Reali-Slim bearings used in semiconductor processing

Without sacrificing bearing accuracy, Kaydon's Reali-Slim bearings can be optimised to minimise friction, outgassing, contamination and wear. Indeed, the company specialises in meeting the specific demands of semiconductor manufacturing by offering a range of options to create the optimum characteristics.

Applied Materials UK therefore selected these custom Reali-Slim bearings 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.

Ion implantation is a process where electrically charged atoms are fired into the silicon wafer to change the electrical properties of the material; the process can be applied at various points in the wafer manufacturing process. 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.

Radial, thrust and moment loads

The UK factory representative for Kaydon Corporation is R A Rodriguez, with which Applied Materials UK worked on this project. The bearing selected was a customised Type X four-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 essential, 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 a PTFE cage.

Bert Webber, Applied Materials' senior design engineer, comments: "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. Another important characteristic for this application was compact design."

Perhaps the best known of the Reali-Slim bearings' characteristics is the design's minimum space requirement. The single four-point contact Reali-Slim bearing 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 preload 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 R.A. Rodriguez.