Measuring and testing – Surface and cutting edge testing – Roughness
Reexamination Certificate
2001-08-08
2004-08-17
Noland, Thomas P. (Department: 2856)
Measuring and testing
Surface and cutting edge testing
Roughness
C702S168000, C702S189000
Reexamination Certificate
active
06776030
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to measuring technique, in particular, to scanning probe microscopy (SPM), in particular, to atomic force microscopy (AFM), to means of topography control and surface properties of samples with the help of scanning probe microscope, and it can be used for receiving of spatial distributions of surface properties and layers, placed on it. In AFM for investigation of sample's surface interaction forces between surface and probe, which is placed very closely to surface (~1 nm) or right on it, are measured. Upon that electric and magnetic forces, besides forces of interatomic interaction, can be registered both in AFM-microscopy and in the applied method.
The highest resolution is achieved upon surface scanning, however, the result is affected by variable friction coefficient owing to tangent slip, by abrasion of probe (the probe can be simply damaged during collision with unevenness, for instance, with walls of surface grooves) and by other factors, caused by constant contact. Besides, friction force hampers probe's movement frequently, bringing in sufficient error, and surface layer is destroyed within scanning process. And finally, adhesion forces bring in sufficient error, holding probe down to surface, increasing friction force upon that, and additionally deforming sample's surface.
An attempt to get over this drawback was done in non-contact vibration methods of microscopy. So noncontact vibration method of information collection and processing is known in scanning probe microscopy, including setting probe, placed at free end of spring console—cantilever, in oscillation by harmonic signal at a frequency of mechanical resonance, maintenance of average distance between probe and surface to be constant and registration of probe coordinates without harmonic component (see EP No0574234, G01B21/30, 1993). The amplitude of probe oscillation changes upon approach of probe to the surface under investigation, consequently their interaction. A tracking system maintains average distance between probe and surface to be constant during scanning process above site under investigation, so that amplitude of probe oscillations is kept equal to predetermined magnitude. As a result, trajectory of probe displacement, disregarding harmonic component, repeats surface's topography, so the coordinates of this trajectory draw up an image of surface under investigation.
Also vibration method of information collection in scanning probe microscopy is known, including setting probe, placed at a free end of cantilever, in oscillation by harmonic signal at a frequency, differing from frequency of mechanical resonance, maintenance of average distance between probe and surface to be constant and registration of probe coordinates without taking into account harmonic component of oscillation phase of cantilever (U.S. Pat. No. W5406832, G01B5/00, 1995). Upon that, average trajectory of probe displacement repeats surface's topography, and map of change of signal phase indirectly characterizes distribution of its properties, as measured shift of phase is none other than a time, when probe is in contact with surface at every point under investigation. This time depends on the magnitude of local adhesion force in appropriate point. Thus the result of use of this kind of information collection is a map, providing distribution of local adhesion force in each point of investigated surface.
Drawbacks of vibration methods are low resolution and indirect character of surface parameters' determination, which result in insufficient accuracy and reliability of received data. Moreover, vibration methods do not enable to separate information about properties of surface layers and sample's surface itself, about its different parameters (owing to ambiguous understanding of reasons of shift of registered parameters); and signal conversions used within their realizabon (for instance, within figuring out of adhesion force using results of phase measurement) and tracking systems (that provide constancy of amplitude) introduce additional errors into final result.
Also a “jumping” method of scanning probe microscopy is known, including measurement of probe coordinates during the process of its approach to sample and move apart of sample and probe with subsequent topography imaging according to measured magnitudes of coordinates in reverse point, moreover the approach is carried out before achievement of constant interaction force: feedback circuit is used for this purpose (see EP No 0584440, G01B7/34, 1993). The information about topography is recorded and used within a generation of probe trajectory during the process of surface scanning; that gives possibility to increase capacity of the method and, at the same time, to exclude undesirable tangent slip of probe on surface. However, this method is not enough informative, as it does not enable to get properties distribution on sample's surface, image of layers, placed on surface. The known method has also high level of error, as it does not consider, that probe deforms surface owing to adhesion force, caused by surface layers and surface heterogeneity. Neglected deformation can depend on properties, distribution, thickness of surface layers, and on variation of properties of surface itself.
Method of information collection and processing within surface scanning is known from U.S. Pat. No. 5,418,363, G01B21/30, 1995. Accumulated data about topography in this method are used for accurate assignment of height of probe disposition above surface and for carrying out of independent electric and magnetic measurement during repeated scanning.
However, error component is not excluded from this method, which is caused by the fact, that information about topography and properties of surface is independently read, moreover topography data are influenced by parameters, characterizing physical properties of next to surface layers and surface contamination. Moreover, information about influence of sample's surface and layers, placed on it, can not be separated in that method.
Method A method of two-parameter control of a sample, is known including the noting of sample coordinate at the moment of achievement of predetermined magnitude of interaction force between sample's surface and probe during the process of surface scanning in order to draw up relief, as well as figuring out of adhesion at one point of surface using force curve, which is read in the conditions of contact between probe and sample, and distribution of the received magnitude of adhesion for all the points of surface.
Evidently, the above mentioned error component drops down upon this, but it is not excluded, and poor reliability of results due to some shifts of adhesion force, caused by heterogeneity of surface properties and shift of thickness of surface layers, really takes place.
The closest prior art to the applied method is method of information collection and processing of sample's surface, including approach of sample and probe, placed on cantilever, before achievement of predetermined magnitude of interaction force of sample's surface and probe before scanning, then noting of topography (of Z-coordinate) in each scanning point upon constant interaction force of sample and probe, reading of force curve portion within the process of instant contact of sample and probe and their subsequent short duration move apart (feedback circuit, retaining interaction force between sample and probe to be constant, is switched off during reading of force curve), storage of force curve and, according to it, determination of adhesion force in a predetermined point, stop for renewal of predetermined magnitude of interaction force between sample and probe and passing to the next point of surface (see U.S. Pat. No. 5,477,732, G01B21/30, 1995). Thus, measurement in each point of this method is carried out within two stages: at first topography is determined, when probe and sample are immobile, in fixed position at the beginning, then inte
Dremov Vjacheslav Vsevolodovich
Kirpichnikov Aleksei Petrovich
Molchanov Sergei Petrovich
Jacobson & Holman PLLC
Noland Thomas P.
Zakrytoye aktsionernoye obschestvo “Autex Ltd”
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