Effects of W nucleation processes on interfacial reliability of W/TiN/SiO2/Si multilayer structure

Abstract

the interfacial adhesion value was lower when diborane gas was used for nucleation process. This was due to the diffusion of boron(B), decomposed from diborane gas, into TiN/$SiO_2$ interface, degrading the interaction between TiN and $SiO_2$. Adhesion gradually decreased as diborane flow rate (250 – 1500 sccm) and soaking time (10 – 60s) increased respectively, with residual stress unchanged. When excess amount of diborane was exposed (1500 sccm, 60s), a new boron layer was formed at W/TiN interface, leading to change in delamination path from TiN/$SiO_2$ to W/TiN, with further decrease in adhesion value. On the other hand, diborane-based W film showed much lower residual stress than silane-based W film throughout the test conditions. This was due to the difference in bulk-W grain size at film coalescence stage. Diborane-W showed larger grain size than silane-W. Applying Hoffman’s grain boundary model, intrinsic stress value of diborane-W and silane-W was calculated and compared. There was a trade-off relationship between diborane-W and silane-W in terms of crack driving force (G) and adhesion value ($G_C$). Based on this study, it is recommended that not only $G_C$ but also G be taken into consideration for precise evaluation of interfacial mechanical reliability.

In this study, two representative reducing agents, diborane ($B_2H_6$) and silane ($SiH_4$), were used to form a nucleation layer for subsequent bulk CVD-W layer. Direct, quantitative comparison of interfacial adhesion energy ($G_C$) between diborane-based and silane-based W nucleation was carried out through 4-point bending (4PB) test. The crack driving force (G) induced by residual stress was measured through wafer curvature method. The result revealed, in both cases, the weakest interface was TiN/$SiO_2$