|Publication number||USRE36488 E|
|Application number||US 09/082,320|
|Publication date||Jan 11, 2000|
|Filing date||May 21, 1998|
|Priority date||Aug 7, 1992|
|Publication number||082320, 09082320, US RE36488 E, US RE36488E, US-E-RE36488, USRE36488 E, USRE36488E|
|Inventors||Virgil B. Elings, John A. Gurley|
|Original Assignee||Veeco Instruments Inc.|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (57), Non-Patent Citations (52), Referenced by (61), Classifications (13), Legal Events (5)|
|External Links: USPTO, USPTO Assignment, Espacenet|
This application is a continuation-in-part of U.S. application Ser. No. 07/926,175 filed Aug. 7, 1992 now U.S. Pat. No. 5,412,980.
1. Field of the Invention
This invention relates to an ultra-low force atomic force microscope, and particularly an improvement to the atomic force microscope described in related commonly owned U.S. patent application Ser. No. 08/147,571 and related U.S. Pat. Nos. 5,229,606 and 5,266,801.
2. Discussion of the Background
Atomic Force Microscopes (AFM's) are extremely high resolution surface measuring instruments. Two types of AFM's have been made in the past, the contact mode (repulsive mode) AFM and the non-contact (attractive mode) AFM.
The contact mode AFM is described in detail in U.S. Pat. No. 4,935,634 by Hansma et al, as shown in FIG. 2. This AFM operates by placing a sharp tip attached to a bendable cantilever directly on a surface and then scanning the surface laterally. The bending of the lever in response to surface height variations is monitored by a detection system. Typically, the height of the fixed end of the cantilever relative to the sample is adjusted with feedback to maintain the bending at a predetermined amount during lateral scanning. The adjustment amount versus lateral position creates a map of the surface. The deflection detection system is typically an optical beam system as described by Hansma et al. Using very small microfabricated cantilevers and piezoelectric positioners as lateral and vertical scanners, AFM's can have resolution down to molecular level, and may operate with controllable forces small enough to image biological substances. Since AFM's are relatively simple, inexpensive devices compared to other high resolution techniques and are extremely versatile, they are becoming important tools in a wide variety of research and high technology manufacturing applications. The contact mode AFM, in which the tip is maintained in continuous contact with the sample, is currently the most common type, and accounts for essentially all the AFM's sold commercially to date.
The contact AFM has found many applications. However, for samples that are very soft or interact strongly with the tip, such as photoresist, some polymers, silicon oxides, many biological samples, and others, the contact mode has drawbacks. As pointed out in Hansma et al, the tip may be attracted to the surface by the thin liquid layer on all surfaces in ambient conditions, thus increasing the force with which the tip presses on the surface. The inventors and others have also observed that electrostatic forces may attract the tip to the surface, particularly for some tip-sample combinations such as silicon nitride tips on silicon oxide surfaces. When the tip is scanned laterally under such conditions, the sample experiences both compressive and shearing forces. The lateral shearing forces may make the measurement difficult and for soft samples may damage the sample. Further, a stick-slip motion may cause poor resolution and distorted images. Hansma et al's approach to this problem was to immerse the tip, cantilever, and sample surface in liquid, thus eliminating the surface layer forces, and for a polar liquid, the electrostatic forces. This technique works very well, and has the further advantage that it allows samples that are normally hydrated to be imaged in their natural state. However for many samples and applications, immersion in liquid is not of much use. Operating in liquid requires a fluid cell and increases the complexity of using the AFM, and for industrial samples such as photoresist and silicon wafers, immersion is simply not practical.
The non-contact AFM, developed by Martin et al, J. Applied Physics, 61(10), 15 May, 1987, profiles the surface in a different fashion than the contact AFM. In the non-contact AFM, the tip is scanned above the surface, and the very weak Van der Waals attractive forces between the tip and sample are sensed. Typically in non-contact AFM's, the cantilever is vibrated at a small amplitude and brought near to the surface such that the force gradient due to interaction between the tip and surface modifies the spring constant of the lever and shifts its natural resonant frequency. The shift in resonance will change the cantilever's response to the vibration source in a detectable fashion. Thus the amount of change may be used to track the surface typically by adjusting the probe surface separation during lateral scanning to maintain a predetermined shift from resonance. This AC technique provides greater sensitivity than simply monitoring the DC cantilever deflection in the presence of the attractive Van der Waals force due to the weak interaction between the tip and surface. The frequency shift may be measured directly as proposed by Albrecht et al. J. Applied Physics, 1991, or indirectly as was done originally by Martin et al.
The indirect method uses a high Q cantilever, such that damping is small. The amplitude versus frequency curve of a high Q lever is very steep around the resonant frequency. Martin et al oscillated the lever near the resonant frequency and brought the tip close to the surface. The Van der Waals interaction with the surface shifts the resonance curve. This has the effect of shifting the resonance closer or further to the frequency at which the lever is oscillated, depending on which side of resonance the oscillation is at. Thus, indirectly, the amplitude of oscillation will either increase or decrease as a consequence of the resonance shift. The amplitude change is measurable (AM type detection). This change in amplitude close to the surface compared to the amplitude far away from the surface (the free amplitude) can be used as a setpoint to allow surface tracking. The direct method measures the frequency shift itself (FM type detection). Both methods are bound by the same interaction constraints.
FIG. 5 illustrates this non-contact operation. The tip is driven at a known amplitude and frequency of oscillation, which is typically near a cantilever resonance. The amplitude of this oscillation is detected by a deflection detector, which can be of various types described in the references. When the tip is sufficiently far away from the surface, it will oscillate at the free amplitudes Ao, as shown in FIG. 5. As shown in FIG. 5, when the tip is brought closer to the surface, the Van der Waals interaction will shift the resonant oscillatory frequency slightly. This shift causes either an increased or decreased amplitude. As, or the frequency shift may be measured directly. This modified amplitude value may be used as a setpoint in the manner of other above described SPM's, such that as the tip is scanned laterally, the tip height may be adjusted with feedback to keep setpoint, As, at a constant value. Thus an image of the surface may be generated without surface contact, and without electrical interaction as needed by a scanning tunnelling microscope STM. The resonant shift may also be caused by other force interactions, such as magnetic field interaction with a magnetic tip. Thus this type of AFM may in theory be easily configured to map a variety of parameters using the same or similar construction.
The Van der Waals force is very weak, and decreases rapidly with separation, so the practical furthest distance for measurable interaction is 10 nm above the surface, as shown in FIG. 1, taken from Sarid, Scanning Force Microscopy, Oxford University Press, 1991. To shift the resonance of the lever, the lever must oscillate within this envelope of measurable force gradient. If just a small portion of the oscillation is within the envelope, the resonance will not be appreciably affected. Thus the oscillation amplitude must be small. A compendium of all non-contact AFM research can be found in Scanning Force Microscopy by Sarid, above noted, no researcher was able to operate a non-contact AFM with a free oscillation amplitude of greater than 10 nm. This limitation as will be shown limits the usefulness of the non-contact method.
Although developed at essentially the same time as the contact AFM, the non-contact AFM has rarely been used outside the research environment due to problems associated with the above constraints. The tip must be operated with low oscillation amplitude very near the surface. These operating conditions make the possibility very likely of the tip becoming trapped in the surface fluid layer described by Hansma et al. This effect is illustrated in FIG. 6, an amplitude versus displacement curve. A cantilever with probe is oscillated at a free amplitude Ao, and the vertical position of the fixed end of the lever is varied from a height where the probe is not affected by the surface to a point where the probe is captured by the surface and oscillation ceases. The curve is typical for oscillation amplitudes of 10 nm or less. Such curves have been measured by the inventors, and were also described by Martin et al, and also by Ducker et al, in "Force Measurement Using an AC Atomic Force Microscope", J. of Applied Physics, 67(9), 1 May 1990. As the curve clearly shows, when the tip is brought near the surface there is a narrow region where the amplitude is affected by the Van der Waals interaction before it becomes abruptly captured by the surface fluid layer, and oscillation becomes very small It is this narrow region in which the non-contact AFM must operate As a surface is scanned, any variations in the surface topography may cause the tip to become captured if the feedback cannot perfectly respond to the topography variations. If the tip does become captured, the control system will lift the fixed end of the lever until the tip breaks free, and then re-establish the setpoint. As can be seen from FIG. 6, there is significant hysteresis in the withdraw process, which will cause serious instability in the image data. Thus non-contact microscopes must scan very slowly so the feedback loop has sufficient time to prevent the tip becoming stuck to the surface. Moreover, because the tip must be operated above the fluid layer, the lateral resolution is inferior to the contact mode. Typically, the noncontact AFM must operate with the tip 5-10 nm above the surface, which limits the lateral resolution to 5-10 nm. Contact mode AFM's typically have lateral resolution of better than 1 nm.
