EXPERIMENTAL-STUDY OF THRESHOLD VOLTAGE FLUCTUATION DUE TO STATISTICAL VARIATION OF CHANNEL DOPANT NUMBER IN MOSFETS

Threshold voltage fluctuation has been experimentally studied, using a newly developed test structure utilizing an 8 k-NMOSFET array. It has been experimentally shown that both V(th) and the channel dopant numb er n(a) distributions are given as the Gaussian function, and verified that the standard deviation of n(a) can be expressed as the square ro ot of the average of n(a), which is consistent with statistics. In thi s study, it has been shown that V(th) fluctuation (deltaV(th)) is main ly caused by the statistical fluctuation of the channel dopant number which explains about 60% of the experimental results. Moreover, we dis cuss briefly a new scaling scenario, based on the experimental results of the channel length, the gate oxide thickness, and the channel dopa nt dependence of deltaV(th). Finally, we discuss V(th) fluctuation cau sed by the independent statistical-variations of two different dopant atoms in the counter ion implantation process.