Scanning probe system for controlling inclination angle of probe tip
阅读说明:本技术 控制探针尖端倾斜角度的扫描探针系统 (Scanning probe system for controlling inclination angle of probe tip ) 是由 安德鲁·汉弗里斯 于 2018-04-06 设计创作,主要内容包括:一种用探针扫描特征的方法,探针包括悬臂支架、从悬臂支架延伸到自由端的悬臂以及由悬臂的自由端承载的探针尖端。测量探针相对于参考表面的定向以生成探针定向测量结果;参考表面限定垂直于参考表面的参考表面轴线,探针尖端相对于参考表面轴线具有参考倾斜角;根据探针定向测量结果改变悬臂的形状,使得探针尖端相对于悬臂支架移动,参考倾斜角从第一参考倾斜角减小到第二参考倾斜角。采用探针扫描样品表面,其中,样品表面限定垂直于样品表面的样品表面轴线,探针尖端具有相对于样品表面轴线的扫描倾斜角。在扫描样品表面期间,移动悬臂支架,使得探针尖端以小于第一参考倾斜角的扫描倾斜角插入到样品表面中的特征中。(A method of scanning a feature with a probe comprising a cantilever support, a cantilever extending from the cantilever support to a free end, and a probe tip carried by the free end of the cantilever. Measuring an orientation of the probe relative to a reference surface to generate a probe orientation measurement; the reference surface defining a reference surface axis perpendicular to the reference surface, the probe tip having a reference tilt angle relative to the reference surface axis; the shape of the cantilever is changed in accordance with the probe orientation measurement so that the probe tip moves relative to the cantilever support, the reference tilt angle decreasing from a first reference tilt angle to a second reference tilt angle. Scanning a sample surface with a probe, wherein the sample surface defines a sample surface axis perpendicular to the sample surface, and the probe tip has a scanning tilt angle with respect to the sample surface axis. During scanning of the sample surface, the cantilever is moved such that the probe tip is inserted into a feature in the sample surface at a scanning tilt angle that is less than the first reference tilt angle.)
1. A method of scanning a feature with a probe comprising a cantilever support, a cantilever extending from the cantilever support to a free end, and a probe tip carried by the free end of the cantilever, the method comprising:
measuring an orientation of the probe relative to a reference surface to generate a probe orientation measurement, wherein the reference surface defines a reference surface axis perpendicular to the reference surface, the probe tip having a reference tilt angle relative to the reference surface axis;
changing the shape of the cantilever according to the probe orientation measurement such that the probe tip moves relative to the cantilever mount and the reference tilt angle decreases from a first reference tilt angle to a second reference tilt angle; and
scanning a sample surface with the probe, wherein the sample surface defines a sample surface axis perpendicular to the sample surface, and the probe tip has a scanning tilt angle relative to the sample surface axis, during scanning of the sample surface, moving the cantilever to insert the probe tip into a feature in the sample surface at the scanning tilt angle, the scanning tilt angle being less than the first reference tilt angle.
2. The method of claim 1, wherein during scanning the sample surface, the cantilever is moved such that the probe tip is inserted into the feature in the sample surface at the scanning tilt angle, the scanning tilt angle being substantially fixed at the second tilt angle.
3. The method of claim 1 or 2, wherein a first driver translates the outrigger in accordance with a first drive signal; and a second driver changes the shape of the cantilever according to a second drive signal.
4. The method of claim 3, wherein scanning the sample surface comprises:
controlling the first drive signal such that the first driver repeatedly drives the cantilever support towards and away from the sample surface in a series of cycles;
generating a surface signal for each cycle upon detecting interaction of the probe tip with the sample surface; and
modifying the second drive signal in response to receipt of the surface signal, the modification of the second drive signal causing the second driver to change the shape of the cantilever such that the probe tip is retracted from the sample surface, wherein, for each cycle, there is a proximity phase before generating the surface signal in which the first driver moves the cantilever support and the probe tip toward the sample surface and a retraction phase after generating the surface signal in which the first driver moves the cantilever support and the probe tip away from the sample surface.
