Diffusion barrier properties of very thin sputtered Ta and reactively sputtered TaN films used as a barrier layer between Cu and Si substrates were investigated using electrical measurement and materials analysis. The Cu/Ta/pt-n junction diodes with the Ta barrier of 5, 10, and 25 nm thicknesses were able to sustain a 30 mm thermal annealing at temperatures up to 450, 500, and 550°C, respectively, without causing degradation to the device's electrical characteristics. The harrier capability of Ta layer can be effectively improved by incorporation of nitrogen in the Ta film using reactive sputtering technique. For the Cu/TaN/pt-n junction diodes with the TaN barrier of 5, 10, and 25 nm thicknesses, thermal stability was able to reach 500, 600, and 700°C, respectively. We found that failure of the very thin Ta and TaN barriers was not related to Ta silicidation at the barrier/Si interface. Failure of the barrier layer is presumably due to Cu diffusion through the barrier layer during the process of thermal annealing via local defects, such as grain boundaries and stress-induced weak points.
This work studies the thermal stability of Cu/WSi x /p ϩ-n and Cu/WSiN/WSi x /p ϩ-n diodes in which the WSi x barrier layers were deposited by chemical vapor deposition to a thickness of about 50 nm using SiH 4 /WF 6 chemistry with the SiH 4 /WF 6 flow rates of 6/2 sccm, while the WSiN layers were formed by in situ N 2 plasma treatment on the chemically vapor deposited WSi x (CVD-WSi x) surfaces. Without N 2 plasma treatment, the thermal stability of Cu/WSi x (50 nm)/p ϩ-n junction diodes was found to reach 500ЊC; with N 2 plasma treatment, the resultant Cu/WSiN/WSi x (50 nm)/p ϩ-n junction diodes were able to retain integrity of electrical characteristics up to at least 600ЊC. Failure mechanism of the WSiN/WSi x bilayer in the Cu/WSiN/WSi x /Si structure was closely related to the WSi x /Si interface reaction and the tungsten silicide formation of the WSi x layer. Thus, barrier capability of the WSiN/WSi x bilayer can be further improved by suppressing the WSi x /Si interface reaction and the silicidation of the WSi x layer. The thermal stability of Cu/barrier/p ϩ-n diodes was further raised to 650ЊC by using a multilayer barrier structure of WSiN/WSi x (50 nm)/WSiN/WSi x (10 nm) or a WSiN/WSi y (y > 1) barrier. We conclude that the post-CVD-WSi x treatment with in situ N 2 plasma is a simple, practical, and efficient method of improving the WSi x-based barrier capability for Cu metallization.
This work investigates the barrier capability of W layers as well as WSiN/WSi x /W stacked layers against Cu diffusion. The W layers were selectively chemical vapor deposited (CVD) in contact holes to a thickness of about 450 nm using SiH 4 reduction of WF 6 . We found that the CVD-W layers functioned as effective barriers against Cu diffusion, and the Cu/W(450 nm)/p ϩ -n junction diodes were able to sustain a 30 min furnace annealing up to 650ЊC without causing degradation in electrical characteristics. The use of WSiN/WSi x /W stacked layers as diffusion layers further improved the thermal stability of Cu/WSiN/WSi x /W(450 nm)/p ϩ -n junction diodes to at least 700ЊC. The WSi x layers were deposited by CVD to a thickness of 75 nm using SiH 4 /WF 6 chemistry, and the subsequent in situ N 2 plasma treatment produced a very thin layer of WSiN on the WSi x surface. This thin WSiN layer was very thermally stable and effective in suppressing Cu diffusion. Failure of barrier capability for the W films was presumably due to interdiffusion of Cu and Si along grain boundaries of the W films, and the interdiffusion was probably enhanced by the formation of WSi 2 . The formation of WSi 2 consumed the W layer and Si substrate, resulting in a volume change in barrier layer, which, in turn, developed local defects, such as microcracks and stress-induced weak points, and thus provided fast paths for Cu diffusion.
Thin-Film properties and barrier effectiveness against copper (Cu) diffusion of a thin amorphous WSi, layer were investigated. The amorphous WSi layer was deposited by the chemical vapor deposition (CVD) method using the SiH4/WF6 chemistry with the activation energy determined to be 3.0 kcal/mol. The CVD-WSi, film has a low film stress, low electrical resistivity, and excellent step coverage. The resistivity of the amorphous CVD-WSi layer increases with the deposition temperature, but the residual stress of the layer decreases with the deposition temperature. The WSi/Si structure is thermally stable up to at least 600°C, while the copper-contacted Cu/WSijSi structure with a 50 nm thick WSi barrier is stable only up to 550°C. Moreover, the Cu/WSijp -n junction diodes can sustain a 30 mm thermal annealing up to 500°C without causing degradation in electrical characteristics. Barrier failure of the WSi layer in the Cu/WSir/Si structure at temperatures above 550°C is attributed to Cu atoms diffusion via fast paths in the WSi layer. These fast paths were presumably developed from grain growth of the WSi layer and/or thermal-stress-induced weak points in the WSi layer.
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