In this study, highly conductive Cu microstructures were formed on a glass substrate using femtosecond laser direct writing. As photon-absorbing nanoparticles, Si nanoparticles were added to the precursor solution. With the intensity ranging from 5.32×10⁹ W·cm^-2 to 8.51×10⁹ W·cm^-2 and the scanning speed ranging from 100 mm·s^-1 to 500 mm·s^-1, the Cu microstructures were formed on substrates. Metallic copper, Cu₂O, and minor Si were found in the copper microstructures. The results show that the continuity of the microstructure, the proportion of Cu, and the conductivity of the microstructures all increased with increasing intensity or decreasing scanning speed. At the scanning speed of 100 mm·s^-1, the lowest sheet resistance of 0.28 Ω·sq^-1 and the lowest electrical resistivity of 4.67×10^-6 Ω·m were obtained. The intensity was two orders of magnitude lower than that in previous work, and the direct writing efficiency was one to three orders of magnitude higher than that in previous work. Moreover, the line width of the microstructure was significantly smaller than the diameter of the laser spot.