5. The method of claim 3 or 4, wherein the first driver is a linear actuator that extends in a substantially straight line when the probe tip is inserted into the feature.
6. The method of any of claims 3 to 5, wherein the second drive signal is substantially fixed when the probe tip is inserted into the feature.
7. The method of any preceding claim, wherein the cantilever is substantially fixed in shape when the probe tip is inserted into the feature.
8. A method according to any preceding claim in which the probe tip is inserted into the feature at the scanning tilt angle which is less than 50%, 30% or 10% of the first tilt angle.
9. A method according to any preceding claim in which the probe tip is inserted into the feature at the scanning tilt angle which is less than 1 degree, preferably less than 0.5 degrees, most preferably less than 0.1 degrees.
10. The method of any preceding claim, wherein measuring the orientation of the probe relative to the reference surface to generate the probe orientation measurement comprises interacting with the reference surface.
11. A method according to any preceding claim, wherein the orientation of the probe tip relative to the reference surface is measured to generate the probe orientation measurement.
12. The method of claim 11, wherein the orientation of the probe tip relative to the reference surface is measured by:
scanning the reference surface with the probe to generate a data set;
analyzing the dataset to identify asymmetric features in the dataset; and
determining an asymmetry in the asymmetric feature to generate the probe orientation measurement.
13. A method according to any preceding claim, wherein the orientation of the cantilever relative to the reference surface is measured to generate the probe orientation measurement.
14. The method of claim 13, wherein the orientation of the cantilever relative to the reference surface is measured by:
illuminating the reference surface with a sensing beam via a lens such that the sensing beam is reflected by the reference surface, generating a beam reflected from the reference surface;
collecting a beam reflected from the reference surface with the lens and directing the beam reflected from the reference surface onto a position sensitive detector that generates a reference measurement indicative of a position of the beam reflected from the reference surface on the position sensitive detector;
illuminating the cantilever with the sensing light beam such that the sensing light beam is reflected by the cantilever, generating a light beam reflected from the cantilever;
collecting a beam reflected from the cantilever with the lens and directing the beam reflected from the cantilever to the position sensitive detector, the position sensitive detector generating a cantilever measurement indicative of a position of the beam reflected from the cantilever on the position sensitive detector; and
and generating the probe orientation measurement result according to the reference measurement result and the cantilever measurement result.
15. The method of any preceding claim, wherein altering the shape of the cantilever comprises flexing and/or twisting the cantilever.
16. The method of any preceding claim, wherein the feature has an entrance and a bottom, a depth D from the entrance to the bottom, a width W at the entrance, and an aspect ratio D/W, the aspect ratio D/W being greater than 1, 2, 5 or 10.
17. The method of any preceding claim wherein the probe tip has a root and a tip, a length L from the root to the substrate, a maximum width W, and an aspect ratio L/W, the aspect ratio L/W being greater than 5, 10 or 15.
18. A method according to any preceding claim, wherein the feature has an inlet, a base and a pair of opposed side walls extending from the inlet to the base.
19. A method of orienting a cantilever relative to a reference surface, the method comprising:
illuminating the reference surface with a sensing beam via a lens such that the sensing beam reflects from the reference surface, generating a beam reflected from the reference surface;
collecting a beam reflected from the reference surface with the lens and directing the beam reflected from the reference surface onto a position sensitive detector that generates a reference measurement indicative of a position of the beam reflected from the reference surface on the position sensitive detector;
illuminating the cantilever with the sensing beam, causing the sensing beam to reflect from the cantilever, generating a beam reflected from the cantilever;
collecting a beam reflected from the cantilever with the lens and directing the beam reflected from the cantilever to the position sensitive detector, the position sensitive detector generating a cantilever measurement indicative of a position of the beam reflected from the cantilever on the position sensitive detector;
changing an orientation of the cantilever relative to the reference surface; and
controlling changing an orientation of the cantilever according to the reference measurement and the cantilever measurement such that the cantilever becomes oriented at a predetermined angle with respect to the reference surface.
