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，要求聚酰亚胺（PI）作为层间绝缘层，以降低介电常数（K）和热膨胀系数（CTE）。到目前为止，几乎没有实用的低K和低CTE PI。由环丁烷四羧酸二酐（CBDA）和反式-1，4-环己二胺（CHDA）合成的全脂环族（脂环族）聚酰亚胺（PI）在普通有机溶剂中不溶，但同时具有高Tg、低CTE和低介电系数（K）的综合性能。据信，低CTE产生机制是基于由热亚胺化诱导的面内链取向。聚酰亚胺溶液的溶液流延工艺（无酰亚胺化）通常不会导致明显的面内取向。本论文以柠康酸酐为原料，通过光二聚反应合成了一种新型的脂环族四羧酸二酐，1，3-二甲基-CBDA。结果表明，由1，3-二甲基-CBDA与TFMB和脂环族二胺合成的脂环族共聚酰亚胺体系，不经酰亚胺化反应，通过简单的溶液流延工艺制备的PI清漆具有较低的CTE（24 ppm/K）、较低的K（2.67）、较高的透明性（T% = 86%@400nm）和良好的膜柔韧性。低CTE对应于高双折射值（An > 0.05），反映了高程度的面内取向。本工作中开发的新材料可应用于半导体器件的层间掺杂。

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.