Thermal Deformation Of EUV Mask And Its Influence On Lithographic Performance

Extreme ultraviolet lithography (EUVL) is one of the promising lithographytechnologies for 45 nm features. EUVL will be required to satisfy the stringenterror budgets, one of which is the thermal distortion of the mask during exposure.The focus of this research was to quantify the thermal distortion, and analyze theinfluence of thermal distortion on lithographic performance. This wasaccomplished with finite element methods which were developed for thisresearch. All of the analysis was for a EUVL system with a throughput of 81wafers-per-hour. The detailed work includes the following two parts.First, analyze the distortion of EUV mask during exposure. The maskreaches a quasi-steady state condition in about 500~600s. In this study, withdifferent substrate materials ULE and Quartz glass used, the influences of mask-to-chuck contact conductance,mask pattern density and the friction betweenmask and chuck were performed. The results show that by increasing the contactconductance,optimizing the pattern density distributions and controlling thefriction between mask and chuck, the thermal response during exposure can beminimized.Second, analyze the influence of thermal distortion on lithographicperformance. For dense lines,semi-dense lines and isolated lines, the maximumresist image CD error variation is 1%,0.5% and 2.87%, respectively;themaximum sidewall angle variation is 2.9°,2.4° and 3.8°, respectively. The resistimage placement error is dependent on thermal distortion and optical aberration,simultaneously. On condition that ignoring the optical aberration, for denselines,semi-dense lines and isolated lines, the maximum resist image placementerror is 5.02nm,5.32nm and 5.53nm, respectively.