Formation of Ultrasmooth and Highly Stable Copper Surfaces through Annealing and Self-Assembly of Organic Monolayers

Abstract

Copper (Cu) has been extensively used as an interconnect material for microelectronic devices because of its high electrical and thermal conductivity and excellent electromigration resistance. However, the formation of relatively rough Cu surfaces ( approximately 5 nm roughness) and Cu-oxide layers upon exposure to air still hinders their reliable application in a wide range of fields. In this article, we show the potential values of highly stable and ultrasmooth polycrystalline bare Cu obtained by simple annealing and chemical modification for a wide range of Cu-based electronic devices. The morphological properties and oxidation behavior of annealed Cu surfaces, before and after coating by self-assembled monolayers of terephthalic acid (TPA), were examined upon exposure to ambient air conditions ( approximately 110 days). Thin films of polycrystalline Cu, deposited on top of an adhesion layer of tantalum nitride (TaN) and annealed for 8 h at 580 degrees C under 2 x 10(-7) Torr, provided ultrasmooth Cu surfaces (R(rms) = 0.15-1.1 nm for fresh samples) and had a stable Cu-oxide layer after 65 days ( approximately 3.5 nm). These observations were perceived to be superior to nonannealed polycrystalline Cu samples. Coating fresh (oxide-free) samples of ultrasmooth Cu with TPA molecules created a closely packed monolayer with a standing-up phase configuration and molecular coverage of approximately 90%. The TPA-coated Cu surface has not shown any detectable oxidation during the first 2 weeks of exposure. The protection efficiency of this layer was found to be superior to those reported earlier on polycrystalline Cu surfaces. The oxidation mechanisms of both annealed and nonannealed Cu surfaces are presented and discussed.

Atomistic details of oxide surfaces and surface oxidation: the example of copper and its oxides

“…Indeed, the surface roughness of metal oxide surfaces has been shown to have a direct influence on their wetting properties towards water, which in turn could have a direct influence on the formation of the native oxide 296 . In particular, very smooth copper surfaces are hydrophobic while rough surfaces (∼ 5 nm-high roughness) are hydrophilic 297 . Furthermore the orientation of the crystallites at the surface influences the wetting properties and the distribution and coverage of water on the surface, especially in the case of copper 298 .…”

Self-assembly of 1,3,5-benzenetribenzoic acid on Ag and Cu at the liquid/solid interface

“…66,67 ). Only a few systems have been examined spectroscopically [68][69][70][71][72] whereas molecularly resolved studies using scanning tunneling microscopy (STM) have been performed only rather recently. [62][63][64][65]73 In these studies Au/mica substrates were used onto which a Ag bilayer or a pseudomorphic (√3×√3)R30° Cu layer were electrochemically deposited in the region positive of the Nernst potential (underpotential deposition, UPD) 74 Notably, a very recent STM study demonstrated that also Ag films are suitable substrates for the assembly of ArCA SAMs.…”

Self-Assembled Monolayers of Oligophenylenecarboxylic Acids on Silver Formed at the Liquid–Solid Interface

“…The solution based studies have been performed almost exclusively on fatty acids (for references see reviews by Ulman 29 and Jadhav 30 ) with the exception of terephthalic acid, 31 alkoxy derivatised biphenyl-, naphthyl-and benzenecarboxylic acid, and terphenylcarboxylic acid. [32][33][34] To this small set of spectroscopic studies, benzene-1,3-dicarboxylic acid (isophthalic acid, IPA), benzene-1,3,5-tricarboxylic acid (trimesic acid, TMA) and biphenyl-3,4′,5-tricarboxylic acid (BPTCA) have recently been added.…”