LARGE-AREA SHOWER IMPLANTER FOR THIN-FILM TRANSISTORS

Solid-state diffusion and conventional ion implantation are not suitable for source and drain regions formation of polysilicon thin-film transistors on glass substrates. A 30 cm diameter large-area low-energy ion shower implanter with RIPE ion source and double-grid extraction system was developed as a possible low-cost solution. The ion beam current density for hydrogen plasma was 100 muA/cm2 for 3 keV implant energy, 300 W RF power, 140 gauss magnetic field and 3 x 10(-4) mbar pressure. The uniformity of beam current density over the central 20 cm diameter was +/- 3.5%. Phosphorus implantation has been performed using a 15% PH3 in H-2 gas mixture. Implantation at 3 keV for 5 min. results in an integrated dose of 2.48 x 10(16) cm-2, with the concentration peak at a depth of 8.3 nm. Planar and mesa diodes fabricated on p-type silicon substrates have yielded fine rectifier characteristics. The shower implanter is thus suitable for TFTs source and drain region formation.