Ultrahigh vacuum electrochemical studies of metals and semiconductor deposition
Gebregziabiher, Daniel Kebreab
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This dissertation describes the growth of nano films by electrochemical methods in an ultrahigh vacuum system (UHV) that is compatible with electrochemical deposition process. The UHV system was equipped with surface analysis techniques such as Auger electron spectroscopy (AES), low energy electron diffraction optics (LEED) and X-ray photoelectron spectroscopy (XPS). The first part of this dissertation deals with the eletrodeposition of copper (Cu) nanofilms as seed layers on ruthenium (Ru) barrier layer for the metallization of integrated circuits. The Cu nano film was deposited by using lead (Pb) as a sacrificial element. A Pb UPD was deposited and this UPD was exchanged for Cu by flowing a solution of Cu+2 ions at open circuit potential in a redox replacement reaction. Since Cu is more noble than Pb, the Cu ions take electrons from Pb to be deposited as Cu atoms. The process should ideally result in the formation of only an atomic layer of Cu. This constituted one deposition cycle and the cycle was repeated several times to grow the Cu nano film. As a continuation of this study, Cu surface passivation was investigated by depositing atomic layers (AL) of different elements on Cu(111). The elements investigated for the passivation of Cu from oxidation included selenium (Se), iodine (I) and tellurium (Te). The purpose of this study was to protect Cu surface from contamination between solutions in a Fab line. The Se, I and Te modified Cu(111) was exposed to ambient air, solution vapors and oxygen and it was concluded that an atomic layer of Te protects the Cu(111) surface the best out of the investigated elements. The second part of this dissertation deals with electrodeposition of germanium (Ge), a semiconductor, from an aqueous solution of Ge. The composition of the deposits was studied using AES and the surfaces were characterized using STM. Analytical techniques such as cyclic voltammetry (CV) and electrochemical quartz microbalance (EQCM) were used to follow the electrodeposition process. It was concluded that the electrochemical deposition of Ge from an aqueous solution was self-limiting even though bulk deposition potentials were used. At very negative potentials Ge forms a germanium hydride passivating layer.