The charging effects of plasma immersion ion implantation (PIII) doping experiments have been investigated using a dynamic sheath model and PDP1 plasma simulation code. When the target has a dielectric film, charge accumulation during PIII can have a profound impact on doping results. Under certain process conditions, it can significantly reduce implant energy and dose and thereby alter the implant profile. In addition, it may degrade device reliability, especially for ultralarge-scale integrated circuit devices. In order to minimize charging effects, shorter pulse widths along with moderate values of plasma density and pulse potential should be used.
The charging and etching effects of hydride and fluoride gases in plasma immersion ion implantation (PIII) doping experiments have been investigated. Both phenomena can affect implant profile and dose, alter device structure, and degrade device reliability. In addition, charge accumulation significantly reduces implant energy. Helium is a good choice as a diluting gas for PIII doping processes due to its low ionization rate, inertness, and minimal etching and charging effects.
A general relation between the implanted dose and the processing time for plasma immersion ion implantation (PHI) can be established through the dynamic sheath model. In practice, etching and charging effects have to be taken into account in PIII dose estimation. Plasma immersion ion implantation (PII) has been tested in fabrication of semiconductor devices with shallow junctions and in hydrogénation of poly-Si thin film transistors (TFT). PIII doping is more suitable than conventional implantation for such applications because of its high dose rate at lower energy. Since the dose rate in PIII does not depend on the area being treated, the effective current will be higher if a larger implanted area is involved. However, the relation between dose and time is not always straightforward. During PIII processing possible etching and charging will affect the total accumulated doses. This paper presents a model for each which allows a proper compensation to be performed.
