JP2009229427A - Surface shape measuring device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface shape measuring device capable of measuring the surface shape of a sample while holding a distance of micron order between a probe and the measured sample. <P>SOLUTION: The probe 2 is allowed to scan in a X-Y plane direction by a probe moving mechanism 3. In a plurality of positions associated with scanning, the position in the Z-axis direction of the probe 2 moved by the probe moving mechanism 3, or voltage applied by a voltage applying mechanism, is changed to generate dielectric breakdown between the probe 2 and the surface of the sample, and the surface shape of the sample is obtained based on the measured results of a position measuring mechanism 4 or a voltage measuring mechanism 6 when the electric breakdown is generated. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a surface shape measuring apparatus capable of measuring a surface shape in a non-contact state.

Conventionally, an atomic force microscope (AFM) has been used as an apparatus for measuring the surface shape in a non-contact manner. A typical AFM includes a probe having a cantilever and a probe tip extending from the cantilever (see, for example, Patent Document 1). In this type of AFM, in order to measure the topography (ie, shape) of the surface of the measurement sample, the probe is scanned over the sample surface. In the scanning operation, either the measurement sample or the probe is translated. When the probe scans the sample surface, atomic force interacts with the probe tip, and the cantilever is biased. By measuring this bias as a function of the probe position with respect to the sample surface, the sample surface A 3D map was created.
JP 2003-344257 A

However, the AFM has the following problems.
First, it is necessary to bring the probe and the measurement sample close to a level at which an atomic force is generated, that is, several nm. For this reason, in a measurement sample having a large step, there arises a problem that the probe collides with the sample during operation. A collision not only makes measurement impossible, but also risks damaging expensive probes. Further, since it is necessary to control a fine probe of nm or less, the apparatus is large and expensive. Further, it is necessary for a skilled engineer to operate such an apparatus, and the measurement is expensive.

  The present invention has been made in view of such points, and an object thereof is to provide a surface shape measuring apparatus capable of measuring the surface shape of a sample while maintaining a micron-order distance between the probe and the measurement sample. To do.

  A surface shape measuring apparatus according to the present invention measures a probe positioned opposite to a sample, a probe moving mechanism that moves the probe in the Z-axis direction perpendicular to the XY plane and the XY plane, and facing the sample, and the position of the probe A position measurement mechanism, a voltage application mechanism for applying a voltage between the probe and the sample surface, a voltage measurement mechanism for measuring a potential difference between the probe and the sample surface, and a control means for controlling each mechanism, The control means scans the probe in the XY plane direction by the probe moving mechanism, and changes the position of the probe in the Z-axis direction by the probe moving mechanism or the applied voltage by the voltage applying mechanism at a plurality of positions accompanying the scanning to change the probe and sample surface. The surface shape of the sample is obtained based on the measurement results of the position measurement mechanism or voltage measurement mechanism when the dielectric breakdown occurs. It is.

  According to the present invention, it is possible to obtain a surface shape measuring apparatus capable of measuring the surface shape of a sample in a state where a distance on the order of microns can be generated, which can cause dielectric breakdown between the probe and the measurement sample. it can.

FIG. 1 is a schematic configuration diagram of a surface shape measuring apparatus 1 according to an embodiment of the present invention. Here, a description will be given based on three-dimensional coordinates in which the depth direction of the paper surface of FIG.
The surface shape measuring apparatus 1 moves a metal probe (hereinafter referred to as a probe) 2 and a probe 2 in the X-axis and Y-axis directions, and in the Z-axis direction (in a direction to increase or decrease the distance from the sample 10). ) A probe moving mechanism 3 that moves up and down, a position measuring mechanism 4 that measures the position of the probe tip 2a, and a voltage applying mechanism 5 that applies a voltage of the order of several KV between the probe 2 and a measurement sample (hereinafter referred to as a sample) 10. And a voltage measuring mechanism 6 that measures the voltage between the probe 2 and the sample 10 (probe voltage), and a control means 7 that controls the entire surface shape measuring apparatus 1. The sample 10 is placed in parallel with the XY plane in the atmosphere. The sample 10 needs to be conductive.

  The control means 7 scans the probe 2 with respect to the sample surface (moves in the XY plane direction), and controls the probe moving mechanism 3 for a measurement operation for moving the probe 2 up and down in the Z-axis direction at a plurality of positions accompanying the scanning. Let me do it. The position measuring mechanism 4 and the voltage measuring mechanism 6 output measurement results to the control means 7, respectively. The control means 7 performs the surface described later based on the measurement results from the position measuring mechanism 4 and the voltage measuring mechanism 6. A shape measurement process is performed, and the surface shape of the sample 10 is measured.

Next, the principle of surface shape measurement according to the present invention will be described.
By disposing the probe tip 2a so as to face the surface of the sample 10, a capacitor structure using the probe 2 and the sample 10 as electrodes, respectively, is formed. When a voltage higher than the dielectric breakdown voltage of air is applied to this capacitor structure portion, dielectric breakdown, that is, discharge occurs between the probe tip 2a and the sample 10, and the voltage drops. In the surface shape measurement of this example, the timing at which discharge occurs is detected, and the surface shape measurement is performed using physical data at that timing.

