JP2010038856A - Scanning probe microscope - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that a highly precise measurement result cannot be obtained owing to distortion of a measured image caused by drifting in measurement of a pattern shape and a pattern arrangement in nanometer order in the fields of semiconductor and storage having further increasing demands in the future. <P>SOLUTION: A previously selected reference pattern region is measured at a certain timing during measurement of a measurement region of sample characteristics with a scanning probe microscope, and the displacement of a probe is corrected while necessarily specifying the displacement in an XYZ axis from a measured image of the reference pattern. Further, the specified displacement and the temperature data in a measurement chamber are used to correct the distortion of the measurement image of the sample characteristics. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a technique for correcting distortion of a measurement image caused by drift in measurement using a scanning probe microscope.

  A scanning probe microscope (SPM) is known as one of measuring techniques for a fine three-dimensional shape. In this method, a sharpened probe (probe) is brought close to or in contact with the sample surface, and at that time, a measurement amount of physical interaction such as an atomic force generated between the probe and the sample is displayed as an image. Is. One of them, AFM (Atomic Force Microscope), is an atomic force acting between the probe attached to the tip of a minute cantilever beam called a cantilever and the sample, that is, between the probe and the sample. It is a technology that measures the fine shape of the sample surface by scanning the sample surface while detecting the contact force by the amount of displacement due to the deflection of the cantilever, and controlling this so that it becomes constant. As a technology that can measure the above, it is widely used in various fields such as biological, physical, semiconductor, and storage.

  However, in the measurement using the scanning probe microscope, there is a problem of distortion of the measurement image peculiar to the scanning probe microscope. Therefore, as the pattern becomes finer, a highly accurate measurement result cannot be obtained. There are various causes of distortion of the measurement image, such as linearity of each axis of XYZ, orthogonality between each axis, interference between each axis, etc. The main cause is nonlinearity of the piezoelectric element used as a drive actuator. The drift of the apparatus etc. which occur with the change of a measurement property or a measurement environment are known.

  Among these, with regard to the nonlinearity of the piezoelectric element, a method of correcting displacement data of the piezoelectric element by measuring the displacement characteristic of the piezoelectric element in advance and using the obtained characteristic data as a software, and a mechanism that uses a displacement sensor. A method of correcting by performing feedback control using a displacement sensor is known. Recently, there is a mechanism using a voice coil motor having high linearity without using a piezoelectric element as an actuator.

On the other hand, as a method for eliminating measurement distortion due to drift, Patent Document 1 discloses a method of directly measuring a relative position change of the probe-sample distance due to drift with a displacement sensor and correcting the measurement distortion. Further, Patent Document 2 includes a plurality of correction probes for measuring the drift amount in addition to the measurement probe, and the probe is controlled so as to follow a specific position of the sample or the sample stage by using the correction probe. A method of correcting a measurement image by calculating a drift amount from a probe movement amount is disclosed.
US Pat. No. 7,249,002 Japanese Patent Laid-Open No. 10-267943

  The distortion of the measurement image due to the drift cannot provide a highly accurate measurement result in the measurement of the pattern shape / pattern arrangement on the nanometer order in the semiconductor and storage fields where further demand will increase in the future. The drift phenomenon is caused by thermal expansion / contraction of the constituent members of the apparatus as shown in FIG. This occurs when the relative position (XYZ position) between the upper samples 101 changes.

  For this reason, for example, when the L & S (Line and Space) pattern 201 shown in FIG. 2 is measured, in a general raster scan, as shown in the L & S measurement image 202, the direction perpendicular to the probe scanning direction (X axis) (Y (Axis), that is, the positional deviation with respect to the direction in which the measurement time elapses (the direction in which the measurement line advances) is noticeable.

The drift amount at this time is the sum of the thermal expansion and contraction amounts of the respective constituent members shown in FIG. 1, and is expressed by the formula (1). The drift amount also varies depending on the arrangement method in addition to the material and size of each constituent member. .
Σ (Δl _i ) = Σ (l _0i · α _i · ΔT) (1)
(Δl _i : Elongation amount of each member due to thermal expansion, l _0i : Initial length of each member, α _i : Thermal expansion coefficient of each member, ΔT: Temperature change)

  In the conventional drift elimination method, the location where the positional relationship between the probe and the sample is measured is different from the actual measurement probe position, so an error occurs in the drift amount generated at each position. Further, since another sensor for measuring the distance between the probe and the sample, or a probe is required, the number of sensors, mechanism units, and control circuits is increased, and there is a problem that the manufacturing cost of the apparatus is increased.

