Effects of Dielectric Roughness on Texture of Both PVD Seed Layers and EP Copper

Abstract

The ability to control the crystallographic orientation of both the seed layer and the electroplated copper grains is important in obtaining highly reliable Cu interconnects for ultra-large scale integration (ULSI) circuitry. One of the factors controlling film texture is the roughness of the deposition surface. In this paper the effects of dielectric roughness on the crystallographic texture of physical vapor deposited (PVD) copper seed layers and, subsequently, on the texture of electroplated (EP) copper have been investigated. Six relevant interlevel dielectric materials were examined: tetraethyloorthosilicate (TEOS), borophosphosilicate glass (BPSG), silane oxide, silicon nitride, SiLKTM (from the Dow Chemical Corporation), and polysilicon were deposited on 200 mm (001) Si wafers. The RMS surface roughness of these dielectric layers, measured by AFM, ranged from 0.32 nm to 20.51 nm. Texture was analyzed on a dedicated x-ray diffractometer equipped with a two dimensional detector collecting incomplete pole figures with a 1.0 degree resolution in pole figure space. The orientation distribution functions (ODF) were calculated using the arbitrary defined cells method and the volume fractions of major fiber texture components were derived from the ODF. The predominant texture components of the PVD and EP copper were (111) and (511) fiber. It was found that the volume fraction of (111) fiber decreased as the dielectric surface roughness increased. One exception was with the SiLKTM dielectric, which produced significantly weaker texture than other dielectrics with similar surface roughness. The copper films deposited on polysilicon, which possessed the roughest deposition surface of all the dielectric films had a random texture. Finally, a mixture of strong (111) and (511) fiber textures of EP copper was achieved on dielectric underlayers with smoother surfaces. The results demonstrate that the deposition surface roughness plays an important role in establishing the texture in overlying PVD and EP Cu films. The texture of PVD and EP copper may serve as a useful indicator of the underlayer roughness.