Browsing by Subject "Polyimide"
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Item Design and development of base-catalyzed materials for microelectronics applications(2016-08) Dick, Andrew R.; Willson, C. Grant, 1939-; Ellison, Christopher J.; Freeman, Benny; Mack, Chris; Ho, Paul SMost lithographic processes in the microelectronics industry rely on the use of processes catalyzed by photochemically generated acids. The generation of organic bases photochemically is much less common, but allows for design of new resolution enhancement techniques and packaging materials. The microelectronics industry has been able to continue its path toward smaller transistors for several decades, but recently 157 nm and EUV lithography processes have faced delays. Alternative strategies such as double patterning are now required to keep the pace of scaling and they greatly increase manufacturing costs. This dissertation discusses a resolution enhancement technique termed pitchdivision designed to extend 193 nm lithography. This process depends on addition of a photobase generator (PBG) to commercial photoresists that enables printing of both positive and negative features, effectively doubling resolution. Using PBGs that require two separate photochemical events to generate base allows for improved image quality over standard PBGs. The use of PBGs in photosensitive polyimide packaging materials is also detailed. In packaging of integrated circuits, there is a need for an insulating material having low dielectric constant that provides support for the wires connecting the silicon chip to the circuit board. Aromatic polyimides meet many of the integration requirements, and can be patterned using PBGs in a base-catalyzed process. However, the UV absorbance of such materials is too high for thick films. The fluorinated polyimide pyromellitic dianhydride-co-2,2’-bis(trifluoromethyl)benzidine (PMDA-TFMB) was therefore auditioned for this use. PMDA-TFMB was printed using 365 nm lithography using near-UV PBGs and achieved resolution as small as 2.5 μm. This material was found to have a dielectric constant around 3.0, and a coefficient of thermal expansion of 6 ppm/K. Further work on the system sought to improve both material properties and lithographic patterning. The use of alternative monomers was explored. New PBGs capable of producing stronger amidine bases were also synthesized and used to cure PMDA-TFMB. Finally, the discovery of new catalysts for low temperature curing of polyimides is described. These materials include organic and inorganic salts that allow for the complete curing of polyimides below 200°C. The material properties of films cured with these catalysts are described.Item Morphological investigation of AFR-PEPA-N imide oligomers and their cured polyimides and the remodification of AFR-PEPA-N to achieve liquid-crystalline behavior(Texas A&M University, 2004-11-15) Murphy, Lindsay AdamsThe morphological investigation of AFR-PEPA-N and the development of a new polyimide have been established herein. AFR-PEPA-N is an imide oligomer that was created out of the need to attain a high temperature polyimide that is also resistant to hygrothermal and thermooxidative degradation. Previously, AFR700B was implemented in aerospace applications, but it was found to be hygrothermally unstable. It experienced a severe drop in its glass transition temperature and composite blistering. AFR700B was improved upon, by altering the chemical structure of the polyimide. The nadic end-cap was removed and replaced by a more hydrolytically stable end-cap. However this phenylethynyl-terminated end-group could possibly create semi-crystallinity or liquid-crystalline characteristics within the polymer. Previous research suggests further study of the relationships between AFR-PEPA-N's oligomer crystallinity and the properties of phenylethynyl-terminated polyimides. This understanding is valuable in processing AFR-PEPA-N by resin transfer molding (RTM) to obtain its optimum properties. The investigation included the identification of a processing window, temperature overlap between the melting of residual crystals and crosslinking reactions, and liquid crystallinity behavior. These reactions were investigated primarily through birefringence. The residual crystals were found to be innate in the oligomer powder and not created by preliminary thermal processing. Therefore a reasonable processing window was found based upon the reduction of crystal size by appropriate dissolution techniques. Possible nematic liquid-crystalline characteristics were found to be present at 360oC. A new imide oligomer, which was based upon AFR-PEPA-N's original structure, was synthesized. The non-linear, flourinated backbone of AFR-PEPA-N was replaced with a co-linear backbone, pyromellitic dianhydride (PMDA). These modifications were made in hopes to improve upon the network structure by it becoming more regular and resistance to nano-sized defects in the final crosslinked structure. The initial characterization found that the new polyimide, AFR-P3, displayed a cure temperature at 350oC. The degree of cure reaches about 80 to 90 percent complete based upon the consumption of the carbon-triple bond. AFR-P3 did not show signs of