The present invention has been made in view of the above points, and provides a method for specifying and correcting the amount of positional deviation between a probe and a sample using a measurement probe.
The scanning probe microscope of the present invention is a scanning probe microscope that measures a sample characteristic by scanning a sample surface with a probe and detecting an interaction between the probe and the sample surface, and measuring the sample characteristic. A reference pattern measuring unit that appropriately measures a preselected reference pattern region at a certain timing, and a positional deviation amount specifying unit that specifies a positional deviation amount between the probe and the sample from a reference pattern measurement image One of correction of the positional deviation of the probe, the positional deviation of the measurement image of the sample characteristic, or the positional deviation correction of the measurement image of the probe and the sample characteristic is performed.
Specifically, as shown in FIG. 3, measurement is performed by moving a sample characteristic measurement region 302 to a reference pattern region 301 selected in advance at a certain timing during measurement using a scanning probe microscope. The position deviation of the XYZ axes is appropriately specified from the image, and the probe position deviation is corrected. Further, the distortion of the sample characteristic image is corrected by using the specified positional deviation amount and the temperature data in the measurement chamber. As a result, the measurement error of the drift amount described above can be eliminated, and the manufacturing cost of the apparatus can be kept low.

  According to the present invention, it is possible to remove the distortion amount of the sample measurement image due to drift, and the flatness evaluation after CMP (Chemical Mechanical Polishing) in semiconductor manufacturing, the line edge roughness evaluation after etching, or the storage field. This contributes to pattern shape evaluation and pattern arrangement evaluation in patterned media production.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 4 shows the configuration of an apparatus that performs this measurement. The apparatus includes a coarse movement stage 402 on which a measurement sample 401 can be placed and moved, a probe 403 that scans the sample, a probe drive unit 404 that drives the probe in the XYZ directions, a deflection of a cantilever that supports the probe 403, Deflection / twist detection unit 405 that detects torsion, drive displacement detection unit 406 that detects the drive displacement of each axis of XYZ, sampling circuit 407 that samples each detected sensor signal, and probe that issues a command to probe drive unit 404 Control unit 408, coarse movement stage 402, overall control unit 409 for controlling the measurement sequence, data storage unit 410 for recording data, arithmetic processing unit 411 for performing arithmetic processing, and display of processing results in the arithmetic processing unit Result display unit 412 and a temperature sensor 413 for measuring the temperature in the measurement chamber.

  The probe driving unit 404 is usually configured using a piezoelectric element whose deformation amount can be controlled by an applied voltage, but other driving elements such as a voice coil motor may be used. Further, the deflection / twist detection unit 405 generally uses optical lever detection composed of a laser and a four-divided light receiving element. In the optical lever detection, the deflection and twist amount of the cantilever supporting the probe 403 can be detected as a change in the laser spot position on the light receiving element. Although an example in which the probe driving unit 404 in the XYZ directions is configured on the probe side has been shown, the present invention can be implemented even if the driving unit in the XYZ directions is configured on the sample side instead of the coarse movement stage 402. There is no problem.

  At the time of measurement, the probe 403 is brought close to or in contact with the sample surface, and the relative position between the probe and the sample is scanned by the coarse movement stage 402 or the probe driving unit 404, and the physical force such as atomic force generated at that time is scanned. The interaction is measured by the sensor of the deflection / twist detection unit 405. The output signal from each sensor is sampled at a fixed timing by the sampling circuit 407, and the probe control unit 408 sends a drive signal to the probe drive unit 404 based on the outputs of the deflection / torsion detection unit 405 and the drive displacement detection unit 406. Output and control the probe position. Further, when the probe reaches each measurement position, each sensor signal is recorded in the data storage unit 410, and a numerical value or an image is displayed on the result display unit 412 through processing in the arithmetic processing unit 411.

  Next, the measurement procedure when carrying out the present invention will be described in detail. As described above, in the present invention, the reference pattern region selected in advance is measured at a certain timing during the measurement of the sample characteristics, and the XYZ misalignment amount is appropriately specified from the reference pattern measurement image to thereby misalign the probe. Make corrections. Further, the distortion of the sample characteristic image is corrected by using the specified positional deviation amount and the temperature data in the measurement chamber.

  First, a reference pattern for specifying the amount of displacement is selected. The reference pattern region 301 exists in a range in which the probe can move from within the measurement region 302, and has a pattern of several hundreds of nm to several μm having edge portions that are linear and intersect with each other as shown in FIG. You can select an area. As the reference pattern, in addition to the concave / convex pattern having a different height from the peripheral portion, a pattern formed of a region having no concave / convex but having a different material from the peripheral portion may be used. In the former case, the pattern can be recognized with a shape image representing the surface shape of the sample. In the latter case, the amount of twisting of the probe that occurs during scanning differs depending on the surface material of the sample. The pattern can be recognized by using the As a method of selecting a reference pattern, the user may manually perform a reference pattern based on an observation image obtained by an optical microscope or a scanning probe microscope, or may automatically perform a search tool based on design data. .

