Contact-displacement PD deposition for electroless copper application
Lau, Ping Ping
Date of Issue2009
School of Materials Science and Engineering
Chartered Semiconductor Manufacturing
Electroless (EL) Cu, a potential seed layer material for Cu interconnects used in nanoelectronics, is intimately dependent on the surface activation of catalytic Pd particles. A comprehensive understanding on the deposition mechanism of Pd particles is thus critically important. In this thesis, the contact-displacement method of depositing Pd onto TiN surface is investigated in depth using statistical methods to track the time evolution of distributions of particle size, range, and density. The three classical phenomena of nucleation, growth, and ripening occur concurrently in this open system, leading to interesting evolution of particle statistics not predicted by any of the classical theories. In particular, there exists a secondary nucleation stage before the onset of ripening, where particle density reaches a maximum. Using this window allows us to achieve EL Cu deposits with very low surface roughness which allows conformal high aspect ratio via fills with satisfactory results. The existence of a nucleation barrier on the trigger point of secondary nucleation is shown to be linked to the formation of a hydrophilic surface associated with the removal of a native Ti oxide. Based on this new insight on surface chemistry, a new “double activation” method is demonstrated in this thesis wherein an etch step containing a hydrophilicity promoter is used. This new activation procedure increases the nucleation rate significantly, and yields more and smaller Pd particles. The larger EL Cu grain size that results yields films that are lower in resistivity by up to 50%. We believe this method is generally applicable to all electroless deposits which are kinetically limited by surface barriers.
DRNTU::Engineering::Materials::Microelectronics and semiconductor materials