Vacuum leakage is the core issue affecting the stability of plasma cleaning machines, and its location needs to be determined comprehensively based on detection methods and equipment characteristics

Helium mass spectrometry leak detection method

Suitable for high vacuum systems (such as molecular pump chambers), by filling the chamber with 0.1MPa helium gas and scanning the flange interface, observation window, gas path solenoid valve and other parts with a leak detector. If a helium leak is detected, tighten the bolts or replace the fluororubber O-ring (such as the Pfeiffer vacuum pump seal). For example, a certain device was unable to achieve a vacuum degree of 1 × 10 ⁻ ³ Pa due to aging of the sealing ring of the pre vacuum chamber isolation door. After replacement, it was restored.

Pressure attenuation test

Suitable for medium to low vacuum systems (such as mechanical pump chambers), record the pressure rise within 1 hour after turning off the vacuum pump. If the rise rate is greater than 0.5Pa/h, it is necessary to check the calibration of the vacuum gauge or the contamination of the chamber wall. In a certain case, virtual leakage was caused by the adsorption of organic matter on the inner wall of the cavity. After plasma cleaning, the pressure rise rate decreased to 0.2 Pa/h.

Vibration signal analysis method

By collecting the vibration signal of the vacuum pump during operation, decomposing it into different frequency components, and locating the leakage point. For example, a device generates a 120Hz vibration signal due to a loose vacuum valve connecting pipe, and the leakage is eliminated after tightening.

2、 Analysis of Reasons for Plasma Ignition Failure

Plasma ignition failure is usually caused by abnormalities in the power supply, gas circuit, or matching system, and should be investigated according to the following logic:

RF power failure

No output power: Test the RF source with a 50 Ω false load. If the power indication is zero, repair the RF module (such as replacing the IGBT tube); If the indication is normal, check whether the RF cable is short circuited or the cavity is contaminated.

Excessive reflected power: Adjust the position of the matching network capacitor blades to ensure that the reflected power is less than 5% of the incident power. In a certain case, due to the initial displacement of the matching capacitor capacitor, the reflected power reached 30%. After recalibration, the ignition was successful.

Abnormal pneumatic system

Insufficient air pressure: Check if the air source pressure is within the range of 0.4-0.6MPa, adjust the pressure reducing valve to match the displayed value of the flowmeter with the process requirements. For example, a certain device was unable to maintain plasma due to low Ar gas pressure (0.2MPa), which was adjusted and restored.

Gas path blockage: Disassemble the gas spray plate, blow the hole with compressed air to remove polymer residue. In a certain case, uneven gas distribution was caused by blockage of the spray hole, and the ignition stability was improved after cleaning.

Electrode and matching system

Electrode contamination: Use sandpaper to polish the oxide layer on the surface of the electrode, or replace it with a new electrode (such as an aluminum substrate electrode with a lifespan of about 2000 hours).

High frequency arc ignition fault: Check the spacing between the spark arrester bars (standard value 0.5mm), and adjust if the spacing is too large; If the black rod is eroded, it needs to be replaced (for example, if a certain equipment cannot initiate an arc due to a distance of 1mm between the black rods, it should be adjusted and restored).

3、 Comprehensive diagnosis case

A certain vacuum plasma cleaning machine has an alarm of "no plasma output". After investigation, it was found that:

Vacuum leakage: The pressure decay test showed a rise rate of 0.8Pa/h, and the helium leak detection was located until the molecular pump flange seal ring aged. After replacement, the vacuum degree was restored.

RF matching anomaly: Reflected power reaches 15%, reduced to 3% after adjusting the matching network capacitor blades.

Electrode contamination: The surface of the upper electrode is covered with black polymer, and after sanding with sandpaper, the plasma density increases by 40%.

Through systematic investigation, the equipment was restored to stable operation, verifying the effectiveness of the three-dimensional diagnostic strategy of "vacuum power gas path".