Ammonia Plasma Surface Treatment for Enhanced Cu–Cu Bonding Reliability for Advanced Packaging Interconnection

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Abstract
With the emergence of 3D stacked semiconductor products, such as high-bandwidth memory, bonding-interface reliability cannot be overemphasized. The condition of the surface interface before bonding is important and can substantially affect product reliability. Plasma technology can be used to control the state of a bonding interface, but various factors of interest, such as surface roughness, chemical bonding state, and surface cleanliness, may depend on the type of gaseous plasma. These factors may increase voids at the interface, which can jeopardize the product reliability. In this study, NH3 plasma surface treatment is investigated and compared with the conventionally preferred surface treatment under Ar plasma. Under the latter method, specific anomalies occurred and led to void formation at the interface during bonding. By contrast, NH3 plasma treatment maintained higher uniformity, higher overall surface conditions, and a smooth reduction process. Furthermore, the formation of a nitride passivation layer effectively inhibited the oxidation of the metal surface, and the flat surface resulted in the decrease in voids compared with the Ar plasma treatment after the copper–copper bonding. From the experimental analysis, we achieved a 12% reduction in resistance in the samples treated with NH3 plasma treatment due to the suppression of surface oxidation. However, it is unfortunate that the shear strength in the experimental samples treated with NH3 plasma treatment needs to be further improved.
Funding Information
  • Korea Evaluation & Planning Institute for Industrial Technology (K_G012002249203)

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