Contaminants and removal mechanisms in semiconductor manufacturing processes
In the semiconductor manufacturing process, cleanliness is one of the most important parameters. As the width of semiconductor grids decreases, the requirements for pollution control become higher and higher. A small pollution may cause a chip to fail and be scrapped, so controlling pollution is one of the most critical steps in the semiconductor manufacturing process.
In general, the classification of pollutants in the semiconductor manufacturing process is roughly as follows:
Classification of Contaminants in Semiconductor Processes
The particles are mainly some polymers, photoresists and etching impurities. Usually introduced in the process, process equipment, environment, gas, chemical reagents and deionized water will introduce particles. Once these particles adhere to the silicon surface, they will affect the formation of geometric features and electrical characteristics in the next process. According to the analysis of the adhesion between the particles and the surface, although the adhesion force shows diversification, it is mainly van der Waals attraction, so the removal method of the particles is mainly to undercut the particles by physical or chemical methods, gradually Reduces the particle's contact area with the silicon surface and eventually removes it.
2) Organic residues
Organic impurities exist in various forms in the IC process, such as human skin oil, clean room air, mechanical oil, silicone resin, photoresist, cleaning solvent, etc. The residual photoresist is the main source of organic contamination in the IC process source. Each type of pollutant has a different degree of impact on the IC manufacturing process. Usually, an organic film will be formed on the surface of the wafer to prevent the cleaning liquid from reaching the surface of the wafer, which will prevent the surface of the silicon wafer from being thoroughly cleaned. The removal of organic residues is therefore often carried out in the first step of the cleaning process.
3) Metal pollutants
In the IC manufacturing process, metal interconnection materials are used to connect individual devices. First, contact windows are made on the insulating layer by photolithography and etching, and then metal interconnections are formed by evaporation, sputtering or chemical vapor deposition (CVD). Connecting films, such as Al-Si, Cu, etc., produce interconnection lines by etching, and then perform chemical mechanical polishing (CMP) on the deposited dielectric layer. This process is also a potential contamination process for the IC manufacturing process. While forming metal interconnections, various metal contaminations will affect device performance, such as forming defects at the interface and introducing stacking faults in subsequent oxidation or epitaxy processes. , PN junction leakage, reducing the lifetime of minority carriers. In addition, during the entire wafer preparation process, the used gases, chemical reagents, utensils, deionized water are not pure enough, the contamination of the equipment itself, and the metal ions carried by the operator will introduce some possible damage to the IC. Mobile ions, most of which are metal ions, and humans are the largest source of introduction. Deposition mechanisms include:
1. Directly bonded to the silicon surface through charge exchange between metal ions and hydrogen atoms on the surface of the silicon substrate. This type of impurity is difficult to remove by wet cleaning processes. Such metals are often noble metal ions, such as gold (AU ), because of its higher electronegativity than Si, it tends to remove electrons from 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 pass through the diluted HF removes the oxide layer and removes it.
4) The oxide layer that needs to be removed
Silicon atoms are very easy to oxidize to form an oxide layer in an environment containing oxygen and water. This layer of oxide is not an oxide layer that needs to exist. It will prevent the normal reaction of the wafer surface from other processes. It can become an insulator, thereby blocking the good electrical properties 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 processed by other processes or after cleaning (due to the strong oxidizing power of hydrogen peroxide, a chemical oxide layer will be formed on the surface of the wafer), the surface will be oxidized layer must be removed. In addition, oxides such as silicon nitride and silicon dioxide deposited by chemical vapor deposition (CVD) in the IC manufacturing process should also be selectively removed in the corresponding cleaning process.
Only by removing all kinds of pollutants as much as possible can a higher production yield be guaranteed. Therefore, the semiconductor cleaning process has always been one of the key points in the semiconductor manufacturing process. The demand for chip localization is increasing day by day, and the process of semiconductor cleaning is also a difficulty that needs to be overcome urgently. Kunshan Zhicheng Automation Equipment Co., Ltd. is committed to the R&D and production of semiconductor wafer cleaning equipment, and the ultimate goal is to realize the complete localization of semiconductor wafer cleaning equipment.