High precision 3D metallic microstructures produced using proton beam micromachining

Abstract

A crucial step in the development of mechanically strong microstructures is the conversion of structures made from resist material of low hardness and strength, to harder and more durable metallic microstructures. The implementation of a post lithographic process step such as electroplating offers the possibility of producing metallic structures. In proton beam micromachining (PBM) a focused MeV beam is scanned in a predetermined pattern over a resist (e.g. PMMA or SU-8), which is subsequently chemically developed. The proton beam in resist follows an almost straight path, enabling the production of microstructures with well-defined rectangular side walls. If the resist layer is laid down with a thickness of typically 50% of the proton range on a conductive substrate, then the end of range straggling and resultant end of range beam broadening does not occur in the resist, but in the substrate. The conducting substrate acts as a seed layer for plating. In this current work, smooth well-defined metallic mi crostructures with a height of 10 μm are produced using electrolytic Ni plating. One spin-off application is that the plated Ni structures, which have excellent side wall definition, exhibit properties that are far superior to the current 2000 lines per inch gold grid resolution standard used by many nuclear microscopy groups worldwide. © 2001 Elsevier Science B.V. All rights reserved.