Abstract:
A probe scanning device has a first tubular member extending in a z direction. A second tubular member has a rear end portion extending into the first tubular member to define a space between an inner peripheral surface portion of the first tubular member and an outer peripheral surface portion of the second tubular member. A probe tip is mounted on a front end portion of the second tubular member. A viscous material is disposed in the space between the first tubular member and the second tubular member. A moving mechanism reciprocally moves the first tubular member in an xy direction, and a voice coil motor drives the second tubular member towards the first tubular member in the z direction. A drive mechanism has a coarse adjustment mode for coarsely moving the probe tip toward a surface of a sample and a measurement mode for fine movement of the probe tip in the z direction to maintain a given relationship between relative positions of the probe tip and the sample surface after coarse movement. A connecting mechanism selectively integrally connects the first tubular member and the second tubular member to one another.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a probe scanning device such as a scanning probe microscope, and particularly relates to a probe scanning device capable of measurement with little temperature drift and low noise. 
     2. Description of the Related Art 
     The applicant has previously invented a probe scanning device having a zooming function shown in FIG.  10  and applied for a patent (Japanese Patent Publication No. Hei. 10-221348). The structure and function of this probe scanning device will be briefly described below. 
     A case  1  has a scanning tube  20  having a thin tube  14  projecting to a sample chamber and a thick tube  15  connected thereto as main components. An inner tube  13  is supported inside the thick tube  15  through the viscous material  17 . The thick tube  15 , the inner tube  13 , and the thin tube  14  are made with the same quality and heat conductivity and the thermal expansion coefficients thereof are substantially equal. A lower melting-point metal holder  74  is fixed to an outer side face of the thick tube  15 . The low melting-point metal holder  74  consists of an insulating material such as ceramic or a super-engineered plastic and a low melting-point metal  75  such as u alloy is insulatively housed in a groove formed on a top face thereof. 
     A first voice coil motor (VCM) is fitted to the top of the case  1 . 
     This first voice coil motor comprises a magnet  2  having a shaft  3 , a needle  4   a  surrounded by a wound on coil  5 , a needle component  4   b  fixed to the needle  4   a , a membrane  6   a , and a fixing component  6   b  fixing an outer circumference of the membrane  6   a . A spindle  8  extending in a z direction is fixed to the needle component  4   b . A detector  9  for detecting a displacement of a tip  10  is installed in a bottom side end of this spindle  8 . 
     The spindle  8  is supported elastically by first and a second springs  11  and  12  held by the inner tube  13 . A heating coil  16  is wound around at a position outside the thick tube  15  and opposite to the viscous material  17 . The heating coil  16  is electrified for softening the viscous material  17  in coarse adjustment of the tip  10  in the z direction. 
     A second voice coil motor, which comprises a magnet  21  having a shaft  22 , a needle  23   a  surrounded by a wound on coil  24 , a needle component  23   b  fixed to the needle  23   a , a membrane  25 , and a fixing component  25   a  fixing the outer circumference of the membrane  25 , is mounted on a side of the case  1 . 
     A thin annular plate spring  23   c  is fitted to a lateral side of the case  1  for preventing the needle  23   a  from making contact with the shaft  22  or the magnet  21 , when the thick tube of the scanning tube  20  tilts in an XY direction. At the thin annular plate spring  23   c , the outer circumference thereof is pushed by the case  1  and the membrane fixing component  25   a  and an inner circumference thereof is pushed by the needle component  23   b  and an annular spring component  23   d . A spindle  27  extending in an x direction is fitted to the needle component  23   b  and the annular spring component  23   d . An open end of the spindle  27  is fixed to a projecting portion  15   a  of the thick tube  15 . 
