Dielectrics stability for intermediate BEOL in 3D sequential integration

3D sequential integration, such as CoolCube™, allows to stack vertically layer of devices. Levels of interconnection, also called intermediate Back-End-Of-Line, are needed between successive layers of transistors to avoid routing congestion. Thus, thermal stability of the dielectrics must be studied in order to fulfil the CoolCube™ requirement: at least to be stable up to 500 °C during 2 h. Consequently, the stability of several barrier layers and oxide based materials has been studied through optical characterizations (ellipsometry, Fourier Transform InfraRed spectroscopy and ellipsometric-porosimetry). SiCO (k = 4.5), in replacement of standard SiCNH (k = 5.6) material as barrier layer seems very promising. Regarding the inter-layer dielectric stability, the state-of-the-art porous SiOCH (k = 2.5) stays suitable for a thermal budget of 500 °C, 2 h.

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