Patent Publication Number: US-2007114441-A1

Title: Scanning stage for scanning probe microscope

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
      This is a Continuation Application of PCT Application No. PCT/JP2006/308661, filed Apr. 25, 2006, which was published under PCT Article 21(2) in Japanese. 
    
    
      This application is based upon and claims the benefit of priority from prior Japanese Patent Application No. 2005-128267, filed Apr. 26, 2005, the entire contents of which are incorporated herein by reference.  
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to a scanning stage used for a scanning probe microscope.  
      2. Description of the Related Art  
      A scanning probe microscope (SPM) is a scanning microscope that mechanically scans a mechanical probe to obtain information on a specimen surface. The scanning probe microscope includes a scanning tunneling microscope (STM), an atomic force microscope (AFM), a scanning magnetic force microscopte (MFM), a scanning capacitance microscope (SCaM), a scanning near-field optical microscope (SNOM), a scanning thermal microscope (SThM), and the like. Recently, a nano-indentator, which urges a diamond probe against a specimen surface to form an impression and analyze it to check the hardness and the like of the specimen, is ranked as one SPM and popular as well as the various types of microscopes described above.  
      For example, a scanning probe microscope is an instrument that raster-scans a mechanical probe and a specimen relatively in an X-Y direction to obtain surface information on a desired specimen region through the mechanical probe. During X-Y scanning, it feedback-controls also in a Z direction so that the interaction of the specimen and the probe keeps constant. Different from regular movement in the X-Y direction, the Z-direction movement is irregular because it reflects the surface configuration and the surface state of the specimen. The Z-direction movement is generally regarded as Z-direction scanning movement. The Z-direction scanning is movement with the highest frequency among scanning in the X, Y, and Z directions.  
      A scanning mechanism used in the scanning probe microscope comprises, e.g., a specimen support that holds an observation specimen and a scanning mechanism that scans the specimen support. As a method of fixing the specimen support to the scanning mechanism, a method that uses a magnet is available. This method is disclosed in, e.g., Jpn. Pat. Appln. KOKOKU Publication No. 6-31737. A conventional scanning probe microscope has a comparatively low scanning speed and acquires one image with several minutes. Thus, the weight of the scanning target is not an issue. Recently, however, an apparatus that can acquire several images within one second has been developed to meet the demand for a higher scanning speed. To increase the scanning speed, the weight of the scanning target must be light. With the method of fixing the specimen support with the magnet, it is difficult to decrease the weight of the scanning target. Jpn. Pat. Appln. KOKAI Publication No. 2003-42931 proposes a method of fixing the specimen support using grease. With this method, as the specimen support is fixed by the grease, the scanning target can be very lightweight. Hence, this method is suitable for increasing the scanning speed.  
     BRIEF SUMMARY OF THE INVENTION  
      A scanning stage for a scanning probe microscope according to the present invention includes a specimen support that holds an observation specimen, and a scanning mechanism configured to move the specimen support in X, Y, and Z directions, the specimen support being fixed to the scanning mechanism by wax.  
      Advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING  
      The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the invention, and together with the general description given above and the detailed description of the embodiments given below, serve to explain the principles of the invention.  
       FIG. 1  is a plan view of a scanning stage for a scanning probe microscope according to the first embodiment of the present invention;  
       FIG. 2  is a sectional view taken along the line II-II of the scanning stage for the scanning probe microscope shown in  FIG. 1 ;  
       FIG. 3  is a plan view of a scanning stage for a scanning probe microscope according to the second embodiment of the present invention;  
       FIG. 4  is a plan view of a scanning stage for a scanning probe microscope according to the third embodiment of the present invention;  
       FIG. 5  is a plan view of a scanning stage for a scanning probe microscope according to the fourth embodiment of the present invention; and  
       FIG. 6  is a plan view of a scanning stage for a scanning probe microscope according to the fifth embodiment of the present invention.  
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      The embodiments of the present invention will be described with reference to accompanying drawing.  
