Characterization of Coating on Fine Interconnect Materials

Interfacial materials, such as intentionally deposited coatings enhance the behavior of interconnect materials by providing unique properties, then the existing interconnects available in the market. For example, an organic coating on ultrafine solder powder particles prevent formation of native oxide, thus reducing the propensity of agglomeration. The powder particles are in the range between 2 and 8μm and organic coating is in a few nanometer thicknesses, which is a challenge to observe, measure its thickness and identify its chemical formulae. The paper discusses characterization of the nano-coating using Transmission Electron Microscope (TEM). Thickness of coating is in the range of 2 to 4.5nm, and it is measured by depth profiling using Auger Electron Spectroscopy (AES). Chemical formulae of the coating is identified using Time of Flight Secondary Ion Mass Spectrometry (ToF-SIMS). The observation resolved ultrafine powder process optimization to manufacture un-agglomerated ultrafine solder powders with high yield. In addition, the powder with clean surface showed good solderability and reliability. Similarly, electrodeposited gold over silver wires are analyzed using ToF-SIMS. Depth profiling of wires with good and inferior bondability differentiated the surface of the wires corresponding to their composition. Hence, their differences were later on resolved by process modification. On the other hand, nano-indentation on coating decipher the mechanical behavior of the wire surface, exhibiting good correlation on wire bond performance. The findings enabled to develop high quality bonding wires through chemical and mechanical analysis. An observation of gold distribution over silver free air ball is also discussed.