An advanced MOS-IC process technology using local oxidation of oxygen-doped polycrystalline silicon films

An advanced MOS process technology based on the local oxidation of oxygen-doped polysilicon (O-POS) films has been developed. The O-POS film deposited directly on silicon was oxidized locally for the active gate area, while the rest of the O-POS film, corresponding to the field region in a MOS-IC, was not oxidized. The threshold voltage for the active gate area was the same value as conventional p- and n-channel MOS devices but the field area had an extremely high threshold voltage of 60 to 100 volts for both p- and n-type silicon substrates. In order to study the dependence of device characteristics on process parameters, the electrical properties in Metal/Oxidized O-POS/Silicon, and Metal/ CVD Oxide/O-POS/Silicon structures were measured while varying the O-POS film thickness, oxygen concentration, local oxidation time, and silicon substrate resistivity. According to these basic studies, the high field threshold voltage is due to the high density of trapping centers existing at the CVD oxide/O-POS interface. As applications of this process technology, a high voltage n-channel MOS device and a silicon-gate C/MOS-IC fabricated without channel stoppers are discussed.