For measuring the frequency shift using amplitude detection, the sensitivity depends on the cantilever having a very sharp resonance peak, which in turn gives a very slow response time because undamped systems require a long time to recover from a perturbation. Thus, sensitivity and response time are inversely coupled. The high Q requirement also places restrictions on the design of the lever to minimize the effect of air as a damping agent. One could improve the time response by using cantilevers which may be operated at a higher frequency, but such levers are stiffer and therefore have reduced sensitivity to the Van der Waals interaction. Thus it can be seen that high sensitivity and fast response are very difficult to achieve with a non-contact AFM. Furthermore, the weak force interaction places restrictions on the height at which the tip may be operated and the amplitude of oscillation. The presence of the fluid layer near this height makes capture of a lever with a small oscillation likely, so slow time response is a serious stability problem. For these reasons, despite their many potential advantages, non-contact AFM's have yet to be successful commercially.
The non-contact AFM has been used successfully in the measurement of magnetic fields on objects such as magnetic storage media. With a tip of, or coated with, magnetic material, the force interaction between the tip and magnetic sample is much stronger than the Van der Waals interactions, and is longer range. Thus, the non-contact FM (also called magnetic force microscope, MFM) may be operated without the need for ultra-high sensitivity, as required for surface profiling. However since magnetic fields are seldom continuous, some interaction is necessary to guide the tip over the surface between magnetic regions. Rugar et al, (Magnetic Force Microscopy, IBM Research Report, Almaden Research Center, Dec. 12, 1990) found that applying an electric field between the tip and sample would produce a larger effect than the Van der Waals force, so the hard disks could be scanned without the probe sticking to the surface. This method limits the technique to conductive surfaces.
Accordingly, one object of this invention is to provide a novel AFM that does not produce shear forces during scanning and does not have the operability limitations of the non-contact AFM.
A further object of the invention is to provide a novel AFM and method to profile surfaces, including soft or sticky surfaces, at high resolution with high sensitivity and fast time response, thus overcoming the drawbacks of prior art contact and non-contact mode AFM's.
It is a further object of this invention to provide an AFM that may map magnetic or other force distributions while retaining the ability to track topography without other force components.
These and other objects are achieved according to the present invention by providing a new and improved AFM and method of operating an AFM, wherein the probe is oscillated at or near resonance or a resonant harmonic to strike the surface of the sample, so that the tip has minimal lateral motion while in contact with the surface, thus eliminating scraping and tearing. The cantilever probe is oscillated at a large amplitude, greater than 10 nm, preferably greater than 20 nm, and typically on the order of 100-200 nm, so that the energy in the lever is large enough, much higher than that lost in each oscillation cycle due to, for example, damping upon striking the same surface, so that the tip will not become stuck to the surface. The oscillation amplitude is affected by the tip striking the surface in a measurable fashion, and this limited amplitude is a direct measure of the topography of the surface. Alternatively, a feedback control can be employed to maintain the oscillation amplitude constant, and then a feedback control signal can be used to measure surface topography. The striking interaction is strong, so the sensitivity is high. The resolution approaches the contact mode microscope because the tip touches the surface. The technique can use high frequency jumps with no loss in sensitivity since the measurement of the amplitude change does not depend on frequency.
The invention may be employed in the measure of magnetic or other force distributions in conjunction with the non-contact method, to track the surface in regions where there is no other force.
In further embodiments, the probe is oscillated and translated across the surface of the sample at constant amplitude and changes in phase are detected and corresponding output signals produced. In another variation, a relative phase between a drive signal causing oscillation of the probe and deflection of the probe is detected and the frequency of oscillation of the probe varied so that the relative phase is kept essentially constant during scanning. An output signal is then produced indicative of variations in the frequency of oscillation of the probe as a function of position during scanning. According to a further embodiment, oscillation frequency is modulated by an amount Δf, changes in relative phase Δp detected, and signals indicative of the slope Δp/Δf output. In a further embodiment, data is obtained by operating at different tapping amplitude setpoints and then compared to discriminate a force dependent sample characteristic.
A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:
FIG. 1 is a graph showing the Van der Waals force as a function of height above a surface, and where a non-contact mode microscope must operate;
FIG. 2 is a simplified functional block diagram of the probe positioning apparatus of a prior art contact mode atomic force microscope;
FIG. 3 is a simplified functional block diagram of the probe positioning apparatus of an atomic force microscope incorporating the present invention;
FIG. 4 is a block diagram of another type of AFM which may use the present invention;
FIG. 5 is an illustration of the operation of a vibrating lever brought close to a surface in the prior art non-contact mode;
FIG. 6 is a graph of an amplitude vs. position curve that illustrates the behavior of the probe oscillation in a prior art non-contact mode AFM as a function of probe height above a surface;
FIG. 7 is an illustration of the operation of a vibrating lever brought close to a surface in a preferred embodiment of the present invention;
FIG. 8 is a graph of an amplitude vs. position curve that illustrates the behavior of the probe oscillation in a preferred embodiment of the present invention as a function of probe height above a surface;
FIG. 9A is an illustration of how the present invention may be used to achieve improved performance when measuring surfaces with steep walls and trenches, and
FIG. 9B is a graph illustrating oscillation amplitude as a function of scan position in the trench of FIG. 9A;
FIG. 10 is an illustration of an alternative approach where the present invention may be used to achieve improved performance when measuring surfaces with steep walls and trenches;
FIG. 11 is a graph of an amplitude-distance curve that illustrates the behavior of the probe oscillation in a preferred embodiment of the present invention as a function of probe height above a surface in a mode where the probe oscillates within the surface fluid layer;
FIG. 12 is a graph of an amplitude-distance curve that stops before the amplitude decreases below a predetermined point;
FIG. 13 is an illustration of how a probe is pulled into a steep wall in the prior art contact AFM; and
FIG. 14a is an illustration of scanning a probe tip in a trench while oscillating the probe tip, and FIG. 14b is a graph illustrating the observed oscillation amplitude resulting from the scanning of FIG. 14a;
FIG. 15 is a block diagram of a further embodiment of the tapping AFM of the present invention, in which probe tip oscillation phase is detected as a function of lateral position during scanning;
FIG. 16 is a block diagram illustrating a further embodiment of a tapping AFM according to the present invention, in which a change in resonant frequency of the oscillating probe tip is detected during tapping at constant amplitude; and
FIGS. 17a and 17c are graphs showing the effect of damping on oscillation amplitude as a function of frequency, and FIGS. 17b and 17d are graphs showing the effect of damping on the slope of the phase vs. frequency curve.
The present invention utilizes the inventors' discovery that if the probe is oscillated at or near one of the resonant frequencies of the lever, that in fact the probe tip has much less of a tendency to stick to the surface because a resonant system tends to remain in stable oscillation even if some damping exists. Thus the preferred embodiment of the present invention utilizes a resonant oscillation of the cantilever at sufficient oscillation amplitude to achieve the advantages described above without the probe becoming stuck to the surface. This preferred embodiment also provides many of the benefits of the non-contact AFM as described above.