  By the way, although the actual surface of the sample 10 has irregularities, the minute portion can be approximated to a parallel plate capacitor. Paschen's law is applied to the voltage at which dielectric breakdown occurs in a parallel plate capacitor.

FIG. 2 shows a Paschen curve. That is, it shows the relationship between the interelectrode distance d according to Paschen's law and the potential (dielectric breakdown voltage) at which discharge occurs in the atmosphere at the interelectrode distance d. Hereinafter, the discharge change when the distance between the probe 2 and the sample 10 is changed will be described using this Paschen curve.
In FIG. 2, the distance d = 0 is a state where the probe tip 2 a is in contact with the sample 10. Consider a case where a voltage of 1000 V is applied and the probe tip 2a is raised (moved in the + direction) in the Z-axis direction from the state where the distance d = 0. In this case, as shown in the Paschen curve, until the distance reaches d0 (≈3 microns), the probe voltage is equal to the applied voltage and is 1000 V, and no discharge occurs. Then, the probe 2 is further raised in the Z-axis direction, and discharge starts when the distance d reaches d0. When the probe 2 is raised in the Z-axis direction as it is, the probe voltage decreases according to the Paschen curve while discharging continues.

  In this way, by moving the probe 2 in the Z-axis direction and changing the distance from the sample 10, discharge occurs at a certain Z coordinate position, and the probe voltage starts to decrease. In the surface shape measurement of this example, the position of the probe 2 at the probe voltage drop start timing, that is, the discharge start position is specified, and the position specification is performed at a plurality of positions in the XY plane direction, whereby the surface shape of the sample 10 is determined. To get.

Next, operation | movement of the surface shape measuring apparatus 1 of this invention is demonstrated.
FIG. 3 is an explanatory diagram of the surface shape measuring operation in the surface shape measuring apparatus 1.
First, the sample 10 is set at a predetermined position and positioned and fixed. Then, the control means 7 drives the probe moving mechanism 3 to move the probe 2 to the measurement start position on the XY plane, and thereafter performs a preparatory operation for determining the position in the Z-axis direction.

  In this example, since it is necessary to cause discharge between the probe 2 and the sample 10 and grasp the discharge start timing, the movement range (probe movement range) of the probe 2 in the Z-axis direction is the probe. It is necessary to generate a discharge while the probe tip 2a is moving within the moving range. However, since the distance between the sample 10 and the probe tip 2a is unknown when the sample 10 is set in the surface shape measuring apparatus 1, it is necessary to first grasp the distance between the probe 2 and the sample 10.

  That is, first, the probe tip 2a is set at a position sufficiently separated from the sample surface (here, for example, 30 microns). Then, for example, 500 V is applied between the probe 2 and the sample 10, and the probe tip 2a is brought closer to the sample surface. Then, as is apparent from the Paschen curve in FIG. 2, the discharge starts when it reaches 25 microns. When the probe 2 is further brought closer to the sample surface, the probe voltage decreases according to the Paschen curve. When d1 is reached, the discharge is terminated, and when the probe tip 2a is brought closer to the sample surface, the probe voltage becomes 500 V, which is the same as the applied voltage.

  The control means 7 checks the probe voltage by the voltage measuring mechanism 6 and stops the descent of the probe 2 at the timing when the probe voltage becomes 500V. The position of the probe 2 at this time is P ′ in FIG. The distance between the probe 2 and the sample surface is d1 (about 4 microns), as is apparent from the Paschen curve in FIG. As described above, first, the distance between the current probe tip 2a and the sample surface can be grasped.

  By the way, in detecting the discharge start timing during the surface shape measurement operation, as described above, the timing at which the probe voltage, which was the same as the applied voltage, starts to decrease is detected. For this reason, it is preferable from the viewpoint of detection accuracy to identify a portion where the probe voltage does not gradually decrease after the discharge starts, but rapidly decreases. Therefore, it is preferable to move the probe 2 in a range in which the rate of change of the dielectric breakdown voltage with respect to the interelectrode distance is high in the Paschen curve, that is, in a range of about 4 microns or less.

  Here, when the applied voltage at the time of the surface shape measurement operation is 1000 V, since the discharge start distance is d0, the probe movement range is determined so as to pass through d0. Specifically, for example, P1 (X0, Y0, Z0−) which is separated by a predetermined distance dz in the ± direction of the Z axis around the point P0 (X0, Y0, Z0) where the distance between the probe tip 2a and the sample surface is d0. d2) to P2 (X0, Y0, Z0 + dz) are set as the probe movement range. Accordingly, since the distance between the probe tip 2a and the sample surface is d1, now, the probe tip 2a is moved from the current position P ', P0, and the distance dz to the movement start position P1 of the probe movement range.

