Synthesis and characterization of a low stress photosensitive polyimide

Use of polyimides with thermal coefficients of expansion comparable to that of the underlying substrate is critical to achieving low stress in microelectronic packaging applications. Photosensitive polyimides are finding increased use because of their significant reduction in device processing steps. A negative working photosensitive polyimide, based on the BPDA/PPD backbone, has been synthesized that incorporates these key features. The polyimide exhibits excellent photosensitivity and lithographic behavior, while retaining many thermal and physical properties of the polymer framework.     

Synthesis and characterization of a positive‐working,aqueous‐base‐developable photosensitive polyimide precursor

A positive‐working, aqueous‐base‐developable photosensitive polyimide precursor based on poly(amic ester)‐bearing phenolic hydroxyl groups and a diazonaphthoquinone photosensitive compound was developed. The poly(amic ester) was prepared from a direct polymerization of 2,2′‐bis‐(3‐amino‐4‐hydroxyphenyl)hexafluoropropane and bis(n‐butyl)ester of pyromellitic acid in the presence of phenylphosphonic dichloride as an activator. Subsequently, the thermal imidization of the poly(amic ester) precursor at 300°C produced the corresponding polyimide. The inherent viscosity of the precursor polymer was 0.23 dL/g. The cyclized polyimide showed a glass‐transition temperature at 356°C and a 5% weight loss at 474°C in nitrogen. The structures of the precursor polymer and the fully cyclized polymer were characterized by Fourier transform infrared spectroscopy and ¹H‐NMR. The photosensitive polyimide precursor containing 25 wt % diazonaphthoquinone photoactive compound showed a sensitivity of 150 mJ/cm² and a contrast of 1.65 in a 3 μm film with 1.25 wt % tetramethylammonium hydroxide developer. A pattern with a resolution of 10 μm was obtained from this composition. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 352–358, 2002     

Photosensitive polyimide/silica hybrid optical materials: Synthesis, properties, and patterning

In conventional ionic salt photosensitive polyimides, large volume shrinkage during imidization would be occurred due to eliminating pendant photosensitive moieties, such as 2-methyl acrylic acid 2-dimethylamino-ethyl ester (MDAE). In this study, the volume shrinkage of photosensitive poly(4,4′-(hexafluoroisopropylidenediphthalic anhydride)-co-oxydianiline) (6FDA-ODA)/MDAE was largely reduced by photocrosslinking MDAE with a coupling agent and the silica domain in the hybrid materials. The used coupling agents were 3-methacryloxypropyl trimethoxysilane (MPTMS) or (4-vinylphenethyl)trimethoxysilane (VPTMS). The coupling agent and the silica domain are designed primarily for reducing the volume shrinkage and enhancing the thermal properties, respectively. The retention of MDAE in the prepared hybrid films is supported by X-ray photoelectron spectroscopy (XPS) and thickness variation during curing process. The silica domain in the hybrid materials from TEM analysis was in the range of 10-50 nm, which was formed by the coupling agent and tetramethoxysilane. The silica domain significantly enhanced the thermal properties of the prepared hybrid films in comparison with parent fluorinated polyimide, including the glass transition temperature and coefficient of thermal expansion. The prepared hybrid materials also exhibited reduced refractive index and optical loss by increasing the silica. The SEM diagram suggested the prepared photosensitive hybrid materials could obtain lithographical patterns with a good resolution. These results indicate that the newly prepared photosensitive polyimide/silica hybrid materials may have potential applications for optical devices.     

Positive‐working aqueous base developable photosensitive polybenzoxazole precursor/organoclay nanocomposites

Positive‐working aqueous base developable photosensitive polybenzoxazole (PBO) precursor/organoclay nanocomposites have been prepared through the addition of an organoclay to a PBO precursor. The organoclay was formed by a cation exchange reaction between a Na⁺‐montmorillonite clay and an ammonium salt of dodecylamine. The PBO precursor used in this study was a polyhydroxyamide that was prepared from a low‐temperature polymerization of 2′2′‐bis(3‐amino‐4‐hydroxyphenyl) hexafluoropropane and 4,4′‐oxydibenzoyl chloride with an inherent viscosity of 0.3 dL/g. The photosensitive resin/clay formulations were prepared from the precursor with 2,3,4‐tris(1‐oxo‐2‐diazonaphthoquinone‐5‐sulfonyloxy)‐benzophenone photosensitive compound and 3–5 wt % organoclay. The PBO precursor/clay was subsequently thermally cured to PBO/clay at 350°C. Both X‐ray diffraction and transmission electron microscope analyses showed that the organoclay was dispersed in the PBO matrix in a nanometer scale. The thermal expansion coefficient of PBO/clay film, which contained 5 wt % organoclay, was decreased 33% compared to the pure PBO film. The PBO/clay nanocomposite films also displayed higher thermal stability, glass transition temperature, and water resistance than the pure PBO film. The photosensitive PBO precursor/clay nanocomposite showed a line/space pattern with a resolution of 5 μm and its sensitivity and contrast were not affected by the organoclay. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 2350–2356, 2005     

