Extreme ultraviolet resist outgassing and its effect on nearby optics

Extreme Ultraviolet Lithography is a promising technology to continue advances in lithography toward smaller features. However, there are still some technical challenges that need to be understood before commercialization of EUV lithography for high volume manufacturing (HVM). Resist outgassing has been identified as one of the critical issues associated with EUV lithography. This may lead to contamination of the Mo/Si multilayer optics from molecules outgassed from EUV resists when they are placed in the vacuum chamber and exposed to EUV radiation. The HVM of EUVL requires 30,000 hours of light on lifetime of these optics. However a comprehensive and detailed study is required to understand what species if any from these photoresists are contaminating the EUV optics. It is also necessary to postulate how many molecules of that species are "too many" to contaminate the optics. It is essential to develop an understanding for the underlying mechanism by which this contamination interacts with the surface of the optics causing their degradation. Before all these can be accomplished, there is a need for accurately measuring outgassing from EUV photoresists both qualitatively and quantitatively.;To date, there have been mixed results from measurements of outgassing from EUV resists performed at various research facilities due to the challenge of accurate quantification of the outgassed species. In view of this need, we have designed and built a well calibrated system which can investigate different candidates of EUV photoresists for outgassing and standardize the procedure and results of outgassing and then eventually correlate these outgassing species with optics contamination empirically. This thesis shows results from comprehensive EUV outgassing testing that uses multiple measurement techniques including quartz crystal microbalance tests to measure the mass loss from the resist, quadrupole mass spectrometry to measure the species and number of molecules outgassed, thermal desorption tube with external gas chromatography and mass spectrometry (GC-MS) analysis to measure the species and quantities trapped for analysis, and pressure rise tests to determine the quantity of molecules outgassed. All of these techniques are compared to help determine the most accurate calibration procedure to measure the actual number and species of molecules leaving the surface of various EUV resists. Finally, optics contamination investigation was carried out in the same system by three different methods. One was the ASML's proposed witness plate experiments where resist and optics are exposed simultaneously to EUV light. The other is the accelerated method, where optics are exposed to EUV light in presence of high concentration of hydrocarbon species which are known to outgas from resist. The third method is a more efficient method where the outgassed molecules are confined in a small volume with little conductance to the vacuum pumps to ensure that the outgassed species are near the optics.