The measurement of the mechanical properties and adhesion of polymeric thin films and coatings poses a number of technical problems. Elastic and viscoelastic properties, residual stress, adhesion, the effects of extended cure, and the effects of adsorbed moisture and process reagents are all critical. A particular challenge is to develop measurement methods which can be used with actual samples, preferably non-destructively. This paper examines a number of methods which have been developed to make these measurements, with emphasis on methods which are sensitive enough to look at the effects of process variation and the effects of moisture exposure. Suspended-membrane methods for measuring elastic and viscoelastic properties, residual stress, and adhesion are combined with optical methods for determining index of refraction and birefringence to yield a family of techniques for performing physical characterization. Recent results on the effects of extended cure and moisture uptake on elastic properties, residual stress, and optical properties will be presented.

The determination of residual stresses in thin polymer coatings is crucial in the prediction of failure due to delamination and cracking. This is especially important in the electronics industry where thin polymer dielectric layers are used. The dielectric layers are often under three-dimensional constraints and have holes through which metal interconnects run. These act as locations of high stress concentration. Three complementary methods have been developed which will provide a better base for understanding the delamination and performance of thin coatings.

These techniques include, a holographic interferometry method for determining the residual stresses in coatings (˜10 μm thick); a deformation calorimetry technique for establishing an energy balance for peel tests; a set of experiments for measuring the nine elasticity coefficients for orthotropic films. The combination of these methods allows a comparison between the residual stresses present in coatings and the contribution of those residual stresses to the work needed for peeling. The knowledge of the stress state and elasticity coefficients is essential for determining the elastic energy in a coating. The total elastic energy which can be stored in a stressed coating increases with the coating thickness. Stressed coatings exceeding a critical thickness will spontaneously delaminate if the elastic energy in the coating is greater than the energy required for debonding. The elastic energy in the coating per unit area at the critical thickness is a measure of the interfacial strength.

The effect of processing on the development of internal stresses in spin coated polyimide films was investigated. The internal stresses are a result of the coefficient of thermal expansion (CTE) mismatch between the polymer and the substrate. Birefringence and CTE were used to characterize the in-plane molecular orientation. In-plane orientation was shown to be sensitive to processing conditions. Increasing the spin speed results in higher in-plane orientation as observed by an increase in birefringence and a corresponding decrease in CTE. Heating rate during cure was observed to have a significant effect on in-plane orientation. Faster heating rates during cure resulted in a lower birefringence. The lower birefringence is attributed to relaxation effects that can occur during a rapid cure. The decrease in orientation was accompanied by an increase in internal stress.

The intrazeolite chemistry of the two germylene complexes Cl2(THF)GeM(CO)5(M = Mo, W) was studied with x-ray absorption spectroscopy (Ge, Mo, W edge EXAFS) and in-situ FTIR/TPD-MS techniques. The slightly decarbonylated GeMo complex interacts with the framework of NaY zeolite at room temperature and retains the Ge-Mo bond up to about 100° C. In proton-loaded HY zeolite, framework interactions increase at elevated temperature, and the attached complex retains the Ge-Mo bond up to about 120° C. The Ge-Mo bond is cleaved at higher temperatures. MoC1x and Mo-Mo species are formed in NaY and HY zeolite, respectively, while GeClx fragments are anchored to the zeolite framework.

The complex Cl2 (THF)GeW(CO) 5 retains all five CO ligands up to about 100° C in both NaY and the proton form. Detectable anchoring occurs at room temperature in NaY and at about 80° C in the proton form. WC1x species are formed upon cleavage of the Ge-W bond at higher temperatures.

The polylmide synthesized from benzophenonetetracarboxylic dianhydride and alkyl-substituted diamines is inherently photosensitive at ≤365 nm, and a solvent soluble, negative-acting system can be formulated from the fully-imidized resin. The lithographic, thermal, mechanical, and electrical properties of the polyimide films have been characterized. This polyimide film shows good thermal, mechanical, and electrical properties, and a 1:1 aspect ratio is consistently achieved on 10 μm thick films. The thermal properties of the films were determined using TGA and TMA methods. The decomposition temperature was 527°C, the weight loss of the cured film at 350°C in nitrogen was 0.04 %/hour and the thermal expansion coefficient was 37 ppm/°C. The dielectric constant and dissipation factor of the film were 3.0 and 0.003 respectively at 4% humidity. The effects of hard-bake time, hard-bake temperature, nitrogen purge rate during heat treatment, and humidity on the thermal and electrical properties of the thin film were also examined, and are presented here. The rate of weight loss of the cured film increases when the rate of nitrogen purge decreases or when the cure temperature increases. Longer heat treatments resulted in a slight decrease in the CTE and an Increase in the Tg. The electrical properties of the films are dependent both on the humidity during measurement and on the hard-bake temperature.