20. The method of claim 19, wherein the reference surface is located in a focal plane of the lens when the reference surface reflects the sensing beam; and, the method further comprises: moving the lens such that the cantilever is located within the focal plane of the lens when the cantilever reflects the sensing light beam.
21. The method of claim 20, wherein the cantilever is positioned in the focal plane of the lens by:
combining the beam reflected from the cantilever with a reference beam in an interferometer to generate an interferogram;
measuring the interferogram and generating an interferometer output;
monitoring the contrast of the interferometer output;
moving the lens such that the contrast is maximized; and
positioning the reference surface in the focal plane of the lens by:
combining the beam reflected from the reference surface with the reference beam in the interferometer to generate an interferogram;
measuring the interferogram and generating an interferometer output;
monitoring the contrast of the interferometer output;
moving the lens such that the contrast is maximized.
22. An apparatus for scanning a sample surface with a probe, the apparatus comprising:
a probe comprising a cantilever support, a cantilever extending from the cantilever support to a free end, and a probe tip carried by the free end of the cantilever;
a first driver configured to translate the outrigger;
a tilt controller configured to generate a tilt control signal;
a second driver configured to change a shape of the cantilever according to the tilt control signal; and
a measurement system configured to measure an orientation of the probe relative to a reference surface, generate a probe orientation measurement,
wherein the probe tip has a reference tilt angle relative to the reference surface;
the tilt controller is configured to receive the probe orientation measurement from the measurement system and control the tilt control signal such that the second driver changes the shape of the cantilever in accordance with the probe orientation measurement, the probe tip moves relative to the cantilever support, the reference tilt angle decreases from a first reference tilt angle to a second reference tilt angle;
the sample surface defining a sample surface axis perpendicular to the sample surface;
the first driver is configured to move the cantilever support such that the probe tip is inserted into a feature in the sample surface; and the number of the first and second groups,
the tilt controller is configured to control the tilt control signal such that the probe tip has a scanning tilt angle relative to the sample surface axis when the probe tip is inserted into the feature, the scanning tilt angle being less than the first tilt angle.
23. The apparatus of claim 22 wherein the first driver is a linear actuator that extends in a substantially straight line when the probe tip is inserted into the feature.
24. The apparatus of claim 22 or 23, wherein the second driver is configured to change the shape of the cantilever by flexing and/or twisting the cantilever.
25. A method of scanning a feature with a probe comprising a cantilever support, a cantilever extending from the cantilever support to a free end, and a probe tip carried by the free end of the cantilever, the method comprising:
measuring an orientation of the probe relative to a reference surface to generate a probe orientation measurement, wherein the reference surface defines a reference surface axis perpendicular to the reference surface, the probe tip having a reference tilt angle relative to the reference surface axis;
changing the shape of the cantilever according to the probe orientation measurement such that the probe tip moves relative to the cantilever mount and the reference tilt angle decreases from a first reference tilt angle to a second reference tilt angle;
scanning a feature with the probe, wherein the feature surface defines a feature axis and the probe tip has a scanning tilt angle relative to the feature axis, during scanning of the sample surface, moving the cantilever support such that the probe tip is inserted into the feature at the scanning tilt angle, the scanning tilt angle being less than the first reference tilt angle.
26. A method of scanning a feature with a probe comprising a cantilever support, a cantilever extending from the cantilever support to a free end, and a probe tip carried by the free end of the cantilever, the method comprising:
measuring an orientation of the probe relative to a reference surface to generate a probe orientation measurement, wherein the reference surface defines a reference surface axis perpendicular to the reference surface and the probe tip has an oblique angle relative to the reference surface axis;
changing the shape of the cantilever according to the probe orientation measurement such that the probe tip moves relative to the cantilever mount and the tilt angle decreases from a first tilt angle to a second tilt angle; and
scanning a sample surface with the probe, wherein, during the scanning of the sample surface, the cantilever is moved such that the probe tip is inserted into a feature in the sample surface, wherein the probe tip is substantially fixed at the second tilt angle.
