Sputter rate variations in silicon under high-k dielectric films

SIMS depth profiles obtained from a B implanted Si sample capped with a thin HfO2 film revealed the presence of several artifacts that make it problematic to determine the distribution and concentration of elements in the underlying Si substrate. The distribution of the B implant, normalized to 30Siþ, was much broader than expected. Variations in the intensities of several matrix species under the HfO2 film were also observed. AFM measurements from the sputtered crater bottoms suggested that sputter-induced surface roughness is present under the high-k/Si interface. The roughness is partially responsible for reducing the sputter rate, which in turn lowers matrix ion intensities. The sputter rate variation can be corrected using the ratio of intensity loss of different matrix species. Use of the variation in the SiOþ intensity to correct the depth scale of the normalized B profile provided the best agreement with the original B implant-only sample. Rotating the sample while profiling improves the shape of the normalized B profile but some sputter rate correction was still necessary. The presence of 10% Hf (atomic) in the Si leads to slight reduction in the SiOþ intensity but the sputter rate does not need correcting. Under these conditions, point-by-point normalization of the B profile to a matrix species cancels out the ion yield variations. At Hf concentrations >10% the combination of ion yield and sputter rate variations complicates the depth profiles. # 2004 Published by Elsevier B.V.