Adjusting of a non-silicon fraction in a semiconductor alloy during transistor fabrication by an intermediate oxidation process

Abstract

The concentration of a non-silicon species in a semiconductor alloy, such as a silicon/germanium alloy, may be increased after a selective epitaxial growth process by oxidizing a portion of the semiconductor alloy and removing the oxidized portion. During the oxidation, preferably the silicon species may react to form a silicon dioxide material while the germanium species may be driven into the remaining semiconductor alloy, thereby increasing the concentration thereof. Consequently, the threshold adjustment of sophisticated transistors may be accomplished with enhanced process uniformity on the basis of a given parameter setting for the epitaxial growth process while nevertheless providing a high degree of flexibility in adjusting the composition of the threshold adjusting material. In other cases, in addition to or alternatively to forming a threshold adjusting semiconductor alloy, a strain-inducing semiconductor alloy may also be provided with enhanced flexibility using the above-described process sequence.