     A third voice coil motor (not shown) is installed in a direction differing by 90° from the second voice coil motor. The third voice coil motor is constituted as being identical or equal to the second voice coil motor. A y direction (a direction at right angles to the paper) spindle connects a movable component fixed to the needle of the third voice coil motor to the thick tube  15 . Driving the second and third voice coil motors allows the tip  10  to scan in the xy direction. A sample table (not shown) is mounted at a position opposite the tip  10  and a sample is mounted on the sample table. 
     An outer tube  71 , of which one end is fixed to the case  1 , extends to the outside of the thin tube  14  in the direction coaxial with the thin tube  14  and so as to project to the sample chamber. At the outer circumference of a front end of the outer tube  71 , a heat conductive cylinder  73  is installed through the insulative member  72  formed from ceramic material. A heating coil  76  is wound around the outer circumference of the heat conductive cylinder  73 . The bottom end of the heat conductive cylinder  73  is embedded in the low melting-point metal  75  of the low melting-point metal holder  74 . 
     According to such a structure, controlling electrification of the heating coil  76  for melting or solidifying the low melting-point metal  75  allows switching spring rigidity of the scanning tube  20  to any one of spring rigidity of the thin tube  14  only or spring rigidity created by adding the thin tube  14  to the outer tube  71 . As a result, even if the driving current supplied to the voice coil motors is equal, a movable range of the scanning tube  20  in the XY direction can be made to be different to express the zooming function. 
     When measuring the sample, first, the heating coil  16  of the thick tube is electrified to raise the temperature of the viscous material  17  so as to finally decrease the viscosity of the viscous material  17 . Next, the voice coil motor is electrified in a z direction to carry out coarse adjustment of the spindle  8  in the z direction. When the tip  10  makes contact with the sample surface and then an extent of bending reaches a predetermined value, electrification of the voice coil motor is suppressed and moving down of the tip  10  is stopped. At this time, coarse adjustment is completed. 
     Subsequently, electrification of the heating coil  16  is suppressed to drop the temperature of the viscous material  17  to a preheated temperature. As a result, viscosity of the viscous material  17  increases resulting in the thick tube  15  with the inner tube  13  becoming substantially integral due to the viscosity of the viscous material  17  and the sample therefore becomes measurable. 
     In the probe scanning device according to the structure as described above, a surface shape of the sample can be accurately measured preferably by lowering a scanning speed of the tip  10  in the xy direction. A resonance frequency of a z axis is a function of a resultant force of a first  11  and a second  12  spring and a mass of the movable portion on the z axis, and thus, if frequency components, when a change of the z axis is subjected to frequency resolution making the scanning speed of the x axis and the y axis to a time axis, contains the resonance frequency of the z axis, increased amplitude is observed in this component. Such resonance can be prevented by lowering the scanning speed in the xy direction. 
     However, when the scanning speed is decreased, time for measurement necessarily increases. 
     The viscous material  17  has a small viscosity at preheating temperatures and the inner tube  13  moves down or up slightly against the thick tube  15 . Therefore, when measurement time becomes longer, a distance of the inner tube  13  which is moved down or up increases which causes data related to the z direction to contain an error corresponding to the distance made by moving down or up. 
     When electrification of the heating coil  16  during measurement is limited, the temperature of individual parts containing the thick tube  15  and the inner tube  13  decreases gradually causing thermal shrinkage and data relating to the z direction therefore contains an error corresponding to thermal shrinkage. 
     SUMMARY OF THE INVENTION 
     The advantage of the present invention is to provide a probe scanning device capable of measurement of high precision and low noise even when measuring at slow scanning speeds. 
     The present invention is characterized by a probe scanning device having a thick tube extended in a z direction and an end thereof supported by a case, an inner tube passing through the inside of the thick tube, a tip mounted on the front end of the inner tube, a viscous material filled in a space between the thick tube and the inner tube, first heating means for heating the thick tube, scanning means for reciprocally moving the thick tube in an xy direction, a voice coil motor for driving the inner tube towards the thick tube in the z direction, first temperature-controlling means for decreasing viscosity of the viscous material by supplying a driving current to the first heating means, and driving means having a coarse adjustment mode for coarsely moving the tip to a surface of a sample and a measurement mode for fine movement of the tip in the z direction to maintain a given relationship between relative positions of the tip and the sample surface after coarse movement, wherein fixing means for selectively fixing the thick tube and the inner tube are also provided. 
