The role of excitation wavelength on debris for Co2 and Nd:YAG laser-produced plasma EUVL sources

Summary form only given. Current visible and ultraviolet light imprinting methods for manufacturing computer chips have reached their maximum limitations and the extreme ultraviolet (EUV) region has been selected as a possible successor. While extreme ultraviolet lithography (EUVL) offers a solution to advancing Moore´s Law, several problems persist pursuant to large-scale industrial and high volume manufacturing. Laser produced plasmas (LPP) from tin targets have been demonstrated to emit EUV radiation (13.5 nm light) with an industrially acceptable conversion efficiency, although debris accumulation on the collector optics is still an issue. Our recent results have shown that CO₂ produced laser plasmas emit less debris compared to YAG LPP. However, CO₂ LPP ions are more energetic compared to YAG LPP ions. The dissimilarity in debris features are explained due to nearly 2 orders difference in critical density of the pump beam as well as variation in the laser energy deposition in these plasmas. This study investigates further the debris emission from CO₂ and Nd:YAG laser produced tin plasmas, focusing specifically on the changes in the debris generation as a function of laser wavelength. Both fundamental and harmonic wavelengths (1064 nm, 532 nm & 266 nm) were used for the Nd:YAG excitation in addition to the comparison with the CO₂ laser excitation. Silicon wafers are placed at various angular positions throughout a stainless steel vacuum chamber and act as witness plates to the YAG and CO₂ plasma debris. Faraday cup data is taken to characterize energy distribution of the debris. The contaminated silicon samples are then transported to the IMPACT facility4 for XPS analysis to determine debris distribution as a function of angle. Finally SEM imaging is performed to elucidate the particle size distribution of the debris.