System for Low-Force Thermocompression Bonding

Abstract

Methods and systems for low-force, low-temperature thermocompression bonding. The present application teaches new methods and structures for three-dimensional integrated circuits, in which cold thermocompression bonding is used to provide reliable bonding. To achieve this, reduction and passivation steps are preferably both used to reduce native oxide on the contact metals and to prevent reformation of native oxide, preferably using atmospheric plasma treatments. Preferably the physical compression height of the elements is set to be only enough to reliably achieve at least some compression of each bonding element pair, compensating for any lack of flatness. Preferably the thermocompression bonding is performed well below the melting point. This not only avoids the deformation of lower levels which is induced by reflow techniques, but also provides a steep relation of force versus z-axis travel, so that a drastically-increasing resistance to compression helps to regulate the degree of thermocompression.

What is claimed is: 
     
         1 . A system for bonding microelectronic elements, comprising:
 a bonding platform for flip-chip bonding, configured to bond elements by compressing them together, without any conductive liquid phase material, thereby deforming contacting metallizations by no more than 40% of their initial height;   an atmospheric plasma applicator, integrated into said bonding platform, which is configured to apply reducing and passivating agents to said contacting metallizations on each said element, by use of plasma-activated radical-enriched gas flow at substantially atmospheric pressure;   wherein said reducing and passivating agents reduce native oxides from said contacting metallizations and passivate said contacting metallizations against re-oxidation prior to bonding said element;   wherein elements are loaded into said bonding platform and aligned for bonding, said atmospheric plasma applicator applies reducing and passivation agents to the contacting metallizations on said elements, and then the elements are bonded.   
     
     
         2 . The system of  claim 1 , wherein said contacting metallizations are deformed by no more than 30% of their initial height. 
     
     
         3 . The system of  claim 1 , wherein said atmospheric plasma applicator comprises a scanning plasma applicator nozzle.