Probe scanning system

Abstract: This specification discloses an apparatus for and a method of moving a probe (1) for causing a physical phenomenon (eg tunnel current) to occur between it and a predetermined object(s). At least one of the probe and the object is driven in a predetermined direction to scan the probe and the object in the predetermined direction relative to one another. A physical phenomenon occurring between the probe and the object is detected (5). At least one of the probe and the object is driven so as to bring the probe and the object close to each other. The drive (7) for the approach of the probe to the object is controlled by detecting the physical phenomenon while scanning (6) in the predetermined direction.

Description: This invention relates to an apparatus for and a method of moving a probe and an object relative to each other according to the preamble of claims 1 and 5. An apparatus and a method of this type are known from REVIEW OF SCIENTIFIC INSTRUMENTS, Vol. 61, No.7, July 1990, New York, pp. 1869 to 1873; K. W. HIPPS et al: "A scanning tunneling microscope with a wide sampling range" or EP-A-0 338 083. In recent years, there has been developed a scanning type tunnel microscope (hereinafter referred to as STM) in which a physical phenomenon such as a tunnel phenomenon observed when a probe is made to approach a sample is utilized to directly observe the surface of a substance and the electron structure near the surface [G. Binning et al., Helvetica Physica Acta, 55,726 (1982)] and thus, it has become possible to measure a real spatial image at high resolving power irrespective of single crystal or amorphous materials. STM also has the advantage that it can accomplish observation with low electric power without imparting damage by an electric current to a medium, and further can operate not only in super-high vacuum but also in the atmosphere and solutions and can be used for various materials, and its wide applications in accordance or research field are expected. Also in industrial field, as disclosed, for example, in Japanese Laid-Open Patent Applications Nos. 63-161552 and 63-161553, attention is paid to the principle that the sizes of atoms or molecules have spatial resolving power, and the application of STM to recording-reproducing apparatuses and putting STM into practical use have been energetically put forward. Now, such STM or recording-reproducing apparatus is directed to measure a tunnel current or the like while the probe is scanned in parallel to the surface of the sample, thereby knowing the physical amount distribution on the surface of the sample, and in order that such purpose may be attained, it is necessary that the sample and the probe be sufficiently close to each other to such a degree that a tunnel current flows between the sample and the probe. However, when there is relatively great unevenness on the surface of the sample, for example, when the approach position of the probe is a concave portion of the sample, collision or contact may be caused between the probe and the sample by scanning being started if not during the approach of the probe to the sample. As a result, not only the sample may be damaged, but also the tip end of the probe may be crushed flat and the radius of curvature thereof may be increased, thus causing a reduction in spatial resolving power. Also in the case of an applied apparatus such as a recording-reproducing apparatus, it is necessary to make the probe approach the recording surface avoiding concave portions of the latter. Also, for such STM or recording-reproducing apparatus to function properly, as described above, it is necessary that the sample and the probe be sufficiently close to each other to such a degree that a tunnel current flows between the sample and the probe and therefore, an appropriate probe approach mechanism for approximating in advance the distance between the sample and the probe to a distance at which the tunnel phenomenon is observed is indispensable. Heretofore, a stepping motor, an inch worm or a laminated piezo-electric member has specifically been utilized as the approach mechanism (Applied Physics Letter, vol. 40 (1982), pp. 178 - 180), but by the conventional approach means, the positional accuracy of the probe cannot be obtained due to parasitic oscillation or creep phenomenon occurring during movement, and the possibility of the probe impacting the sample when the probe is made to approach the sample is high. This leads to the problem that not only the sample is damaged, but also the tip end of the probe is crushed flat and the radius of curvature thereof is increased, thus causing a reduction in spatial resolving power. W. Göpel et al. ,,Sensors", Vol. 1, "Fundamentals and General Aspects", 1989, VCH, Weinheim, DE, Chapter 17 ,,Automated Manufacturing" pp. 446-454 discloses an ultrasonic distance sensor emitting focused ultrasonic pulses and receiving ultrasonic pulses reflected from the surface of a workpiece, so as to detect different distances between the workpiece surface and a robot hand. In view of the above-described example of the prior art, it is the primary object of the present invention to provide an apparatus for and a method of moving a probe and an object relative to each other which enables such an approaching operation that a probe does not contact or collide with a sample or the like when the probe approaches the sample or when the probe starts to scan the sample. This is achieved by the present invention in accordance with the features of claims 1 and 5, respectively. