Two-Step Plasma Treatment on Sputtered and Electroplated Cu Surfaces for Cu-To-Cu Bonding Application

Abstract

The technology trends of next generation electronic packaging are moving toward heterogeneous 3D packaging systems. One of the key processes of 3D packaging system is Cu-to-Cu bonding, which is highly dependent on the planarized, activated, and oxygen-free Cu surface. A two-step plasma treatment is studied to form a Cu surface that does not react with oxygen and improves the Cu bonding interface quality at low bonding temperature (300 °C). In this study, the effects of two-step plasma treatment on both sputtered and electroplated Cu surfaces were evaluated through structural, chemical, and electrical analysis. The Cu bonding interface was studied by scanning acoustic tomography analysis after the thermocompression bonding process. Both sputtered and electroplated Cu thin films had the preferred orientation of (111) plane, but sputtered Cu exhibited larger grains than the electroplated Cu. As a result, the roughness of sputtered Cu was lower, and the resistivity was higher than that of electroplated Cu. Based on X-ray photoelectron spectroscopy analysis, the sputtered Cu formed more copper nitrides and fewer copper oxides than the electroplated Cu. A significant improvement in bonding quality at the Cu bonded interface was observed in sputtered Cu.

Communication—Exploration of Plasma Oxidized Copper Oxide as a Copper Passivation Layer

“…Also, the as-sputtered deposited Cu thin film has a larger resistivity than the electroplated Cu film has. 38 The annealing step can change the grain size and film resistivity, and therefore, the lifetime of the Cu line. 39 Since the Cu sample in this study was not annealed before the EM stress, its resistance remains high, which can cause the quick raise of temperature and shorten the lifetime.…”

Recent progress on bumpless Cu/SiO2 hybrid bonding for 3D heterogeneous integration

“…Metastable Cu x N y , which is more hydrophilic than bare Cu, was induced by Ar/N 2 plasma in their research. Park et al (2020b), Seo et al (2020), Park et al (2020a) and Seo et al (2019) researched Ar, N 2 and Ar-N 2 two-step plasma to bond Cu-Cu wafers and Cu/SiO 2 hybrid wafers. Remote mood plasma is applied.…”

Direct metal to metal bonding method for heterogenous 3D integration

“…2.2.2.1 Cu-Cu Thermo-compression Bonding with Copper Nitride PassivationStudies have used metastable copper nitride that was created with Ar + N2 plasma treatment to passivate the copper surface and prevent it from oxidation[12] [25][26]. One advantage of copper nitride passivation over SAM is that the nitrogen from the decomposed copper nitride can diffuse through the Cu when the surfaces are in contact unlike the alkane-thiol, which is required to be purged from the Cu surface before contact.…”