用于光刻调焦调平的反射式投影光学系统设计

Design of Reflective Projection Optics Used in Lithographic Focusing and Leveling System

调焦调平传感器是光刻机关键分系统之一,用于曝光前对硅片高度形貌进行测量。投影光学系统是调焦调平传感器的核心,其成像质量直接影响传感器测量精度。根据调焦调平传感器的测量原理与像差理论,分析得到投影光学系统放大倍率、畸变、远心度和分辨率对调焦调平系统测量精度的影响规律。为此,优选反射式投影光学系统设计方案,该方案具有结构简单、无色差,畸变小等特点,并利用ZEMAX软件进行设计优化和公差分析,所设计系统工作波长为600~1000 nm,放大率为1.000,视场3 mm×26 mm范围内弥散斑均方根半径小于0.189μm,调制传递函数为0.74@33 lp/mm,最大畸变为0.0008%,远心度为0.04 mrad。结合目前光机制造和装配能力可知,用于光刻调焦调平的反射式光学投影系统设计可工程实现。

The focusing and leveling sensor is one of the key subsystems in lithography system.It is used to measure the height map of silicon wafers before exposure.The projection optics is the most important module of the focusing and leveling sensor,its'imaging quality directly affect the measurement accuracy of the sensor.According to the measurement principle of the sensor and aberration theory,the influence of magnification,distortion,tele-centricity,and resolution on the measurement accuracy of focusing and leveling sensor is analyzed.A reflective optical design is chosen for the projection optics,which has characteristics of simple structure,no chromatic,and small distortion.After the optimization and tolerance analysis by using Zemax software,the working wavelength of designed system is 600-1000 nm,root-mean-square radius of the diffuse spot is less than 0.189μm within a field of view of 3 mm×26 mm,its magnification is 1.000,maximum distortion is 0.0008%,modulation transfer function is 0.74@33 lp/mm,and tele-centricity is 0.04 mrad.The results show that the reflective optical design for lithographic focusing and leveling sensor is engineering feasible with the current opto-mechanical manufacturing and assembling capability.