     FIRST EMBODIMENT  
      A scanning stage for a scanning probe microscope according to the first embodiment is shown in  FIGS. 1 and 2 . Referring to  FIGS. 1 and 2 , the scanning stage includes a specimen support  9  that holds an observation specimen and a scanning mechanism that is allowed to move the specimen support  9  in X, Y, and Z directions. The scanning mechanism includes an X-Y stage including a movable portion  4 , X-Y elastic members  6 A,  6 B,  6 C, and  6 D, Z elastic members  7 A,  7 B,  7 C, and  7 D, and a stationary portion  5 ; a stationary base  1  to which the X-Y stage is fixed; an X piezoelectric element  2 A that is an X actuator for moving the movable portion  4  in the X direction; a Y piezoelectric element  2 B that is a Y actuator for moving the movable portion  4  in the Y direction; and a Z piezoelectric element  3  that is a Z actuator for moving the specimen support  9  in the Z direction.  
      The stationary portion  5  is fixed in the stationary base  1  by adhesion or screw fastening. The movable portion  4  is connected to the stationary portion  5  through the Z elastic members  7 A to  7 D. The Z elastic members  7 A to  7 D support the movable portion  4  with high rigidity in the Z direction. The Z elastic members  7 A to  7 D are arranged at positions substantially equidistant from the center of the movable portion  4 . The center of gravity of the movable portion  4  is located at almost the center of the movable portion  4 . The movable portion  4  is connected to the stationary portion  5  through the X-Y elastic members  6 A to  6 D. The X-Y elastic members  6 A to  6 D support the movable portion  4  with high rigidity in the X-Y direction. The X-Y elastic members  6 A to  6 D are arranged symmetrically with respect to each of the X and Y driving axes. The X-Y elastic members  6 A and  6 C are located on an X-axis, and the X-Y elastic members  6 B and  6 D on a Y-axis. The X-Y elastic member  6 A is provided with a pressing portion  8 A, against which the X piezoelectric element  2 A for X-direction driving is abutted. The X-Y elastic member  6 B is provided with a pressing portion  8 B, against which the Y piezoelectric element  2 B for Y-direction driving is abutted.  
      The X-Y stage constituted by the movable portion  4 , the X-Y elastic members  6 A to  6 D, the Z elastic members  7 A to  7 D, and the stationary portion  5  is obtained by cutting from one integral component and made of a material such as aluminum. The stationary base  1 , which fixes the X-Y stage, may be of the same material as the X-Y stage, but it may be preferably made of a material, e.g., stainless steel, which has a higher Young&#39;s modulus than that of aluminum.  
      One end of the X piezoelectric element  2 A for X-direction driving abuts against the pressing portion  8 A, and the other end is fixed to the stationary base  1 . The X piezoelectric element  2 A is arranged so that a predetermined pilot pressure acts on it along the X-axis. The central line of the X piezoelectric element  2 A extends through almost the center of gravity of the movable portion  4 . One end of the Y piezoelectric element  2 B for Y-direction driving abuts against the pressing portion  8 B, and the other end is fixed to the stationary base  1 . The Y piezoelectric element  2 B is arranged so that a predetermined pilot pressure acts on it along the Y-axis. The central line of the Y piezoelectric element  2 B extends through almost the center of gravity of the movable portion  4 .  
      The Z piezoelectric element  3  for Z-direction driving is fixed to the upper surface of the movable portion  4 . The central line of the Z piezoelectric element  3  extends through almost the center of gravity of the movable portion  4 . The surface of the Z piezoelectric element  3  is covered with a resin the like. The specimen support  9  is fixed to the upper surface of the Z piezoelectric element  3  by wax  10 . The thinner the wax  10  is, the more firmly the specimen support  9  is fixed.  
      Wax has a very high viscosity at room temperature. The viscosity of the wax is adjustable by compounding. For example, even a wax that is pasty at room temperature has a coefficient of kinematic viscosity of about 2,000 [mm 2 /s]. According to experiments, the wax that is employed in the present invention is almost solid. For example, silicone grease has a coefficient of kinematic viscosity of about 60 [mm 2 /s] at room temperature and about 30 [mm 2 /s] at 100° C. Semi-solid wax has a coefficient of kinematic viscosity of about 1,000 or more [mm 2 /s] at room temperature and about 15.3 [mm 2 /s] at 100° C.  
      The specimen support  9  may be fixed to the upper surface of the Z piezoelectric element  3  by use of a plastic adhesive in place of the wax  10 .  
      The observation specimen is fixed to the specimen support  9 . The observation specimen may be fixed to the specimen support directly or through a medium that fixes the observation appropriately.  
