Precise positioning system for UV exposure masks

Precise positioning system for UV exposure masks

Precise positioning system for UV exposure masks

Precise positioning system for UV exposure masks

Steinmeyer Mechatronik GmbH, in cooperation with August Steinmeyer GmbH & Co. KG, has developed a high-precision positioning system for use in a dry nitrogen atmosphere or vacuum. The mask system is ideal 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 screws from Albstadt are used in it, which meet particularly high requirements for uniformity of preload and running quality in the application.

The three linear axes of the positioning system are parallel-kinematic in design: two vertical axes in the X direction and one transverse in the Y direction. The two vertical axes generate a vertical stroke when moving simultaneously and a rotation when moving in opposite directions. This enables high-precision linear and rotational positioning of the masks down to the sub-micrometer range.

Ball screw meets high requirements

Ground miniature ball screws with a spindle diameter of 12 mm from August Steinmeyer are used in this very precise positioning system. These are equipped with a flanged single nut with 4-point contact, single-gear reversing and optional ceramic balls. The high geometric quality and surface finish of the backlash-free preloaded components ensure ideal synchronization in the application and enable the smallest positioning increments. The assemblies undergo application-oriented series testing before delivery. The service life has been proven in dry nitrogen atmosphere and vacuum.

Use in a dry nitrogen atmosphere or vacuum requires the selection of special materials and lubricants. Hardenable stainless steel is therefore used in the ball screw. In addition, to minimize scattered radiation, all structural parts of the mask system are provided with an anodized coating optimized for UV absorption. The ultraviolet light application also prohibits hydrocarbons for the components and assemblies of the three-axis mask system. Therefore, a fluorine compound-based lubricant is used that is chemically and physically very stable, shows no degradation under ultraviolet radiation and has an extremely low outgassing rate. It has been specially developed by the user for this application and adapted for use in preloaded ball screws.

Optimal for service and maintenance

For maintenance, the exposure masks can be moved laterally out of the optical axis into service positions. If necessary, a magnetically preloaded quick-change mechanism ensures that the mask can be replaced quickly and easily in just a few steps. Maintenance of the motors and end-position sensors, which are designed as interchangeable modules, is just as uncomplicated.

For low-effort integration into the control system of the machine under series production conditions, the specified band of the no-load torque must be precisely set by means of the preload during assembly of the ball screw. This is a prerequisite for stable tuning of the control system and reduces downtimes in the event of maintenance, since the PID parameters do not have to be found again in the event of replacement. The stability of the running characteristics over the service life achieved in this way also increases operational reliability, since the motor control always runs in the optimally tuned range, which in turn is the prerequisite for achieving very small positioning increments below micrometers.

The positioning system is available in several travels to suit different mask sizes and can also be customized to suit applications. Clean room or vacuum versions are available as options. Application examples can be found in semiconductor imagesetters, but also in the inspection of masks.