The vacuum workpiece stage system is a key subsystem of EUV lithography (EUVL). Since the EUVL uses a step scanning exposure method, the imaging quality of the lithography machine depends not only on the quality of the optical system, but also on the dynamic positioning and dynamic synchronizing performance of the workpiece table and the mask table, so the mechanical structure of the workpiece table system Dynamic performance is as important as the quality of the optical system. The operation accuracy, speed, acceleration, and dynamic positioning and scanning synchronization performance of the workpiece stage and mask stage are important factors that affect the imaging quality, overlay accuracy and yield of the entire machine. The relative position error of the workpiece table and the mask table can lead to feature size misalignment (engraving accuracy) and wafer feature size (CD) uniformity deterioration and image blurring. Only in the ideal state where the mask table and the workpiece table are relatively stationary Quality can be completely determined by the optical system. In addition, the workpiece stage and mask stage control system is the control body of the whole machine. The control of almost all optical and electro-mechanical components (such as alignment, shutter, leveling and focusing, film feeding, environment and process, etc.) The workpiece table and the mask table are closely related, which undoubtedly greatly increases the difficulty in the design, manufacture, movement and environmental control of the workpiece table, especially the structural design and motion control of the workpiece table become particularly critical. The characteristics and working principle of 2EUVL workpiece stage system EUV lithography technology can be divided into three categories: (1) EUV feature technology such as light source, multilayer film and reflection optics; (2) Lithography that is different from other optics, but Commonly used technologies in non-optical lithography, such as vacuum technology and pollution control technology; (3) The extension of optical lithography technology, such as the workpiece stage, wafer calibration sensor, focus sensor and so on. Workbench technology is not a proprietary technology of EUVL but its high-resolution and high-yield features provide a higher fund project for the design, manufacture, and control of scanning workbench: The Chinese Academy of Sciences “Funded with Talents from Abroad†in 2001 Project (20011215); National 863 MEMS Major Special Fund Support Project (2003AA40415 (1) requirements. In addition EUVL is strictly synchronized in high vacuum environment, and their motion trajectory is also a strict process in the process of die and wafer movement speed motion position test system H镪 Test bench work, so the workpiece stage subsystem drive, guidance, testing, control and other institutions not only have high accuracy and stability, but also to adapt to the vacuum environment 2 - 3. EUVL workpiece stage system is generally It consists of a workpiece table, a mask table, and a corresponding measurement and control circuit, which is the EU-VL principle device diagram proposed by ASML for a 50-nm technology node.EUV light projected on the mask is reflected and passes through a narrow slit to enter the optical lens. The ratio of 4 4 is compressed and exposed on the wafer, the lens is fixed, and the wafer and mask are scanned in opposite directions. Its movement speed is 44. In order to guarantee the exposure quality of the wafer, the research status of 3EUVL workpiece stage technology in the whole exposure is currently the highest level of research on EUVL mainly by NIKON of Japan, CANON and several major companies of ASML in the Netherlands, and Sandia Lawrence Livermore Laboratory of America. For some research institutes, the core goal is to accelerate the commercialization of the EUV lithography machine, and to improve the precision, speed, and vacuum adaptability of the worktable, the ASML and Carl Zeiss and Oxford Instruments are the main targets. Etc. is working on an EUV lithography system development project (EUCLIDES), and has now designed a system structure, a vacuum workpiece stage and an EUV lithography test platform a version, a workpiece stage, a wafer transfer system, and a pollution control subsystem. Taking into account the physical and technical limitations of the vacuum environment, a preliminary test of the synchronization performance of the workpiece stage and the mask stage in the air environment shows that the average moving error (MA) of the workpiece stage-mask table is 2 nm, and the average moving scale NIKON launched a single guide rail, follow-up table, and electromagnetic drive in 1994 The machine's precision workpiece table was introduced in 1996, and the guideless workpiece stage was introduced in 1996. The EUV workpiece stage introduced by CANON adopts linear motor drive, air floatation guide structure and reaction force absorption device, which improves the stability of the workpiece stage system. The gas is used as a support, the frictional resistance is small, the moving speed is fast, the precision is high, there is no crawling, and the almost identical dynamic and static friction coefficient can be obtained, and the sensitivity of the workpiece stage is added, but compared with the magnetic levitation guide rail, the stiffness of the air floatation guide rail is relatively small. . The movement, guidance, circuit and test system are united to make the entire workpiece stage an organic whole in order to achieve the required functional requirements. The control system of the lithography machine workpiece stage includes hardware and software. Based on this, it realizes certain motion control and compensation functions. The acceleration, speed, and wafer adjustment time of the workpiece stage are important indicators that determine the productivity of the lithography machine. At a certain sampling rate, the controller compares the measured position information of the workpiece stage and mask table with the target position, and combines feedback and feedforward control methods to make the position error as close to zero as possible. Feedback Control Using Digital Filters The compensation amount is generated and the measurement error is compensated; while the feedforward is to correct the position error of the disturbance force before it occurs. Due to the cross coupling between the axes and the nonlinearity of the drive, the control method of the workpiece stage also becomes quite complicated. The position accuracy in the EUV exposure process is determined by various factors such as the stiffness of the entire structure, the accuracy of the feedback sensor and the corresponding circuit, and the control method used to process the sensor data. Schematic diagram of position feedback control for workpiece stage. The position information of the workpiece stage in all directions is detected by the interferometer and fed back to the controller. The controller compares it with the target position to correct the movement in real time. The movement of the workpiece stage must not only be accurate, but also have a high speed and stability. Therefore, the speed ring and the acceleration ring must be added to the control. This is the profile of the acceleration during the exposure of the workpiece stage. It can be seen from the figure that the movement of the workpiece stage can be summarized into four stages: the stability control of the start stage and the steady-state motor is generally combined with PID and feedforward control. The position sensor detects the displacement of the motor and estimates the speed and acceleration based on the position information, thereby controlling the motor speed and acceleration parameters. Synchronous control mainly includes the following three methods: a control strategy mainly based on workpiece stage motion, a control strategy mainly based on mask stage motion, and a control strategy mainly based on both synchronous and coordinated motions. Procof Li Hong, Zhou Yunfei. 100nm step scanning lithography machine wafer stage masking stage motion structure design Emerging Lithographic Zhu Xi, Yin Wensheng, Duan Guanghong. Lithography machine ultra-precision workbench. Electronic industry-specific equipment, 2004 Scan table technology for exposure equipment. Special Equipment for the Electronic Industry, 1999, Hu Xuxiao, Tai Xianqing, Yang Keji. Stepper Scanner Synchronization Control and Wafer Deformation Error Compensation Technology Research . China Mechanical Engineering, 2004, 15(3) 192-195.
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Research on EUV Lithography Vacuum Workpiece Technology
Research on EUV Lithography Vacuum Workpiece Technology
Core Tip: The vacuum workpiece stage system is a key subsystem of EUV lithography (EUVL). Since the EUVL uses a step-scanning exposure method, the imaging quality of the lithography machine depends not only on the quality of the optical system, but also on the dynamic positioning and dynamic synchronizing performance of the workpiece table and the mask table.