Development of a precision dual level stage system for the dimensional metrology of large range surface topography

This paper presents the design and fabrication of a precision dual level stage composing a dimensional metrological system for large range surface topography, such as mask patterns for lithography, fine artifacts on a semi-conductor wafer and micro roughness on a large specular surface. The stage was configured as dual level, a fine stage on a coarse stage, to obtain large moving range and high resolution simultaneously. In the design of the coarse stage, we focused on a simple structure with low profile to achieve insensitivity to vibration and high accuracy. Therefore, a high quality flat surface plate was used as the reference plane of the coarse stage's movement, instead of a conventional simple stacking of two long stroke one-axis stages. The surface plate also has a role of metrological frame for very low thermal expansion coefficient and its size is 800 mm x 800 mm. The coarse stage is guided horizontally by a cross structure with two precision straight bars perpendicularly linked and vertically by the surface plate. The sliding pads made of PTFE are used to guarantee the smooth motion of the coarse stage for both horizontal and vertical directions. The fine stage fixed on the coarse stage generates five-axis fine motion, such as two-axis in-plane translation, one-axis in-plane and two-axis out-of-plane rotation. The fine stage is composed of flexure guided structures and actuated by five PZTs. The developed dual level stage can achieve a large range of 200 mm x 200 mm and a nanometric resolution simultaneously. Its movement is monitored and controlled using a five-axis laser interferometer system to be applied to a dimensional metrology having direct meter-traceability.