Quantification of germanium in Si1-xGex alloys by negative mode ToF-SIMS: the interest of the full spectrum method

The abundance of work on Si1-xGex-based devices demonstrates the importance of compositional characterization of such materials. The matrix effect in SIMS limits accurate concentration determination to a certain range of x. In previous works it was shown that this limitation can be surpassed by following MCs2+ secondary ions which allows Ge concentration to be quantified in the x = 0.05 to 0.85 range. Here an alternative protocol for Ge quantification using negative ion detection in ToF-SIMS is investigated. The negative secondary ion emission from epitaxially grown Si1-xGex was studied with a TOF SIMS V from ION-TOF GmbH. Although a fair linear correlation between ion ratios and Ge/Si layer composition ratios was found, non linear behavior was still present, hampering the precision of the method. Therefore, an alternative protocol was investigated, the full-spectrum method, which states proportionality between composition of the secondary ion beam and that of the actual material. SiGe layers were depth profiled with a long cycle time to allow detection of SinGem clusters up to n, m = 6. The Ge (Si) composition of the secondary ion beam was calculated and compared with the composition as determined by XRD. Excellent linear correlation is observed. The repeatability of the method and the influence of the sputter beam energy on the secondary ion beam composition were also studied. Copyright (C) 2010 John Wiley & Sons, Ltd.