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a block diagram showing the circuit construction of a first embodiment of the present invention. Figure 2 is a cross-sectional view of the surface of a sample. Figure 3 is a time chart for illustrating the operation of the first embodiment. Figure 4 is a block diagram showing the circuit construction of a second embodiment of the present invention. Figure 5 is a time chart for illustrating the operation of the second embodiment. Figure 6 is a time chart for illustrating the operation of a third embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In a first embodiment of the present invention which will hereinafter be described, a probe moving apparatus is confirmed at first on the highest convex portion of the surface of a sample in which the approach of a probe to the sample is within a sweep range. Description will hereinafter be made in detail with reference to the drawings. Figure 1 is a block diagram showing the circuit construction of the first embodiment, and shows a case where the probe 1 is made to approach the sample S while a tunnel current is observed. It is to be understood that the sample S, as shown, for example, in Figure 2, is a silicon substrate on which straight grooves Sc each having a width of 1 µm and a depth of 0.1 µm are etched at intervals of 2 µm. The probe 1 is provided on a fine movement section 2 using, for example, a piezo-electric actuator, and the fine movement section 2 is mounted on a coarse movement section 3 movable over a wide range by the use, for example, of a stepping motor or the like. A weak bias voltage is applied between the sample S and the probe 1 by a bias circuit 4, and the tunnel current flowing between the two is measured by a tunnel current detection section 5. The fine movement section 2 is adapted to sweep (vibrate at a constant amplitude) within a range of a width of e.g. 2 µm along the sample S in a direction orthogonal to the straight grooves Sc by a sweep driving circuit 6. Further, the fine movement section 2 is designed to be finely movable toward the sample S within a range of e.g. maximum 0.2 µm or so by an approach driving circuit 7 with the aid of a laminated piezo-electric member or the like, and the coarse movement section 3 is designed to be coarsely moved toward the sample S at a step of 0.1 µm within a movement range of e.g. 10 mm or so, and the operations of the sweep driving circuit 6 and the approach driving circuit 7 are controlled by a sequence control circuit 8, and the probe 1 approaches the sample S by an operation as described below without colliding with the sample S until the tunnel current is observed by the tunnel current detection section 5. That is, the probe 1 is first kept away from the sample S, and the sweep of the fine movement section 2 is started by the sweep driving circuit 6. Then, it is confirmed whether the tunnel current flows, while the fine movement section 2 is stretched to a maximum distance toward the sample S as the sweep is continued as shown in Fig. 3 (a). If the tunnel phenomenon does not appear and the tunnel current is not observed, the fine movement section 2 is immediately contracted and the coarse movement section 3 is advanced by one step (b). Since one step of the coarse movement section 3 is 0.1 µm, the probe 1 exists within a range examined from the stretch 0.2 µm of the fine movement section 2 at the last time. That is, the probe 1 is not brought closer to the sample S by coarse movement than during the last fine movement, and the tunnel current does not begin to flow during this coarse movement. Subsequently, whether the tunnel current flows in the process wherein the fine movement section 2 is again stretched to the maximum as the sweep is continued is examined. If the tunnel phenomenon does not appear and the tunnel current is not observed, the fine movement section is contracted and by coarse movement, the probe 1 is brought close to the sample S by a further step. Thereafter, the above-described operation is repeated, and at a point of time (d) whereat the tunnel current is observed, the approach step is completed, the sweep is stopped and thus, the sequence control is terminated. According to such a method, the tunnel current is observed at first on the convex portions of the sample S without fail, and it never happens that the probe 1 goes into the recesses such as the grooves Sc, and the collision of the probe 1 with the sample S can be avoided when scanning is started. Not only the recesses are avoided, but also any abnormal convex portion which may be present on the sample S can be detected when the probe 1 approaches the sample S and therefore, the probe 1 can be made to sweep the sample avoiding such portion, and approach only the normal portion of the sample. Description will now be made of an embodiment we have actually used for STM. STM comprises a construction as shown in Figure 1. The probe 1 is moved up and down in a direction perpendicular to the surface of the sample by feedback control so that the tunnel current flowing by a predetermined