In plasmonic lithography, when using a scanning probe in contact mode, degradation of the line pattern quality occasionally occurs due to variations of probe tip velocity or a stick/slip motion. To avoid poor pattern quality caused by such variations in probe tip motion, we analyzed the motion of the probe tip by using a frictional model based on conventional contact mechanics. The motion of the probe tip was numerically analyzed in terms of adhesion force and probe velocity, which are the dominant factors in micro/nanoscale motion. It was found that stick/slip spacing has a roughly positive relationship with the maximum adhesion force between the substrate and probe tip, and a negative relationship with the probe velocity. Combining the probe tip motion with the exposure model of a near-field wave, we analyzed the quality of line patterns that resulted from various stick/slip spacing in terms of line-edge roughness.