JP2009006471A - Nano tweezers and gripping method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide nano tweezers capable of sensibly detecting that an arm contacts an object. <P>SOLUTION: Nano tweezers comprise a pair of openable and closable arms, an electrostatic actuator 6, to which an opening/closing drive voltage is applied and which drives at least one of the pair of the arms to be opened and closed, an amplifier 91 for self-oscillating by using an electric equivalent circuit of the electrostatic actuator 6 as a feedback circuit and vibrating the arms by the self-oscillation, and a vibrations change detection part 93 for detecting the change of the vibration caused by the contact of the arm to an object. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a nanotweezers for handling a minute work and a gripping method using the nanotweezers.

  In nano tweezers for handling minute workpieces, there is known an apparatus for detecting gripping of a sample by utilizing a change in the capacitance of a comb actuator (for example, see Patent Document 1).

JP 2006-210566 A

  However, since the apparatus described above determines whether or not the actuator has been grasped by detecting a change in the capacity of the actuator, there has been a problem in detection sensitivity, detection stability, and the like.

The nanotweezers according to the invention of claim 1 includes a pair of arms that can be opened and closed, an electrostatic actuator that is applied with an opening and closing drive voltage to drive at least one of the pair of arms, and an electrical equivalent circuit that the electrostatic actuator has. A self-excited oscillation by using as a feedback circuit, and an amplifier that vibrates the arm by the self-excited oscillation, and a vibration state detection unit that detects a change in the vibration state due to the contact of the arm with an object. .
The nanotweezers according to the invention of claim 2 are self-excited by using a first arm that opens and closes, a second arm that includes an electrostatic actuator, and an electrical equivalent circuit of the electrostatic actuator as a feedback circuit. And an amplifier that vibrates the second arm by the self-excited oscillation, and a vibration state detection unit that detects a change in the vibration state due to the contact of the second arm with the object. The first and second arms It is characterized by holding a sample.
According to a third aspect of the present invention, in the nanotweezers according to the first or second aspect of the present invention, the nanotweezers include gain adjusting means for adjusting the gain of the amplifier so that the amplitude of the arm oscillated by self-oscillation is constant when not in contact. It is characterized by that.
According to a fourth aspect of the present invention, in the nanotweezers according to any one of the first to third aspects, the gripping detection means for detecting gripping of the sample by the arm based on a change in the vibration state detected by the vibration state detection unit. Is further provided.
According to a fifth aspect of the present invention, in the nanotweezers according to any one of the first to fourth aspects, the change in the vibration state is caused by changing the amplitude of the resonance vibration, the change in the frequency, and the phase due to the contact of the arm with the object. One of the changes.
The invention according to claim 6 is the nanotweezers according to any one of claims 1 to 5, wherein the electrostatic actuator includes a stationary comb electrode part and a movable comb electrode connected to the arm and driving the arm. Part.
The invention of claim 7 is a method for gripping a sample by the nano tweezers according to claim 1, wherein the sample is placed on the nano tweezers until a change in vibration is detected by the vibration change detecting unit. If the change in vibration is detected by the vibration change detection unit, the nano tweezers are moved by a predetermined amount in the direction opposite to the direction of the placement unit, and the arm is moved by the electrostatic actuator after the movement. When the vibration is detected by the vibration change detection unit, the arm drive by the electrostatic actuator is stopped.

  According to the present invention, gripping by an arm can be detected with high sensitivity by detecting a change in vibration.

  Hereinafter, the best mode for carrying out the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing an embodiment of nanotweezers according to the present invention. As will be described later, the nanotweezers 1 are formed on a semiconductor substrate by using a micromachining technique to which a semiconductor process technique is applied. The nanotweezers 1 are used by being mounted on a moving mechanism such as an XYZ stage, and are used for handling a micron order sample.

  On the pedestal 7, arms 3A and 3B for holding the sample and electrostatic actuators 6A and 6B for opening and closing the arms 3A and 3B to the left and right are formed. A micron-order sample is gripped by the grip portion 30 formed at the tip of the arms 3A and 3B. As will be described later, the electrostatic actuators 6A and 6B are driven and controlled by the drive circuit unit 9.

  FIG. 2 is an enlarged view showing details of the grip portion 30, and the grip portion 30 is formed by thinning the tip portions of the arms 3 </ b> A and 3 </ b> B in a stepped manner. The width W and thickness t of the grip portion 30 that holds a micron-order sample are set to the same size as the sample, such that W = 1 to 30 μm and t = 1 to 25 μm. The length L of the grip part 30 is set to about 100 μm, which is slightly longer than the sample.

  The electrostatic actuator 6A for driving the left arm 3A in FIG. 1 includes a fixed electrode 60a fixed on the base 7 and a movable electrode 61a connected to the arm 3A. Similarly, the electrostatic actuator 6B that drives the right arm 3B includes a fixed electrode 60b fixed on the pedestal 7 and a movable electrode 61b connected to the arm 3B. The opposing surfaces of the fixed electrodes 60a and 60b and the movable electrodes 61a and 61b extending in the vertical direction in the figure are comb-shaped as will be described later.