高温热处理对聚酰亚胺薄膜性能的影响

研究了高温热处理对聚酰亚胺(PI)薄膜拉伸性能和热性能的影响。在薄膜完全环化后,随着热处理温度的升高,薄膜的拉伸强度、弹性模量先增大后基本保持不变,断裂伸长率先保持不变后明显降低,热膨胀系数也显著降低,而薄膜的玻璃化转变温度略有增大。高温热处理工艺可制备高强度和低热膨胀系数的高性能PI薄膜。     

Preparation of a nanosilica‐modified negative‐type acrylate photoresist

A new type of negative photoresist, which incorporated nanosized silica into a photosensitive acrylic resin, was developed. First, free‐radical polymerization was employed to synthesize the acrylic resin, poly[methyl methacrylate/methacrylic acid/3‐(trimethoxysilyl) propyl methacrylate], and then a silica precursor, prepared by hydrolysis and condensation of tetraethoxysilane in a sol–gel process, was introduced into the as‐formed resin solution. After the addition of photosensitive monomers and photoinitiators, a negative‐type organic–inorganic photoresist was produced. The morphology of the UV‐cured photoresist, as observed by field emission scanning electron microscopy, indicated that the size of the silica domain in the material could be reduced from 300 to about 50 nm by appropriate dosage of 3‐(trimethoxysilyl) propyl methacrylate. Thermogravimetric analysis, dynamic mechanical analysis, differential scanning calorimetry, and thermal mechanical analysis were used to evaluate the thermal and dimensional stabilities of the cured photoresists. It was found that the thermal decomposition temperature and glass‐transition temperature increased, whereas the thermal expansion coefficients before and after the glass transition decreased, with increasing silica content. The incorporation of 3‐(trimethoxysilyl) propyl methacrylate also enhanced the thermal and dimensional stabilities; however, the level of enhancement was moderate for the thermal decomposition temperature and thermal expansion coefficient and low for the glass‐transition temperature. In addition, a photoresist coated on a copper substrate demonstrated high hardness (5H) and strong adhesion (100%) with a resolution of 30 μm. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008     

Preparation and properties of thermally conductive photosensitive polyimide/boron nitride nanocomposites

A new thermally conductive photoresist was developed. It was based on a dispersion of boron nitride (BN) nanoflakes in a negative‐tone photosensitive polyimide (PSPI) precursor. 3‐Mercaptopropionic acid was used as the surfactant to modify the BN nanoflake surface for the dispersion of BN nanoflakes in the polymer. The thermal conductivity of the composite films increased with increasing BN fraction. The thermal conductivity of the PSPI/BN nanocomposite was up to 0.47 W m⁻¹ K⁻¹ for a mixture containing 30 wt % nanosized BN filler in the polyimide matrix. Patterns with a resolution of 30 μm were obtained from the PSPI/BN nanocomposites. The PSPI/BN nanocomposites had excellent thermal properties. Their glass‐transition temperatures were above 360°C, and the thermal decomposition temperatures were over 460°C. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Mechanical properties of honeycomb prepared from aromatic polyimide film

Aromatic polyimides have many advantages such as low thermal expansion coefficient, good electrical insulation, and self-extinguishing properties. We tried to use polyimide film for honeycomb structure. Polymide honeycomb core and sandwich panel were prepared from polyimide film, i.e., UPILEX R, and adhesive by the expansion method. Mechanical properties, i.e., compressive, crushed, shear, and flexural strengths, were evaluated for this core and panel. Compressive and crushed properties increased largely with the density of the honeycomb, whereas shear and midspan flexural properties did not vary so much with the density, because these failures occured in the adhered interface. Strong adhesion is required for improving the latter properties. © 1993 John Wiley & Sons, Inc.     

