Advanced front-end processes for the 45 nm CMOS technology node

Abstract

The process development focus for 45 nm technology node is very firmly on the transistor and substrate. Formation of ultra-shallow, abrupt and well-activated extension regions remains one of the challenges. For p-type metal oxide semiconductor (PMOS) transistors, co-implantation of fluorine and boron in a pre-amorphised substrate can significantly improve the activation, abruptness and junction depth. Here, we show results of an optimisation study of both F and Ge energies, and of F dose. The process window for optimisation was found to be reasonably large. For n-type metal oxide semiconductor (NMOS) transistor, antimony has been investigated as an option for source/drain extension formation. This study shows that a 1 × 10 15 cm −2, 5 keV antimony (Sb) implant under solid phase epitaxial regrowth conditions can meet the 45 nm node requirements. The damage evolution has also been studied in detail using medium energy ion mass spectroscopy (MEIS). On the anneal side, we report an optimisation study of Ge pre-amorphisation energies and doses for a 1 × 10 15 cm −2, 500 eV B implant using a scanning laser millisecond anneal technique and show that under the right conditions one can get very close to the 45 nm node requirements. Full melt laser thermal processing (LTP) is another option to achieve the required junctions. The activation, diffusion and de-activation behaviour of Sb under LTP conditions has been investigated. The effects of LTP on silicon-on-insulators (SOI) wafers have also been investigated for low energy arsenic implants. It was found that careful optimisation is required due to the different thermal response of the SOI substrate compared to bulk. Ultra-shallow junction formation on SOI wafers was further investigated for low energy boron implants (200 eV–5 keV) into different SOI thicknesses and an initial comparison between B and BF 2 implants was performed. The regrowth rate of amorphous layers in bulk and SOI was measured as a function of B implant dose for 500 eV B implants.