The Mechanical Design of a 3 axis nano-contouring Stage

This paper describes the design of the mechanical components for a 3axis nanoresolution contouring stage, which is to be used to investigate positioning and measurement error sources with a view to standardisation of stage characterisation in general. The design is an iterative process of theoretical calculation, 3D modelling and FEA. The stage itself is of monolithic flexure design combined with capacitance positioning sensing and 4-pass Michelson interferometer calibration. It is to be operated within an environmentally controlled vacuum chamber while thermal shielding will be used to avoid hot spots and to reduce thermal gradients. A 3D isostatic mounting arrangement is used to provide thermally stable location at a designated "sweet point", and to mechanically decouple the stage and the metrology frame from their support location (thus reducing stress and distortion). To minimise the relative movement of metrology components arising from thermal expansion, careful attention is also given to the geometry of both stage and metrology frame. Commercially available mirror mounts are used to provide the flexibility required to achieve measurement axis orthogonality and minimisation of measurement nonlinearity due to mirror and capacitance plate tilting. This flexibility will also allow for experimentation and tolerance limit identification. Additional brackets allow for measurement and movement axis alignment thus minimising Abbe and Cosine errors.