Mirror-Polishing Residual Damage characterization in the Subsurface of Si Wafers Using N 2 Laser /mm-Wave Photoconductiv
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*Kanagawa Institute of Technology, Atsugi, Kanagawa, 243-02 Japan **Sumitomo Sitix Corp., Silicon Research & Development Center, Kishima, Saga, 849-05 Japan
ABSTRACT The problem is occurring that gate oxide integrity (GOI) might be influenced on the residual subsurface damages induced by mirror polishing. The correlations between mirror polishing conditions, micro roughness, and photoconductivity amplitude (PCA) signals are measured and discussed in a small roughness region of micro roughness R-rms such as 0.095 nm to 0.247 nm. The theoretical analysis shows that PCA signal is possible to reflect a subsurface lifetime.The discussions lead to result that the GOL is mainly dependent on subsurface damages in such small roughness region, PCA signals measured with an UV/mm-wave noncontact technique correlate closely with the GOI yield. It is concluded that the PCA technique makes it possible to characterize subsurface damages and to estimate GOI yield. INTRODUCTION As the device dimension reduces and the device fabrication number in ULSI increases, strict characterization of the subsurface, interface, and surface of Si wafers is strongly demanded. The correlation between the gate oxide integrity (GOT) and the surface micro roughness has been
reported[1-3]. However, if the GOI is influenced by not only surface roughness but also subsurface damage, we have to consider about the influe\nce of the subsurface damage. However, we have not any tools to detect or observe such the damage. The minority carrier recombination lifetime is well known to be very sensitive to the defects, heavy metals contamination. Noncontact lifetime measurement is one of the most powerful technique to evaluate the crystal quality in Si wafers and the wafer processes for the device fabrication. The most popular technique for measuring the lifetime is the photoconductivity decay technique. Ogita has proposed a new photoconductivity technique for characterizing the subsurface and epilayer property in epitaxial wafer by using an UV laser to excite carriers and a mm-wave probe to detect the photoconductivity change[4-7]. The lifetime measurement [8] and photoconductivity amplitude (PCA) technique have revealed the existence of the residual damage left in the subsurface after final mirror polishing[67]. Further, the techniques also have revealed that the damage can be removed by the SCI cleaning[6-7]. However, we have not had any reports about correlations between gate oxide integrity, subsurface damages, and mirror polishing conditions. Furthermore, there has not been any tools to characterize or detect the subsurface damages. The PCA signal obtained with the UV/mm-wave technique owns the high sensitivity to the subsurface properties as described above. Thus, the target of this study is to confirm that the PCA technique characterizes the subsurface damage and the GOI is influenced by the subsurface damage induced by the mirror polishing. 209 Mat. Res. Soc. Symp. Proc. Vol. 477 ©1997 Materials Research Society
PCA TECHNIQUE The laser pulse with T, in
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