Specification of mechanical support structures to prevent SU-8 stiction in high aspect ratio structures

Densely packed high aspect ratio structures are difficult to fabricate due to surface adhesion effects which lead to pattern collapse during processing. However, it is possible to fabricate such structures in SU-8 by means of a top-plate support member which stiffens the overall structure and prevents pattern collapse. We have fabricated a variety of structures in SU-8 up to 1.5 mm high and with feature sizes in the 10-50 mm range. We investigate theoretical, computational and experimental approaches for predicting the thickness of the top-plate supports as a function of the aspect ratio and spacing of the structures. We demonstrate the fabrication of a number of densely packed high aspect ratio structures with top-plate supports that approach the minimal thickness sufficient to prevent pattern collapse.