Deposition and Integration of a Novel Ultra-Low k (2.2)Material

Abstract

Increasing demands for faster chip speed and reduced power consumption aredriving the semiconductor industry to develop insulating layers with lowerdielectric constants. As the dielectric constant of a material is reduced,however, it becomes increasingly difficult to achieve the mechanicalstrength required to manufacture a multilevel interconnect. A new route tothe synthesis of mesoporous silica has been demonstrated on 200 mm wafers.Silicate precursors dissolved in supercritical CO₂ are infusedinto a block copolymer film. The polymer is then removed, but the resultingporous SiO₂ replicates its ordered structure, enhancing thestrength of the network. Incorporation of alkyl silicates further improvesthe film properties. Post-treatment to cap residual silanol groups rendersthe surface of the film hydrophobic and stabilizes it to air exposure. Byappropriate choice of the block copolymer and other process parameters, thepore size and density can be varied and k values as low as 1.8 can beachieved. For a film with a dielectric constant of 2.25, the pore size is ∼4nm. The hardness and modulus are 1.1 GPa and 7.8 GPa, respectively, asmeasured by nanoindentation. Four-point bend measurements yield fractureenergies of 9.8 J/m². More importantly, the film can withstandchemical mechanical planarization (CMP) using standard oxide polishingconditions.