Project focus

  • Mechanical design and analysis of a 6-DoF precision positioning system
  • System modeling, control loop design and implementation
  • Prototype design, system integration and testing

Description

Schematic of the aim4np concept showing an industrial robot with a metrology platform (MP) measuring a sample on a measurement table.

Fig. 1 Vibration isolation concept for in-line nanometrology

Robot based in-process metrology is a key enabling technology for upcoming production systems and is considered as one of the most important preconditions for future production. Measuring properties at the nanometer scale such as topography, morphology and roughness within a production line becomes increasingly important for quality control and process monitoring tasks to make high tech production more efficient. Atomic Force Microscopes [AFM] and related scanning probe microscopes are commonly used to investigate the samples under test in great detail and with the required accuracy and spatial resolution. Such metrology tools are usually applied in a vibration-free scientific environment which is completely contrary to a production environment. Production facilities are populated with machines and working personal that introduce environmental vibrations typically exceeding the structure size of the sample. Comparable instruments that are compatible with production environments do not exist but are an absolute necessity to make the step into the next production era.

Within the scope of this project, a novel approach is developed for robot-based in-line metrology to isolate nanoscale measurements from environmental vibrations. Instead of isolating sample and robot from floor vibrations by means of passive or active vibration isolation aids, the distance between sample and metrology tool is kept constant. This is realized by a metrology platform, which will be brought in close proximity to the sample by an industrial robot. It is equipped with high precision position sensors, which measure the distance between sample and metrology platform. A six degree of freedom actuator creates the force for tracking the sample. Tracking of the sample is facilitated by a high bandwidth feedback control, hence forming a vibration-free environment for the nanoscale measurement directly in the production line.

Mechatronic Design and System Integration

On-site vibrations measurements are conducted to derive system requirements, and to specify requirements on the component level. A holistic design approach is applied that considers control relevant requirements already in the mechanical and electronic design steps to achieve a high performance of the mechatronic system. For example, such requirements concern the need for compactness and high stiffness of the inspection tools as they are actively moved by the platform, which is in conflict with their usage in vibration-free environments.

This results in a compact six degrees of freedom Lorentz actuator (zero stiffness actuation) with a gravity compensator powered by high bandwidth current controlled amplifiers, and a balanced design to minimize actuation power.  By using finite element analysis tools, the structural stiffness of the platform is analyzed with the aim to enable high bandwidth position control.

Laboratory prototype setup of the aim4np system with tracking actuator, metrology platform, AFM, and tracking sensors highlighted. Close-up inset shows AFM probe on the sample.

Fig. 2 Experimental metrology platform setup with on-board AFM

Precision Motion Control

Model based control techniques are applied to incorporate higher order plant dynamics such as caused by structural resonances of the mechanical structure. A system model is built to decouple the MIMO plant, resulting in the implementation of SISO controllers for each degree of freedom. Switching control techniques are researched to operate the metrology platform in two different modes, which are the control with sensors mounted in the actuator and the control with the tracking sensor. Further new approaches are developed to allow high bandwidth control of a body with high resonance frequencies that is mechanically coupled to a body exhibiting low resonance frequencies.

Scientific Imaging and Metrology Systems

An AFM head with a self-sensing cantilever is installed and used as inspection tool. Imaging of test gratings, plastic injection samples and nanowires could be successfully demonstrated.

Comparison of AFM images: laboratory measurement on vibration-isolated setup (left), corrupted AFM image due to vibrations in office environment (middle), and improved AFM image quality with high-bandwidth metrology platform in aim4np (right).

Fig. 3 AFM imaging in a noisy environment

Videos

Prototype

Applications

  • In-line metrology
  • Nanopositioning systems

Related publications

Project partners

Funding

EU FP7 Project, opens an external URL in a new window