Etching-back of uniaxially strained silicon on insulator investigated by spectroscopic ellipsometry



Spectroscopic Ellipsometry was employed to study the etching process of uniaxially strained Si (sSi) layers obtained by direct wafer bonding of Si wafers in a mechanically bent state followed by thinning one of the Si wafers, the donor wafer, by the smart-cut process, keeping the other, the handle wafer intact. The smart-cut process requires a high dose hydrogen implantation into the donor wafer prior to bonding. As a result of the implantation conditions a ∼600 nm uniaxially sSi layer could be transferred onto the handle wafer. In order to thin down and smooth the surface damage of the transferred layer induced by the implantation and splitting process, the samples were dipped in a solution of tetra-methyl ammonium hydroxide (TMAH). The thicknesses of the transferred sSi layers determined from ellipsometry were in good agreement with those obtained from Transmission Electron Microscopy (TEM), while the roughness values were matching those obtained from Atomic Force Microscopy (AFM). The etching rate has also been determined. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)