BPDA-PDA poly(amic acid) precursor was functionalized through its carboxylic acid groups being linked with a crosslinkable aminoalkyl methacrylate, 2-(dimethylamino)ethyl methacrylate (DMAEM), by acid/base complexation. BPDA-PDA polyimide films, which were thermally imidized from the precursors complexed with various amounts of DMAEM, were characterized by means of wide angle x-ray diffraction, stress-strain analysis, and residual stress analysis. The structure and properties of the BPDA-PDA polyimide film were dependent upon the history of the precursor, that is, the complexation of the poly(amic acid) precursor with DMAEM. The molecular packing order was enhanced with the history of DMAEM loading while the molecular order along the chain axis was disrupted. Overall, physical properties, such as mechanical properties and residual stress, were degraded with DMAEM loading. The moisture induced stress relaxation behavior was sensitive to the history of DMAEM loading, whereas the creep induced stress relaxation was varied little due to its high Tg. These properties are understood in terms of structure/property relationships, as well as microvoids, which were possibly generated by outgassing the bulky DMAEM pendent groups during thermal imidization.

Studies were made of the physical properties of the commercially available polyimide Upilex-SGA, which is prepared from biphenyl dianhydride and p-phenylene diamine. Annealing the Upilex-SGA for 2 hr Linder N2 at 400°C gave a film that expanded continuously when heated at a fixed rate, in contrast to the as-received film. The linear expansion showed a change of slope at 84°C and also at 295°C, the later being Tg. The thermal coefficient of linear expansion at all temperatures was very small, even above 295°C it is 27.8 × 10−6. Its stress-strain curve did not exhibit a yield point, even though its ultimate elongation is ˜23%. Similar behavior is shown by the PMDA-ODA polyimide, except its ultimate elongation is ˜70%,. The unusual stress- strain curves exhibited by these polyimides is undoubtedly caused by their liquid-crystalline morphology. The stress-relaxation modulus was measured at 0.5% extension and 12 temperatures from 30 to 330°C. Derived isochrones showed that the 1-s tensile modulus at 20°C is 9.0 GPa, but at 330°C it is 2.0 GPa. Creep curves were also measured at a stress of 30 MPa and at 10 temperatures from 30 to 340° C. Master curves prepared from the relaxation and creep data are discussed briefly and evidence is given which, show that the superposition method is not truly valid for this polyimide, which actually is not surprising.

The electrical properties of gold – polyimide - silicon structures were investigated experimentally by capacitance – voltage (C – V) measurement. Polyimide films were deposited on silicon substrate by using ionized cluster beam deposition (ICBD) of PMDA-ODA followed by in-situ thermal curing in N2 atmosphere. The resulting C – V plots show hysteresis, and it was believed to be due to the injection of carriers. The interface trap density is fairly low because of the clean interface provided by ICB technique.

The behavior of glassy polymers was studied with the aid of mechanical tests on the basis of free volume. Three types of experiments were carried out and interpreted using modern ideas about the structure of free volume. They were: 1. The study of changes in the total free volume occurring as a result of deformation (by measurement of density) 2. The study of micro voids and their changes on deformation using small angle X-ray scattering (SAXS) and positron annihilation 3. The study of mobile regions by the measurement of dielectric loss (using an original interpretation) during deformation. This allows several parts of the total free volume to be distinguished and investigated. A model for the free volume relaxation during deformation is proposed.

Aromatic polyimides because of their structure process a unique property combination of outstanding thermal stability and radiation and solvent resistance. Their excellent mechanical and electrical properties make polyimides the materials of choice for a wide range of applications in the electronics industry. Polyimides have long been amorphous materials but recently, flexible hinge groups containing ether and ketone linkages have been incorporated into the polymer backbone [1]. This results in increased flexibility and development of crystallinity. The introduction of crystallinity is an effective means of improving the melt processability, however, little work has been done to determine the effects of crystallinity on the insulating characteristics of polyimides. Here we report the dielectric behavior for the semicrystalline polyimide New-TPI [2], which is synthesized by Mitsui Toatsu Chemical Co. and film processed by Foster-Miller, Inc. We have used dielectric relaxation to study New-TPI, especially its behavior near Tg.

Free-standing polyimide film is used extensively in tape automated bonding (TAB) and flexible printed circuit (Flex) applications because of its excellent chemical, mechanical, and electrical properties. Kapton polyimide film has been the material of choice for many years. Recently, a new polyimide film, Upilex, has been introduced into the marketplace. The primary property differences between Kapton and Upilex result from differences in the chemical composition of each film. A review of property/product performance indicates that Upilex S is preferred with respect to dimensional stability, metal/polyimide and adhesive/polyimide adhesion, chemical inertness and glass transition temperature.

The UV laser ablation of three thermostable polymers, polyimide, polyphenylquinoxaline and Teflon AF of interest for microelectronics is presented. Direct absorption of the laser beam is not possible by Teflon, but a doping technique is described.

