Influence of Cu Seed Deposition Temperature on Electroplated Cu Texture Formation in Damascene Structures
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5Conexant Systems Inc., 4311 Jamboree Road, Newport Beach, CA 92660. ABSTRACT The deposition temperature of the PVD Cu seed layer has a critical impact on the subsequent electroplated Cu film. Sheet resistance transformation of electroplated Cu on 50'C seeded Cu was more than twice faster than on 150'C seeded Cu. X-ray pole figure analysis on a 3 mm x 3 mm dense array of 0.35 gm Cu damascene lines at spacing of 0.4 pim revealed significant grain orientation differences between directions parallel and perpendicular to the Cu lines. It was observed that for both seed process temperatures, the (II I) pole figures showed a sharper texture parallel to the trench direction than to the perpendicular direction. After annealing at 450'C for 30 minutes, a (511) secondary orientation emerged and the (111) texture along the trench direction became even sharper. Perpendicular to the trench, the (111) texture split into two peaks after anneal, exhibiting near fiber texture. The deviation of the two splits from normal was 2.40 tilt towards the trench wall indicating strong interaction between trench sidewall and electrodeposited Cu inside the trench. The (111) pole figure analysis also revealed a 20% contribution of Cu growth directly from the side walls.
Although the pole figure pattern of
150'C seeded sample resembles that of the 50'C seeded sample, the (111) fiber texture of a 50'C seeded sample was always stronger and sharper. INTRODUCTION Recent studies have found that electroplated Cu films undergo significant film transformation at room temperature, in which the film sheet resistance is reduced 20% and average grain size grew from an initial 0.1 ptm to several microns [1-4]. Since a Cu seed layer is needed prior to Cu electroplating to initiate Cu nucleation during the plating process, the microstructure of the seed layer is expected to be a controlling factor for the morphology of as-plated Cu films. Studies have found that the PVD Cu seed layer deposition temperature has a profound impact on the Cu electroplating film properties. A temperature change from 150'C to 50'C resulted in a 19% resistance reduction in damascene Cu lines [5]. The difference in resistance was attributable to the seed layer microstructure where the average grain size of a 50'C seed was 400 A with a RMS of 11 AI compared to the average grain size of 1000 A with a RMS of 37 A for the 1501C seed [5]. Using an array of diagnostic analytical tools including XRD, 4-point probe, and stress gauge, we characterized Cu films electroplated on seed layers deposited at 50'C and 150'C PVD susceptor temperatures. It was found that the seed layer deposition temperature influenced the electroplated Cu film microstructure significantly and resulted in large differences in 393 Mat. Res. Soc.
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