| Summary: | 碩士 === 國立成功大學 === 材料科學及工程學系碩博士班 === 94 === Because of the shape effect of substrate, the current density will concentrate on a tip. The present work investigated the behavior of electroplating Cu on a probe tip. AFM probes were used as electrodes for the electroplating system and the tips were fixed head to head in the opposite direction. The present work studied the distribution of deposited layer on the substrate having a very small tip and compared with the distribution of deposited Cu layer using lithography to expose the area on a tip. The experiments were divided into two parts： electroplating Cu layer on an AFM probe without coating photoresist； electroplating Cu layer on an AFM probe with an open area on tip by lithography. The lithography used in the experiment was electron beam lithography,
The results of electroplating Cu layer on an AFM probe without coating photoresist revealed that the Cu layer was deposited on the probe with the minimum current density 0.1 A/dm2 to overcome the overpotential resulting from activation polarization. The change of contact resistance influenced the thickness of as-deposited layer, the nodule size and the degree of deposited Cu layer covering on a AFM probe. The AFM tip was found to be difficult for electroplating Cu layer.
However the results of electroplating Cu layer on a AFM probe with an open area on tip by lithography showed that open area and tip had deposited layer but the shape effect still can’t be found. The results revealed another reason to affect the behavior of electroplating on a tip.
Synthesizing both experimental results revealed the AFM tip as the hardest site to be deposited. The main reason was that the tip size with nanometer scale caused the surface energy to change and elevated the overpotential of the AFM probe tip. The total resistance of electric current path also increased resulting in the same situation.
The growth mode of electroplating Cu layer on an AFM tip revealed that no matter what the current density was, the tip was covered with Cu layer grew up from the side of tip finally. The longer the distance away from the tip, the thicker the thickness of Cu layer. This result was not related to the anisotropy growth between both electrodes due to current density concentrating on the tip.
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