The surface cleaning process of single crystal silicon has been widely applied in silicon wafers, mainly using wet cleaning methods, using various solvents and supplemented by ultrasound and megahertz to clean the surface of single crystal silicon. However, there are problems such as environmental pollution and complex processes, and dry cleaning methods such as plasma cleaning have significant advantages compared to others.

Plasma cleaning originated in the early 20th century, mainly using the physical and chemical effects of low-temperature plasma to clean residual organic pollutants on the surface of optical components, and is considered an alternative process to wet cleaning. Its main working principle is: under low pressure environment, process gases such as Ar and O2 are excited by charges, lasers, etc. to form plasma, generating a large number of active particles such as ions, electrons, free radicals, and photons (high-energy rays); The gas excited into a plasma state undergoes chemical adsorption with the surface of optical components to generate volatile molecules, physical sputtering, and other processes to remove surface pollution from the components.

According to the different reactions that occur during the cleaning process, plasma cleaning can be divided into plasma physical cleaning and plasma chemical cleaning. The plasma physical cleaning excited by inert gases such as Ar mainly relies on physical sputtering removal, without chemical reactions. There is no residual oxide layer on the cleaned surface, and the cleaning efficiency is poor. It deteriorates the surface roughness to a certain extent and can improve the adhesion of the material surface. The plasma chemical cleaning using reactive gases such as O2 is mainly based on chemical reaction removal, with high cleaning efficiency and effective removal of organic pollutants. It will increase the content of active functional groups (oxygen, nitrogen, etc.) on the surface of the component, improve surface wettability, but residual oxides will remain on the surface of the component.

This article mainly studies the influence of plasma cleaning processes using different types of gases argon and oxygen on the surface roughness of single crystal silicon. In the experiment, plasma cleaning was used to treat two single crystal silicon surfaces with consistent surface quality after the same polishing process. The surface roughness and weak photothermal absorption level of single crystal silicon before and after cleaning were tested to investigate the effect of plasma cleaning on the surface roughness of single crystal silicon.

Changes in surface roughness

Figure 1 shows the comparison of surface roughness and PSD curve of single crystal silicon before and after plasma cleaning measured by a white light interferometer. From the measurement results, it can be seen that the RMS value of the surface roughness of single crystal silicon increased by about 0.25nm before and after plasma cleaning. However, from the corresponding PSD curves, there was no significant change before and after plasma cleaning, indicating that plasma cleaning has an impact on the surface roughness measured by the white light interferometer in the spatial frequency range.

Effect of plasma cleaning on surface roughness (white light interferometer)

From the results of surface roughness and PSD curve, it can be seen that plasma cleaning can achieve the purpose of cleaning and pretreatment on the surface of single crystal silicon, while also having a relatively small impact on the surface roughness of single crystal silicon. Compared to argon plasma cleaning, oxygen plasma cleaning has a smaller impact.