27. A method of scanning a feature with a probe comprising a cantilever support, a cantilever extending from the cantilever support to a free end, and a probe tip carried by the free end of the cantilever, the method comprising:
measuring an orientation of the probe relative to a reference surface to generate a probe orientation measurement, wherein the reference surface defines a reference surface axis perpendicular to the reference surface and the probe tip has a reference tilt angle relative to the reference surface axis;
changing a shape of the cantilever according to the probe orientation measurement such that the probe tip moves relative to the cantilever support, the reference tilt angle decreases from a first reference tilt angle to a second reference tilt angle, and the shape of the cantilever changes to a scanning shape; and
scanning a feature with the probe, wherein during scanning the sample surface, the cantilever support is moved such that the probe tip is inserted into the feature, wherein a shape of the cantilever is substantially fixed to the scanned shape.
Technical Field
The present invention relates to a method of scanning a feature with a probe and a corresponding apparatus, and a method of orienting a cantilever relative to a reference surface.
Background
WO2016/198606 describes a known scanning probe system. The system has a probe including a cantilever extending from a base to a free end, and a probe tip carried by the free end of the cantilever. The first driver is provided with a first driver input, the first driver being arranged to drive the probe in accordance with a first drive signal at the first driver input. The second driver is provided with a second driver input, the second driver being arranged to drive the probe in accordance with a second drive signal at the second driver input. The control system is arranged to control the first drive signal to cause the first driver to drive the base of the cantilever towards and away from the surface of the sample repeatedly in a series of cycles. The surface detector is arranged to generate a surface signal for each cycle when it detects interaction of the probe tip with the surface of the sample. The control system is further arranged to modify the second drive signal in response to the surface signal received from the surface detector, the modification of the second drive signal causing the second driver to control the probe tip.
US2014/0289911 discloses a method of observing the surface of a sample. The probe is brought into close proximity with and scanned over a first sample. A response of the probe to its interaction with the sample is monitored using a detection system, and a first data set indicative of the response is acquired. The probe and/or sample are tilted at an angle. After the tilting step, the probe is scanned over the first sample or the second sample, the response of the probe to its interaction with the scanned sample is monitored using the detection system, and a second data set indicative of the response is acquired. The method comprises the additional step of analysing the first data set to determine the tilt angle prior to tilting the probe and/or sample.
US2017/0016932 discloses a probe system comprising a probe having a first arm and a second arm and a probe tip carried by the first arm and the second arm. The illumination system is arranged to deform the probe by illuminating at a first actuation position of the first arm and at a second actuation position of the second arm, respectively, with respective illumination powers. The actuation controller is arranged to control the irradiation power at each actuation position independently so as to control the height and tilt angle of the probe and thus the height and lateral position of the tip. The first and second arms are mirror images of each other on opposite sides of a plane of symmetry through the probe tip. A detection system is also disclosed which not only generates a height signal by measuring the height of the probe tip, but also generates a tilt signal by measuring the tilt angle of the probe from which the lateral position of the tip can be determined.
WO2015/197398 describes a method of inspecting a sample surface using a probe tip carried on a cantilever. If the probe tip scans a portion of a sample surface having a high aspect ratio, the cantilever will twist, tilting the probe tip.
US2008/0223117 describes another known scanning probe microscope.
US2017/0059609 describes an optical axis adjustment method for a scanning probe microscope.
