Nanocrystalline silicon carbide ͑SiC͒ thin films were deposited by plasma enhanced chemical vapor deposition technique at different deposition temperatures (T d) ranging from 80 to 575°C and different gas flow ratios ͑GFRs͒. While diethylsilane was used as the source for the preparation of SiC films, hydrogen, argon and helium were used as dilution gases in different concentrations. The effects of T d , GFR and dilution gases on the structural and optical properties of these films were investigated using high resolution transmission electron microscope ͑HRTEM͒, micro-Raman, Fourier transform infrared ͑FTIR͒ and ultraviolet-visible optical absorption techniques. Detailed analysis of the FTIR spectra indicates the onset of formation of SiC nanocrystals embedded in the amorphous matrix of the films deposited at a temperature of 300°C. The degree of crystallization increases with increasing T d and the crystalline fraction (f c) is 65%Ϯ2.2% at 575°C. The f c is the highest for the films deposited with hydrogen dilution in comparison with the films deposited with argon and helium at the same T d. The Raman spectra also confirm the occurrence of crystallization in these films. The HRTEM measurements confirm the existence of nanocrystallites in the amorphous matrix with a wide variation in the crystallite size from 2 to 10 nm. These results are in reasonable agreement with the FTIR and the micro-Raman analysis. The variation of refractive index ͑n͒ with T d is found to be quite consistent with the structural evolution of these films. The films deposited with high dilution of H 2 have large band gap (E g) and these values vary from 2.6 to 4.47 eV as T d is increased from 80 to 575°C. The size dependent shift in the E g value has also been investigated using effective mass approximation. Thus, the observed large band gap is attributed to the presence of nanocrystallites in the films.

Low-k films with k of 2.5–2.9 were deposited under different conditions of pressures and temperatures using a plasma-enhanced chemical vapor deposition (PECVD) system. These films were prepared using a new liquid precursor, tetravinyltetramethylcyclotetrasiloxane (TVTMCTS) and H2 carrier gas. The rf power was kept as low as possible to maintain the original ring structure in the films. The as-deposited films were annealed and the dielectric and optical properties were investigated. Identification of the absorption bands in the IR spectra for as-deposited films reveals a broadband around 950–1200 cm−1 arising from the Si–O stretching mode of the ring (1065 cm−1) and chain structure (1000 cm−1), respectively; a band at 750–900 cm−1 due to Si–O bending (790 cm−1); Si–CH3 rocking mode (760 cm−1); a sharp band centered at 1260 cm−1 due to a Si–CH3 bending mode; and a broadband at 2800–3000 cm−1 due to the CH group. A comparison of the IR spectra of the PECVD film and TVTMCTS liquid reveals that vinyl vibrations (Si–CH=CH2) at 960, 1410, and 3030–3095 cm−1 for CH2 and at 1598 cm−1 for C=C present in the liquid were not detected in the CVD films. Hence C=C bonds were broken in the plasma polymerization process. As the pressure and the deposition temperature (TD) increased, the intensity of the Si–O vibration arising from the ring structure increased and decreased, respectively. Thus by tuning the pressure and TD we can control the structure of the film. There is a good correlation found between the Si–CH3 and Si–O ring intensities and k values; the increasing Si–CH3 and Si–O ring is accompanied by decreasing k. The films were thermally stable up to 400 °C annealing temperature.

No abstract

No abstract

No abstract

We present a supercritical CO 2 (SCCO 2 ) process for the preparation of nanoporous organosilicate thin films for ultralow dielectric constant materials. The porous structure was generated by SCCO 2 extraction of a sacrificial poly(propylene glycol) (PPG) from a nanohybrid film, where the nanoscopic domains of PPG porogen are entrapped within the crosslinked poly(methylsilsesquioxane) (PMSSQ) matrix. As a comparison, porous structures generated by both the usual thermal decomposition (at approximately 450°C) and by a SCCO 2 process for 25 and 55 wt% porogen loadings were evaluated. It is found that the SCCO 2 process is effective in removing the porogen phase at relatively low temperatures (<200°C) through diffusion of the supercritical fluid into the phase-separated nanohybrids and selective extraction of the porogen phase. Pore morphologies generated from the two methods are compared from representative three-dimensional (3D) images built from small-angle x-ray scattering (SAXS) data.

No abstract

Supercritical carbon dioxide (SCCO2) extraction of a CO 2 -soluble poly(propylene glycol) (PPG) porogen from poly(methylsilsesquioxane) (PMSSQ) cured to temperatures adequate to initiate matrix condensation, but still below the decomposition temperature of the porogen is demonstrated to produce nanoporous, ultralow dielectric constant thin films. Both closed and open cell porous structures were prepared simply by varying the porogen load in the organic/inorganic hybrid films. The porogen loads investigated in the present work ranged from 25 -55 wt.%. Structural characterization of the samples conducted using transmission electron microscope (TEM), small angle X-ray scattering (SAXS) and Fourier transform infrared spectroscopy (FTIR) confirms the successful extraction of the porogen from the PMSSQ matrix at relatively low temperatures (≤200 o C). The standard thermal decomposition process is performed at much higher temperatures (typically in the range of 400 o C-450 o C). The values of dielectric constants and refractive indices measured are in good agreement with the structural properties of these samples. SLAC-PUB-9990June 2003 Work supported in part by the Department of Energy contract DE-AC03-76SF00515. 2With the ever-growing demand for higher speed in computers, the feature dimensions of integrated circuits (IC) continue to shrink. As a consequence, narrower and thinner metal lines are being used in ICs and the spacing between the metal lines is also being reduced. The former increases the wiring resistance (R) whereas the latter increases the capacitance (C), resulting in an increase in the interconnect (RC) delay. In order to reduce R, copper is being used instead of aluminum for back-end-of-the-line (BEOL)wiring. In an effort to reduce the capacitance, the main focus of current research has been the development of suitable insulating materials with lower dielectric constants (k) than One promising class of low-k candidates is spin-on glasses, such as the organosilicate poly(methylsilsesquioxane) (PMSSQ), having an empirical formula (CH 3 -SiO 1.5 ) n . This material has an inherently low value of k, low moisture uptake, and excellent thermal stability up to 500 o C. 3 The k value can be further lowered by introducing nanoporosity through the incorporation and subsequent thermal degradation of pore generating organic materials, termed porogens, into the PMSSQ matrix. [4][5][6] However, there are some inherent disadvantages with the thermal degradation route to nanoporosity. The process window can be narrow since the porogen decomposition must occur below the glass transition (T g ) of the thermally stable phase (when plasticized with the porogen) so that the nanopores formed do not collapse. Since many organic polymers have relatively low T g s compared to their degradation temperatures, this processing constraint can lead to incomplete porogen decomposition often resulting in char formation. Therefore, it is of interest to develop a lower temperature process for the introduction of porosity. High...