An investigation of the role of the time averaged ion beam current density upon the defect densities in thin film SIMOX

Abstract

The effect of the time averaged ion beam current density on the material quality of thin film SIMOX has been investigated. Thin film SOI/SIMOX material has been produced by 200 keV oxygen implantation into 3 in. Fz wafers with a background temperature of 680°C. The dose range of 5 × 10 17−7 × 10 17 O +/ cm 2 was selected to be near the dose threshold for the formation of a continuous buried oxide after implantation and annealing which is thought to be between 5 × 10 17 and 6 × 10 17 O +/cm 2 for 200 keV [A.E. White et al., Appl. Phys. Lett. 50 (1987) 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 with an elliptical shape and an area of 0.7 cm 2. The beam current density 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 the y direction and 66 Hz in the x direction. The dependence of the defect density upon time averaged oxygen ion beam current for densities from 2.5 to 8 μA/cm 2 has been investigated. The measured buried oxide layer thickness ( t SiO 2 ) was ~ 1000 Å and the silicon overlayer thickness ( t Si) was ~ 4000 Å for a dose of 5×10 17 O +/cm 2. Samples were annealed in either nitrogen ambient at 1320°C for 6 h or (argon+ 0.5% oxygen) at 1300°C for 6 h. Ramp up and cool down rates between 10°C/min and 5°C/min have been used. Material analysis using TEM (cross section and plan view) of both as-implanted and annealed samples as well as etch pit counting of annealed material reveal that the defect density is sensitive to the ion beam current density. For annealed material etch pit and TEM data reveal that samples implanted with 7×10 17 O +/cm 2 are highly sensitive to the time averaged beam current density. A reduction in the pit density from 1× 10 7 cm−2 down to 2 × 10 6 cm −2 for an increase in the time averaged beam current density from 2.5 to 3.7 μA/ cm 2 has been recorded. Clearly this is significant for the processing of thin film SIMOX structures.