Thin silicon dioxide films are commonly used as insulating layers in metal-insulator structures, such as integrated circuits and multichip modules. These films are either thermally grown or deposited by thermal or plasma-enhanced chemical vapor deposition (PECVD). The advantage of PECVD is that lower deposition temperatures can be used avoiding defect formation, diffusion, and degradation of the metal layer. However, the low deposition temperature of the PECVD process has a negative effect on the quality of the silicon dioxide. Oxides produced at low temperatures contain more silanol and water impurities and are more porous than those deposited at higher temperatures. The deposition parameters, including substrate temperature, RF power, pressure, and reactant gas flow rate, affect the silanol and water concentration. The substrate temperature has the largest effect on the silanol concentration of the oxide. Using a large RF power, high pressure, and low nitrous oxide to silane ratio will minimize the silanol concentration at a given temperature. This will minimize the dielectric constant and maximize the etch resistance of the oxide produced.
A new force field has been customized for the variation of polynorbornene that contains a bicycloheptane group in the backbone structure. The force field was developed from ab initio density functional theory (DFT), and semiempirical electronic structure calculations for both stereochemical dimers of the 2,3 exoexo isomer of polynorbornene. The bond length and bond angle parameters were determined using the HF/ 6-311G** ab initio SCF method. The intrinsic torsion potential was determined using the AM1 semiempirical method and the van der Waals parameters are kept same as in the Dreiding 2.21 force field. Both the bonded and torsional energy functions compared well to DFT calculations. The equilibrium geometry and the torsional energetics of the customized force field differ significantly from generic force fields such as Dreiding. Comparisons to experimentally determined geometry and infrared and Raman spectra were used to determine the optimum ab initio and semiempirical method to use for force field parametrization. The new force field reproduces a polynorbornene dimer crystal structure to a high degree of accuracy.
The effects of spinning speed, substrate material, and thermal treatment on the optical anisotropy of spin‐coated polyimide films have been examined using the Metricon 2010 Prism Coupler to measure the birefringence. A decrease in the molecular orientation, as determined by birefringence, with increasing film thickness has been attributed to a stress gradient in the thickness of the film and the presence of air‐polymer‐substrate interfaces. The extent of the thickness dependence is a function of the polymer chain rigidity associated with the polyimide chemistry. The birefringence of the polymer film is also influenced by the substrate material due to the coefficient of thermal expansion mismatch between the film and the substrate. In addition, as a result of potential interdiffusion of solvent molecules and polymer segments between multiple layers of film, the birefringence in polyimide films obtained from multiple coatings of polyamic acid depends on the thermal treatment between the individual coatings. The birefringence of PMDA/ODA polyimide film derived from polyamic acid solution increases as the imidization temperature is increased to 400°C. For preimidized polyimide, the birefringence initially increases upon solvent removal, but decreases above 200°C, possibly indicating the occurrence of thermal cross‐linking. © 1993 John Wiley & Sons, Inc.
Dynamic viscosity and ionic conductivity were measured simultaneously during the cure of a digylcidyl ether of bisphenol‐A (DGEBA) epoxy resin with diamino‐diphenyl sulfone (DDS) by mounting a microdielectric sensor into the plates of a rheometer. Two different cure temperatures were examined. Periodically, throughout the cure, samples were removed from the plates of the rheometer, quenched, and analyzed for the glass transition temperature and epoxide conversion. The relationship between conductivity and viscosity appeared to be independent of cure temperature. A linear relation with a slope of −1 was observed between the natural logarithms of conductivity and viscosity during the cure up to approximately 85% cure conversion. It was hypothesized that the reaction rate was hindered by diffusion at this stage in the polymerization. A free volume relationship was used to successfully correlate conductivity with viscosity up to the diffusion limited region. ©1995 John Wiley & Sons, Inc.
Single‐chain Monte Carlo simulations of polynorbornene were carried out for three stereochemical isomers. These simulations employed custom force field parameters derived from ab initio and semi‐empirical quantum calculations. The scaling of intrinsic viscosity with molecular weight was determined from these simulations. An unusually large variation in this scaling was obtained, which is attributed to the large degree of steric hindrance inherent in this form of polynorbornene that retains the bicyclo‐heptane ring in the backbone. The same scaling was measured for three commercial samples of this polymer produced using three different catalysts. The simulation and experimental results were consistent and the former were used to estimate the stereochemical configuration of the commercial samples. The simulation results for a stereoregular isomer of polynorbornene were also consistent with previous RIS model results. These structure‐property relationships extracted from the simulations are potentially useful in the commercialization of polynorbornene for interlayer dielectric applications in electronic packaging.
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