Development of a Real-Time Boron Concentration Monitoring Technique for Plasma Doping Implantation

Abstract

Plasma doping (PLAD) technology is widely used in the semiconductor industry. One of the problems associated with PLAD is precise dosage control and monitoring during the doping process. Excessive boron doping into the n-type poly gate will affect the p-MOSFET threshold voltage. In this study, we develop a novel method for the real-time monitoring of the boron concentration as it penetrates into an oxide film. We attempted to determine whether the real-time monitoring of the boron concentration can be replaced by measuring the thickness of the damaged layer remaining after plasma doping and a cleaning process, since the thickness of the damaged layer can be measured relatively easily in real time by means of ellipsometry. It is found that as the plasma doping energy is increased, the boron concentration increases linearly, with a strong correlation (R2 = 0.98) between the plasma doping energy and the boron concentration. Moreover, there is a close relationship between the plasma doping energy and the thickness of the damaged layer. As the doping energy is increased, the thickness of the damaged layer also increases linearly. We also find a close correlation (R2 = 0.92) between the change in the thickness of the damaged layer and the p-MOSFET threshold voltage. In summary, there are very good correlations between the plasma doping energy and the concentration of boron, the doping energy and the thickness of the damaged layer, and the thickness of the damaged layer and the threshold voltage. It is proven that the concentration of boron penetrating into the oxide layer can be monitored by measuring the thickness of the damaged layer in real time.