Real-time measurement of dielectric thickness on a millimeter scale using triple-frequency in inductively coupled plasma

The dielectric thickness is measured using a floating probe with triple-frequency in inductively coupled plasma (ICP). Previous studies show that they can only measure the thickness on a micrometer scale when using low frequencies (~30 kHz). In this study, we propose an electrical diagnostic method to measure the thickness of a thick dielectric using triple high frequency (600 kHz, 800 kHz, 1 MHz). Since the impedance of a dielectric is inversely proportional to applied frequency, the thickness of a thick dielectric could be measured using high frequencies. The capacitance and thickness of the dielectric were measured by applying small sinusoidal voltage signals (~2 V) with three different frequencies. The experiments are taken under argon gas, pressure range from 5 mTorr to 25 mTorr, and ICP power range from 100 W to 300 W condition. Several heights of dielectric (silicon dioxide cylinder) attached to the top of the probe tip. The results were in good agreement with the actual thickness range from 1 mm to 5 mm.