Defect free diamond films have tremendous potential in a variety of areas including optoelectronics and have been the focus of several studies. Before diamond growth, a seeding treatment to substrate is mandatory, which itself is a source of contamination and degrades the quality of diamond. In the present study, diamond films without seeding treatment were grown on silicon using hot filament chemical vapour deposition. As a result of dry ultrasonic process, the diamond film with continuous layer was grown over unseeded substrate. At nucleation stage, carbon containing species were trapped by the uniformly created network of pits. Film grown at 2.0 vol.-% CH4 in H-2 and substrate temperature of 850 degrees C showed higher purity than that grown at 3.0 vol.-% CH4 in H-2 and substrate temperature of 1000 degrees C. Films grown over seedless substrates were also compared with those grown with seeding treatment.