193 nm激光下不同含量Y杂质CaF_(2)晶体辐照损伤研究

Irradiation Damage of CaF_(2)with Different Yttrium Concentrations under 193 nm Laser

氟化钙晶体的抗辐照性能是其在深紫外光刻应用中的关键性能之一,目前氟化钙晶体在193 nm激光辐照下的损伤过程尚不清楚。本文报道了193 nm激光辐照下氟化钙晶体的损伤行为及影响损伤的关键缺陷因素。通过193 nm激光辐照试验,发现晶体损伤主要表现为晶体内部产生的辐照诱导色心与表面产生的辐照诱导损伤坑。通过紫外–可见分光光度计对辐照诱导色心分析,并将不同色心吸收系数与Y杂质含量进行线性拟合。结果表明:Y离子具有与F心结构波函数发生重叠的低位轨道,两者发生轨道杂化易形成色心稳定结构;线性拟合结果表明Y离子含量与氟化钙晶体本征色心之间存在线性关系,说明Y元素是影响色心形成的关键杂质离子。实验表征了辐照诱导损伤坑的元素分布和结构缺陷。EDS结果表明损伤坑处伴随着钙元素含量上升和氟元素含量下降,证实H心扩散、F心聚集导致了辐照损伤;EBSD结果表明表面辐照损伤优先在位错处产生。因此,降低杂质含量及位错密度是提高氟化钙晶体在193 nm激光下抗辐照损伤性能的重要途径。

Radiation resistance of CaF_(2) crystal is one of the critical properties in the application of deep ultraviolet lithography,but the damage process under 193 nm laser irradiation is still unclear.This paper reports the damage behavior of CaF_(2) crystals under 193 nm laser irradiation and the key defect factors affecting the damage.Through the 193 nm laser irradiation experiment,it is found that the crystal damage is mainly manifested as the radiation-induced color centers inside the crystal and the radiation-induced damage pits on the surface.Irradiation-induced color centers were analyzed by UV-visible spectrophotometer,and linear fitting was performed between absorption coefficients of different color centers and Y impurity contents.The results show that Y ion has a low-order orbit that overlaps with the F center structure wave function,and hybridizes to form a stable structure.There is a linear relationship between Y ions contents and intrinsic color centers of CaF_(2) crystals,confirming that Y element is the key impurity ion affecting the formation of color centers.Energy dispersive X-ray spectrometer(EDS)results show that the content of calcium in the damage pits increases and the content of fluorine decreases,which confirms that the diffusion of H centers and the aggregation of F centers lead to irradiation damage.Electron backscatter diffraction(EBSD)results show that surface irradiation damage occurs preferentially at dislocations.Therefore,reducing the impurity content and dislocation density is an important way to improve the anti-irradiation damage performance of calcium fluoride crystals under 193 nm laser.