Abstract: Herein,we addressed the problem of bombardment damage and over-sputtering etching,originated from wide energy spreading of ion beam,especially those high energy ions,in film growth by RF magnetron sputtering.The solution was a 27.12 MHz substrate bias.The influence of 27.12 MHz bias on the energy distribution of ion-beam was investigated with retarding field energy analyzer.The results show that a 27.12 MHz substrate bias made the difference.To be specific,the bias significantly decreased the density of high-energy ion and simultaneously increased the density of low-energy ion,markedly narrowing the energy spreading,obviously shifting the energy distribution of ion to low energy and greatly improving the film quality,possibly because the bias voltage greatly prolonged the transit time of ions(τ_i) across the sheath,resulting in significantly-increased collision cross-section between sputtering ion and neutrals,and a narrower energy distribution of the ion beam.