Substrate cleaning using a remote hydrogen rf-plasma

The substrates (wafers) used in semiconductor processing have a surface oxide layer (the so-called native oxide layer) and a hydrocarbon contamination layer that must be removed before growing an epitaxial film of good quality. In this work, low temperature remote rf-hydrogen plasma cleaning of II-VI and silicon semiconductor surfaces was investigated as a preparation for subsequent deposition in molecular beam and gas source molecular beam epitaxy environments. The plasma was characterized using mass spectrometric methods to determine the identity and relative fluxes of ionic and neutral species and to determine the kinetic energies of the ionic species. Etching studies were then performed using x-ray photoelectron spectroscopy (XPS) to monitor the changes of chemical composition of the surface as a function of exposure to the hydrogen plasma. For cadmium mercury telluride (CMT) and cadmium zinc telluride (CZT) the hydrogen plasma readily removes the oxide and an amorphous Te overlayer left behind by standard wet chemical processing of these substrates. Following the removal of these layers the H-plasma etches HgTe, in the case of CMT, and CdTe, in the case of CZT. For silicon, the remote rf H-plasma was found to be ineffective at removing either the native oxide, or the oxide left by standard wet chemical processing. The hydrocarbon impurities were removed for all substrates. These results suggest a suitable low temperature dry etching technique for II-VI semiconductors in a UHV environment.