Porous Organosilicates for On-Chip Applications: Dielectric Generational Extendibility by the Introduction of Porosity

Abstract

Dense alkyl-functionalized organosilicates have dielectric constants that are 25-30% lower than silica, which allows ultralow dielectric targets(κ< 2.2) to be achieved at reduced porosity levels relative to those required for silica. Partially condensed silsesquioxane derivatives (RSiO1.5),, generate highly crosslinked organosilicate films upon thermal and/or radiation curing. We have demonstrated that porous methyl silsesquioxane (MSSQ) thin films can be generated utilizing a sacrificial macromolecular porogen approach and a number of effective porogen classes have been identified. A key feature in this process is the compatibility of the porogen and the matrix polymer at low levels of vitrification. This allows the formation of nanoscopic domains of porogen in the vitrifying matrix prior to the removal of the porogen to generate the porosity. This is achieved through judicious selection of porogen and matrix prepolymer molecular weights as well as by control of porogen functionality, end groups, and macromolecular architecture. Optimization of structural and processing parameters allow the film dielectric constant to be varied continuously from 2.8-1.4 simply by changing the porosity level of the matrix. Although closed-cell structures are achieved for loading levels below 30%, subsequent percolation and interconnection at higher loading levels still result in nanoscopic pore diameters (< 500 Å).