voltage applied between the sample S and the probe 1 by the bias circuit 4 may become constant. By the use of the sweep driving circuit 6, the probe 1 is swept in parallel to the surface of the sample, and a system which reads out the then upward and downward movement of the probe 1 as a signal and outputs if as an image is STM. Again in that case, collision may often occur between the probe 1 and the sample S at the first stage of approach of the former to the latter, thus damaging the sample S or the probe 1. So, we have repeatedly carried out a series of experiments of spacing the probe 1 apart from the sample S, again making the probe 1 approach the sample S and observing the sample, by the use of the present invention. As a result, it has been confirmed that the disturbance or the like of the tunnel current caused by the damage of the sample S by the collision during sweep becomes null and an image of high spatial resolving power can be observed with good reproducibility and the probability of collision or contact has decreased. Description will further be made of an embodiment in a case where we have used the present invention for an information processing apparatus. Describing first the basic operation of the information processing apparatus, the construction of Figure 1 is used and a recording medium is used in lieu of the sample S, and in addition to the aforedescribed STM operation, a particular voltage signal based on recording information is superposed on a bias voltage by the bias circuit 4, whereby an electrical variation is caused on the surface of the recording medium corresponding to the then position of the probe 1 and information is written onto the recording medium. Also, reading-out is effected by an electric current signal obtained by the STM operation or a signal indicative of the upward and downward movement of the probe 1, and erasing is effected by applying a predetermined voltage signal to that same position to thereby restoring the electrical state change on the surface of the recording medium to the original state. As regards a specific embodiment, as disclosed in Japanese Laid-Open Patent Applications Nos. 63-161552 and 63-161553, a recording medium comprising LB film (two-layer film) of a polymer (for example, polyimide) of heterocyclic compounds laminated on a gold (Au) electrode was disposed in lieu of the sample S of Figure 1, and recording, reproduction and erasing were effected. In such an apparatus, a voltage obtained by superposing continuous pulse waves of crest values -6V and +1.5V on a bias voltage by the bias circuit 4 was applied between the recording medium and the probe 1 while the probe 1 was scanned in XY direction so that the tunnel current might be constant, whereby the electrical writing of information was effected and further, the recorded surface was again scanned by the probe 1 and the reading-out of recording information was effected from an STM image using a variation in the tunnel current obtained by the tunnel current detection circuit 5. As a result, it could be confirmed that the recording information and reproduced information coincided with each other with good reproducibility even if the above-described operation was repetitively performed. From this, it can be seen that the probe 1 can be made to approach the recording surface without destroying the recording medium even when the above-described operation is repetitively performed. Also, it was confirmed that when the operation of superposing a pulse voltage of crest value 3V on a bias voltage between the recording medium and the probe 1 by the bias circuit 4 at a point of time whereat the probe 1 approached an area on the recording medium on which recording was effected in the course of scanning, the recorded information was erased from the STM image reproduced. Again in this case, of course, the collision of the probe 1 with the recording medium could be effectively prevented by the approach mechanism of the present invention. The method according to the present embodiment can be applied to any apparatus in which an approach mechanism can be operated while a probe is scanned in parallel to the surface of a sample, and is not restricted in the shape of the sample and the mechanism and structure of sweep and approach. Also, in the present embodiment, description has been made of an STM and an information processing apparatus for measuring tunnel current as physical information, whereas the present invention is equally applicable to measuring apparatuses for observing the force between atoms, capacity, magnetic flux, magnetic force, etc. As described above, the probe moving apparatus according to the above-described embodiment can accomplish measurement while keeping the shape of the top end of the probe sharp without causing the probe to collide with the sample because the probe does not go into the recess of the sample, and observation higher in spatial resolving power becomes possible. Also, the probe is not damaged and therefore, the interchange of the probe is not required, and this leads to the advantage that the simplification and compactness of the system can be achieved in STM and information recording apparatuses. Further, it is also possible to avoid uneven portions of the sample and make the probe selectively approach a flat portion of the