Copper Metallization Layers On Bismuth-telluride Substrates: Effectiveness of Cr, Pt, And Ta_40Si_14N_46 Thin Films as Diffusion Barriers

摘要

For power-chip coolign devices based on Bi_2Te_3 thick films, copper is a desirable choice as metallic conductor, bacause it has high thermal conductivity and low electrical resistivity. On the other hand, Cu shows donor activity in Bi_2Te_3 , and is known for its high diffusivity in bismuth-telluride and the rapid formation of Cu_2Te. Therefore, the deployment of a chemically inert, low resisitivity diffusion barrier between the Cu metallization layer and the themoelectric base material is indispensable. In this paper we report on the effectiveness fo ilms of Cr, Pt, and Ta_40Si_14N_46 as diffusion barriers at temperatures up to 350 deg C for Cu overlayers on Bi_2Te_3 bulk substrates. Te films, each about 100 nm thick, were magnetron-deposited on the bi2 Te3 followed by about 300 nm thick copper overlayers without breaking vacuum. The samples were annealed in vacuum at temperatures of 200 and 350 deg C for up to 50 h. The performance of the metals and the tantalum-silicon-nitride films as diffusion barriers for Cu inward and Bi and Te toward diffusion was evaluated by 2.0 MeV~4 He backscattering spectrometer and x-ray diffraction. While the Cr and pt film fiail already after hours of annealing at 200 deg C, the Ta_40Si_14N_46 film remains intact at this temperature after vacuum heat treatment for 50 h, and even at 350 deg C for 1 h as well. Ta-Si-N, and related ternary materials of this type, have already shown to be highly effective barriers in Cu/Si contacts. This study demonstrates that their field in application extends quite beyond Si-based technology.