Quartz crystal and oscillator form a resonant circuit, generating a stable oscillation signal. The oscillation frequency of the new chip is 6MHz. When the chip is coated, its resonant frequency will decrease due to the increase in weight and surface tension of the chip. This frequency change is detected by a frequency meter, and the thickness of the coating layer on the chip is calculated based on the frequency change rate, material density, material acoustic resistance, and other parameters. Finally, the coating rate is calculated based on the change in film thickness per unit time.

Firstly, install the crystal oscillator at the front end of the probe and place it in the vacuum chamber. Set the "tool factor" (used to calibrate factors such as density and stress) and required thickness of the thin film material in the monitor. Then start coating, and the monitor displays the current thickness and deposition rate in real time. When the thickness reaches the preset value, the monitor sends a signal to automatically close the baffle or evaporation source and stop coating.

The film thickness gauge can directly measure the mass thickness, with a simple principle that is almost applicable to all types of materials (metals, media, etc.), and can simultaneously monitor the thickness and deposition rate, control process stability, and have lower equipment and consumables (crystal oscillators) costs compared to optical methods. However, the thickness measured is on the crystal oscillator, not on the actual substrate, which may result in positional errors. It is sensitive to temperature changes and requires stable working conditions. If the coating on the crystal oscillator is too thick, it will fail and needs to be replaced. When using, it is necessary to choose the use of the film thickness gauge according to the actual situation.