sample, and this is useful in information recording and reproduction. A second embodiment of the present invention will be explained below in detail according to Figures 4 and 5. Figure 4 is a block diagram showing the circuit construction of STM, and shows a case where a probe 11 is made to approach a sample S while a tunnel current is observed. In Figure 4, the probe 11 is provided on a fine movement section 12 using, for example, a piezo-electric actuator, and the fine movement portion 12 in turn is mounted on a coarse movement section 13 movable over a wide range, for example, by the use of a stepping motor or the like. The operations of the fine movement section 12 and the coarse movement section 13 are controlled by a sequence control circuit 14. Also, a weak bias voltage is applied between the sample S and the probe 11 by a bias circuit 15, and a tunnel current flowing between the two is measured by a tunnel current detection section 16. The fine movement section 12 is designed to be finely movable within a range of e.g. maximum 0.2 µm or so by a laminated piezo-electric member or the like, and the coarse movement section 13 is designed to be coarsely movable within a movement range of e.g. 10 mm or so at a step of 0.1 µm, and the fine movement section 12 and the coarse movement section 13 are both controlled by the control circuit 14, and the probe 11 approaches the sample S by the operation as will be described below without colliding with the latter until the tunnel current is observed by the tunnel current detection section 16. Figure 5 is a time chart showing the amounts of movements of the fine movement section 12 and coarse movement section 13 at this time and the tunnel current detected. That is, the probe 11 is first kept spaced apart from the sample S, and it is confirmed whether the tunnel current flows, while the fine movement section 12 is stretched to a maximum distance 0.2 µm (a). If the tunnel phenomenon does not appear and the tunnel current is not observed, the fine movement section 12 is immediately contracted. Subsequently, the coarse movement section 13 is moved by one step (b). Since one step of the coarse movement section 13 is 0.1 µm, the probe 11 exists within a range examined by the stretch 0.2 µm of the fine movement section 12 at the last time. That is, the probe 11 does not become closer the sample S by the coarse movement than during the last fine movement, and the tunnel current does not begin to flow during this coarse movement. Subsequently, it is examined whether the tunnel current flows in the process of moving the fine movement section 12 again to a maximum distance. If the tunnel phenomenon does not occur and the tunnel current is not observed, the fine movement section 12 is contracted and again by coarse movement, the probe 11 is brought close to the sample by a further step (c). Thereafter, the above-described procedure is repeated, and at a ponit of time (d) whereat the tunnel current is observed, the approach process is completed and thus, sequence control is terminated. Figure 6 is a time chart during approach control in a third embodiment, and the apparatus construction of this embodiment is similar to that of Figure 4 and need not be shown and described. The present embodiment is applicable to a case where the driving of the coarse movement section 13 is not of the step type as in the case of a laminated piezo-electric member. That is, during the forward movement of the fine movement section 12, the coarse movement section 13 is stopped, and in accordance with the backward movement of the fine movement section 12, the coarse movement section 13 is moved forward at a speed at greatest below the speed of the backward movement of the fine movement section 12. Again in this case, by coarse movement, the probe 11 does not become closer to the sample S than the range of the last fine movement, and the tunnel current does not begin to flow during coarse movement. In any of the above-described systems, the tunnel current begins to flow without fail during fine movement and is not at all affected by parasitic oscillation which is a problem arising when the coarse movement section 13 is driven. Therefore, an abnormal increase in a spike-like tunnel current produced upon completion of approach when the probe is made to approach the sample in the prior-art approach mechanism can be prevented, and the probability with which damage is caused by the collision of the tip end of the probe 11 with the sample S can be greatly decreased. Description will now be made of an embodiment we have actually used for STM. STM is of a construction as shown in Figure 4. The probe 11 is moved up and down in a direction perpendicular to the surface of the sample by feedback control so that the tunnel current flowing by a predetermined voltage applied between the sample S and the probe 11 by the bias circuit 15 may become constant. At the same time, the probe 11 is moved in parallelism to the surface of the sample, and a system which reads out the then upward and downward movement of the probe 11 as a signal and outputs it as an image is STM. Again in that case, collision may often occur between the sample S and the probe 11 at the first stage of approach of the probe to the sample, thus damaging the sample S or the probe 11. So, we carried out a series