Anisotropic Thermal Expansion Behavior of Thin Films of Polymethylsilsesquioxane, a Spin-on-Glass Dielectric for High-Performance Integrated Circuits

Abstract

Thin films of poly(methylsilsesquioxane) (PMSSQ) are candidates for use as interdielectric layers in advanced semiconductor devices with multilayer structures. We prepared thin films of PMSSQ with thicknesses in the range 25.0-1151.0 nm by spin-casting its soluble precursor onto Si and GaAs substrates with native oxide layers and then drying and curing the films under a nitrogen atmosphere at temperatures in the range 250-400 degrees C. The out-of-plane thermal expansion coefficient alpha(perpendicular) of each film was measured over the temperature range 25-200 degrees C using spectroscopic ellipsometry and synchrotron X-ray reflectivity, while the in-plane thermal expansion coefficient alpha(parallel) of each film was determined over the temperature range 25-400 degrees C by residual stress analysis. PMSSQ films cured at higher temperatures exhibited reduced thermal expansion, which is attributed to the denser molecular packing and higher degree of cross-linking that arises at higher temperatures. Surprisingly however, all the PMSSQ films were found to exhibit very strong anisotropic thermal expansion; alpha(perpendicular) and alpha(parallel) of the films were in the ranges 140-329 ppm/ degrees C and 12-29 ppm/ degrees C respectively, depending on the curing temperature. This is the first time that cured PMSSQ thin films have been shown to exhibit anisotropic thermal expansion behavior. This anisotropic thermal expansion of the PMSSQ thin films might be due to the anisotropy of cross-link density in the films, which arises because of a combination of factors: the preferential orientation of methyl groups toward the upper film surface and the preferential network formation in the film plane that occurs during curing of the confined film. In addition, the film electron densities were determined using synchrotron X-ray reflectivity measurements and the film biaxial moduli were obtained using residual stress analysis.

Synthesis and Characterization of Methyltriethoxysilyl-Mediated Mesoporous Silicalites

“…The structures and the properties of mesoporous materials can be diversely adjusted by a sophisticated choice of organic templates, reaction parameters, and auxiliary cationic framework sources [1,6,[20][21][22][23][24][25][26]. Especially, some organic silanes, such as alkylalkoxysilane, SiR'(OR) 3 , (R' and R = methyl, ethyl, or propyl), have been used to prepare amorphous silicalites [27][28][29][30][31][32]. Therefore, the addition of organic silanes can change the pore structures of typical mesoporous silicalites.…”

Refractive Indexes of Porous Thin Films Prepared From Organic-templated Polymethylsilsesquioxanes

“…The refractive indexes of the porous films decreased with the increase of initial m-PCL loadings, resulting in increasing porosities of the films. The organic templates added to the PMSSQ composite films completely decomposed at elevated temperature, and remained voids in the films [3][4][5][6][7][8][9][10][11][12][13]16]. In addition, there are many previous studies for the size and structure of the pores generated in PMSSQ films [3][4][5][6][7][8][9][10].…”

“…The polymer structure is based on an alternating silicon-oxygen network with methyl pendant groups, as well as hydroxyl and ethoxy functional groups. More detailed information about PMSSQ is available elsewhere [13,16,17]. As shown in Fig.…”

Structural analysis of thin films of novel polynorbornene derivatives by grazing incidence X-ray scattering and specular X-ray reflectivity along with ellipsometry

“…The M-2000 ellipsometer, which was equipped with a home made hot stage and an Eurotherm temperature controller with a K-type thermocouple, was used to perform in-situ measurements as a function of temperature during the heating of the films, according to the following protocol: sample temperature was raised from 303-423 K in increments of 5 K, with a heating rate of 3.0 K min À1 for each step and a soaking time of 5 min at each temperature. Using the same heating protocol, measurements were additionally performed on the same silicon substrates without the polymer film in order to determine the values of the refractive index n and extinction coefficient k as a function of temperature of the silicon substrate used in the film preparation (Oh & Ree, 2004). The thus-obtained temperaturedependent n and k data of the substrate were used in the analysis of the ellipsometry data of the films deposited on the substrates.…”