Larry F. Rhodes

Low k, Porous Methyl Silsesquioxane and Spin-On-Glass

Low dielectric constant, porous silica was made from commercially available methyl silsesquioxane (MSQ) by the addition of a sacrificial polymer, substituted norbornene polymer containing triethoxysilyl groups (NB), to the MSQ. The silsesquioxane-NB polymer film mixture was thermally cured followed by decomposition of the NB at temperatures above 400°C. The dielectric constant of the MSQ was lowered from 2.7 to 2.3 by creating 70 nm pores in the MSQ. The voids created in the MSQ exhibited a closed-pore structure. The concentration of NB in the MSQ affected the number of pores but not their size. Porous films were also created in a methyl siloxane spin-on-glass and its dielectric constant was lowered from 3.1 to 2.7. Infrared spectroscopy was used to follow the curing of the MSQ and decomposition of the NB.

Air-channel fabrication for microelectromechanical systems via sacrificial photosensitive polycarbonates

This research involves the fabrication of encapsulated air-channels via acid-catalyzed degradation of photosensitive polycarbonates (PCs). There is a need for lower-temperature, degradable polymeric materials to fabricate buried air-channels for microelectromechanical systems (MEMS), microfluidic devices, and micro-reactors. Some polycarbonates undergo thermolytic degradation in the temperature range of 200 to 350/spl deg/C. These polycarbonates are also known to undergo acid-catalyzed decomposition in the presence of catalytic amounts of acid. A small percentage of an acid in the polycarbonate formulation can greatly reduce the onset of decomposition temperature to the 100 to 180/spl deg/C temperature range. The photoacid and thermal acid induced degradation behavior of PCs and its use as a sacrificial material for the formation of air-gaps have been studied in this work. The decomposition of several polycarbonates with the aid of in situ generated photo-acid has been demonstrated and applied to the fabrication of micro air-channels. Based on FT-IR, mass spectrometry, and thermogravimetric analysis (TGA), a degradation mechanism was proposed.

Chemically Bonded Porogens in Methylsilsesquioxane I. Structure and Bonding

Porous methylsilsesquioxane (MSQ, films were created by making polymer blends with trimethoxysilyl norbornene (TMSNB) and triethoxysilyl norbornene (TESNB), where the polymer served as a sacrificial place-holder. Upon exposure to elevated temperatures, the polymers decomposed within the MSQ matrix to form nanosize voids in the films. Different pore microstructures were observed by transmission electron microscopy and atomic force microscopy, depending on the functional groups on the polymeric sacrificial material used. The differences in microstructure have been correlated to variations in the chemical reactivity between the sacrificial polymer and the MSQ matrix. Solid-state and nuclear magnetic resonance, and Fourier transform infrared spectroscopy have been used to study the chemical structure of the TMSNB and TESNB:MSQ mixtures. Indications of a chemical bond between the TMSNB and the MSQ have been found in these mixtures; however, the same results were not observed for the TESNB system. The addition of an acid catalyst to the TESNB was found to induce a reaction between the TESNB sacrificial polymer and the MSQ. The percent weight loss of the MSQ and its mixtures (with TMSNB and TESNB) were used to evaluate the polymer residue.

Porous Methylsilsesquioxane for Low-k Dielectric Applications

A commercially available spin-on glass ~methylsilsesquioxane, MSQ! was modified by the introduction of porosity. The porosity reduced the effective dielectric constant of the MSQ by the incorporation of air. The pores were created by adding a sacrificial polymer ~substituted norbornene polymer! to the silsesquioxane matrix. The sacrificial material was thermally decomposed to form nanosize voids within the films. The physical and electrical properties of the porous films were studied as a function of the reactivity of the sacrificial polymer with the glass, and the loading and molecular weight of the sacrificial polymer. Transmission electron microscopy was used to evaluate the porous microstructure. Cross-sectional images show pores of nearly spherical geometry with 5-20 nm diam. The dielectric constant and the index of refraction of the porous MSQ were lower after the decomposition of the sacrificial material. The dielectric constant decreased from 2.7 for a nonporous MSQ film to ;2.2 for a film with 30 wt % loading of the sacrificial polymer. In a similar way, the index of refraction was reduced from 1.42 to 1.29 for the porous MSQ film. The mechanical properties were evaluated using nanoindentation techniques. This paper focuses on the significant improvements observed upon introduction of porosity to the films. The fracture toughness, or the resistance to crack propagation, increased dramatically with porosity, as compared with the nonporous MSQ films. As a result, thicker MSQ films can be fabricated without spontaneous cracking. The elastic modulus and the hardness of the porous films were measured and showed a reduction in both properties with increasing porosity in the film.

Fabrication of microchannels using polynorbornene photosensitive sacrificial materials

© 2003 The Electrochemical Society, Inc. All rights reserved. Except as provided under U.S. copyright law, this work may not be reproduced, resold, distributed, or modified without the express permission of The Electrochemical Society (ECS).

Chemically Bonded Porogens in Methylsilsesquioxane II. Electrical, Optical, and Mechanical Properties

The electrical, optical, and mechanical properties of porous methylsilsesquioxane (MSQ) films created using two different sacrificial polymers: trimethoxysilyl norbornene (TMSNB), and triethoxysilyl norbornene (TESNB) were evaluated in this study. The introduction of porosity lowered the dielectric constant, the index of refraction, and the elastic modulus and hardness of the films as compared to the nonporous MSQ films. The dielectric constant was lowered from 2.7 for a pure MSQ film to 2.35 for a film with 30 wt % initial concentration of TMSNB. Similarly, the index of refraction was lowered from 1.42 to 1.30 for a 30:70 wt %. TMSNB:MSQ film. The TMSNB:MSQ films showed a transition from closed-to-open cell porosity in the range from 20 to 30 wt % loading of sacrificial polymer as determined from positron annihilation spectroscopy. Improvements in the fracture toughness were observed for the TESNB:MSQ films as compared to the pure MSQ or TMSNB:MSQ films.

