Dot-array implantation for patterned doping of semiconductors

Abstract

Novel ion beam processing for microelectronic applications has been performed by doping silicon with a focused ion beam tool. A Ga+ ion beam with a energy between 10 and 50keV was used for p-doping of Si. The ion beam could be focused to an effective beam diameter in the sub-micron range with the smallest focus own below 10nm. In contrast to conventional implantation with a broad ion beam where the doped area is assigned by a hardmask the implantation was achieved by scanning a focused ion beam over the designated implantation area. With this approach not only the hardmask becomes obsolete because of the electronic beam guidance. Moreover, different doses may be implanted on the same wafer. An additional feature is the inhomogeneous implantation in a pixel-array, where the distance between exposed pixels can be deliberately varied. Even single spots can be independently doped with the focused gallium beam. Due to lateral scattering of ions in the semiconductor the circular implantation area is larger than the beam diameter. With a variation of the pixel spacing we could intentionally obtain either a overlap or a separation of implantation spots. With a four-point method we have investigated the conductivity of the dot-array implanted area.The conductivity of the p-doped region could be deliberately scaled by varying the pixel spacing, the implantation dose and the ion energy. The effective implantation diameter of a single pixel could be determined. This modified implantation approach was also used to fabricate functional p-channel MOSFET’s. The Ga implantation with a focused ion beam was used for p-doping of source and drain regions of the transistor device. The utilization of this dot-array implantation with a FIB for semiconductor circuitry demonstrates the potential application of this approach. With the laterally inhomogeneous implantation dot-arrays of doped zones in the nanometer range could be fabricated.