We have investigated the effect of the experimental variables such as temperature and pressure on conformality of Co films deposited over high aspect ratio trenches using Co 2 (CO) 8 as a precursor. The results show that the conformality of Co films is a strong function of temperature and process pressure. Lowering the pressure and temperature significantly improves the conformality. As the pressure decreases from 0.6 Torr to 0.2 Torr at 50 ? C , the bottom coverage of Co films over 0.2μm width trenches with an aspect ratio of 13 to 1 significantly increases to 85%. However, further increasing the temperature from 50 to 60 ? C at the pressure of 0.2 Torr degrades the bottom coverage to 14%. In contrast, the extremely low pressure of 0.03 Torr allows the excellent conformal deposition of Co films up to 70 ? C . This can be attributed to the suppression of homogeneous reaction in the gas phase, which can create the intermediate products with high sticking coefficient. In addition, the Co films deposited at 50 ? C show the low resistivity with negligible contamination. As a result, the newly developed Co process using MOCVD can be implemented into the next generation devices with complex shapes.