  The movable electrodes 61a and 61b of the electrostatic actuators 6A and 6B are elastically fixed to the pedestal 7 by the support portions 62, respectively. An arm switching voltage is applied between the electrode terminal 80 of the fixed electrode 60a and the electrode terminal 81 of the movable electrode 61a, and between the electrode terminal 82 of the fixed electrode 60b and the electrode terminal 83 of the movable electrode 61b. Is done. When the arm opening / closing voltage is applied, the movable electrode 61a moves in the right direction in the figure and the movable electrode 61b moves in the left direction in the figure by electrostatic force. As a result, the arms 3A and 3B are closed.

  The arms 3 </ b> A and 3 </ b> B are elastically fixed to the pedestal 7 via the support portion 63. An electrode terminal 84 is connected to the arms 3A and 3B via a support portion 63, and the arm 3A and 3B are electrically operated and an electrical measurement is performed using the electrode terminal 84. Can do. The left arm 3A is connected to the left movable electrode 61a by a connecting member 8 provided at the lower portion of the arm 3A. Similarly, the right arm 3B is connected to the right movable electrode 61b by the connecting member 8. As a result, the sample is gripped by the left and right grip portions 30.

  FIG. 3 is an enlarged view showing a connecting portion between the left arm 3A and the movable electrode 61a. The arm 3A is connected to the movable electrode 61a via the connecting member 8. FIG. Insulating layers 102 are formed between the arm 3A and the connecting member 8 and between the movable electrode 61a and the connecting member 8, respectively. When the movable electrode 61a moves to the right side in the figure by electrostatic force, the arm 3A also moves to the right side in conjunction with the movement. The right arm 3B, the fixed electrode 60b, and the movable electrode 61b have the same structure except that they are horizontally reversed.

  FIG. 4 is a diagram showing a cross-sectional shape of the nanotweezers 1, and shows the A-A ′ cross section, the B-B ′ cross section, the C-C ′ cross section, and the D-D ′ cross section of FIG. 1. As shown in the AA ′ cross section, the BB ′ cross section, and the CC ′ cross section, the pedestal 7 is formed with through holes 7a and 7b. The arms 3A and 3B and the electrostatic actuators 6A and 6B are formed of these through holes 7a and 7b. It is formed so as to be bridged over the through holes 7a and 7b.

  The electrostatic actuators 6A and 6B are formed on the base 7 via the insulating layer 102. Similarly, the arms 3 </ b> A and 3 </ b> B connected by the connecting member 8 are also formed on the base 7 through the insulating layer 102. The D-D ′ cross section is a cross section of the electrode terminals 80 to 84 in FIG. 1, and the electrode terminals 80 to 84 are also formed on the base 7 via the insulating layer 102. As described above, the nanotweezers 1 is formed on a three-layered substrate composed of two upper and lower silicon layers sandwiching an insulating layer, for example, an SOI (silicon on insulator) substrate. The arms 3A and 3B, the electrostatic actuators 6A and 6B, and the electrode terminals 80 to 84 are formed using the same silicon layer. In addition, the manufacturing method of the nano tweezers 1 is mentioned later.

<Operation description>
In the nanotweezers 1 of the present embodiment, as described above, a DC voltage is applied to the electrostatic actuators 6A and 6B, and the voltage values are controlled to perform the opening and closing operations of the arms 3A and 3B. Furthermore, the electrostatic actuators 6A and 6B are self-excited to vibrate the arms 3A and 3B, and the gripping by the arms 3A and 3B is detected by a change in the minute vibration when the sample is gripped.

  First, the electrostatic actuators 6A and 6B in which the electrical system and the mechanical system are coupled by the arm opening / closing voltage oscillate at a predetermined frequency by applying an alternating voltage, that is, the electrostatic actuators 6A and 6B. Will function as a vibrator.

  FIG. 5A is an enlarged view showing the structure of the fixed electrode 60a and the movable electrode 61a of the electrostatic actuator 6A, and FIG. 5B shows an equivalent circuit of the electromechanical coupling system in the electrostatic actuator 6A. FIG. Since the electrostatic actuator 6B is the same, the electrostatic actuator 6A will be described below as an example. In general, in the electrical / mechanical coupled system, the conservation law of electrical energy and mechanical energy is established, and here, it is modeled on the assumption that the arm switching voltage is small and the displacement of the movable electrode and the fluctuation of the charge amount are small. .

The opposing part of the fixed electrode 60a and the movable electrode 61a has a comb-tooth shape, and the comb teeth 600 formed on the fixed electrode 60a and the comb teeth 610 formed on the movable electrode 61a alternately enter the other party. Yes. A capacitance C ₀ is generated between the comb teeth 600 and 610. This electrostatic capacity C ₀ represents the total electrostatic capacity between the comb teeth 600 and 610 on which many irregularities are formed. Further, m is the mass of the movable part (arm 3A and movable electrode 61a), k is the spring constant, rf is the mechanical resistance, and v is the vibration speed of the movable part 12. A is a coupling coefficient between the mechanical system and the electrical system by applying the arm switching voltage E _0. When an AC voltage for exciting vibration is applied, a current i2 flows through the electric system, and the electrostatic actuator 6A is driven.

