Thin film detection employing frequency shift in sheath current oscillation

For an end point detection of etching in ULSI fabrication processes, the be havior of the sheath oscillating current was theoretically and experimental ly investigated under the radio frequency bias application. The oscillation of the displacement current in sheath was numerically calculated employing the fluid equations of plasma, and its frequency spectrum was analyzed in computational Fast Fourier Transformation. The results showed that the shif t occurred mainly at lower regime than the center frequency under the condi tion of an relatively small bias voltage change. This behavior of the frequ ency shift was also confirmed by a simple experiment. A new method is propo sed for detection technique of thin insulation film on substrate in process employing the frequency shift of this kind.