A plasma stripper, also known as a plasma etch and strip system, is core processing equipment in the electronic manufacturing industry, including semiconductor manufacturing, microelectronics packaging, and PCB processing. It is primarily used to remove photoresist, organic impurities, oxide layers, and other contaminants from the surface of workpieces. Through the dual action of physical bombardment and chemical reactions by plasma, it achieves highly efficient, precise, and non-destructive surface cleaning, providing a pristine surface foundation for subsequent processes such as thin-film deposition, soldering, and bonding.
Core Working Principle
The fundamental working principle of a plasma stripper is based on low-temperature plasma technology. Gas is excited within a sealed vacuum chamber to generate plasma. The high-energy particles in the plasma (such as electrons, ions, and free radicals) interact with the photoresist and impurities on the workpiece surface to achieve stripping. The stripping process occurs in two stages:
- Physical Bombardment Stage: High-energy ions strike the workpiece surface at high speeds, breaking the chemical bonds between photoresist molecules and causing the fragmentation and peeling of the resist layer.
- Chemical Reaction Stage: Active free radicals in the plasma (such as oxygen and hydrogen radicals) undergo oxidation and decomposition reactions with the fragmented resist molecules. This converts them into volatile substances like carbon dioxide, water, and small organic molecules, which are then exhausted from the chamber via a vacuum pump to complete the cleaning process. Depending on process requirements, different reaction gases such as oxygen, argon, or hydrogen can be selected to adapt to the removal of various types of photoresists.
Core Structure
The core structure of a plasma stripper consists of five key modules that work in tandem to ensure stripping precision and process stability:
- Vacuum Chamber: Made of corrosion-resistant, highly sealed stainless steel, this is the core area where plasma is generated and the stripping reaction takes place. It is equipped with a workpiece tray to accommodate wafers, PCBs, chips, and other workpieces of different sizes. The chamber must possess excellent vacuum retention capabilities to prevent air from interfering with the plasma reaction.
- Gas Supply System: Comprising gas cylinders, pressure-reducing valves, mass flow controllers, and gas mixers, this system precisely controls the type, flow rate, and ratio of reaction gases to meet various stripping process requirements and ensure stable plasma concentration.
- Plasma Generation System: The core of this system includes an RF (radio frequency) power supply and electrodes. By applying a high-frequency voltage via the RF power supply, the gas inside the chamber is ionized to generate low-temperature plasma. The RF power can be flexibly adjusted according to the workpiece material and resist thickness.
- Vacuum System: Consisting of a mechanical pump and a turbomolecular pump, this system is responsible for evacuating the chamber to the specified vacuum level and promptly exhausting volatile impurities generated by the reaction to maintain internal chamber cleanliness.
- Control System and Safety Devices: Equipped with a touchscreen controller, this system allows users to set process parameters such as vacuum level, RF power, gas flow rate, and stripping time, while monitoring the equipment's operating status in real time. Safety devices include vacuum interlocks, over-temperature protection, gas leak alarms, and emergency stop buttons to eliminate safety hazards such as vacuum failure and gas leaks.
Application Areas
The application areas of plasma strippers are highly concentrated in the electronic manufacturing and semiconductor industries, covering multiple core processing steps.
- Semiconductor Manufacturing: Used for post-lithography resist stripping and surface cleaning before wafer bonding, ensuring the precision of wafer circuit patterns and the reliability of bonding.
- Microelectronics Packaging: Used for surface resist stripping and impurity removal on chips and lead frames to enhance adhesion during packaging and soldering.
- PCB Manufacturing: Used for surface cleaning of flexible PCBs and high-density interconnect (HDI) boards to remove residual resist and organic impurities from the manufacturing process, ensuring circuit conductivity.
- Optoelectronic Displays: Used for surface treatment of OLED panels and photovoltaic components to remove photoresist and oxide layers, thereby improving the luminous efficiency and lifespan of the devices.
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