HANCOCK, N.H. " A fundamentally new approach to creating nanostructures by forming them with supercritical fluids could be used to make dielectric films used in semiconductor processes.
The approach is being forged in a joint project between the University of Massachusetts Amherst and Novellus Systems Inc. (San Jose, Calif.). The supercritical state can be created by adjusting the pressure and temperature of a material so that it exists in a fluid state above its critical point.
The researchers, led by Rajaram Pai at UMass, found that supercritical carbon dioxide becomes an excellent medium for depositing inorganic compounds in tiny convoluted cavities formed in block copolymers. The supercritical medium is able to carry larger quantities of the compounds into the cavities than would be possible with a gas, and the diffusion rate is much higher than liquids. In fact, the reaction speed is so high that the process would fit neatly into existing semiconductor fab lines.
Block copolymers are structures formed from two types of polymers that intermingle. By chemically removing one of the polymers, a complex three-dimensional nanoscale structure results. The supercritical carbon dioxide completely filled the empty spaces in the structure with silicon alkoxides in a process that strongly resembles the biomineralization processes used by nature to create materials like sea shells.
The process created dielectric films with a dielectric constant of 1.8 that were mechanically robust and could be processed with standard chemical-mechanical polishing methods.