Towards The Design Of Ultra-Low Dielectric Constant Materials
The inherent trade-off of porosity and mechanical properties in ultra-low dielectric constant (ULK) organosilicate glass (SiCOH) materials is a critical challenge in semiconductor processing. Numerous post-deposition processes have been studied to achieve simultaneous low-k materials with adequate mechanical rigidity, including thermal annealing. Typically, these thermal anneals are characterized by times on the order of seconds to minutes at relatively low temperatures (below 500°C). The goal of this work was to study the potential advantages of sub-millisecond time-frame anneals at extreme temperatures up to 1200°C. I began by establishing an atomic layout for the amorphous film, and then developed methods of verifying its relevant properties, like porosity, dielectric constant, Bulk and Young's Moduli. I then studied the effects of rapid thermal processing on the structure of ultra-low k materials using Molecular Dynamics computer simulations employing a force-field which enables bond rearrangements, called REAX-FF. This was compared with direct experimental measurements during CO2 laser-induced spike annealing. Results show structural evolution with increasing temperature leading to densification of the SiOx network, reduction in the concentration of sub-oxides, and loss of remnant organic moieties from original SiCOH structures. These results provide atomic-scale structure and chemical intuition to guide the development of future low-k materials. Current efforts are focused on exploring potential new classes of ULK materials, using the information gleaned from our study of organosilicate glasses as a guide. Ideally a ULK material should be: thermally stable to high temperatures, mechanically strong, chemically resistant, have low polarizabilities and high porosity, with pores no larger than 2nm in diameter. Porous organic polymers, or POPs, are highly interconnected and therefore mechanically stable, but have large ringed structures which frustrate packing and promote high intrinsic material porosities. I have created models of these materials using Molecular Dynamics in order to predict their dielectric and mechanical properties, and therefore their potential viability as future ULK materials.
molecular dynamics; ultra-low dielectric constant; organosilicate glass
Thompson, Michael Olgar; Ober, Christopher Kemper
Ph.D. of Chemical Engineering
Doctor of Philosophy
dissertation or thesis