Existing development of AFM's using oscillation of the probes has been directed at avoiding surface contact, as described above, and as such is limited in practicality despite the potential advantages of the technique. For applications where the non-contact mode is desired, the inventors have found that the amplitude-distance curve of FIG. 6 can of be of great aid in establishing the setpoint for non-contact mode operation. Using the amplitude-distance curve, one can optimize the operating frequency, free amplitude and setpoint to achieve the most suitable operating characteristics for a particular sample and cantilever combination. This novel application of the curve was clearly not anticipated by Ducker or Martin. Using the computational and display capabilities of typical scanning probe microscopes, SPM's, the lever may be oscillated and the lever vertical position varied, while the curve is displayed on a terminal. The various parameters may be varied, such that desired operating conditions may be determined, and used when the SPM is in the imaging mode.
The AFM of the present invention does not avoid contact with the surface. Thus, the invention is not limited in the amplitude of oscillation, and in fact as will be shown, very large amplitudes compared to the non-contact mode are advantageous. In FIG. 6, it is shown that for small oscillation amplitudes as the tip is brought near the surface, it becomes trapped by the fluid layer and oscillation ceases abruptly. If the oscillation amplitude is larger, greater than 10 nm, preferably greater than 20 nm and typically 100-200 nm, then the energy in the oscillation may be sufficient in most cases to overcome the stickiness of the surface for a wide range of vertical positions of the lever.
FIG. 7 shows that for a large free amplitude, Ao, the lever may be brought down to where the tip strikes the surface. The energy lost by striking the surface and overcoming the fluid layer attraction limits the oscillation to a reduced value, A, but does not stop the oscillation as happens for low drive oscillation amplitudes. The difference in behavior for higher amplitude oscillations is illustrated in FIG. 8 where the curve of FIG. 6 is duplicated for a free amplitude, Ao, of greater than 10 nm. As can be seen, there is wide range of limited amplitudes, with the probe striking the surface, that could be used as an operating point for a feedback loop. Abrupt capture of the probe does not take place, so stable operation is possible. As the curve shows, the lever may be further lowered such that oscillation is stopped. The withdraw characteristics are similar to the low amplitude case in that the amplitude increases gradually until a point is reached where the cantilever breaks free and resumes oscillation at the free amplitude.
According to the present invention, the AFM is then operated at or near a cantilever resonance with sufficient amplitude that upon the probe striking the surface, the amplitude of oscillation of the probe is affected and the probe does not stick to the surface. A preferred version of this invention can be practiced on the AFM of FIG. 3. In FIG. 3, the tip is driven at a known amplitude and frequency oscillation, which is typically near a cantilever resonance. The amplitude, Ao, of this oscillation is detected by the deflection detector of FIG. 3, which is of the type shown in FIG. 2 and described by Hansma et al. When the tip is sufficiently far away from the surface, it will oscillate at the free amplitude, Ao, as shown in FIG. 7. The amplitude is measured in the AFM of FIG. 3 as an RMS value of the AC deflection detector signal. As shown in FIG. 7, when the tip is brought closer to the surface, striking the surface will limit, typically due to damping, the oscillatory motion. The amount of change is measurable as a decreased RMS value, As. This modified amplitude value may be used as a setpoint in the manner of other above described SPM's, such that as the tip is scanned laterally, the cantilever height may be adjusted with feedback to keep the RMS setpoint, As, at a constant value. Alternatively, changes in the amplitude of oscillation themselves can be used as a direct measure of surface topography. Thus, an image of the surface may be generated. The preferred embodiment uses a digital processor to provide the servo control by means of feedback programs executed by the processor. An analog feedback system is also possible. Strain gauges, such as resistive or piezo-resistive strain gauges or piezoelectric elements built into the cantilever arm, may be employed in place of the optical deflector detector shown.
As shown in FIG. 4, this version of the invention may also be implemented with other types of AFM's. For instance, the Compact AFM, disclosed in U.S. Pat. No. 5,189,906, describes an AFM where the probe is scanned rather than the sample. This AFM has provision to attach the probe to a separate positioner, which may be used to impart the oscillation, such that a setpoint may be established for contact with the surface.
This preferred embodiment of the invention has several advantages. This AFM can be operated with extremely light tapping forces. In general, the inventors have found that even using relatively stiff levers, on the order of 10's of newtons per meter in order to give high frequency oscillations such as up to 2 MHz, the forces on the sample are still extremely light. For instance, it is easy to establish a setpoint that is 10 nm less than the free oscillation amplitude, which may be on the order of 100 nm. Thus the energy in the lever oscillation is much higher than that lost in each cycle by striking the surface. A conservative estimate of the actual force imparted to the surface is to assume the contact is inelastic and therefore the bending of the lever due to surface contact is just the amplitude gained in one cycle, approximately (Ao -As)/Q, where Q is the quality factor of the lever. Typical silicon levers have Q's of 100 to 1000, so for a setpoint 10 nm below the free amplitude of 100 nm the force per strike is 0.1 to 1 nanonewtons for a cantilever with a force constant of 10 newtons/meter. A contact mode AFM is limited to a contact force of about 50 nN in air due to the fluid layer attraction, and this can be reduced to about 1 nN operating in a liquid cell. So the present invention has extremely light contact forces and no shear forces at all. Thus, this technique is comparable to the non-contact mode in terms of surface damage, and operates much more stably and reliably. This mode effectively eliminates the effect of the surface fluid layer which limits the utility of both prior art contact and noncontact mode systems, and the advantage of operation under liquid disappears for many applications.
The invention also can achieve very high resolution. The oscillation can potentially be at very high frequency since only a very small lever must be driven, and because the low striking forces allow stiff levers to be used. This mode does not require resonant operation per se, but requires sufficient energy in the oscillation to overcome the stickiness of the surface. Thus in practice, resonant operation is necessary, but the higher harmonies of the resonant frequency may be usable. The inventors have successfully operated the invention at oscillation frequencies of up to 2 MHz. It is straightforward to oscillate at a frequency that for typical scan sizes and rates will cause the tip to strike the surface many times before it has displaced laterally by one tip diameter. Thus the lateral resolution is only limited by the tip size, which is much better resolution than achieved by prior art non-contact AFM's, whose resolution is determined by the height of the tip above the surface. Since the vertical deflection detector for a typical AFM has sub-nanometer resolution, the invention will also be able to maintain the setpoint to sub-nanometer accuracy. The invention has been successfully used to measure surface roughness on polished silicon of under 1 angstrom RMS. The invention does not depend on Van der Waals interactions like the non-contact AFM to sense the surface, so it can operate under fluids for samples that need to be hydrated.
As can be seen from FIG. 8, the region of stable operation for the invention is forgiving, but if the probe does become stuck to the surface there is significant hysteresis in the recovery process. The probe has to be pulled away a relatively large distance, then it will abruptly restart the free oscillation. It then has to be brought back to the operating height. If the setpoint amplitude As is too low, the tip may remain oscillating in the surface fluid layer with the feedback system not trying to pull the tip loose. The inventors have found that this type of scanning is stable, but gives low resolution similar to the non-contact method. The amplitude-distance curve of FIGS. 6 and 8 is of great utility in evaluating the stickiness of a surface and choosing an Ao and an As that will produce satisfactory operation.
The preferred method of operation is to select a free amplitude Ao such that the amplitude versus approach curve of FIG. 8 gives a continuous, stable decrease of amplitude as the lever is brought closer to the surface. The amplitude will depend on the tip sharpness, cantilever stiffness, and the sample surface, as well as current environmental conditions such as humidity. Preferably, in an SPM where this curve may be produced, displayed and adjusted in real time, the operator can determine a suitable free amplitude by starting with a low amplitude and increasing it until the curve changes shape from a curve like FIG. 6 to a curve like FIG. 8. The preferred setpoint for high resolution imaging topography is an As that is greater than the amplitude at which the cantilever breaks free on the withdraw portion of FIG. 8. This point is labeled Ap. If one operates at a setpoint above Ap, then if the tip does become stuck to the surface, the feedback will return to a condition where the lever is free of the surface liquid layer.
