Towards Understanding the Roles of Organic Bath Additives in Copper Electroless Deposition on Self-assembled Monolayers


December 2022


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Organic bath additives are commonly used in solution-based deposition techniques to improve the properties of the desired material. However, despite their wide application, studies on understanding the roles of these additives are limited. In this dissertation, we employed multiple surface characterization techniques including X-ray photoelectron spectroscopy (XPS), time-of- flight secondary ion mass spectrometry (TOF SIMS), Raman spectroscopy, scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS), atomic force microscopy (AFM), and optical microscopy to investigate the effect monoethanolamine, diethanolamine, triethanolamine, urea, guanidine, and thiourea as bath additives in the electroless deposition of copper on self-assembled monolayers (SAMs). Using XPS and TOF SIMS, we observed that electrolessly deposited copper is more adherent on the –CH3 terminated SAMs. TOF SIMS spectra also showed that the mono- and triethanolamine interact with the –CH3 terminated SAM via the amine functional group while diethanolamine adsorbs flat on the SAM surface. These interactions allowed the deposition of copper wires via electroless nanowire deposition on micropatterned substrates (ENDOM). Fragment ions in the TOF SIMS spectra showed various interactions of the hydroxyl group of ethanolamines with the –OH terminated SAMs. This indicates that polar ethanolamines interact strongly with the hydroxyl-terminated SAM surface. We also demonstrated a switch from copper electroless deposition at low concentrations of thiourea to copper sulfide deposition at high concentrations of thiourea. We synthesized copper wires using thiourea as bath additive in ENDOM. A method of depositing Cu/CuxS layer via a two-step solution-based technique is also presented. The electron-donating property of the heteroatom in bath additives (urea, guanidine, and thiourea) influences its stabilizing ability. Thiourea inhibited the electroless deposition process which allowed the deposition of small particles resulting in smooth copper film. Also, regardless of the bath additive heteroatom, smoother films were deposited at pH 9. At pH 12, we observed two layers of deposit: (a) ion-by-ion growth of the underlayer and (b) cluster-by-cluster growth of the overlayer. Copper wires deposited using guanidine as bath additive at pH 9 are more uniform. Lastly, we proposed methods to optimize the crossbar wire synthesis using multiple ENDOM processes.



Chemistry, Analytical, Chemistry, General