Ultra Low-K Inorganic Silsesquioxane Films with Tunable Electrical and Mechanical Properties

Abstract

Low-k dielectric films have been developed using a new silsesquioxane based chemistry that allows both the electrical and mechanical properties to be tuned to specific values. By controlling the composition and film processing conditions of spin-on formulations, dielectric constants in the range 1.5 to 3.0 are obtained with modulus values that range from 1 to 30 GPa. The modulus and dielectric constant are tuned by controlling porosity, which varies from 0 to >60%, and final film composition which varies from HSiO_3/2 to SiO_4/2. The spin-on formulation includes hydrogen silsesquioxane resin and solvents. Adjusting the ratio of solvents to resin in the spin-on formulation controls porosity. As-spun films are treated with ammonia and moisture to oxidize the resin and form a mechanically self-supporting gel. Solvent removal and further conversion to a more “silica-like” composition occur during thermal curing at temperatures of 400 to 450°C. The final film composition was controlled through both room temperature oxidation and thermal processing. Final film properties are optimized for a balance of electrical, mechanical and thermal properties to meet the specific requirements of a wide range of applications. Processed films exhibit no stress corrosion cracking or delamination upon indentation, with indenter penetration exceeding the film thickness, and followed by exposure to water at room temperature. Films also exhibit high adhesive strength (> 60MPa) and low moisture absorption. Processing conditions, composition and properties of thin are discussed.