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Low-pressure aluminum planarization for sub-0.5-um contact and via holes

A novel Al-0.5%Cu planarization technology for interconnects is presented using a low pressure Al physical vapor deposition process (or MaxFillTM), capable of filling high aspect ratio (A/R >= 3) via holes at wafer temperatures of less than or equal to 400 degree(s)C. Excellent Al film reflectivity and surface smoothness are achieved due to hardware modifications to the sputter tool and a modified process flow. A high level of vacuum integrity and cleanliness of the system dramatically reduces the time required to fill 0.35 micrometers via holes with aspect ratios of 3, resulting in a throughput in the excess of 24 wafers per hour. In the present work, a comparison of the film morphology between the traditional Two Step Planarization and MaxFillTM processes is presented, which shows the improved grain orientation, reflectivity and film roughness of the MaxFillTM process. The smooth surface morphology of the MaxFillTM process allows easier alignment during subsequent photolithography. In addition to the film properties, electrical results are presented that show that this new deposition technique can planarize 0.35 micrometers structures with A/R's >= 3 with via resistance values that are lower by a factor of 2.5 than comparable chemically vapor deposited W plug vias.