Ion-implanted hyperabrupt junction voltage variable capacitors

Voltage variable capacitors have been fabricated using ion implantation and a PtSi Schottky barrier to obtain a high degree of control over the doping in a hyperabrupt diode structure. Three methods for obtaining the desired doping in the hyperabrupt region have been investigated, including diffusion from a low energy predeposition and higher energy implantations with no diffusion. The characteristics for two different profiles, made using diffusion to drive in an ion predeposition, agree well with theoretical calculations if a Gaussian diffusion profile peaked at the surface is assumed cm²/s for phosphorus at 1100°C in an oxygen ambient). It has been found that the device parameter spread of about 7 percent is dominated by nonuniformities in the donor concentration of the epitaxial layer. Parameter variations due to sources other than the epitaxial layer doping are about 3 percent. Low-dose channeling implantations have been made to tailor the profile such that the sensitivity-( ) is nearly constant