Heat transport in thin dielectric films

Heat transport in 20–300 nm thick dielectric films is characterized in the temperature range of 78–400 K using the 3ω method. ${\mathrm{SiO}}_2$ and SiN${}_{\mathrm{x}}$ films are deposited on Si substrates at 300 °C using plasma enhanced chemical vapor deposition (PECVD). For films $\text{>100}$ nm thick, the thermal conductivity shows little dependence on film thickness: the thermal conductivity of PECVD ${\mathrm{SiO}}_2$ films is only $\text{∼10}$ % smaller than the conductivity of ${\mathrm{SiO}}_2$ grown by thermal oxidation. The thermal conductivity of PECVD SiN${}_{\mathrm{x}}$ films is approximately a factor of 2 smaller than SiN${}_{\mathrm{x}}$ deposited by atmospheric pressure CVD at 900 °C. For films $\text{<50}$ nm thick, the apparent thermal conductivity of both ${\mathrm{SiO}}_2$ and SiN${}_{\mathrm{x}}$ films decreases with film thickness. The thickness dependent thermal conductivity is interpreted in terms of a small interface thermal resistance $R_I.$ At room temperature, $R_I{\text{∼2×10}}^{\text{−8}}$ K m${}^2$ W${}^{\text{−1}}$ and is equivalent to the thermal resistance of a $\text{∼20}$ nm thick layer of ${\mathrm{SiO}}_2$ .