Activation trends in millisecond annealing of heavy n-type doping of silicon

Abstract

CMOS scaling is increasingly being hindered by the rapid rise in the transistor's parasitic resistance as the source/drain (s/d) contact area is reduced. Increased dopant activation at the s/d is essential for reducing the contact resistivity but is limited by solid solubility, electrical deactivation, segregation at interfaces and by temperature limits imposed by process integration requirements. A recent study of millisecond annealing (MSA) of high-dose ion implants of As and P in preamorphized Si suggests paths for electrical activation improvements even for peak temperatures <1200°C. However, in anneals where the temperature varies rapidly throughout the heating cycle it can be difficult to identify which parts of the heating profile should be optimized. This paper identifies ways to assess the importance of different aspects of the heating cycle. The analysis reveals significant differences in the factors affecting high-dose As and P activation. For high-dose P samples the pulsed heating plays the dominant role in activation, whereas for As the thermal exposure during the isothermal cooling immediately after the pulse is more important.