| Summary: | 博士 === 國立中央大學 === 機械工程研究所 === 97 === Micrometer metallic pillars were fabricated by the intermittent micro-anode guided electroplating (MAGE) process in order to study (1) the localization of the pillar bottom, (2) the surface morphology of the pillars and (3) the cross-sectional structure along the axis of the micro pillars. The results and contributions of these studies were summarized as follows.
(1). Two modes (i.e., one-step and multi-step) of the MAGE process were employed to explore the localization of localized electrochemical deposition (LECD). Circular area around the pillar bottom on the substrate was measured and its diameter was estimated to define the localization of the micro pillars. A tiny hillock was fabricated in one-step MAGE process. The diameter (i.e., localization) of the circle around the pillar bottom increases with increasing the electric biases between the micro anode and the substrate. In the multi-step MAGE process, the diameter of the circle increases with increasing the pillar height and levels off at a critical localization (Dc). The magnitude of the critical localization was found to be a function of electric bias and the initial gap between the micro anode and the pillar top deposited previously. The less the electric bias and the initial gap in multi-step MAGE, the diameter of the circular area around the pillar bottom is smaller. A model of micro-electroplating is proposed based on an electric strength ratio (i.e., Ecore/Ep) between the conical core strength (Ecore) to the conical periphery strength (Ep) and the electric voltage responsible for the critical localization. The strength ratio can be used as a criterion to predict whether a localization diameter increases or not.
(2). Micrometer copper features fabricated by intermittent MAGE revealed different structures depending upon the experimental conditions. A hollow micro tube was developed at 4.0 V with an initial distance of 2μm/step. With decreasing the voltage from 4.0 to 3.2 V but increasing the initial distance from 2 to 25μm/step, a dense copper column with a smooth surface was formed instead of a rough-surfaced tube. The dense column was based on a substrate where revealed a larger area of circle around the column compared to that for the hollow tube. Finite element analysis is useful to establish a model for illustrating different morphologies of the micro features attained from MAGE process. According to this model, the structure is determined by the ratio (i.e., Ee/Et) of field strength at the periphery (Ee) to that in the center (Et) of the location. Hollow tubes were fabricated at a ratio higher than 1.5; dense pillars were attained at a ratio less than 1.0.
(3). The internal structure of the micro feature was illustrated by examining the cross-sectional morphology along its axis. Fixing an initial inter-electrode distance of 2μm/step, the intermittent-MAGE conducted at 3.2 to 3.6V led to a micro structure with rough surface and porous internal. With increasing the voltage from 3.6 to 3.8V, a micro tube with rough surface was fabricated. Up to 4.0V, an imperfect micro tube with highly rough surface was formed. The mechanism of LECD under different conditions is illustrated by a sequence of models proposed.
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