Without any sacrifice in bearing accuracy, the Kaydon Corporation Reali-Slim bearings can be optimised to minimise friction, outgassing, contamination and even wear. Indeed the company specialises in meeting the specific demands of semiconductor manufacturing by offering a range of options to create the optimum characteristics.
These custom Reali-Slim bearings were therefore the ideal choice for Applied Materials UK in Horsham for a gripper arm assembly on its Quantum X ion implant machine for the processing of silicon wafers. This is a single wafer, high current implanter using fixed beam technology. The gripper assembly is responsible for loading the wafer into the implant chamber and the role of the Kaydon bearings is to support the rotation of the gripper.
UK factory representative for Kaydon Corporation is bearing specialist RA Rodriguez with whom Applied Materials UK worked on this project. The bearing selected was a customised Type X 4-point contact bearing that accepts radial, thrust and moment loading. It was supplied with a flanged outer race for fixing to the gripper arm plate.
AISI 440C stainless steel races and balls were a must as the application called for contaminant-free, no-lube operation. This material choice ensures minimum surface degradation and particulate formation that is common in harsh environment applications. To accommodate the low torque operation under vacuum the bearing was also specified with PTFE cage.
"The gripper arm assembly and therefore the bearings needed to operate in a high vacuum environment of 10-7 Torr. They also had to be electrically conductive," explains Applied Materials senior design engineer, Bert Webber. "Another important characteristic for this application was compact design"
Perhaps the best known of the Reali-Slim characteristics is the design's minimum space requirement. The single 4-point contact Reali-Slim effectively replaced the need for Applied Materials to specify two bearings, making the design more compact and simplifying the mounting. In addition to the obvious cost savings this arrangement also created space for easy installation and maintenance and also saved weight.
The ability of this Type 'X' bearing to carry three types of loading simultaneously is thanks to the gothic arch geometry of the inner and outer races. It was also supplied with internal diametral pre-load to ensure zero free-play. This is accomplished by using balls that are larger than the space provided in the raceways. The balls and raceways therefore have some elastic deformation in the absence of an external load.
Such is the popularity of these thin section bearings for semiconductor applications that Kaydon has now produced a dedicated brochure. This publication and indeed the entire Reali-Slim range are available in the UK from RA Rodriguez in Letchworth.
