纳米聚酰亚胺超薄膜的多级松弛与热转变★

doi:10.6023/A25050197

摘要/Abstract

聚酰亚胺(PI)薄膜因优异的耐高温性、绝缘性及化学稳定性, 广泛应用于光电器件与半导体封装领域. 纳米厚度PI薄膜的松弛行为关系到其热稳定性和尺寸稳定性等性质, 是影响PI薄膜应用的重要物理性质. 本工作用介电松弛和动态力学分析研究了PI的多级松弛行为, 明确PI的α和β松弛的温度区间; 利用椭圆偏振光谱表征纳米级厚度PI薄膜的热膨胀和松弛行为, 探究薄膜厚度对PI分子热运动的影响. 结果表明, 当膜厚降低至100 nm以下时, 与链段运动关联的α松弛温度(T_α)随膜厚降低而减小, 而与芳环振动相关的β松弛温度(T_β)保持不变; 同时, 薄膜的热膨胀系数随厚度减小显著增大. 本研究揭示了PI本体及超薄膜的松弛行为, 为开发高稳定、低膨胀的超薄封装材料提供了理论指导.

关键词: 聚酰亚胺, 松弛, 椭圆偏振光谱, 热膨胀, 纳米受限

Polyimide (PI) films are widely used in semiconductor packaging due to their excellent properties, including low dielectric constant, high temperature resistance, and enhanced thermal and chemical stability. In recent decades, the development of modern nanotechnology has led to devices being downsized to the nanoscale, and packaging these nanodevices would require ultrathin films of PI. Understanding the thermal transition and molecular relaxation of the PI ultrathin films is essential for high-quality microelectronic packaging. Although the dynamics of bulk PI have been extensively studied using techniques such as broadband dielectric spectroscopy (BDS) and dynamic mechanical analysis (DMA), the impact of reduced film thickness on these dynamics remains unclear. In this study, we used temperature-variable spectroscopic ellipsometry to examine the thermal expansion and molecular relaxation of PI films as thin as 6 nm, and concurrently, the bulk dynamics of PI were investigated using BDS and DMA for comparison purposes. The PI films were prepared by the heat imidization of poly(amide acid) films, which were polymerized using biphenyltetracarboxylic diandhydride (BPDA) and 4,4'-oxydianiline (ODA). In 300-nm-thick films, we observed the α-relaxation arising from the segmental cooperative rearrangement, and the β-relaxation originating from phenyl ring motion at approximately 260 ℃ (T_α) and 99 ℃ (T_β), respectively. As the film thickness decreased below 100 nm, T_α decreased. Specifically, T_α decreased by 30 ℃ for 6-nm PI films. In contrast, T_β remains unchanged in the ultrathin films, indicating a thickness-independent β-relaxation. Furthermore, the coefficients of thermal expansion increased remarkably with a reduction in film thickness across various temperature ranges (i.e., T<T_β, T_β<T<T_α, and T>T_α), indicating that ultrathin PI films are more sensitive to temperature variations than bulk samples. Such observation of the thickness-dependent thermal expansivity and T_α of ultrathin PI films provide a deep understanding of the effects of nanoconfinement on the dynamics of polymers with rigid chain backbones, which is also meaningful for designing and fabricating stable nano-devices based on ultrathin PI films.

Key words: polyimide, relaxation, ellipsometry, thermal expansion, nanoconfinement

引用此文

徐全印, 石欣阳, 罗锦添, 左彪. 纳米聚酰亚胺超薄膜的多级松弛与热转变^★[J]. 化学学报, 2025, 83(9): 1006-1012.

Quanyin Xu, Xinyang Shi, Jintian Luo, Biao Zuo. Relaxation and Thermal Transition of Nanoscale Polyimide Ultrathin Films^★[J]. Acta Chimica Sinica, 2025, 83(9): 1006-1012.

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图/表 9

图1. (a)制备BPDA-ODA型聚酰亚胺(PI)薄膜的路径图, (b)聚酰胺酸(PAA)的1H NMR谱图和(c) PAA与PI薄膜的FT-IR谱图

Figure 1. (a) Synthesis route for the BPDA-ODA polyimide (PI) films, (b) 1H NMR spectrum of poly(amido acid) (PAA) and (c) FT-IR spectra of PAA and PI films

图2. (a) 不同温度下PI膜的介电损耗谱, (b) T=310 ℃时的介电损耗谱及其HN函数拟合结果(虚线). 膜厚为80 μm

Figure 2. (a) Dielectric loss of polyimide film at different temperatures, (b) Dielectric loss at T=310 ℃ and the dashed line shows the HN function fitting. Thickness of the film is 80 μm

图3. PI膜的α和β松弛时间与1000/T的关系图. 黑色虚线为VFT方程拟合的结果(公式2), 红色虚线为Arrhenius方程拟合的结果(公式3)

Figure 3. α and β relaxation time plotted as a function of the inverse temperature for polyimide film. The dotted lines (red and black) are the fitting of the data to the VFT and Arrhenius equation, respectively

图4. PI膜的储能模量(E')及损耗因子(tan δ)的温度依赖性. PI的膜厚为80 μm

Figure 4. Temperature dependence of storage modulus (E') and loss factor (tan δ) of polyimide film. Thickness of the film is 80 μm

图5. (a) 300 nm PI膜的厚度与(b)膨胀系数的温度依赖性

Figure 5. (a) Temperature dependence of the thickness and (b) the thermal expansion coefficient of the 300 nm thick polyimide film

图6. PI薄膜的(a)归一化厚度(h/h0, h0为薄膜在330 ℃下的膜厚)和(b)膨胀系数随温度的变化. 图(b)中的曲线经过纵向平移, 以更好地展示其差异

Figure 6. (a) Normalized thickness (h/h0, h0 is the thickness of films at 330 ℃) and (b) thermal expansion coefficient as a function of temperature for polyimide ultrathin films. The curves in panel (b) have been vertically shifted for better presentation of their difference

图7. PI超薄膜的(a) Tα, Tβ及(b) k的膜厚依赖性

Figure 7. Film thickness dependence of (a) Tα, Tβ and (b) k for polyimide ultrathin films

图8. PAA薄膜高温亚胺化制备PI薄膜的升温程序图

Figure 8. Temperature protocol for preparing PI films by imidization of PAA films at high temperature

图9. (a) 20 nm PAA薄膜及其(b)经过高温亚胺化后得到的PI超薄膜表面形貌的AFM图

Figure 9. AFM morphological images of (a) 20 nm PAA film and (b) the corresponding PI films by imidization

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