Development of the measurement method of dielectric constant of low-k film in the millimeter wave region

We have developed a free-space transmittance measurement method to study the dielectric property of a thin and low-dielectric (low-k) film in the millimeter wave region. The discovery is that multi-reflection keeps the height of the repeated peaks of the transmittance almost constant and that their widths quickly narrow with increase in the incident angle. We report the relative transmittance spectrum obtained from a 10 μm thick silicon dioxide film on a 700 μm thick silicon substrate near the electromagnetic waves of frequency 65 GHz.