Preventing Fiber Contamination in Wafer Track Tools and Scanners with PolyCHECK® and MiraWIPE®

Date: 12/20/2024     By: 59Clean

Introduction

In wafer fabs, contamination in track tools, such as the TEL Lithius Pro, can lead to significant production inefficiencies and wafer defects. Fiber-shaped particles, especially those originating from polyester-based cleaning materials, can easily migrate from the track to downstream tools like scanners, where their impact becomes even more severe. Traditional particle sampling techniques often fail to collect sufficient material for precisely identifying organic contaminants, such as polyester fibers. As a result, these fibers, a significant source of particle excursions and scratch defect incidents, frequently go undetected. Foamtec’s PolyCHECK® sample collection system and MiraWIPE fiber-free wipers offer a more effective solution for identifying and preventing these contamination issues.

The Limitations of Traditional Sampling Techniques

Conventional surface sampling methods, such as tape or SEM stubs, are widely employed to investigate particle contamination sources in wafer fabs. However, these techniques often collect an insufficient amount of sample, making it difficult to precisely identify organic particles like polyester fibers. Because traditional methods focus more on inorganic materials and metal-based contaminants, organic sources of contamination, including fibers from cleaning materials, are often overlooked.

In the case of tools like the TEL Lithius Pro, polyester wipers used during preventive maintenance (PM) can shed fibers onto sensitive surfaces. These fibers can then migrate through the tool, causing particle excursions and contributing to scratch defect incidents. However, due to the limitations of traditional sampling techniques, the presence of polyester fibers often goes undetected, allowing the contamination to persist.

The Impact of Fiber Contamination in Track Tools and Scanners

Track tools like the TEL Lithius Pro, responsible for wafer coating and developing, are particularly vulnerable to fiber contamination from cleaning materials. The more polyester wipers are used, the more fibers they shed due to poor abrasion resistance. Fibers can easily accumulate in critical areas like the FOUP entrance, Transfer Chambers, and wafer handling systems and then be transferred onto the wafer itself.

Once on the wafer, these fibers can migrate downstream to scanners, where the consequences are much more severe. In scanners, fibers trapped between the wafer and critical surfaces, such as the wafer table or Temperature Stabilizing Unit (TSU), can prevent proper vacuum alignment, leading to low vacuum errors, wafer misalignment, and out-of-spec overlay. This results in tool downtime, increased rework, and reduced yield​.

The TEL Lithius Pro analysis revealed that fibers, mainly polyester and cellulose, were detected between the wafer and tool surfaces. The fibers, which came from cleaning wipers, were contributing to contamination and tool errors. However, traditional sampling techniques had failed to identify these fibers as the source of the contamination​.

How PolyCHECK® Overcomes Traditional Sampling Limitations

Foamtec’s PolyCHECK® system addresses the limitations of traditional sampling methods by providing a more comprehensive approach to particle analysis. PolyCHECK® wipers are specifically designed to collect a statistically significant sample of particles, including both inorganic and organic materials, allowing for more precise identification of fiber-based contamination.

In a recent PM on the TEL Lithius Pro track tool, engineers used PolyCHECK® wipers to collect samples from areas showing signs of contamination. After analyzing the collected material under UV light and through additional chemical analysis, they conclusively identified polyester fibers as a major source of contamination. Traditional sampling techniques had missed these fibers but were now recognized as a leading cause of particle excursions and potential scratch defect incidents​.

This more detailed particle analysis provided by PolyCHECK® enables engineers to take targeted corrective actions, such as switching to fiber-free wipers, to prevent further contamination.

MiraWIPE: A Fiber-Free Cleaning Solution for Track and Scanner Tools

While PolyCHECK® helps engineers identify fiber contamination more accurately, Foamtec’s MiraWIPE ensures that no new fibers are introduced during cleaning. MiraWIPE is a fiber-free wiper made from polyurethane foam, which eliminates the risk of fiber shedding during PMs. Its superior abrasion resistance ensures that repeated wiping does not generate new fibers, making it an ideal solution for both track tools and scanners.

By using MiraWIPE instead of traditional polyester wipers, fabs can prevent fiber contamination from occurring in the first place. MiraWIPE’s woven microfiber fabric enhances cleaning efficiency and reduces the risk of particle migration, keeping tools cleaner and reducing the likelihood of particle excursions.

Real-World Success in Preventing Fiber Contamination

The combination of PolyCHECK® and MiraWIPE has proven highly effective in preventing fiber contamination in track and scanner tools. In an analysis of the TEL Lithius Pro track tool, polyester fibers were identified using PolyCHECK®, which traditional sampling methods had failed to detect​. If not addressed, these fibers would have migrated to the scanner, leading to tool errors and wafer defects.

Conclusion

Traditional particle sampling techniques often fail to collect enough sample material to accurately identify organic contaminants like polyester fibers, which are a major source of particle excursions and scratch defect incidents in wafer fabs. Foamtec’s PolyCHECK® system provides a more thorough approach to identifying contamination sources, while MiraWIPE offers a fiber-free cleaning solution that prevents fibers from being introduced into track and scanner tools. These solutions help fabs reduce tool downtime, prevent wafer defects, and optimize yield.

MiraWIPE® Product Info: https://www.59clean.com.tw/en/html/product/show.php?pid=239&cid=93&cid2=91

PolyCHECK® Product Info: https://www.59clean.com.tw/en/html/product/show.php?pid=274&cid=93&cid2=90