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Magical crystal ion etching frequency fine tuning

It is not easy to manufacture a perfectly qualified quartz crystal oscillator. In addition to more than 30 processes, various advanced technologies are used to ensure the high precision, high stability and high performance of the crystal oscillator. Next, Beijing Jintiantongye The four methods of the ion etching frequency fine-tuning method of the quartz patch crystal oscillator, the ion beam current density, the ion etching frequency fine-tuning processing technology and the frequency fine-tuning method are introduced.

1. Ion etching frequency fine-tuning method Figure 4-1 is a schematic diagram of frequency fine-tuning based on ion etching technology. The ion etching frequency is fine-tuned. When the irradiation area is less than 2~3mm2, close to 10mA can be obtained when the beam voltage is lower than 100V. /cm2 high current density ion beam, the etching speed of the ion beam can be adjusted in a wide range. The figure uses a small hot cathode PIG type ion gun. The discharge gas uses Ar, and the flow rate is as small as 035 cc/min. A permanent magnet is placed around the cylindrical anode so that a magnetron having a magnetic field added in the axial direction becomes an ion lens, and the ion beam can be focused. The high-density plasma obtained after the discharge of the hot cathode magnetron is extracted after applying a high voltage of up to 1200 V between the masked molybdenum sheet and the accelerated molybdenum sheet. And the speed of the plasma can be adjusted by controlling the hot cathode. The quartz crystal oscillator is irradiated with an ion beam, and the electrode film of the quartz crystal is subjected to sputter etching so that the frequency rises and the frequency is finely adjusted. During the adjustment, the frequency of the quartz patch crystal oscillator is monitored by the network analyzer through the π loop, and when the target frequency is reached, the etching is stopped and the adjustment is completed. Because the quartz crystal is connected to the π loop by a capacitor, the positive charge of the ion beam cannot flow to the GND and accumulate on the quartz wafer, causing the quartz wafer to be positively charged. As a result, not only the frequency trimming speed is lowered, but also the quartz wafer is not vibrated, and the frequency of the quartz crystal oscillator cannot be monitored and adjusted. To this end, a neutralizer must be used to neutralize the positive charge on the quartz wafer.

2. Ion beam current density In Figure 4-1, in order to improve the operability and simplify the parameter setting in the automation process, only the beam voltage and the discharge current are controlled, while the discharge voltage and the Ar flow rate remain unchanged, and the acceleration voltage is taken. 20% of the beam voltage.

3. Ion etching frequency fine-tuning processing technology The crystal ion etching frequency fine-tuning processing technology and the vacuum evaporation frequency fine-tuning have similarities and differences. First of all, both frequency fine-tuning methods must be carried out under high vacuum conditions. Therefore, it is necessary to confirm whether the vacuum degree of the vacuum chamber meets the requirements before processing, and generally requires 1×103Pa or more. Secondly, it must be confirmed that the water-cooling equipment of the vacuum chamber is not leaking. When using the vacuum pump, it is necessary to confirm that the vacuum chamber is not contaminated by oil. Then, it is necessary to ensure that the quartz crystal oscillator and the quartz crystal resonator are free from foreign matter such as dust or dirt. In order to effectively control the foreign matter, the processing environment is preferably a purification space of 5000 or less. In addition to paying attention to the above requirements, the ion etch frequency trimming process must also pay attention to the frequency shift problem within a few seconds after ion etching. This problem will directly affect the production efficiency and the pass rate. 4. Frequency fine-tuning method The frequency of the quartz crystal oscillator is determined by the thickness of the quartz crystal crystal wafer and the thickness of the electrode film. For this reason, the frequency of the quartz crystal oscillator can be adjusted by adjusting the thickness. Quartz crystal oscillator is made by cutting the quartz crystal wafer from the quartz crystal at a certain angle, then grinding it according to a certain size, and then coating the metal electrode layer on both sides of the wafer. At this time, the target frequency is different from 2000ppm to 3000p0m, and each electrode The layer is connected to the pin and the surrounding electronic components form an oscillating circuit, and then the frequency is fine-tuned so that the difference from the target frequency can be reduced to less than 2 ppm. Finally, the package is completed. The frequency trimming of the quartz crystal oscillator is to measure the frequency of each quartz crystal while adjusting the thickness of the electrode film. Change the frequency to or near the target frequency. There are two main methods for adjusting the thickness of the electrode film, vacuum evaporation and ion beam etching. In the vacuum evaporation method, the thickness of the electrode film is continuously increased by heating and evaporation on the electrode film of the quartz crystal crystal wafer to achieve the purpose of adjusting the frequency. This method is simple in structure and easy to control. The disadvantage is that a multilayer electrode film is formed on the surface of the quartz crystal crystal wafer, and the adhesion degree is deteriorated. When the quartz crystal oscillator is miniaturized, the position of the original electrode film and the adjustment film is shifted, and the electrical performance of the quartz crystal oscillator is lowered. The ion etching frequency fine adjustment method uses an ion beam to record an electrode film and adjust the frequency of the quartz crystal oscillator.

Therefore, the multilayer electrode film is not produced, and the positional deviation of the electrode film and the adjustment film does not occur, and the electrical properties of the quartz crystal oscillator are not lowered. 4-1 Frequency fine-tuning diagram based on ion etching technology When performing ion etching frequency adjustment, the time required for the ion beam to etch a product is 1~2 seconds, and the waiting time is about 2 seconds. The waiting time includes The measurement time of the conveyance and frequency of the product. During the waiting time, the baffle is closed. If the ion gun continues to have ion beam extraction during this time, the 0.5 mm thick stainless steel baffle will be quickly perforated and scrapped. For this reason, the ion beam extraction of the ion gun must be stopped during the waiting time. The high-voltage relay can be used to cut off the power supply of the ion gun, except for the discharge power of the ion gun (which can maintain the discharge stability of the ion gun). Thus, there is no etching of the ion beam during the waiting time, so that the service life of the baffle is greatly increased. At the same time, since the operating speed of the high-voltage relay is fast, the operating time is much less than the operating time of the mechanical baffle, so the adjustment accuracy can be improved. 4-2 Discharge current and current density at different beam voltages Figure 4-2 shows the electrode film of the quartz crystal with different beam voltages, with the change of discharge current (the distance from the ion gun accelerated molybdenum sheet is 25mm) The measured current density. As can be seen from the figure, for different beam voltages, when the discharge current changes, there is a corresponding discharge current to maximize the current density. In this paper, the fine-tuning of the crystal ion etching frequency is performed by using the maximum current density of different beam voltages. When the adjustment speed is set, the beam voltage is determined according to the calculation, and then the discharge current is calculated according to the maximum current density at the voltage.