Strain Analysis of Copper Films During Wet-Chemical Deposition.

Abstract

Electroless (chemical) copper deposition, followed by electrolytic (galvanic) copper deposition, is used to construct electrical interconnects for electronic components on insulating substrate materials. As smooth substrates, such as glass or flexible materials like polyimide or polyethylene terephthalate, are used increasingly, achieving the required level of adhesion becomes more difficult. The film strain is one key variable that influences film adhesion. Standard X-ray diffraction based strain analysis was adapted for in situ strain monitoring during and after wet-chemical copper deposition. The results show that adding nickel suppresses an initial compressive strain that frequently appears in Ni-free baths. Adding ruthenium complexes to a standardized electroless copper formulation gradually shifts the strain from tensile to compressive. Spontaneous recrystallization at room temperature was monitored in detail for films obtained by direct current galvanic copper plating.