     (1) The probe scanning device has a fixing means for selectively fixing the thick tube and the inner tube. 
     (2) The probe scanning device is characterized in that the fixing means comprises: a low melting-point metal holder fixed to the inner tube and insulatively housing a low melting-point metal, a heat conductive member fixed to the thick tube through an insulant and with an end thereof being positioned so as to be embedded in the low melting-point metal, second heating means for heating the heat conductive member, second temperature-controlling means for controlling the supply of driving current to the second heating means in order to allow a temperature of the heat conductive member to rise to a first temperature, at which the low melting-point metal softens during coarse adjustment, and drop to a second temperature, at which the low melting-point metal hardens during measurement. 
     (3) There is also provided means for detecting an offset current contained in a driving current of the voice coil motor, wherein the first temperature-controlling means controls a driving current to be supplied to the first heating means to raise the temperature of the thick tube to a temperature, at which viscosity of the viscous material drops during coarse adjustment, and allows the temperature, at which the offset current is reduced in the measurement, to be reached. 
     (4) The probe scanning device is characterized in that each temperature-controlling means comprises holding means for holding a driving signal, which is supplied to each heating means, during measurement. 
     According to the characteristic (1) as described above, the thick tube and the inner tube are firmly fixed by the solidification of the low melting-point metal and a positioning shift with respect to time can therefore be prevented. 
     According to the characteristic (2) as described above, the temperature of the heat conductive cylinder is lowered to a temperature at which the low melting-point metal is solidified, and heat shrinkage of the heat conductive cylinder in the z direction can be cancelled by thermal expansion of the thick tube and the inner tube. 
     According to the characteristic (3) as described above, the temperature drift caused by a temperature change during measurement can be eliminated not by supplying the offset current to the voice coil motor, but rather by thermal expansion or heat shrinkage of the thick tube and the inner tube. 
     According to the characteristic (4) as described above, an output signal from a first and second temperature-controlling unit are held during measurement and hence, regardless of the change of an ambient temperature and temperature drift in a controlling system, an image with less noise can be obtained. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a sectional view showing a structure of a primary part of the first embodiment of the probe scanning device of the present invention. 
     FIG. 2 is a sectional view showing a structure of a primary part of the first embodiment of the probe scanning device of the present invention. 
     FIG. 3 shows a block diagram representing the structure of a controlling system of the second embodiment. 
     FIG. 4 is a flowchart showing the operation of the second embodiment. 
     FIG. 5 shows a sectional view presenting a structure of a primary part of the probe scanning devices, which are the third and the fourth embodiments of the present invention. 
     FIG. 6 is a block diagram showing the structure of the controlling system of the third embodiment. 
     FIG. 7 is a flowchart showing the operation of the third embodiment. 
     FIG. 8 is a block diagram showing the structure of the controlling system of the fourth embodiment. 
     FIG. 9 is a flowchart showing the operation of the fourth embodiment. 
     FIG. 10 is a sectional view showing the structure of the primary part of the probe scanning device having a conventional zooming mechanism. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention will be described in detail as follows with reference to the drawings. FIG. 1 is a sectional view showing a structure of a primary part of a first embodiment of the probe scanning device fabricated by applying the present invention, and with the same numerals as above indicating the same portions. 
