Bias frequency dependence of pn junction charging damage induced by plasma processing

Abstract

Plasma-induced charging damage to pn junction in metal-oxide-semiconductor field-effect transistors (MOSFETs) was studied by using an inductively coupled plasma (ICP) reactor with Ar gas. The junction leakage current ( I leak) was measured for various source/drain to well in MOSFETs and simple diode structures. Two different rf bias frequencies, 13.56 MHz and 400 kHz, were utilized to investigate the effect of frequency on an increase in I leak. The I leak of n +/p and p +/n junctions was found to increase by a plasma treatment. In particular, more severe damage was observed for n +/p junction in both n-channel MOSFETs and the diodes. These observed results imply that plasma plays a role primarily as a positive current source. With regard to the rf bias frequency effects, samples exposed to the 400-kHz plasma were found to suffer from larger I leak than those to the 13.56 MHz. From capacitance–voltage ( C– V) measurement of junction capacitance changes, we also clarified that the observed increase in I leak was attributed to the defect density at pn junction created by the plasma charging damage.