An n-channel mosfet process using high energy ion implanted boron for field and active device doping

This paper describes a 5 mask process (6 masks with overlay pyrolytic oxide) for fabricating aluminum-gate n-channel MOS circuits having enhancement and depletion devices, and which can operate from a single +5 volt supply. Two ion-implant steps are used, a high energy boron implant to dope the surface, and a phosphorus implant to make the depletion devices. The boron implant is used to prevent surface inversion on the high resistivity p-type silicon substrate and also to set the threshold of the enhancement devices. Doubly-charged boron (B⁺⁺) at 210 keV is used to penetrate the 9000 Åthick field oxide. This places the peak of the implanted ion distribution just inside the silicon surface. The performance of MOS/LSI circuits having enhancement and depletion devices made using this process is described.