Multiscale Simulation of Atomic Layer Deposition in a Nanoporous Material

A multiscale simulator for alumina film growth inside a nanoporous material during an atomic layer deposition process is developed. The model combines a continuum description at the macroscopic level of precursor gas transport inside a nanopore during exposure to each of the two precursor species (trimethyaluminum and water) with a lattice Monte Carlo simulation of the film growth on the microscopic scale. Simulation results are presented for both the Monte Carlo simulation and for the multiscale system, the latter illustrating how nonuniform deposition along the nanopore can occur when insufficient precursor exposure levels are used. 1 Simulation of film growth in ALD Atomic Layer Deposition (ALD) is a thin film deposition process in which the growth surface is exposed to reactive precursor gases in an alternating fashion. A characteristic of the surface adsorption and reaction mechanisms is that they are normally self limiting, allowing for atomically accurate control of film thickness and uniform deposition over complex surface topologies. ALD is an important unit operation in manufacturing nanoscale devices. ALD, in fact, is the key enabling technology in Intel’s current 45nm transistor technology where it is used to deposit the HfO2 gate oxide [2]. Another example of ALD use is the production of the nanolaminates for large-scale flat-panel electroluminescence displays [11]. ALD has even greater potential in future manufacturing and research applications, such as in the deposition of gate dielectrics for carbon nanotube transitors [12], nanoelectrodes for studying single molecules [9], and other nanoparticle [10] and nanolaminate [6] applications. ALD is an inherently dynamic process characterized by multiple time scales: a faster time scale corresponding to the molecular events taking place during each exposure cycle, and the slower overall nucleation and steady growth1 time scales [8]. Likewise, multiple length scales are found in these systems where macroscopic length scales (100’s of μm) correspond to gas phase transport effects, and microscopic scales characterize the atomistic nature of the film growth. An approach to coupling modeling elements across these scales to simulate ALD growth of alumina films inside nanopores of high aspect ratio is the topic of this letter. 1.1 Al2O3 ALD We consider Al2O3 ALD, one of the most widely studied ALD systems (see, e.g., [3, 14]) and the material system used to modify nanostructured catalytic membrane pore size [5, 13]. Amorphous Al2O3 The cycle-integrated growth rate defining the total film thickness added during each exposure cycle.