  After the reference pattern is selected by the above processing, the reference pattern region 501 before the measurement of the sample characteristics is preliminarily measured with a scanning probe microscope, and the angles 504 and 505 of the respective edges 502 and 503 with respect to the XY axes and the edge crossing are measured. The XY coordinates of the position 506 are obtained. Further, using the calculated XY coordinates of the edge intersection position 506 as a reference, an arbitrary position on the reference pattern is determined as the reference point 507, and the coordinates (X0, Y0, Z0) of the reference point 507 are recorded.

  After preliminary measurement of the reference pattern, measurement of sample characteristics is started. During the measurement of the sample characteristics, the reference point 507 determined in the preliminary measurement is appropriately measured, and the positional deviation amount of each axis due to the drift is specified. In addition, the temperature in the measurement chamber is measured together with the sample characteristics at each measurement point.

  Hereinafter, a method for specifying the positional deviation amount of each axis by measuring the reference point 507 will be described with reference to FIG. As shown in FIG. 6, scanning is performed in the direction of each edge of the reference pattern, and the position on each edge is specified. The scan position performs a scan (602, 603) that passes through the center point 601 of the reference pattern initial position so that the probability of catching each edge with respect to drift in all directions is high, and the scan direction in each edge direction is an edge. An arbitrary point (604, 605) on each edge that intersects with is specified.

  However, the scanning method for specifying an arbitrary point on each edge is not limited to the above-described scanning method, and may be specified using another scanning method. When the arbitrary positions 604 and 605 on each edge in the reference pattern are specified, the coordinates of the edge crossing position 606 after the position shift can be calculated from the angles 504 and 505 specified in the preliminary measurement.

Here, since the positional relationship between the edge intersection position 606 and the reference point is known by preliminary measurement, the reference point 607 after the positional deviation is specified from the calculated edge intersection position, and the height (Z) at the reference point is measured. . As a result, the positional deviation amount (ΔX, ΔY, ΔZ) due to the drift is calculated from the coordinates (X0, Y0, Z0) of the reference point 507 before the positional deviation and the coordinates (X0 + ΔX, Y0 + ΔY, Z0 + ΔZ) of the reference point 607 after the positional deviation. ) can be calculated, the command position of the probe so as to cancel the positional deviation amount _{(V X, V Y, V} Z) to _{(V X -ΔX, V Y -ΔY} , V Z -ΔZ) the correction To do. Thereby, it is possible to prevent the evaluation pattern from being greatly deviated from the measurement region due to the drift position deviation.

  However, only by correcting the probe position deviation described above, the sample measurement image acquired between each reference pattern measurement (from the i-th reference pattern measurement to the i + 1th reference pattern measurement) is distorted. Since this occurs, a method of correcting this distortion will be described with reference to FIG. Since the drift amount is proportional to the temperature change in the measurement chamber as shown in the equation (1), correction is performed using the temperature data in the measurement chamber acquired at the same timing as the sample measurement.

First, the difference (ΔX, ΔY, ΔZ) of the positional deviation of the probe specified by the i-th reference measurement and the i + 1-th reference pattern measurement, and the i-th reference pattern measurement (701), and the i + 1-th time From the temperature difference ΔT _i in the measurement chamber at the time of reference pattern measurement (702) (see FIG. 7), the positional deviation amount of the probe per unit temperature (dX) between each reference measurement by using Equation (2) , DY, dZ) can be calculated.
dX = ΔX / ΔT, dY = ΔY / ΔT, dZ = ΔZ / ΔT (2)
Furthermore, the temperature data T _i in the measurement chamber at the time of the i-th reference pattern measurement, and the temperature data T _k at the time of acquisition of the k th sample measurement image P _k = (X _k , Y _k, D _k ) (703) are _obtained . By using it, the correction amount (ΔCX _k, ΔCY _k, ΔCZ _k ) of each pixel can be determined from the equation (3).
ΔCX _k = (T _k −T _i ) dX, ΔCY _k = (T _k −T _i ) dY,
ΔCZ _k = (T _k −T _i ) dZ (3)

Here, when the sample characteristic image is a surface shape image, by adding (ΔCX _k , ΔCY _k , ΔCZ _k ) to (X _k , Y _k, D _k ), respectively, the XY plane and height due to drift are added. Directional distortion can be corrected. In addition, the present invention can be applied even when the sample characteristic image is a physical quantity other than the surface shape image, for example, friction characteristics, elastic characteristics, attractive force, electromagnetic characteristics, and optical characteristics. In this case, the ΔCX _k , ΔCY _k ) can be added to (X _k , Y _k, ) to correct the measurement distortion in the XY plane.

