Pore characteristics of low-dielectric-constant films grown by plasma-enhanced chemical vapor deposition studied by positron annihilation lifetime spectroscopy

The pore characteristics of plasma-enhanced chemical-vapor-deposition (PECVD)-grown low-dielectric-constant (low-k) porous films, grown with dual-frequency power sources and with a source gas of hexamethyldisiloxane, have been studied by positron annihilation lifetime spectroscopy. Six low-k films of different dielectric constants (2.66-4.13) were prepared by changing the low frequency (380 kHz) power of the PECVD process. The long-lived component due to pick-off annihilation of ortho-positronium strongly depends on the low frequency power. Based on the empirical relationship between the orthopositronium lifetime and the cavity volume, average pore volumes were estimated to be 0.23-0.85 nm(3), The correlation between the pore size and dielectric constant was discussed.