With respect to the electrostatic actuator 6A shown by the equivalent circuit in FIG. 5B, the linear approximation basic equation is expressed as in the equations (1) and (2). Note that C _S is a stray capacitance, and an equation was established by replacing C ₀ of the equivalent circuit of FIG. 5B with C ₀ + C _S.
i ₁ = jω (C ₀ + C _S ) e ₁ + (E ₀ C ₀ / X ₀ ) ν ₁ (1)
f ₁ = jωmν ₁ + r _f v ₁ + kν ₁ / jω + E ₀ C ₀ e ₁ / X ₀ (2)
However, i ₁ is an alternating current value, e ₁ is the amplitude of the input AC voltage, ν ₁ is the vibration speed of the movable part, and f ₁ is an external force acting on the movable part. X ₀ is the inter-comb distance in the initial state.

From Expressions (1) and (2), when the external force is zero, the relationship between the absolute value | Y | of the admittance of the electrostatic actuator 6A and the angular frequency ω can be expressed as Expression (3). Here, A = E ₀ C ₀ / X ₀ .

FIG. 6 shows an admittance curve representing the angular frequency dependence of the admittance value | Y |. This admittance curve is a characteristic curve of an electrical / mechanical coupling system. On the other hand, a straight line (broken line) represented by | Y | = ω (C ₀ + C _S ) is a characteristic curve in the case of only an electric system without a mechanical system, and the following expression (4) is established in expression (3). The characteristic curve in the case is shown.
A ² −2ω (C ₀ + C _S ) (ωm−k / ω) = 0 (4)

When the angular frequency ω that satisfies Equation (4) is referred to as the oscillation angular frequency ω1, the oscillation angular frequency ω ₁ is the angular frequency at the intersection of the admittance curve and the straight line represented by | Y | = ω (C ₀ + C _S ). It is. The oscillation angular frequency ω ₁ is a value close to the resonance angular frequency ω ₀ , and when the electrostatic actuator 6A is driven at the oscillation angular frequency ω ₁ , the characteristics of the mechanical system are canceled as described above, and the admittance measurement only for the electric system is performed. It becomes possible.

The resonance angular frequency omega ₀ is the peak angular frequency of admittance curve is located at slightly higher than omega _p, a peak angular frequency omega _p of the admittance _curve, the bottom of the angular frequency of the portion showing a concave curve Assuming ω _b , the relationship between the resonance angular frequency ω ₀ and the oscillation angular frequency ω ₁ can be expressed by equation (5).

  Thus, it was found that the electrostatic actuator 6A functions as a resonance circuit. Therefore, in this embodiment, the self-excited oscillation drive mechanism is configured using the electrostatic actuator 6A and the amplifier.

  FIG. 7 is a block diagram showing a drive circuit unit 9 for driving the electrostatic actuator 6. In this figure, the electrostatic actuator 6 is drawn based on the L, C, R resonance circuit which the comb drive (COMB-DRIVE) originally has. That is, FIG. 7 shows the drive circuit 9 with the comb drive (COMB-DRIVE) regarded as a passive two-terminal element.

The drive circuit unit 9 includes an amplifier 91 having a comb drive (electrostatic actuator) 6 as a feedback circuit, and an AGC (automatic gain) that generates a gain control voltage Vc by comparing the output voltage V ₀ of the amplifier 91 with a reference voltage Vr. A control) circuit 95 and a DC power source 92 for applying a bias DC voltage E ₀ to the comb drive (electrostatic actuator) 6. The bias applying DC power source 92 can be referred to as an “arm opening / closing DC power source” when focusing on the function of the electrostatic actuator.

  When the comb drive (electrostatic actuator) 6 is inserted into the feedback circuit of the amplifier 91, the present embodiment pays attention to the following points.

First, since the internal resistance of the DC power source 92 to which the bias DC voltage E ₀ is applied is very small, it is necessary to prevent the feedback signal from passing through the DC power source 92 side. Therefore, in this embodiment, the high resistance R _high is inserted in series with the DC power source. This prevents the bias DC power source 92 from affecting the feedback path.

Second, the DC power source 92 for bias application is in a floating state as a DC circuit from the circuit system including the amplifier 91, and at the same time, blocking is performed so that a DC voltage is not directly applied to the terminal (output terminal & input terminal) of the amplifier 91. - a capacitor _{C B} are inserted.

Next, the voltages V ₁ and V ₂ of each terminal in the comb drive (electrostatic actuator) 6 will be described. The voltage V ₁ is a value obtained from the design value of the DC bias circuit in the amplifier 91. Generally, when only the single power supply voltage (+ B) is used, V ₁ = + B / 2. On the other hand, when using both power supply voltages (± B), V ₁ = 0.

As apparent from the equivalent circuit of the comb drive (electrostatic actuator) 6, the voltage V < _b > ₂ does not pass a DC current, so V ₂ = E ₀ . Here, E ₀ is a bias DC voltage E ₀ applied to the comb drive (electrostatic actuator) 6. The comb drive (electrostatic actuator) 6 is opened and closed according to the difference between the voltage V ₁ and the voltage V ₂ set in this way. In other words, the potential difference between terminals necessary to open and close the comb drive (electrostatic actuator) 6 is | V ₁ −V ₂ |.