     The present embodiment is constituted by materials such as super-invar (31% Ni-5% Co—Fe) having a very small thermal expansion coefficient. A heating coil  16  is wound around the outer circumference of a thick tube  15 , and a temperature sensor  91  is installed to measure its temperature. A cylindrical heat conductive cylinder  83  is fixed to a front end of the thick tube  15  through an insulative member  82  such as ceramic or a super-engineered plastic. A heating coil  86  is wound around the outer circumference of the heat conductive cylinder  83  and a temperature sensor  92  is installed to measure its temperature. An annular low melting-point metal holder  84  is fixed to the outer circumference of the inner tube  13 . The low melting-point metal holder  84  consists of an insulating material such as ceramic or a super-engineered plastic, and a low melting-point metal  85  such as u alloy insulatively housed in a recess or groove  84   a  formed on the top face of the low melting-point metal holder  84 . As shown on in FIG. 1, the thick tube  15  is in the form of a first tubular member and the inner tube  13  is in the form of a second tubular member having a portion extending into the first tubular member. 
     In the outer circumference of the front end of the outer tube  71 , the heat conductive cylinder  73  is installed through the insulative member  72  formed from ceramic material. A heating coil  76  is wound around the outer circumference of the heat conductive cylinder  73 , and a temperature sensor  93  is installed to measure its temperature. 
     The heat conductive cylinder  83 , the low melting-point metal  85 , and its holder  84  function as connecting or fixing means for integrally connecting or fixing the thick tube  15  to the inner tube  13  during measurement. The heat conductive cylinder  83  and the low melting-point metal holder  84  are positioned to embed the front end of the heat conductive cylinder  83  in the low melting-point metal  85  within a range of coarse adjustment of the inner tube  13 . 
     The sample table  31  is mounted at a position opposite to the tip  10  and the sample  32  is mounted on this sample table  31 . The sample table  31  is mounted on a coarse adjustment x,y,z stage  33 . 
     Output signals of individual temperature sensors  91 ,  92 , and  93  are inputted into temperature monitors  40   a ,  40   b , and  40   c , respectively. Individual temperature monitors calculate temperatures of individual units based on the output signals of individual temperature sensors for reporting a result of operation to a temperature-controlling unit  41 . 
     The temperature-controlling unit  41  controls a driving current to be supplied to individual heating coils  16 ,  86 , and  76  for maintaining the temperature of individual units to a predetermined temperature. 
     In a probe scanning device of such a structure, the heating coils  16  of the thick tube  15  are first electrified for raising the temperature of the viscous material  17  to cause a decrease in its viscosity. Thereafter, to maintain the predetermined viscosity of the viscous material  17 , electrification of the heating coils  16  is controlled by the temperature-controlling unit  41  based on the output signal of the temperature sensor  91 . 
     Next, the heating coil  86  is electrified for raising the temperature of the heat conductive cylinder  83  to melt the low melting-point metal  85 . In this way, fixing state of the thick tube  15  to the inner tube  13  is released. 
     Next, the voice coil motor in a z direction is electrified to carry out coarse adjustment of the spindle  8  in the z direction. The inner tube  13  moves down to the sample at a predetermined speed and the tip  10  arranged in its front end approaches a surface of the sample. When the tip  10  makes contact with the sample surface and then an extent of bending reaches a predetermined value, electrification of the voice coil motor is suppressed and moving down of the tip  10  is stopped. At this time, coarse adjustment is completed. 
     Then, electrification of the heating coil  86  is suppressed to cause temperature of the heat conductive cylinder  83  to fall to cause solidification of the low melting-point metal  85 . In this way, the thick tube  15  and the inner tube  13  are firmly fixed resulting in substantial integration of both the tubes. 
     Following this step, when the voice coil motor in a z direction is subjected to fine adjustment to keep a distance to a constant between the tip  10  and the sample surface for scanning the tip  10  in the xy direction, the driving current of the voice coil motor can express a shape of the sample surface. During this step, in this embodiment, the inner tube  13  causes no positioning shift against the thick tube  15 , and therefore, even in the case where the scanning speed in xy direction is low and requires a long time for measurement, high precision measurement becomes possible. 
