Texture Evolution in Al(Cu) Interconnect Materials
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Texture Evolution in Al(Cu) Interconnect Materials C.E. Murray and K.P. Rodbell IBM T.J. Watson Research Center, Yorktown Heights, NY 10598 ABSTRACT An investigation of the microstructural evolution of Al(Cu) thin films deposited on a variety of interlevel dielectric (ILD) layers was performed. A combination of X-ray texture measurements and scanning electron microscopy (SEM) was employed to link the texture behavior of the as-deposited Al(Cu) films at different thicknesses to the observed morphological development within the films. Three regimes of texture were revealed, corresponding to (1): Al(Cu) island growth and individual island coalescence, (2): fully coalesced film and the onset of grain growth and (3): extensive grain growth. The first and last of these regimes exhibited offset (111) texture, in which the maximum diffracted intensity from Al (111) is offset from the substrate normal. However, the position of maximum offset texture differed between the first and third stages of growth, indicating that two different mechanisms were responsible. The offset (111) texture observed in the third regime of Al(Cu) film microstructure was due to the faceting of grain surfaces. The time required for the films to reach these three stages depended on the effective diffusivity of the Al atoms on the ILD surfaces, which differed in chemistry and topography. INTRODUCTION As microelectronic device dimensions shrink, the first stages of microstructural evolution within the metallization can play a greater role in the ultimate microstructure of the interconnects. The need for thinner films and more complex structures places greater demands on the amount of material required for coalescence and conformal coverage of the underlying geometries. The use of interlevel dielectric (ILD) layers, necessary in the construction of multilevel circuitry, alters the deposition surface conditions which impacts the adatom nucleation density and subsequent island coalescence of the overlying Al(Cu) films. Previous studies [1-3] have demonstrated that roughness of the deposition surface affects the Al(Cu) film texture. In this study, we address the variation in the evolution of Al(Cu) texture deposited on a variety of interlevel dielectrics (ILD), with differing chemistries and roughnesses. By examining the morphology of island or Volmer-Weber growth of Al(Cu) on ILD’s, we are able to link measured x-ray texture information to the observed microstructure within the Al(Cu) films. EXPERIMENTAL Five types of interlevel dielectric (ILD) layers were deposited on 200 mm diameter Si (100) wafers. Silicon nitride (Si3N4) films were created using a low pressure chemical vapor deposition (CVD) furnace process through a combination of ammonia (NH3) and dicholorsilane (SiH2Cl2) at 7600 C. Silane oxide films were produced through a pyrolytic oxidation of silane (SiH4) at 4500 C. Phosphosilicate glass (PSG) was deposited through a simultaneous pyrolysis of silane (SiH4) and phosphine (PH3) gases in an oxygen atmosphere at 4300 C. The resultant SiO2 films c
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