Electrodes 60a of the electrostatic actuator 6A, the 61a, arm switching voltage _{E 0} is applied by the arm opening and closing DC supply 92. The arm switching voltage by controlling the E _0, arms 3A, the opening and closing operation of 3B is performed. An output signal from the amplifier 91 is supplied to the contact / gripping detection circuit 93. The contact / gripping detection circuit 93 includes, for example, a voltage comparator or a frequency comparator (not shown) in order to detect the contact state or gripping state of the sample. That is, the contact / gripping of the sample is detected by monitoring the output voltage value of the amplifier 91 using a voltage comparator. When the frequency comparator is used, the contact / gripping of the sample is detected by monitoring the frequency of the signal output from the amplifier 91.

  By configuring an oscillation circuit with the amplifier 91 and the comb drive (electrostatic actuator) 6, when a voltage is applied to the electrostatic actuator 6A, the arms 3A and 3B vibrate at the resonance frequency. When the vibrating arms 3A and 3B come into contact with a sample or other object, R, C, and L of the equivalent circuit change, and the amplitude and frequency of vibration change. In the present embodiment, the vibration / frequency change is detected by the contact / gripping detection circuit 93, whereby the arm 3A, 3B grips the sample, and the arm 3A, 3B contact was detected.

  However, it has been found that when the arm 3A, 3B is opened / closed by changing the arm opening / closing voltage, the amplitude and frequency of vibration change depending on the magnitude of the arm opening / closing voltage, that is, depending on how the arms 3A, 3B are opened. In order to obtain sufficient contact detection accuracy, it is necessary to reduce the amplitude of the arms 3A and 3B to about 100 nm. However, if the amplitude becomes small, the vibration becomes unstable due to the viscosity of the air, etc., and even if the amplitude becomes small due to instability, there is a possibility that it is erroneously determined as gripping.

Therefore, in the present embodiment, the gain of the amplifier 91 is adjusted by the AGC circuit 95 so that the output voltage V ₀ from the amplifier 91 becomes constant even when the input V ₁ changes due to opening and closing of the arm. Therefore, in a free state where the arms 3A and 3B are not holding anything, the arms 3A and 3B vibrate with a constant amplitude. However, in order to enable the contact / gripping detection circuit 93 to detect the contact or gripping state, the gain control function of the AGC circuit 95 is set to an appropriate value in advance. Since this gain setting is a design matter, detailed description thereof is omitted.

In FIG. 7, a voltage-controlled variable gain amplifier is used as the amplifier 91, and an AGC circuit 95 is constituted by an output level detector (not shown), an error detection circuit (not shown), and a control circuit (not shown). I did it. That is, the error of the reference voltage Vr which is previously set DC voltage to monitor the output voltage V ₀ which amplifier 91 at the output level detector (not shown), is output from the output level detector (not shown) Comparison is made by a detection circuit (not shown). An error detection circuit (not shown) outputs an error signal k as a comparison result to a control circuit (not shown). A control circuit (not shown) supplies a gain control voltage Vc such that the error signal k (not shown) becomes zero to the control terminal of the amplifier 91. Amplifier 91 amplifies the input voltage V1 at a gain corresponding to the input gain control voltage Vc, and outputs an output voltage V _0. In the present embodiment, the gain control voltage Vc is increased as the output voltage V ₀ increases, and the gain of the amplifier 91 is controlled to decrease, thereby controlling the output voltage V _{0 to} be constant.

FIG. 8 shows an example of the AGC circuit 95. The output voltage V ₀ of the amplifier 91 is full-wave rectified, and the gain control voltage Vc is output as a result of comparing the full-wave rectified voltage with the reference voltage −Vr from the subsequent operational amplifier. The gain control voltage Vc is input to the gate of the FET 97, and the gain of the amplifier 91 is changed by changing the gate voltage. Since the gain control voltage Vc is controlled such that the error signal k becomes zero, an output voltage V ₀ having a constant amplitude is obtained.

Figure 9 is a diagram illustrating the AGC function, the arms 3A when changing arm switching voltage E ₀ and the gain control voltage Vc, the amplitude of 3B, is data measured using a laser Doppler vibrometer. The vertical axis represents amplitude, and the horizontal axis represents gain control voltage Vc. Curves L1 to L4 were obtained for four types of switching voltages 16, 18, 20, and 22V. For example, when the gain control voltage Vc is fixed to Vc = 1V and the AGC function is not activated, when the switching voltage is set to 16V, the amplitude of the arms 3A and 3B becomes about 3 μm, the switching voltage is increased to 18V, and the arm 3A , 3B is closed, the amplitude of vibration increases to about 7 μm.

  Therefore, in order to keep the amplitude constant regardless of the opening / closing of the arm, the gain control voltage Vc may be changed in synchronization with the change of the opening / closing voltage. For example, when the arm is closed by changing the switching voltage to 16V, 18V, or 20V, the amplitude is about 3 μm by changing the gain control voltage Vc to 1V, 1.2V, or 1.3V in synchronization with the change. Can be held in.

