Deep x-ray lithography for micromechanics

Micromechanical processing tools fall into three basic categories: bulk micromachining of single crystal materials, surface micromachining with deposited films and lateral sacrificial etching, and high aspect ratio processing of polymers and metals. The third category includes LIGA and LIGA-like processing which shares with high aspect ratio processing the need for thick polymer layers with good chemical behavior, acceptable mechanical properties and minimal built-in strain. A decal technique via solvent bonding of thick, essentially strain free polymethyl methacrylate sheets has been used as an alternative to casting and in situ polymerization to avoid the strain difficulty. Final photoresist thicknesses between 100 to 500 micrometers are achieved by precision mechanical milling, prior to x-ray exposure. The photoresist process has been used to produce structures with structural heights to 500 micrometers and run-outs of less than 0.1 micrometers per 100 micrometers of structural height in a LIGA-like processing sequence which combines the LIGA process concept with surface micromachining.

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