Formation of Silicon Ultra Shallow Junction by nonmelt excimer laser treatment A. Florakis, A. Papadimitriou, N. Chatzipanagiotis, and D. Tsoukalas Department of Applied Physics, School of Applied Science National Technical University of Athens Athens, Greece Mail to: anflorak@central.ntua.gr Abstract- Implementation of Plasma Doping and nanosecond laser annealing in the non-melt regime has shown to hold great promise for the realization of Ultra Shallow Junctions, designed for the sub 45nm node. This work includes extensive simulation of these two emerging techniques using the Synopsys Sentaurus Process software tool which are compared with experimental data after each process step. The results reveal consistency between simulation and experiment. It is thus concluded that existing simulation approach based mostly on Kinetic Monte- Carlo method allows for sufficient physical understanding of the underlying mechanisms for these advanced process steps. I. INTRODUCTION The continuous size decrease of Complementary metal- oxide-semiconductor (CMOS) devices puts severe limits to junction formation processes, such as implantation and thermal activation. The requirements for the upcoming generation of sub 45nm devices, regarding the critical parameters of junction depth, sheet resistance and abruptness, necessitate careful Source/Drain formation engineering. Several studies [1,2] have shown the merits of combining ultra low energy dopant implantation alongside to nanosecond laser annealing techniques able to deliver very limited thermal budget in Silicon bulk. The minimization of the induced energy leads to high level of electrical activation, while retaining the shape of dopant concentration profile. BF 3 PLAsma Doping (PLAD), stands as a promising candidate for the replacement of the conventional ultra low energy ion implanters, due it's capability to deliver ions at energies less than O.2keV and thus creating ultra shallow as implanted concentration profiles (xj<10nm). Moreover, co- implantation of Fluorine improves junction's morphological and electrical characteristics both by enhancing the electrical activation and limiting Boron diffusion [3]. However, there are some issues that should be dealt, before the introduction of plasma implantation in full production scale. Primarily, actual implanted dose is significantly lower than the nominal one. In addition, induced dopants present a wide range in terms of energy and kind of species due to the very nature of the method. Therefore the simulation of the process is vital in order to achieve the desired as implanted characteristics. On the other hand, Excimer Laser Annealing (ELA) is ideal for the formation of shallow junctions, as the delivered light energy is transformed into heat within the first layers of 978-1-4244-4353-6/09/$25.00 ©2009 IEEE N. Misra and C. Grigoropoulos Department of Mechanical Engineering University of California, Berkeley Berkeley, CA United States the lattice due to high absorption coefficient value of Silicon at this wavelength (248nm). In addition, ultra fast temperature ramp up and ramp down rates lead to annealing times significantly smaller than the characteristic times of phenomena that are associated with diffusion, such as extended defects dissolution. This work presents simulation results compared with experimental data of the three process steps involved, namely plasma doping, laser induced heating of silicon and diffusion/activation of dopants. This comparison reveals really good agreement between the two approaches, supporting a sufficient level of understanding of physical mechanisms involved. II. EXPERIMENTS AND SIMULATIONS BF 3 plasma was used for implanting boron ion in n-type silicon wafers. Nominal values of implantation energy and dose are O.4keV and 3E15cm- 2 respectively. During implantation procedure, a significant amount of damage is accumulated in the first silicon layers, while the majority of Boron atoms, are not in substitutional sites, and therefore do not contribute to conductivity. In order to recrystallize silicon and activate the dopants, a KrF Excimer laser irradiation (A=248nm, FWHM=20ns) has been performed. A variety of annealing conditions, regarding the energy fluency and the number of pulses has been implemented so as to investigate the effect of these two parameters in the activation and the kinetics of boron dopants. Irradiation has been carried out at room temperature. The use of complete homogenization array resulted in a top-hut spatial distribution of the energy over a Smmx Smm area. In order to investigate the effect of the laser annealing in dopant concentration profiles, a series of SIMS measurements were performed. A possible melting of silicon leads unavoidably to boron diffusion, as Boron diffusivity in Silicon is several orders higher in liquid phase than in solid. SIMS analysis was conducted using an IMS CAMECA instrument with an O 2 primary beam at 1.lkeV. The irradiation in every combination of energy fluency and number of pulses, have led to profile movement not more than 2nm. As the junction depth Xj of the as implanted sample is 13nm, irradiations resulted in the formation of highly abrupt (2.4 nm/decade) and ultra shallow (xj=15nm) junctions. The morphological characterization of