Lithographic Characteristics and Thermal Processing of Photosensitive Sacrificial Materials

Previously, a novel method for fabricating microfluidic and microelectromechanical devices with buried microchannel structures using thermally sacrificial polymers was reported. These previous methods required separate lithographic and etching sequences to pattern the sacrificial polymer. In this work, a more advanced approach in which the sacrificial material is radiation sensitive and can be patterned directly using standard lithographic techniques is explored. The lithographic performance of a new class of photosensitive polynorbornene (PNB) sacrificial materials has been characterized. The effect of soft bake and postexposure bake (PEB) on the cross-linking of photodefinable PNB has also been investigated. It was found that significant cross-linking of PNB occurs after exposure during the subsequent postexposure bake. However, this phenomenon is strongly dependent on the soft bake conditions used in preparing the sample, presumably due to varying levels of residual solvent content. This may he due to the high mass transport of the reactive species because of evaporation of residual solvent and shrinking of polymer matrix during the PEB profess. No noticeable influence of residual solvent on cross-linking has been found during exposure.

Synthesis and Characterization of a New Family of Square-Planar Nickel(II) Carbonyl Derivatives

The reaction of [NBu(4)](2)[Ni(C(6)F(5))(4)] (1) with solutions of dry HCl(g) in Et(2)O results in the protonolysis of two Nibond;C(6)F(5) bonds giving [NBu(4)](2)[[Ni(C(6)F(5))(2)](2)(mu-Cl)(2)] (2 a) together with the stoichiometrically required amount of C(6)F(5)H. Compound 2 a reacts with AgClO(4) in THF to give cis-[Ni(C(6)F(5))(2)(thf)(2)] (3). Reacting 3 with phosphonium halides, [PPh(3)Me]X, gives dinuclear compounds [PPh(3)Me](2)[[Ni(C(6)F(5))(2)](2)(mu-X)(2)] (X=Br (2 b) or I (2 c)). Solutions of compounds 2 in CH(2)Cl(2) at 0 degrees C do not react with excess CNtBu, but do react with CO (1 atm) to split the bridges and form a series of terminal Ni(II) carbonyl derivatives with general formula Qcis-[Ni(C(6)F(5))(2)X(CO)] (4). The nu(CO) stretching frequencies of 4 in CH(2)Cl(2) solution decrease in the order Cl (2090 cm(-1))>Br (2084 cm(-1))>I (2073 cm(-1)). Compounds 4 revert to the parent dinuclear species 2 on increasing the temperature or under reduced CO pressure. [NBu(4)]cis-[Ni(C(6)F(5))(2)Cl(CO)] (4 a) reacts with AgC(6)F(5) to give [NBu(4)][Ni(C(6)F(5))(3)(CO)] (5, nu(CO)(CH(2)Cl(2))=2070 cm(-1)). Compound 5 is also quantitatively formed ((19)F NMR spectroscopy) by 1:1 reaction of 1 with HCl(Et(2)O) in CO atmosphere. Complex 3 reacts with CO at -78 degrees C to give cis-[Ni(C(6)F(5))(2)(CO)(2)] (6, nu(CO)(CH(2)Cl(2))=2156, 2130 cm(-1)), which easily decomposes by reductive elimination of C(6)F(5)bond;C(6)F(5). Compounds 3 and 6 both react with CNtBu to give trans-[Ni(C(6)F(5))(2)(CNtBu)(2)] (7). The solid-state structures of compounds 3, 4 b, 6, and 7 have been established by X-ray diffraction methods. Complexes 4-6 are rare examples of square-planar Ni(II) carbonyl derivatives.

Heterometallic species containing Cp2MH2 (MMo and W) and Cu+ or Ag+ are inner sphere redox intermediates

Abstract Reaction of Cu(NCMe)4+ with Cp2MH2 (M  Mo or W) in a 1:2 mole ratio yields (Cp2MH2)2Cu+, as the PF6− salt. IR and 1H NMR data are consistent with a structure in which all hydrides are bridging M to copper. An X-ray diffraction structure determination of the compound with MMo confirms this conclusion; the unit cell contains two crystallographically-independent cations with significantly different CuH4 coordination geometries: the MoH2 planes have dihedral angles of 31.1 and 51.0°. Crystallographic data (at −157 °C): a=20.263(6), b=10.434(2), c=21.109(6) A, Z=8 in space group Pbnb. Additional Cu(NCMe)4+ has no effect on (Cp2WH2)2Cu+. Reaction of Cp2WH2 with AgBF4, gives first (Cp2WH2)2Ag+, which shows Ag/hydride coupling in the 1H NMR spectrum at −75 °C. Additional Ag+ in MeCN gives oxidation to equimolar Cp2WVIH3+ and Cp2WIVH(NCMe)+, via the adduct (Cp2WH2Ag)22+, whose IR spectrum is consistent with μ3-hydrides. While(Cp2WH2)2Ag+ is not oxidized by Cu(NCMe)4+, (Cp2WH2)2Cu+ is completely oxidized by Ag+, suggesting that the aggregate (Cp2WH2MM′)22+ has inequivalent sites for M and M′, and thus two isomeric forms.

Synthesis, characterization and reactivity of some rhenium phosphite complexes

Abstract The preparation and characterization of some Re(III), Re(IV) and Re(V) chloro phosphite complexes are reported. Both Re(III) and Re(IV) complexes react with sodium borohydride, yielding the corresponding polyhydrides, ReH5[P(OEt)3]3 and ReH7[P(OEt)3]2. The thermal and photochemical reactivity of these complexes is described.