While semiconductor manufacturers continue to push the limits on device architecture and manufacturing equipment capabilities, improving contamination control within the cleanroom is a continuous challenge. Despite the constant efforts to reduce contamination and defectivity within the fab, the threat of defect excursion occurrence is constantly present. Defect excursions may occur at any point throughout the manufacturing process, so prompt detection and response is critical in reducing excursion impact. Although identifying the excursion’s root cause is difficult and time-consuming, the leading cause is random particle contamination. Cleanroom manufacturing environments commonly have numerous sources of contamination and are very difficult to definitively identify and create countermeasures to eliminate them.
Device manufacturers understand the correlation between defectivity performance and device yield/reliability, so there is already a paramount focus on defect reduction and continuous improvement efforts in most fabs. Failure to reduce or eliminate sources of random particle contamination throughout a fab significantly increases the risk of defect excursions, yield stagnation, latent device failures, and reduced fab efficiency. All of which inflict detrimental effects on the reputation of the manufacturer, customer satisfaction, and the business relationships that keep fabs in operation.
Many fabs rely upon detecting defect abnormalities via inline metrology or final electrical testing, which detect problems after they have already occurred. The scale of impact is directly proportional to the point of abnormality detection and how quickly a response is executed. This causes defect excursion investigations to be carried out retroactively and almost always fails to identify a definitive root cause for the excursion. Equipment and environmental contamination investigations are time-consuming and labor-intensive, but if they also fail to provide a definitive root cause identification, then the lost production time and resource allocation are wasted without progress towards reoccurrence prevention. During excursion investigations, particulate samples are collected via Carbon adhesive stubs from surfaces for identification analysis. Sample collections via Carbon adhesive stubs are the industry standard but restrict the surface area being sampled and often fail to collect all foreign materials from the suspect surfaces. Carbon adhesive stubs are costly and can also leave adhesive residuals on critical surfaces, which creates additional work post sampling. To reduce these issues, Foamtec has developed a user-friendly surface sampling solution that allows surfaces to be sampled and analyzed quickly and at far lower costs than traditional methods. Our PolyCHECK inspection products, available as wipers or swabs, feature a lightly charged black material that attracts and capture contaminants as they are wiped across a surface. They enable large surface areas or tight clearance areas to be efficiently sampled, and the black material provides visual identification of contamination. PolyCHECK products may be bagged and labeled for submission to the laboratory, where contaminants can be lifted directly from PolyCHECK material surface to a Carbon stub for analysis to be performed.
Although SEM-EDX analysis is the most widely used analysis technique for contamination identification, there are some significant gaps in this analysis. SEM-EDX may provide suitable identification of inorganic or metallic contaminants, but as several sources of random particle contamination within a cleanroom are organics, this analysis technique is often unsuccessful at identifying a root cause. Organic contaminants can be challenging to identify via SEM-EDX analysis due to organic contamination sources all yielding similar EDX traces of predominant organic elemental peaks.
Figure 1 shows the SEM-EDX results of two fiber particles sampled from an Applied Materials Endura Front End Module (FEM) Robot with Foamtec’s PolyCHECK wiper. While the SEM images provide enough detail to identify the particles as fibers or stringers, the EDX analysis produces similar elemental plots for both samples indicating common organic Carbon and Oxygen peaks. The root cause source for the contaminants remains uncertain without more advanced analysis techniques being performed. With several sources of organic fiber or stringer particles present in the fab environment, such as wipers, garments, hairnets, facial coverings, process residuals, the EDX analysis alone cannot definitively identify the contamination root cause. Failure to diagnose and eliminate the root cause source(s) will lead to continued defectivity issues and possible excursion reoccurrence.
As tech nodes continue to evolve and defectivity becomes a primary yield & reliability inhibitor, fabs are dedicating teams to contamination and defect reduction to improve their ability to identify and eliminate contamination sources. These teams typically oversee contamination investigations and particle defect identification analysis within onsite laboratories or outside laboratory partners. The main issue these teams face is that the most prolific defects observed are organics.
With SEM-EDX analysis limitations for organics, contaminants are commonly misclassified as process byproducts or unknown defects with no root cause assignment. To improve organic contamination identification, Foamtec recommends using FTIR analysis techniques, which are very effective in identifying organics through IR spectrum comparison to known organic material spectrum collections.
Figure 2 demonstrates how Foamtec’s FTIR analysis capabilities were used to definitively identify the organic contamination samples from Figure 1. As SEM-EDX analysis failed to provide enough information on the two fiber samples, actions could not be carried out to find the root cause sources. With the identification of these two seemingly identical fiber particles as two separate material fibers, the customer collaborated with Foamtec to further analyze their fab consumables to identify the sources of these fiber particles. Figure 3 below shows how this customer’s POR polyester cleanroom wiper (TX1010 Vectra Alpha 10®) was provided to Foamtec for a comparative FTIR evaluation vs. the unknown sample #4 and our FTIR contamination reference library, proving that the sample #4 fiber originated from their POR polyester wiper.
Foamtec International is dedicated to supporting our customers to identify contamination sources and provide them with effective products to enhance cleaning efficiency and eliminate contamination across the entire cleanroom. Foamtec has been serving the advanced cleanroom manufacturing industry for more than 25 years and continues to evolve via innovative product development and new support services that make our customer objectives possible. We would be happy to support your efforts to identify and eliminate chronic contamination issues that impact fab performance. If you have questions or would like to learn more about the topics discussed in this write-up, please contact Foamtec International via phone or email to connect with an experienced staff member today.