Measuring and testing – Surface and cutting edge testing – Roughness
Reexamination Certificate
1998-12-09
2001-10-30
Noland, Thomas P. (Department: 2856)
Measuring and testing
Surface and cutting edge testing
Roughness
C073S001890, C250S306000
Reexamination Certificate
active
06308557
ABSTRACT:
CROSS-REFERENCES TO RELATED APPLICATIONS
Not Applicable.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not applicable.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a device that scans in a raster mode, particularly a raster microscope, with compensation of the disturbing effects of mechanical vibrations on the scanning process.
Devices which scan a specimen in a raster scanning process have achieved great importance in recent years, particularly in the high resolution investigation of specimens, and above all because of improved displacement devices, for example, highly accurate piezo translators, and the advancing development in the production of sensors and sensing elements which, according to the form of embodiment, receive a tunnel current or indicate the action of a force. The topography of a specimen can easily be surveyed, or locally resolved bonding conditions, for example of macromolecules, can be disclosed. Here resolutions down to the nanometer or subnanometer range are attained. For this reason, the actual resolving ability of such devices depends strongly on the external effects from the surroundings. A large role is played here by mechanical vibrations, for example, air vibrations or also bodily vibrations, which can be produced by movements of the building, for example. The disturbing motions produced in this manner, for example those of the microscope table on which the specimen is supported, can easily be of the order of several micrometers, which corresponds to a signal to noise ratio of <10
−3
. The high resolution of the devices can thus be only used when the disturbing effect is reduced by corresponding devices.
2. Discussion of Relevant Art
According to the state of the art, active or passive vibration damping or vibration insulating devices are used, for example. However, such devices are very expensive. Particularly at very low disturbing frequencies, such as can arise, for example, from vibrations of buildings, these devices moreover offer only a limited protection. In addition, such systems are extremely slow, because of their intrinsic vibration behavior.
SUMMARY OF THE INVENTION
The invention thus has as its object to provide a device, which does not have the disadvantages of the devices according to the state of the art.
This is provided surprisingly easily by means of a device according to the present invention. Accordingly, the device which scans in a raster mode includes a sensor that senses mechanical vibrations and drives a filter whose output is connected to an adder together with the output of the device for producing a signal for adjusting the distance between a specimen and a scanning sensor, wherein the output of the adder controls the device for changing the distance between the specimen and the sensor, so that the disturbing effects of mechanical vibrations on the scanning process are substantially compensated.
The financial cost for a device according to the invention, in particular for removing the disturbing effects of mechanical vibrations, is minimal in comparison with the devices according to the state of the art. Since only electrical components are used besides the sensor for sensing the mechanical vibrations, the response to external disturbances is extremely fast, and furthermore is not limited by the intrinsic vibration properties of other mechanical devices.
If the filter is adjustable and the output of the adder is connected to the control input of the filter, the output signal of the adder can be kept substantially constant over time by this feedback, by the adaptation of the filter, and thus the effect of mechanical vibrations on the scanning process can be automatically compensated. In order to separate the effect of the disturbance on the measurement signal from a real change of the measurement value because of “bringing up” another measurement point on the specimen, the adaptation or the equalization of the filter is carried out at points in time at which the displacement device is not active and the measurement process for the corresponding point on the specimen has been concluded.
In order to simplify the adaptation of the filter, the filter can be digitally constructed. The arrangement of the sensor for sensing the mechanical vibrations can be optimized for the respective construction; for example, the sensor can be installed on a microscope table on which the device is supported which scans in a raster mode, the sensor being arranged adjacent to the specimen in order to sense the mechanical vibrations. In given cases it is however also possible to arrange this sensor at a remote place, for example on the floor on which the microscope table is supported.
The sensor for sensing the mechanical vibrations can pick up the displacement and/or the acceleration of the associated vibration, according to requirements. Sensing of the acceleration makes possible a more rapid reaction of the system to the disturbance.
According to the degree of compensation required, a vibration sensor for sensing the mechanical vibrations can be extended substantially perpendicular to the plane of displacement; however, a vibration sensor can also be used which senses vibrations in three axes. This enables disturbances to be sensed which, for example, bring about a displacement of the specimen and the sensor relative to each other in the plane of displacement. This also relates in particular to disturbing vibrations which are produced by the device itself, e.g., by the displacement device which moves the sensor over the specimen, for example.
If the three outputs of the three-axis vibration sensor are respectively connected to the input of a filter, the outputs of the filters being connected to the adder, the disturbances of the measurement signal can be taken into account and compensated for all three spatial directions. If all the filters are respectively adjustable, and the output of the adder is respectively connected to the control input of the filter, the signal at the output of the adder is effectively substantially constant over time, by means of the adaptation of the individual filters, and all disturbances which are brought about by vibrations are substantially compensated.
The device according to the invention can be used for all devices which scan in the raster mode. This relates in particular to force microscopes, for example “atomic force” microscopes or “van der Waals” microscopes, and also electronic and optical scanning tunneling microscopes.
There is furthermore the possibility of modifying, according to the invention, existing devices which scan in a raster mode, or of combining the device according to the invention with mechanical vibration damping and insulating devices.
REFERENCES:
patent: 5049745 (1991-09-01), Rogen et al.
patent: 5866796 (1999-02-01), Chic et al.
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