In-line observation and classification of water marks after drying was investigated with the experimental understanding of causes of these water marks in terms of wettability of wafer and drying methods. The hydrophilic wafers did not created any water marks with either spin or vapor dries. The spin dry of hydrophobic wafers created a large quantity of water marks independent of the air exposure time. The patterned wafers with both hydrophobic and hydrophilic sites created water marks even in IPA vapor dry. Hydrophilization of HF etched wafers is a way to prevent the water mark form being created. Ozonated DI water was evaluated and appliced to pre gate oxidation wet cleaning processes after HF etching of silicon wafers for the prevention of water marks. No metallic contamination was observed not only in ozonated water cleaned wafer surfaces byt also ozonated water itself. No water marks and particle addition were observed in ozonated water last cleaned wafers. GOI, Ibd and Vbd evaluation of ozonated water last cleaned MOS device showed the equivalent or better results than HF last cleaned wafers.