Application of Quartz Crystal in Vacuum Coating Thickness Measurement Technology

Precise industrial coating techniques usually require that the plating source be evaporated under vacuum. The vacuum state is a good coating environment free of dust and airflow. The coating thickness monitoring of the plated parts is the key to the completion of the vacuum coating process. It shows that the plating on the plated source is ultra-thin, and the resolution of the film thickness monitoring system is extremely demanding. The thickness measurement environment is a closed vacuum state, and the film thickness test has a fast and dynamic response. The coating source is Diversity. The use of traditional industrial eddy current and microwave thickness measurement techniques is difficult to meet the complex thickness measurement requirements. For this purpose, a novel thickness measurement method is adopted, in which the quartz crystal and the plating member are placed in the same vacuum coating environment, with the plating of the plating member. With the addition of the thickness, the plating source coating attached to the surface of the quartz crystal will also be added at the same rate and thickness, by monitoring the change in the resonant frequency of the plating thickness of the quartz crystal surface. In order to monitor the plating thickness changes on the plating. Where: C is the equivalent static capacitance; Cq is the equivalent dynamic capacitance; q is the equivalent dynamic inductance; q is the equivalent dynamic resistance.

The quartz crystal T is connected to the transistor c+b equivalently as an inductor, and the dynamic capacitance Cq is far smaller than other capacitances. The coupling between the transistor and the quartz resonator is very loose, so as to ensure that the oscillation frequency is not affected by the variation of the transistor parameters. Ensure that the oscillator has good stability and anti-interference in the coating thickness detection process. The oscillation frequency expression of this circuit is: +Cl (1) Cl is the total load capacitance, and ClCt, C2Ct, its expression is: Substituting equation (2) into equation (1), considering Cq (+Cl) Let 11 + C be developed using the binomial theorem, taking the first two terms as the resonance frequency 1+. In practical applications, the oscillation frequency error due to wafer processing error and crystal aging can be caused. The external load can be fine-tuned by using a series load capacitor Ct so that the oscillation frequency of the quartz crystal oscillator can reach the nominal frequency.

3 implementation of thickness measurement bookmark5 3.1 material quartz crystal vacuum coating thickness sensor probe, the nominal frequency can be 5 ~ 6MHz, using AT cutting method, the shape of a flat disc shape, diameter of 0.55 inches, thickness of 0.011 Inches, double-sided gold plating. One side is connected to the housing of the probe holder, exposed to the vacuum chamber as a plating source precipitation surface, and the other side is connected to the external oscillator of the vacuum chamber through the coaxial cable.

3.2 Connection In principle, the quartz crystal probe in the stainless steel bracket can be installed anywhere in the vacuum chamber, but to improve the accuracy, the probe should be placed about 10 inches from the vapor plating source and should be located as far as possible in the middle of the base layer area. Using an aviation plug and a 6-inch coaxial cable as the feedback line, the quartz crystal probe was led out of the vacuum chamber and connected to the oscillator. Using an aviation plug and a 10-inch coaxial cable, the oscillation signal of the oscillator is amplified and sent to the thickness gage.

3.3 Processing Thickness Gauge Under the CPU monitoring, complete the data acquisition, calculation, display and output functions. During the coating process, the surface of the quartz wafer is continuously coated with a deposition medium, so that the surface of the crystal gradually becomes thicker, which causes the natural frequency of the crystal to gradually decrease. The CPU will obtain a constantly changing frequency signal, and the CPU calculates and converts the frequency change amount into a corresponding value. The thickness variation can be displayed or executed at any time by the thickness variable. The thickness gauge displays the final coating thickness and the actual oscillation frequency.

By properly selecting the quartz crystal material, properly connecting the crystal probe, the oscillator and the thickness gauge, and accurately processing the frequency signal, the crystal can accurately monitor the coating thickness of the plated part from 1 to 999999 A, and the thickness resolution can reach 1 A. Therefore, there are: The high-frequency oscillation circuit composed of a quartz crystal can accurately measure the thickness of an evaporative or shallow-thin ultrathin coating film, and has a high resolution and a simple structure but is easily affected by external interference signals. In practice, attention should be paid to the proper use of soldering and connection methods. The structure of the oscillation circuit can be the quartz crystal oscillation basic circuit in this article. The relevant parameters and connection organization of the quartz crystal and oscillator in this article are proved by experiments and practice. e is an effective and reliable wvw.cnki.net by the oscillation frequency f0 1 of the visible shunt type quartz crystal oscillator and is connected in parallel to the inherent series resonant frequency of the quartz crystal/

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