Mesoporous Materials and Methods
A novel process by which well ordered mesoporous films can be created by the three-dimension replication of pre-organized block copolymer templates using supercritical fluids. Mesoporous silicate, carbon and titanium dioxide films have been prepared by the infusion and selective condensation of precursors within one phase domain of highly ordered, preformed block copolymer templates using supercritical carbon dioxide as the reaction medium. The template is then removed to produce the mesoporous oxide. To date we have replicated ordered spherical and cylindrical morphologies to yield titania, silica, organosilicate and mixed silica/organosilicate mesostructures in films over 1 micron thick while maintaining all the structural details of the sacrificial copolymer template.
Principal applications involve the preparation of device quality thin films for microelectronics, separations, sensors and energy conversion. Extensive development of ultra-low k dielectric thin films (ULKs) has taken place. For ULKs, the first-generation of templates yielded films dielectric constants as low as 1.8. A film with k = 2.2 was selected for further evaluation and found to survive CMP in a planar test stack. The process can be scaled for full wafer production on a Si platform using existing production scale (200 mm and 300 mm wafer) tools for SCF processing.
Advantages of this approach include rapid and high degrees of network condensation, low film stress, rapid cycle times, stable templates and precursors and opportunities for pore alignment direct patterning strategies. Phase-segregated block copolymer films with cylindrical domains oriented normal to the substrate can be replicated to yield the corresponding silicate mesostructures containing arrays of continuous, perpendicular channels with tunable pore sizes. Direct pattering of mesoporous films using optical lithography for selective area exposure of templates containing photoacid generators prior to precursor infusion has been demonstrated.
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