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
C-V
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
(D = 2.38 \times 10^{-13}
cm
²
/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-(
dC/C)(V/dV
) is nearly constant