If the arm 3A, 3B comes into contact with a sample or another object while vibrating, the sample is gripped by the arms 3A, 3B, or is closed until the arms 3A, 3B come into contact with each other, the equivalent circuit R, C, L Changes to change the amplitude and frequency of vibration, and the change is detected by the contact / gripping detection circuit 93. For example, before and after contact, the output voltage V ₀ changes from the state shown in FIG. 10A to the state shown in FIG. The output voltage V ₀ is converted into a DC signal is compared in size to a reference value, it is determined that a contact state or the grip state if equal to or less than the reference value.

  When the arms 3A and 3B come into contact with the sample or hold the sample, the AGC circuit 95 operates to maintain the amplitude of the arms 3A and 3B at a predetermined value, and gain control supplied to the control terminal of the amplifier 91 is performed. The voltage Vc changes. Therefore, a change in vibration may be detected from a change in the gain control voltage Vc supplied to the amplifier 91, thereby detecting contact. Since the change in the gain control voltage Vc is detected prior to the change in amplitude or frequency, contact detection with higher sensitivity can be performed.

  As described above, in the nanotweezers 1 of the present embodiment, the electrostatic actuators 6A and 6B are oscillated to cause the arms 3A and 3B to vibrate slightly, and the change in vibration when the arms 3A and 3B come into contact with the sample or the like. Detecting contact and gripping. Further, the AGC circuit 95 is used to keep the vibration amplitude constant. Therefore, compared with the conventional method of detecting the capacitance change of the electrostatic actuator, the stability of detection sensitivity and detection accuracy is excellent. In the case of the present embodiment, the detection sensitivity is determined by the Q value of the natural vibration, and a sensitivity improvement of 10 to 100 times can be expected as compared with the case where the capacitance change is used. Further, since self-excited oscillation using an electrostatic actuator as a vibrator is used, the circuit is excellent in terms of simplification.

  In the above-described embodiment, both the arms 3A and 3B are vibrated. However, only one of them may be vibrated and contact detection and grip detection may be performed by the vibrating arm. Further, only one of the arms may be opened / closed and oscillated.

  Furthermore, one arm may be driven to open and close by another type of actuator that changes to the electrostatic method, and the other arm may be caused to vibrate only by the electrostatic actuator, and contact detection or grip detection may be performed by that arm. As another type of actuator, there is a thermal actuator that drives an arm by thermal expansion. In this case, the AGC circuit 95 may be omitted because the vibrating arm does not perform the opening / closing operation, but it is preferable to use the AGC circuit 95 in order to vibrate the arm stably with a minute amplitude.

<< Description of manufacturing process >>
Next, a manufacturing method in the case where the nanotweezers 1 are formed using an SOI (silicon on insulator) substrate will be described. In the following, a method for forming the arms 3A and 3B and the electrostatic actuators 6A and 6B will be described, and the description and illustration of the drive circuit unit 9 will be omitted. The drive circuit unit 9 may be formed on the same silicon layer as that constituting the arms 3A and 3B and the electrostatic actuators 6A and 6B by a semiconductor process technique, or a circuit element created separately may be arranged on the pedestal 7. Anyway.

  As shown in FIG. 11A, the substrate 100 used for forming the nanotweezers 1 includes a base layer 101 made of <110> -oriented single crystal silicon, an insulating layer 102 made of silicon oxide, and a <110> -oriented single crystal. A silicon substrate in which silicon layers 103 made of silicon are sequentially stacked is used. As the silicon substrate 100, not only an SOI substrate but also a substrate having a single crystal silicon layer on a glass substrate, a substrate having an SOI layer on an amorphous silicon substrate or a polysilicon substrate, or the like can be used. That is, if the uppermost layer is the silicon layer 103 having the <110> orientation and the silicon substrate has a layer structure in which the insulating layer 102 is formed below the silicon layer 103, the base layer 101 is formed in multiple layers. It does not matter as a structure.

An example of the thickness of each layer of the silicon substrate 100 will be described. The silicon layer 103 is 25 μm, the insulating layer 102 is 1 μm, and the base layer 101 is 300 μm. In addition, a region for forming one nanotweezers on the silicon substrate 100 has a rectangular shape of several mm in both length and width. In the step shown in FIG. 11A, an aluminum layer 104 having a thickness of about 50 nm is formed on the surface of the silicon layer 103 by sputtering or vacuum deposition.

  Next, as shown in FIG. 11B, a resist 105 having a thickness of about 2 μm is formed on the surface of the aluminum layer 104, and the resist 105 is exposed and developed by photolithography to thereby form the resist shown in FIG. 11C. A pattern 105a is formed. FIG. 14 is a perspective view of the silicon substrate 100. On the upper surface of the aluminum layer 104, resist patterns 105a corresponding to the arms 3A and 3B, the electrostatic actuators 6A and 6B, and the like are formed. In addition, FIG.11 (c) shows the F-F 'cross section of FIG.

