Subject: thermal vias for QFN package

Hi, i'm designing a board with a thermally enhanced QFN package (4x4mm) which has a thermal pad of 2x2mm. I need to place some thermal vias (5) on this 2x2mm pad. please could you let me know if this is possible and what the minimum size is for the vias. I have tried 0.3mm but the DRC (Eagle) causes errors for drill size and clearance. I would like to use the pool service for this board.
Many thanks.