Veeco Instruments Inc.

Bruker Nano Gmbh

Colin T Farrell

Erik Novak

Bryan W Guenther

Der-Shen Wan

Joanna Schmit

Mark A Schmucker

Anthony L Martinez

Michael B Krell

Jan Van Burken

Jon D Herron, Jr

A reference surface is used to develop an empirical plot between a parameter of interest, such as roughness or modulation, and the position of the reference mirror in an interferometer by repeating measurements of the reference surface at different positions of the reference mirror so as to identify the in-focus position of the reference mirror. Serial quality-control measurements of samples of interest are carried out with the reference mirror in such in-focus position until a predetermined quality-control event triggers an automated system re-calibration by re-measuring the reference surface and, if the result does not correspond to the in-focus position of the reference mirror according to the plot, by finding a new in-focus position for the reference mirror using the same plot or, alternatively, a new similarly produced plot. Sample measurements are then resumed with the mirror placed at that new position.

Automated re-focusing of interferometric reference mirror

A side camera is combined with a conventional optical metrology system to image the object during the focusing scan performed in normal focusing procedures. The camera is positioned in fixed spatial relation to the objective and with its focal plane in substantial alignment with the optical axis of the objective so as to image the object during the scan. The camera is used to monitor the illumination spot formed on the object by the beam projected through the system's objective. The in-focus position is found by moving the object such that the illumination spot coincides with the objective's focus seen through the camera.

Camera-aided focusing in optical metrology

The power input to the light source of a microscope is varied as necessary to maintain a constant degree of detector saturation as the objective is moved toward a best-focus position. Focus is found by tracking the source's intensity necessary to maintain the detector irradiance at a constant level. The in-focus position is reached when the power input (and correspondingly the intensity of the light emitted by the source) reaches a minimum. The concept can be applied in a similar manner to minimize or eliminate tilt in a sample.

Tilt minimization through intensity control of light source

Focus assist through intensity control of light source

An illumination system for an interferometer combines a white-light source and a green source with a reflective green dichroic filter. When the green source alone is energized for PSI measurements, the output of the illumination system is green only. When a white-light output is desired for VSI measurements, both sources are energized and the intensity of the green light is judiciously calibrated to match the spectral band filtered out by the dichroic mirror. Therefore, the system can switch between green and white light simply by changing the selection of energized sources, without any mechanical switching and attendant delays and vibrations. Multiple narrowband sources may be combined with white light in a similar manner.

Variable-wavelength illumination system for interferometry

The movable point source aperture used in conventional autocollimators for measuring tilt in a microscope's test sample is replaced by a fixed laser diode. The diode is turned on only for the duration of the tilt measurement, when light is delivered to the optical system of the microscope without obstruction of the normal illumination path. Similarly, the two switchable optical systems conventionally used in the metrology and tilt-measurement legs of the microscope are replaced by two permanently positioned independent imaging systems. Such optical decoupling of the two types of measurement eliminates the need for switching lens systems, which enables shorter measurement cycles, reduces mechanical vibrations, and simplifies hardware control mechanisms.

Microscope with fixed-element autocollimator for tilt adjustment

An electronic template delineating distinct selected patterns corresponding to predetermined regions of interest in a sample part is used to limit analysis to those regions. The surface of the sample is first measured using conventional techniques. The data so acquired are used to identify boundaries between distinct regions, which are then compared to a predetermined pattern boundary in the template to find a best-fit match. The position of the pattern is then shifted to overlay the match, thereby automatically aligning the template's selected patterns with the regions of interest in the sample surface. As a result, profilometric analysis can be limited to the regions of interest. Correction factors are also assigned to each selected pattern in the template to account for physical differences in the corresponding regions of interest of the sample part that affect the profilometric measurement.

Alignment and correction template for optical profilometric measurement

In the process of converting an interferogram phase map to a surface profile, in the absence of tilt, a histogram of occurrences of phase values is created from phase data. Useful data are identified in bins with contents that exceed a threshold value. Where useful data wrap around the end of the histogram, a selected amount of phase shift is added to the phase data to move them all within the ends of the histogram. Where tilt is present, the phase data are differentiated to produce slope data and a histogram of occurrences of slope values is created. A best-fit amount of tilt is determined from the slope histogram by selecting the bin at the average between two points on the histogram curve that are a predetermined percentage of the maximum height of the curve. Thereafter, the best-fit tilt is subtracted from the original phase data to eliminate tilt.

Reduced noise sensitivity method and apparatus for converting an interferogram phase map to a surface profile map

An electronic template representing the topography of a magnetic head being tested and delineating distinct patterns corresponding to particular regions of interest, such as ABS surfaces, is provided in order to limit analysis of the sample's surface to such regions. The outline of the slider positioned within the field of view of an interferometric microscope is identified by measuring the modulation of incident light at each pixel inside and outside the contour of the sample using the loci of perceivable fringe contrast as the criterion for establishing the location of such edges. Once the outline of the slider within the plastic tray is so established, the slider is shifted within the field of view to match the position of the template, thereby automatically achieving a precise alignment of the template with the boundary of the slider. In turn, the template patterns will also be aligned with the regions of interest in the magnetic head and interferometric analysis can be limited to data corresponding to the pixels contained within those patterns. Curve-fitting schemes can be used to facilitate and expedite the process of identifying the contour of the slider sample. In the case of conventional magnetic-head sliders, which are substantially rectangular in plan view, straight-line fitting between a few data points along two adjacent edges is sufficient to find the location of the edges and the corner between them, which in turn can be used is straightforward manner to align the template with the slider.

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Green Valley, AZ, United States of America

Colin T Farrell