Amorphous W₄₀Re₄₀B₂₀ diffusion barriers for <Si>/Al and <Si>/Cu metallizations

The performance of W₄₀Re₄₀B₂₀ metallic amorphous thin film alloys as diffusion barriers between monocrystalline silicon substrates (<Si>) and aluminum or copper overlayers is reported. The films are deposited using d.c. and r.f. magnetron co-sputtering. Their crystallization temperature and resistivity are about 900°C and 200 μohmscm, respectively. The <Si>/W₄₀Re₄₀B₂₀/Al and <Si>/W₄₀Re₄₀B₂₀/Cu metallizations were vacuum-annealed at different temperatures for 30 min and characterized by ⁴He backscattering spectrometry, X-ray diffraction, scanning electron microscopy in combination with energy-dispersive analysis of X-rays, and electrical measurements on shallow junction diodes. The <Si>/W₄₀Re₄₀B₂₀/Al structure was stable up to 500 °C and failed at 550 °C due to chemical reactions between the barrier and aluminum. A formation of cracks in the bilayer <Si>/W₄₀Re₄₀B₂₀/Cu structure is responsible for its failure at 600 °C. The results demonstrate that it is fruitless to raise the crystallization temperature of an amorphous metallic film if its ability to react with the adjacent materials is not suppressed as well.