Molecular dynamics study of texture control under ion beam assisted deposition.
Dong, Liang
2000
Abstract
Polycrystalline thin films, grown by almost any method, exhibit at least some degree of crystallographic texture. Ion beams have been employed to control thin film out-of-plane and in-plane texture. In order to effectively control texture evolution during ion beam assisted deposition (IBAD), it is necessary to develop a working understanding of the texture development mechanisms. We employ molecular dynamics simulations to study the texture control mechanisms. Based on the understanding of the texture evolution mechanisms, we study the Al thin film hillock problem, combined control of out-of-plane and in-plane texture, and in-plane texture control of MgO thin films. <italic>Identification of texture control mechanisms</italic>. We perform a series of three-dimensional molecular dynamics simulations on both bicrystals and single crystals. The effects of ion beam energy, orientation and flux on the development of out-of-plane and in-plane textures are studied by measuring sputtering yield and observing atomic structure of the system as it develops as a function of time. We find that preferential sputtering and differential damage caused by the ion beam are responsible for the texture modification. Then we design a series of simulations to distinguish between these mechanisms with the goal of identifying the dominant texture control mechanism. It is found that in a system with mobile grain boundaries, recrystallization-like grain boundary migration caused by differential damage is the dominant texture modification mechanism. <italic>A solution to metal thin film hillock problem</italic>. One common problem in all multi-level interconnect technologies is the formation of hillocks or protrusions from the surface of the metal film or line. One approach to solve hillock problems is to change the predominant film texture from that of the highest yield stress orientation to one of the weakest orientations. Simulations show that ion beam can be used to change the thermodynamically favored out-of-plane orientation to a different orientation which could prevent hillocking. Experiments confirm the validity of the proposed solution. <italic>Combined thin film out-of-plane and in-plane texture control </italic>. Complete control of the texture of a growing film would require both the ability to determine the in-plane and out-of-plane texture simultaneously. Computer simulations and experiments show that one ion beam can create out-of plane texture with two twin-related in-plane orientations for fcc film. We theoretically demonstrate that it is not possible to completely control both the in-plane and out-of-plane texture with a single ion beam in high symmetry crystals (without twin related components) and propose a two ion beam method that will insure complete texture control. <italic>In-plane texture control in Mg-O thin film</italic>. MgO thin films with in-plane texture have been used as structural templates for the deposition of superconducting thin films. Simulations show that by appropriately choosing the ion beam-thin film orientation, it is possible to effectively control in-plane texture. We also demonstrate that the existence of critical angle for channeling is one important reason for the difficulty in achieving sharper in-plane textures.Subjects
Ion Beam Assisted Deposition Ion-beam-assisted Deposition Molecular Dynamics Polycrystalline Thin Films Study Texture Control Under
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