     Meanwhile, during a measurement term as described above in this embodiment, the individual temperature monitors  40  always monitor the temperature of individual units for ordinary control of electrification of individual heating coils by the temperature-controlling unit  41  to keep individual temperatures to predetermined temperatures, and hence, high precision measurement becomes possible and is not influenced by temperature drift. 
     In addition, in this embodiment, the case  1  is constituted by a super-invar of a very small thermal expansion coefficient, and effects of temperature drift can be further reduced. 
     FIG. 2 is a sectional view showing the structure of a main parts of a second embodiment of the probe scanning device fabricated by applying the present invention, and the numerals that are the same as in the above represent the same or similar parts. 
     According to the first embodiment, after completion of coarse adjustment in the z direction, when electrification of the heating coil  86  is suppressed to cause the temperature of the heat conductive cylinder  83  to fall to fix the thick tube  15  to the inner tube  13 , the heat conductive cylinder  83  thermally shrinks so as to pull the tip  10  upward. 
     At this time, the offset current flows through the voice coil motor in the z direction in order to compensate for a difference in a distance caused by this thermal shrinkage. 
     The offset current always flowing through the voice coil motor not only causes the observation range of the z direction to narrow, but also causes heat generated by the voice coil motor to increase so as to subject individual units to thermal expansion so that temperature drift occurs in all the directions x, y, and z. 
     In order to solve such new technical problems, in the second embodiment of the present invention described below, calculation is carried out in advance for the predetermined temperature T 4  in order to ensure correspondence of the substantial heat shrinkage (i.e., a pull-up distance of the tip  10 ) of the heat conductive cylinder  83  in the z direction, when the temperature T 83  of the heat conductive cylinder  83  falls with a sum of the substantial thermal expansion (i.e., a pull-down distance of the tip  10 ) of the thick tube  15  and the inner tube  13  in the z direction, when the temperature of the thick tube  15  is further raised from the temperature for coarse adjustment to the temperature for the predetermined temperature, to cause cancellation of these two values. 
     During measurement, electrification of the heating coils  16  is controlled to keep the temperature of the thick tube  15  at a predetermined temperature. 
     In FIG. 2, output signals from the individual temperature sensors  91 ,  92 , and  93  are inputted into the temperature monitor  61 . The temperature monitor  61  calculates the temperature of individual units based on the output signal of the individual temperature sensors and supplies the results to the temperature-controlling units  60   a ,  60   b , and  60   c . The temperature-controlling unit  60  controls the electrification of individual heating coils  16 ,  86 , and  76  to keep the temperature of individual units at the predetermined temperature. 
     The VCM driving unit  64  drives the voice coil motor  9  in the z direction based on displacement detected from the tip  10  by a detector  9 . An operation controlling unit  62  controls each unit according to an operation mode (the coarse adjustment mode or measurement mode). 
     FIG. 3 is a block diagram showing the structure of the main part of the first and the second temperature-controlling units  60   a  and  60   b , and with the same numerals as above indicating the same or similar portions. 
     In the desired temperature-setting unit  611  for coarse adjustment in the second temperature-controlling unit  60   b , a temperature, higher than a melting point of the low melting-point metal  85  is set as the desired temperature T 1  of the heat conductive cylinder  83  in coarse adjustment. For the desired temperature-setting unit  612  for measurement, a temperature lower than a solidifying temperature of the low melting-point metal  85  is set as the desired temperature T 2  of the heat conductive cylinder  83  during measurement. However, an excessively low temperature increases heat shrinkage of the heat conductive cylinder  83  during measurement and therefore, in this embodiment, the temperature is set to be 1 to 2 degrees Celsius lower than the solidifying temperature. 
     A comparing unit  614  compares the desired temperature T 1  selected by the change switch  613  with a real temperature T 83  detected for the heat conductive cylinder  83  by the temperature sensor  92  for outputting its differential signal ΔT to a PI controlling unit  616 . The PI controlling unit  616  supplies the driving signal to the heating coil  86  through a driver circuit  618  to make the differential signal ΔT zero. 
