The performance of W40Re40B20 metallic amorphous thin firm 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 degrees C and 200 mu Omega cm, respectively. The (Si)/W40Re40B20/Al and (Si)/W40Re40B20/Cu metallizations were vacuum-annealed at different temperatures for 30 min and characterized by He-4 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 degrees C and failed at 550 degrees C due to chemical reactions between the barrier and aluminum. A formation of cracks in the bilayer (Si)/W(40)R(40)B(20)/Cu structure is responsible for its failure at 600 degrees C. The results demonstrate that it is fruitless to raise the crystallization temperature of an amorphous metallic him if its ability to react with the adjacent materials is not suppressed as well.