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Proceedings Paper

Optical Profilometer For Monitoring Surface Contours Of Si Power Devices
Author(s): H. P. Kleinknecht; H. Meier
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Paper Abstract

The fabrication of power transistors and thyristors involves the etching of deep grooves (30-100μm) into the Si wafers. These grooves separate electrically the individual devices from one another, and they are the site where the high collector field meets the surface and where the passivating glass and oxide layers have to be applied. Therefore, the groove depth has to be monitored and controlled in manufacturing to ∓5%. Since the dimensions are large compared to the wavelength of light, and since the surfaces can be rough (etch pits) the usual interference techniques can not be used. The light section microscope technique, used up to now, is slow, inaccurate and operator dependent. We describe an optical profilometer essentially consisting of a high-power microscope equipped with a laser attachment which automatically steers and holds the microscope focussed to the sample surface. The automatic focussing uses the beam of a He-Ne laser, which is coupled into the microscope by beam splitters and goes through the objective lens to form a fine spot (0.5)μm) on the sample surface. From there it is reflected back through the objective and projected into a focus outside the microscope. The position of this focus is a function of the sample surface height, and it is sensed by an arrangement of apertures and photodiodes, which drive a feedback servo-motor for microscope focussing. An electronic depth gauge (LVDT) resting on the shoulder of the microscope measures the vertical excursions of the microscope, which follow the sample contour. This instrument is fast, accurate (+ lμm) with a range of well over 100 humand can be connected directly to a data terminal.

Paper Details

Date Published: 26 October 1983
PDF: 8 pages
Proc. SPIE 0398, Industrial Applications of Laser Technology, (26 October 1983); doi: 10.1117/12.935386
Show Author Affiliations
H. P. Kleinknecht, Laboratories RCA Ltd. (Switzerland)
H. Meier, Laboratories RCA Ltd. (Switzerland)

Published in SPIE Proceedings Vol. 0398:
Industrial Applications of Laser Technology
William F. Fagan, Editor(s)

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