The evolution of ripple morphology on Si surface has been studied as a function of ion fluence for 500 eV Ar+ ion sputtering at an incidence angle of 65°. The ripple wave vector is oriented parallel to the ion beam direction, following BH theory of ion sputtering. Up to certain fluence, the ripple ordering and amplitude is found to increase with simultaneous decrease of defects, but they tend to saturate at larger fluences. Coarsening behaviour of ripple wavelength is observed after a certain fluence showing the development of nonlinearity in the system. For high fluence, the ripple pattern neither disappears nor the surface exhibits kinetic roughening. These results are discussed in the context of non-linear continuum models.