Disclosure of Invention
A first aspect of the invention provides a method according to claim 1 and an apparatus according to
The orientation of the probe relative to the reference surface is measured prior to insertion of the probe tip to generate a probe orientation measurement. The reference surface may be a portion of the surface of a sample or the surface of a reference specimen. The shape of the cantilever is changed in accordance with the probe orientation measurement to move the probe tip relative to the cantilever support, the reference tilt angle of the probe tip relative to the reference surface decreasing from the first tilt angle to the second tilt angle. At its most basic, the probe orientation measurement may only be used to determine the direction of pivoting of the probe tip required to reduce the reference tilt angle. For example, the probe orientation measurement may be used to determine whether to twist the cantilever clockwise or counterclockwise to decrease the reference tilt angle. Alternatively, the probe orientation measurement may be used to determine the magnitude of the pivoting of the probe tip required to minimise the reference tilt angle-ideally the reference tilt angle is reduced to zero so that the probe tip does not tilt when inserted into the feature.
The sample surface defines a sample surface axis perpendicular to the sample surface, and the probe tip has a scanning tilt angle relative to the sample surface axis. Typically, the sample surface axis is substantially parallel to the reference surface axis. During scanning of the sample surface, the cantilever is moved so that the probe tip is inserted into the feature in the sample surface at a scanning tilt angle that is at least less than the first reference tilt angle, and preferably the scanning tilt angle is substantially less than the first reference tilt angle. Typically, the probe tip is substantially fixed at a second reference tilt angle relative to the sample surface axis when inserted into the feature, optionally with small dithering oscillations on either side of the second reference tilt angle.
The scan tilt angle may remain fixed throughout the scan or may be varied, for example by retracting the probe rapidly after insertion into the feature.
Typically, measuring the orientation of the probe relative to the reference surface to generate the probe orientation measurement includes interacting with the reference surface, for example, by optically measuring the orientation of the reference surface (e.g., by reflecting the sensing beam off the reference surface) or by scanning the reference surface with the probe.
The probe orientation measurement may be a direct measurement of the orientation of the probe tip, or the probe orientation measurement may also be a measurement of the orientation of the cantilever from which the orientation of the probe tip can be inferred.
Changing the shape of the cantilever may include flexing the cantilever, twisting the cantilever, or simultaneously or sequentially flexing or twisting the cantilever. Preferably, the cantilever can be flexed and twisted, as flexing and twisting the cantilever enables control of the tilt angle, and minimizing the tilt angle in both axes. Alternatively, the deflection and torsion of the cantilever can be separately and independently controlled.
Further preferred features of the first aspect of the invention are set out in the dependent claims.
A second aspect of the invention provides a method of orienting a cantilever according to claim 19. A second aspect provides an optical method of orienting a cantilever before scanning a recessed feature such as a trench, hole, well or pit with a probe tip as in the first aspect of the invention.
Preferred features of the second aspect of the invention are set out in the dependent claims.
Yet another aspect of the invention provides a method of scanning a feature with a probe comprising a cantilever support, a cantilever extending from the cantilever support to a free end, and a probe tip carried by the free end of the cantilever, the method comprising: measuring an orientation of the probe relative to a reference surface to generate a probe orientation measurement, wherein the reference surface defines a reference surface axis perpendicular to the reference surface, the probe tip having a reference tilt angle relative to the reference surface axis; changing the shape of the cantilever according to the probe orientation measurement to move the probe tip relative to the cantilever support, the reference tilt angle decreasing from a first reference tilt angle to a second reference tilt angle; scanning a feature with a probe, wherein the feature defines a feature axis and the probe tip has a scanning tilt angle relative to the feature axis, during scanning of a sample surface, moving the cantilever support to insert the probe tip into the feature at the scanning tilt angle, the scanning tilt angle being less than a first reference tilt angle.
The characteristic axis is typically perpendicular to the sample surface, but alternatively the characteristic axis may be inclined at an oblique angle to the sample surface.
