Amorphous binary M(=Mo, Ta or W)-Si and ternary M-Si-N, r.f.-sputtered from M,Si, and WSi2, targets, are assessed as diffusion barriers between silicon substrates and copper overlayers. By I(V) tests of the metallizations on n(+)p shallow junction diodes, the ternary M-Si-N barriers prevent copper from reaching the silicon at 800 degrees C or higher during a 30 min heat treatment in vacuum. Failure of the metallizations correlates with the crystallization temperature of the barrier, which is presumably a prelude to fast grain-boundary diffusion. Metal-rich Mo-Si-N and W-Si-N barriers liberate nitrogen during annealing, which poses a limitation to their crystallization temperatures. No reaction products of copper with metal-rich M-Si or M-Si-N barriers are observed, which is in agreement with our recent thermodynamic modelling of the M-Si-Cu ternary systems.