Chemical-mechanical Polishing of Copper Using Molybdenum Dioxide Slurry
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Slurries containing molybdenum oxide abrasives (MoO2, isoelectric point ∼pH 2) with potassium iodate (KIO3) as the oxidizing agent were used to polish copper disks and films, yielding relatively high removal rates. The relatively high copper removal rates observed were due to the in situ generation of I2 by the reaction between KIO3 and MoO2. The surface quality of the polished Cu films, however, was very poor with surface roughness values as high as 140 nm. A second polishing step using a dilute colloidal silica suspension containing H2O2, benzotriazole, and glycine at pH 4 improved the post-polish surface quality, final surface having surface roughness values as low as 0.35 nm.
I. INTRODUCTION
The demand for smaller, faster devices has led the integrated circuit (IC) industry to continually increase the device density on a chip while simultaneously reducing feature dimensions. Copper interconnects and multilevel metallization (MLM) schemes were introduced to meet some of these challenges.1,2 With the employment of MLM in the ultra-large-scale-integrated (ULSI) circuit fabrication technology, repeated planarization of different surface layers with tolerance of a few nanometers is required. Presently, chemical-mechanical planarization (CMP) is the only technique that can meet this requirement.3–6 The damascene process3 is currently used in conjunction with CMP in the fabrication of multilevel copper interconnects for advanced logic and memory devices. In this fabrication scheme, trenches are first patterned in a dielectric material at each level. After the barrier, seed and copper fill are sequentially deposited in the dielectric trenches;7 CMP is used to remove excess copper and create a planar surface for subsequent fabrication of additional levels of metallization. CMP involves removal of material by a combined action of chemical and mechanical means. Chemicals aid in material removal by modifying the surface film while abrasion between the particles in the slurry, pad, and the modified film facilitates mechanical removal. Material removal solely involving chemicals usually leads to
a)
Present address: Portland Technology Development Group, Intel, Hillsboro, OR. b) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2005.0305 J. Mater. Res., Vol. 20, No. 9, Sep 2005
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uniform etching of both elevated and recessed regions and does not level the topography. The synergistic interplay between chemical and mechanical components in the slurry is often the key to effective planarization. Polishing slurry therefore forms one of the prime components in a typical CMP process. One important requirement of successful copper CMP slurry is a high polish rate leading to short copper overburden polishing times while minimizing dishing and erosion and other surface defects. As these requirements are becoming more stringent with the continually diminishing feature sizes, much effort is being devoted to discover new and better abrasives an
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