Based in Colorado Springs, CO, USA
Proactive Particle Control in UPW
How to manage particles in a UPW System?
If you are involved in ultrapure water (UPW) technology as a UPW user, system operator, or supplier you should/must be interested in particle control. The International Roadmap for Devices and Systems (IRDS) and the industry in general recognizes that particles are potentially among the most critical factors for defects generated within UPW system, even more so for leading edge semiconductor technology. As microchip geometries move towards close-to-atomic scale, the critical or killer particle size (currently ~3.5 nm as defined by IRDS) has become smaller than the capability of advanced measurement techniques. This situation has been true in UPW for nearly a decade, with particle metrology suppliers investing in closing the gap, while the gap has only been increasing. The presence of dissolved particle precursors (defined as dissolved high molecular weight polymers) makes this even more of a challenge, because UPW systems were not designed to treat or prevent the release of particle precursors.
What makes particles so difficult to control?
Metrology: No widely available metrology exists to monitor sub-10 nm particles.
Filter Performance: Filtration capability at the killer particle size is marginal.
Particle Precursors: Dissolved high molecular weight polymers may become killer particles when they attach to the wafer and the water dries out.
High Purity Materials: High purity materials, such as filters and ion exchange resin, shed significant number of particles at killer sizes and larger.
Controlling Colloidal Silica: Colloidal Silica needs to be controlled. It is commonly present in UPW and very difficult to detect with existing measurement technologies. It is most difficult to maintain with current filtration processes.
What can I do about it?
Particles represent a huge risk to yield. The IRDS recently proposed a new proactive approach to deal with these technological gaps and associated risks, as opposed to traditional reactive strategies. The IRDS helps to drive development and updates to standards published by the SEMI organization. SEMI standards are considered a go-to reference for quality control and performance in the industry. SEMI Task Forces coordinate synchronization between IRDS, which defines advanced technology needs, and solutions that SEMI standards can enable. These standards help to drive quality control and continuous technology improvement.
So which documents among the 1000+ published SEMI standards & safety guidelines are relevant to particles in UPW?
The listed standards are reviewed in pace with IRDS roadmap updates
A series of three SEMI UPW standards (F61, F63, F75) can be used to provide recommendations for monitoring and controlling quality of UPW from the UPW plant through to the point-of-use (POU). SEMI F63 is the standard defining the quality of UPW for semiconductor manufacturing and can be used to establish performance criteria when purchasing UPW purification equipment, to set the process control parameters for UPW-system operation, and to establish quality expectations for the supplied UPW. SEMI F61 describes the engineering and component requirements for performance of a UPW system used in semiconductor manufacturing, and SEMI F75 describes potential sources of contaminants, their impact on semiconductor manufacturing, and available options for monitoring these contaminants.
To ensure the best performance and adequate water quality from a UPW system, there is a need to combine the right technologies and processes. UPW technology is mature and has not changed significantly for a long period of time. However, research conducted by IRDS suggests that the higher complexity of advanced semiconductor devices have increasing susceptibility to contaminants that cannot be detected by today’s existing particle metrology. As a result, additional solutions are necessary to address this issue. Those solutions include: a) new technologies, b) new metrology, and c) a new approach to quality assurance/quality control (QA/QC).
A holistic approach requires the understanding of what needs to be addressed (very small particles and particle precursors). In the category of new technologies, there is a need to develop new materials that will not leach contaminants and filtration technology to remove the smallest particles and particle precursors. Metrology-wise there is a need to develop and qualify more sensitive methods to reliably measure sub-10 nanometer sized particles. For QA/QC processes, it is important to not only have the correct SEMI standards but to inform the industry about the use of these SEMI standards. For example, filter performance (SEMI C79) and ion exchange resin cleanliness standards (SEMI C93) have been in publication for several years, but are still not being extensively used.
Significant collaborative effort is required to ensure a high yield in advanced semiconductor manufacturing. By using a combined approach to proactive particle control that addresses new technologies, metrology, and QA/QC processes, the industry has the best chance of tackling this substantial challenge.
How several of the SEMI high purity materials standards can be used to enable proactive particles control at a fab
If you are looking for additional information about industry roadmap development, or SEMI UPW standards development, please contact Slava Libman, CEO at FTD and UPM Co-Moderator. Click here to contact FTD or UPM.
Bonnie Marion is the R&D Lead for Water Systems at FTD. Her expertise includes water treatment processes and analytical chemistry.