Structure-Property Relationships of Nano-Foam Polyimide Films with Low Dielectric Constant and High Thermal Stability

摘要

Thin films of aromatic polyimides have been of considerable interest owing to their application in microelectronic packaging devices.1'2 In this regard, the lower dielectric constants of aromatic polyimide films, ca. 3.0-3.5, as compared with those of inorganic ceramic packaging materials (e =9.3 for alumina) present a significant advantage in terms of lowering the crosstalk noise and propagation delay. For advanced applications like Inlerlevel dielectrics for CMOS microprocessors, there exists a critical need for low dielectric materials compatible with device processing conditions, in order to enable the speed/performance gains through smaller device dimensions. For this case, the requirement is to lower the dielcclric constant below ca. 2.5 in order to derive* real benefits over the currently available inorganic materials with ε'-4. For this purpose, the synthesis of foamed structures of high temperature polyimide were studied by utilizing block copolymer approach.4"6 The foams are prepared from block copolymcre consisting of thermally labile blocks and thermally Stable matrix polymers. The desired size and shape of nano-foam domains were controlled by the initial micro-phase separated block copolymer morphology.