Yet another aspect of the invention provides a method of scanning a feature with a probe comprising a cantilever support, a cantilever extending from the cantilever support to a free end, and a probe tip carried by the free end of the cantilever, the method comprising: measuring an orientation of the probe relative to a reference surface to generate a probe orientation measurement, wherein the reference surface defines a reference surface axis perpendicular to the reference surface, the probe tip having an oblique angle relative to the reference surface axis; changing the shape of the cantilever according to the probe orientation measurement to cause the probe tip to move relative to the cantilever support and the tilt angle to decrease from the first tilt angle to the second tilt angle; scanning the sample surface with the probe, wherein during the scanning of the sample surface, the cantilever support is moved to insert the probe tip into the feature in the sample surface, wherein the probe tip is substantially fixed at the second oblique angle. The tilt angle is typically fixed within a range of ± 0.1 degrees — that is, the tilt angle may vary slightly since the amplitude of the dithering oscillation is not greater than 0.1 degrees.
Yet another aspect of the invention provides a method of scanning a feature with a probe comprising a cantilever support, a cantilever extending from the cantilever support to a free end, and a probe tip carried by the free end of the cantilever, the method comprising: measuring an orientation of the probe relative to a reference surface to generate a probe orientation measurement, wherein the reference surface defines a reference surface axis perpendicular to the reference surface, the probe tip having a reference tilt angle relative to the reference surface axis; changing a shape of the cantilever according to the probe orientation measurement result to move the probe tip relative to the cantilever holder, the reference tilt angle decreasing from the first reference tilt angle to the second reference tilt angle, and the shape of the cantilever changing to a scanning shape; the feature is scanned with a probe, wherein during scanning of the sample surface the cantilever support is moved to insert the probe tip into the feature, wherein the shape of the cantilever is substantially fixed to the scanning shape. Generally, the scan shape is fixed within a range of ± 0.1 degrees — that is, since the amplitude of the dither oscillation is not more than 0.1 degrees, the scan shape may be changed so that the tilt angle of the probe is slightly changed.
Drawings
Embodiments of the invention will be described with reference to the accompanying drawings, in which:
FIG. 1 shows a scanning probe microscope system;
FIG. 2 is a top view of a probe with a rectangular cantilever;
FIG. 3 shows an end view of the probe of FIG. 2;
FIG. 4 is a top view of a probe with a two-arm cantilever;
FIG. 5 shows an alternative configuration of a probe tip;
FIG. 6 shows the detector in detail;
FIG. 7a shows an optical measurement of a reference surface;
FIG. 7b shows two positions of a beam reflected from a reference surface on a segmented photodiode;
FIG. 8a shows an optical measurement of a cantilever;
FIG. 8b shows the position of the beam reflected from the cantilever on the segmented photodiode after the cantilever is bent down the desired cantilever angle;
FIG. 9 shows an alternative optical measurement of the cantilever;
FIG. 10 illustrates adjustment of probe tilt angle by twisting the cantilever;
FIG. 11a shows the probe tip tilted at a first reference tilt angle relative to a reference surface;
FIG. 11b shows the position of a beam reflected from the cantilever on the segmented photodiode when the probe tip is tilted at a first reference tilt angle;
FIG. 12a shows the probe tip tilted at a second reference tilt angle relative to the reference surface;
FIG. 12b shows the position of the beam reflected from the cantilever on the segmented photodiode when the probe tip is tilted at a second reference tilt angle;
figure 13a shows the probe tip scanning the trace of a groove in the sample surface;
FIG. 13b shows the groove axis;
FIG. 14 is a side view of a cantilever inserted into a trench with the probe tip tilted at a low or zero scan tilt angle relative to the sample surface axis and the trench axis;
FIG. 15 shows the probe tip interacting with the bottom of the trench and rapidly retracting due to the straightening of the cantilever;
FIG. 16 shows the dithering of the cantilever during surface inspection;
FIG. 17 is an end view of a cantilever inserted into a trench with the probe tip tilted at a low or zero scan tilt angle relative to the sample surface;
FIG. 18 shows a probe tip interacting with the bottom of the trench and retracting rapidly due to twisting the cantilever;
fig. 19 shows the trace of the probe tip scanning groove as shown in fig. 17 and 18; and
fig. 20 and 21 show an alternative probe orientation measurement process in which the probe tip scans a symmetrical groove or other concave feature.
