIG. 29(a), by turning off the power source209and the supporting member25is caused to vibrate by the exciter unit of the AFM system. Laser light may be radiated onto either the arm201or the arm202. In this case, the front end of the arms201and202, i.e., the front tip formed by the holding portions201aand202ainFIG. 29(a) or the front tip formed by the projections201band202binFIG. 29(b), functions as the probe portion.

While the manufacturing process for manufacturing the nanotweezer1includes additional steps for doping boron and for generating stress by annealing the drive units203and204having been doped with boron, the nanotweezer1can be otherwise manufactured by adopting a manufacturing method similar to the manufacturing method in the first embodiment or the third embodiment. As in the first and third embodiment, the drive units203and204are formed with the upper Si layer31(seeFIG. 1) of an SOI wafer.

A mask pattern is formed on the upper Si layer31of the SOI wafer prepared as explained earlier and areas where the drive units203and204are to be formed are doped with boron. More specifically, boron ions are implanted at the drive unit areas by using an ion-implanting device. Subsequently, the supporting member25, the arms201and202, the drive units203and204and the like to constitute the nanotweezer1are formed by adopting a manufacturing method similar to the manufacturing method adopted in the first or third embodiment. Once the nanotweezer1is formed on the SOI wafer, the nanotweezer1is separated from the SOI wafer through etching and the drive units203and204are annealed through a heat treatment.

FIG. 31(a) shows the nanotweezer1separated from the SOI wafer, with its arms201and202in an open state. Namely, the arms201and202are formed in the open state through etching. Then, the implanted boron replaces Si at an Si lattice site through annealing. Since the atomic radius of boron is smaller than that of Si, stress along the compressing direction is generated by replacing with boron at a lattice site. As a result, the drive units203and204contract and the front ends of the arms201and202are set in a closed state, as shown inFIG. 31(b), through the heat treatment. It is to be noted that the drive units203and204may be doped with boron by using a resist mask after defining the structural elements of the nanotweezer1through etching.

FIG. 32presents an example of a variation of the nanotweezer1shown inFIG. 29. The nanotweezer achieved in this variation includes electrodes207and208located at the bases of the arms201and202. A power source209A is connected between the electrodes205and207and a power source209B is connected between the electrodes206and208. Thus, the arms201and202can be individually driven to open/close and by supplying an electrical current to the drive units203and204while holding the specimen, the level of the holding force can be adjusted. However, it goes without saying that the power sources209A and209B may remain in an OFF state while the specimen is held. It is to be noted that the nanotweezer1achieved in the variation can be engaged in an open/close operation similar to that of the nanotweezer illustrated inFIGS. 29 and 30simply by connecting a power source between the electrodes205and206.

While the arms201and202in either of the nanotweezers shown inFIGS. 30 and 32are driven to open by supplying an electrical current to the drive units203and204and thus causing thermal expansion of the drive units203and204, either of these nanotweezers may further include another drive mechanism in addition to the drive units203and204doped with boron, which drives the arms201and202in the opening direction. The drive units203and204in the nanotweezer adopting such a structure simply function as a force-applying mechanism that applies a force to the arms201and202along the closing direction. The drive units203and204in either of the nanotweezers illustrated inFIGS. 30 and 32, which do not include such an additional drive mechanism, function both as the force-applying mechanism and the drive mechanism. The drive mechanism may be a thermal actuator that drives the arms through the process of thermal expansion or it may be an electrostatic actuator that drives the arms by using static electricity. In addition, if the drive mechanism is provided as a component independent of the force-applying mechanism, the distance between the arms201and202prior to the annealing process may be set small enough to be considered practically zero, since the arms201and202can be subsequently set in an open state via the drive mechanism.

While the front tip of a holding portion or a projection formed at the nanotweezer is used as the probe portion during specimen observation in the first through fourth embodiments described above, a normally closed nanotweezer, such as that achieved in the fourth embodiment, with which the specimen can be held between the arms201and202in the power OFF state, can be used in specimen observation conducted by holding a probe member. In such a case, it is not necessary to form the projections201band202binFIG. 29(c).

As explained above, with the nanotweezer achieved in the fourth embodiment, which enters the closed state when the power is turned off, can be used to continuously hold the specimen in the power OFF state. Thus, power consumption at the nanotweezer in the fourth embodiment can be reduced over the normally open nanotweezers achieved in the first through third embodiments. It is to be noted that the normally closed structure is adopted in a nanotweezer which opens/closes to the left and the right in the fourth embodiment, a normally closed structure may be likewise achieved in a sliding-type nanotweezer such as that disclosed in the second or third embodiment.

It is to be noted that, the present invention may be adopted in conjunction with a single-crystal Si wafer instead of an SOI wafer used in each of the embodiments explained above. Since an Si wafer does not include an SiO2layer32functioning as a stopper for the ICP-RIE process, it will be necessary to control the conditions under which the ICP-RIE process is executed. In order to etch the Si wafer to a depth of 5 μm at the {100} plane of Si, a mixed gas containing SF6and C4F8, for instance, may be used as a reaction gas and in such a case, the etching process will need to be executed for approximately 1.7 minutes with the high frequency power output level set at 600 W. The use of an Si wafer, which is less expensive than an SOI wafer, and can be processed through exactly the same manufacturing steps as those described in reference to the embodiments except that the ICP-RIE process conditions need to be adjusted as described above, will achieve a further reduction in the manufacturing cost.

The present invention is not limited to the embodiments explained above in any way whatsoever, as long as the features characterizing the present invention are not compromised. For instance, the extent of change in the amplitude of the vibration at the observation probe is measured by adopting an optical lever method in the embodiments described above, any of various measurement methods, including measurement of change in the capacitance, may be adopted instead. In addition, the nanotweezer achieved in any of the embodiments may be used in, for instance, a scanning probe microscope system (SPM system) that detects static electricity or a frictional force, instead of an AFM system. Moreover, the movable arm20or70or the arms201and202may be driven by static electricity or expansion/contraction of a piezoelectric film instead of via a thermal actuator. The holding portion22at the movable arm20, the holding portion72at the movable arm70, or the holding portions201aand202aat the arms201and202or the projections201band202bat the arms201and202may assume any of various shapes and they do not need to be formed in a projecting shape. Furthermore, a specimen may be observed by using the observation probe10or60or the arms201and202in a contact mode instead of the tapping mode. In addition, the observation probe10or60may also have a function of moving toward the specimen holding position as does the movable arm20or70, in addition to the observation function.

The disclosures of the following priority applications are herein incorporated by reference: