AVS2000 Session EL-TuP: Poster Session
Tuesday, October 3, 2000 5:30 PM in Room Exhibit Hall C & D
Tuesday Afternoon
Time Period TuP Sessions | Topic EL Sessions | Time Periods | Topics | AVS2000 Schedule
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EL-TuP-1 Polarization Effect on Copper Electroplating in Presence of Thiourea Additives
C.-L. Cheng, Y.-S. Lin (Chung-Yuan University, Taiwan) Copper metallization will play an important role in future microelectronic processing because Cu has lower resistivity and higher electromigration resistance compared to Al. Copper could be deposited by either physical sputtering, chemical vapor deposition (CVD), or electrochemical deposition. Since electroplating has advantages of low processing temperature, short processing time, and simple deposition facilities, which compared to traditional sputtering and CVD, electroplating becomes the most attractive techniques implemented in Cu metallization. Polarization becomes very important in Cu electroplating because it could effect formation of copper grain and copper filling mechanism. One common method to change the degree of polarization is using chemical additives during electroplating. In order to realize polarization effect on copper formation during electroplating, we choose a series of thiourea additives: thiourea, N-acetylthiourea, and N,N-diethylthiourea used as chemical additives on copper electroplating. Since N,N-diethylthiourea has a pair of electron-pushing groups (di-ethyl groups), it could enhance electron density around sulfur atom to increase interaction with copper ions and make polarization higher. The results are shown polarization will become higher when N,N-diethylthiourea is present and lower when N-acetylthiourea (electron puller) is existed. The finer grain size of copper forms when the higher polarization appears. Based on this study, we demonstrate that N,N-diethylthiourea could be used to act as gap filling promoters without void formation in the 0.25 micrometer dimension of trench with an aspect ratio of 4. |
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EL-TuP-2 Low Temperature, Single-Source CVD of ZrB2 and HfB2 Films as Cu Diffusion Barriers and Interconnects in Next-Generation ULSI
J.H. Sung, D.M. Goedde, G.S. Girolami, J.R. Abelson (University of Illinois at Urbana-Champaign) Thin films of the metallic ceramics ZrB2 and HfB2 have high electrical conductivity and are very effective diffusion barriers against copper; hence, they are attractive as interconnect and barrier materials for next-generation ULSI technology. Previously, we deposited highly conformal (~ 100 % bottom coverage) ZrB2 and HfB2 films using Zr(BH4)4 and Hf(BH4)4 single-source precursors in a CVD reactor with a remote hydrogen plasma source. The atomic H enhanced the release of excess B from the growth surface at low temperature, producing stoichiometric films with excellent properties. The film structure could be controllably varied from amorphous to polycrystalline by varying the substrate temperature from 250 - 800 °C, while maintaining stoichimetry. Here, we demonstrate that a single layer of ZrB2 or HfB2 can successfully replace the complex W/TiN/TiSi2 multilayer that is currently used for ULSI metallization of Si. To achieve low contact resistivity on p-type Si, we adjust the ZrB2 or HfB2 stoichiometry during the initial deposition in order to provide a controlled source of excess B atoms. This is done by briefly reducing the remote hydrogen plasma power, which increases the B content above stoichiometric ratio. We will also present results for ZrB2 or HfB2 deposited at < 300 °C: electrical resistivity less than 40 µmΩ-cm, effective diffusion barrier against Cu during annealing to 700 °C for 1 hour, and low specific contact resistivity. |
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EL-TuP-3 Study of Electrical and Interfacial Properties of CVD-W/n-Si0.83Ge0.17/Si(001) Schottky Contacts
Y.C. Jang, K.S. Kim, D.O. Shin (Sungkyunkwan University, South Korea); K.-H. Shim (Electronics and Telecommunications Research Institute, South Korea); S. Youn, K. Roh, Y. Roh, N.-E. Lee (Sungkyunkwan University, South Korea) The formation of metal contacts on Si1-xGex alloys plays an essential role in the various devices utilizing Si1-xGex/Si including heterojunction bipolar transistors, and photodetectors. Therefore, interactions between the metals and the Si1-xGex layers are of technical and scientific interests for understanding of Schottky barrier formation. Chemical vapor deposited W as a refractory metal has been commonly used in microelectronics industry and has several characteristics that make it very attractive candidates for contact metallization. The effective Schottky barrier height measurements on the CVD-W/n-Si1-xGex(001) system, however, have not reported so far as we know. In this study, we investigated the electrical properties of CVD-W/n-Si1-xGex(x=0.17) and CVD-W/n-Si schottky contacts. Fully-strained 90-nm-thick n-type Si0.83Ge0.17 epitaxial thin film with the P concentration of 5x1017 cm-3 was deposited on p-type Si(001) substrate at the substrate temperature of 650°C by LPCVD utilizing SiH4, GeH4, PH3, and H2 gases. W layers were grown by LPCVD using the WF6, SiH4, and H2 at the growth temperature of 350 - 550°C. W Schottky contacts with various sizes from 0.2 mm2 to 0.5 mm2 were defined by photolithography and etching. Electrical properties of the CVD-W/n-Si0.83Ge0.17 Schottky diodes were characterized by I-V measurements in the forward-biased direction at room temperature. The measured effective Schottky barriers (ΦBn) for CVD-W/n-Si0.83Ge0.17 and CVD-W/n-Si were 0.553 eV and 0.671 eV at the W deposition temperature (450°C).The structural, chemical and interfacial properties of CVD-W/n-Si1-xGex(x=0.17) interfaces were analyzed by XRD, TEM, RBS, and AES. The correlation between electrical and structural properties of their interfaces will be discussed. |
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EL-TuP-4 Work Function and Barrier Height Correlation for Al/GaAs Schottky Contacts Modified by Ultra-Thin, Doped Si and Ge Interlayers
T.A.R. Müller, M.I. Nathan (University of Minnesota); A. Franciosi (University of Minnesota and Universita' di Trieste); C.J. Palmstrom (University of Minnesota) A promising alternative to alloyed contacts to GaAs, which suffer from lateral diffusion and spiking problems, is the deposition of ultra-thin (<2ML) Si-films on GaAs prior to contact formation with the metal. It has been shown1,2 that these engineered interfaces can be used to increase or decrease the barrier height of Al to n-GaAs, depending on whether the Si is co-deposited with a group-III or group-V element, respectively. Although the cause for this change in barrier height is still unclear, it has been proposed that the formation of dipoles at the interface is responsible for the change in barrier height,1 where the orientation of the dipoles is determined by whether Si bonds to a group-III or group-V element at the GaAs surface. In principle, the magnitude of the dipoles is sensitive to the interface chemistry and composition. In-situ work function measurements performed at different stages of growth of Si/GaAs and Ge/GaAs layers will be presented and related to electrical measurements of the barrier height after subsequent deposition of Al used to form the Schottky contact. In the Si/GaAs system, we find that, compared to the work function of the GaAs(001)c(4x4) starting surface, the co-deposition of Si with Al leads to a sharp decrease in the work function by 0.3eV with a corresponding increase in the barrier height to >1eV, while the co-deposition of Si with As shows an increase in the work function of 0.2eV for a Si-coverage of 0.5ML. The corresponding barrier height lies in the 0.2eV range. In this talk, we report a systematic study of the effect of Ge interlayers (<4ML) on the barrier height and compare the data to barrier heights observed for similar Si interlayer thicknesses. |
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EL-TuP-5 Enhancement of Mobility with Double Delta-doped Quantum Wires by Focused Ion Beam
S. Choi, M. Leung, G. Stupian, N. Presser (The Aerospace Corporation); C. Lee (Honam University, Korea) 100nm wide delta-doped quantum wires were fabricated by the Molecular Beam Epitaxy (MBE) and a subsequent Focused Ion Beam (FIB) milling process. Ion beam focused to submicrometer diameters offers a radical departure from the conventional fabrication routine for quantum wires such as electron beam lithography. First of all,all the double delta-doped AlGaAs/GaAs quantum well structures were grown by solid source MBE system. N-type delta-doping was made in the spacer region close to the well during the MBE growth. The structures grown are a single well with two 100nm AlGaAs spacers. 5 micrometer wide Hall bar mesas were prepared by the optical lithography and a subsequent chemical etching. Next, 100nm wide AlGaAs/GaAs quantum wires were made by a 25KeV focused Gallium ion beam at 10pA current. The excited subbands in the quantum well structures may have significant amount of carrier densities placed in the undoped region where Coulombic scattering is reduced. In addition to the delta-doping effect on the reduction of scattering, one dimensional confinement effect due to 100nm wide wire structures may contribute to the enhancement of mobility along the wire direction. As a result, three times enhancement of mobility compared to the quantum well structures were found in the low temperature Hall measurements with double delta-doped quantum wires. This type of structures and a fabrication technique may show great promise for obtaining high mobility with high densities for semiconductor devices. |
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EL-TuP-6 Implantation of AlAs Etch-Stop Layers by MBE for Recessed Gate P-HEMTs
G. Zhou, W. Liu, M. Lin (Alpha Industries, Inc.) The AlGaAs/InGaAs/GaAs pseudomorphic high electron mobility transistor (p-HEMT) has been widely accepted for many high-performance, low cost millimeter-wave applications and high-speed digital circuits. In HEMTs fabrication process, one of the most critical steps is gate recess etching. This is because recess groove profiles have significant influences on the DC and RF performance of devices and integrated circuits as a whole. Wet-chemical etching is a conventional but important approach to conducting recess etching due to its ease of use and its capability to tailor device performance. To precisely control the gate recess process, the implantation of an etch-stop layer into the p-HEMT device structure is highly desirable. AlAs is a traditional etch-stop material to GaAs because of its high etching selectivity (~ 400x) and near perfect lattice match. For a reliable and controllable etching process, a reasonable thick etch-stop is desired. However, due to its large bandgap (~2.2eV) and higher defect density (DX center, for example), thick AlAs layer may cause ohmic contact problem and other side-effects which would degrade the device performance. We report the study of MBE growth of AlGaAs/InGaAs pHEMT structure with double AlAs etch-stop layers. The thickness of the AlAs etch-stoppers ranging from 1.0 to 2.5 nm. The structures were studied by Hall measurement, high-resolution x-ray diffraction, photoluminescence (PL) and photoreflectance (PR). The selective etching behavior was verified by etching profiles of time dependent sheet charge density from Hall measurements. The correlation between the etching selectivity and ohmic contact resistivity, as well as the device performance of the p-HEMT structure was compared for different structures to get the optimum AlAs thickness. |
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EL-TuP-7 Early Growth Studies of Barium Magnesium Fluoride onto (111)-oriented Silicon Substrates
A. Martinez, W. Gomez, M. Rodriguez (University of Puerto Rico) We have grown barium magnesium fluoride films (BMF) onto (111)-oriented silicon substrates using molecular beam epitaxy. The early stages of growth were studied through the performance of X-ray photoelectron spectroscopy measurements on interrupted growth runs without exposing films to atmosphere. It was observed that exposure of the Si substrate to the BMF vapor at a substrate temperature of 950C for periods of 10 seconds, removed the native oxide layer from the substrate. Subsequent growth onto substrates pretreated in this way resulted in highly textured (020)-oriented BMF films, as evidenced by x-ray diffraction studies. Films grown without the pretreatment did not display this high degree of texture. |
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EL-TuP-8 Fabrication of Smooth Diamond Films on SiO2 by the Addition of Nitrogen to the Gas Feed in Hot-filament CVD
V. Baranauskas, A.C. Peterlevitz, Z. Jingguo, S.F. Durrant (Universidade Estadual de Campinas, Brazil) Diamond films of low roughness have been deposited onto thermally oxidized Si substrates by a process of anisotropic crystalline growth induced by nitrogen in a Hot-Filament Chemical Vapor Deposition (HFCVD) reactor. Ethanol (C2H5OH), diluted in hydrogen and nitrogen, was used as the source of carbon. At high concentrations, nitrogen tends to suppress diamond growth in the < 100 > direction, which allows the growth of square mesoscopic crystals of great area in the directions parallel to the surface of the substrate. These mesoscopic structures of low thickness stack upon each other, forming a thick diamond coating of uniform thickness. Analysis of the coatings made by micro-Raman spectroscopy and atomic force microscopy (AFM) revealed that it is possible to obtain diamond coatings of high quality of roughness comparable that of the SiO2 at the diamond/SiO2 interface, and the roughness at the growth surface corresponds to the thickness of the steps of the mesoscopic structures. The microscopic mechanisms that involve the possible passivation of the <100> diamond surface by nitrogen are also discussed. |
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EL-TuP-9 Nanocrystalline Diamond and Nano-carbon Structures Produced using a High Argon Concentration in Hot-filament CVD
V. Baranauskas, A.C. Peterlevitz, H.J. Ceragioli, S.F. Durrant (Universidade Estadual de Campinas, Brazil) Nanocrystalline diamond and nano-carbon structures in the form of wires have been grown by the introduction of argon at high concentrations (60 % to ~ 99.5 % vol. Ar) into the feed mixture (ethanol and hydrogen) of a hot-filament CVD reactor. Besides the chemical inertness of argon, its presence in the gas phase changes the kinetics of the carbon deposition process. The addition of argon induces an increase in the density of vacancy defects in the diamond structure, increases the flaws between the grains, the porosity of the films, and forms new carbon structures. The range of concentration of argon used in this work is very interesting since it covers the phase transition between porous diamond ( ~60 % vol. Ar) and carbon nanowires ( ~ 99.5 % vol. Ar). A critical discussion of the growth kinetics and morphological data obtained by scanning electron microscopy (SEM), micro-photoluminescence and micro-Raman spectroscopy are discussed. |
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EL-TuP-10 Bonding Chemistry of Alternative Gate Dielectrics: Is there Really an Alternative Gate Dielectric that can Meet SIA Roadmap Expectations for Performance, Reliability and Process Integration?
G. Lucovsky (North Carolina State University) This paper presents a new classification scheme for non-crystalline metal oxides that have been considered as replacements for SiO2 in Si devices with channel lengths < 100 nm.. The scheme is based on relative bond ionicity, and the scaling parameter is the difference in the Pauling electronegativity, ΔX, between the oxygen, X(O), and metal (semiconductor), X(M), atoms. This approach distinguishes between three groups of non-crystalline elemental oxides with different bonding micro-structures: i) ΔX < 1.6 - covalent random networks such as SiO2, B2O3, and P2O5, ii) 1.6< ΔX < 2.0 - random amphoteric networks with interstitial ions such as Al2O3 and Ta2O5, and iii) ΔX > 2 - random close packed ionic structures such as Zr(Hf)O2, and Y(La)2O3. This approach has been extended to binary oxides and alloys. Systematic trends in atomic bonding arrangements and thermal stability with increasing ΔX are addressed for i) elemental oxides such as Al2O3, Ta2O5 and ZrO2, and ii) binary silicate alloys, such as (ZrO2)x(SiO2)(1-x) that span the entire range of ΔX. As ΔX increases, the atomic coordination of the metal atom increases, and thermal stability with respect to crystallization decreases. Three factors limit application of alternative oxides/silicates with Δ X> 1.6 as gate dielectrics in Si devices. These are i) reactions with Si substrates, and/or intentionally-grown thin SiO2 interfacial layers that occur during film deposition and/or annealing, ii) thermal stability against chemical phase separation and/or crystallization which limits post-deposition processing temperatures, and iii) an inherent ion polarization contribution to the frequency dependent conductance that can degrade high frequency electrical performance. |
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EL-TuP-11 Electrical Properties of (Ba,Sr)TiO3 Capacitors by Inductively Coupled Plasma Etching
S.-K. Choi, N.-H. Kim, E.-G. Chang (Chungang University, Korea); T.-H. Kim (YIT, Korea); C.-I. Kim (Chungang University, Korea) Recently, (Ba,Sr)TiO3 high dielectric thin films have received much attention as a new dielectric material for high density dynamic random access memories (DRAMs) because of their high relative dielectric constant and small variation in dielectric properties with frequency. It is well known that BST films are difficult to be etched, but good etch rate with high selectivity to etch mask was obtained by result of our former study.1 However, It was scarcely verified the possibility of etched thin films under these conditions for the appliance of practical devices. In this study, high density plasmas etching damage to the electrical properties of Pt/(Ba,Sr)TiO3/Pt high dielectric capacitors was evaluated under Ar bombardment and Ar/Cl2/BCl3 etch plasmas. And the etch parameters were changed as gas mixing ratio, coil rf power, dc bias voltage and chamber pressure. Capacitance and leakage current of BST capacitors, before and after etching, are compared to examine the etching damage. The capacitance and dielectric dissipation factors were measured by using an HP 4192 impedance/gain-phase analyzer at 10 kHz, and the leakage current density was determined by using an HP 4145B semiconductor parameter analyzer. The change of capacitance and leakage current represented the physical effect of ion bombardment. The crystal structure of the etched samples was investigated by x-ray diffraction (XRD) to observe the variation of phases. The improved etching condition with the consideration of capacitance and leakage current of BST capacitor could be obtained by analyzing correlation between electrical properties and various etching parameters. . |
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EL-TuP-12 (1-x)SrTiO3-xPbTiO3 Thin Films Grown by RF Sputtering on Pt/TiNX AND RuO/TiNX Electrodes
E.M. Guerra (CICESE, Mexico); A.F. Cruz (IMRE, Mexico); J.S. Beltrones (UNAM, Mexico) (1-x)SrTiO3(ST)-xPbTiO3(PT)polycrystalline thin films were deposited at different temperatures and pressures by argon ion rf sputtering on Pt/TiNx/SiO2/Si and RuO/TiNx/SiO2/Si substrates in presence of different concentration of Oxygen. The polycrystalline (ST-PT) perovskite phase formation is confirmed by x-ray diffraction (XRD) analysis and the grain growth dynamics is studied by scanning electron microscopy (SEM). The nature of the ferroelectric layer-electrode interface is analyzed by transmission electron microscopy (TEM) as well as the effect of its characteristics in the performance of the multilayer system. The dielectric properties of the ST-PT thin films were characterized through P-E hysteresis measurements. The microstructural results obtained for the (1-x)SrTiO3-xPbTiO3 films on Pt/TiNx/SiO2/Si and RuO/TiNx/SiO2/Si substrates were correlated to the ferroelectric properties. |
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EL-TuP-13 Etching Mechanism of Y2O3 Thin Flims in Cl2/Ar Plasma
Y.C. Kim, B.J. Min (Chungang University, Korea); Y.T. Kim (KIST, Korea); C.-I. Kim (Chungang University, Korea) Many researchers have proposed to insert such buffer layers as Y2O3 and CeO2 for ferroelectric gate structures. In particular, Y2O3/Si shows excellent interface properties and ferroelectrics deposited on Y2O3 film show excellent fatigue characteristics. The dielectric constant of Y2O3 film ranges from 14 to 17. Hence, Y2O3 films are expected to be used a buffer layer in the ferroelectric gate structure. In this study, etching mechanism of Y2O3 thin film was systematically investigated by using inductively coupled Cl2/Ar plasma. Etching characteristics of the Y2O3 thin film were investigated by using plasma diagnostic tools in conjunction with the surface analysis after etching. The etch rate of Y2O3 film, and selectivity of Y2O3 film to PR and SiO2 were examined as functions of Cl2/Ar gas mixing ratio, coil rf-power, dc bias voltage, chamber pressure, and substrate temperature. The etched surface of Y2O3 film was examined with x-ray photoelectron spectroscopy (XPS) and secondary ion mass spectrometry (SIMS). The etch profile of Y2O3 film was examined with scanning electron microscopy (SEM). The concentrations of the etching species in the plasma were determined by using optical emission spectroscopy (OES). Plasma potential and floating potential, electron density and ion current density in the plasma were determined by using Langmuir probe. Y2O3 film was more effectively etched by Ar ion bombardment than by chemical reaction with Cl radical, but the etch rate of Y2O3 film was enhanced by chemical reaction with Cl radical. In this study, for the first time, we introduced the use of Cl2/Ar plasma system in Y2O3 etching. |
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EL-TuP-14 Etch Characteristics of CeO2 Thin Films as a Buffer Layer for the Applications of MFIS-FeRAM
C.-S. Oh (Chungang University, Korea); K.-H. Kwon (Hanseo University, Korea); T.-H. Kim (YIT, Korea); C.-I. Kim (Chungang University, Korea) Cerium oxide (CeO2) thin film has been proposed as a buffer layer between the ferroelectric film and the Si substrate in Metal-Ferroelectric-Insulator-Silicon (MFIS) structures for ferroelectric random access memory (FeRAM). CeO2 thin film has properties of high thermal stability, high dielectric constant and good lattice match with Si. Since the etching of CeO2 thin film has not been reported, we studied the etch characteristics of CeO2 thin films by using high density plasma etching system. In this study, CeO2 thin films were etched with a CF4/Ar gas combination in an inductively coupled plasma (ICP). Mask made use of photoresist (PR). The experiment was done by controlling the etching parameters such as gas mixing ratio, radio frequency power, direct current bias, and chamber pressure. The surface reaction of the etched CeO2 thin films was investigated with x-ray photoelectron spectroscopy (XPS) using narrow scan spectra. Ar ion bombardment is more dominant than chemical reaction between Ce and F. The results of XPS analysis were verified by results of secondary ion mass spectrometer (SIMS) analysis and results were the same. In addition, Optical emission spectroscopy (OES) was investigated to analyze density of F radical and Ar ion in plasma. Ion current density was measured by using single Langmuir probe. The etch products were also determined using a quadrupole mass spectrometer (QMS). The profile of etched CeO2 thin film investigated with scanning electron microscopy (SEM). |
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EL-TuP-15 The Interface Formation of Ta and Low-k Plasma-polymerized Para-xylene (PPpX) and Cyclohexane (PPCHex) and the Diffusion Properties
K.J. Kim, K.S. Kim, Y.C. Jang, G.Y. Yeom, N.-E. Lee, Y.C. Quan, J. Choi, C.Y. Park, D.-Y. Jung (Sungkyunkwan University, South Korea) In order to decrease the RC delay of integrated circuit, there have been extensive research activities on Cu interconnect technology utilizing low dielectric constant (low-k) interlayer dielectric materials and Cu to replace the conventional Al metallization scheme. One of the candidates for low-k dielectrics is the organic thin films prepared by various methods. Particularly, low-k plasma-polymerized organic films containing no F which causes various corrosion problems are very promising. However, they do not provide a good interfacial adhesion to metals due to the absence of bonding states between metals and plasma-polymerized low-k organic films. In this study, we investigated the interface formation and diffusion properties between Ta and low-k plasma-polymerized para-xylene (PPpX) and cyclohexane (PPCHex) thin films as a function of O2 or N2 plasma-treatment conditions using XPS and RBS. Low-k plasma-polymerized thin films were prepared on silicon substrates by PECVD using the para-xylene and cyclohexane precursors at the substrate temperature of 45°C. PPpX and PPCHex were shown to have the dielectric constant as low as 2.70 and thermal stability up to 450°C. Plasma-treatments were performed by MEICP at the inductive power of 400W by keeping the O2 and N2 flow at 10sccm, respectively. Ta with the film thickness of 40Å was deposited using an electron-beam evaporator at room temperature. These samples were annealed at 450 ~ 500°C in vacuum in order to investigate the interface formation and diffusion of Ta into low-k films. We found that the Ta-C, due to newly created additional functional group, was formed between Ta layer and plasma-treated low-k films, judged from XPS measurements. The diffusion of Ta into the PPpX and PPHex was negligible in the detection limit of RBS. |
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EL-TuP-16 Structure Effects of Pendant Groups on Dielectric Constant and Thermal Properties of Polyimides
L.-Y. Wang (National Taiwan University); P. Chang, C.-L. Cheng (Chung-Yuan University, Taiwan) Polyimides exhibit high thermal and mechanical properties, are easily processable as thin films from soluble precursors, and have desirable dielectric properties. In this study, we investigate the structure-property on a series of polyimides which contain alkyl side groups. Two series of high molecular weight polyimides have been synthesized by the reaction of benzophenonetetracarboxylic dianhydride (BTDA) or hexafluoroisopropylidene bis(phthalic anhydride) (6FDA) with 4,4’-methylenedianiline (MDA), 4,4’-methylene-bis-(2,6-dimethylaniline) (MBDMA), 4,4’-methylene-bis-(2,6-diethylaniline) (MBDEA) or 4,4’-methylene-bis-(2,6-diisopropylaniline) (MBDIA). The introduction of fluorine into polyimides may vary free volume and polarizability and effect dielectric constant and thermal properties. The introduction of different side groups may change free volume and effect dielectric property. In this research, a detailed structure effect on the dielectric constant and thermal properties of polyimides containing alkyl side groups will be illustrated. |