Monitoring thin film deposition

A system for monitoring thin film deposition in a deposition chamber, the system comprising:

• a measurement circuit, a quartz crystal and a cable interconnecting the quartz crystal and the measurement circuit, wherein the measurement circuit comprises:
• a synthesizer coupled to a controller for generating a modulated signal using a low frequency signal selected in the range of 1 Hz to 1000 Hz and a high frequency signal selected in the range of 4 MHz to 7 MHz;
• a demodulator;
• and
• a phase detector for measuring a phase of the envelope in order to determine a thin film deposition thickness;
• in which the quartz crystal is located in the deposition chamber and drawing current from a component of the modulated signal generated by the synthesizer, wherein the quartz crystal produces an amplitude modulated signal, the demodulator demodulates the amplitude modulated signal to produce an envelope of the amplitude modulated signal, and the phase detector measures a phase of the envelope to determine a thin film deposition thickness;
• wherein the measured phase of the envelope being equal to the phase of the low frequency signal of the modulated signal indicates that the quartz crystal is in resonance at the selected high frequency signal given the thin film deposition thickness, wherein the cable connects, in a T-network, the quartz crystal located in the deposition chamber, the synthesizer and the demodulator for demodulating the amplitude modulated signal, and wherein the high frequency signal of the modulated signal generated by the synthesizer is selected such that a length of the cable does not affect thin film deposition thickness detection due to internal reflection and standing waves, thereby enabling the length of the cable to be greater than 4.5 m or greater than one quarter the wavelength of the signal.