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Monitoring the Etching of Silicon Wafers by Neutron Activation Analysis

IP.com Disclosure Number: IPCOM000096714D
Original Publication Date: 1963-Oct-01
Included in the Prior Art Database: 2005-Mar-07
Document File: 1 page(s) / 11K

Publishing Venue

IBM

Related People

Sprokel, GJ: AUTHOR

Abstract

The process of removing surface material from a silicon wafer by etching can be achieved with a high degree of accuracy. The process involves drawing off, at a desired time, an aliquot of etching solution from the bath in which the silicon wafer is immersed. Then, the aliquot is irradiated in a neutron generator along with a suitable standard for a period of from five to ten minutes. The count rates of the standard and the aliquot are obtained. From the observed count rates, the silicon removed is calculated, taking into account well-known corrections for half-life, counter dead time and background.

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Monitoring the Etching of Silicon Wafers by Neutron Activation Analysis

The process of removing surface material from a silicon wafer by etching can be achieved with a high degree of accuracy. The process involves drawing off, at a desired time, an aliquot of etching solution from the bath in which the silicon wafer is immersed. Then, the aliquot is irradiated in a neutron generator along with a suitable standard for a period of from five to ten minutes. The count rates of the standard and the aliquot are obtained. From the observed count rates, the silicon removed is calculated, taking into account well-known corrections for half- life, counter dead time and background.

The sensitivity of the method depends on the intensity of the neutron flux, the time of irradiation, the counting time and the background. Under standard laboratory conditions, 50 micrograms of silicon can be detected. This is equivalent to 10 microinches in depth being etched from a wafer having a surface area of one square centimeter. This method has rather distinct advantages. The depth of etching can be determined from the known area. Chemical separation is not necessary. The single gamma peak at 1.78 mev for the reaction of Si/28/ (n, p) Al/28/ falls well outside the background region caused mainly by the contents of the etching solution.

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