Chemical structures and properties of low thermal expansion coefficient polyimides

The relationships, between chemical structures of various aromatic polyimides and their thermal expansion coefficients, were investigated and the properties of low thermal expansion polyimides were elucidated. Such low values were observed for polyimides obtained from pyromellitic dianhydride or 3,3′,4,4′-biphenyltetracarboxyIic dianhydride and aromatic diamines, which included only benzene or pyridine rings fused at para-positions without a flexible linkage. It was proposed that these low thermal expansion coefficients were related to the linearity of their polymer molecular skeletons. In particular, PIQ-L100 (Hitachi Chemical Co. Ltd) is one such low thermal expansion polyimide and, it has excellent mechanical properties, thermal stability, and low absorbed moisture content.     

Photosensitive poly(amic acid)/organoclay nanocomposites

A project was carried out aimed at reducing the coefficient of thermal expansion (CTE) of photosensitive polyimide formulations (photoresists) through the incorporation of small amounts of an organoclay. The organoclay was formed by a cation exchange reaction between a NA⁺-montmorillonite clay and an ammonium salt of dodecylamine. Two polyimide precursors, a poly(amic ester) (PAE) and a poly(amic acid) (PAA), were used in this study. The PAE was prepared by direct polymerization of 2,2′-bis-(3-amino-4-hydroxyphenyl)hexafluoropropane and bis(n-butyl)ester of pyromellitic acid in the presence of phenylphosphonic dichloride as an activator. The polymer had an inherent viscosity of 0.23 dL/g. The PAA copolymer was prepared by polymerization of pyromellitic dianhydride, oxydiphthalic anhydride and oxydianiline. The polymer had an inherent viscosity of 1.00 dL/g. Two photosensitive resin/clay formulations were prepared from these two PI precursors using 2,3,4-tris(1-oxo-2-diazonaphthoquinone-5-sulfonyloxy)-benzophenone as the photosensitizer and 3 wt% organoclay. The films obtained from the PAA formulation were transparent and tough, while the films prepared from the PAE formulation were opaque and brittle. Both X-ray diffraction and transmission electron microscope analyses showed that, although the organoclay was not dispersed well in the PAE matrix, it was dispersed in the PAA matrix on a nanometer scale. The clay particles remained well dispersed after the PAA film was thermally imidized. The CTE of the polyimide film obtained was 23% lower than that of a similar film that did not contain the organoclay. The temperature at which the polyimide underwent a 5% weight loss when subjected to TGA in nitrogen was also increased by 13%. The photosensitive PAA/clay nanocomposite showed a sensitivity of 301 mJ/cm² and a contrast of 1.66 when a 0.2 wt% tetramethylammonium hydroxide developer was used. A line/space pattern with a resolution of 10 μm was obtained from this formulation.     

Preparation of Fully Imidized Hyperbranched Photosensitive Polyimide with Excellent Organosolubility and Thermal Property Based on 4,4'-(Hexafluoroisopropylidene) Diphthalic Anhydride (A<Subscript>2</Subscript>) and 1,3,5-Tris(4-aminophenoxy)benzene (B<Subscript>3</Subscript>)

Summary A negative-tone hyperbranched photosensitive polyimide (HB-PSPI) based on a new triamine, 1,3,5-tris(4-aminophenoxy)benzene (TAPOB), and 4,4'-(hexafluoroisopropy1idene)diphthalic anhydride (6FDA) was synthesized. The photosensitive cinnamate groups were incorporated at the periphery of thepolymer by the reaction of cinnamoyl chloride with the terminal phenol groups of the fully imidized hyperbranched polyimide, which was obtained via the end group modification of the anhydride-terminated hyperbranched poly(amic acid) precursor. The polymer showed good thermal property with 10 wt % loss temperature at 517 °C, and exhibited excellent organosolubility even in acetone and 1,1,2-trichloroethane. Photolithographic property of the polymer was examined by UV exposure. SEM analysis revealed that highly resolved patterns with a line width of 10 pm were obtained; and well-defined line as thin as 3pm in width could be patterned, though the line edges were jagged and rounded due to the broad molecular weight distribution. Received: 8 August 2002/Revised version: 10 October 2002/ Accepted: 26 November 2002 Correspondence to Jie Yin     

Studies on PI/PI adhesion strength

The adhesion of polyimide to polyimide was studied by measuring the peel strength of various polyimide–polyimide composites. Different factors such as diffusion of polyamic acid to polyimide substrate, contact angle, wettability, and the thermal expansion coefficient of polyimide films and the presence of siloxane can affect this adhesion and are discussed in this article. © 1994 John Wiley & Sons, Inc.     

