Optimization of Vth roll-off in MOSFET's with advanced channel architecture -: Retrograde doping and pockets

Device optimization in the case of retrograde channel profiles (RCP) and pockets is a very complex task, which also implies some particularities in the V-th-L behavior, unusual when using uniform doping. The more difficult and inefficient may be in this case an optimization based on random cut-and-try experiments or that based on comprehension-lacking simulation. The analysis presented in this paper is based on a simple but exhaustive analytical model, Thanks to that we were able to thoroughly explain the physics behind the retrograde profiles and pockets, We have found some very interesting features as for example the existence of the optimal doping and peak position of RCP, minimizing the roll-off, In the case of pockets we have discovered the existence of an ideal, asymptotic V-th-L curve (dependent only on the amount of roll-up one wishes to allow) and have shown how to chose the pocket implantation conditions in order to follow the ideal curve to the shortest channel lengths. Finally, the model and the acquired know-how are demonstrated experimentally to give excellent improvements when applied to optimization of an 0.15 mu m technology.