Improvement Of Wafer Handling Robot And Its Positioning Accuracy Analysis

With the progress of semiconductor manufacturing automation, wafer handling robot has become a key unit in semiconductor manufacturing processes such as grinding, polishing, etching, assembly and package. Its handling stability and repeatability will directly or indirectly affect the quality of IC components, and the reasonability of mechanical and control systems will have direct impact on the accuracy, stability and security of the robot. Some defects existed in the former developed wafer handling robot, such as poor stability of control system and low repeatability which couldn't satisfy the requirements of wafer precise positioning, so the robot needs further improvement.This paper deals with key technical issues such as internal wires mutually winding and belt wheel slipping on the basis of the mechanical structure and the drive principles. By calibrating the end arm, installing limit switches and adjusting motor control parameters, the accuracy, security and the dynamic performance of the robot are upgraded. According to the position control mode of pulse plus direction, servo motor drivers and programmable multi-axis motion controller are connected, and then an experimental platform of wafer handling robot is perfected, which would lay a foundation for the follow-up hardware debugging, motion control and repeatability positioning accuracy analysis.In accordance with the working principles and motion characteristics of the wafer handling robot, the controlling scheme of "PMAC+PC" is applied. The PC is in charge of the non real-time motion control, and the PMAC is in charge of real-time tasks. After feed forward control is employed, a systemic structure including multiple controls of feedback and feed forward is realized. By setting the PID parameters in controller, systemic control precision is improved and good servo rigidity, stable system and small following error are obtained.With regard to the software controlling, the user-friendly interactive interface is designed, and more new functions such as real-time control for servo drive system, motion procedures and PLC programs to be called and robot tri-axial linkage are added.Finally, debugging work of wafer handling robot is completed through calling control programs, and repeatability is analyzed. A lot of data about robot's lift, rotation and radial movement, which are collected in the designated locations, is conveyed to control procedures for compensation. So, repeatability of robot is improved(radial repeatability is±0.12mm, rotary repeatability is±0.03°, up and down repeatability is±0.04mm), which ensures the wafer positioning accuracy.