Using the amplitude-distance curve to evaluate and select operating parameters is important because the actual behavior of the lever is sample and condition dependent. For most samples, for some value of Ao, a curve such as FIG. 8 may be produced, and if an As is selected greater than Ap, stable operation will result in the imaging mode. However, some combinations of sample and conditions will not allow an amplitude-distance curve such as shown in FIG. 8. Either the pull-off curve or the approach curve may not follow the same pattern. For instance, the pull-off may be abrupt, indicating that the lever is affected little by the fluid layer on pull-off. This condition does not usually affect stable operation. Another condition may be an abrupt capture on approach, similar to small oscillation (non-contact) operation. For this case, it is vital to adjust the parameters to achieve as wide an operating region as possible. Moreover, the amplitude-distance curve may be used to set operating parameters that result in interesting and potentially useful modes. If As is set lower than Ap for a sample that has an amplitude-distance curve like FIG. 8, then if the lever can be initially pushed into the sticking position, the feedback loop will then maintain an imaging mode where the tip is oscillating within the fluid layer, and not actually in contact with the surface. This is a very stable non-contact mode. In this mode the instrument is essentially imaging the surface fluid layer, and the topography of this layer compared to the topography of the surface may provide useful information. The resolution is lower than when striking occurs, but is comparable to the less stable prior art non-contact mode where the tip is above the layer and the free amplitude oscillation is small. Another potential mode occurs if the lever is oscillated below resonance when the tip is far from the surface. When the tip is withdrawn, the fluid layer attached to the lever will lower the resonance such that the oscillation response to the drive signal may be actually larger than the free amplitude because the drive signal is now closer to resonance. This case is illustrated in FIG. 11. The inventors have noticed that this mode is highly sample dependent, and thus may contain useful information about the surface fluid layer. Although both of these modes should be avoided for reliable topographic measurements, they illustrate the usefulness of the amplitude-distance curve to intelligently select operating parameters, and the potential diversity of applications for the invention.
Because stiff levers are typically used for the invention for high frequency operation, the inventors have found it is often useful when generating amplitude-distance curves to limit the distance over which the curve is obtained. If the lever is pushed sufficiently far into the surface that oscillation has ceased, then the force on the sample is simply the displacement of the lever times the spring constant. Typical levers suitable for this invention have spring constants many times those used in conventional contact AFM's, so the force exerted in an amplitude-displacement curve at the end where oscillation ceases can be very large. The sample and the cantilever may be damaged by the operation of obtaining the curve. Thus, the amplitude may be monitored during the distance modulation, and the lever only pushed into the sample until a predetermined decrease in amplitude is observed, and then pulled away. For instance, the digital controller that operates the scanner can be programmed to move the sample toward the cantilever until a certain amplitude or fraction of the free amplitude is reached and then caused the sample to be retracted. The user could enter the target amplitude into the controller. Such a curve is shown in FIG. 12. The probe is pushed into the sample until an amplitude Amin is observed, and no further. The setpoint can be picked on the sloped part of the curve Amin. This technique will prevent damage to tip and sample during the amplitude-distance curve operation.
The invention can also be used to measure attractive force distributions such as magnetic fields, in a mixed mode operation, using both the invention and the prior art non-contact mode. For instance, if a magnetic tip is used, and a surface is scanned with alternating magnetic and non-magnetic regions, the reduction in amplitude will be affected not only by the tip striking the surface but also by the effect of the magnetic force gradient on the resonant frequency of the cantilever, as described above (if the driving frequency is slightly above the resonant frequency). Over areas where the magnetic field decreases the oscillation amplitude below the setpoint, the feedback will raise the lever to maintain the setpoint, such that the magnetic areas will appear in the image as regions of increased height. If the magnetic field interaction is strong enough, the tip will no longer be striking the surface over the magnetic regions. In regions with no magnetic field, the feedback will return the tip to the striking mode to maintain the setpoint. This same technique is potentially useful to measure other parameters such as electric field, which with appropriate tips and electronics may also exert force interactions on oscillating probes.
Another problem with contact mode prior art AFM's is that they have poor performance when measuring steep sample features, such as trenches on integrated circuits. There are at least two problems associated with steep features. The first is that when the tip scans into the feature it twists laterally, and this lateral twist is not detected or interpreted properly by the vertical deflection detector. The second problem is that suitable tips need to be long and narrow to get into the grooves so these tips are not very stiff laterally. As the tip approaches the sidewall, attractive forces tend to pull the tip toward the surface as shown in FIG. 13, and the tip tends to stick to the surface because of surface tension as the scan moves away from a wall. Both of these effects distort measurements of linewidth or step height that need to be made to accuracies of fractions of a percent. Since the sticking may depend on ambient conditions, such as humidity, the measurements can vary from day to day. A modification of the invented technique can be used for such measurements.
As shown in FIG. 9A, the oscillation can be done in a horizontal direction, using a probe with a suitable shape in a trench or near any step. If the probe is scanned laterally in the trench or near a step while oscillating laterally, the free oscillation amplitude will decrease when the wall is touched, as shown in FIG. 9B. Thus a setpoint for horizontal motion may be established that causes the probe to contact a trench or step sidewall with a series of taps so that measurement accuracy will be unaffected by attractive forces or sticking. This setpoint can be used to maintain the probe at a sidewall with low force and no sticking. The probe could then be scanned vertically and served laterally to maintain the setpoint in order to profile the wall. Alternatively, linewidth could be measured if the probe is scanned back and forth across a trench, such that the lateral motion reverses direction when a wall is encountered, as determined by the oscillation amplitude reducing to a setpoint at the walls. This process could be repeated as the probe is scanned along the trench to measure variations in linewidth, or a combination of lateral and vertical profiling could be used.
Yet another technique to measure steep walls is shown in FIG. 10. If the lever is mounted at an angle to the surface, preferably greater than the half angle of the probe, and the probe is oscillated perpendicular to the lever then the probe will scan along the surface until the wall is encountered, and will follow the wall up, because the oscillation setpoint will be affected both by the floor and the wall. Thus an x-z profile of the wall and floor will be produced. This approach will even work for undercut walls depending on the shape of the tip and nature of the undercut.
Another mode is to increase the amplitude of oscillation in a trench until the tip hits both sides. The tip could then be scanned laterally across the trench as shown in FIG. 14a so that the point of maximum oscillation is found. This maximum oscillation will be where the tip is in the center of the groove, hitting each side equally. This amplitude, Amax, shown in FIG. 14b, combined with the width of the tip, will give a measure of the width of the groove. One could then trace this cut vertically.
Further embodiments of the present invention utilize the phenomenon that as the probe taps the surface of the sample, the attractive force caused by the capillary forces on the tip and any momentary adhesion between the tip and sample material affect both the resonant frequency of the cantilever and the phase between the signal driving the cantilever oscillation and the actual oscillation of the free end of the cantilever. Although the invention relies on the probe oscillation having sufficient energy to prevent any long term, i.e., more than a small fraction of an oscillation cycle, sticking of the probe tip to the surface, the short period in each cycle where the probe strikes the surface will result in some adhesion. This momentary adhesion may depend on the elasticity or damping of the probe-surface contact and will measurably affect the resonant frequency and phase of the cantilever oscillation.
This measurement of phase or resonant frequency during tapping of the probe against the surface is typically used as a chemical force microscope where the tip is made from a particular material or coated with a particular material so that the adhesion of the tip could be tailored to be specific to a certain substance on the surface. The phase or frequency measurement is then used to find and image where the specific substance is on the surface. An example of this is an antibody antigen interaction, where a specific antibody or antigen is placed on the tip in order to find its corresponding antigen or antibody on the surface. A prior art chemical force microscope is described by Frisbie, et al., SCIENCE 265:2071-2074, 1994, where a frictional force measured by the tip dragging across the surface is used to image the position of a specific chemical on the surface with different chemicals placed on the tip. As pointed out earlier, though, this dragging of the tip across the surface has adverse affects and should be avoided. For instance, the dragging might remove the material coated to the tip. According to the present invention, the tapping while measuring phase or resonant frequency is used as a measure of adhesion or chemical interaction
In a preferred embodiment, the cantilever is oscillated and feedback is used to control the vertical position of the fixed end of the cantilever so that the oscillation of the cantilever is at a constant amplitude as the tip taps the surface, and changes in phase, from as small as 0.01 degrees to several degrees, are recorded as a function of the tip lateral position during scanning. An image is then made of the phase measurement as a function of lateral position, i.e., X and Y. Such a device is shown in FIG. 15, where a phase detector is included, with the detected phase being sent to the processor for storage and display.
