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Multiple-Reflection Corrections to the Oxygen Measurements in Rough Silicon Wafers

IP.com Disclosure Number: IPCOM000046871D
Original Publication Date: 1983-Aug-01
Included in the Prior Art Database: 2005-Feb-07
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Cadwallader, RH: AUTHOR [+3]

Abstract

The oxygen and carbon content of silicon wafers may be measured by an infrared (IR) absorption method described in the American Society for Testing Materials method ASTM F-121. Such method requires the surfaces of the wafer to be parallel and polished in order to make appropriate multiple reflection corrections arising because of the high reflectivity of silicon in air. The method transmits IR energy through the wafer, and it is difficult to separate the single-pass transmitted beam from those beams involving plural reflections. We have found that the method can be extended to a wafer having a rough surface. In such measurements, an explicit mathematical relationship exists between the extra transmission and extra reflection beams due to multiple internal reflections of silicon surfaces in a silicon wafer.

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Multiple-Reflection Corrections to the Oxygen Measurements in Rough Silicon Wafers

The oxygen and carbon content of silicon wafers may be measured by an infrared (IR) absorption method described in the American Society for Testing Materials method ASTM F-121. Such method requires the surfaces of the wafer to be parallel and polished in order to make appropriate multiple reflection corrections arising because of the high reflectivity of silicon in air. The method transmits IR energy through the wafer, and it is difficult to separate the single- pass transmitted beam from those beams involving plural reflections. We have found that the method can be extended to a wafer having a rough surface. In such measurements, an explicit mathematical relationship exists between the extra transmission and extra reflection beams due to multiple internal reflections of silicon surfaces in a silicon wafer. The extra reflection beams contain information regarding the bulk of the wafer because the beams or energy that accounts for extra reflection has to go through the wafer either twice or as multiples thereof. In accordance with this method, the transmitted energy is measured and an uncorrected oxygen determination [Oi]T (uncorr) is calculated. The reflected energy is also measured with polished surface facing the source, and the oxygen content [Oi]R is calculated from reflection spectrum. This content is then multiplied by the factor Re- t, where R = reflectivity of polished sili...