WP1: Sensor development 

The  aim  of  this  workpackage  is  to  develop  interferometric  based  measurement  systems  leading  to  better calibration of motion systems in industrial use and will support the two other workpackages by providing high performance metrology systems to complement available tools.

The sensor development is limited to interferometric methods to allow for traceable measurements. Two of the  developments  deal  with  multiaxis  systems,  which  will  be  capable  of  simultaneous  measurements  and allow for cost effective techniques which can be transferred to industry. The third development deals with an improved  straightness  interferometer,  as  commercial  systems  today  are  not  suitable  for  ultra  precision applications. The developments will support the measurements to be done in WP2 and WP3. 

Leading NMI:  NPL

WP2: Straightness and Orthogonality

The aim of this workpackage is the validation and crosscheck of methods to determine 2D-straightness and orthogonality of ultra high precision measurement and production machines. Straightness and orthogonality are  key  parameters  of  2D-measurement  and  production  systems  like  mask  measurement  machines  or electron beam writers in the semiconductor manufacturing process. But 2D-reference systems or artefacts can  also  be  used  to  check  in  different  orientations  the  behaviour  of  full  3D  tools  or  components  of  more general motion systems. Common methods to determine straightness and orthogonality are the calibration of L-shaped measurement mirrors to be integrated  in the measurement system or the use of self calibration methods. 

The calibration of the measurement mirrors by Fizeau interferometer is common in 3D-CMM systems. One challenge  of  this  method  is  the  referencing  of  the  external  measured  values  to  the  machine  coordinate system.  Another  limitation  is  the  accuracy  of  Fizeau  interferometers  in  the  order  of  5  nm,  which  can  be overcome by the use of deflectometric methods like direct deflectometry, difference deflectometry or exact autocollimation deflectometric scanning [14,15], which allows for sub-nm accuracy but has a limited lateral resolution. Also in the machine the spot of the laser beam is some millimetres in diameter, requiring a match of  the  lateral  resolution  to  optimise  this  method.  While  in  2D  only  one  orientation  of  the  external measurement setup is necessary  to measure the topography,  with the same mounting conditions as later used in the machine, for 3D mirrors this is a challenge as the topography measurement must be done in different orientations. Additionally, if necessary for the dynamic, clamping forces must be taken into account and the influence of ageing due to gravitational forces has to be investigated. 

In mask measurement tools the preferred methods for correcting straightness and orthogonality errors are self calibration methods by measuring sequentially in rotated and shifted positions of the mask. The limitation of  this  method  is  the  reproducibility  of  the  mask  mounting  and  of  the  tool  with  changed  load  conditions. Additionally, the method is time consuming, especially if no automatic handler is available. A comprehensive analysis of the measurement uncertainty of this method is still missing. 

An alternative for straightness calibration is the direct use of deflectometric methods for the online correction of the topography of the mirrors in the calibration of straightness reference standards like 2D-line standards or interferometers as described in WP1. Due to easy implementation the TMS method has been selected for the PTB length comparator. Theoretical analyses have shown that uncertainties below one nm are possible, EMRP  but the performance of the method must still be proven. Orthogonality on 2D-line standards can be calibrated by a length comparator using the method of multilateration, which means a measurement of distances of a grid of points under different orientations. A measurement uncertainty analysis has to show how much grid points are necessary for sub-nm accuracies.

All these methods have to be compared to allow for a secure base for the choice of an appropriate method in ultra precision engineering.

Leading NMI:  PTB

WP3: Characterisation of motion systems in six degrees of freedom 

The aim of this workpackage is the characterisation of different motion systems in six degrees of freedom. To meet the requirement for more accurate traceable characterisation of stages used for nanometrology a test bed  will  be  constructed.  It  will  serve  two  purposes  within  the  project:  firstly  it  can  be  used  for  stage characterisation,  and  secondly  it  can  be  used  for  the  verification  of  the  performance  of  the  sensors developed in WP1.   A  second  class  of  motion  systems  are  high  precision  coordinate  measurement  systems,  where  the measurement range is at least some 100 mm, which requires a more sophisticated correction of topographic influences of guidance elements and measurement references. An example is  the newly developed NMM with  a  travel  range  of  200  mm  x  200 mm  x  50 mm.  Many  techniques  for  the  characterisation  have been developed  for  CMMs  but  it  must  be  checked  whether  they  correspond  to  uncertainties  in  the  nanometre range. The most complex class of systems combines linear and large angular motion like Hexapods or combination of linear and rotation axes. This allows for more universal solutions for measurement and production and will also become more important in  ultra precision  engineering  and for nanotechnologies. The problem is that proven techniques like laser interferometers cannot be used in the traditional way. One way to overcome this problem is the use of coordinate measurement machines with tactile or optical probing of reference points on the motion stage. This method is time consuming as after every motion step the reference points must be localised one after another. Another solution is the use of laser tracers which use balls as angle insensitive reflectors. Tracers are commonly used in large scale applications. By increasing the number of tracers they are able to dynamically measure the motion of a stage in all six degrees of freedom  simultaneously. Both methods will be analysed and compared in this task. 

Leading NMI:  CMI

WP4: Creating Impact 

The transfer of knowledge generated during the project into industry will be an essential aspect of this JRP. A stakeholder committee will be formed at the start of the project from industrial and academic collaborators that will help to steer the project and will also receive results of the project first-hand. The project is targeted at the entire semi-conductor and MEMs manufacturing supply chain as demonstrated by the collaborators, which include manufacturing companies, instrument manufacturers and research institutes. The aim of this workpackage is to disseminate the project results to the Stakeholders and to create impact for industry, service providers and the scientific community.

Leading NMI:  METAS

WP5: Management and Coordination 

The project will be coordinated and managed by PTB.

Leading NMI:  PTB