Integrated design of high performance mechatronics for optical inline metrology systems

Abstract

High precision inline metrology systems are considered one of the most important preconditions for future production, as they are the key technology to fulfill the ever increasing demand on productivity and precision of production systems. Due to their non-contacting principles, high throughput rates and high precision, optical sensing principles are of particular interest for these metrology systems. To enable high precision 3D measurements and to overcome the performance limitations arising from optical inline metrology systems based on standard automation components, integrated mechatronic design concepts are needed that consider all system components and the targeted application from the very beginning of the development. The fusion of integrated high performance mechatronics and motion control - both clearly enabling technologies for high tech imaging and measurement systems - and optical components, by carefully considering their interrelations and interplay, provides the basis for this approach. For providing increased flexibility to inline metrology systems, robot-supported systems are commonly employed to extend the positioning range of metrology tools. To provide the required positioning precision, which is typically limited by the precision of the industrial robot, a metrology platform for a combined optical metrology system is developed. The integrated design of the platform, including a decoupling mechanism, enables the definition of individual control targets for the two mounted metrology systems by using only a single actuator. Additionally a reduced current consumption, compared to a classical rigid design, and modal filtering of unwanted structural modes is enabled by the integrated system design. To advance point wise optical measurement principles to areal metrology tools, without the performance limiting need to introduce a relative movement between sensor and sample, fast steering mirrors (FSMs) are proposed to manipulate only the optical path of the sensor. For a precise scanning motion of the FSMs feedback control is inevitable, such that an intuitive tuning method for proportional-integral-derivative (PID) controllers, as well as single- and dual-tone controllers and a model-free phaselocked- loop-based control structure, tailored for desired Lissajous trajectories, are developed. Lissajous trajectories are of particular interest for imaging applications, as they provide an overview over the entire scan already after a fraction of the scan time, and it is shown, that together with their tailored controllers, they outperform the state of the art PID controller with raster trajectories in terms of the tracking error. The integrated system design approach is extended from the control design to the design of the mechanical plant, by adapting the dynamics of the FSM for the desired Lissajous trajectory, resulting in a one order of magnitude reduced current consumption and a 64 times larger scan area. Extending the integrated system design further to the actuator technology, a novel hybrid reluctance tip/tilt actuator is developed to overcome physical limitations imposed by the established voice coil and piezo actuation technologies. Considering the integration with optical sensor systems a compact new FSM system concept with large angular range is designed based on this novel actuator, utilizing only a single permanent magnet to bias the actuators for both axes. The constructed prototype provides an angular range of ±3◦ at a closed-loop bandwidth of 1 kHz, clearly outperforming established voice coil and piezo actuation technologies.