Effects of Silicon Ion Implantation Upon Thin Gate Oxide Integrity
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EFFECTS OF SILICON ION IMPLANTATION UPON THIN GATE OXIDE INTEGRITY G.-S. LEE,* J.-G. PARK,* S.-P. CHOI,* C.-H. SHIN,* KWAK,* C.-K. SHIN,* W. L. SMITH,** and S. HAHNt
Y.-B.
SUN,*
Y.-S.
*Samsung Electronics, Quality Control 1st Section, Kyungki-do, Korea "**Therma-Wave, Inc., Mission Falls Court, Fremont, CA 94539 U.S.A. tDepartment of Materials Science and Engineering, Stanford University, Stanford, CA 94305 U.S.A.
ABSTRACT In this study, using oxide breakdown voltage and time-dependent-dielectric breakdown measurements, thermal wave modulated reflectance and chemical etching/optical microscopy, we investigated effects of Si ion implantation upon formation of D-defects and thin gate oxide integrity. Our data show that addition of Si ion implantation with a dose of up to 1013 ions/cm2 improves oxide integrity if the implantation is done at a certain step just before sacrificial oxidation in the Mb DRAM process. However, no improvement in oxide integrity is observed when the same implantation is done on the virgin wafer surfaces at the start of the same Mb DRAM process. We discuss our hypothesis that the improvement in oxide integrity is due to a reduction in the D-defect density in the near-surface region of the wafer. INTRODUCTION Point defects in silicon single crystals have been extensively studied. Among many reported defect structures in open literature, two different types of point defect clusters have been well known, namely, A- and D-defects. A-defects were reported as silicon interstitial dislocation loops by transmission electron microscopy (TEM) observation [1]. In contrast, it is difficult to confirm the composition of D-defects. D-defects have been shown to affect thin oxide integrity [21; for this reason, these defects have recently been investigated extensively. By using a technique involving inner diffusion of vacancies or of interstitial silicon atoms after annealing in various kinds of ambient [31, Abe reported that D-defects contained vacancy agglomerates. Since vacancy-nature defects are very difficult to observe directly, rather indirect methods have to be used to gain further insights in these defects. One of the external methods to reduce the concentration of vacancies (and vacancy-related defects) near the surface region is the implantation by silicon ion. In this investigation, we studied effects of silicon ion implantation upon formation of D-defects and thin gate oxide integrity with oxide breakdown voltage and time-dependent-dielectric breakdown characteristics measurements, thermal wave modulated reflectance (mapping and imaging modes), and chemical etching/optical microscopy. THERMAL WAVE MODULAI ED REFLE(T-ANCE A. Mapping Mode In the commercially available apparatus employed here [4], thermal waves are generated and detected using two low-power laser beams focused to a 0.8 Prm spot diameter on the' wafer surface. This method has been described previously [5,6].
Mat. Res. Soc. Symp. Proc. Vol. 262. @1992 Materials Research Society
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B. Imaging Mode The imaging mode of the the
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