Effects of Plasma Surface Treatment on the Self-forming Barrier Process in Porous SiOCH
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1079-N03-10
Effects of Plasma Surface Treatment on the Self-forming Barrier Process in Porous SiOCH Seung-Min Chung1, Junichi Koike1, and Zsolt Tökei2 1 Dept. of Materials Science, Tohoku University, 6-6-11 Aoba, Aramaki, Aoba-ku, Sendai, 9808579, Japan 2 IMEC, Kapeldreef 75, B-3001 Leuven, Belgium ABSTRACT Self-forming barrier process was carried out on a porous low-k material with the Cu-Mn alloys. The effects of various surface treatments were investigated in the sample having a pore size of 0.9 nm and a porosity of 25%. Before and after annealing, samples were analyzed in cross section with transmission electron microscopy (TEM) and energy dispersive x-ray spectroscopy (EDS). Concentration profile was also analyzed with time-of-flight secondary ion mass spectroscopy (ToF-SIMS). The results indicated the penetration of Cu into the low-k interior during deposition, followed by the segregation of Cu at the low-k/Si interface during subsequent annealing. Although a diffusion barrier layer was formed and no further Cu penetration was not observed during annealing, initial Cu penetration in the deposition process was detrimental and should be prevented by restoring the plasma damage on the low-k surface. INTRODUCTION As the device size shrinks to 32 nm node and beyond, the formation of a thin and conformal barrier layer has become a bottleneck in producing reliable interconnect structures. Various deposition methods have been investigated in combination with the search for new barrier/adhesion materials [1]. Assurance of reliability requires prevention of Cu penetration into a low-k layer and adhesion between the low-k and the diffusion barrier layer [2, 3]. Recently, a self-forming process has been successfully demonstrated in a dual-damascene structure by using a Cu-Mn alloy as a seed layer [4-6]. Although this process appears to be desirable for a future technology node, the previous works used plasma TEOS oxide as a dielectric layer and little information is available for advanced low-k dielectric materials. In the present work, we employed the self-forming barrier process with a Cu-Mn alloy film on a low-k material. Since low-k surface is modified upon plasma exposure, we investigated the effects of various surface treatments on diffusion barrier formation behavior. EXPERIMENT Porous low-k films of SiOCH (k=2.5) were synthesized with plasma enhanced chemical vapor deposition (PECVD) on Si wafers. Pore size and porosity were 0.9 nm and 25%, respectively. The low-k films were subjected to various plasma surface treatments in order to understand their influences on the self-forming barrier process with the Cu-Mn alloy. The types of plasma treatment and the corresponding gases are listed in Table 1. Etching was performed with a CH4CH2F2 based plasma to investigate the influence of plasma damage during via and trench etching. After etching, either an oxygen or a N2/H2 plasma treatment was carried out. It is expected that the application of the oxygen plasma will lead to surface oxidation and form a thin oxide layer,
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