AN INVESTIGATION OF THE ROLE OF THE TIME-AVERAGED ION-BEAM CURRENT-DENSITY UPON THE DEFECT DENSITIES IN THIN-FILM SIMOX

The effect of the time averaged ion beam current density on the materi al quality of thin film SIMOX has been investigated. Thin film SOI/SIM OX material has been produced by 200 keV oxygen implantation into 3 in . Fz wafers with a background temperature of 680 degrees C. The dose r ange of 5 x 10(17)-7 X 10(17) O+/Cm-2 was selected to be near the dose threshold for the formation of a continuous buried oxide after implan tation and annealing which is thought to be between 5x10(17) and 6x10( 17) O+/cm(2) for 200 keV [A.E. White et al., Appl. Phys. Lett. 50 (198 7) 19; P.L.F. Hemment et al., Vacuum 36 (1986) 877; Y. Li et al., in: Proc. V Int. Symp. on SOI Technology and Devices (The Electrochemical Society, 1992) p.368 [1-3]]. The accelerator generates a beam spot wit h an elliptical shape and an area of 0.7 cm(2). The beam current densi ty within this spot ranged between 0.04 and 0.14 mA/cm(2). The oxygen ion beam was electrostatically scanned with a frequency of 425 Hz in t he gamma direction and 66 Hz in the x direction. The dependence of the defect density upon time averaged oxygen ion beam current for densiti es from 2.5 to 8 mu A/cm(2) has been investigated. The measured buried oxide layer thickness (t(sio2)) was similar to 1000 Angstrom and the silicon overlayer thickness (t(si)) was similar to 4000 Angstrom for a dose of 5 x 10(17) O+/cm(2). Samples were annealed in either nitrogen ambient at 1320 degrees C for 6 h or (argon + 0.5% oxygen) at 1300 de grees C for 6 h. Ramp up and cool down rates between 1O degrees C/min and 5 degrees C/min have been used. Material analysis using TEM (cross section and plan view) of both as-implanted and annealed samples as w ell as etch pit counting of annealed material reveal that the defect d ensity is sensitive to the ion beam current density. For annealed mate rial etch pit and TEM data reveal that samples implanted with 7X10(17) O+/cm(2) are highly sensitive to the time averaged beam current densi ty. A reduction in the pit density from 1x10(7) cm(-2) down to 2X10(6) cm(-2) for an increase in the time averaged beam current density from 2.5 to 3.7 cm mu.A/cm(2) has been recorded. Clearly this is significa nt for the processing of thin film SIMOX structures.