Next, as shown in FIG. 11D, the aluminum layer 104 is etched with a mixed acid solution using the resist pattern 105a as a mask to expose the silicon layer 103. Next, as shown in FIG. Thereafter, the silicon layer 103 is anisotropically etched in the vertical direction by ICP-RIE (Inductively Coupled Plasma-Reactive Ion Etching). This etching is performed until the insulating layer 102 is exposed. After the etching is completed, the resist pattern 105a and the aluminum layer 104 are removed with a sulfuric acid / hydrogen peroxide mixed solution (see FIG. 12A).

  FIG. 15 is a perspective view showing the substrate 100 after the resist pattern 105a and the aluminum layer 104 are removed. A three-dimensional structure is formed on the insulating layer 102 by the same silicon layer 103. The three-dimensional structure includes a portion 103a constituting the arms 3A and 3B, a portion 103b constituting the electrostatic actuators 6A and 6B, a portion 103c constituting the electrode terminals 80 to 84, and a portion constituting the guard 4 described later. 103d.

Next, a resist 106 is applied so as to cover the exposed insulating layer 102 and silicon layers 103 (103a to 103d) (see FIG. 12B). The coating thickness of the resist 106 is about 10 μm. Thereafter, the mask pattern is transferred to the resist 106 by photolithography and developed, thereby forming a resist pattern 106a in which the resist 106 at the tip of the arm constituent portion 103a is removed in a rectangular shape as shown in FIG. Then, ICP-RIE, normal RIE, or the like is performed using the resist pattern 106a as a mask, and the tip portion of the arm constituent portion 103a is processed into a shape and size that match the gripping target of the nanotweezers.

  Next, as shown in FIG. 12C, the substrate 100 is turned upside down, and an aluminum layer 107 is formed on the surface of the base layer 101 by sputtering or vacuum evaporation. The thickness of the aluminum layer 107 is about 50 nm. Then, after forming a resist 108 on the aluminum layer 107 to a thickness of about 2 μm, a resist pattern is formed by photolithography, and the aluminum layer 107 is etched with a mixed acid solution using the resist 108 as a mask (FIG. 13 ( a)).

FIG. 17 is a perspective view showing the shapes of the resist 108 and the aluminum layer 107. FIG.
FIG. 17A is a cross-sectional view taken along the line GG ′ of FIG. 17, and a cross section of the arm portion 103 a formed of the silicon layer 103 is illustrated on the lower side (surface side) of the insulating layer 102. As can be seen from FIG. 17, the resist 108 has portions R1 and R2 corresponding to the guard 4 and the connecting portion 5 described later, a portion R3 corresponding to the base 7 and a portion R4 corresponding to the connecting member 8 of FIG. Conversely, portions corresponding to the through holes 7a and 7b shown in FIG. 4 are removed, and the base layer 101 is exposed.

  Thereafter, the base layer 101 is etched by ICP-RIE using the resist 108 and the aluminum layer 107 formed on the base layer 101 as a mask. The base layer 101 is etched in the vertical direction by anisotropic etching, and the etching is performed until the insulating layer 102 is exposed. After the etching is completed, the resists 108 and 106 and the aluminum layer 107 are removed with a sulfuric acid / hydrogen peroxide mixed solution (see FIG. 13B).

FIG. 18 is a diagram showing the back side of the base layer 101 shown in FIG. Etching forms the base 7 having the through holes 7a and 7b, the guard 4, the connecting portion 5 and the connecting member 8 in the base layer 101. On the substrate 100, a plurality of nanotweezers 1 on which guards 4 are formed are formed. Next, the insulating layer 102 made of silicon oxide exposed on the pedestal is etched using a buffered hydrogen fluoride solution. As a result, the insulating layer 102 is removed except for a region sandwiched between the silicon layer 103 and the base layer 101 (see FIG. 13C).

  FIG. 19 is a perspective view showing the surface side of the base layer 101, and FIG. 13C shows the H-H 'cross section of FIG. An insulating layer 102 is interposed between the electrode portion 103 and the base portion 101. Thereafter, as shown in FIG. 13D, a conductor film 109 made of aluminum or the like is formed on the exposed base layer 101 and on the silicon layer 103 constituting each structure by a vacuum deposition method or the like. . The thickness of the conductor film 109 is 500 nm or less.

In this way, the nano tweezers 1 including the guard 4 is formed. Depending on the object to be gripped, the grip portion 3a may be further machined by a processing apparatus such as FIB. The guard 4 protects the arms 3 </ b> A and 3 </ b> B of the nanotweezers 1 and is connected to the pedestal 7 by a connecting portion 5. When using the nano tweezers 1, the connecting portion 5 is folded and the guard 4 is removed from the nano tweezers 1.

[Modification]
FIG. 20 is a diagram illustrating an example of nanotweezers using a thermal actuator. The arm 3 </ b> A that opens and closes is provided with a thermal actuator including drive levers 23 and 24. On the other hand, the arm 3 </ b> B provided with the electrostatic actuator 6 </ b> B does not perform an opening / closing operation but only performs a vibration operation. As for the drive levers 23 and 24, each beam part 23a and beam part 24a are connected to arm 3A. The width in the X direction of the beam portion 24a is made narrower than that of the beam portion 23a.

