Surface treatment of wire bonding metal pads

✍ Scribed by S. Alberici; D. Coulon; P. Joubin; Y. Mignot; L. Oggioni; P. Petruzza; D. Piumi; L. Zanotti

• Book ID: 104305982
• Publisher: Elsevier Science
• Year: 2003
• Tongue: English
• Weight: 686 KB
• Volume: 70
• Category: Article
• ISSN: 0167-9317
• DOI: 10.1016/s0167-9317(03)00418-0

✦ Synopsis

The random formation of micrometric crystals on Al bonding pads can be an issue affecting wire bonding metal pad quality. The dry etch chemistry used to remove final passivation dielectric layers from the top of the bonding Al pad area is in fact based mainly on fluorine-containing gases (such as CF , CHF , etc.) which can leave fluorine as a residual on the 4 3 metal pad surface as bonded or ''free'' AlF , especially in the metal grain boundary zones. Fluorine contamination on the Al 3 wire bonding pads, under particular temperature and humidity conditions, causes the formation of Al(OH) and Al / fluorine 3 compound crystallites, not allowing, as a consequence, growth of the superficial and homogeneous natural Al O layer. This 2 3

paper concerns the analytical methods used to reveal the formation of such crystal defects and the operative solutions effective in preventing them, leaving the metal pad surface in the optimal condition for subsequent wire bonding operations.