Polyimide is commonly used in the microelectronic industry for interconnection applications because of its ability to planarize features typically found on an IC chip. A mathematical model is developed to describe fluid flow on a rotating disk based on the principles of mass and momentum conservation. Constitutive relationships necessary for this model are proposed. Experimental data for polyimide precursor solutions are presented which enable the determination of parameters for the constitutive equations. This model is used to describe the film profiles over flat surfaces and near micron-sized features. Attention is focused on the coupling between mass transport and fluid flow as well as the effects of surface tension on film profiles over topographical features.

This paper reports the results of a planarization process of polyimide which has been utilized as a passivation material in multilevel interconnection. The degree of planarization with spin-coated polyimide over metal topography is only 10–20% due to crosslinking and shrinking of the polymer during the curing process. Polystyrene used as sacrificial planarizing film can achieve <95% planarity over 100μm metal pad with 1μm height. A conformal polystyrene film can be spin-coated onto the polyimide surface without adhesion promoter. The topography of polyimide over the metal pattern can be planarized with thermal reflow of the polystyrene by baking the film below 250°C. The planarity of this sacrificial film, polystyrene, can be transferred to polyimide by etch-back without degrading the polyimide surface properties which has been examined by X-ray photoelectron spectroscopy.

The reactions between PPQ and several acidic solutions have been studied. Protonation reactions have been evidenced using U.V.- Visible spectroscopy. PPQ revealed three different states concerning these completely reversible reactions. Each state exhibits a specific colour: Pale yellow (as deposited PPQ), and gold yellow and purple red for, respectively, the first and the second protonation states. Using IR spectroscopy, it has been shown that the protons are fixed at the nitrogen sites of the polymer. A possible degradation of the PPQ related to the protonation reactions is also studied, and thus technological solutions are proposed.

New liquid crystalline thermosets have been prepared from end-functional monomers and oligomers of varying molecular weight. Both triazine and epoxy networks were explored. Of primary interest was the exploitation of the mesophase properties of these networks for developing polymers with high thermal stability and low coefficients of thermal expansion (CTE). Curing was carried out either within the nematic mesophase or the isotropic phase of the prepolymers. Transition temperatures associated with the mesophase were observed to change after curing under these two sets of conditions. The networks with the highest crosslink density were found to exhibit the lowest CTE values. Crosslinking of these thermosets was also carried out in the presence of a 13.5 Tesla magnetic field to determine the effect of orienting fields on the curing of the LC network. Orientation parameters as measured by wide angle x-ray diffraction were as high as 0.6. Values of the coefficient of thermal expansion as low as 15 ppm were achieved in the aligned direction. Of the two resin types, those with the triazine crosslinks had the lowest thermal expansion coefficient. Other thermal properties of these networks will be discussed.

In an assembly of aligned, thermotropic polyester macromolecules, such as a fiber, the flexibility and deviations from rectilinearity occasioned by in-chain ArCOAr or ArOAr units are reflected sensitively by overall stiffness (initial modulus) and elasticity (elongation at break). The influence of frequency and placement of these units, as well as the effect of ring substituents, is discussed.

In a few cases where carbonyl or other units are regularly placed at suitable intervals along the chain, the latter apparently is extended as a low amplitude, regular helix which, in terms of physical properties, approximates to a straight, rod-like conformation. In situations where the angulation created by a carbonyl unit is immediately cancelled by an adjacent m-phenylene ring, the extended macromolecule is virtually rectilinear and, though marginally liquid crystalline, may provide some of the strongest organic fibers known.

12 polyesters with branched spacers and 7 polyesters with linear spacers were synthesized and characterized.

A thermotropic liquid crystalline copolymer consisting of bisphenol E diacetate, isophthalic acid and 2,6-naphthalene dicarboxylic acid was blended with polyether imide by dissolving in a mixed solvent of phenol/1,1,2,2-tetrachloroethane in a ratio of 60/40 w/w and co-precipitating the ternary solution in non-solvent (methanol). Wide-angle x-ray diffraction and differential scanning calorimetry studies revealed that the blends were completely amorphous with a single glass transition temperature. The single phase was probably entrapped during solvent removal, but these mixes were unstable and phase separated upon heating. Mesophase structure developed in the LCP rich region with continued annealing. The evolution of crystalline texture was monitored by time-resolved wide-angle x-ray diffraction following a temperature jump from ambient to 265 °C. The recrystallization process of LCP was found to slow down in the blend state relative to that of the neat LCP.

Polyimides are an important class of polymeric materials used in microelectronics fabrication. These polymers could be used even more extensively if it were possible to improve their moisture resistance. We are using plasma processing techniques to modify the moisture resistance of polyimide films. Films are exposed to nitrogen trifluoride plasmas to introduce fluorine into the surface of the polyimide. Fluorination is monitored with x-ray photoelectron spectroscopy and Fourier transform infrared absorption spectroscopy. Water contact angle measurements are used to assess the hydrophobicity of the treated surfaces. Thus far, we have demonstrated that this plasma treatment is a good way of introducing fluorine into the polyimide surface, and that these treatments do enhance the hydrophobic nature of polyimide.