Department of Electronics. University of Valladolid
Motivation
The level of refinement reached by today's materials processing technologies is calling for new modeling and simulation schemes, capable of handling the rich variety of interaction mechanisms that govern such complex processes at the atomic level. These modeling needs are a subject of increasing concern for the semiconductor industry as manifested already in the 1997 SIA Roadmap which identifies atomistic process modeling among the difficult challenges below 100 nm: "Continuum physics models are no longer sufficient below 100 nm. Tools are needed for the physical and chemical processes at an atomic level". Molecular dynamics (MD) is the most accurate atomistic simulation technique and it can provide valuable microscopic information to other simulation techniques. However, due to the fact that it simulates all the lattice atoms and, most importantly, that it uses an almost constant timestep on the order of the femtosecond (10-15 s), the time scale that can be simulated by MD is restricted to the order of nanoseconds. The Kinetic Monte Carlo (KMC) method, instead, is an event-driven technique, i.e., simulates events (e.g. diffusion hops) at random, with probabilities according to their respective event rates. In this way it self-adjusts the time-step as the simulation proceeds and, thus, is able to simulate the time scales involved in typical technological processing steps (seconds to hours). The use of the KMC method within a non-lattice scheme allows reaching the size dimensions of current ULSI devices keeping the advantages of atomistic simulations. In contrast, a lattice KMC approach can be usefull for the simulation of the structural evolution of polycrystalline materials. The Binary Collision Approximation (BCA) is suitable to simulate the Ion Implantation process used for doping, with ion energies ranging from few KeV to several MeV. Atomistic Process
Simulation at e-UVA
The development and improvement of atomistic simulation models and tools has been the goal of our research efforts for more than one decade. The main approches we have used are: |
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Molecular Dynamics
Simulation of ion-induced damage, amorphization and recrystallization in silicon using classical potentials. More recently, we have started to used tight-binding molecular dynamics and ab-initio methods to study the properties of amorphous silicon. Kinetic Monte Carlo Process Simulation: DADOS
“DADOS” is an atomistic KMC simulator, designed
for front-end processing of deep sub-micron silicon devices. DADOS uses ion implant cascades calculated by BCA in order
to simulate the diffusion related to ion implantation processes. DADOS has been included in the atomistic option of the Sentaurus Process simulator, comercialized
by Synopsys Inc, CA. KMC simulation of nucleation, growth and structural evolution under annealing conditions of polycrystalline aluminum thin-films Binary Collision Approximation
Simulation of ion implantation, primarily in Silicon and III-V semiconductors, both crystalline and amorphous. Improvement of physical models and computation efficiency. |
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