of experiments of spacing the probe 11 apart from the sample S, again making the probe approach the sample and observing the sample, by the use of the present invention. As a result, it was confirmed that the disturbance or the like of the tunnel current caused by the damage of the sample S by the collision during approach became null and an image high in spatial resolving power could be observed with good reproducibility and the probability of collision or contact decreased. Description will further be made of an embodiment in a case where we have used the present invention for an information processing apparatus. Describing first the basic operation of the information processing apparatus, the construction of Figure 4 is used and a recording medium is used in lieu of the sample S, and in addition to the aforedescribed STM operation, a particular voltage signal is superposed on a bias voltage by the bias circuit 15, whereby an electrical variation is caused on the surface of the recording medium corresponding to the then position of the probe 11 and information is written onto the recording medium. Reading-out is effected by an electric current signal obtained by the STM operation or a signal indicative of the upward and downward movement of the probe 11, and erasing is effected by applying a predetermined voltage signal to that same position to thereby restore the electrical state change on the surface of the recording medium to the original state. As regards a specific embodiment, as disclosed in Japanese Laid-Open Patent Applications Nos. 63-161552 and 63-161553, a recording medium comprising LB film (two layer film) of a polymer (for example, polyimide) of heterocyclic compounds laminated on a gold (Au) electrode was disposed in lieu of the sample S of Figure 4, and recording, reproduction and erasing were effected. In such an apparatus, a voltage obtained by superposing continuous pulse waves of crest values -6V and +1.5V on a bias voltage by the bias circuit 15 was applied between the recording medium and the probe 11 while the probe 11 was scanned in XY direction so that the tunnel current might be constant, whereby the electrical writing of information was effected and further, the recorded surface was again scanned by the probe 11 and the reading-out of recording information was effected from an STM image using a variation in the tunnel current obtained by the tunnel current detection circuit 16. As a result, it could be confirmed that the recording information and reproduced information coincided with each other with good reproducibility even if the above-described operation was repetitively performed. From this, it can be seen that the probe 11 can be made to approach the recording surface without destroying the recording medium even when the above-described operation is repetitively performed. Also, it was confirmed that when the operation of superposing a pulse voltage of crest value 3V on a bias voltage between the recording medium and the probe 11 by the bias circuit 15 at a point of time where at the probe 11 approached an area on the recording medium on which recording was effected in the course of scanning, the recorded information was erased from the STM image reproduced. Again in this case, of course, the collision of the probe 11 with the recording medium could be effectively prevented by the approach mechanism of the present invention. According to our experiment, it was confirmed that the recording information and reproduced information coincided with each other with good reproducibility and even if the scanning for recording and reproduction was repetitively effected, the probe 11 could be made to approach the surface of the recording medium without destroying the recording medium. Also, it was confirmed that when the scanning for superposing a pulse voltage of crest value 3V on a bias voltage was effected at a point of time whereat the probe 11 approached an area on the recording medium on which recording was effected, the recorded information was erased from the read-out signal reproduced. In the above-described embodiment, the constructions and amounts of movement of the fine movement section 12 and coarse movement section 13 are not restricted to what have been aforedescribed. For example, even if a DC servo-motor, an inch worm or the like is used, application is readily possible and similar utilization can be made. Also, the second and third embodiments have both been described with respect to cases where the present invention is applied to STM for measuring a tunnel current as physical information and an information processing apparatus, but the present invention can likewise be applied to a measuring apparatus or the like for observing the force between atoms, capacity, magnetic flux, magnetic force, etc. As described above, the probe moving apparatus according to any of the second and third embodiments enables the probe to approach the sample without colliding with the latter and therefore, can use the probe while keeping the shape of the tip end thereof sharp and thus, observation higher in spatial resolving power becomes possible. Also, the interchange of the probe becomes unnecessary because the probe is not damaged, and this leads to the simplification and compactness of the system in STM or an information recording apparatus.

