This work investigates the physical and electrical properties of two species of inorganic C-doped low dielectric constant (low-k) chemical vapor deposited (CVD) organosilicate glasses (OSGs, alpha -SiCO:H). They are both deposited by plasma-enhanced CVD (PECVD) processes using methylsilane [(CH3)SiH3, 1 MS]- and trimethylsilane [(CH3)(3)SiH, 3 MS]-based gases as the reagents, and are designated as OSG1 and OSG2, respectively. Experimental results indicate that the thermal stability temperature of OSG1 is 500 degreesC, while that of OSG2 is 600 degreesC, based on the results of thermal annealing for 30 min in an N-2 ambient. The deterioration of the low-k property in OSG1 is predominately due to the thermal decomposition at temperatures above 500 degreesC of methyl (-CH3) groups, which are introduced to lower the density and polarizability of OSGs. For the Cu-gated oxide-sandwiched low-k dielectric metal-insulator-semiconductor (MIS) capacitors, Cu permeation was observed in both OSG1 and OSG2 after the MIS capacitors were bias-temperature stressed at 150 degreesC with an effective applied field of 0.8 MV/cm. Moreover, Cu appeared to drift more readily in OSG1 than in OSG2, presumably because OSG1 has a more porous and less cross-linked structure than OSG2. The Cu penetration can be mitigated by a thin nitride dielectric barrier.