Positron annihilation lifetime spectroscopy study of self-assembled porous low-k films

We investigated advanced, self-assembled, porous organosilicate glasses with varying porogen level, resulting in varying dielectric constants (k-values ranging from 1.8 to 2.7, including a non-porous reference sample with 3.0). We used positron annihilation lifetime spectroscopy (PALS) to determine the pore size. The pores are fabricated by self-assembly into the OSG by a sol-gel process. The pore size is a critical parameter to characterize the quality of the OSG thin film. Other critical parameters, which were not investigated in this study are connectedness of pores and pore size distribution. Porous OSG is used in the microelectronic industry as insulating material for the wiring of microchips. Since pores not only lower the k-value, but also degrade mechanical stability of film stacks in microchips, knowledge of pore characteristics is crucial. Low-k materials are a necessity to lower microchip power consumption, maintain signal speed and reduce coupling in the relentless icroelectronics miniaturization process.