Light Sources and Materials for EUV Lithography

The field of semiconductor manufacturing is heavily dependent on the process of photolithography. Photoresists undergo chemical changes when exposed to light, allowing for patterning of the silicon before other processing steps such as etching and ion implantation are performed. The current state of the art technology is Extreme Ultraviolet lithography. Light-matter interactions are critical to this field. They are exploited in two areas: the source of the EUV light, and in photoresist materials for the lithography itself. Currently, a tin laser produced plasma is used by industry as the light source, but in the past Free Electron Lasers were considered. Light-matter interactions, relevant to both fields, were studied in this project. A laser produced plasma based EUV light source was built in order to study the spatial and temporal characteristics of the light and plasma. The differences in using tungsten and tin as the source material were investigated. Spectral intensities on the order of 10^13 photons s^−1 nm^−1 sr^−1 at a wavelength of 13.6 nm (photon energy= 91.2 eV) were achieved with both materials. The interaction of intense EUV light with matter was also investigated through the analysis of multiphoton ionisation of neon at the EUVL photon energy of 93 eV, previously recorded at the FLASH FEL. Peak intensities on the order of 10^16 W.cm^−2 allowed for the detection of sequential one-plus-two photon double ionisation. EUVL resist candidates (e.g., nanoparticle and metal-inorganic based) demand strong EUV absorbers, namely metals. Relaxation dynamics of chromium-oxalate coordination compounds, previously reported as potential EUV resist candidates, were investigated with the aid of low temperature phosphorescence and time-resolved infrared spectroscopy. Excited state lifetimes ranging from milliseconds to picoseconds were revealed.