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Optoelectronic Determination of Insulator Thickness

IP.com Disclosure Number: IPCOM000080648D
Original Publication Date: 1974-Jan-01
Included in the Prior Art Database: 2005-Feb-27
Document File: 2 page(s) / 28K

Publishing Venue

IBM

Related People

Patrin, NA: AUTHOR

Abstract

This is an electrical test site for a silicon wafer, for determining and monitoring the insulator thickness on post metal wafers in an opto-electronic fashion.

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Optoelectronic Determination of Insulator Thickness

This is an electrical test site for a silicon wafer, for determining and monitoring the insulator thickness on post metal wafers in an opto-electronic fashion.

Conventional ellipsometric insulator thickness measurements rely on the optical detection of extrema in the wavelength dependent reflection coefficient of oxidized semiconductor surfaces. For all conventional oxide thicknesses used in silicon device processing, the transmission of light into the silicon is related to the reflection coefficient of the oxide. By incorporating a simple electrical test site such as the one shown in the figure, insulator thicknesses can be determined opto-electronically.

The individual photodetector arranged in the array consists of an N+ diffusion 10 made in the form of a ring in a P-type substrate 11. Overlying the substrate 11 and the ring 10 is an oxide layer 12 and a metallic ring 13 aligned over the diffused ring 10. Electrical contact is made to the diffused ring 10 and to the substrate 11 to properly bias the diffused ring, and to electrically measure the photocurrent and thereby determine the maxima and minima, while the wavelength of the light that is permitted to enter the silicon substrate is varied. Since the maxima and minima wavelengths of the light introduced into the body are known functions of insulator thickness, the insulator thickness can be readily determined from the determination of photocurrent maxima...