Detailed Description
A scanning probe microscope system according to an embodiment of the invention is shown in fig. 1. The system comprises a first driver 4 and a probe comprising a
The
The
The
The wavelength of the
In an alternative embodiment, as shown in fig. 4, the
The
Alternatively, the coating of the two cantilever beams may be on opposite sides: that is, the coating on the
Returning to fig. 1, the first driver 4 is a piezoelectric actuator that expands and contracts up and down in the Z-direction according to a first drive signal at a
The
Ideally, the outputs from the photodetectors 121, 122 are complementary sine and cosine signals with a phase difference of 90 degrees. Also, they should have no dc offset, equal amplitude, and depend only on the position of the cantilever and the wavelength of the laser 101. When the optical path difference changes, the outputs of the photodetectors 121, 122 can be monitored using existing methods to determine and correct for errors due to the outputs of the two photodetectors not being perfectly harmonic (of equal amplitude and in phase quadrature). Similarly, the dc offset level may also be corrected according to methods known in the art.
These photodetector outputs are suitable for use with conventional interferometer reversible fringe counting and fringe subdividing devices 123, which may be provided as dedicated hardware, FPGAs, DSPs or programmed computers. The phase quadrature fringe counting device is capable of measuring the displacement of the cantilever position to an accuracy of lambda/8. Namely, it is 66nm for 532nm light. Existing fringe subdivision techniques based on signal arctangent allow for improved accuracy to the nanometer scale or less. In the above embodiment, the reference beam 104 is set to have a fixed optical path length with respect to the Z position of the
The
Returning to fig. 1, the output of the
The reflected beam is also split by the beam splitter 106 into a first component 107 and a second component 110. The first component 107 is directed to a segmented four
Fig. 7-9 illustrate a method of measuring and orienting the reflective upper surface of
As shown in fig. 6, the lens 105 is first moved in the Z-direction by the lens driver 81 until the
As shown in fig. 7a, the sensing light beam 103 passes through the lens 105 and reflects from the
Next, as shown in FIG. 8a, the probe is introduced and the lens 105 is moved upward so that the reflective upper surface of the
The position of the beam reflected from the cantilever on the
The above orientation process is controlled by a
In an alternative zeroing method shown in fig. 9, after performing the sample measurement procedure as shown in fig. 7a, the detector driver 82 moves the
In this case, as shown in FIG. 6, the detector driver 82 receives the offset distance D2 from the
At this point, the
In the embodiment shown in fig. 8a, the
As shown in fig. 11a and 12a, the
Fig. 11b shows the reflected
The probe orientation measurement Δ from the
As mentioned above, the
After orienting the
FIG. 13a shows the trajectory of the tip of the probe tip when the
Before generating the surface signal there is initially a
As described above, the XY raster scanning motion is imparted to the
The first drive signal varies at a substantially constant and predetermined rate during most of the time during the
Next, the
In the above embodiment the dither signal is tuned to the flexural or torsional resonance frequency of the
The probe is advanced towards the surface until the
In generating the surface signal, a surface height calculator 21 (or any other suitable measurement system) measures the surface height based on the
During the tip approach phase, the second drive signal is high, so the
In generating the surface signal, the
During the first part of the support retraction phase, the
Fig. 16 is a graph showing the angle of the cantilever with respect to the sensing light beam 103 immediately before and after surface detection. As described above, a periodic dither signal is used to modulate the
The precise trajectory of the probe depends on many factors, such as the nature of the sample interaction and the speed of approach. The interaction may occur over more or fewer cycles than shown at 71 in fig. 16. There may also be a time constant associated with probe relaxation.
