| Material Purity, Handling and Installation Advances in Mechanical Brush Scrubbing Applications |
|
Kristan Bahten & Daniel T. McMullen Rippey
Corporation Abstract: With the economic pressures now effecting many disk drive and semiconductor manufacturers, cost of ownership and product yield issues are increasingly more important. Ever increasing technology demands are putting ever more stringent requirements on critical substrate cleaning. The vast majority of semiconductor and disk media manufacturing operations involve at lease one brush scrubbing step. Overall cleaning performance for brush scrubbing operations is often influenced by factors that can be easily overlooked. The cleanliness of the brush roller, contamination of the brush during handling, and the quality of the brush installation can have a dramatic effect on brush scrubbing performance. A new PVA (polyvinyl alcohol) product innovation has eliminated the need for pre-cleaning, significantly reduced or eliminated the break-in period for new PVA brush rollers, and reduced particle and trace metal contaminant levels. Although contamination can be significantly reduced by the use of an ultra-clean scrubbing device, like the new Rippey Microclean PVA, the benefits can be diminished by an improper fit or contamination during installation. The importance of the cleanroom glove cleanliness and the alignment and fit of the brush on the mandrel are often underestimated. This paper presents the significant improvements that have been made in the cleanliness levels of PVA brush rollers and the proper handling and installation of the rollers to reduce contaminate levels. A comparison of contamination found on several types of cleanroom gloves as well as a novel brush installation device will be included. The paper concludes with a summary of how those improvements will positively impact the cleanliness and performance of brush scrubbing. Data: Through a proprietary microcleaning process, Rippey Corporation has produced a high purity PVA sponge product that offers significant reductions in contamination levels from particles, ionic species, and other trace metals. This new PVA product was evaluated by ion chromatography, inductively coupled plasma mass spectroscopy, non-volatile residue analysis, and particle analysis to confirm that the contaminants have been successfully removed by the microcleaning process. Product packaging and preservation methods are also critical elements for microcontamination control. PVA can be highly susceptible to biodegradation if not properly handled. This biodegradation can be a source of particle generation. The particles are the microbial bodies themselves, as well as fragments of the damaged polymer matrix. This new product innovation includes double bagged clean room packaging for ease of use, combined with a new dilute alkaline chemical preservative that is compatible with most traditional cleaning chemistries. The installation process, inserting the PVA brush roller onto the scrubber core, can be a significant source of contamination. Traditionally brush rollers are installed on the core through a series of stretching, twisting and massaging motions. Each of these actions involves extensive contact between the gloves and the brush roller. This is important for two reasons: extensive contact between the glove and the brush will increase the transfer of any trace level contaminates to the brush and, bunching and twisting of the brush on the core will result in poor cleaning performance. Three types of cleanroom gloves were evaluated by Ion Chromatography for extractable ionic contaminates. Although all of the gloves tested were cleanroom class 100 certified, each showed significant levels of extractable ions. Data presented in this paper will show that significant contamination can be transferred to the brush roller during installations with new cleanroom gloves. The paper will further show that simply rinsing the gloves, with DI water, prior to handling the brush rollers significantly reduce the level of contaminates transferred to the brushes during the installation process. As significant as cleanliness, the brush needs to be installed on the core in a uniform manner so it will contact the wafer evenly and with equal pressure. A poor brush installation resulting in misalignment or bunching of the brush on the core can result in several undesirable consequences: physical damage to the brush causing particles and poor cleaning, shortened brush lifetime and performance. Anyone familiar with brush installation knows that the process can be difficult and time consuming. The new Rippey Quick-Fit™ brush installation device substantially reduces the amount of handling, time and effort required in obtaining a proper fit on the core. The results are improved brush cleanliness and performance. The paper concludes with a summary of the methods, when implimented, can greatly reduce secondary contamination and improper installation for improved cleaning performance. Conclusion: Microcontamination control is critical in cleaning applications of semiconductor and disk media. The importance of the brush should not be underestimated considering that the brush is the only solid material that generally comes into direct contact with the face of the wafer. The cleaning performance of the brush is influenced not only by the tool and the chemistry but also by the quality of the installation, cleanliness and handling of the brush. A cleaner brush, and a quicker, easier and more uniform fit and alignment of the brush will show their benefits in yield, labor, productivity and overall Cost of Ownership. References:
Acknowledgments: The authors would like to acknowledge the support of their colleagues Casey Bombien, Steve Montague, and Brian Reichert towards the successful completion of this work.
|