      The operation will be described. For example, a case of displacing the observation specimen, i.e., the specimen support  9 , in the X direction will be described. To drive the movable portion  4  in the X direction, a voltage is applied to the X piezoelectric element  2 A to extend and contract it. As one end of the X piezoelectric element  2 A is fixed to the stationary base  1 , a displacement of the X piezoelectric element  2 A displaces the pressing portion  8 A abutted against the other end of the X piezoelectric element  2 A. This displacement is transmitted to the X-Y elastic member  6 A. Since a thin leaf spring portion of the X-Y elastic member  6 A extending parallel to the X-axis has high X-direction rigidity, the displacement is transmitted to the movable portion  4 . The X-Y elastic member  6 C on the X-axis, which is arranged symmetrically with respect to the Y-axis, does not hinder the displacement of the movable portion  4  because a thin leaf spring portion of the X-Y elastic member  6 C extending parallel to the Y-axis has low X-direction rigidity. Also, the X-Y elastic members  6 B and  6 D, which are arranged on the Y-axis, do not hinder the displacement of the movable portion  4  either, because thin leaf spring portions of the X-Y elastic members  6 B and  6 D extending parallel to the Y-axis have low X-direction rigidities. Furthermore, the Z elastic members  7 A to  7 D, which support the movable portion  4  with high rigidity in the Z-direction, do not hinder the displacement of the movable portion  4  because the Z elastic members  7 A to  7 D have low rigidities in the X-Y direction. So, the movable portion  4  displaced in the X direction in accordance with the extension and contraction of the X piezoelectric element  2 A.  
      Furthermore, when the movable portion  4  is to move in the X direction, since the X-Y elastic members  6 A to  6 D are arranged symmetrically with respect to the driving axes, the movable portion  4  displaces linearly in an X-Y plane without rotating. Also, when the movable portion  4  is to move in the X direction, since the Z elastic members  7 A to  7 D, which are arranged on the lower surface of the movable portion  4 , serve as parallel leaf springs, the upper surface of the movable portion  4  moves horizontally without inclination. Furthermore, since the line of driving force extending in the driving direction through the center of the piezoelectric element passes through the center of gravity of the movable portion, even when the movable portion  4  moves at high speed, the angular momentum by an inertia force does not occur readily, so that the movable portion  4  displaces highly accurately without rotation.  
      When the X piezoelectric element  2 A displaces, a reaction force accompanying deformation of the X-Y elastic member  6 A acts on the stationary base  1  at a portion that fixes the X piezoelectric element  2 A. Since the stationary base  1  is made of a material having a high Young&#39;s modulus and the portion that fixes the X piezoelectric element  2 A does not deform much, the displacement of the X piezoelectric element  2 A is mostly transmitted to the pressing portion  8 A.  
      This discussion concerning movement in the X direction applies to the movement in the Y direction as well.  
      To move the observation specimen, i.e., the specimen support  9 , in the Z direction, a voltage is applied to the Z piezoelectric element  3  to extend and contract it.  
      When moving the specimen support  9  as described above, the higher the moving speed of the specimen support  9 , the larger the inertia force of the specimen support  9 . When the specimen support  9  is placed in the water to observe a living specimen, the resistance force of water acting on the specimen support  9  increases. Since the specimen support  9  is fixed by the wax  10 , even when the specimen support  9  receives an inertia force or a resistance force, it moves to follow the movement of the scanning mechanism well. As a result, an observation image that correctly reflects the shape of the observation shape and does not include much distortion can be obtained stably.  
      When the specimen support  9  is to be removed after the observation is finished, a release agent such as an organic solvent is applied to the wax  10 , dissolving the wax  10  to allow easy removal of the specimen support  9 . At this time, since the surface of the Z piezoelectric element  3  is covered with the resin material  11 , the Z piezoelectric element  3  is not damaged by the organic solvent.  
     SECOND EMBODIMENT  
      A scanning stage for a scanning probe microscope according to the second embodiment is shown in  FIG. 3 . The configuration of this embodiment is obtained by adding a heat source and a temperature controller to the configuration of the first embodiment. The configuration and the operation of the scanning mechanism are the same as those of the first embodiment.  
      A heater  12  is arranged to surround a Z piezoelectric element  3 . The ON/OFF operation and the temperature setting of the heater  12  are controlled by a controller  13 .  
      When mounting a specimen support  9 , the heater  12  is turned on, heating wax  10  to decrease its viscosity. Only light pressure is applied on the specimen support  9 , so that an excessive portion of the wax  10  is squeezed out from under the lower surface of the specimen support  9 , decreasing the thickness of the wax  10 . After that, the power supply of the heater is turned off, increasing the viscosity of the wax  10  to firmly fix the specimen support  9 .  
