ABSTRACT
Plasma processing is a key technology for fabrication of advanced Cu low-k interconnects. The process can significantly damage the low-k dielectrics, degrading the electrical property and reliability of the interconnect structure. As technology advances with continued device scaling, plasma damage of low-k dielectrics becomes more critical, making plasma damage one of the main impediments to a successful integration of low-k dielectrics. This chapter provides a review of recent studies on the characteristics and mechanisms of plasma damage of low-k dielectrics. It discusses first the molecular structure and bonding characteristics of low-k dielectrics, providing
useful information to understand plasma damage which can be traced to changes in the bonding characteristics. This follows with a discussion on damage induced by CO2 plasma to porous low-k dielectrics, which represents an oxidative plasma process used for photoresist stripping and one of the most damaging plasma processes. Several aspects of CO2 plasma damage are investigated, including changes in bonding configurations, the formation of carbon depletion layer, the shrinkage of film thickness, the densification of surface layer, and the increase of the effective dielectric constant. Then the mechanism of plasma damage was investigated using “gap structures” to delineate the roles of various plasma species (ions, photons and radicals) and to study the effect of low-k material properties including pore size, porosity, and carbon concentration. Two mechanistic models were developed to account for plasma damage: a plasma-altered layer model to analyze the chemical effect in the low-ion-energy region and a sputtering yield model to analyze the physical effect in the high-ion-energy region. This chapter is concluded with a discussion of dielectric recovery of plasma damage based on a silylation process in combination with UV radiation.