In another embodiment, the resonant frequency of the cantilever, which is typically 100-300 KHz, normally 150 KHz, is tracked during tapping at constant amplitude, the change in frequency giving an indication of a change in momentary adhesion between the tip and surface. This is done with a second feedback loop operating to keep the phase constant by varying the drive frequency of the cantilever. If the phase is kept constant at, for instance, 90° then the drive frequency tracks the resonant frequency of the system, and gives a measure of the adhesion between the tip and sample. Typically, the resonant frequency varies in a range of 0.1 to 100 Hz. In this embodiment, one always drives the cantilever at the same point on the resonance curve, so the force of tapping would remain constant during imaging. This regulation of the frequency to follow the resonant frequency is also useful in cases where one wants to use a very light tapping force, which requires that the tapping force be well regulated, i.e., that the free amplitude Ao does not vary as it would if the resonant frequency varies and the drive frequency stays fixed. Also, the frequency of resonance is more related to physical parameters of the oscillator than a phase measurement and allows a calculation of the adhesive force knowing other parameters of the cantilever. This frequency tracking embodiment is shown in FIG. 16.
One can gain more information about the interaction between the tip and surface during tapping by modulating the cantilever drive frequency, typically by an amount of 1-5 KHz, and observing the corresponding change in phase, i.e., determining the slope of the phase vs. frequency curve during tapping. For a Lorenzian shaped curve, which is the resonance curve of amplitude (A) vs. frequency (f) for an harmonic oscillator, as shown in FIGS. 17a and 17c, this slope as shown in FIGS. 17b and 17d is related to the width of the curve and therefore is a measure of the damping forces on the oscillator. As shown in FIG. 17c in relation to FIG. 17a, higher damping results in a broader cantilever resonance curve (γ1 <γ2 at the same amplitude), which, as shown in FIGS. 17b and 17d, decreases the slope (Δp/Δf, where Δp is a change in phase produced by a change Δf in frequency) of the phase curve in the region around the resonance. Thus, modulating the cantilever drive frequency by an amount Δf, monitoring the ratio Δp/Δf, and computing the slope Δp/Δf provides a measure of the probe-sample interaction. In another embodiment of this invention, this damping is measured as a function of X and Y to produce an image of damping forces over the scanned surface. This is done in the frequency feedback method where the modulation is done while the average frequency is controlled to keep the average phase constant, i.e., the frequency is modulated about the resonant frequency. This will produce a modulation Δp of the phase about the phase setpoint.
In the above described embodiments, feedback control of the amplitude and/or phase servos and/or frequency modulation are usually performed digitally by means of a digital computer, so that feedback control and modulation control can be programmed so that they do not conflict.
The adhesion and damping between the sample and probe may be dependent on the tapping force, which is controlled by the setpoint amplitude, the lower the setpoint the higher the force. Thus, the previous described measurements of phase, frequency, or damping could be made as a function of the tapping amplitude setpoint, by varying the tapping amplitude setpoint at each data point, each scanline, or each complete image. Comparison of the data obtained at different tapping amplitude setpoints can be made either qualitatively (visually) or quantitatively (arithmetically), according to this embodiment, and is useful to discriminate force dependent sample characteristics.
This measurement of phase or resonant frequency while tapping also provides information about surface coverage of substances put down on the surface of the sample, such as oil or lubricating layers on the sample, or monomolecular films applied to the surface.
The phase of the cantilever oscillation will not only be sensitive to adhesion, but also may be affected by long range forces such as electric and magnetic forces. These forces are measured more sensitively by lifting the cantilever off the surface so that phase shifts due to adhesion are avoided. This method of measuring long range forces is described in U.S. Pat. No. 5,308,974 by the same inventors.
Obviously, numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein.
|Cited Patent||Filing date||Publication date||Applicant||Title|
|US33387 *||Oct 1, 1861||Improvement in printing-presses|
|US34489 *||Feb 25, 1862||Improvement in metallic cases for pictures, cards|
|US2405133 *||Oct 7, 1942||Aug 6, 1946||Brush Dev Co||Method and means for measuring surface roughness|
|US2460726 *||Jan 11, 1943||Feb 1, 1949||Brush Dev Co||Surface roughness measuring device|
|US3049002 *||Feb 24, 1959||Aug 14, 1962||Hermann Hediger||Device for measuring the roughness of surfaces|
|US3378648 *||Dec 31, 1964||Apr 16, 1968||Gen Electric||Doped piezoresistive phonograph pickup|
|US4106333 *||Aug 9, 1976||Aug 15, 1978||Ernst Salje||Method of and apparatus for examining the roughness of surfaces|
|US4359892 *||Dec 15, 1980||Nov 23, 1982||U.S. Philips Corporation||Arrangement for measuring surface profiles|
|US4724318 *||Aug 4, 1986||Feb 9, 1988||International Business Machines Corporation||Atomic force microscope and method for imaging surfaces with atomic resolution|
|US4868396 *||Oct 13, 1987||Sep 19, 1989||Arizona Board Of Regents, Arizona State University||Cell and substrate for electrochemical STM studies|
|US4902892 *||Oct 13, 1988||Feb 20, 1990||Agency Of Industrial Science And Technology, Kosaka Laboratory Ltd.||Method of measurement by scanning tunneling microscope|
|US4935634 *||Mar 13, 1989||Jun 19, 1990||The Regents Of The University Of California||Atomic force microscope with optional replaceable fluid cell|
|US5015850 *||Jun 20, 1989||May 14, 1991||The Board Of Trustees Of The Leland Stanford Junior University||Microfabricated microscope assembly|
|US5047633 *||May 3, 1990||Sep 10, 1991||Amersham International Plc||Imaging apparatus and method|
|US5162653 *||Nov 25, 1991||Nov 10, 1992||Hitachi, Ltd.||Scanning tunneling microscope and surface topographic observation method|
|US5186041 *||Mar 16, 1992||Feb 16, 1993||International Business Machines Corporation||Microprobe-based CD measurement tool|
|US5189906 *||Apr 19, 1991||Mar 2, 1993||Digital Instruments, Inc.||Compact atomic force microscope|
|US5212987 *||Nov 15, 1991||May 25, 1993||Hommelwerke Gmbh||Acoustic screen scan microscope for the examination of an object in the short-range field of a resonant acoustic oscillator|
|US5224376 *||Feb 6, 1992||Jul 6, 1993||Digital Instruments, Inc.||Atomic force microscope|