And when said preparation stage is complete | finished, it will enter into surface shape measurement operation | movement.
The control means 7 applies 1000 V by the voltage application mechanism 5, raises the probe 2 from P 1 to P 2 by the probe moving mechanism 3, and monitors the probe voltage during this period based on the measurement result from the voltage measurement mechanism 6. Then, the probe position P3 (x0, y0, z3) when the discharge starts is acquired by the position measurement mechanism 4. When the probe position P3 (x0, y0, z3) at the start of discharge is acquired in this way, the control means 7 lowers the height of the probe tip 2a to the original height position (height position z0-dz). Then, the probe 2 is moved in the XY directions and stopped, and the same operation as described above is performed at the stop position to acquire the probe position at the start of discharge. By performing this process while scanning in the XY directions, the distribution of the height position of the probe 2 at the start of discharge can be obtained, and the surface shape of the sample 10 can be measured.

  As described above, in the present embodiment, since the shape of the sample surface is measured using the discharge in the atmosphere, the surface shape can be measured with the probe 2 and the sample 10 separated by several microns. That is, as is clear from the Paschen curve shown in FIG. 2, the distance at which discharge occurs is in the order of microns, so by using discharge for surface shape measurement, the distance between the probe 2 and the sample 10 is The measurement can be made larger than the conventional AFM. Therefore, when measuring the shape of the sample surface having nano-order irregularities, the shape measurement can be performed without fear of the probe 2 colliding with the sample surface. Further, since the collision of the probe 2 with the sample surface can be avoided, there is no risk of damaging the probe 2. Further, since the up and down control of the probe 2 may be in the micron order, the technique by the skilled worker as described above is unnecessary, and the apparatus can be simple and low cost.

  A further advantage is that the position resolution in the Z-axis direction is high. As shown in the Paschen curve of FIG. 2, the relationship between the breakdown voltage and the interelectrode distance has a sensitivity of 10 V / nm when the interelectrode distance is about 4 microns or less. That is, if it exceeds 4 microns, the slope of the Paschen curve is gentle and the amount of change in voltage is small, whereas if it is less than 4 microns, the slope is abrupt and the amount of change in voltage is large. In other words, high resolution can be obtained in the Z-axis direction. Therefore, by setting the probe movement range to 4 microns or less, the voltage drop timing, that is, the discharge start timing can be specified with high accuracy. Therefore, the height position can be specified with high accuracy. Such high resolution in the Z-axis direction is a feature not found in conventional contact-type surface step meters, AFMs, and the like.

  In this embodiment, the probe 2 is moved upward (or lower) and the distance between the probe tip 2a and the sample surface is changed to obtain the discharge start timing. The discharge start timing may be obtained by keeping the voltage constant and increasing the applied voltage. In this case, the distance between the probe tip 2a and the sample 10 can be acquired from the voltage when the discharge starts and the Paschen curve in FIG. That is, for example, it is assumed that the applied voltage is increased from 0 V and discharged when the voltage reaches 500 V. In this case, the distance between the probe tip 2a and the sample 10 can be calculated as d1 microns from the Paschen curve in FIG. By scanning the probe 2 on the XY plane while maintaining its height position, the distribution of the distance from the probe tip 2a to the sample 10, that is, the shape of the sample surface can be determined.

It is a schematic block diagram of the surface shape measuring apparatus of one embodiment of this invention. It is a figure which shows a Paschen curve. It is operation | movement explanatory drawing at the time of the surface shape measurement in a surface shape measuring apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Surface shape measuring apparatus 2 Probe 2a Probe tip 3 Probe moving mechanism 4 Position measuring mechanism 5 Voltage application mechanism 6 Voltage measuring mechanism 7 Control means 10 Sample

Claims (4)

A probe disposed opposite the sample;
A probe moving mechanism for moving the probe in the Z-axis direction perpendicular to the XY plane and the XY plane and facing the sample;
A position measuring mechanism for measuring the position of the probe;
A voltage application mechanism for applying a voltage between the probe and the sample surface;
A voltage measuring mechanism for measuring a potential difference between the probe and the sample surface;
Control means for controlling each of the mechanisms,
The control means causes the probe moving mechanism to scan the probe in the XY plane direction, and changes a position in the Z-axis direction of the probe by the probe moving mechanism or an applied voltage by the voltage applying mechanism at a plurality of positions accompanying the scanning. And generating a dielectric breakdown between the probe and the sample surface, and obtaining a surface shape of the sample based on a measurement result of the position measuring mechanism or the voltage measuring mechanism when the dielectric breakdown occurs. Surface shape measuring device.   The control means obtains the position of the probe when dielectric breakdown occurs by moving the probe in the Z-axis direction by the probe moving mechanism while applying a predetermined voltage by the voltage applying mechanism. The surface shape measuring apparatus according to claim 1, wherein   3. The surface shape measuring apparatus according to claim 2, wherein a distance of movement of the probe in the Z-axis direction is set to a range of 4 microns or less from the sample surface.   The control means changes the voltage applied by the voltage application mechanism while keeping the position of the probe in the Z-axis direction at a predetermined position, and obtains the measurement result of the voltage detection means when dielectric breakdown occurs, The surface shape measuring apparatus according to claim 1, wherein a distance between the probe and the sample surface is calculated from a measurement result and a Paschen curve.

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