When 3:30 PM - 5:00 PM Feb 15, 2008
Where 1670 CSE
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Christopher Soles, NIST


Nanoporous Organosilicate Films and Nanostructures Patterned by Nanoimprint Lithography

Nanoporous organosilicate materials have applicability for a range of technologies, including catalyst supports separations, membranes, laser materials, optical waveguides, sensors, and biological devices. Most notably, spin-on organosilicates are extremely attractive as interlayer dielectric insulator materials (ILDs) for semiconductor interconnects. In this application, very high levels of well-controlled, nanoscale porosity are requisite to reduce the dielectric constant (k) of the material and provide effective capacitive shielding between the densely packed conduction lines, which are separated by sometimes less than 100 nm. In addition to a very low k, the ILDs must also have tightly controlled pore structures that prohibit Cu ion interdiffusion between the conduction lines, maintain a low coefficient of expansion to minimize thermal mismatch stresses, and exhibit sufficient mechanical strength to withstand the harsh integration process associated with semiconductor fabrication. However, it is difficult to rationally control the synthetic processes for these materials and optimize all of these properties without the detailed structural information that relates the physical properties to the material structure. To guide this materials development our group has developed powerful measurement platforms based on X-rays, neutrons, and ion beams to characterize structural details of highly porous organosilicate materials. I will describe in detail these methodologies that can be used to quantify the average film density, density of the wall material between the pores, total porosity, pore size distributions, pore interconnectivity, chemical composition, film thickness, and the thermal expansion coefficient of thin organosilicate films. Relevant examples will be provided to illustrate how different processing conditions have a dramatic affect on the relevant characteristics of the porosity. Specifically, I will show how these measurement technologies were instrumental in molecularly tailoring high modulus organosilicate materials with a low coefficient of thermal expansion. I will then introduce a new and exciting nanoimprint lithography process to directly pattern such high-performance organosilicate materials through a mechanical stamping. This direct stamping process has the potential to eliminate the use of sacrificial deep UV photoresist formulations for defining the patterns, thereby greatly simplifying the interconnect fabrication process. By utilizing these high modulus materials we have been able to directly imprint, with high fidelity, organosilicate patterns with very high levels of porosity, pushing well below the ultra-low dielectric mark of k = 2. I will describe in detail how the direct imprinting process affects the porosity of these materials relative to their non-patterned analogs.