In IC manufacturing processes, the wafer cleaning process is of paramount importance. A qualified wafer must undergo multiple complex cleaning steps to remove contaminants from the wafer surface, as these contaminants can directly or indirectly affect the performance of the chip.

IC Process Flow Diagram

Contaminants on the surface of silicon wafers are mainly classified into three categories：

Impact of Contaminants on Wafer Performance

From the table above, it is clear that any type of contaminant can impact wafer performance, with severe cases potentially causing the entire wafer to be scrapped. This highlights the importance and necessity of wafer cleaning. Over the years, various wafer cleaning methods have been developed, with the main current approaches being categorized into wet cleaning and dry cleaning. Dry cleaning methods primarily include plasma cleaning and vapor phase cleaning technologies. The cleaning principle involves heating chemical gases to a plasma state, which then react with the wafer surface to produce volatile by-products that are subsequently removed by vacuum extraction.

Dry Cleaning Methods and Limitations

The advantage of dry cleaning lies in the absence of wastewater after cleaning and the ability to selectively perform localized cleaning on chips. However, vapor-phase chemical methods cannot selectively react only with surface metal contaminants and will inevitably interact with the silicon surface. Therefore, dry cleaning cannot fully replace wet cleaning, and a combination of both dry and wet cleaning methods is typically employed in the process.

Principles and Techniques of Wet Cleaning

The principle of wet cleaning involves adding different chemical reagents that react with corresponding contaminants, which are then rinsed away along with the reagents using ultra-pure water. To date, wet chemical cleaning technology remains the primary cleaning method in the semiconductor IC industry, with the RCA cleaning process being the most classic example. The RCA cleaning process was introduced in 1965 by Kern and Puotinen at the RCA Laboratories in Princeton, N.J., and consists of a series of systematic cleaning steps using Standard Cleaning Solution 1 (SC-1), composed of hydrogen peroxide and an alkaline solution, and Standard Cleaning Solution 2 (SC-2), composed of hydrogen peroxide and an acid.

Details of the RCA Cleaning Process

The RCA cleaning process is characterized by selecting appropriate wet electronic chemicals based on the types of contaminants to be removed and performing different cleaning steps in sequence to eliminate various impurities attached to the wafer. The cleaning solutions used are high-purity, electronic-grade chemicals, which are costly. To optimize usage, the RCA cleaning process is designed to recycle the cleaning solutions, necessitating additional filtration steps to remove impurities. As mentioned earlier, the RCA cleaning process involves large amounts of acids and bases, so it is essential to consider the filter cartridge chemical resistance while filtering contaminants. Different usage points require corresponding filter cartridge. Membrane Solutions, with decades of expertise in the filtration industry, offers a range of filtration solutions tailored for the RCA cleaning process, with the following products available for customers:

Since the filter cartridge come into direct contact with the cleaning solution, they themselves can be a source of contamination. Therefore, to prevent secondary contamination of the cleaning solution, the cleanliness of the filter cartridge is of utmost importance.

Ensuring Filter Cartridge Cleanliness

To ensure the cleanliness of the filter cartridge, high-purity filters must undergo tests for metal ion release, particle shedding, TOC, and resistivity. Membrane Solutions has a CNAS-certified testing center to support and guarantee product testing.

Stringent Production Controls for High-Purity Filters

In addition, the production processes for high-purity filter cartridge are strictly controlled. First, key production steps such as pleating and welding are carried out in a Class 100 cleanroom, while the cleaning process is conducted in a Class 1,000 cleanroom. Second, the raw materials for high-purity filter cartridge are inspected, graded, and preliminarily cleaned. Third, a customized filter cleaning procedure is employed, with each filter undergoing multiple cleaning steps. As shown in the chart below, these effective cleanliness control measures ensure that Membrane Solutions filter cartridge achieve high levels of cleanliness in terms of minimal metal ion and particle release.

Comparison of Metal Content Between Membrane Solutions and Competitor Filter Cartridge 

Comparison of Particle Shedding Between Membrane Solutions and Competitor Filter Cartridges

Conclusion: High-Purity Filtration Solutions by Membrane Solutions

In summary, Membrane Solutions offers robust product capabilities, with customizable high-purity filtration solutions that meet the cleanliness control requirements of high-end clients, reduce the risk of secondary contamination, and help lower costs and increase efficiency, creating a win-win partnership.

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