Effect of Fluorine Co-Implant on Boron Diffusion in Germanium Preamorphized Silicon During Post-LSA Rapid Thermal Annealing

Fluorine co-implant has been shown to reduce boron transient enhanced diffusion and deactivation when coupled with conventional spike rapid thermal anneals (RTA). For ultrashallow junction formation beyond the 45 nm technology node, non-melt laser spike anneal (LSA) is a promising diffusion-less annealing candidate. In this paper, the effect of fluorine co-implant on boron diffusion during LSA and the subsequent post-LSA thermal budget is evaluated. Silicon wafers were implanted with germanium, fluorine, and subsequently boron ions. Non-melt LSA was carried out at a temperature range from 1150 to 1350°C, followed by RTA at 825°C for 30 s. Secondary ion mass spectrometry confirms that in the presence of fluorine, retarded boron diffusion is observed at LSA temperatures below 1250^°C. As the LSA temperature is increased or when a subsequent soak RTA is carried out, enhanced boron diffusion is observed. The reduced boron diffusivity at LSA temperatures below 1250°C is attributed to the efficient capture of interstitials released from the end-of-range defects by fluorine-vacancy clusters during the millisecond anneal. As the thermal budget is increased, excess interstitials caused by the fluorine implant are released, thus increasing the boron diffusion.

I. Introduction

The semiconductor industry relies mainly on the continuous reduction of the complementary metal-oxide-semiconductor dimensions to achieve a constant improvement of silicon-based device performance. Dopant implantation in amorphized silicon (-Si), obtained by means of a preamorphization implant (PAI), aids in ultrashallow junction formation via the reduction in the dopant channeling tails [1]. Unfortunately, PAI causes the formation of a damaged layer, known as the end-of-range (EOR) region, super-saturated in excess interstitials, beyond the amorphous-crystalline interface. Annealing is therefore required to recrystallize the -Si and to electrically activate the dopant. Depending on the PAI recipe and annealing, these defects can release a huge amount of interstitials, resulting in boron transient enhanced diffusion (TED) [2].