Plasma processing has been widely used in the semiconductor and other industries for many decades. Plasma processing is used for tasks such as cleaning, etching, milling, and deposition. More recently, plasma processing has been used for doping. Plasma doping is sometimes referred to as PLAD or plasma immersion ion implantation (PIII). Plasma doping systems have been developed to meet the doping requirements of state-of-the-art electronic and optical devices.
Plasma doping systems are fundamentally different from conventional beam-line ion implantation systems that accelerate ions with an electric field and then filter the ions according to their mass-to-charge ratio to select the desired ions for implantation. In contrast, plasma doping systems immerse the target in a plasma containing dopant ions and then bias the target with a series of negative voltage pulses. The term “target” is defined herein as the workpiece being implanted, such as a substrate or wafer being ion implanted. The negative bias on the target repels electrons from the target surface thereby creating a sheath of positive ions. The electric field within the plasma sheath accelerates ions toward the target thereby implanting the ions into the target surface.
Conventional beam-line ion implantation systems that are widely used in the semiconductor industry have excellent process control and also excellent run-to-run uniformity. Conventional beam-line ion implantation systems also provide highly uniform doping across the entire surface of state-of-the art semiconductor substrates. Plasma doping systems for the semiconductor industry must also have a very high degree of process control. However, in general, the process control of plasma doping systems is not as good as conventional beam-line ion implantation systems.