New DLTS Peaks Associated with New Donors and Rodlike Defects in Czochralski Silicon
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NEW DLTS PEAKS ASSOCIATED WITH NEW DONORS AND RODLIKE DEFECTS IN CZOCHRALSKI SILICON AND MINORU YONETA YOICHI KAMIURA, FUMIO HASHIMOTO, Faculty of Engineering, Okayama University, Okayama 700,
Japan
ABSTRACT We have studied the effects of low-temperature preannealing and carbon on new donor formation at 650 0 C in phosphorus-doped Czochralski (CZ) silicon
by deep-level transient spectroscopy (DLTS).
In not preannealed carbon-lean
samples, only a weak continuous DLTS spectrum often reported so far was observed. The intensity of this broad feature became significantly stronger in not preannealed carbon-rich samples. On the contrary, preannealed samples showed no such continuous spectra but two new DLTS peaks arising from shallow donor levels. Carbon enhanced the low-temperature peak, but retarded the high-temperature one. The latter peak is in strong correlation with the rodlike defect. INTRODUCTION
Oxygen-related donors, called new donors (NDs),
have been recognized to
be created by annealing CZ silicon at 600 to 800 0 C [1-9]. However, little has been known about their electronic properties. Hall experiments indicated that the activation energy of NO level varied from 30 to 120 meV depending upon annealing temperature and duration [10]. DLTS experiments showed no discrete electronic levels but only continuous spectra explained by interface states at the surface of SiOx precipitates [11, 12]. On the contrary, admittance spectroscopy experiments revealed a discrete peak at Ec19 meV ascribed to a level localized within the quantum well surrounding small positively charged oxide precipitates [13, 14]. On the other hand, two kinds of structural defects, oxide platelet precipitates and elongated rodlike defects (RLDs) have been observed by transmission electron microscopy (TEM) [15-18]. However, connections between these defects and NDs have not been clear yet. In this paper, we present results of DLTS experiments on the effects of low-temperature preannealing and carbon atoms involved in crystals on ND formation at 650 0 C, and discuss the correlations of observed DLTS peaks with NDs and the above structural defects. EXPERIMENTAL
We used two kinds of n-type CZ crystals with comparable phosphorus densities (4-7xi0 1 4 cm- 3 ) and oxygen densities (8-10xl0 1 7 cm- 3 ) but different carbon densities; one is a normal crystal (C-lean) with a low carbon density less than IxlO1 6 cm-3 , and the other (C-rich) is a carbon-doped one (l.5xl17 cm- 3 ). Experimental details of heat treatments of samples and measurement procedure of resistivity and DLTS were the same as described in our previous paper [19]. Wright etching [20] was applied to reveal defects. TEM observations were done in the bright field under an accelerating voltage Mat. Res. Soc. Symp. Proc. Vol. 163. s1990 Materials Research Society
292
of 200kV. RESULTS AND DISCUSSION Figure 1 shows the effects of low-temperature preannealing and carbon on DLTS spectra due to NDs generated at 6500 C. In a carbon-lean sample annealed directly at 650 0 C for 1.5xl0 4 mi
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