Transistor with highly uniform threshold voltage

Abstract

Embodiments of the present invention relate to processes utilized in the manufacturing of a semiconductor device having transistors to achieve high uniformity of threshold voltages. The invention does so by ensuring high uniformity of impurity concentration in the substrate. In one embodiment, a method for manufacturing a semiconductor device having transistors with high uniformity of threshold voltages comprises providing a substrate and a source of impurities, and disposing the substrate and the source of impurities in a first oxygen gas at a first initial temperature and heated to a first target temperature at a first temperature rate to drive the impurities into the substrate. The first initial temperature is sufficiently low to prevent the oxygen from diffusing into the substrate. The substrate is disposed in a second oxygen gas at a second initial temperature and heated to a second target temperature at a second rate to form an oxide layer on the substrate. The second rate is high enough for rapid formation of the oxide layer on the substrate so as to prevent the impurities driven into the substrate from diffusing out from the substrate.