Tencor Instruments

Electro Scan, Inc.

Metrologix, Inc.

Philip R Rigg

Mehrdad Nikoonahad

Kevin M Monahan

Keith B Wells

Guillermo L Toro-Lira

Alan H Achilles

Nolan V Frederick

Neil Baumgarten

David S Calhoun

The position detector has a sensitivity characteristic graded along a direction transverse to the surface, so that the output of the position detector is used to determine a height of the surface. A surface height detection and positioning device for use in a surface inspection system. An incident beam of light impinges obliquely upon the surface, and a position detector is disposed to receive specularly reflected light, producing a plurality of electrical signals, with a mechanical window, defining an aperture, placed in front of the detector. The aperture's width, along the scan direction, is of sufficient size so as to create a train of signals from each of the plurality of electrical signals, having a frequency equal to the scan frequency. These electrical signals carry information responsive to both the position of reflected beam impinging on the detector and the beam's intensity and are, in turn, related to a height of the surface. To abrogate information responsive to intensity variations at the position sensitive detector, an electronic circuit is employed which determines the sum and the difference of the plurality of signals relating to wafer height and beam intensity, producing a summed signal and a difference signal respectively. The difference signal is then divided by the summed signal, thereby producing a normalized signal which represents the height of the wafer surface without regards to these reflected beam intensity variations. These signals are synchronized to the scan frequency which facilitates removing unwanted signals resulting from thermal drifts and ambient light.

Optical wafer positioning system

Improved techniques for imaging high-aspect-ratio structures such as contact holes utilize two signal detection sub-systems, one optimized for imaging at the top and another optimized for imaging at the base of submicrometer structures. These detection systems produce signals that can be combined in real-time to produce an image which resembles the 'extended focus' images obtained with confocal optical microscopes. Unlike the confocal image, however, the resulting image has the inherent linearity and resolution characteristics of electron-beam technology. Using the new approach, the signal, rather than exhibiting a near-zero minimum at the base of the structure as is typical of the prior art, exhibits its maximum at the base of the structure, allowing high-precision measurement with no need for extrapolation.

Detection system for precision measurements and high resolution

An apparatus and method for continuously improving the signal-to-noise ratio of a stationary video image by digital integration, without the loss of signal amplitude incurred by conventional designs. The apparatus includes a sampling analog-to-digital converter for digitizing an input video signal frame which is supplied to a calculating device along with a preceding video signal frame supplied from the output of the calculating device through a memory device. These features, in conjunction with other digital logic components, form a digital recusive filter. The calculating device sums new and previously stored data for each pixel in amounts scaled to counteract the loss of signal range that occurs as the random-noise component averages to zero. By appropriate selection of operating parameters, the method can be used to maintain or even boost the amplitude of a video signal while simultaneously enhancing its signal-to-noise ratio.

Apparatus and method for improving the signal-to-noise ratio of video

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Saratoga, CA, United States of America

Philip R Rigg