  The drive levers 23 and 24 of the thermal actuator are connected to the power supply unit 200. The power supply unit 200 includes two variable power supplies 200 a and 200 b connected in series. The minus side of the variable power supply 200 a is connected to the drive lever 23, and the plus side of the variable power supply 200 b is connected to the drive lever 24. The connection point between the variable power supplies 200a and 200b is set to the ground potential.

  The resistance value of the beam portion 24a is set to be larger than that of the beam portion 23a. When electric power is supplied from the power source unit 200 to the drive levers 23 and 24, the beam portion 24a that generates a large amount of Joule heat is larger. Thermal expansion is greater than As a result, the arm 3A is closed so that the arm 3A is inclined with the portion 20a where the width of the root portion is narrowed as a fulcrum. The vibration drive on the arm 3B side is the same as that of the nanotweezers described above and will not be described. However, the same effect as that of the above-described embodiment can be obtained.

<Description of gripping action>
Finally, an example of the gripping operation by the nano tweezers 1 will be described with reference to FIGS. As described above, the nanotweezers 1 can be moved in a three-dimensional direction by an XYZ stage or the like. First, as shown in FIG. 21A, with the arms 3A and 3B opened, the nanotweezers 1 are moved in the Z-axis direction to bring the arms 3A and 3B closer to the sample 300. At this stage, since the arms 6A and 3B are in a free state, they vibrate with a predetermined amplitude by self-excited oscillation.

  Next, as shown in FIG. 21B, when the sample 300 is brought into contact with the stage 302 on which the sample 300 is placed, the vibrations of the arms 3A and 3B are reduced when the sample 300 is brought into contact. If the restraining force due to contact is very small, the AGC circuit 95 can maintain the amplitude at a predetermined value. However, if the restraining force exceeds a range where the amplitude can be maintained at the predetermined value, the amplitude becomes smaller than the predetermined value. When the force pressing the arms 3A and 3B against the base 302 increases and the restraining force further increases, the amplitude cannot be kept constant, and the vibrations of the arms 3A and 3B stop. FIG. 21B shows a state where the vibration is stopped.

  In this case, the contact of the arms 3A and 3B with the table 302 can be detected by any one of a change in frequency, a change in amplitude, and a change in control voltage Vc as described above. For example, when the amplitude becomes smaller than the reference value, it is determined that the arms 3A and 3B are in contact with the table 302.

  In FIG. 21C, the arms 3A and 3B are lifted by a small amount in order to shift to the gripping operation. As a result, the arms 3A and 3B vibrate again. When the arms 3A and 3B are slightly raised from the table 302, the arm opening / closing voltage is increased and the closing operation of the arms 3A and 3B is started as shown in FIG. When the arms 3A and 3B grip the sample 300 as shown in FIG. 22B, the vibration of the arms 3A and 3B is stopped by the gripping force. The stop of the vibration of the arms 3A and 3B is detected by the contact / gripping detection circuit 93 of FIG. If gripping is detected, the increase in arm open / close voltage is stopped and held at the voltage at the time of gripping detection. Thereafter, the XYZ stage is driven to move the nanotweezers 1 while holding the sample 300 as shown in FIG. 22C, and transport the sample 300 to a desired position.

  The drive circuit unit 9 and the contact / grip detection circuit 93 shown in FIG. 7 detect the contact / grip state of the comb drive by detecting the vibration amplitude. However, in order to detect the contact / gripping state of the comb drive, it is also possible to detect the contact / gripping state based on frequency detection or to detect the contact / gripping state based on phase detection. Hereinafter, a contact / gripping detection circuit including a frequency detection system and a contact / gripping detection circuit including a phase detection system will be described.

FIG. 23 shows a contact / gripping detection circuit including a vibration frequency detection system. In this figure, components similar to those in FIG. 7 are denoted by the same reference numerals as in FIG. In this figure, unlike FIG. 7, the positive feedback path of the amplifier 91 includes a bandpass filter BPF and a phase shifter PS. The oscillation frequency can be finely adjusted by adjusting the phase shifter PS. FM demodulator FMDM outputs the frequency deviation signal by detecting the frequency shift amount with respect to the reference frequency f _0. The frequency deviation signal is input to the contact / gripping detection circuit 93A, and based on a determination result by a threshold circuit (not shown), the contact with the sample or the gripping state is detected.

  FIG. 24 shows a contact / gripping detection circuit including a phase detection system. In this figure, components similar to those in FIG. 7 are denoted by the same reference numerals as in FIG. In this figure, the band-pass filter BPF and the phase shifter PS are included in the positive feedback path of the amplifier 91 as in the case of FIG. The oscillation frequency can be finely adjusted by adjusting the phase shifter PS. In this figure, a phase detector PHDET is provided, and a phase shift amount is converted into a voltage with an arbitrary phase (using a free state phase) adjusted in advance as a zero phase. The output signal of the phase detector PHDET is input to the contact / gripping detection circuit 93B, and the contact or gripping state with the sample is detected based on the determination result by a threshold circuit not shown.