Claims: An apparatus for moving a probe (1) and a predetermined object (S) relative to each other to make said probe approach said object, comprising: actuator means (2, 3) for driving at least one of said probe and said object so as to approach said probe and said object relative to each other, a detection section (5) for detecting the spacing between said probe and said object, and a control section (14) for controlling the approach of said probe and said object based on the detection result of said detection section to thereby avoid collision of said probe and said object, characterized in that said actuator means is arranged to cause said probe and said object to approach while moving relatively said probe and said object in a direction parallel to a surface of said object, and said detection section (5) is arranged to detect that the spacing between said probe (1) and said object (S) has reached a predetermined spacing, by detecting the tunnel current flowing between said probe and said object, the force between atoms of said probe and said object, the capacity or the magnetic flux between said probe and said object. An apparatus for effecting information detection from a predetermined object and/or information input to said predetermined object based on the apparatus according to claim 1, wherein said information detection from said object and/or said information input to said object (S) is effected by said probe (1). An apparatus according to claim 2, further having a scanning mechanism for scanning said probe (1) along the surface of said object (S), wherein during the scanning by said scanning mechanism, the surface information of said object is detected through said probe. An apparatus according to claim 2 or 3, wherein the recording and/or reproduction of an information is effected on a recording medium as said object (S) through said probe. A method of moving a probe (1) and a predetermined object (S) relative to each other to make said probe approach said object, comprising: a first step of driving at least one of said probe and said object so as to approach said probe and said object relative to each other, a second step of detecting the spacing between said probe and said object, and a third step of controlling the approach of said probe and said object based on the detection result of said second step to thereby avoid collision of said probe and said object, characterized in that said probe and said object are caused to approach in said first step while moving relatively said probe and said object in a direction parallel to a surface of said object, and the spacing between said probe (1) ) and said object (S) is detected via the tunnel current flowing between said probe and said object, the force between atoms of said probe and said object, the capacity or the magnetic flux or force between said probe and said object.

Inventors: MIYAZAKI TOSHIHIKO, OGUCHI TAKAHIRO, SAKAI KUNIHIRO, SHIDO SHUN-ICHI, MIYAZAKI, TOSHIHIKO, OGUCHI, TAKAHIRO, SAKAI, KUNIHIRO, SHIDO, SHUN-ICHI, MIYAZAKI, TOSHIHIKO, C/O CANON KABUSHIKI KAISHA, OGUCHI, TAKAHIRO, C/O CANON KABUSHIKI KAISHA, SAKAI, KUNIHIRO, C/O CANON KABUSHIKI KAISHA, Shido, Shun-Ichi, c/o Canon Kabushiki Kaisha
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1992
Main classification: G01N27
IPC codes: G01N27, G11B9