Mechanical,thermal and electrical properties of multi‐walled carbon nanotube/aluminium nitride/polyetherimide nanocomposites

A series of polyimide‐based nanocomposites containing polyimide‐grafted multi‐walled carbon nanotubes (PI‐g MWCNTs) and silane‐modified ceramic (aluminium nitride (AlN)) were prepared. The mechanical, thermal and electrical properties of hybrid PI‐g MWCNT/AlN/polyetherimide nanocomposites were investigated. After polyimide grafting modification, the PI‐g MWCNTs showed good dispersion and wettability in the polyetherimide matrix and imparted excellent mechanical, electrical and thermal properties. The utilization of the hybrid filler was found to be effective in increasing the thermal conductivity of the composites due to the enhanced connectivity due to the high‐aspect‐ratio MWCNT filler. The use of spherical AlN filler and PI‐g MWCNT filler resulted in composite materials with enhanced thermal conductivity and low coefficient of thermal expansion. Results indicated that the hybrid PI‐g MWCNT and AlN fillers incorporated into the polyetherimide matrix enhanced significantly the thermal stability, thermal conductivity and mechanical properties of the matrix. Copyright © 2012 Society of Chemical Industry     

Effects of reactive end-capper on mechanical properties of chemical amplified photosensitive polyimide

Photosensitive polyimide (PSPI) was synthesized and characterized to replace the conventional polyimide buffer layer because direct patterning with PSPI could reduce the processing procedure to the half. Since PSPI should be dissolved in alkaline aqueous solution and have good mechanical properties after imidization, low molecular weight of PSPI was synthesized with reactive end-capper, which could extend the chain length of PSPI during imidization. Therefore norbornene end-capped PSPI precursor was synthesized with various 5-norbornene-2,3-dicarboxylic anhydride (NDA) content.Although molecular weight of PSPI decrease with increasing NDA content, the elongation at break and the glass transition temperature (T_g) of PSPI films imidized at 300 °C increased with increasing NDA content. On the other hand, elongation at break of PSPI films imidized at 350 °C decreased but T_g of those increased with increasing NDA content. Above T_g, thermal expansion coefficient decreased dramatically by introducing NDA end-capper. From mechanical and thermal properties of PSPI, it appears that low molecular weight of PSPI can be chain-extended and crosslinked during imidization.     

New positive-type photosensitive polyimide: poly(hydroxyimide) with diazonaphthoquinone

A positive working photosensitive polyimide based on polyhydroxyimide (PHI) and 2,3,4-tris[1-oxo-2-diazonaphthoquinone-4-sulfonyloxy] benzophenone (D4SB) as a photoreactive compound has been developed. The PHI was prepared by the ring-opening polyaddition of 4,4′-hexafluoroisopropylidenebis(phthalic anhydride) (6FDA), 4,4′-diamino-4″-hydroxytriphenylmethane (DHTM), and 4,4′-oxydianiline (ODA), followed by thermal cyclization in refluxing xylene. The PHI film showed excellent transparency to UV light. The photosensitive polyimide containing 30 wt% of D4SB showed a sensitivity of 250 mJ/cm² and a contrast of 5.2 when it was exposed to 436 nm light followed by developing with a 1% aqueous tetramethylammonium hydroxide (TMAH) solution at 35°C.     

A chemically amplified positive-working photosensitive polyimide based on a blend of poly(amic acid ethoxymethyl ester) and poly(amic acid)

We prepared a novel chemically amplified photosensitive polyimide based on a blend of poly(amic acid ethoxymethyl ester) (PAAE) and poly(amic acid); this blend produces polyimide (PI) films with improved mechanical properties after imidization with photoacid generator (PAG). PAAE and poly(amic acid) were end-capped with 5-norbornene-2,3-dicarboxylic dianhydride and 2,3-dimethyl maleic anhydride, respectively, to lower their molecular weights without compromising the properties of the resulting PI films. As a result of the blending of these PI precursors, the mechanical properties of the PI films were found to be less affected by the strong acid generated from the PAG than PI films fabricated by imidization of PAAE alone. The relatively high solubility of the blended PI precursor film in basic aqueous solutions was found to be effectively controlled by the use of a high-temperature post-exposure bake process to partially imidize the end-capped PAA. It was found that a 10-μm-thick film of the PSPI precursor system containing 13 wt% PAGs exhibits a sensitivity (D⁰) of 700 mJ/cm² when developed with 2.38 wt% aqueous tetramethyl ammonium hydroxide solution at room temperature. A fine positive pattern was fabricated in a 12 μm thick film with 1000 mJ/cm² of i-line exposure. The resultant PI film was also found to exhibit excellent mechanical and thermal properties, which are critical to its practical use as a stress buffer layer in semiconductor packaging.     