|US5229606 *||Jun 5, 1989||Jul 20, 1993||Digital Instruments, Inc.||Jumping probe microscope|
|US5237859 *||May 30, 1991||Aug 24, 1993||Digital Instruments, Inc.||Atomic force microscope|
|US5254854 *||Nov 4, 1991||Oct 19, 1993||At&T Bell Laboratories||Scanning microscope comprising force-sensing means and position-sensitive photodetector|
|US5266801 *||Jan 26, 1993||Nov 30, 1993||Digital Instruments, Inc.||Jumping probe microscope|
|US5289004 *||Apr 10, 1992||Feb 22, 1994||Olympus Optical Co., Ltd.||Scanning probe microscope having cantilever and detecting sample characteristics by means of reflected sample examination light|
|US5308974 *||Nov 30, 1992||May 3, 1994||Digital Instruments, Inc.||Scanning probe microscope using stored data for vertical probe positioning|
|US5345815 *||Sep 30, 1992||Sep 13, 1994||Board Of Trustees, Leland Stanford Jr. University||Atomic force microscope having cantilever with piezoresistive deflection sensor|
|US5347854 *||Sep 22, 1992||Sep 20, 1994||International Business Machines Corporation||Two dimensional profiling with a contact force atomic force microscope|
|US5363697 *||Apr 29, 1992||Nov 15, 1994||Matsushita Electric Industrial Co., Ltd.||Scanning probe microscope, molecular processing method using the scanning probe microscope and DNA base arrangement detecting method|
|US5406832 *||Jul 2, 1993||Apr 18, 1995||Topometrix Corporation||Synchronous sampling scanning force microscope|
|US5408094 *||May 4, 1993||Apr 18, 1995||Olympus Optical Co., Ltd.||Atomic force microscope with light beam emission at predetermined angle|
|US5412980 *||Aug 7, 1992||May 9, 1995||Digital Instruments, Inc.||Tapping atomic force microscope|
|US5415027 *||Nov 5, 1993||May 16, 1995||Digital Instruments, Inc.||Jumping probe microscope|
|US5418363 *||Feb 25, 1994||May 23, 1995||Digital Instruments, Inc.||Scanning probe microscope using stored data for vertical probe positioning|
|US5436448 *||Jan 6, 1993||Jul 25, 1995||Hitachi, Ltd.||Surface observing apparatus and method|
|US5481908 *||Apr 28, 1993||Jan 9, 1996||Topometrix Corporation||Resonance contact scanning force microscope|
|US5519212 *||Jan 31, 1995||May 21, 1996||Digital Instruments, Incorporated||Tapping atomic force microscope with phase or frequency detection|
|US5625142 *||Jul 11, 1995||Apr 29, 1997||Topometrix Corporation||Resonance contact scanning force microscope|
|US5681987 *||Apr 12, 1996||Oct 28, 1997||Topometrix Corporation||Resonance contact scanning force microscope|
|US5742172 *||Oct 11, 1996||Apr 21, 1998||Seiko Instruments Inc.||Scanning probe microscope and method for obtaining topographic image, surface potential image, and electrostatic capacitance distribution image|
|USRE33387||Nov 16, 1988||Oct 16, 1990||International Business Machines Corporation||Atomic force microscope and method for imaging surfaces with atomic resolution|
|USRE34489||Jun 4, 1992||Dec 28, 1993||The Regents Of The University Of California||Atomic force microscope with optional replaceable fluid cell|
|CA1270132A *||Sep 26, 1986||Jun 12, 1990||Gerd Karl Binnig||Method and atomic force microscope for imaging surfaces with atomic resolution|
|EP0290647B1 *||May 12, 1987||Jul 24, 1991||International Business Machines Corporation||Oscillating quartz atomic force microscope|
|EP0397416A1 *||May 4, 1990||Nov 14, 1990||AMERSHAM INTERNATIONAL plc||Imaging apparatus and method|
|EP0587459A1 *||Mar 31, 1993||Mar 16, 1994||Digital Instruments, Inc.||An ultra-low force atomic force microscope|
|JP6194157A||Title not available|
|JP6201315A||Title not available|
|JP6201371A||Title not available|
|JP62130302U||Title not available|
|JP63309802A||Title not available|
|JPH0682248A *||Title not available|
|JPH06194157A *||Title not available|
|JPH06201315A *||Title not available|
|JPH06201371A *||Title not available|
|JPS62130302A *||Title not available|
|JPS63309802A *||Title not available|
|WO1992012398A1 *||Dec 30, 1991||Jul 23, 1992||The Board Of Trustees Of The Leland Stanford Junior University||Piezoresistive cantilever for atomic force microscopy|
|1||A. L. Weisenhorn et al., "Forces in atomic force microscopy in air and water", Appl. Phys. Lett, vol. 54, No. 26, Jun. 26, 1989, pp. 2651-2653.|
|2||*||A. L. Weisenhorn et al., Forces in atomic force microscopy in air and water , Appl. Phys. Lett , vol. 54, No. 26, Jun. 26, 1989, pp. 2651 2653.|
|3||*||AutoProbe XL2, Multiple Mode Large Sample AFM for Sub angstrom Resolution, Park Scientific Instruments, 2 pages.|
|4||AutoProbe XL2, Multiple Mode Large Sample AFM for Sub-angstrom Resolution, Park Scientific Instruments, 2 pages.|
|5||D. Rugar et al., "Magnetic force microscopy: General principles . . . media", J.Appl. Phys., vol. 68, No. 3, Aug. 1, 1990, pp. 1169-1183.|
|6||*||D. Rugar et al., Magnetic force microscopy: General principles . . . media , J.Appl. Phys., vol. 68, No. 3, Aug. 1, 1990, pp. 1169 1183.|
|7||D. Sarid et al., "Review of scanning force microscopy", J. Vac. Sci. Technol. B vol. 9, No. 2, Mar./Apr. 1991, pp. 431-437.|
|8||*||D. Sarid et al., Review of scanning force microscopy , J. Vac. Sci. Technol. B vol. 9, No. 2, Mar./Apr. 1991, pp. 431 437.|
|9||*||Encyclopedia of Physics, 2 nd Ed. Interatomic and Inermolecular Forces. p. 545.|
|10||Encyclopedia of Physics, 2nd Ed. Interatomic and Inermolecular Forces. p. 545.|
|11||Frisbie et al., "Functional Group Imaging by Chemical Force Microscopy", Science, vol. 265, Sep. 10, 1994, pp. 2071-2073.|
|12||*||Frisbie et al., Functional Group Imaging by Chemical Force Microscopy , Science, vol. 265, Sep. 10, 1994, pp. 2071 2073.|
|13||G. Binnig et al., "Atomic Force Microscope", Physical Review Letters, vol. 56, No. 9, pp. 930-933, Mar. 3, 1986.|
|14||*||G. Binnig et al., Atomic Force Microscope , Physical Review Letters , vol. 56, No. 9, pp. 930 933, Mar. 3, 1986.|
|15||Giambattista et al, "Atomic resolution images of solid-liquid interfaces", Proc. Natl. Acad. Sci. USA, vol. 84, pp. 4671-4674, Jul. 1987.|
|16||*||Giambattista et al, Atomic resolution images of solid liquid interfaces , Proc. Natl. Acad. Sci. USA, vol. 84, pp. 4671 4674, Jul. 1987.|
|17||IBM Technical Disclosure Bulletin, vol. 32, No. 7, Dec. 7, 1989, New York, U.S., p. 168 "Microprobe-Based CD Measurement Tool".|
|18||*||IBM Technical Disclosure Bulletin, vol. 32, No. 7, Dec. 7, 1989, New York, U.S., p. 168 Microprobe Based CD Measurement Tool .|
|19||L. M. Roylance et al., "A Batch-Fabricated Silicon Accelerometer" IEEE Transactions on Electron Devices, vol. ED-26, No. 12, pp. 11-1917, Dec. 1979.|
|20||*||L. M. Roylance et al., A Batch Fabricated Silicon Accelerometer IEEE Transactions on Electron Devices , vol. ED 26, No. 12, pp. 11 1917, Dec. 1979.|
|21||M. Anders et al., "Potentiometry for thin-film structures", J.Vac. Sci. Technol. A, vol. 8, No. 1, Jan.Feb. 1990, pp. 394-399.|
|22||*||M. Anders et al., Potentiometry for thin film structures , J.Vac. Sci. Technol. A, vol. 8, No. 1, Jan.Feb. 1990, pp. 394 399.|
