Deactivation of non-melt laser annealed boron ultra-shallow junctions.

The demand for faster, smaller and cheaper electronic devices such as mobile phones and mp3 players, together with Moore's law, are the driving forces behind the miniaturisation of transistors in silicon-based processors and memory. As the aggressive downscaling of the transistors continues, stringent requirements are placed on the most difficult parts of the transistor to fabricate: the source/drain extension regions, which are required to be ultra-shallow and highly-active. Today, the most common technique to produce these regions is to pre-amorphise the surface region with a relatively high mass ion, typically germanium, and then implant low energy boron into the amorphous region. During subsequent annealing, solid phase epitaxial re-growth transforms this region back to its original crystalline structure, with the boron incorporated substitutionally. However, excess silicon interstitials remaining just beyond the original amorphous/crystalline interface position condense into clusters which evolve into extended defects known as End of Range (EOR) defects. During annealing, silicon interstitials are released from the EOR defects and their coupling with boron leads to Transient Enhanced Diffusion (TED) and Boron-Interstitial Cluster (BIC) formation. These processes, in turn, lead to increased junction depth and reduced dopant electrical activation respectively. In addition, any defects that remain in the sample provide current leakage paths through the junction that degrades transistor performance. Therefore novel techniques in transistor fabrication are needed to overcome these problems. Laser annealing is one such technique where the very high temperature for a very short time gives an advantage over conventional rapid thermal annealing in terms of a shallower junction depth and higher boron electrical activation. This thesis investigates the use of a scanning non-melt laser to anneal boron implanted into germanium pre-amorphised silicon to form ultra-shallow junctions for future transistors. It is demonstrated that ultra-shallow junctions (~16nm) are formed that are highly active (~6x10 20 cm-3). The deactivation and diffusion during post-laser rapid thermal annealing due to excess silicon interstitials being released from EOR defects can be minimised by optimising the laser annealing conditions resulting in a thermally stable ultra-shallow junction. Furthermore by optimising the germanium pre-amorphising implant, EOR defects can be eliminated by the laser annealing