We report the formation of self-assembled monolayers (SAMs) onto gold substrates by exposure to lithium dialkyldithiocarbamate salts [(Li+(R2DTC-), where R = n-propyl, n-butyl, n-octyl, n-decyl, n-dodecyl, or n-octadecyl] in ethanol or methylene chloride. The crystallinity and composition of the monolayers were assessed by polarized modulation infrared reflection absorption spectroscopy (PM-IRRAS), wettability was characterized by contact angles of water and hexadecane, thickness was measured by spectroscopic ellipsometry, and barrier properties determined by electrochemical impedance spectroscopy. While the shorter R2DTC-s formed monolayers with liquid-like packing, monolayers prepared from the longest R2DTC- (where R = n-octadecyl) exhibit similar thickness, crystallinity, wettability, and capacitance as monolayers prepared from n-octadecanethiol. The hydrocarbon chains within the monolayers prepared from (C18)2DTC- are less canted on average than those prepared from n-octadecanethiol. Nonetheless, the (C18)2DTC- SAM exhibits an order of magnitude lower resistance against the penetration of redox probes, which is attributed to a higher density of pinhole defect sites.
Chemical-mechanical planarization (CMP) is a process of oxidizing and chelating the copper overburden present in an interconnect device while mechanically polishing the surface of the wafer. Because the use of condensed CO 2 as the solvent for CMP would be environmentally and technically advantageous, several substituted bis(acetylacetonate)ethylenediimine (R 4 BAE, where R ) CH 3 or CF 3 ) and lithium or sodium dialkyldithiocarbamate (M + (R 2 DTC -), where M + ) Li + or Na + and R ) ethyl, n-propyl, n-butyl, or 1,1,1trifluoroethyl) ligands were used with t-butylperacetate (t-BuPA, as oxidant) for the oxidative dissolution of copper(0) in supercritical (sc) CO 2 at 40 °C and 170-210 bar or in hexanes at 40 °C and atmospheric pressure. The reaction products from the copper etching were determined to be Cu(R 4 BAE) or Cu(R 2 DTC) 2 , respectively. The R 2 DTCligands had higher etch rates than the R 4 BAE ligands with comparable substituents, and the lithium dialkyldithiocarbamate salts gave higher copper etching rates than their sodium counterparts. The highest average etch rates were observed for Li((CF 3 CH 2 ) 2 DTC): 16.7 nm/min in sc CO 2 and 11.2 nm/min in hexanes. While hexanes have similar physical properties when compared to sc CO 2 , the rates of copper(0) removal with the R 2 DTCligands were 17-49% higher in sc CO 2 than in hexanes at comparable temperatures and solvent densities. Scanning electron microscopy (SEM) images of the postreaction copper surfaces using the various ligands showed significant variations in surface roughness. X-ray photoelectron spectroscopy (XPS) measurements indicated that the lower R 4 BAE etch rates may be due to surface passivation by the R 4 BAE ligands and/or the Cu(R 4 BAE) complexes.
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