Double-layered Structure of Surface Modification of Low-k Dielectrics Induced by He Plasma
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Double-layered Structure of Surface Modification of Low-k Dielectrics Induced by He Plasma Ken-ichi Yanai, Tadayoshi Hasebe, Kouji Sumiya, Seiki Oguni, and Kazuhiro Koga Consortium for Advanced Semiconductor Materials and Related Technologies (CASMAT), 1-280, Higashi-koigakubo, Kokubunji-shi, Tokyo 185-0014, Japan ABSTRACT Surface modification of a p-SiOC film induced by Helium (He) plasma was investigated using various measurements. Differential Fourier transform infrared absorption (FT-IR) spectra and the etch-depth measurements with the immersion in the mixed hydrofluoric acid (HF) indicate that the almost all of Si-CH3 bonds are broken in the modification layer, resulting in carbon-depletion, an SiO2-like composition. The x-ray photoelectron spectroscopy (XPS) measurements at different take-off angles reveal that the modified surface forms a double-layered structure, a thin carbon-rich top layer (about 1 nm thick) on a thick carbon-depletion layer (about 20 nm thick) with the irradiation of He plasma over 300 W. Atomic force microscopy (AFM) observations show that the modified surface is the smoothest in the case of the carbon-depletion surface. INTRODUCTION One of key issues in Cu/low-k interconnect is to control and design interfaces between a low-k layer and its stacks. Thus a surface of a low-k layer is usually treated by He plasma to improve adhesion to the cap SiO2 film, avoiding the delamination failure in the Cu-CMP process [1, 2]. For the precise control of this treatment, it is essential to understand comprehensively the mechanical properties of the surface modification layer on the basis of its microscopic characteristics involving chemical bonds and surface morphology of the modification layer. There are many reports about the characterization of the modification layers of a low-k film induced by the various plasmas [3 – 5]. However the studies were limited about the plasmas of etching or ashing processes and the discussion was focused only on the electrical properties, mainly on the degradation of the dielectric constant. In this paper, the modification layers of p-SiOC films treated with the different He plasma powers were characterized using various methods. The changes in chemical bonds and atomic composition of the modification layer were analyzed from differential FT-IR and XPS measurements respectively. The layered structure of the modified surface was estimated from
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the etch depth with the immersion in the mixed HF solution and XPS at different take-off angles, 90˚ and 10˚. The morphology of the modified surface was observed by AFM. EXPERIMENT Samples are p-SiOC films (k=3.0) of about 90-nm thickness, deposited on p-type Si wafers by the plasma chemical vapor deposition using tri-methyl-silane and oxygen gases. The plasma power, gas pressure and substrate temperature in the deposition process, are 1100 W, 4.0 Torr and 350 degrees respectively. The surfaces of these films are treated with He plasma of different powers under the gas pressure of 6.0 Torr at the substrate temper
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