Patent Number: 061005347
Section: description

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be explained based on embodiments with reference to the drawings. (1) First Embodiment Referring to FIG. 1, there is illustrated an microscopic area scanning apparatus according to a first embodiment of the present invention. In FIG. 1, three hollow-cylindrical piezoelectric elements 101 (two are shown in the figure) are vertically fixed at an interval of 120 degrees on a horizontal circumferential plane of a table 105 such that their top free ends are equal in height to one another. Each of the hollow cylindrical piezoelectric elements 101 each have a ball 102 axially held on the top free end by bolt. This ball 102 is slidably fitted by upper and lower halves of exactly the same two ball retainers 103 having a hole in an bottomless cup form. The ball 102 and the ball retainer 103, at least one of them, is formed by a surface film of a soft metal or a solid lubricant in order to provide smoothness at a surface thereof. With this structure, there is no necessity of applying a lubricating oil or grease to the ball 102 and the ball retainer 103. Consequently, it is possible to prevent drift or creep from occurring due to the lubricating oil or grease. The use in a vacuum is also available. The ball is desirably formed of phosphor bronze or stainless steel (SUS304 or the like) polished at the surface to have a surface film 108 formed by ion plating of a soft metal such as gold, silver, or lead. The surface film 108 may be alternatively formed by sputtering with molybdenum disulfide as a solid lubricant. Besides, a copper-based alloy (sintered bearing alloy) containing a solid lubricant may be used. Meanwhile, the ball retainer 103 may use a SKS material (alloy tool steel) polished at a surface, an SUJ material (bearing steel) plated by a hard chromium plating, or a surface-polished stainless steel (SUS304 or the like). Although in this embodiment the surface film 108 is provided on the surface of the ball 102, a surface film 108 may be formed on the ball retainer 103 similarly to the ball 102. The upper and lower ball retainers 103 are press-fitted in respective holders 106a. Each of these two holders 106a is provided with a flange 106b. The both flanges 106b have bolts arranged, at right and left symmetric locations, to penetrate through a gap defined therebetween. The flange 106b uses a plate material of a stainless steel (SUS304-CSP) or a spring phosphor bronze to have an elasticity. This elasticity is desirably given to such a degree that a resonant frequency is not lowered for the microscopic area scanning apparatus. With such a structure, the gap between the two flanges 106b is adjusted by tensioning the bolts 106 to thereby control the exerted pressure to the ball 102. This allows a frictional force acting between the surface film 108 of the ball 102 and the ball retainer 103 to be controlled to a desired magnitude. As this frictional force is intensified, a coupling rigidity of the ball 102, the surface film 108 and the ball retainer 103 increases to increase the resonant frequency in XYZ directions of the microscopic area scanning apparatus. A sample stage 104 is fixed to one inner point of a ring member 107. The fixed position of the sample stage 104 to the ring member 107 is fixed with one ball retainer 103. The remaining two ball retainers 103 are fixed to the ring member 107. The ring member 107 is designed to have a rigidity with respect to a radial direction lower than that of the sample stage 104. The ring member 107 also has a rigidity with respect to a Z direction equivalent to a rigidity of the sample member 104 with respect to the Z direction. In this structure, errors in XY directions of the hollow cylindrical piezoelectric elements are absorbed by radial deflection of the ring member 107. The ring member 107 has its rigidity low in a radial direction but high in a height direction, having no effects upon resonant frequency with respect to the Z direction. The sample stage 104 is substantially of a rigid member, and uses a material that is light in weight without deviation in mass. The sample member 104 is formed desirably of an aluminum alloy (e.g. A6061, A5052) or a thin stainless plate (e.g. SUS304) in a disc form with a rib for enhancing rigidity. This structure provides a higher resonant frequency characteristic in Z direction than the conventional structure to the microscopic area scanning apparatus while scanning in X and Y directions as the conventional. (2) Second Embodiment At Referring to FIG. 2, there is illustrated a second embodiment of a microscopic area scanning apparatus of the present invention. In FIG. 2, three hollow-cylindrical piezoelectric elements 101 are vertically fixed at an interval of 120 degrees on a horizontal circumferential plane of a table 105 such that their top free ends are equal in height to one another. The hollow cylindrical piezoelectric elements 101 each have a ball 102 comprising a magnetic material axially held on the top free end by adhesion. This ball 102 is fitted and covered on a ball retainer 103 formed of a permanent magnet material having a hole in a bottomless cup form. The ball 102 and the ball retainer 103, at least one of them, is formed by a surface film of a soft metal or solid lubricant in order to provide smoothness at a surface thereof. In this embodiment, a surface film 108 is formed on the ball retainer 103. In this structure, there is no necessity of applying a lubricating oil or grease to the ball 102 and the ball retainer 103. Consequently, it is possible to prevent drift or creep from occurring due to the lubricating oil or grease. The use in a vacuum is also available. The ball 102 uses a magnetic material such as a ferromagnetic material, desirably a ferromagnetic stainless steel (SUS420J2, SUS440C, etc.) having a polished surface and electroless plated with nickel. The ball retainer 103 uses a permanent magnetic material high in holdability, desirably a neodymium (Nd) based material polished and nickel plated to have a surface film formed thereon of gold, silver, lead, molybdenum disulfide or the like, or a samarium-cobalt (Sm--Co) based material polished to form thereon a surface film 108 of