     In the desired temperature-setting unit  601  for coarse adjustment in the first temperature-controlling unit  60   a , a temperature allowing sufficient lowering of viscosity of the viscous material  17  is set as the desired temperature T 3  of the thick tube  15  during coarse adjustment. The desired temperature T 4  of the thick tube  15  during measurement is set at the desired temperature-setting unit  602  for measurement. This desired temperature T 4  is set to a value corresponding to the substantial heat shrinkage (i.e., the pull-up distance of the tip  10 ) of the heat conductive cylinder  83  in the z direction, when the temperature of the heat conductive cylinder  83  is dropped from T 1  to T 2 , with the sum of the substantial thermal expansion (i.e., a pull-down distance of the tip  10 ) of the thick tube  15  and the inner tube  13  in the z direction, when the temperature of the thick tube  15  is further raised from T 3  to T 4 , to cause cancellation of these two values. 
     The comparing unit  604  compares the desired temperature T 3  or T 4  selected by the change switch  603  with the real temperature T 15  detected for the thick tube  15  by the temperature sensor  91  for outputting its differential signal ΔT to the PI controlling unit  606 . The PI controlling unit  606  supplies the driving signal to the heating coil  16  through the driver circuit  608  to make the differential signal ΔT zero. 
     On the other hand, an operation of the present embodiment will be described in detail as follows with reference to a flow chart of FIG.  4 . 
     In an initial state, the operation-controlling unit  62  works in coarse adjustment mode, the desired temperature T 3  in coarse adjustment is selected by the change switch  603  in the first temperature-controlling unit  60   a , and the desired temperature T 1  during coarse adjustment is selected by the change switch  613  in the second temperature-controlling unit  60   b.    
     In step S 1 , the first and the second temperature-controlling units  60   a  and  60   b  are urged to supply the driving current to the heating coils  16  and  86  for raising the temperature of the thick tube  15  and the heat conductive cylinder  83 . In step S 2 , a determination is made as to whether or not the temperature T 15  detected for the thick tube  15  by the temperature sensor  91  and the temperature T 83  detected for the heat conductive cylinder  83  by the temperature sensor  92  reach the desired temperatures T 3  and T 1 , respectively. 
     When both the temperature of the thick tube  15  and the heat conductive cylinder  83  reach the desired temperature, in step S 3 , the VCM driving unit  64  is energized for coarse adjustment of the spindle  8  in the z direction. In step S 4 , a determination is made as to whether or not the tip  10  reaches the sample surface based on the extent of bending of the tip  10 . When it is determined that the tip  10  reaches the sample surface, in step S 5 , the VCM driving unit  64  suppresses electrification of the voice coil motor to stop downward movement of the tip  10 . In other words, coarse adjustment is completed and measurement mode is started. 
     In measurement mode, in step S 6 , the change switch  603  of the first temperature-controlling unit is switched to the desired temperature (T 4 ) for measurement and the change switch  613  of the second temperature-controlling unit  60   b  is switched to the desired temperature (T 2 ) for measurement. 
     In step S 7 , a determination is made as to whether or not the temperature T 83  of the heat conductive cylinder  83  has fallen to the desired temperature T 2 . When the temperature T 83  of the heat conductive cylinder  83  has fallen to the desired temperature T 2 , the thick tube  15  becomes integrally formed with the inner tube  13 . Then, in step S 8 , whether or not the temperature T 15  of the thick tube  15  has reached the desired temperature T 4  for measurement is determined. When the temperature T 15  of the thick tube  15  reaches the desired temperature T 4 , measurement is carried out in step  9 . 
