Simulated Thermal Annealing of Low-k Organosilicate Glass Materials Using the Reax-FF Force Field

             The continued shrinking of microelectronic devices has led to the need for lower dielectric constant (low-k) materials in back-end interconnect structures to reduce resistive-capacitive delay in signal propagation. In order to reach lower dielectric constants traditional materials are used as a starting point, but are fabricated to promote the formation of pores. Higher levels of porosity reduce the dielectric constant, but also result in a loss of mechanical strength.

            We have modeled low-k organosilicate glasses using molecular dynamics techniques in order to understand the relationship between the material's structure, porosity, dielectric constant, and mechanical strength. In this paper, we use the REAX-FF force field to model the material's atomic interactions. This force field is unusual because it allows for the breaking and forming of bonds during the simulation. This capability allows us to follow the evolution of the bonding environment of the material's structure as we change the thermal environment of the system. Ultra-rapid thermal annealing is of interest since it offers the potential to strengthen the material with minimal increase in dielectric constant.

            We begin by establishing a starting REAX-FF model of these SiCOH-type materials with the appropriate composition and bulk properties to match an experimental film. We then simulate thermal annealing of this material, after establishing a simulation-derived glass transition temperature (T_g) (~1000 K) to use as a point of reference. By comparing the structure at T_g with the starting structure, as well as with the structures at various temperatures along the way, we are able to link temperature to structural and property changes. We will show how the structure evolves with increased temperature to eventually result in a point of pore collapse and higher dielectric constants. We also suggest processing paths to lead to a balance between mechanical strength and dielectric constant and draw comparisons to experimental results.