Thermal stability and interfacial reaction of barrier layers with low-dielectric-constant fluorinated carbon interlayer

The thermal stability of low-dielectric-constant (epsilon) interlayers for advanced ULSI's is studied. Thickness decreases by 7 and 4% with annealing from 390 to 450 degrees C in poly-arylether and hydro-organo-siloxane polym er layers. The thickness variation is as low as 2% in the carbon-rich fluor inated carbon (FC) (F/C = 0.90) layer at temperatures between 250 and 450 d egrees C. The composition of F/C decreases markedly with the increase of te mperature above 450 degrees C in high F/C composition, such as 1.20 and 1.2 8, FC layers. However, this composition is invariable with annealing at 450 degrees C in layers with low F/C composition (F/C = 0.90) because F does n ot leave the F-C bond in this layer. The barrier effect for a FC low epsilo n interlayer is studied in titanium nitride (TiN) and tantalum nitride (TaN ) barrier layers. When polycrystalline TiN and TaN barrier layers are used, significant interfacial reaction occurs at low temperatures. That is, Ti a nd Ta of TiN and TaN layers diffuse deeply into the FC: laver at 350 degree s C. Penetration of F from the FC layer into these barrier layers occurs re spectively at 450 degrees C. However, diffusion of Ta and F into FC and TaN can be suppressed if a microcrystalline TaN (TaN0.90) barrier layer is use d; such a N-rich microcrystalline TaN layer can be deposited by reactive sp uttering.