Miniature ball screw drives in vacuum or nitrogen environments

Three-axis mask system for use in standard, electron beam, high-resolution, and automated UV lithography. (Photo: August Steinmeyer GmbH & Co. KG)

In the positioning system from Steinmeyer Mechatronik, ground miniature ball screw drives from August Steinmeyer are used. (Photo: August Steinmeyer GmbH & Co. KG)

Positioning system from Steinmeyer Mechatronik for fine XY-Theta alignment of exposure masks with up to 0.03 µrad. (Photo: August Steinmeyer GmbH & Co. KG)

The Steinmeyer Mechatronik GmbH has developed a highly precise positioning system in cooperation with August Steinmeyer GmbH & Co. KG for use in dry nitrogen atmospheres or vacuum. The mask system is ideally suited for use in standard as well as high-resolution UV lithography and enables very fine XY-Theta alignment of exposure masks with up to 0.03 µrad. Miniature ball screw drives from Albstadt are used, which meet especially high requirements for uniform preload and running quality in the application.

The three linear axes of the positioning system are arranged in a parallel kinematic configuration: two vertical axes in the X direction and one transverse in Y direction. The two vertical axes generate a vertical lift during simultaneous movement and a rotation during opposite movement. This allows highly precise linear and rotational positioning of the masks down to the sub-micrometer range.

Ball screw drive meets high requirements

In this very precise positioning system, ground miniature ball screw drives with a spindle diameter of 12 mm from August Steinmeyer are used. These are equipped with a flange single nut with 4-point contact, single-thread deflection, and optionally ceramic balls. The high geometric quality and surface finish of the backlash-free preloaded components ensure an ideal running behavior in application and enable the smallest adjustment increments. The assemblies undergo application-oriented series testing before delivery. The lifespan has been demonstrated in dry nitrogen atmospheres and vacuum.

The use in dry nitrogen atmospheres or vacuum requires the selection of special materials and lubricants. Therefore, a hardenable stainless steel is used in the ball screw drive. To minimize stray radiation, all structural parts of the mask system are also coated with an anodizing layer optimized for UV absorption. The use under ultraviolet light also prohibits hydrocarbons for the components and assemblies of the three-axis mask system. For this purpose, a fluorine-based, chemically and physically very stable lubricant is used, which shows no degradation under ultraviolet radiation and has an extremely low outgassing rate. It was specially developed by the user for this application and adapted for use in preloaded ball screw drives.

Optimal for service and maintenance

For maintenance, the exposure masks can be moved out laterally from the optical axis into service positions. A magnetically preloaded quick-change mechanism ensures a quick and easy exchange of the mask with just a few hand movements if needed. Maintenance of the motors and end-position sensors, which are designed as exchange assemblies, is equally straightforward.

For seamless integration into the machine control under series conditions, the preload of the ball screw drive must be precisely adjusted during assembly using the specified free-run torque band. This is a prerequisite for stable tuning of the control and reduces downtime during maintenance, as the PID parameters do not need to be readjusted in case of replacement. The stability of the running characteristics achieved over the lifespan thus also increases operational safety, since the motor control always runs in the optimally tuned range, which in turn is a prerequisite for achieving very small adjustment increments below micrometers.

The positioning system is available in several travel paths suitable for different mask sizes and can also be customized for specific applications. Optionally, cleanroom or vacuum versions are available. Application examples can be found in semiconductor exposure tools, but also in mask inspection.