Performance evaluation of MOSFETs with discrete dopant distribution by one-by-one doping method

Abstract

This paper presents the fabrication and measurements of MOSFETs with various dopant distributions in the channels for investigating the impact of discrete dopant distribution on device performances. Phosphorus-ions are implanted orderly into the channels as well as asymmetrically into one side of channels both with ordered and random distribution by single-ion implanter with capability of one-by-one doping. Electrical measurements reveal that the threshold voltage (V th ) fluctuation for the ordered dopant arrays is less than for conventional random doping and the device with ordered dopant array exhibits two times the lower average value (-0.4V) of V th shift than the random dopant distribution (-0.2V). We conclude that the observed lower value originates from the uniformity of electrostatic potential in the channel region due to the ordered distribution of dopants. We also observe deviation in subthreshold current when interchanging the source and drain terminals. The subthreshold current is always larger when the dopants are located at the drain side than at the source side for both ordered and random distribution cases. We believe that this increase in current is caused by the suppression of injection velocity degradation in the source side. Accurately controlling both the amount and the positioning of dopant atoms is critical for the advancement of extending CMOS technologies with reduced variation caused by random dopant fluctuation.