Influence of Chemical-Mechanical Polishing Process on Time Dependent Dielectric Breakdown Reliability of Cu/Low-k Integr
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1157-E05-02
Influence of Chemical-Mechanical Polishing Process on Time Dependent Dielectric Breakdown Reliability of Cu/Low-k Integration Yohei Yamada and Nobuhiro Konishi Micro Device Division, Hitachi, Ltd., 6-16-3, Shinmachi Ome-shi, Tokyo 198-8512, Japan ABSTRACT The effects of defects caused by Cu chemical-mechanical polishing (CMP) on time-dependent dielectric breakdown (TDDB) in a damascene structure incorporating a low-k interlevel dielectric layer were investigated experimentally. Comb line capacitor structures were prepared with one of three types of defects (rough Cu surface corrosion, Cu depletion, or crevice corrosion) and stressed at 3.2 to 6.2 MV/cm at 140°C. The first two defects had an insignificant effect on the TDDB characteristics while crevice corrosion at the edges of wires significantly degraded them. Investigation of the effects of Cu oxidation during post-CMP cleaning on the TDDB characteristics revealed that the formation of a non-uniform oxide layer accompanying deionized water rinsing was due to the dissolution of Cu oxide during the post-CMP cleaning process. When a barrier metal slurry containing a soluble inhibitor was used, non-uniform oxide formation on the Cu surfaces during post-CMP cleaning degraded the TDDB characteristics. These results demonstrate the importance of uniform Cu oxidation during post-CMP cleaning for improving the TDDB characteristics.
INTRODUCTION As integrated circuit device density continues to increase and circuit line widths continue to shrink, a low-dielectric-constant (low-k) interlayer and low-resistivity copper (Cu) metallization in the back end of line interconnects are becoming increasingly important in determining device performance. This interlayer and metallization reduce interconnect resistance capacitance delay, cross-talk noise, and power consumption. However, the long-term reliability of low-k dielectric materials is rapidly becoming a critical technical challenge. Low-k time-dependent dielectric breakdown (TDDB) is one of the most important reliability-related issues faced during development of Cu/low-k structures, because low-k materials generally have lower intrinsic breakdown strength than SiO dielectric materials [1–4]. One factor affecting this reliability is the integrity of the diffusion barrier/low-k interface after chemical-mechanical polishing (CMP). A previous study of the effect of the solution used for post-CMP cleaning on the TDDB characteristics [5] showed that, when a barrier metal slurry with a water-soluble inhibitor is used, the characteristics are significantly affected by the type of solution used. We have now investigated the effects of the CMP process on the TDDB characteristics. Copper corrosion is a critical factor in the Cu metallization process. Severe corrosion can significantly reduce the wafer yield and even minor corrosion can lead to reliability problems. We first investigated the effects of rough Cu surface corrosion, Cu depletion, and crevice corrosion on the TDDB characteristics. Next, we examined the effect
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