Surface chemistry research of electronic processes and electronic devices
Date
2018
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Publisher
University of Delaware
Abstract
Surface chemistry and analysis is important in many different disciplines. In this dissertation, the role of surface chemistry in improving performances of electronic devices are discussed. Two different perspectives are investigated.
In the first topic, atomic layer etching (ALE) of transition metals using Cl2 and acetylacetone (acac) was studied. Etching of transition metals is one of the major challenges in MRAM fabrication. The etching performance on different metals, including etching rates, self-limiting behaviors, and influence of temperature and RF power, was studied. We successfully etched Fe and Co thin films by forming volatile metal complexes at low temperature with cyclic reactions of Cl2 and acac.
The mechanism of acac reacting on Cl-modified Fe surfaces was investigated using in situ x-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) simulation. The surface was first activated with Cl2 gas, and then the top layer of metal was removed by acac reaction. The extent of Cl2 reaction determined the etching rate. At substrate temperatures lower than 135 degree C, the acac could not remove the chlorine. The reaction of acac on chlorinated Fe surface is likely following a complex pathway instead of simple acac substitution for Cl2. Acac decomposition may play an important role in the process.
The acac reaction on Cl-modified Co surfaces was also investigated by in situ XPS. The Cl2 adsorption on Co surfaces is much weaker than on Fe surface. The remaining organic groups on the Co surface show little carbanion and C-O groups after acac exposure, indicating a different mechanism comparing with the Fe surface.
In the second topic, surface photovoltage (SPV) measurements using XPS was utilized for measuring the band bending on organic molecule modified semiconductor surfaces. The interaction between the phthalocyanine dye molecule and different metal oxide powders was measured by the SPV analysis. The F64PcZn molecule is likely acting as a p-type semiconductor, and, due to the new charge distribution, changes the bend-banding at the substrate surface. The interaction between organic molecule and Si surfaces was also investigated. For n-type Si samples, SPV measurements indicate a downward band bending of benzoquinone (BQ) passivated samples. The BQ-Si sample has the largest band bending, indicating a strong field-effect contribution to eliminate the recombination of electrons and holes on the surface.