Effects of ultrasonic agitation and electrolyte additives on microstructure and mechanical property of electroplated Cu films

• Main Authors: Lu, Yi Sheng, 呂易昇
• Other Authors: Liao, Chien-Neng
• Format: Others
• Language: zh-TW
• Published: 2015
• Online Access: http://ndltd.ncl.edu.tw/handle/22837010330085172303

碩士 === 國立清華大學 === 材料科學工程學系 === 103 === Electroplating is a main-stream process used to fill the metal layer of integrated circuits. However, owing to the complication of the circuit structure, the metal layer may suffer local stress concentration, leading to device failure. Nanotwinned Cu that has high mechanical strength and good electrical conductivity is considered as an excellent interconnect material. By using the pulse-current deposition method, we are able to introduce a nanotwinning structure in Cu metallization with various twin spacing. Nonetheless, the pulse-current electrodeposition has a lower deposition rate than the direct-current one, which may not be the promising solution for industrial fabrication process in terms of run rate and cost considerations. In this study, we intend to investigate the effects of ultrasonic agitation and electrolyte additives on microstructure and mechanical property of Cu films prepared by direct-current electroplating method. Both the ultrasonic agitation and specific electrolyte additive can enhance average grain size of the electroplated Cu films according to the images obtained by scanning electron microscopy and focused ion beam system. The x-ray diffraction results show that the Cu films prepared with ultrasonic agitation and electrolyte additive have enhanced (111)-oriented film texture. In an electroplating process with ultrasonic agitation, a two-dimensional layer growth mechanism prevails owing to the reduced diffusion layer thickness and overpotential together with the enhanced surface diffusion of Cu adatoms. The function of electrolyte additive adsorbed on the cathode surface may decrease the available nucleation sites and enhance the two-dimensional growth as well. Based on the microstructure inspection and nano-indentation measurements, ultrasonic agitation and appropriate electrolyte additive can raise the possibility of forming dense nanotwinning structure and increase the hardness of electroplated Cu films.