In situ sample temperature measurement in plasma immersion ion implantation

Plasma immersion ion implantation (PIII) is an excellent surface modification technique because it is not restricted by the line-of-sight limitation that plagues conventional beamline ion implantation. However, the lack of in situ monitoring has hampered wider acceptance of the technique in industry. It is known that the implantation temperature has a large influence on the surface properties of the treated specimens in addition to the more obvious parameters such as implantation voltage, pulse duration, pulsing frequency, and so on. Direct measurement of the target temperature is complicated by the sample high voltage as well as by interference from the electromagnetic field and plasma. In this article, we present a novel interference-free, in situ temperature measurement technique employing a shielded thermocouple directly attached to the sample stage. Our experiments show that the setup can monitor the target temperature in real time, even under severe arcing conditions. Our results also indicate that in a hot filament glow discharge radiation heating is quite small, and sample heating is primarily caused by ion bombardment during the PIII cycles. The new design will open up other possibilities such as in situ dose monitoring if, for example, the thermocouple is replaced by a Faraday cup.