Reducing the qualification time of low energy phosphorus ion implantation process using spectroscopic ellipsometry for dynamic random access memory production line


 In this study, a new method has been applied to monitor the low energy phosphorus ion implantation process in dynamic random access memory (DRAM) production line using spectroscopic ellipsometry (SE). The dose sensing ability of SE is similar level to that of wavelength dispersive X-ray fluorescence (XRF) and the energy sensing ability is almost twice stronger than that of XRF. The coefficient of determination of SE has been confirmed that it is higher than 95% both for the implantation dose and energy as variables. In the case of XRF measurement, the photoresist (PR) must be removed by ashing and strip processes before measuring the phosphorus concentration to avoid the chamber contamination in high vacuum. However, there is free of contamination issue for SE in the presence of PR, so the phosphorus concentration can be monitored by SE immediately after implantation. Consequently, the qualification time can be reduced at least as much as waiting and running time of the ashing and the strip processes. It is worth to note that the measuring speed of SE is 33 times faster than that of XRF. Considering the advantage of fast speed of SE measurement, the number of measurement points was increased from 5 to 21 including 8 points of wafer edge to enhance monitoring of product quality. In this work, the qualification time has been reduced effectively by 39.2% in average in production lines by using SE technology.