|23||Marti et al., "Mechanical and thermal effects of laser irradiation on force microscope cantilevers", Ultramicroscopy 42-44 (1992) pp. 345-350 (published Jul. 1992).|
|24||*||Marti et al., Mechanical and thermal effects of laser irradiation on force microscope cantilevers , Ultramicroscopy 42 44 (1992) pp. 345 350 (published Jul. 1992).|
|25||Martin et al., "Atomic force microscope-force mapping and profiling on a sub 100 Å scale", J.Appl. Phys. vol. 61, No. 10, May 15, 1987.|
|26||*||Martin et al., Atomic force microscope force mapping and profiling on a sub 100 scale , J.Appl. Phys. vol. 61, No. 10, May 15, 1987.|
|27||*||McGraw Hill Dictionary of Scientific and Technical Terms, p. 2117.|
|28||McGraw-Hill Dictionary of Scientific and Technical Terms, p. 2117.|
|29||Nyyssonen et al., "Two-dimensional atomic force microprobe trench metrology system", J. Vac. Sci. Technol., B9, 3612-3616 (1991) Nov./Dec.|
|30||*||Nyyssonen et al., application of a two dimensional atomic force microscope system to metrology, Proc. SPIE, vol. 1556, 79 87 (1991).|
|31||Nyyssonen et al., application of a two-dimensional atomic force microscope system to metrology, Proc. SPIE, vol. 1556, 79-87 (1991).|
|32||*||Nyyssonen et al., Two dimensional atomic force microprobe trench metrology system , J. Vac. Sci. Technol., B9, 3612 3616 (1991) Nov./Dec.|
|33||P.C.D. Hobbs, et al., "atomic Force Microscope: Implementations", SPIE vol. 897 canning Microscopy Technologies and Applications (1988), pp. 27-30.|
|34||*||P.C.D. Hobbs, et al., atomic Force Microscope: Implementations , SPIE vol. 897 canning Microscopy Technologies and Applications (1988), pp. 27 30.|
|35||R. Elandsson et al., "Atomic force microscopy using optical interferometry", J.Vac. Sci. Technol. A, vol. 6, No. 2, Mar./Apr. 1988, pp. 266-270.|
|36||*||R. Elandsson et al., Atomic force microscopy using optical interferometry , J.Vac. Sci. Technol. A, vol. 6, No. 2, Mar./Apr. 1988, pp. 266 270.|
|37||R. Erlandsson et al., "A scanning force microscope designed for . . . ", Microscopy, Microanalysis, Microstructures 1(1990) pp. 471-480.|
|38||*||R. Erlandsson et al., A scanning force microscope designed for . . . , Microscopy, Microanalysis, Microstructures 1(1990) pp. 471 480.|
|39||T.R. Albrecht et al., "Frequency modulation detection using . . . sensitivity", J. Appl. Phys., vol. 69, No. 2, Jan. 15, 1991, pp. 668673.|
|40||*||T.R. Albrecht et al., Frequency modulation detection using . . . sensitivity , J. Appl. Phys., vol. 69, No. 2, Jan. 15, 1991, pp. 668673.|
|41||Tansock et al., "Force measurement with a piezoelectric cantilever in a scanning force microscope", Ulramicroscopy 42-44 (1992) 1464-1469.|
|42||*||Tansock et al., Force measurement with a piezoelectric cantilever in a scanning force microscope , Ulramicroscopy 42 44 (1992) 1464 1469.|
|43||Umeda et al., "Scanning attractive force microscope using photothermal vibration", J. Vac. Sci. Technol. B, vol. 9, No. 2, Mar./Apr. 1991, pp. 1318-1322.|
|44||*||Umeda et al., Scanning attractive force microscope using photothermal vibration , J. Vac. Sci. Technol. B, vol. 9, No. 2, Mar./Apr. 1991, pp. 1318 1322.|
|45||Umemura et al, "High resolution Images of Cell Surface Using a Tapping-Mode Atomic Force Microscope", Jpn. J. Appl. Phys. vol. 32 (1993) pp. L1711-L1714, Part 2, No. 11B, Nov. 15, 1993.|
|46||*||Umemura et al, High resolution Images of Cell Surface Using a Tapping Mode Atomic Force Microscope , Jpn. J. Appl. Phys. vol. 32 (1993) pp. L1711 L1714, Part 2, No. 11B, Nov. 15, 1993.|
|47||W. A. Ducker et al., "Force measurement using an ac atomic force microscope", J. Appl. Phys., vol. 67, No. 9, May 1, 1990, pp. 4045-4052.|
|48||*||W. A. Ducker et al., Force measurement using an ac atomic force microscope , J. Appl. Phys. , vol. 67, No. 9, May 1, 1990, pp. 4045 4052.|
|49||*||Webster s New Dictionary of Synonyms, p. 784 785 and p. 812 813.|
|50||Webster's New Dictionary of Synonyms, p. 784-785 and p. 812-813.|
|51||William A. Ducker et al., "Rapid measurement of static and dynamic surface forces", Appl. Phys. Lett, vol. 56, No. 24, Jun. 11, 1990, pp. 2408-2410.|
|52||*||William A. Ducker et al., Rapid measurement of static and dynamic surface forces , Appl. Phys. Lett, vol. 56, No. 24, Jun. 11, 1990, pp. 2408 2410.|
|Citing Patent||Filing date||Publication date||Applicant||Title|
|US6250143 *||Aug 31, 1999||Jun 26, 2001||Agere Systems Guardian Corp.||Method of mapping a surface using a probe for stylus nanoprofilometry having a non-circular cross-section|
|US6499340 *||Feb 18, 1999||Dec 31, 2002||Seiko Instruments Inc.||Scanning probe microscope and method of measuring geometry of sample surface with scanning probe microscope|
|US6518570 *||Apr 3, 1998||Feb 11, 2003||Brookhaven Science Associates||Sensing mode atomic force microscope|
|US6818891 *||Jun 9, 2000||Nov 16, 2004||Brookhaven Science Associates||Sensing mode atomic force microscope|
|US6838889||Jan 17, 2001||Jan 4, 2005||Veeco Instruments Inc.||Method and apparatus for reducing the parachuting of a probe|
|US6879152 *||Aug 30, 2002||Apr 12, 2005||Hitachi, Ltd.||Evaluation system and method of measuring a quantitative magnetic field of a magnetic material|
|US6935167||Mar 15, 2004||Aug 30, 2005||The Board Of Trustees Of The Leland Stanford Junior University||Harmonic cantilevers and imaging methods for atomic force microscopy|
|US7055378||Aug 11, 2003||Jun 6, 2006||Veeco Instruments, Inc.||System for wide frequency dynamic nanomechanical analysis|
|US7089787||Jul 8, 2004||Aug 15, 2006||Board Of Trustees Of The Leland Stanford Junior University||Torsional harmonic cantilevers for detection of high frequency force components in atomic force microscopy|
|US7095020 *||Sep 3, 2004||Aug 22, 2006||Brookhaven Science Associates||Sensing mode atomic force microscope|
|US7146034||Dec 9, 2003||Dec 5, 2006||Superpower, Inc.||Tape manufacturing system|
|US7260980 *||Mar 10, 2004||Aug 28, 2007||Adams Jesse D||Liquid cell and passivated probe for atomic force microscopy and chemical sensing|
|US7302833||Jul 11, 2006||Dec 4, 2007||The Board Of Trustees Of The Leland Stanford Junior University||Torsional harmonic cantilevers for detection of high frequency force components in atomic force microscopy|
|US7404314||Oct 23, 2007||Jul 29, 2008||The Board Of Trustees Of The Leland Stanford Junior University||Atomic force microscope using a torsional harmonic cantilever|
|US7451638||Jul 22, 2005||Nov 18, 2008||The Board Of Trustees Of The Leland Stanford Junior University||Harmonic cantilevers and imaging methods for atomic force microscopy|
|US7509844 *||May 31, 2006||Mar 31, 2009||Applied Materials, Inc.||Atomic force microscope technique for minimal tip damage|
|US7584653||May 18, 2006||Sep 8, 2009||Veeco Instruments, Inc.||System for wide frequency dynamic nanomechanical analysis|
|US7603891 *||Oct 5, 2006||Oct 20, 2009||Asylum Research Corporation||Multiple frequency atomic force microscopy|
