To clarify the influence of crystal-originated “particles” (COPs) on gate oxide integrity (GOI), a new GOI evaluation method has been developed. This method compares the GOI of a metal oxide silicon (MOS) capacitor which includes a COP with a MOS capacitor that is COP-free by measuring the capacitors' I–V characteristics. Furthermore, to study the relationship between the shape of COP and GOI, the COP microstructure on the wafers was observed by atomic force microscopy (AFM) in the as-received state, after NH4OH/H2O2/H2O (SC-1) cleaning, high temperature annealing and repolishing. It was found that the presence of COP was the main cause of GOI failure and also that the shape of COP was closely related to the GOI yield. The microstructure of the original COP in a crystal is concluded to be an octahedral void and the same as an IR scattering defect.
Microstructure shape of “crystal-originated particles” (COP's) on mirror-polished silicon wafers (a) as received, (b) cleaned with NH4OH/H2O2/H2O solution (SC-1), and (c) annealed at high temperature (∼1150° C) in O2/N2 mixture or in H2, were observed using a scanning electron microscope (SEM), transmission electron microscope (TEM) and atomic force microscope (AFM). Elemental analysis of the COP's was also made using TEM-energy dispersion X-ray spectroscope (EDX). The COP was a pyramidal pit with {111} sidewalls, or a vertical cave having some facets of {111}. In a part of the COP, oxygen was detected by TEM-EDX.
It was suggested that the microstructure shape of the COP's has been determined until the mirror polishing is finished. The size of the COP becomes larger and the slopes of the COP become gentler after an anneal in 3% O2/N2 at 1150° C for 4 h and removal of the SiO2 layer by HF solution. The depth of the COP becomes shallower, its size larger and its corners rounder by annealing in H2 at 1100° C for 1 min. The COP's disappear by anealing in H2 at 1150° C for 4 h.
Influence of Fe contamination in CZ-grown silicon single crystal on oxidation-induced stacking fault (OSF) generation density, carrier recombination and generation lifetimes, and gate oxide integrity (GOI) yield characteristics was experimentally investigated. Two Fe-doped silicon ingots were grown and tested. Concentration of Fe-B ([Fe-B]) in these silicon ingots measured by deep level transient spectroscopy (DLTS) was about 5×1011 cm-3 and 5×1012 cm-3, respectively. OSF density generated by three-step annealing showed dependence on [Fe-B]. Carrier recombination lifetime (τ r) showed good correlation with [Fe-B], and a quantitative relationship was established. OSF density after one-step annealing, carrier generation lifetime (τ g) and GOI yield were not so dependent on [Fe-B].
The evaluation of B gettering for Fe impurities in p/p+ Si epitaxial wafers was carried out, after intentional Fe contamination, by measuring the Fe concentration in the epitaxial layer using deep level transient spectroscopy (DLTS). As the surface [Fe] before diffusion was increased, [Fe] in epitaxial layer also increased. As B concentration in the p+ substrate was raised, B gettering efficiency became higher. On comparison of the experimental results with the segregation gettering model, it was concluded that B gettering for Fe does not occur at a high temperature such as 800° C or 1100° C. B gettering for Fe can be inferred to occur below 600° C during the cooling process.
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