Robert Alan Moline

Tapered windows in SiO 2 by ion implantation

The enhanced etch rate of ion damaged SiO 2 has been used to controllably taper steps in thermally grown SiO 2 . A 50-keV Ar+implantation with a dose of 3 × 1013/cm2produces a uniform taper of 35-45° with no vertical step at the top edge of the window. These results are observed by viewing the sample on edge with a scanning electron microscope (SEM). The taper angle of the oxide varies from near vertical (90°) at a dose of 4 × 1012/cm2to very small angles at large dosages.

Recoil Implantation of 18 O from SiO 2 by Heavy Projectiles

The recoil implanation yield of oxygen atoms recoiled from thin, 18O enriched SiO2 layers into silicon substrates has been studied using the 180(p,α)15N nuclear reaction. For 24 keV Kr projectiles the 180 yield peaked at a thickness (~150 A) which approached the expected range of the Kr in SiO2, and ~2.5 oxygen atoms recoiled into the Si for each projectile. The cross section for recoiling into the Si was ~5 × 10-17 cm2/oxygen atom in the near-linear region stated above. For a fixed SiO2 thickness, the yield increased slightly with decreasing projectile energy until the projectile range was no longer greater than the oxide thickness.

Novel applications of ion implantation to LSI processing

Ion implantation has been successfully utilized to simplify the fabrication of a 1024 bit IGFET random access memory array ina novel manner. IGFET integrated circuits Often require enhanced surface doping to suppress unwanted spurious channels between devices. Using conventional diffusion technology, an extra masking level is required to form these regions. A technique has been developed which eliminates this extra mask by uniformly increasing the doping in the surface layer of the silicon and then controllably compensating the enchanced doping in the windows patterned to form gate oxide regions. Threshold voltage control is excellent, mobilities are normal and no undesirable effects have been observed if care is exercised in controlling the implanted doses.