|US7805173||Nov 15, 2006||Sep 28, 2010||Superpower, Inc.||Tape manufacturing system|
|US7963153||Dec 12, 2007||Jun 21, 2011||Applied Materials, Inc.||Non-destructive ambient dynamic mode AFM amplitude versus distance curve acquisition|
|US7975315 *||Jul 27, 2007||Jul 5, 2011||National University Corporation Kanazawa University||Atomic force microscope|
|US8024963||Jun 16, 2008||Sep 27, 2011||Asylum Research Corporation||Material property measurements using multiple frequency atomic force microscopy|
|US8387443||Sep 11, 2009||Mar 5, 2013||The Board Of Trustees Of The University Of Illinois||Microcantilever with reduced second harmonic while in contact with a surface and nano scale infrared spectrometer|
|US8448501||Oct 20, 2009||May 28, 2013||Oxford Instruments Plc||Multiple frequency atomic force microscopy|
|US8533861||Nov 23, 2011||Sep 10, 2013||The Board Of Trustees Of The University Of Illinois||Magnetic actuation and thermal cantilevers for temperature and frequency dependent atomic force microscopy|
|US8555711||Sep 23, 2011||Oct 15, 2013||Asylum Research Corporation||Material property measurements using multiple frequency atomic fore microscopy|
|US8677809||Oct 21, 2010||Mar 25, 2014||Oxford Instruments Plc||Thermal measurements using multiple frequency atomic force microscopy|
|US8719960||Jan 30, 2009||May 6, 2014||The Board Of Trustees Of The University Of Illinois||Temperature-dependent nanoscale contact potential measurement technique and device|
|US8769710 *||Nov 13, 2012||Jul 1, 2014||Agilent Technologies, Inc.||Atomic force microscope system using selective active damping|
|US8849611||Nov 26, 2008||Sep 30, 2014||Intermodulation Products Ab||Intermodulation scanning force spectroscopy|
|US8914911||Mar 14, 2013||Dec 16, 2014||The Board Of Trustees Of The University Of Illinois||Magnetic actuation and thermal cantilevers for temperature and frequency dependent atomic force microscopy|
|US8931950||Aug 20, 2009||Jan 13, 2015||The Board Of Trustees Of The University Of Illinois||Device for calorimetric measurement|
|US9069007||May 28, 2013||Jun 30, 2015||Oxford Instruments Plc||Multiple frequency atomic force microscopy|
|US9207167||Feb 10, 2015||Dec 8, 2015||Bruker Nano, Inc.||Peak force photothermal-based detection of IR nanoabsorption|
|US9291640||Feb 11, 2014||Mar 22, 2016||Bruker Nano, Inc.||Method and apparatus of using peak force tapping mode to measure physical properties of a sample|
|US9322842||May 27, 2014||Apr 26, 2016||Bruker Nano, Inc.||Method and apparatus of operating a scanning probe microscope|
|US9383388||Apr 21, 2015||Jul 5, 2016||Oxford Instruments Asylum Research, Inc||Automated atomic force microscope and the operation thereof|
|US20020093349 *||Jan 17, 2001||Jul 18, 2002||Su Quanmin C.||Method and Apparatus for Reducing the Parachuting of a Probe|
|US20030146380 *||Feb 11, 2003||Aug 7, 2003||Hough Paul V.C.||Sensing mode atomic force microscope|
|US20030214285 *||Aug 30, 2002||Nov 20, 2003||Tomokazu Shimakura||Property evaluating system and method for magnetic material|
|US20050029450 *||Sep 3, 2004||Feb 10, 2005||Hough Paul V.C.||Sensing mode atomic force microscope|
|US20050034512 *||Aug 11, 2003||Feb 17, 2005||Su Chanmin Quanmin||System for wide frequency dynamic nanomechanical analysis|
|US20050199047 *||Mar 10, 2004||Sep 15, 2005||Adams Jesse D.||Liquid cell and passivated probe for atomic force microscopy and chemical sensing|
|US20060005614 *||Jul 8, 2004||Jan 12, 2006||Board Of Trustees Of The Leland Stanford||Torsional harmonic cantilevers for detection of high frequency force components in atomic force microscopy|
|US20060236757 *||Jul 11, 2006||Oct 26, 2006||The Board Of Trustees Of The Leland Stanford Junior University||Torsional Harmonic Cantilevers For Detection Of High Frequency Force Components In Atomic Force Microscopy|
|US20060257286 *||Oct 15, 2004||Nov 16, 2006||Adams Jesse D||Self-sensing array of microcantilevers for chemical detection|
|US20060272399 *||May 18, 2006||Dec 7, 2006||Veeco Instruments, Inc.||System for wide frequency dynamic nanomechanical analysis|
|US20070093376 *||Nov 15, 2006||Apr 26, 2007||Superpower, Inc.||Tape manufacturing system|
|US20070245815 *||Oct 5, 2006||Oct 25, 2007||Proksch Roger B||Multiple frequency atomic force microscopy|
|US20070277599 *||May 31, 2006||Dec 6, 2007||Wang Chikuang C||Atomic force microscope technique for minimal tip damage|
|US20080041143 *||Oct 23, 2007||Feb 21, 2008||The Board Of Trustees Of The Leland Stanford Junior University||Atomic Force Microscope Using A Torsional Harmonic Cantilever|
|US20090013770 *||Jun 16, 2008||Jan 15, 2009||Roger Proksch||Material property measurements using multiple frequency atomic force microscopy|
|US20090139315 *||Dec 12, 2007||Jun 4, 2009||Chikuang Charles Wang||Non-destructive ambient dynamic mode afm amplitude versus distance curve acquisition|
|US20100024082 *||Jul 27, 2007||Jan 28, 2010||National University Corporation Kanazawa University||Atomic force microscope|
|US20100043107 *||Oct 20, 2009||Feb 18, 2010||Asylum Research Corporation||Multiple Frequency Atomic Force Microscopy|
|US20100312495 *||Nov 26, 2008||Dec 9, 2010||Haviland David B||Intermodulation scanning force spectroscopy|
|US20110061452 *||Sep 11, 2009||Mar 17, 2011||King William P||Microcantilever with Reduced Second Harmonic While in Contact with a Surface and Nano Scale Infrared Spectrometer|
|US20110078834 *||Jan 30, 2009||Mar 31, 2011||The Board Of Trustees Of The University Of Illinois||Temperature-Dependent Nanoscale Contact Potential Measurement Technique and Device|
|US20110154546 *||Oct 21, 2010||Jun 23, 2011||Roger Proksch||Thermal measurements using multiple frequency atomic force microscopy|
|US20140137300 *||Nov 13, 2012||May 15, 2014||Agilent Technologies, Inc.||Atomic force microscope system using selective active damping|
|WO2010065131A2||Dec 4, 2009||Jun 10, 2010||Anasys Instruments||High frequenct deflection measurement of ir absorption|
|U.S. Classification||250/234, 250/307, 977/875, 73/105, 977/881, 250/306, 977/863|
|International Classification||G01Q60/24, G01Q60/34|
|Cooperative Classification||B82Y35/00, G01Q60/34|
|European Classification||B82Y35/00, G01Q60/34|
|Oct 19, 1999||AS||Assignment|
Owner name: VEECO INSTRUMENTS INC., NEW YORK
Free format text: MERGER;ASSIGNOR:DIGITAL INSTRUMENTS, INC.;REEL/FRAME:010320/0799
Effective date: 19980529
|Sep 30, 2003||FPAY||Fee payment|
Year of fee payment: 8
|Nov 21, 2007||FPAY||Fee payment|
Year of fee payment: 12
|Sep 28, 2010||AS||Assignment|
Owner name: VEECO METROLOGY INC., CALIFORNIA
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:VEECO INSTRUMENTS INC.;REEL/FRAME:025051/0290
Effective date: 20100928
|Jun 11, 2012||AS||Assignment|
Owner name: BRUKER NANO, INC., CALIFORNIA
Free format text: CHANGE OF NAME;ASSIGNOR:VEECO METROLOGY INC.;REEL/FRAME:028350/0511
Effective date: 20101007