Plasma is the fourth state of matter, composed of a large number of charged particles (electrons, ions) and neutral particles, and has unique electromagnetic properties. According to the Saha equation, more than 99% of substances in nature exist in the form of plasma, such as nebulae, the sun (wind), lightning, auroras, etc. Gas discharge is the most commonly used way to generate plasma under artificial or laboratory conditions, and common forms of discharge include arc discharge, spark discharge, glow discharge (such as fluorescent lamps, neon lights), etc. According to different temperatures, plasma can be divided into low-temperature plasma, thermal plasma, and high-temperature plasma. For example, the tokamak device (artificial sun) used for artificial nuclear fusion research and the plasma used in nuclear fusion power generation are typical high-temperature plasmas. Low temperature plasmas are characterized by their low macroscopic temperature and non thermal equilibrium (electron temperature is much higher than heavy particle temperature) The unique physical and chemical properties have been widely applied in fields such as material processing, chip manufacturing, and space electric propulsion, and have become a key driving force supporting the development of related fields.

Ashing process is an important surface cleaning technique in semiconductor manufacturing, widely used to remove photoresist residues. In the semiconductor manufacturing process, photoresist serves as a mask to provide protection during the etching process. However, after etching is completed, photoresist often remains on the wafer surface, which can have a negative impact on subsequent process steps. Therefore, developing efficient removal methods is the key to improving manufacturing quality.

Plasma ashing process

The core of plasma ashing process is to effectively remove photoresist through plasma oxidation reaction. In this process, radio frequency or microwave ionization of gas (such as oxygen or fluorine gas) under low pressure environment is usually used to generate plasma. The active substances generated in the plasma, such as atomic oxygen or fluorine radicals, have extremely strong reactivity and can undergo chemical reactions with photoresist, thereby achieving efficient removal.

Specifically, the basic components of photoresist are hydrocarbon organic compounds, and the plasma ashing process involves the reaction between active substances in the plasma and photoresist. 

According to different requirements, ashing processes can be divided into several types. High temperature ashing (stripping) aims to remove as much photoresist as possible, suitable for large-area removal, while residual removal (Descum) is specifically used to remove photoresist residue in slits or features, solving common problems in high detail patterns. These different types of ashing processes provide flexible solutions for semiconductor manufacturing to meet different process requirements.

The importance of ashing technology in semiconductor manufacturing cannot be ignored. Firstly, ensuring the complete removal of photoresist is the foundation for achieving accurate patterning in subsequent processes. Secondly, the consistency and uniformity of the ashing process are crucial for the performance and reliability of semiconductor devices. In addition, advanced ashing technology is committed to removing photoresist while minimizing damage to the underlying wafer surface. The achievement of this goal is of great significance for improving the overall quality of the device.