To minimize the measurement uncertainty of one dimensional length measurements on line scales, linear encoders and
interferometers the PTB in cooperation with the Dr. Johannes Heidenhain GmbH had built up a new length comparator.
The Nanometer Comparator [1,2] has already proven its performance during the measurements of incremental encoders
and line scales with an expanded measurement uncertainty of below 5 nm [3,4,5]. Due to the introduction of double and
multiple exposure in advanced lithography techniques the overlay and registration metrology requirements will
drastically increase so that reference metrology tools need to be developed further to be able to follow the resulting
decrease of the specifications. Therefore, the PTB further develops the new 1D vacuum comparator to add a
measurement possibility for straightness and to reach a measurement accuracy in the sub nanometer range [6]. One key
development will be the interferometric measurement of all six degrees of freedom of the measurement slide of the
comparator. A new multi axis heterodyne interferometer electronics and optical interferometer designs minimizing
nonlinearities by spatially separated beams are under development.
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