A Study on Photo-Assisted Electrochemical Etching and Ultrasonic Agitation in Supercritical Electroplating Process

• Main Authors: Yang,Hsi Min, 楊錫閔
• Other Authors: 徐正會
• Format: Others
• Language: zh-TW
• Published: 2017
• Online Access: http://ndltd.ncl.edu.tw/handle/e3hedg

博士 === 國立臺北科技大學 === 機電科技研究所 === 105 === This study can be divided into “Fabrication of Though-Silicon Via Arrays by Photo-Assisted Electrochemical Etching and Supercritical Electroplating” and “The Influence of Ultrasonic Agitation on Supercritical Electroplating”. In the first part, the study aims to fabricate high aspect ratio Through Silicon Via (TSV) by Photo-Assisted Electrochemical Etching (PAECE) and Supercritical CO2 Copper Electroplating. Blind-holes silicon array was first fabricated by PAECE. By studying the etching parameters, including HF concentration, etchant temperature, stirring speed, Tetrabuthyl ammonium percholate (TBAP) content and Ohmic contact thickness, the array of pores with aspect ratios of 1:45 (height=250 μm; diameter=5.5 μm) was obtained successfully. Moreover, TBAP and Kodak Photo-Flo (PF) solution were added into the etchant to acquire smooth sidewalls for the first time. TBAP was added for the first time to serve as an antistatic agent in deionized water-based etchant to prevent side-branch etching, and PF was used to degasify hydrogen bubbles in the etchant. The effect of gold thickness over Ohmic contact was investigated. Randomized etching was observed with an Au thickness of 200 Å, but it can be improved by increasing the etching voltage. The silicon mold of through-holes was filled with metal using supercritical CO2 copper electroplating, which features high diffusivity, permeability and density. The TSV structure (height=220 μm; diameter=6 μm; aspect ratio=1:35) was obtained at a supercritical pressure of 2000 psi, temperature of 50℃ and current density of 3 A/dm2 in 2.5 hrs. In the other part, the study aims to use ultrasound (42 kHz) in supercritical CO2 (SC-CO2) electroplating process to investigate the effect of ultrasonic powers and supercritical pressures on the properties of copper films. From the results it was clear that ultrasound enhances emulsification effect and higher ultrasonic irradiation resulted in higher current efficiency, grain refinement, higher hardness, better surface roughness and higher internal stress. The optimal parameters were set to obtain the deposit at pressure of 2000 psi and ultrasonic irradiation of 0.157 W/cm3. Compared with SC-CO2 electroplating process, the current efficiency can be increased from 77.57% to 93.4%, the grain size decreases from 24.34 nm to 22.45 nm, the hardness increases from 92.87 Hv to 174.18 Hv, and the surface roughness decreases from 0.83 μm to 0.28 μm. Therefore, this study has successfully integrated advantages of ultrasound and SC-CO2 electroplating, and proved that applied ultrasound to SC-CO2 electroplating process can significantly improve the mechanical properties of the coating.