Papers by Author: Wilfried Lerch

Abstract: This paper reviews the physics and the potential application of ion-implanted vacancies for high-performance B-doped ultra-shallow junctions. By treatment of silicon films with vacancygenerating implants prior to boron implantation, electrically active boron concentrations approaching 1021 cm-3 can be achieved by Rapid Thermal Annealing at low temperatures, without the use of preamorphisation. Source/drain (S/D) junctions formed by advanced vacancy engineering implants (VEI) are activated far above solubility. Furthermore, in the case of appropriately engineered thin silicon films, this activation is stable with respect to deactivation and the doping profile is practically diffusionless. Sheet resistance Rs is predicted to stay almost constant with decreasing junction depth Xj, thus potentially outperforming other S/D engineering approaches at the ‘32 nm node’ and beyond.

Abstract: In this contribution we illustrate some important features of the development of models for the simulation of advanced annealing processes. Taking arsenic as example we discuss the challenges that the last technology trends represent for process modeling. Issues like shallow implants, high doses, low total thermal budgets, and steep temperature profiles are discussed, highlighting the physical phenomena to take into account, and how to design models that reproduce them. We also discuss with examples how important are the critical evaluation of known parameters and established approaches, and the extraction of parameters from experiments. Finally we show some applications of our model for spike and flash annealing of arsenic implants.

Abstract: In this paper, we investigate the evolution of extended defects during a millisecond Flash anneal after a preamorphising implant. The experimental results, supported by predictive simulations, indicate that during the ultra-fast temperature ramp-up and rump-down occurring in a millisecond Flash anneal, the basic mechanisms that control the growth and evolution of extended defects are not modified with respect to the relatively slower annealing processes, such as “soak” and “spike” Rapid Thermal Annealing. In addition, we have observed a decrease in the number of trapped interstitials in the End-Of-Range (EOR) defects when decreasing the Ge+ amorphisation energy from 30 keV down to 2 keV. This result is ascribed to two concomitant phenomena: (i) the increase of the initial number of interstitials, Ni, created by the amorphisation step, when the implant energy is decreased and (ii) the efficient interstitial annihilation at the silicon surface, whose recombination length, Lsurf, is in the nanometer range even at the very high temperatures employed in millisecond Flash anneals.

Abstract: Millisecond annealing (MSA) has been developed over the last several years as a viable approach to achieve the high electrical activation, limited diffusion and high abruptness needed for junctions in the sub-65nm regime. This paper will provide an overview of the technology including the motivation, technology and some process results. Both main approaches for MSA, sub-melt laser and flash lamp annealing will be discussed as well as the potential challenges to bring these technologies into mainstream manufacturing.

Abstract: This work presents a summary on the use of rapid thermal processing for implant annealing. It gives a short historical overview of rapid thermal processing systems and the first implant anneal processes on these newly developed tools. We then looked in detail on the soak anneal and spike anneal processes and the influence of certain process parameters. For the soak anneal influences of the ambient, either oxidizing or nitriding, were evaluated. The results of spike anneal processes are influenced by the pre-stabilization temperature, ramp-up and ramp-down rate, peak temperature, and gaseous ambient. The need for shallow, abrupt and highly activated junctions leads to co-implantation of species like fluorine or carbon in conjunction with pre-amorphization. Nowadays, combinations of spike and millisecond annealing as well as millisecond annealing alone are in the focus.

Abstract: In this work we present a comprehensive comparison of ultra thin thermally nitrided (TN) to plasma nitrided (PN) gate dielectrics (GD). We will show that thermal nitridation is a promising technique to increase the nitrogen concentration up to 25%. Furthermore, we will demonstrate that ultra thin thermally nitrided GD have the potential to be an alternative solution compared to plasma nitrided GD. This work includes the analysis of physical and electrical parameters as well as reliability results from reliability characterization. Additionally, we investigated the impact of Deuterium on electrical parameters and reliability behavior.

Abstract: The study of fast diffusion processes in materials requires short isothermal annealing treatments combined with an accurate temperature measurement. The paper discusses the special demands on rapid thermal annealing (RTA) devices in diffusion research and how these can be met in practice. The scientific impact of RTA for diffusion research in semiconductors is demonstrated by several examples dealing with fast impurities in Ge and Si.

Abstract: We have designed a set of experiments in which a controlled supersaturation of vacancies can be maintained constant during annealing of a boron implant. In presence of voids, a remarkable reduction of boron diffusivity is observed and, for low fluence B implantation, TED can be totally suppressed. We show that the presence of nanovoids in the B implanted region is not a prerequisite condition for the reduction of B diffusivity. Large voids located at more than 100 nm apart from the B profile still show the same effect. Small voids can also be used to increase the activation of boron. All these results are consistent with the hypothesis that, during annealing, vacancies are injected from the voids region towards the Is rich region in the implanted region where they massively recombine. Finally, we show that BICs cannot be simply dissolved by injecting vacancies into the region where they stand.

Abstract: We have developed a diffusion and activation model for implanted arsenic in silicon. The model includes the dynamic formation of arsenic-vacancy complexes (As4V) as well as the precipitation of a SiAs phase. The latter is mandatory to correctly describe concentrations above solid solubility while the former are needed to describe the reduced electrical activity as well as the generation of self-interstitials during deactivation. In addition, the activation state after solid-phase epitaxy and the segregation at the interface to SiO2 are taken into account. After implementation using the Alagator language in the latest version of the Sentaurus Process Simulator of Synopsys, the parameters of the model were optimized using reported series of diffusion coefficients for temperatures between 700 °C and 1200 °C, and using several SIMS profiles covering annealing processes from spike to very long times with temperatures between 700 °C and 1050 °C and a wide distribution of implantation energies and doses. The model was validated using data from flash-assisted RTP and spike annealing of ultra-low energy arsenic implants.

Abstract: The continuous scaling of electron devices places strong demands on device design and simulation. The currently prevailing bulk transistors as well as future designs based on thin silicon layers all require a tight control of the dopant distribution. For process simulation, especially the correct prediction of boron diffusion and activation was always a problem. The paper describes the model developed for boron implanted into crystalline silicon and shows applications to hot-shield annealing and flash-assisted rapid thermal processing.