(214p) 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.