Research On A New Type Of Three-Degree-of-Freedom Piezoelectric Actuator And Its Application In Lithography Projection Objective

The lithography machine is the core manufacturing equipment in the semiconductor industry.The lithography projection objective is the core component of the lithography machine.Its performance determines the extreme resolution of the lithography machine exposure system and the critical dimension(CD)of the microelectronic chips.The continuous reduction of the chip nodes has increasingly strict requirements on the imaging quality of the lithography projection objective.In the process of the integrated adjustment of the lithography projection objective and the exposure of the lithography machine,the imaging quality of the projection objective needs to be compensated and adjusted with nanometer driving and positioning technology to reduce the aberration of the projection optical system and improve the resolution of the lithography projection objective.In order to improve the stiffness and stability of the piezoelectric actuated adjustment mechanism in the lithography projection objective,research has been carried to develop a new type of multi-degree-of-freedom piezoelectric actuator,using the multi-degree-of-freedom actuating scheme,the adjustment mechanism is directly driven,providing a new solution for the positioning and adjustment of optical elements in lithography projection objective.Therefore,this paper adopts a multi-DOF driving scheme to research and develop a new type of three-degree-of-freedom(3-DOF)piezoelectric actuator,and successfully applies it to the image quality compensation adjustment mechanism of the lithography projection objective,realizing the high-precision positioning adjustment of the optical elements with multi-degree-of-freedom.The main research work of this paper is as follows:1.The basic principle of piezoelectric actuating,the basic principle of flexible hinge and stiffness modeling,and the principle of high-precision motion measurement based on capacitive sensors are studied.Schemes of multi-DOF micro-motion measurement using capacitive sensors are proposed.2.A 3-DOF piezoelectric actuator is proposed and designed,and the motion transfering equation from the input voltage to the output attitude of the piezoelectric actuator is analyzed and established.A test platform is built to test and study the motion performance of the 3-DOF piezoelectric actuator.The motion resolution of the prototype actuator in the X/Y/Z direction can reach 15nm/16nm/21 nm and the motion speed under 2Kg load is 52.3μm/s /82.8μm /s /29.5μm/s.The open-loop waveform generation and trajectory planning algorithm is designed,and the open-loop trajectory tracking characteristics of the 3-DOF piezoelectric actuator are studied.The open-loop trajectory tracking experiments are carried out for different trajectories and the tracking accuracy of circular/elliptical/rectangular trajectory is less than 0.23μm/0.29μm /0.32μm.3.The dynamic analysis and modeling method of the 3-DOF piezoelectric actuator are studied.The model of piezoelectric stack actuator under constraint condition is established,the parameters in the mechanism model of piezoelectric stack are estimated with identification method.The stiffness model of flexible mechanism is established with flexibility matrix method,the dynamic motion equation of the 3-DOF piezoelectric actuator system is established based on Lagrange method.The modality of the actuator under zero input condition is analyzed,and a mathematical model of the actuator under multi-input condition is established,the time domain responses of the actuator are analyzed and tested based on its mathematical model.The correctness of the modeling method is verified by the comparison of the time domain analyzed response and tested response,which also testifies the accuracy of the established dynamic model of the 3-DOF piezoelectric actuator.4.Using the developed three-degree-of-freedom piezoelectric actuator as the core driving elements,two kinds of multi-degree-of freedom adjustment mechanisms for image quality compensation of the lithography projection objective are designed.The motion function and adjustment performance of the mechanisms are tested and studied.When the planar two-degree-of-freedom mechanism is used to adjust a curved mirror,the adjustment stroke of the mechanism in the macro-motion mode can reach ±2mm,the adjustment speed is larger than 4mm/s,and the adjustment resolution can reach 15 nm in the micro-motion mode.When the five-degree-of-freedom adjustment mechanism is used to adjust a plane mirror,the displacement adjustment error in the open-loop state is less than 0.21μm,the rotation adjustment error is less than 2.3μrad,the displacement adjustment repeatability error is less than 0.11μm.The repeatability deviation of the rotation adjustment is below0.76μrad,and the RMS change of the surface shape of the plane mirror introduced at different positions during the adjustment process is less than 3nm,which satisfies the requirements of the application in the lithography projection objective.