Sheet resistance measurement for ultra-high energy ion implantation

Abstract

Ion implanters require high energy to improve the light sensitivity of advanced image sensors with deep photodiode structures. Although high energy ion implanters enable deep implantation, the conditions near the wafer surface may differ from those in shallow implantation. As the implantation energy increases, the dopant ions are implanted deeper into the wafer. Consequently, the conventional four-point probe tools are inappropriate for measuring the electrical sheet resistance of the wafer. As an alternative, a sacrificial oxide layer is applied to the wafer surface and then removed after ion implantation, which allows measuring the sheet resistance of such wafers.