Miniaturized, microfabricated microelectromechanical systems-based wafer probes are used here to evaluate different contact pad metallization at low tip forces (<mN) and low skate on the on-wafer pads. The target application is low force RF probes for on-wafer measurements which cause minimal damage to both probes and pads. Low force enables the use of softer, more conductive metallisation. We have studied four different thin film contact pad metals based on their thin film electrical resistivity and micro-hardness: gold, nickel, molybdenum, and chromium. The contact pads sizes were micrometre (1.9 × 1.9 µm²) and sub-micrometre (0.6 × 0.6 µm²). The contact resistance of Au–Au, Ni–Au, Mo–Au, and Cr–Au was measured as a function of tip deflection. The tip force (loading) of the contacts was evaluated from the deflection of the cantilever. It was observed that an overtravel of 300 nm resulting in a contact force of ∼400 µN was sufficient to achieve a contact resistance <1 Ω for a sub-micrometre gold contact pad. Our results are compared with an analytical model of contact resistance in loaded metal-metal contacts—a reasonable fit was found. A larger contact resistance was observed for the other metals—but their hardness may be advantageous when probing other materials. Using a combination of a rigid silicon cantilever (>1000 Nm⁻¹) and small contact pads enabled us to show that it is the length of the pad (in contact with the surface) which determines the contact resistivity rather than the total contact pad area.

中文翻译：

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用于低接触力低滑动晶圆上测量的小型化微制造硅微悬臂式晶圆探针中的焊盘金属化比较

此处使用基于微型化、微加工微机电系统的晶圆探针来评估在低尖端力 (<mN) 和晶圆上焊盘上的低滑移情况下的不同接触焊盘金属化。目标应用是用于晶圆上测量的低力射频探针，对探针和焊盘的损坏最小。低力可以使用更柔软、导电性更强的金属化层。我们根据薄膜电阻率和微硬度研究了四种不同的薄膜接触焊盘金属：金、镍、钼和铬。接触垫尺寸为微米（1.9 × 1.9微米m ² ) 和亚微米 (0.6 × 0.6微米米² )。Au-Au、Ni-Au、Mo-Au 和 Cr-Au 的接触电阻被测量为尖端偏转的函数。从悬臂的挠度评估触点的尖端力（负载）。观察到 300 nm 的超行程导致 ∼400 的接触力微米对于亚微米金接触垫，N 足以实现 <1 Ω 的接触电阻。我们的结果与负载金属-金属接触中的接触电阻分析模型进行了比较——找到了合理的拟合。对于其他金属，观察到较大的接触电阻——但在探测其他材料时，它们的硬度可能是有利的。使用刚性硅悬臂梁（>1000 Nm ^-1）和小接触垫的组合使我们能够证明是垫的长度（与表面接触）决定了接触电阻率，而不是总接触垫面积.