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Quasi-resonant charge exchange processes between the vacant He 1sstate and the 4fstate of Ta and W target atoms were investigated. Oscillatory structures specific to the quasi-resonant charge exchange were observed in the yield curves of scattered He+ions. From the inverse incident velocity plots of the oscillation peaks, the phase development areas, , for both systems were evaluated in terms of the quality factor Qto discuss the "sharpness" of the quasi-resonant charge exchange process. Major components in the spectral density functions obtained by the Fourier transform of these oscillatory curves strongly suggested that the oscillations were responsible for a quantum interference between incident He+ions and target atoms forming a collision complex during the surface collision.