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Cause analysis of poor vacuum plasma cleaning equipment effect

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16 Mar,2021

Cause analysis of poor vacuum plasma cleaning equipment effect:
The vacuum plasma cleaning equipment relies on the high-energy particle flow of specific substances in the plasma to wash the surface of the object, and produces physical washing (such as argon plasma) or chemical reaction (oxygen plasma) to achieve the function of removing dirt on the surface of the object. Currently, plasma cleaning systems are designed to produce plasma by lowering the pressure in the reaction chamber and then introducing a suitable gas and starting power at a certain rate. Therefore, what is the reason for the poor effect of vacuum plasma cleaning equipment? Let's analyze it together.

CRF vacuum plasma
1. Influence of electrode on cleaning effect of vacuum plasma cleaning equipment:
The design of the electrode directly affects the cleaning effect of the vacuum plasma cleaning equipment, mainly including the material, layout and size of the electrode. For the internal electrode plasma cleaning system, because the electrode is in contact with the plasma, the electrode of some materials will be corroded or sputtered by some plasma, causing unnecessary pollution, changing the electrode size, and affecting the stability of the plasma cleaning system. The arrangement of electrodes has an important effect on the cleaning speed and homogeneity of plasma. A smaller electrode spacing confines the plasma to a narrower area, resulting in a higher density and faster cleaning. With the increase of interval, the cleaning rate decreases gradually, but the uniformity increases gradually. The size of the electrode in the plasma system determines the total capacity of the system. In plasma cleaning systems, the electrodes are distributed in parallel and are usually used as pallets. Larger electrodes can clean more parts at one time, improving the efficiency of equipment operation.

 

2. Influence of working pressure on cleaning effect of vacuum plasma cleaning equipment:
The working pressure is an important parameter of vacuum plasma cleaning equipment. Pressurization means that the density of the plasma increases and the average energy level of the particles decreases. The increase of density can significantly improve the cleaning speed of plasma system for chemical-based plasmas, while the effect is not obvious for physical-based plasmas. In addition, the change of pressure will also lead to the change of the plasma cleaning reaction mechanism. For example, CF4/O2 plasma is used in silicon wafer etching process, which plays a leading role under low pressure. With the increase of pressure, chemical etching gradually strengthens and gradually occupies the dominant position.

 

3. Influence of power supply power and frequency on cleaning effect of vacuum plasma cleaning equipment:
The power supply will affect a variety of plasma parameters, such as electrode temperature, generated self-bias and cleaning efficiency. The plasma cleaning speed increases with the increase of the output power and reaches the peak gradually, while the self-bias voltage increases with the increase of the output power. In the process of plasma self-biasing, frequency is an important parameter, and the power range is basically unchanged. With the increase of frequency, the effect of self-biasing is gradually weakened. Moreover, with the increase of frequency, the electron density in the plasma increases gradually, and the mean energy level decreases gradually.

 

4. The influence of the choice of working gas on the cleaning effect of vacuum plasma cleaning equipment:
In the process design of vacuum plasma cleaning equipment, the choice of process gas is the key. Although most gases or mixtures of gases can remove contaminants in many cases, the rate of purification can vary and can be tens of times higher. For example, different proportions of sulfur fluoride (SF6) are added to oxygen (O2) as a process gas to clean the plexiglass. Reasonable selection of process gas can greatly improve the cleaning speed.

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