Diamond-like carbon (DLC) films were prepared on Si substrates using a variety of positively and negatively pulsed voltages ( V p and V n), by a bipolar-type plasma based ion implantation system, and adhesion strength and toughness of the samples were examined in terms of the higher critical load ( L c2) and the scratch crack propagation resistance (CPRs) by a micro-scratch test. Cross sectional transmission electron microscopy (TEM) and Raman spectroscopy were also carried out to examine the microstructure of the samples. The L c2 and CPRs were increased by increasing V p and V n. TEM observation showed that a graphite-like form, such as turbostratic structure, is increased by increasing V p and V n. Raman spectra also indicated that the clustering of aromatic rings is enhanced at high V p and V n. From these results, it is suggested that the increase of the graphite-like form at high V p and V n should reduce the internal stress. In addition, it may act as a lubricant, resulting in the enhancement of the adhesion strength and the toughness of the films. The I D/ I G obtained from Raman spectra measured at the different points of the pre-scratched region, the cracking region and the partial destruction region was varied, and a tentative explanation was made on the basis of a 3 stage model.