     According to this embodiment, temperature drift in the z direction caused by integration of the thick tube  15  with the inner tube  13  through lowering the temperature of the heat conductive cylinder  83  is eliminated not by supplying the offset current to the voice coil motor, but by thermal expansion of the thick tube  15  and the inner tube  13 . Thus, temperature drift caused by the offset current flowing continuously through the voice coil motor in the z direction can be completely prevented. 
     FIG. 5 is a sectional view showing the structure of a main part of a third embodiment of the probe scanning device fabricated by applying the present invention, with the same numerals as above indicating the same or similar parts. 
     The present embodiment is characterized in that the offset current-detecting unit  63  for detecting the offset current, which is contained in the driving signal outputted from the VCM driving unit  64 , is installed, the first temperature-controlling unit  60   a  raises the temperature of the thick tube  15  to a temperature at which viscosity of the viscous material decreases in coarse adjustment, and lowers the temperature to a temperature at which the offset current falls during measurement. 
     FIG. 6 is a block view showing the structure of a main part of the first and the second temperature-controlling units  60   a  and  60   b , with the same numerals as above indicating the same or similar parts. 
     At the desired temperature-setting unit  601  for coarse adjustment in the first temperature-controlling unit, a temperature allowing sufficient lowering of viscosity of the viscous material  17  is set as the desired temperature T 3  of the thick tube  15  during coarse adjustment. A comparing unit  604  compares the desired temperature T 3  during coarse adjustment T 3  with a real temperature T 5  of the thick tube  15 , which is detected by the temperature sensor  91 , to output a differential signal ΔT. 
     The change switch  605  outputs an offset signal Soff, which represents the offset current value detected by the offset current-detecting unit  63 , or the differential signal ΔT to a PI-controlling unit  606 . The output signal of the PI-controlling unit  606  is supplied to the heating coil  16  through a driver circuit  608 . 
     In the desired temperature-setting unit  611  for coarse adjustment in the second temperature-controlling unit  60   b , a temperature, higher than a melting point of the low melting-point metal  85  is set as the desired temperature T 1  of the heat conductive cylinder  83  during coarse adjustment. At the desired temperature-setting unit  612  during measurement, a temperature, lower than a solidifying temperature of the low melting-point metal  85 , is set as the desired temperature T 2  of the heat conductive cylinder  83  during measurement. 
     The comparing unit  614  compares the desired temperature T 1  or T 2  selected by the change switch  613  with the real temperature T 83  detected for the heat conductive cylinder  83  by the temperature sensor  92  to output its differential signal ΔT to the PI controlling unit  616 . The output signal of the PI-controlling unit  616  is supplied to the heating coil  86  through the driver circuit  618 . 
     On the other hand, the action of the present embodiment will be described in detail as follows with reference to a flow chart of FIG.  7 . 
     The initial state is in the coarse adjustment mode and hence, it is defined that the comparator  604  is selected by the change switch  605  in the first temperature-controlling unit  60   a  and the desired temperature (T 1 ) in coarse adjustment is selected by the change switch  613  in the second temperature-controlling unit  60   b.    
     In step S 1 , the first temperature-controlling unit  60   a  and the second temperature-controlling unit  60   b  are urged to supply the driving current to the heating coils  16  and  86  for raising the temperature of the thick tube  15  and the heat conductive cylinder  83 . In step S 2 , a determination is made as to whether or not the temperature T 15  detected for the thick tube  15  by the temperature sensor  91  and the temperature T 83  detected for the heat conductive cylinder  83  by the temperature sensor  92  reach the desired temperatures T 3  and T 1 , respectively. 
     When both the temperature of the thick tube  15  and the heat conductive cylinder  83  reach the desired temperature, in step S 3 , the VCM driving unit  64  is energized for coarse adjustment of the spindle  8  in the z direction. In step S 4 , determination is made on whether or not the tip  10  reaches the sample surface based on the extent of bending of the tip  10 . When it is determined that the tip  10  reaches the sample surface, in step S 5 , the VCM driving unit  64  suppresses electrification of the voice coil motor to stop downward movement of the tip  10 . In otherwords, coarse adjustment is completed for starting the measurement mode. 