  As a timing for measuring the reference pattern, a constant measurement is performed so that the reference pattern area is measured for each predetermined line so that the positional deviation of the probe due to drift becomes smaller than the reference pattern area 501. Set the line period. Note that the amount of drift per line can be estimated from the temperature change amplitude and period, and further from one line measurement time (calculated from the measurement range, number of measurement points, scanning speed, etc.).

Alternatively, as shown in FIG. 7, the temperature change (ΔT) in the measurement chamber exceeds a predetermined threshold (ΔT _th ) (704), or the direction of temperature change (temperature rise and fall) changes (705). ), Perform reference measurement after the end of the measurement line. Also in this case, similarly to the above, the temperature change threshold is set so that the positional deviation of the probe due to drift is smaller than that of the reference pattern region. In addition, when the measurement time per line is short and the drift amount between one line measurements is very small, the reference pattern is measured for each line, and only the probe misalignment correction is performed for each line. It becomes possible to acquire a measurement image with almost no distortion.

  The present invention contributes to flatness evaluation after CMP in semiconductor manufacturing, line edge roughness evaluation after etching, or pattern arrangement evaluation and pattern shape evaluation in patterned media manufacturing in the storage field.

FIG. 1 is an explanatory diagram showing the thermal expansion / contraction of the apparatus constituent members of the scanning probe microscope and the mounting range of the temperature sensor. FIG. 2 is an explanatory diagram showing distortion of the sample measurement image due to drift. FIG. 3 is an explanatory diagram showing sample characteristics and the probe movement path when measuring the reference pattern. FIG. 4 is an explanatory view showing the apparatus configuration of a scanning probe microscope for carrying out the present invention. FIG. 5 is an explanatory diagram showing a reference pattern in the present invention. FIG. 6 is an explanatory diagram showing a reference pattern measuring method in the present invention. FIG. 7 is an explanatory diagram showing the temperature change in the measurement chamber and the measurement timing of the reference pattern in the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 Sample 102 Sample stage 103 Probe 201 L & S pattern 202 L & S measurement image 301 Reference pattern area 302 Measurement area 401 Sample 402 Coarse movement stage 403 Probe 404 Probe drive section 405 Deflection / twist detection section 406 Drive displacement detection section 407 Sampling circuit 408 Probe control unit 409 Overall control unit 410 Data storage unit 411 Operation processing unit 412 Result display unit 413 Temperature sensor 501 Reference pattern area 502 Edge 503 Edge 504 Angle with respect to X axis 505 Edge angle with respect to Y axis 506 Edge crossing position 507 Reference point 601 Central point of reference pattern initial position 602 Scan passing through center point 603 Scan passing through center point 604 Intersection of scan and edge 605 Crossing point of scan and edge 606 Edge crossing position 607 Reference point 701 Timing of i-th reference measurement 702 Timing of i + 1-th reference measurement 703 Acquisition timing of k-th sample measurement image P _k 704 Threshold of temperature change determined in advance 705 Timing when temperature change direction changed

Claims (6)

  In a scanning probe microscope that scans the sample surface with a probe and measures the sample characteristics by detecting the interaction between the probe and the sample surface, a pre-selected reference at a certain timing during measurement of the sample characteristics A reference pattern measuring unit that appropriately measures a pattern region, and a positional deviation amount specifying unit that specifies an amount of positional deviation between the probe and the sample from a reference pattern measurement image, and correcting the positional deviation of the probe, or A scanning probe microscope characterized in that either the positional deviation correction of the measurement image of the sample characteristic or the positional deviation correction of the probe and the measurement image of the sample characteristic is performed.   2. The scanning probe microscope according to claim 1, wherein the reference pattern region is formed in a region having a height different from that of the peripheral portion or a region having a material different from that of the peripheral portion, and has edge portions that are linear and intersect with each other. A scanning probe microscope characterized by that.   2. The scanning probe microscope according to claim 1, wherein the sample characteristic is a surface shape of the sample, a friction characteristic, an elastic characteristic, an attractive force, an electromagnetic characteristic, or an optical characteristic.   2. The scanning probe microscope according to claim 1, wherein the timing for measuring the reference pattern region is a predetermined line every predetermined time.   The scanning probe microscope according to claim 1, further comprising a temperature measurement unit that measures a temperature in the measurement chamber, and using the temperature data in the measurement chamber during measurement of the sample characteristic, the position of the measurement image of the sample characteristic A scanning probe microscope characterized by performing displacement correction.   6. The scanning probe microscope according to claim 5, wherein the timing of measuring the reference pattern region is changed when a temperature change in the measurement chamber exceeds a predetermined threshold value, or the direction of the temperature change in the measurement chamber changes. A scanning probe microscope characterized by being either of the above.

Images