Low-k interlayer dielectric materials:: Synthesis and properties of alkoxy-functional silsesquioxanes

Two new types of silsesquioxanes, (HSiO3/2)(y)[((BUO)-B-t)SiO3/2](z) or T(H)Q and (HSiO3/2)(x)(RSiO3/2)(y)[(tBuo)SiO3/2](z) or T(H)T(R)Q (R = octadecyl), were synthesized and studied as low-k dielectric materials for electronic applications. The materials were prepared by cohydrolysis and condensation of alkoxy monomers, (AcO)(2)Si((OBu)-Bu-t)(2), HSi(OEt)(3), and CH3(CH2)(17)Si(OMe)(3). Spectroscopic data supported retention of tertiary alkoxy groups [((BuO)-Bu-t)SiO3/2 or ((BuO)-Bu-t)(2)SiO2/2] and presence of silanol. The molecular weight of (HSiO3/2)(x)[((BuO)-Bu-t)SiO3/2](z) increased with the T/Q ratio, while that for (HSiO3/2)(x)(RSiO3/2)(y)[((BuO)-Bu-t)SiO3/2](z) exhibited less dependence on composition. The tert butoxy groups were eliminated in both materials at low temperatures (< 450 degrees C), and subsequent decomposition of octadecyl group (R) in (HSiO3/2)(x)(RSiO3/2)(y-)[((BuO)-Bu-t)SiO3/2](z) occurred through cleavage and re-distribution of carbon-carbon bonds (430-550 degrees C). Heating at 450 degrees C for 2 h afforded porous solids. The total pore volume of materials derived from (HSiO3/2),[(tBuO)SiO3/2](z) determined by nitrogen sorption porosimetry increased with increasing Q content up to 0.313 cm(3)/g or 38% porosity by volume. The porosity for (HSiO3/2)(x)(RSiO3/2)(y)[((BO)-B-t)SiO3/2](z) ranged from 32 to 54% (0.349-0.701 cm(3)/g), which represented an similar to 10% increase over (HSiO3/2)(x)[((BuO)-Bu-t)SiO3/2](z). Thin films prepared from (HSiO3/2)(x)[((BuO)-Bu-t)SiO3/2](z) exhibited a modulus between 10 and 19 GPa, but had a high dielectric constant due to residual silanol. Incorporation of RSiO3/2 group allowed for formation of porous materials with low silanol contents. The dielectric constant and modulus of (HSiO3/2)(x)(RSiO3/2)(y)-[((BuO)-Bu-t)SiO3/2](z) were in the range of 1.7-2.6 and 1.8-4.7 GPa, respectively.