提高深紫外光刻照明系统扩束单元光束均匀性的方法

Methods of Enhancing Uniformities of Output Beams from Beam Expanding Unit for Illumination System of Deep-Ultraviolet Lithography

在曝光线宽为90nm节点的投影光刻机照明系统中,针对准分子激光光源扩束后出射光束均匀性较差的问题,用高斯光束边缘叠加能够提高均匀性的原理对反射式扩束单元进行了分析。结果表明,平行反射式扩束单元出射光束之间叠加尺寸与反射板某区域透射率存在矛盾,制约了照明光束均匀性的提高。为此,提出了非平行反射扩束镜组,推导了出射光束尺寸、叠加子光束个数与两反射镜楔角之间的关系式,确定了楔角的取值范围和扩束单元的结构形式。通过建模分析,验证了设计的扩束单元在实现光束一维扩束的同时,不仅减小了叠加光束的干涉散斑效应,还提高了光束均匀性。

According to the problem of bad uniformities of expanding beams for excimer laser of projected lithography which holds 90 nm exposure linewidth, a kind of reflective beam expanding unit is modified based on the principle that the beam edges of Gaussian type can be superposed to enhance uniformities. It is shown that there is a contradiction between the sizes of superposing beams and the transmission rate on some areas of the parallel-reflective beam expander, in that case the improved capacities for the beam uniformities are restricted. Based on the above analysis, a non-parallel reflective beams expanding unit is proposed. The relational expressions about output beam sizes, number of superposed sub-beam units and wedge angle between two mirrors are deduced and the span of wedge angle and the structure of beam expanding unit are determined based on the deduced equations. The proposed beam expanding unit is proved to be useful to achieve beam expanding, as well as to reduce the interfering speckle effects. And the uniformities of output beams is increase.