Enhancing Device Performance by Single Ion Implantation

As the size of semiconductor devices continues to shrink, the normally random distribution of the individual dopant atoms within the semiconductor becomes a critical factor in determining device performance - homogeneity can no longer be assumed. To fabricate semiconductor devices in which both the number and position of the dopant atoms are precisely controlled, we have developed single-ion implantation technique. This technique enables us to investigate the electrical properties of semiconductor devices such as one with random dopant distribution, one with ordered dopant distribution, and one with asymmetric dopant distribution.

We have achieved the single-ion doping technique by equipping a conventional focused ion beam apparatus with a special feedback control system. The ion beam separated by an E x B mass filter is chopped by an electric deflector in front of a small aperture. The probability of the ion extraction is set to be less than 1% by reducing the ion beam current and chopping the ion beam with a high velocity. When the ion beam is chopped many times, an ion passes through the aperture. The number of ions extracted from the aperture obeys the Poisson distribution. We detect secondary electrons emitted from the sample surface in response to the single-ion incidence, count up the number of incident ions, stop ion beam chopping, and focus the ion beam at the next aiming point. This procedure is repeated until the intended ion alignment is achieved on the sample surface. The error in the alignment position is less than 60 nm, and more than 20 ion species including boron, phosphorus, and arsenide can be implanted one by one.

Thus far, we have succeeded in enhancing the performance of MOSFETs by fabricating an ordered dopant array in the channel. Currently, the channel length has shrinked to only a few nanometers, and the fluctuation in the threshold voltage becomes a serious issue. We will overcome this fluctuation by the single-ion implantation.


T.Shinada, S.Okamoto, T.Kobayashi, I.Ohdomari: Enhancing semiconductor device performance using ordered dopant arrays, Nature 437, 2005, 1128-1131.

I.Ohdomari: Single-ion irradiation: physics, technology and applications, Journal of Physics D-Applied Physics 41, 2008, 043001.

M.Hori, T.Shinada, K.Taira, N.Shimamoto, T.Tanii, T.Endo, I.Ohdomari: Performance enhancement of semiconductor devices by control of discrete dopant distribution, Nanotechnology 20, 2009, 365205.