  In the above-described embodiment, the nanotweezers are formed by processing the silicon substrate. However, the present invention is not limited to such a forming method, and nanotweezers may be formed by various forming methods. In addition, the above description is an example to the last, and this invention is not limited to the said embodiment at all unless the characteristic of this invention is impaired.

It is a figure which shows one Embodiment of the nanotweezers by this invention. FIG. 4 is an enlarged view showing details of a grip part 30. It is an enlarged view which shows the connection part of arm 3A and the movable electrode 61a. It is a figure which shows the cross-sectional shape of nano tweezers, and is a figure which each shows the A-A 'cross section, B-B' cross section, C-C 'cross section, and D-D' cross section of FIG. (A) is an enlarged view showing the structure of the fixed electrode 60a and the movable electrode 61a of the electrostatic actuator 6A, and (b) is a diagram showing an equivalent circuit of an electromechanical coupling system in the electrostatic actuator 6A. It is a figure which shows the admittance curve showing the angular frequency dependence of admittance value | Y |. 3 is a block diagram illustrating a drive circuit unit 9. FIG. 2 is a diagram illustrating an example of an AGC circuit 95. FIG. It is a figure which shows the measurement data of the amplitude of arms 3A and 3B when changing the switching voltage and the gain control voltage Vc. Is a diagram showing an example of the output voltage V ₀ before and after contact, showing (a) is a signal before contact, (b), each signal after contact. It is a figure explaining the manufacture procedure of nano tweezers, and a process progresses in order of (a)-(d). It is a figure which shows the process following the process of FIG. 11, and a process progresses in order of (a)-(c). It is a figure which shows the process following the process of FIG. 12, and a process progresses in order of (a)-(d). It is a perspective view of the silicon substrate 100 of FIG.11 (c). It is a perspective view which shows the board | substrate 100 after removing the resist pattern 105a and the aluminum layer 104. FIG. It is a perspective view which shows the resist pattern 106a. It is a perspective view which shows the shape of the resist 108 and the aluminum layer 107 of Fig.13 (a). It is a figure which shows the back surface side of the base layer 101 shown in FIG.13 (b). It is a perspective view which shows the surface side of the base layer 101 of FIG.13 (c). It is a figure which shows an example of the nano tweezers using a thermal actuator. It is a figure explaining the holding | grip operation | movement by the nano tweezers 1, and operation | movement is performed in order of (a)-(c). It is a figure which shows the procedure following the holding | grip operation | movement shown in FIG. 21, and operation | movement is performed in order of (a)-(c). It is a figure which shows the contact and holding | grip detection circuit provided with the vibration frequency detection system. It is a figure which shows the contact and holding | grip detection circuit provided with the phase detection system.

Explanation of symbols

  1: Nano tweezers, 3A, 3B: Arm, 6A, 6B: Electrostatic actuator, 8: Connecting member, 9: Drive circuit section, 11: Resonance circuit, 23, 24: Drive lever, 60a, 60b: Fixed electrode, 61a 61a: movable electrode, 91: amplifier, 92: DC power supply, 93: contact / gripping detection circuit, 95: AGC circuit, 600, 610: comb teeth, 300: sample

Claims (7)

A pair of arms that can be opened and closed;
An electrostatic actuator to which an open / close drive voltage is applied and which drives to open / close at least one of the pair of arms;
An amplifier that self-oscillates by using an electrical equivalent circuit of the electrostatic actuator as a feedback circuit, and vibrates the arm by the self-excited oscillation;
A nanotweezers comprising: a vibration state detection unit that detects a change in vibration state due to contact of the arm with an object. A first arm that opens and closes;
A second arm with an electrostatic actuator;
An amplifier that self-oscillates by using an electrical equivalent circuit of the electrostatic actuator as a feedback circuit, and vibrates the second arm by the self-excited oscillation;
A vibration state detection unit that detects a change in vibration state due to contact of the second arm with an object;
A nanotweezers characterized in that a sample is gripped by the first and second arms. The nanotweezers according to claim 1 or 2,
Nano tweezers comprising gain adjusting means for adjusting the gain of the amplifier so that the amplitude of the arm oscillating by the self-oscillation is constant when not in contact. In the nanotweezers according to any one of claims 1 to 3,
The nanotweezers further comprising gripping detection means for detecting gripping of the sample by the arm based on the change in the vibration state detected by the vibration state detection unit. In the nanotweezers according to any one of claims 1 to 4,
The change in the vibration state is any one of a change in amplitude, a change in frequency, and a change in phase due to contact of the arm with the object. In the nanotweezers according to any one of claims 1 to 5,
The electrostatic actuator has a stationary comb electrode part and a movable comb electrode part connected to the arm and driving the arm. A method for gripping a sample with the nanotweezers according to claim 1,
Move the nanotweezers in the direction of the placement part on which the sample is placed, until the vibration change is detected by the vibration change detection part,
If the vibration change is detected by the vibration change detection unit, the nanotweezers are moved by a predetermined movement amount in a direction opposite to the direction of the placement unit,
After the movement, the arm is closed by the electrostatic actuator,
When the vibration change is detected by the vibration change detection unit, the holding operation of the arm by the electrostatic actuator is stopped.

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