Ultra Low-K Inorganic Silsesquioxane Films with Tunable Electrical and Mechanical Properties
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Thomas A. Deis, Chandan Saha, Eric Moyer, Kyuha Chung, Youfan Liu, Mike Spaulding, John Albaugh, Wei Chen, and Jeff Bremmer
Dow Corning Corporation, Midland, MI 48611 U.S.A.
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 HSiO3/2 to SiO4/2. 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 450ºC. 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. INTRODUCTION Multilevel interconnect technology beyond the 0.18 micron technology node requires interlayer dielectric (ILD) materials with low permitivity values. An inorganic material and a unique process method have been developed to meet this need. A commercially viable process has been developed that produces controlled void volume in hydrogen silsesquioxane (HSQ) based films and results in a more “silica” like film. New advances in the formulation and D5.18.1
processing allow for fast, simple processing that significantly improved both the mechanical and electrical properties of hydrogen silsesquioxane resin. In addition the dielectric constant value and mechanical properties of films processed using this method can be tuned over a wide range to meet specific needs. EXPERIMENTAL Thin films are processed by spin coating a solution onto a silicon wafer, treating the asspun film with moist ammonia, and then thermally curing the film. The initial solution was comprised of hydrogen silsesquioxane (HSQ) resin and two solvents. One solvent, a low boiling solvent, was used to control the thickness of the as-spun film. The second solvent was a high boiling solvent, which remained with the resin in the as-spun film. The ratio of the resin to high boiling solvent was used to control the de
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