Novel positive‐working aqueous‐base developable photosensitive polyimide precursors based on diazonaphthoquinone‐capped polyamic esters

Novel positive‐working aqueous‐base developable photosensitive polyimide (PSPI) precursors based on partially diazonaphthoquinone (DNQ)‐capped polyamic esters bearing phenolic hydroxyl groups and a DNQ photosensitive compound (PIC‐3) were developed. The partially DNQ capped polyamic esters were prepared from an esterification reaction of 1,2‐naphthoquinone diazide‐5‐sulfonyl chloride with the polyamic esters. The partially DNQ capped polyamic esters decreased the dark film loss effectively in the aqueous‐base developer and were able to make thicker film resists compared to the uncapped polyamic esters. The 25 mol % DNQ‐capped BisAPAF–PMDA polyamic ester and BisAPAF–ODPA polyamic ester containing 25 wt % PIC‐3 photosensitive compound showed a sensitivity of 176 and 185 mJ/cm², and a contrast of 1.68 and 1.02, respectively, in a 3‐μm film with 1.25 wt % tetramethylammonium hydroxide developer. A pattern with a resolution of 5 μm was obtained from both PSPI precursor compositions. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 2293–2300, 2003     

Thin films of organic polymer composites with inorganic aerogels as dielectric materials: polymer chain orientation and properties

Summary High temperature poly(p-phenylene biphenyltetracarboximide) nanocomposite films with inorganic particulates, which are applicable to the fabrication of microelectronic devices, were prepared from the poly(amic acid) and silica aerogels with a size of ca. 150 nm in diameter by solution blending and subsequent conventional polyimide film formation process. The structure and properties were measured. By the composite formation, the optical and dielectric properties were improved due to the low dielectric constant characteristic of silica aerogels, whereas the interfacial stress and thermal expansion coefficient were significantly degraded by a large disturbance in the polymer chain in-plane orientation caused by silica aerogels despite of their low thermal expansivity. This indicates that in the rigid type of polymer composites with inorganic particulates, the orientation of polymer chains still plays a critical role on the physical properties.     

Preparation and properties of LDHs/polyimide nanocomposites

Layered double hydroxides/polyimide (LDHs/PI) nanocomposites were prepared from solution of polyamic acid (polyimide precursor) and LDH-amino benzoate using N,N-dimethylacetamide as a solvent. LDH-amino benzoate (LDH-AB) was obtained by coprecipitation method. The amino benzoate, grafted on the surface of the Mg/Al nanolayers, as a connector improved the compatibility between the inorganic Mg/Al nanolayers and the organic polyimide molecules. The dispersion behavior of Mg/Al nanolayers was investigated by transmission electron microscopy and X-ray diffraction, indicating that the Mg/Al nanolayers were exfoliated in PI matrix to form LDH-AB/PI nanocomposites. The maximum tensile strength and elongation of the LDH-AB/PI nanocomposites were found with the LDH-AB content of 5 and 4 wt%, respectively. The initial tensile modulus of these nanocomposites was increased with the LDH-AB content. These nanocomposites exhibited higher storage and loss moduli compared to those of pure PI. T_g of these nanocomposites increased with the LDH-AB content. Coefficients of thermal expansion (CTE, below and above T_g) of these nanocomposites deceased with the LDH-AB content. The thermal properties of these nanocomposites were enhanced by the incorporation of Mg/Al nanolayers in PI matrix.     

A photosensitive polyimide using an alkaline aqueous solution as a developer

Compared with the nonphotosensitive polyimide, the photosensitive polyimide has become very important in the simplification of the patterning process. Its importance has prompted the development of a new type of photosensitive polyimide, using an alkaline aqueous solution as a developer. This photosensitive polyimide allows the formation of 40-μm-square via-holes in a film with a thickness of 15 μm and exhibits excellent physical properties after curing.