Electroless copper deposition was performed by activation of Ta/SiO2/Si substrates using PdCl2/BOE/HNO3 displacement solution. Field emission scanning electron microscope (FESEM) and X-ray diffraction (XRD) were employed to investigate the effects of activation time and ultrasonic on surface morphology and structure of electrolessly deposited copper films. The results show that the coverage of copper films decreased gradually with the activation time increasing from 30 s to 150 s when the plating progressed without ultrasonic, while the high coverage of copper films was held with the activation time increasing when the ultrasonic was involved. The analysis of XRD indicates that the diffraction intensity of Cu (111) and (200) orientation increased obviously after the ultrasonic was introduced. When the activation time was 60 s, the diffraction intensity ratio of Cu (111) orientation to (200) orientation (I(111)/I(200)) was 4.53. The results of electroless Cu deposition on Ta/SiO2/Si substrates with trench patterns show that the presence of ultrasonic in electroless Cu plating can remarkably improve the effect of filling in trenches