Radiant energy – Photocells; circuits and apparatus – With circuit for evaluating a web – strand – strip – or sheet
Patent
1997-09-17
1999-06-08
Westin, Edward P.
Radiant energy
Photocells; circuits and apparatus
With circuit for evaluating a web, strand, strip, or sheet
356376, G01B 1124
Patent
active
059106603
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a device and a method for defining three-dimensional structures having submicrometer sizes. Structures in the submicrometer range are generally measured, for example, using scanning microscopes, wherein the object to be measured is moved through a servo device and the surface structure of the object being measured is scanned using a precision probe tip. The precision probes used in such methods are frequently damaged, resulting in undesirable interruptions in operation. In addition, the forces exerted by the precision probe on the surface of the object range from 0.1.times.10.sup.-9 to 1.0.times.10.sup.-9 newtons. Even these slight forces can result in a shift in positions on the object being measured.
Thus, there is a need for a method and a device that will not require a mechanical element to scan the surface of the object being measured.
SUMMARY OF THE INVENTION
In accordance with the invention, a device and method for defining a three-dimensional structure of an object having a submicrometer size splits a coherent electromagnetic radiation beam into two partial beams including a first partial beam and a second partial beam. The first partial beam is focused on the object. The wavelength of the radiation beam is preferably equal to a focal diameter of the object. The first partial beam is reflected from or dispersed from the object to yield a first radiation directed toward a locus. The second partial beam is directed toward the locus. The first radiation and the second radiation form an electromagnetic combination in a region of the locus. The positions of the partial beams are displaced relative to detectors associated with the locus to obtain radiation intensity values and initial phase values for a group of different coordinates of loci. Second phase values are established from the initial phase values via multiplication of the initial phase values by one or more predetermined values to provide information for generating a magnified image representative of the object.
The method and the device of the present invention produce improved resolution in comparison with optical microscopes limited by optical diffraction. In comparison to mechanical probing, the method and device of the invention reduces downtime in scanning operations by eliminating the need to replace mechanical probe tips, which are often particularly susceptible to damage.
An object is irradiated by two partial beams at different positions. The object is defined through an analysis of spatial and temporal complex amplitudes (intensity and phase angle distribution) proceeding from the object.
The concept of different beam positions for the two partial beams is understood to mean positions which generate different radiation fields created by superimposing the two partial beams at the locus of the detectors in the detector field. The phase angles of these various radiation fields differ at one and the same detector locus by different fractions of a complete wave oscillation. Thus, from preferably at least 3 measurements taken at one and the same locus, the amplitude and phase of the superimposed field can be positively determined. Since one of the partial beams comes from the object being measured, the measured, superimposed radiation field contains the information on the structure of the object.
As described in detail below, different beam positions can be generated, for example, within one beat cycle of a beat frequency state for the two partial beams which exhibit slightly different radiation frequencies. Of course, one partial beam may also be slowed down with regard to the other by a desired fraction of a wavelength, and its beam configuration may be modified. Such a deceleration of the partial beam can, for example, be effected using electro-optical, acoustic-optical, magneto-optical components, mechanical phase shifting elements, etc.
At least three measurements are preferably taken per locus for phase determination. It is possible, however, to proceed with fewer measurements
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"Fringe Multiplication Methods For Digital Interferometric Fringes", Applied Optics, Oct. 1989, vol. 28, No. 20, pp. 4323-4327.
"Digital Holography--A New Method Of Laser Metrology", Laser Und Optoelektronik, Oct. 1994, vol. 26, No. 5, pp. 40-45.
"Real-Time Two-Dimensional Surface Profile Measurement In A Sinusoidal Phase-Modulating Laser Diode Interferometer", Optical Engineering, Aug. 1994, vol. 33, No. 8, pp. 2754-2758.
Hodel Walter
Romano Valerio
Weber Heinz Paul
Heinz Paul Weber
Pyo Kevin
Westin Edward P.
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