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Determination of Boron Concentrations in Silicon

IP.com Disclosure Number: IPCOM000078116D
Original Publication Date: 1972-Nov-01
Included in the Prior Art Database: 2005-Feb-25
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Ziegler, JF: AUTHOR

Abstract

Boron is a commonly used impurity used to dope silicon when manufacturing semiconductor devices. It is possible to profile boron concentration using electrical characteristics, but the concentration obtained is not that of the total distribution, but only that of the electrically active boron. In many device fabrication processes this is not adequate. For example, for boron doped epitaxy layers, the final electrically active boron concentration may be more dependent on the final temperature cycle, than on the absolute amount of boron present. This is because a significant fraction of the boron may be made nonsubstitutional by an incorrect temperature cycle.

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Determination of Boron Concentrations in Silicon

Boron is a commonly used impurity used to dope silicon when manufacturing semiconductor devices. It is possible to profile boron concentration using electrical characteristics, but the concentration obtained is not that of the total distribution, but only that of the electrically active boron. In many device fabrication processes this is not adequate. For example, for boron doped epitaxy layers, the final electrically active boron concentration may be more dependent on the final temperature cycle, than on the absolute amount of boron present. This is because a significant fraction of the boron may be made nonsubstitutional by an incorrect temperature cycle.

A nuclear reaction comprising the following is used to determine boron concentration: B/10/ + n-- He/4/ (1.MeV) +Li/7/ (0.8 MeV).

The sample containing boron impurities is placed in a beam of thermal neutrons. The neutrons react with the boron and produce highly energetic ions of He/4/ and Li . These are detected and their energy measured.

Since the ions will lose a bit of their energy coming out of the sample, this energy loss will determine the depth in the sample where the ion originated. Since the reaction cross section of B/10/ + n is known, the total number of ions detected can be converted to boron concentration.

The method is a noncontact method which is nondestructive. This is so, because only about 10/6/ of the boron atoms actually react with the beam,...