Sub-quarter-micrometer gate-length p-channel MOSFETs with shallow boron counter-doped layer fabricated using channel preamorphization

A technique for forming shallow boron-doped layers for channel doping using preamorphization (channel preamorphization) is described. An extremely shallow boron-doped layer for shallow channel doping has been formed using preamorphization and rapid thermal annealing. Boron peak concentration around the surface is 3.5×10¹⁸ cm ^-3, and the depth at which the boron concentration becomes 10 ¹⁷ cm^-3 is 450 Å. In contrast, the depth is as large as 900 Å for nonpreamorphized samples. It is found that the shallow boron-doped layer formation is made possible because enhanced diffusion arising from ion implantation damage as well as the channeling in boron ion implantation is suppressed by preamorphization. It is also found that preamorphization does not affect MOS capacitor characteristics so long as the amorphous/crystalline interface is sufficiently deep, which allows that channel preamorphization is readily applicable to channel doping in MOSFET fabrication. To substantiate the experimental results, buried-channel p-MOSFETs with a shallow boron counterdoped layer using channel preamorphization have been successfully fabricated. Channel preamorphization did not degrade carrier mobility and improved MOSFET characteristics in the sub-quarter-micrometer-gate-length region suppressing short-channel effects due to the shallower counterdoped boron profile. High-performance 0.2-μm-gate-length p-MOSFETs with good subthreshold characteristics have been fabricated