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Impurity Profiling by Chemical Techniques

IP.com Disclosure Number: IPCOM000074872D
Original Publication Date: 1971-Jun-01
Included in the Prior Art Database: 2005-Feb-23
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Reuter, J: AUTHOR [+2]

Abstract

This technique can be used to obtain impurity profiles in silicon or other semiconductor materials.

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Impurity Profiling by Chemical Techniques

This technique can be used to obtain impurity profiles in silicon or other semiconductor materials.

Knowing the impurity profile for device studies is very important. For P and As, radio tracer techniques are used for total concentration profiling in semiconductors. For boron, radio tracer techniques are impractical. Incremental sheet resistance techniques for most concentrations deviate from the true dopant concentrations, hence cannot be used for total impurity profiling.

In this method, a measured area of a doped wafer to be profiled is anodically oxidized to a calculated oxide thickness. The oxide on the wafer is then dissolved in a measured amount of hydrofluoric acid solution having a PH in the range of 1 to 2.5. A complexing agent, as for example methylene blue, is then added to the solution. The complexing agent forms a colored complex ion with the boron which is capable of absorbing ultra-violet radiation. The solution containing the complex ion is then extracted with a suitable extracting solvent, as for example 1-2 dichloroethane, which separates the complexed boron ions from the remaining solution, including the excess methylene blue. The ultraviolet absorption of the extracted solution at approximately .660Mu is then measured on a spectrophotometer. Use of an absorption calibration chart reveals the molar concentration of the complexed ion in the extracted solution. Thus, knowing the volume of the silicon whi...