Feasibility of Detecting Barrier Layer to Low-k Transition in Copper Cmp Using Raman Spectroscopy
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FEASIBILITY OF DETECTING BARRIER LAYER TO LOW-K TRANSITION IN COPPER CMP USING RAMAN SPECTROSCOPY S. Kondoju1, C. Juncker1, P. Lucas1, S. Raghavan1, P. Fischer2, M. Moinpour3 and A. Oehler4 1 Department of Materials Science and Engineering, University of Arizona, Tucson, AZ 2 Intel Corp., Components Research, Portland, OR 3 Intel Corp., Fab Materials Operation, Santa Clara, CA 4 Intel Corp., Fab Materials Operation, Portland, OR
In copper CMP, transitions from copper to barrier as well as barrier to dielectric layer are typically sensed in situ using an optical reflectance technique. Spectroscopic techniques such as Raman, which allow monitoring the vibrational modes of silicon and low-k layers, have interesting potential for detecting these transitions. In this paper the use of Raman spectroscopy in detecting in situ removal of barrier layers from CDO materials is reported. Intensities of Raman peaks characteristic of Si-Si vibrations from Si substrate and C-H vibrations from low-k materials have been used for monitoring CDO layer thickness and detecting removal of Ta overlayer. An abrasion cell is integrated with a Raman spectrometer to demonstrate the feasibility of Raman monitoring in-situ. Capabilities and limitations of the Raman spectroscopic method are discussed. INTRODUCTION Introduction of low-dielectric constant (k) materials, replacing silicon dioxide, has reduced the time delay (RC delay) and enhanced the performance of integrated circuits (IC) significantly. These low-k materials, which have a significant amount of organic character, are characterized by a dielectric constants smaller than 3. In 2000, IBM announced the development of Cu interconnects for the 130-nm node with SiLK™, a low-k dielectric material developed by the DOW Chemical with a dielectric constant (k) of about 2.7. SiLK™ is a polyphenylene based material and typically applied using a spin-coating technique. Chemical vapor deposited low-k materials containing C, H, O and Si, generally referred to carbon-doped oxides (CDO), are now commercially available under the trade names Black Diamond and Coral. These appear to be the materials of choice for current generation copper dual damascene based interconnect schemes. The fabrication of copper interconnect structures is achieved by chemical mechanical planarization (CMP) steps. In copper CMP, the overabundance of copper is first removed, stopping on the barrier layer such as Ta. The barrier layer is then removed, creating a structure of copper lines embedded in a dielectric matrix. The transition of Cu to Ta as well as Ta to the dielectric material is sensed by an optical technique based on reflectance [3]. The use of spectroscopic techniques that are sensitive to silicon, carbon and hydrogen vibrations provides the possibility of monitoring carbon based low-k layers and detecting transition associated with the removal of Ta barrier layers. Since CMP is carried out in aqueous media, an IR spectroscopic technique is not very desirable due to the strong interference of the water si
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