Process effects of double step DRIE and Ni-Co electroplating for a trench-type cantilever probe for a fine-pitched MEMS probe card

This paper describes the effects of a process of double step deep reactive ion etch (DRIE) using an inductively coupled plasma (ICP) etch system and nickel-cobalt electroplating for a trench-type cantilever probe for a fine-pitched micro-electro mechanical systems (MEMS) probe card. The cantilever probe tip was formed inside silicon after double step DRIE to make a cantilever beam and pyramid type cantilever probe tip and electroplated in a nickel-cobalt solution to produce compliant and wear resistance structures. The advantage of a trench-type cantilever probe tip is that it can be used for a fine-pitch MEMS probe card. For forming the cantilever beam and pyramid probe tip in a trench, DRIE conditions were developed by varying the flow rate of SF(6) and C(4)F(8). For electroplating the tip in a deep trench, use of a seed layer was investigated on the bottom of the tip using electron probe microanalyzers (EPMA) and scanning electron microscopy (SEM) for analysis. To reduce tensile stress and to electroplate uniformly over a 6 in. wafer, a cathode mask was employed. Contact force was measured with varying composition of nickel-cobalt. As the percentage of cobalt increased. contact force was improved without depressions. The wafer was exposed to X-rays to investigate the quality of nickel-cobalt electroplating, such as the presence of seams or voids. There were no broken cantilevers or significant degradation after 1,000,000 touchdowns. (C) 2009 Elsevier B.V. All rights reserved.