Development of High Temperature Polymers Possessing Low Dielectric Constant, Low Coefficient of Thermal Expansion, and High Transparency and Their Application to Electronic Devices.

在微电子应用中，作为层间介质的聚酰亚胺(PI)被要求同时降低介电常数K和热膨胀系数CTE。到目前为止，实用的Low-K和Low-CTE PI很少。由环丁四酸二酐(CBDA)和反式-1，4-环己二胺(CHDA)合成的全环脂肪族(脂环族)聚酰亚胺(PI)具有高玻璃化温度(Tg)、低热膨胀系数(CTE)和低介电系数(K)的综合性能，但在普通有机溶剂中不表现出溶解性。认为低CTE的产生机制是基于热亚胺化诱导的面内链取向。聚酰亚胺溶液的溶液浇注过程(没有亚胺化)通常不会引起明显的面内取向。在本工作中，我们通过柠檬酸酐的光二聚反应合成了一种新型的脂环型四元酸二酸酐-1，3-二甲基-CBDA。结果表明，由1，3-二甲基-CBDA与TFMB和环状脂肪族二胺合成的脂环型共聚酰亚胺体系，其PI清漆无需亚胺化即可得到低的热膨胀系数(24ppm/K)、低的K(2.67)、高的透明度(T%=86%@400 nm)和良好的涂膜柔韧性。较低的CTE对应较高的双折射值(AN&GT；0.05)，反映了较高程度的面内取向。本工作所开发的新材料可应用于半导体器件的层间介质。

In microelectronic applications, polyimides (PIs) used as interlayer dielectrics are demanded to decrease both the dielectric constant (K) and the coefficient of thermal expansion (CTE). There are so far few practical low-K and low- CTE PIs. The present scientific research reports that a wholly cycloaliphatic (alicyclic) polyimide (PI) derived from cyclobutanetetracarboxylic dianhydride (CBDA) and trans-1,4-cyclohexanediamine (CHDA) accomplished a combined properties of a high Tg, a low CTE, and a low dielectric coefficient (K) simultaneously, although the PI showed no solubility in common organic solvents. It is believed that the low CTE generation mechanism is based on the in-plane chain orientation induced by thermal imidization. The solution-casting process (without imidization) of polyimide solutions does not usually cause pronounced in-plane orientation. In this work, we synthesized a novel cycloaliphatic tetracarboxylic dianhydride, 1,3-dimethyl-CBDA from photodimerization of citraconic anhydride. The results revealed that a cycloaliphatic copolyimide system derived from 1,3-dimethyl-CBDA with TFMB and cycloaliphatic diamines leads to a low CTE (24 ppm/K), a low K (2.67), high transparency (T% = 86% @400nm), and good film flexibility by the simple solution-casting of its PI varnish without imidization process. The low CTE corresponds to a high value of birefringence (An > 0.05) reflecting a high extent of in-plane orientation. The new materials developed in this work can be applied to interlayer dielectrics in semiconductor devices.