The Removal of Copper Oxides by Ethyl Alcohol Monitored In Situ by Spectroscopic Ellipsometry

Abstract

As an interconnect material, copper has the disadvantage of not forming self-limiting oxides, which can negatively affect device performance and reliability. Undesired oxide layers need to be removed by in situ cleaning, before the copper is subjected to subsequent depositions. We have used ethyl alcohol (C 2 H 5 OH) as a vapor phase reducing agent to remove copper oxides formed on electroplated copper films upon exposure to the ambient. Spectroscopic ellipsometry has been used to monitor the reduction process in situ. Ex situ characterization using X-ray photoelectron spectroscopy and atomic force microscopy support in situ measurements. While oxide removal can be achieved at temperatures as low as 130°C, independent of oxide layer thickness and composition, it occurred more efficiently at 200°C, showing compatibility with the low temperature (Ͻ400°C) processing requirements of low dielectric constant materials. The initial reaction involves the reduction of Cu 2ϩ to Cu ϩ species followed by a second phase consisting of Cu ϩ conversion to elemental copper, producing a clean metal surface. Reduction of Cu 2ϩ to Cu ϩ species is the rate-limiting step as evidenced by enhanced sensitivity to the reaction temperature.

Growth and Characterisation of Pulsed-Laser Deposited Tin Thin Films on Cube-Textured Copper at Different Temperatures

“…Unfortunately, most of them were led to increasing of the resistivity of copper, deterring the use of that alloy as the RABiTS's substrate material. Besides, the copper oxidation is not only problem in RABiTS technology and the significant approaches have been performed in fields like electrochemistry [22,41,42] or deposition of CVD-grown graphene [11,12], either. The most effective methods of in situ stripping of copper oxide contain a low-energy ion-beam cleaning [5] and an annealling in hydrogen reducing atmosphere at 1000°C [11].…”

Atomic layer deposition of zirconium oxide on copper patterned silicon substrate

“…• C. 12 Therefore, the use of alcohol as a reducing agent appears more attractive than the conventional thermolysis or hydrogen reduction routes for SALD. Additionally, ethanol has potential to serve dually as an oxygen source.…”

Formation of thin oxide layer on surface of copper caused by implantation of high-energy oxygen ions

“…On the other side copper lacks of a self-passivating oxide films [1][2][3][4][5][6][7][8][9][10], as it is the case, for example, for aluminum or indium. Typically, as a result of oxidation a multilayered structure is formed on surface with composition CuO/Cu 2 O/Cu [2,4,7,9]. Several works reported about inhomogeneous surface of the oxide surface [7,9,11] with typical inplane size of inhomogeneities of several microns.…”

“…Typically, as a result of oxidation a multilayered structure is formed on surface with composition CuO/Cu 2 O/Cu [2,4,7,9]. Several works reported about inhomogeneous surface of the oxide surface [7,9,11] with typical inplane size of inhomogeneities of several microns.…”

“…XPS allows to define binding energies of surface elements and thus detects presence of copper and different oxides [1][2][3][6][7][8]. Since the crystallographic parameters of copper and its various oxides differs, XRD enables to investigate them in detail [2,8].…”