Advanced Preclean Chamber for Ubm/Rdl Contact Resistance Improvement in Advanced Node Packaging Application

Abstract

Next-generation Under Bump Metallization (UBM) size reduction and increasing polymer thickness bring about thermomechanical benefits such as reduced low-k stress for advanced semiconductor packages. In addition, the adoption of fluorinated polymers provides low-k passivation which reduces signal delay and power consumption. However, these inflections at advanced nodes create new challenges for bump contact resistance ($\mathrm{R}_{\mathrm{C}}$) due to increased polymer outgassing and smaller via size. This paper describes an advanced pre-clean chamber and optimized pre-clean process condition developed to improve $\mathrm{R}_{\mathrm{C}}$ on various polymers. It is shown that the improved pre-clean efficiency results in significantly lower carbon, oxygen and fluorine contaminants at the Ti/Al interface, measured by TEM/EDX analysis. The $\mathrm{R}_{\mathrm{C}}$ values measured on a test vehicle with three-wire Kelvin test structures demonstrated a >60% lower $\mathrm{R}_{\mathrm{C}}$ and improved $\mathrm{R}_{\mathrm{C}}$ standard deviation. The new pre-clean chamber also enables higher throughput while maintaining a low wafer temperature for outgassing control.