Effective Defect Control in TiN Metal Hard Mask Cu/Low-k Dual Damascene Process

Metallic hard masks (MHM) are routinely employed in Cu/low k dual damascene (DD) etching, but can create defectivity problem. N2 plasma post-etch treatment (N2PET) based on high substrate temperature has been developed to provide effective TiFx residue reduction and MHM defect prevention without low k damage and productivity concerns. Strong gains in surface de-fluorination with substrate temperature and N2PET time was determined. SLIC, XPS, SEM data show 90% reduction of F residue on TiN and no defects on pattern at optimized N2PET. AES and EELS data show that "TiFx" defects are actually TiOx crystals covered by TiFx residue catalyzing the crystal growth. N2PET de-fluorination and defect growth are in focus of this study. An alternative approach in preventing defect growth by surface passivation in CF4/C4F8 etch chemistry was also studied. Both methods, N2PET cleaning and surface passivation, provide effective defect control in TiN MHM Cu/low-k DD etch process.