Photolithography on bulk micromachined substrates

Photolithography on high topography substrates, such as the sidewalls or the bottom of cavities and trenches created by bulk micromachining, enables the design of complex three-dimensional structures. When a contact lithography system is used to pattern such substrates, local gaps exist between the mask and the substrate. In this paper we investigate the deformation of patterns as a result of these local gaps. We determine the position accuracy and the minimum size of features that can be patterned as a function of the gap distance. Deformations introduced by the optical system are quantified for a common exposure tool, and compared to pattern deformation due to variations in photoresist layer thickness. Finally, methods to improve the quality of patterns transferred through gaps up to 350 µm are discussed