4-Stesmans-JAP-1047-1994 - G eneration aspects of the...

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Generation aspects of the delocalized intrinsic EX defect in ther A. Stesmans and F. Scheerlinck Department of Physics, Katholieke Universiteit Leuven, 3001 Leuven, Belgium (Received 23 August 1993; accepted for publication 4 October 1993) A K-band electron-spin-resonance study of the appearance of the delocalized intrinsic EX center in dry thermal SiOz was performed on (001) and ( 111) Si/SiOZ. The defect is found in both structures in nearly identical spin densities, 1.2X 10 ” cm- ’ being the maximum area1 density. Variation of Si precleaning treatments showed the center ’s generation to depend on the initial surface condition of the c-Si substrate. For fixed initial surface conditions, however, systematic variation of the oxidation temperature ( 760-930 “C!) , oxidation time (a few min up to 24 h ) , and oxygen pressure ( -24 and - 110 kPa), in combination with stylus protilometry, revealed the area1 density to be zolely determined by the grown oxide thickness (d,,), EX being detectable from d ,~70 A onwards, with a maximum intensity at d,,,=: 125 A. Etch back experiments showed the defects to reside in the top 45 8, of the oxide layer, with the largest local volume density ( -3 x lOI cme3> occurring near the ambient/SiOa interface. With growing oxide thickness, the spatial profile remains largely unchanged, the mere effect being changes in the overall EX area1 density. Alternated isochronal anneals in H2 and vacuum revealed the defect ’s thermochemical properties to be dominated by the interaction with H,, in a very similar fashion as for the Pb center at the ( 111) Si/SiOz interface. Possible hints of these growth aspects as to the nature of the EX defect are discussed. I. INTRODUCTION The Si/SiOZ structure is still the basic ingredient in today ’s semiconductor technology and continuous effort is therefore invested in optimizing the quality of the various constituents of this entity. The detrimental intluence de- fects may have on the otherwise excellent electrical prop- erties of this successful structure has been a major stum- bling block since the advent of semiconductor technology. Hence, optimum device operation requires strict ways to limit these to acceptable levels, a search often guided by the understanding of the natures of these defects. The pres- ence, for instance, of electronic states within the band gap of silicon at the Si/SiOZ interface is partly responsible for alteration of the channel conductance and for threshold voltage shifts in MOS (metal-oxide-semiconductor) field- effect transistors. Similarly, charge trapping defects in the gate oxide can-if present substantial amounts- produce a space-charge layer strong enough to alter device characteristics through the effect of band bending. The de- fect aspect of the MOS structure has become more strin- gent than ever: not only will the relative impact of the nonscaling Si/SiOZ interface increase with reducing gate oxide thickness (now entering the sub 100-A region), but, moreover, severe demands will be placed upon the quality of the thin thermal oxides. As studied by electron
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4-Stesmans-JAP-1047-1994 - G eneration aspects of the...

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