Willem D. van Amstel

A fast optical scanning deflectometer for measuring the topography of large silicon wafers

A compact scanning deflectometer is presented for the fast topography measurement of semiconductor wafers. The technique, however, is equally well suited for any flat or slightly curved specular reflective surface. The measurement principle is based on the 2D measurement of the local slope vector by means of a narrow Laser beam scanning rapidly across the sample surface. The fast linear scanning is combined with sample rotation to measure the complete surface of circular samples. There is no physical contact to the measured surface. The topography of the sample is derived from the slope data by a novel 2D integration method, which is robust with respect to noise in the slope signals. We present the full-size topography of unpatterned and patterned wafers of different polishing quality.

Minideflectometer for measuring optical finish quality

The principle of scanning deflectometry is presented as a simple method for measuring optical figure finish quality of odd shaped high-gloss surfaces.

Design of a compact 3D laser scanner

A design study for a compact 3D scanner, called Coplan, is presented. The Coplan is intended to be used for high speed, in-line coplanarity and shape measurement of electronic components, like Ball Grid Arrays and Surface Mount Devices. The scanner should have a scan length of at least 2 inches and a resolution of 5 micrometers in all 3 dimensions. First an analysis of two different scan schemes is made: a so-called pre-objective scheme using an F-(theta) scan lens and a post- objective scheme using a so-called banana field flattener, consisting of a convex, cylindrical hyperbolic mirror and a concave, cylindrical parabolic mirror. Secondly, an analysis of height resolution requirements for triangulation and confocal depth sensing has been made. It is concluded that for both methods of depth sensing a synchronous scheme with a 50-60 degrees detection angle in cross scan direction is required. It is shown that a post-objective scheme consisting of a banana mirror system combined with triangulation height detection offers the best solution for the optical requirements.

Two- and three-dimensional laser scanners for fast dimensional measurements and inspection

A family of high performance industrial laser scanners has been developed at Philips, based on a unique, reflective, field flattening system as an alterative for f-(Theta) scan lenses that are usually applied in laser scanners. This novel scan approach enables pure telecentric and flat field scanning of wide formats at very high resolution and speed. The attractive features of this particular scan concept are demonstrated by two different 2-D industrial inspection problems that have been solved at Philips during the last ten years.

Optical testing of long cylindrical lenses by means of scanning deflectometry

We present an extremely simple and powerful test set-up for measuring the position and the focal line straightness (lateral) and flatness (longitudinal) of cylindrical lenses, in particular of very long cylindrical lenses. Measurement results are presented for 330 mm and 650 mm long plano- convex cylindrical lenses with a focal length f approximately equals 48 mm, showing that a (lateral) straightness measurement accuracy of about +/- 1 micrometers is achieved easily with a set-up using not much more than a laser, a simple beam deflector from a barcode scanner, a PSD (position-sensitive photo diode) with associated electronics and a translation stage. A fully automated cylindrical lens test set-up version, using a PC for control and data processing will be explained. For the 330 mm long cylindrical lenses, the lateral straightness showed better than between 3 and 10 micrometers (peak to peak) and the longitudinal flatness between 20 and 80 micrometers (peak to peak) without corrective bending. It will be demonstrated that the aberration coefficients, as measured by this physical ray tracing approach, are in accordance with the results from numerical simulation by means of a commercially available ray-tracing program.

Principles of the ideal scanner model: an analytical theory of the banana mirror system

The banana mirror system is an alternative approach for the design of telecentric laser scanners with a large scan format instead of using an f-(theta) scan lens. We developed an analytical model describing the ideal banana scanner configuration, that consists of a converging beam which is deflected as a pure cone (generating a primary scan circle) and a combination of a hyperbolic and a parabolic cylindrical mirror. this model is called the Ideal Scanner Model (ISM). We will introduce the concept of conical deflection and present the basic features of the ISM theory.

Optical figure testing by scanning deflectometry

Scanning Deflectometry is a powerful method to measure optical figure quality of various optical components and systems in a simple way. This principle uses detection of slope deviations rather than optical path length variations. As an example, the design of a basic deflectometer for testing flat mirrors is presented.