Dynamic Structures and Materials has developed a precision R-Theta air bearing stage design for 300 mm wafer process applications and for other machining and inspection applications. Using a rotary and linear stage combination reduces overall footprint by up to 50% and provides unique benefits relative to a conventional X-Y configuration. The ability to access all areas of a workpiece in a smaller footprint can greatly increase accuracy by reducing thermally and statically induced deformations that might occur in large overhanging gantries. Thermal and structural compensation generally add unnecessary mass and cost in an X-Y stage system.
DSM's R-Theta design incorporates a rotary air bearing stage driven by a DC brushless, slotless rotary motor and an anti-backlash transmission system. A version of the stage is shown at right with a 12-inch square aperture to provide access to the workpiece from above and below. Strong emphasis is placed on bearing and drive design to enable sub-arc second positioning capability. Overall moving mass is minimized to increase the achievable acceleration of the stage which reduces machining and inspection cycle times. Air bearings are used instead of conventional rolling or sliding contact bearings because of their low synchronous and asynchronous errors, low runout, zero static friction and wear, and high stiffness. Digital encoder feedback is incorporated into the stage.
The Theta Stage's 360° rotational capability reduces the travel range required by the linear stage to that region between the center and the outer edge of the workpiece. This further reduces the footprint of the system. The linear stage is composed of a linear dovetail air bearing slide coupled to a linear motor with a 20 nanometer resolution encoder.
This stage has been successfully integrated into a precision machine developed to fabricate and inspect large arrays of micro-through features. The table at right presents the stage components' performance specifications.