Due to the small amplitude periodic dithering motion of the probe tip, the angle of the cantilever oscillates slightly as the probe tip moves toward the sample surface, as shown at 70. However, as the probe tip moves towards the sample surface, the angle may be considered substantially constant because the amplitude of the dithering motion shown in FIG. 16 is small compared to the amplitude of the translation of the cantilever's substrate towards and away from the sample surface, which is typically about 500 and 1000nm, much larger than the 1-10nm amplitude of the dithering motion shown in FIG. 16. Similarly, the
When the probe tip and the base of the cantilever are translated together towards the sample surface, the
In response to the received surface signal, the shape of the cantilever changes such that the angle of the cantilever relative to the sensing light beam 103 changes. In the embodiments presented above, the heating of the cantilever is reduced by turning off the
The height signal from the interferometer 10 can be used both by the
In this case, the system may selectively use a DC threshold detection method to generate the surface signal, rather than the resonance detection method described above with respect to fig. 16. The
As mentioned above, during the
The
In summary, the following steps: in the initial orientation process shown in fig. 7a to 12b, the orientation of the probe relative to a reference surface 90 (the reference surface being part of a reference sample on the
When the probe is inserted into the
The scanning tilt angle of the probe tip increases slightly as the tip moves along the
As shown in fig. 14, the
Similarly, the probe tip has a root and a tip, a length L from the root to the tip, a maximum diameter Wc at its root, and an aspect ratio L/Wc greater than 5, 10, or 15.
In the example of fig. 3, the high aspect
In the example of fig. 5, the root diameter Wc of the
The method of WO2015/197398 is not suitable for scanning high aspect ratio recessed features such as trenches, holes, wells or pits because a highly inclined probe tip will collide with the
An optical calibration procedure for determining the tilt angle of the
Fig. 20 and 21 show the
The dashed lines in fig. 20 and 21 indicate the portions of the trenches that can be accessed by
The method of measuring and aligning the
SPIP (see http:// www.imagemet.com) and Gwyddion (free and open source software) (see http:// gwydddion. net) of Image Metrology A/S are two Image processing packages that can be used to generate and analyze a sample map.
The asymmetry of the imaged feature can be determined by line profile analysis, that is, by extracting a line of data from the image and analyzing the line of data. The line data may be extracted along the scanning direction of the probe or in any direction, and may be an average value of a plurality of lines or an interpolation value to reduce noise.
Optionally, the asymmetry of the imaging feature may also be determined by tip shape characterization, illustratively as described in:
http:// gwydddion. net/documentation/user-guide-en/tip-fusion-artifacts. html; or
·J.S.Villarubia,J.Res.Natl.Inst.Stand.Technol.102(1997)425
Figure 21 shows the probe scanning the same surface feature when correctly aligned. In this case, the tip will move along a symmetrical path. The symmetry of this path is reflected in the image and it is then known that the probe is correctly aligned.
The reference surface has a known arrangement of features which are expected to generate characteristic signals in the data. Deviations between the observed and expected signals can be used to infer misalignment of the probe. Optionally, the reference surface has high aspect ratio features (e.g., trenches or peaks) with a higher aspect ratio (length/width) than the probe tips.
In the optical measurement process of fig. 11b, a probe orientation measurement Δ is obtained by reflecting the sensing beam off the cantilever. In the direct probe tip measurement procedure described above, the probe orientation measurement results are instead obtained by scanning the symmetrical features as in fig. 20 to generate a map of the reference surface, which is then analyzed to derive the probe orientation measurement results. The probe orientation measurements are used to infer and correct for misalignment of the probe relative to a reference surface.
As described in fig. 7-12 or fig. 21, once the probe has been oriented relative to the reference surface, multiple samples can be scanned without having to repeat the orientation process. The probe orientation process will be repeated periodically for a given probe and/or when the probe is replaced.
Each of the electronic components shown in the figures and described in the text (e.g.,
Although the invention has been described above with reference to one or more preferred embodiments, it will be appreciated that various changes or modifications may be made without departing from the scope of the invention as described in the appended claims.