Exploring the limits of pre-amorphization implants on controlling channeling and diffusion of low energy B implants and ultra shallow junction formation

Reducing channeling of B implants and transient enhanced diffusion (TED) is very critical for the formation of ultra shallow junctions required for deep sub-micron devices. As the ion energy required for junction formation is reduced (<5 keV) due to device shrinking, the use of high tilt angle (typically 7-10 deg) becomes ineffective in suppressing channeling. The formation of a thin amorphous layer close to the surface prior to B implant has shown to be very efficient in eliminating channeling. Such layers can be formed using a Ge⁺ implant, and the thickness of the amorphous layers can be varied with Ge ⁺ ion energy and dose. In addition if optimized, Ge⁺ pre-amorphization implants (PAI) can also minimize the TED of B by reducing the concentration of point defects generated by B implants. However, a Ge PAI itself introduces point defects and can result in TED with sub keV B implants. This paper explores the limits and optimized conditions of Ge PAI prior to low energy B implants (=1 keV) for the formation of junctions for deep sub-quarter micron devices