Design And Development Of Monitor System For Ultra-precision Grinding Machine

Ultra-precision grinding machine is one of the key equipments in integrated circuit manufacturing, which is mainly used in both manufacture of primary wafer and backside thinning of patterned wafer. To improve the machining precision in the process of wafer grinding, on-line monitoring of the grinding process has become the current trend.In the process of grinding, the grinding force is a key physical parameter, generally reflecting properties and state of material, and the characteristics of grinding wheel and abrasion state. It is an effective method to control the grinding process, through on-line measuring grinding forces and real-time self-adapting the grinding parameters in terms of the measuring results. The wafer thickness has to be measured in process, in such a way that the feeding speed of grinding wheel can be controlled to ensure the uniformity of the wafer manufacture precision and wafer thickness. Besides, wafer is held by vacuum chuck, and the vacuum pressure not only ensures the firmness of the chucked wafer, but also affects wafer surface shape. According to such requirements, a monitor system for wafer-rotating grinding machine is designed and developed, fulfilling functions of on-line monitoring the grinding forces and the vacuum degree of vacuum chuck, in-process measuring the thickness of wafer and controlling the machine movements.The contact thickness measuring equipment consists two one-point gauges of linear variable differential transformer using the method of measuring step height to satisfy the precision of wafer manufacturing. Quartz piezo-electric sensors are used to on-line measuring three-dimensional grinding forces, the measurement of which are compared with thresholds for monitoring the grinding process. A silicon diffusion pressure sensor is used to measure vacuum degree of chuck table to ensure that wafer is firmly chucked during grinding.The monitoring system runs on a host IBM-PC. A data-acquisition card and an I/O card are used as input and output devices for incoming signals and control signals. The software for this monitor system is written in Visual C++, The software performs data acquisition, processing, and monitoring of grinding forces, vacuum degree and wafer thickness, It then sends out switching signals to control the magnetic valves and relays for equipment control. Control signals are sent out to adjust feeding speed of the grinding wheel in response to measured thickness.The experimental results indicated that the wafer thickness measurement equipment can measure wafer thickness accurately, high speed grinding forces data can be real-time measured without loss and vacuum degree can be monitored. The whole design is feasible and reliable, and the designated functionalities are all achieved successfully. This provides support for the development and production of ultra-precision grinding machine and research work of grinding technology from a technical point of view.