Thermal scaling and relaxation of the interface width in an electrophoretic deposition of polymer chains is examined by a three-dimensional Monte Carlo simulation on a discrete lattice. Variation of the equilibrium interface width W-r with the temperature T shows deroughening W-r similar to T-delta, with delta similar to (1)/(4), at low temperatures and roughening W-r proportional to T-v, with v similar to 0.4, at high temperatures. The roughening-deroughening transition temperature T-t increases with longer chain lengths and is reduced by using the slower segmental dynamics.