     In the measurement mode, in step S 6 , the change switch  613  of the second temperature-controlling unit  60   b  is switched to the side of the desired temperature T 2  during measurement. In step S 7 , the change switch  605  of the first temperature-controlling unit  60   a  is switched to the offset signal Soff side. Instep S 8 , a determination is made as to whether or not the temperature T 83  of the heat conductive cylinder  83  has fallen to the desired temperature. In step S 9 , a determination is made as to whether or not the offset signal Soff is stabilized in the action-controlling unit  62 . When the offset signal Soff is determined to be stabilized, measurement is carried out in step S 11 . 
     According to the present embodiment, the temperature drift in the z direction, which is caused by the temperature change during measurement, can be eliminated not by supplying the offset current to the voice coil motor, but by thermal expansion or heat shrinkage of the thick tube  15  and the inner tube  13 . Thus, the temperature drift due to heat generation and the change of ambient temperature, which are caused by the offset current flowing continuously through the voice coil motor in the z direction, can be completely prevented. 
     FIG. 8 is a sectional view showing the structure of a primary part of a fourth embodiment of a probe scanning device fabricated by applying the present invention, with the same numerals as above indicating the same or similar portions. The present embodiment is characterized in that in the first and the second temperature-controlling units  60   a  and  60   b , holding circuits  607  and  617  are added to individual later stages of the PI controlling unit  606  and  616 , respectively. 
     FIG. 9 is a flowchart showing an operation of the present embodiment, and same processing as that of the third embodiment is carried out from step S 1  to step S 9 . 
     In the present embodiment, when it is determined that the offset signal Soff is stabilized in step S 9 , a hold signal Shold is supplied to individual hold circuits  607  and  617  of the first and the second temperature-controlling units  60   a  and  60   b  instep S 10 . Individual hold circuits hold the input signal on the timing of the hold signal Shold. 
     In step S 11 , measurement is started. 
     According to the present embodiment, the output signals from the first and the second temperature-controlling units  60   a  and  60   b  are held during measurement to keep heat generated by individual heating coils constant and therefore, regardless of the change of the ambient temperature and the temperature drift in the controlling system, an image with a less noise can be obtained. 
     According to the present invention, the following effects can be achieved. 
     (1) In the probe scanning device in which the thick tube is selectively integrated with the inner tube according to an operation mode, integration of the thick tube with the inner tube is achieved by solidifying the low melting-point metal and shifting of the position of the thick tube from the inner tube over time can be prevented. Therefore, even in the case where the scanning speed in the xy direction is low so as to require a long time for measurement, high precision measurement becomes possible. 
     (2) During measurement, electrification of individual heating coils is controlled to keep the temperature of individual parts to a predetermined temperature and high precision measurement not influenced by temperature drift therefore becomes possible. 
     (3) The configuration is provided using a material such as super-invar with a very small thermal expansion coefficient and hence, influence of temperature drift can be further reduced. 
     (4) When the temperature of the heat conductive cylinder is decreased to the temperature at which the low melting-point metal solidifies, heat shrinkage of the heat conductive cylinder in the z direction is cancelled by thermal expansion of the thick tube and the inner tube and no offset current flows in the voice coil motor in the z direction. Temperature drift caused by flow of the offset current in the voice coil motor can therefore be prevented. 
     (5) Temperature drift in the z direction, which is caused by temperature change during measurement, can be eliminated not by supplying the offset current to the voice coil motor, but by thermal expansion or heat shrinkage of the thick tube  15  and the inner tube  13 . Temperature drift caused by a continuous flow of offset current through the voice coil motor in the z direction can therefore be completely prevented. 
     (6) The output signals from the first and the second temperature-controlling units are held during measurement and an image with less noise can therefore be obtained regardless of the change of the ambient temperature and temperature drift in the controlling system.