ICMCTF2004 Session C3: Engineered Photonic Thin Films and Structures

Cermet films of gold and aluminum oxide were sputter deposited onto silicon substrates. These films consisted of small gold grains embedded in a matrix of aluminum oxide, and were designed to absorb visible radiation and reflect infrared radiation. Ex situ and in-situ spectroscopic ellipsometry were used to characterize film optical constants from vacuum ultraviolet to middle infrared. The optical constants, for cermet films with gold volume fractions ranging from 0 to 1, were used in predictive optical models. Thermal performance was optimized by weighting the fit of the predictive optical models to an ideal reflectance spectrum. The weighting factor emphasized fitting in more significant spectral ranges and deemphasized fitting in less significant wavelength ranges. Emittance and absorptance were calculated along with a new figure of merit based on energy balances. Reflectance data were used to verify film performance.

Research supported by NASA Glenn Research Center grant number NAG3-2219.

Many research groups both in academia and in industry are currently developing innovative nanoscale devices which could have a tremendous impact in the general areas of photonics and electronics. However techniques for fabricating these devices and nanostructures must be available for use with production tools in order for them to find real applications. There are currently two major approaches under study as fabrication methods for nanodevices: these are microfabrication based techniques and molecular assembly techniques. The microfabrication approach, which is to be discussed here, is strongly based on the technology developed over the past decades for the fabrication of electronic devices and integrated circuits. The continued miniaturisation of these devices has far surpassed expectations for a technology developed initially for micrometer sized structures, and this approach now encompasses the fabrication of devices with dimensions well below 100 nm, even in production environments. There are also methods under study which do not yet meet industry standards in terms of, for example, throughput and repeatability, but which have shown significant promise. These include new techniques such as nano-imprint lithography, as well as established research tools such as electron beam lithography, which are becoming more and more relevant as several equipment manufacturers are now developing new types of production level tools.

The International Techology Roadmap for Semiconductors is the established norm by the semiconductor integrated circuit (IC) industry to assess the technology requirements over the next fifteen years. The objective of this roadmap is to ensure that all the players involved in the development of integrated circuit fabrication technology can focus on the advancements needed in performance in order to meet future generations of semiconductor ICs. It is hard to ignore this roadmap since by definition it covers state of the art microfabrication technology that would appear likely to be put to use for nanodevice fabrication. Lithography is one important aspect of the roadmap and this is of great concern for the development of fabrication techniques suitable for nanodevice fabrication. While the list of candidate technologies for sub-100 nm resolution has evolved over the years, the current list in the roadmap still includes extreme ultraviolet lithography, proximity X-ray lithography, projection electron lithography, direct-write electron lithography, as well as extensions of the current deep ultraviolet (DUV) lithography using schemes such as optical proximity correction and phase shift masks. While it is very debatable as to which one, if any, of these technologies will ever be adopted in a production environment, there is a growing feeling that the industry may adopt a mix and match approach, making use of high resolution but lower throughput techniques such as electron beam lithography for specific applications. And while this latter technique is well known, several recent advances show promise for novel nanodevice fabrication. These include several methods which do away with the problems associated with electron beam resists, problems which become extremely severe at very high resolution. New sensitive layers have recently appeared which can be deposited by evaporation techniques, opening the way for extremely fine lithography patterning on fully 3-dimensional surfaces, well beyond the capabilities of current DUV lithography. This paper will discuss the deposition methods and properties of these new electron sensitive layers, their use in the fabrication of advanced devices, and their impact on the competitive positioning of electron beam lithography with respect to the other competing technologies for the sub-100 nm technology market. Other applications of these new resist materials in other types of lithography (such as the preparation of advanced masks for nano-imprint lithography) will also be addressed.