Investigation on Effect of Plasma Treatments on Ultra-Low-K Film and Gold Film

Abstract

The effect of different plasma treatments on the properties of porous SiOCH ultra-low-dielectric-constant (ULK) film have been studied first. The SiOCH ULK films with NH3 only and H2/NH3 plasmas treatments resulted in various degrees of degradation of surface chemical bonds, Si-CH3 and Si-H and electrical properties. Surface roughness of the films with plasma treatments became smoothened. H2/NH3 plasmas treatment caused more SiOCH ULK film structural change and electrical deterioration compared with NH3 only plasma treatment. Moreover, after H2/NH3 two-step treatment, Ebd decreased by 22% as compared with the as-cured film. Afterward, the effect of different plasma treatments on the interfacial bonding configurations and adhesion strengths between porous SiOCH ULK film and SiCN etch stop layer have been investigated. From X-ray photoelectron spectroscopic analyses, interlayer regions of about 10 nm thick with complicated mixing bonds were found at SiOCH/SiCN interfaces. With plasma treatments, especially H2/NH3 two-step plasma, a carbon-depletion region of about 30 nm thick with more Si-O related bonds of high binding energy formed at the interface. Furthermore, the adhesion strengths of the SiOCH/SiCN interfaces were measured by nanoscratch and microscratch tests. For the untreated interface, the adhesion energy was obtained as about 0.22 and 0.44 J/m2 by nanoscratch and microscratch tests, respectively. After plasma treatments, especially the H2/NH3 treatment, the interfacial adhesion energy was effectively improved to 0.41 and 0.89 J/m2 because more Si-O bonds of high binding energy formed at the interfaces. Finally, by exposure to O2-plasma, gold films were oxidized. Gold oxide (Au2O3) has a short halflife of 22 h at 22 ℃ and 166 h at 0 ℃, with an activation energy of dissociation of 57 kJ/mol, indicating instability even at low temperatures. The results of electrical resistance also revealed that the electrical properties are not degraded after O2-plasma cleaning of the surface of gold due to the restoration of elemental gold.