Development of easy-to-use surface passivation schemes for lifetime measurements on monocrystalline Si with (100)-orientation

In this paper we report on modified "dry" chemical surface passivation schemes for contactless microwave-detected photoconductance decay measurements on Si (100) substrates. By varying the HF-concentration in the aqueous HF-solution and the preceeding chemical oxidation treatment it was found that the best passivation occurs after dipping in a 49%-HF-solution resulting in surface recombination velocities around 300 cm/s. Such a value is however still not sufficient for measuring bulk lifetimes >50 microseconds on wafers with typical thicknesses. To reduce further the surface recombination velocity, we investigate the influence of modifications of the normal HF-dip. Additions of HCl and isopropanol have been studied. Finally, a method based on stabilization of the surface passivation after the HF-dip by means of covering the wafer with a iodine-containing solid passivation layer is presented. The stability of the different passivation solutions are compared. The resulting hydride-configuration after the different surface treatments is studied by means of Fourier transform infra-red measurements with multiple internal reflection on double-sided mirror-polished substrates. This allows the identification of the detailed structure of the H-surface coverage (dihydrides, disturbed dihydrides, monohydrides).