Selectivity loss (i.e. deposition on a mirror-smooth finished silicon surface) during diamond film growth using a selective deposition technique was investigated. CH4-CO2 gas mixtures without supplying hydrogen were used to enhance the nucleation density. After pattern generation and ultrasonic agitation pretreatment, the Si substrates were dipped into a solution of HF:HNO3:H2O (1:1.1:10) for various lengths of time to increase the pattern definition during the second period of diamond film growth. It was found that the selectivity loss in the diamond films could be significantly reduced by increasing the dipping time. The nuclei formed in the nucleation step were etched using the above solution, which reduced the selectivity loss. Scanning electron microscopy and electron spectroscopy for chemical analysis were used to examine the selectivity loss and morphological change of the as-grown diamond films. It was also found that a higher CH4 concentration resulted in a high selective loss of diamond growth.