A novel spin on material derived from perhydropolysilazane that converts into ultra-low k inorganic films is described in this paper. The obtained films, cured at 400°C in N2 atmosphere, exhibit dielectric constants as low as 1.6 which do not change after holding the wafers in a clean-room mbient for 2 months. Cross-sectional SEM images of the cured films show the aggregation of small granules with diameters ranging from 5 to 30 nm. The films can be obtained by conventional SOG process: spin-coating, baking and curing, without any additional process such as hydrophobic treatment.
The average atomic compositions of the films are, Si/O/N/C = 40/55/5/0.5 (atomic %), by XPS analysis. These results indicate that the films have hydrogen silicon oxynitride structures. No evolution of H2O and NH3 was detected by TDS analysis in the temperature range of RT to 800°C. Hydrophobic Si-H and Si-H2 groups remaining in the film might prevent water absorption, resulting in the low dielectric constant.
The remainder of Si-H and Si-H2 constituents in the cured films is the result of selective oxidation reactions of perhydropolysilazane in the baking process with the use of a specific catalyst. The structures of the films are tailored by altering the amount of the catalyst. In this study, we also demonstrate the relationship between the effect of the catalyst and the film properties.