Pollution and removal mechanism in semiconductor manufacturing process

Cleanliness is one of the most important parameters in semiconductor manufacturing process. With the decrease of semiconductor gate width, the requirements for pollution control are higher and higher. A tiny pollution may lead to the failure and scrapping of a chip, so controlling pollutants is one of the most critical steps in semiconductor manufacturing process.

In general, the pollutants in the semiconductor process are roughly classified as follows

Classification of pollutants in semiconductor process

1) Granules

The particles are mainly some polymers, photoresists and etching impurities. It is usually introduced in the process, and particles will be introduced into process equipment, environment, gas, chemical reagent and deionized water. Once these particles adhere to the silicon surface, they will affect the formation of geometric characteristics and electrical characteristics of the next process. According to the analysis of the adhesion between the particles and the surface, although the adhesion shows diversity, it is mainly van der Waals attraction. Therefore, the particle removal method mainly undercuts the particles by physical or chemical methods, gradually reduces the contact area between the particles and the silicon surface, and finally removes them.

2) Organic residue

Impurities in IC cleaning process, such as organic solvents, grease and so on, are the main sources of impurities in IC cleaning process. Each pollutant has different degrees of impact on the IC process. Usually, an organic film will be formed on the wafer surface to prevent the cleaning solution from reaching the wafer surface, which will prevent the silicon wafer surface from being completely cleaned. Therefore, the removal of organic residues is often carried out in the first step of the cleaning process.

3) Metal pollutants

In the process of IC manufacturing, metal interconnection materials are used to connect each independent device. Firstly, the contact window is made on the insulating layer by photolithography and etching, and then the metal interconnection film, such as Al Si, Cu, etc., is formed by evaporation, sputtering or chemical vapor deposition (CVD). The interconnection is generated by etching, and then the deposition medium layer is subjected to chemical mechanical polishing (CMP). This process is also a potential contamination process for IC process. While forming metal interconnection, various metal contamination will affect the device performance, such as forming defects at the interface, introducing stacking faults in subsequent oxidation or epitaxy processes, PN junction leakage, and reducing the service life of a few current carriers. In addition, in the whole process of wafer preparation, the purity of gases, chemical reagents, utensils and deionized water used is not enough, the contamination of the equipment itself and the metal ions carried by the operators will introduce some movable ions into the IC. Most of these ions are metal ions, and people are the largest introduction source. The deposition mechanism includes:

1. Through the charge exchange between metal ions and hydrogen atoms on the surface of silicon substrate, it is directly bonded to the silicon surface. This type of impurities is difficult to be removed by wet cleaning process. This kind of metal is often noble metal ions, such as gold (AU). Because its negative charge is higher than Si, it tends to take electrons out of silicon for neutralization and deposit on the silicon surface.

2. The second mechanism of metal deposition occurs during oxidation. When silicon is oxidized, Al, Cr and Fe tend to oxidize and enter the oxide layer. This metal impurity can be removed by removing the oxide layer in diluted HF.

4) Oxide layer to be removed

Silicon atoms are very easy to oxidize in an environment containing oxygen and water to form an oxide layer. This oxide layer is not the required oxide layer. It will prevent the wafer surface from normal reaction in other process processes. It can become an insulator, so as to block the good electrical contact between the wafer surface and the conductive metal layer. At the same time, in order to ensure the quality of the gate oxide layer, If the wafer is subjected to other process operations or after cleaning (a chemical oxide layer will be formed on the wafer surface due to the strong oxidizing force of hydrogen peroxide), the surface oxide layer must be removed. In addition, silicon nitride, silicon dioxide and other oxides deposited by chemical vapor deposition (CVD) in the IC process should also be selectively removed in the corresponding cleaning process.

Only by removing all kinds of pollutants as much as possible can we ensure a higher production yield. Therefore, semiconductor cleaning process has always been one of the key points in semiconductor manufacturing process. With the increasing demand for chip localization, the process of semiconductor cleaning is also a difficult point to be overcome. Kunshan Zhicheng automation equipment Co., Ltd. is committed to the R & D and production of semiconductor wafer cleaning equipment. The ultimate goal is to realize the complete localization of semiconductor wafer cleaning equ