      When removing the specimen support  9  the power supply of the heater  12  is turned on, so that the viscosity of the wax  10  decreases again, allowing the specimen support  9  to be removed from the Z piezoelectric element by a small force. Hence, no excessive force acts on the Z piezoelectric element to damage it.  
      In AFM observation, if the heater is turned on, it can control the temperature of the observation specimen and the surrounding temperature to an arbitrarily set temperature.  
     THIRD EMBODIMENT  
       FIG. 4  shows a scanning stage for a scanning probe microscope according to the third embodiment. The configuration of this embodiment is obtained by adding a heat source and a temperature controller to the configuration of the first embodiment. The configuration and the operation of the scanning mechanism are the same as those of the first embodiment.  
      A heater  14  is placed near the scanning mechanism. The ON/OFF operation and the temperature setting of the heater  14  are controlled by a controller  13 . Wax is applied to a specimen support  9  on the heater  14 . With the heater  14  being turned on, wax  10  is applied to the lower surface of the specimen support  9 , and the specimen support  9  is placed on the heater  14 . This heats the wax  10  to decrease its viscosity. Only light pressure is applied on the specimen support  9 , so that an excessive portion of the wax  10  is squeezed out from under the lower surface of the specimen support  9 , decreasing the thickness of the wax. After that, when the specimen support  9  is placed on a Z piezoelectric element  3 , the wax  10  cools down to increase its viscosity. This and the small thickness of the wax  10  firmly fix the specimen support  9 .  
     FOURTH EMBODIMENT  
       FIG. 5  shows a scanning stage for a scanning probe microscope according to the fourth embodiment. The configuration of this embodiment is obtained by adding a heat source and a temperature controller to the configuration of the first embodiment. The configuration and the operation of the scanning mechanism are the same as those of the first embodiment.  
      The specimen support  9  is mounted on and removed from by use of a holding tool heater  15  configured to hold a specimen support  9 . For example, the holding tool heater  15  is similar to a pair of tweezers with a heater. The holding tool heater  15  allows holding the specimen support  9  to move it freely. The ON/OFF operation and the temperature setting of the holding tool heater  15  are controlled by a controller  13 .  
      When the specimen support  9  is held with the holding tool heater  15  to be fixed to the Z piezoelectric element  3 , the holding tool heater  15  is turned on, heating the wax to decrease its viscosity. Only light pressure is applied on the specimen support  9 , so that an excessive portion of the wax  10  is squeezed out from under the lower surface of the specimen support  9 , decreasing the thickness of the wax. Then, the power supply of the heater is turned off, or the specimen support  9  is removed from the holding tool heater  15 , cooling down the wax to increase viscosity, so that the specimen support  9  is fixed firmly. When removing the specimen support  9 , the power supply of the holding tool heater  15  is turned on, so that the viscosity of wax  10  holding the specimen support  9 , allowing the specimen support  9  to be removed from the Z piezoelectric element by only a small force. Hence, no excessive force acts on the Z piezoelectric element to dam age it.  
     FIFTH EMBODIMENT  
       FIG. 6  shows a scanning stage for a scanning probe microscope according to the fifth embodiment. The configuration of this embodiment is obtained by changing the specimen support in the configuration of the first embodiment. The configuration and the operation of the scanning mechanism are the same as those of the first embodiment.  
      A specimen support  16  has a groove  16   a  on the lower surface, i.e., on the surface that is to be bonded to a Z piezoelectric element  3 . After the specimen support  16  is mounted on the upper surface of the Z piezoelectric element  3 , the specimen support  16  is slid several times along the upper surface of the Z piezoelectric element  3 , so that an excessive portion of wax  10  enters the groove  16   a  to decrease the thickness of the wax  10 . So, the specimen support  16  is fixed firmly. When the specimen support  16  is to be removed, a release agent is applied to the wax  10 . The release agent flows along the groove  16   a  to facilitate removal of the specimen support  16 . When an adhesive is used in place of the wax  10 , the same effect can be obtained.  
      So far the embodiments of the present invention have been described with reference to the drawing. Note that the present invention is not limited to these embodiments. Various changes and modifications may be made without departing from the spirit and scope of the invention.  
      Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.