Novel methods for low resistance ultra-shallow junction formation.

摘要

Source Drain parasitic resistance is expected to become one of the major roadblocks to the continued improvements of device performance. Going by the ITRS roadmap, the source drain parasitic resistance is expected to become as much as 26% of the intrinsic device resistance by the 45 nm technology node. As the active concentration in current junctions is approaching the electrical solubility limits, it is unlikely that the current method of junction formation will be able to provide the low resistance junctions required for future technology nodes. It is clear that new annealing techniques that yield active concentrations well above the solubility limit are needed to allow continued scaling of MOS devices.; In the first half of my thesis, I will present a new method to obtain B active concentrations above the electrical solubility limits. We show that the boron activation obtained after SPER increases with the temperature at which the regrowth is carried out. Further, by carrying out the regrowth at a high temperature it is possible to obtain active concentrations as high 6.5 x 1020/cm3---which is well above the solubility limits of B in silicon. Subsequent anneals that reduce the leakage current without significant deactivation or diffusion are presented. Finally, we observed that the active B is stable through back end thermal budgets.; Pulsed laser annealing is another technique that can give active concentrations well above the solubility limits. The main drawback to junction formation using this method is that light interacts with the patterned surface resulting in (among other effects) the melting and deforming of the poly gate the S/D regions melt. The latter part of my thesis presents a new technique that uses selective absorption to selectively melt the source drain regions without melting the poly gate. Possible solutions to other issues are also discussed. With the increased importance of SiGe as the source-drain material, we also study the stability of various dopants activated using pulsed laser annealing as a function of the germanium fraction.