2 - Analytical Model for Spike Annealed Diffusion Profiles of Low-Energy and High-Dose Ion Implanted Impurities

Abstract

Spike annealing, where the isothermal time period is zero or quite short, enables to obtain these shallow junctions. Combined with low-energy ion implantation, this technology is hence frequently used in the high-speed Metal-Oxide Semiconductor Field Effect Transistor (MOSFET) processes. Temperature is always time dependent in these processes, and one needs to acquire accurate parameters over a wide temperature range including the transient effects of the processes to analyze these processes. This kind of rigorous treatment has been performed in commercial process simulators. Many ambiguous models and their related parameters exist. Therefore, it is difficult to obtain a clear idea of how to optimize the spike annealing conditions. This chapter presents a study in which a diffusion model with the constant surface concentration based on the nonlinear diffusion equation is derived. It extends the model for high-concentration-diffusion profiles to accommodate spike annealed diffusion profiles and the corresponding junction depth, and shows the optimum condition to obtain shallow the junctions with abrupt profiles. The model well expresses the diffusion data in the high-concentration region, but deviates from the data in the low-concentration region, where transient enhanced diffusion or the as-implanted profile dominates the junction depth.