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Goldsilicafilm forms a film of SiO2 with gold in colloidal dispersion. It is
applied to silicon wafers by spinning or spraying. When heated to temperatures in excess
of 900oC, gold atoms will diffuse from the SiO2 layer into the
silicon. The gold atoms dissolved in the silicon will act as recombination centers and
limit the lifetime of excess minority carriers in the silicon lattice. Goldsilicafilm,
unlike Goldfilm, is designed for application to the polished surface of the wafer. Gold
diffusion is obtained without surface pitting. In this way, a most efficient gold doping
process may be carried out by introducing the gold from the active surface.
Application of Goldsilicafilm:
Goldsilicafilm is applied to the wafer surface, through windows in the masking oxide. Spin speeds of 3000 to 6000 rpm are adequate. A glassy film with gold dispersed in it will form after 5 to 10 seconds of spinning. The wafers may then be diffused, or if it is desired to store the wafers prior to diffusion, they should be heated at 200-250oC for 10 to 15 minutes to harden the film.
No particular dependence of gold doping concentration on ambient atmosphere has been observed. The gold saturation concentration introduced into the silicon will be temperature dependent, and will follow the same temperature concentration curve usually observed for gold in silicon. Goldsilicafilm will provide sufficient gold to saturate a 10 mil silicon wafer at 1200oC.
After diffusion, Goldsilicafilm is removed by soaking the wafers in 10% HF or buffered HF solution for two to three (2-3) minutes.
GOLDSILICAFILM With Phosphorous - GOLDSILICAFILM With Boron
These doped Goldsilicafilm formulations are supplied as two solution formulations labelled "A" and "B". While both the "A" and "B" components have extended shelf lives, the mixtures exhibit stability on storage of 1 to 2 weeks. For use, the "A" and "B" components are mixed in equal volume about 1 hour prior to use. They are then applied in the same manner as is Goldsilicafilm. The doped Goldsilicafilm will then yield N+ and P+ layers with deeper diffused gold region immediately ahead of the N+ or P+ region. In this way, emitter diffusion and lifetime control are carried out in a single step. The Phosphorous or Boron surface concentration will be 1x1020 atoms/cm3, and normal emitter diffusion processes may be employed.
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