gold, silver, lead, molybdenum disulfide or the like. Although in this embodiment formed the surface film 108 is formed on the ball retainer 103, the ball 102 may be formed, at a surface, with a surface film 108 using a soft metal such as gold, silver or lead or a solid lubricant such as molybdenum disulfide. Where the ball 102 is of a permanent magnet or electromagnet and the ball retainer 103 is of a magnetic material as discussed above, the ball 102 can be exerted by pressure due to a magnetic force acted by between the ball 102 and the ball retainer 103. If the ball 103 is made of an electromagnet, the frictional force between the ball 102 and the ball retainer 103 can be adjusted to a desired degree by controlling a magnetic force applied between the ball 102 and the ball retainer 103. A sample stage 104 is fixed to one inner point of a ring member 107. The fixed position of the sample stage 104 to the ring member 107 is fixed with one ball retainer 103. The remaining two ball retainers 103 are fixed to the ring member 107. The ring member 107 is designed to have a rigidity with respect to a radial direction lower than that of the sample stage 104. The ring member 107 also has a rigidity with respect to a Z direction equivalent to a rigidity of the sample stage 104 with respect to the Z direction. In this structure, errors in XY directions of the hollow cylindrical piezoelectric elements are absorbed by radial deflection of the ring member 107. The ring member 107 has its rigidity low in a radial direction but high in a height direction, having no effects upon resonant frequency with respect to the Z direction. The sample stage 104 is substantially of a rigid member, and uses a material that is light in weight without deviation in mass. The sample member 104 is formed desirably of an aluminum alloy (e.g. A6061, A5052) or a thin stainless plate (e.g. SUS304) in a disc form with a rib for enhancing rigidity. This structure provides a higher resonant frequency characteristic in Z direction than the conventional structure to the microscopic area scanning apparatus while scanning in X and Y directions as the conventional. Referring to FIG. 3, there is shown a typical view in operation of the microscopic area scanning apparatus of the first embodiment of the present invention. To scan over the sample stage 104 in an arrow direction as viewed in the figure, the three hollow cylindrical piezoelectric elements 101 (two in number in the figure) may be moved by bending in a same amount and in a same direction. On this occasion, each of the balls 102 placed at the respective free end of the hollow cylindrical piezoelectric members moves along a circular path about the fixed end of the hollow cylindrical piezoelectric member 101. The ball 102 is in a slidable linear contact with the ball retainer 103 through the surface film 108. The movement of the hollow cylindrical piezoelectric element 101 due to inclination, i.e. the movement of the ball 102 due to inclination, is absorbed by sliding between the ball 102 and the ball retainer 103. Thus, the circular-path motion of the ball 102 is transformed into linear motion in the ball retainer 103. The ball 102 is in linear contact with the ball retainer 103 through the surface film 108. The linear contact allows the ball 102 to be applied by a force, thus providing a high Z-directional coupled rigidity as compared with connection by an elastic hinge. Also, the frictional slide with the ball 102 and the ball retainer 103 exhibits an extremely low frictional coefficient of approximately 0.002-0.003. This value is as low as approximately one-tenth of surface-contact frictional coefficient (approximately 0.3). There is no tendency of causing smoothless motion (hereinafter referred to as stick-slip phenomenon), with a capability of precise movement. Thus, the combination of the ball 102 and the ball retainer 103 is preferred as an element for the microscopic range scanning apparatus. Therefore, it is possible to scan over the sample stage 104 with smoothness without causing stick-slip phenomenon during its movement from a start of scan, i.e. the state of FIG. 1 to a mid-process of scan, i.e. the state of FIG. 3. Referring to FIG. 4, there is illustrated a perspective view of a displacement-error absorbing means as one structural example of the microscopic area scanning apparatus of the present invention. The displacement-error absorbing means has a structure that a ring member 107 inscriptively fixed with a sample stage 104, wherein one ball retainer 103 fixed to a fixing portion for the ring member 107 and the sample stage 104 and remaining two ball retainers 103 fixed to the ring member 107. The error caused in horizontal displacement of the hollow cylindrical piezoelectric elements encountered during X-Y scanning is absorbed by radial deflection of the ring member 107. Since the rigidity of the ring member 107 is low in a radial direction but high in a height direction, the deflection in the ring member 107 has no effect upon the resonant frequency in the Z direction. As explained above, this invention is a microscopic area scanning apparatus used for scanning over a sample placed on a scanning probe microscope (SPM) that is represented by an atomic force microscope (AEM) or a scanning near optical field microscope (SNOM), wherein at least three hollow cylindrical piezoelectric elements are provided each of which is driven in three XYZ directions by one of divided electrodes. The microscopic area scanning apparatus comprises: three or more hollow cylindrical piezoelectric elements arranged on a circumference of a common plane; a plurality of balls each axially provided at a free end of the hollow cylindrical piezoelectric element; ball retainers each for rotatably and slidably holding a plurality of a respective ball in contact therewith; a sample stage fixed to the ball retainers; and a table for fixing the hollow cylindrical piezoelectric elements on the circumference of the common plane. Therefore, the present invention has an effect to solve the problem raised by the conventional microscopic area scanning apparatus, and realize a microscopic area scanning apparatus satisfying both of a wide scanning range and a high z-direction resonant frequency.