Characteristics of W thin film deposited by indirect inductively coupled plasma assisted sputtering

Tungsten (W) has a short electron mean free path (EMFP) of 19 nm and a high melting point (3673 K), and, therefore, is being actively studied as one of the next generation thin interconnector materials replacing Cu. In this study, DC magnetron sputtering of W thin film assisted by indirect inductively coupled plasma (ICP) (where, the ICP is located near the substrate) has been investigated for the deposition of 20 nm thick W thin films with a low resistivity and the results were compared with those deposited by direct ICP assisted DC magnetron (where, the ICP is located near the DC magnetron). The W thin films deposited with the indirect ICP assisted sputtering showed the continuous decrease of the W resistivity from 76.5 (0 W) to 22.2 (500 W) Ohm-cm with the increase of ICP power. In the case of W thin film deposited with direct ICP assisted sputtering, even though the resistivity was initially decreased with the ICP power, the resistivity was increased at high ICP powers due to the increased W surface roughness. The lower W resistivity at high ICP powers for the indirect ICP assisted DC sputtering was related to the change of crystal structure to BCC from A-15 and lower oxygen content in the film due to the higher ion flux to the substrate without increasing the surface roughness.