liquid-crystalline behavior. However, there will be future work in creating a more rigid-rod, self-assembling oligomer that can attain optimum thermal and mechanical properties.Item Photocrosslinkable nonlinear optical polymers and directly-patternable polyimide dielectrics(2014-08) Bell, William Kenneth, III; Willson, C. Grant, 1939-; Ellison, Christopher; Anslyn, Eric; Ho, Paul; Keatinge-Clay, Adrian; Rose, MichaelThe development of high-efficiency nonlinear optical (NLO) polymers has opened up many opportunities in the field of electro-optics. However, current NLO polymers do not meet stability requirements for semiconductor integration. In an effort to improve this, we examined the effects of crosslinking following electric field poling. A series of photocrosslinkable polymers bearing side chain chromophores was synthesized, poled and evaluated on the basis of the thermal stability of Second Harmonic Generation. Photoinitiation allowed for control of the onset of curing. Crosslinking was monitored by FTIR and optimal conversion was achieved by applying a slow temperature ramp during exposure. The ultimate stability of the poled polymers was directly related to the number of crosslinking substituents attached to the chromophore pendant group. With two reactive groups per chromophore significant SHG was retained at temperatures beyond the polymer Tg. In integrated circuit packaging there is a need for directly-patternable polymers of low dielectric constant. Bridging the gap between the high-value silicon chip and circuit board is a substrate comprising alternating layers of metal conductor and polymer dielectric. PMDA-ODA, an aromatic polyimide, meets many of the requirements for integration and can be patterned using a photobase generator (PBG). Due to absorbance by the PMDA-ODA precursor, this PBG must have activity at visible wavelengths. Several oxime urethanes were synthesized and evaluated as candidate long wavelength PBG. These compounds exhibit clean photochemistry and high visible light sensitivity. Unfortunately, carbamate thermal stability is insufficient for patterning PMDA-ODA. For improved material properties, PMDA-TFMB, a fluorinated polyimide, was also evaluated. Importantly, the polymer precursor is sufficiently transparent to employ thermally-stable near-UV photobases. With photobase, 2.5 micron features were resolved in PMDA-TFMB. An ancillary benefit of this methodology is reduced cure temperature (~200 °C), a traditional drawback of polyimides. This material demonstrates a dielectric constant near 3 and a thermal expansion coefficient (CTE) of approximately 6 ppm/°C in-plane. Through-plane thermal expansion is somewhat problematic, with a CTE of approximately 160 ppm/°C, and will likely require a nanoparticle composite strategy. However, this combination of material and lithographic properties make PMDA-TFMB a promising candidate for this application.Item Synthesis and cure characterization of high temperature polymers for aerospace applications(Texas A&M University, 2006-04-12) Li, YuntaoThe E-beam curable BMI resin systems and phenylethynyl terminated AFR-PEPA-4 oligomer together with an imide model compound N-phenyl-[4-(phenylethynyl) phthalimide] were synthesized and characterized. E-beam exposure cannot propagate the polymerization of BMI system until the temperature goes up to 100oC. However, a small amount of oligomers may be generated from solid-state cure reaction under low E-beam intensity radiation. Higher intensity E-beam at 40 kGy per pass can give above 75% reaction conversion of BMI with thermal cure mechanism involved. NVP is a good reactive diluent for BMI resin. The cure extents of BMI/NVP increase with the increase of the dosage and applied dosage per pass. The reaction rate is much higher at the beginning of the E-beam cure and slows down after 2 dose passes due to diffusion control. Free radical initiator dicumyl peroxide can accelerate the reaction rate at the beginning of E-beam cure reaction but doesn??t affect final cure conversion very much. According to the results from FT-IR, 200 kGy total dosage E- beam exposure at 10 kGy per pass can give 70% reaction conversion of BMI/NVP with the temperature rise no more than 50oC. The product has a Tg of 180oC. The predicted ultimate Tg of cured AFR-PEPA-4 polyimide is found to be 437.2oC by simulation of DSC Tg as a function of cure. The activation energy of thermal cure reaction of AFR-PEPA-4 oligomer is 142.6 ?? 10.0 kJ/mol with the kinetic order of 1 when the reaction conversion is less than 80%. The kinetics analysis of the thermal cure of N-phenyl-[4-(phenylethynyl) phthalimide] was determined by FT-IR spectroscopy by following the absorbance of the phenylethynyl triple bond and conjugated bonds. The thermal crosslinking of N-phenyl-[4-(phenylethynyl) phthalimide] through phenylethynyl addition reaction has a reaction order of 0.95 and an activation energy of 173.5 ?? 8.2 kJ/mol. The conjugated bond addition reactions have a lower reaction order of 0.94 and lower activation energy (102.7 ?? 15.9 kJ/mol). The cure reaction of N-phenyl-[4-(phenylethynyl) phthalimide] can be described as a fast first-order reaction stage followed by a slow second stage that is kinetically controlled by diffusion.