Silicon wafer cleaning agent is widely used in photovoltaic, electronic and other industries. Because of the pollution of silicon wafer in the transport process, the surface cleanliness is not very high, which has a great impact on the corrosion and etching to be carried out, a series of cleaning operations should be carried out on the surface of silicon wafer first. The general idea of cleaning is first to remove the organic contamination on the surface and then dissolve the oxide film, because the oxide layer is 'contaminated and trapped', which can cause epitaxy defects, and then remove particles, metals, etc., while passivating the surface of silicon wafer.

RCA cleaning method

RCA cleaning process, also known as industrial standard wet cleaning process, was proposed by Kem and Puuotinen of American Radio Corporation (RCA) in the 1960s, hence its name.

RCA wet cleaning consists of two different chemical solutions, the main components of which are shown in Table 2.1, Table 2.2 and Table 2.3.

SPM has high metal oxidation ability, which can dissolve metal in cleaning solution after oxidation, and can oxidize organic matter to produce carbon dioxide and water. Cleaning silicon wafers with SPM can remove all kinds of organic contamination and some metals on the surface. When the contamination is very serious, it is difficult to remove them.

DHF can remove the natural oxide film on the surface of silicon wafer and inhibit the formation of oxide film. It is easy to remove Al, Fe, Zn, Ni and other metals on silicon surface, as well as hydroxides on natural oxide film. When the natural oxide film is corroded, the silicon wafer is hardly corroded.

Basic RCA Cleaner Formula

SC-1 cleaning solution is an alkaline solution which can remove particles and organic substances. Because hydrogen peroxide is a strong oxidant, it can oxidize the surface and particles of silicon wafer. The oxide layer on the particles can provide dissipation mechanism, split and dissolve the particles, destroy the adhesion between the particles and the surface of silicon wafer, and break away from the surface of silicon. The oxidation effect of hydrogen peroxide also forms a protective layer on the surface of silicon wafer, preventing particles from re-adhering to the surface of silicon wafer. Subsequently, the silicon wafer is immersed in 10% HF solution for 2 minutes, which can remove the naturally formed oxide film on the surface of the silicon wafer and inhibit the formation of oxide film again. At the same time, HF acid can also dissolve the metal contaminants attached to the oxide film.

SC-2 wet cleaning process is used to remove metal from silicon wafer surface. Only in the solution with high oxidation capacity and low PH value can the metal fouling on the surface be removed. At this time, the metal is oxidized into ions and dissolved in acid solution, and the electrons in the metal and organic fouling are captured and oxidized by the cleaning solution. Thus ionized metals dissolve in solution, while organic impurities are decomposed. This is the mechanism of RCA cleaning method. Continue to clean silicon wafer with HF at room temperature for 2 minutes, and finally remove the residual lotion several times with deionized water ultrasonic cleaning.

RCA Cleaner Formula

Solution proportion of improved RCA cleaning process

RCA-1 (H_2O/NH_4O_H/H_2O_2) lotion: The natural oxide layer (SiO_2) and Si on the surface of silicon wafer are corroded by NH_4O_H, so the particles attached to the surface of silicon wafer are dispersed in the cleaning solution, thus removing the particles on the surface. While NH4OH corrodes the surface of silicon, H2O2 forms a new oxide film on the surface of silicon oxide.

RCA-2 (H_2O/HCl/H_2O_2): Used for removing metal contamination such as Ni, Fe, Mg on the surface of silicon wafer, Fe and Zn can be removed at room temperature.

Modified RCA Cleaner Formula

HF/O3 cleaning method

HF/O3 trough cleaning method

Because the reduction potential of ozone is higher than that of sulfuric acid, hydrochloric acid and hydrogen peroxide, the removal efficiency of organic substances and metals by ozone super-clean water is higher than that by traditional SC, SPM and RCA. In addition, this method can be cleaned at room temperature without waste liquid treatment, so it has a great advantage over the traditional method.

ASTEC Germany has designed a set of cleaning process based on HF/O3, called ACD. The method consists of cleaning and drying, and is widely used for cleaning 300mm silicon wafers. Cleaning steps: cleaning - rinsing with pure water - drying, can be added with pure water, HF, O3, surfactant, ultrasonic cleaning.

HF/O3 Monolithic Cleaning Method

The rotary cleaning method of HF/O3 single chip developed by Sony Company of Japan can effectively remove organic, inorganic and metal contamination on silicon surface. There are three feeding systems on this equipment, which can supply HF acid, ozone dissolved oil and ultra-pure water to the center of silicon wafer at the same time. In this process, the ultra-pure water of HF acid and dissolved oil ozone is supplied alternately to the silicon wafer center, and each reagent is supplied alternately for about 10 seconds, then the pure water is supplied for washing. Finally, the silicon wafer is dried by rotary drying method. In order to avoid the water mark on the surface of silicon wafer caused by rotary drying method, nitrogen can be used instead.

Hot Washing Silicon Film Forming Agent

Hot-state silicon-washing film-forming agent, including agent A and agent B, contains strong alkaline catalyst 5%~35%, inorganic solvent 65%~95%, chromogenic agent trace, raw material total is 100%; agent B contains analytical pure sodium phosphate 03%~3%, analytical pure hydrazine 0.05%~2%, with two inorganic solvents, the total raw material is 100%; when used, agent A and agent B are mixed in proportion of 1:10, the specific gravity of solution is 1% after mixing. 008g/ml~1.031g/ml.