Development of a Robust KIO3 Tungsten CMP Process
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ABSTRACT A production worthy, Tungsten Chemical Mechanical Polish (CMP) process using a commercially available K10 3 slurry was developed, characterized, and tested for sub-0.35pm multilevel interconnect fabrication. The effects of pre-tungsten CMP process on tungsten polish are reported in detail. A head-to-head comparison of the optimized K10 3 process with the standard Fe(N0 3)3 process is described. Critical CMP tool parameters (process and hardware) were flexed using statistically valid experimental designs. The advantages and disadvantages of a post tungsten polish, oxide buff, are discussed. Across-wafer non-uniformity, specifically the enhanced polish rate of tungsten at the wafer edge, was significantly reduced with the optimized process parameters and hardware setup. Also, an automated endpoint system was utilized and a set of robust endpoint algorithms were developed to minimize the amount of oxide loss during tungsten CMP processing. Finally, the positive effects of the optimized KIO 3 tungsten CMP process on interconnect integration and die yield are reported. INTRODUCTION As circuit density increases in VLSI technology, Chemical Mechanical Polishing (CMP) of dielectric material has been widely utilized in the semiconductor manufacturing flow for planarization purpose. However, results from shrinking device geometry have also shown that Al step coverage in contacts and vias limits interconnect design [1]. To ensure sufficient Al
step coverage, sloped or wet/dry processing for vias or low-aspect-ratio vias are necessary. Conventional processing therefore places restrictions on circuits packing density. The difficulties met using these traditional processes lead to their replacement with high-aspectratio, anisotropically etched vias and contact holes and use of chemical vapor deposited (CVD) tungsten (W) to form plugs [2]. Following the CVD W deposition, a blanket W removal process is required. A plasma etchback process has been used for blanket W removal in the early process flow due to availability of the equipment and process chemistry [2 - 5]. However, the W plasma etchback process has inherited several problems due to its design: (1) high defect density due to the gas used in the plasma, such as SF 6 , which is a highly polymer generating gas. (2) Due to the poor selectivity to oxide by using SF6 plasma chemistry, the process requires high selectivity of W to liner metal - usually TiN. (3) Additional overetch is required to compensate for etch nonuniformity. This results in severe W recess in the plug area. (4) severe loading effect on plug recess, due to pattern density. Because the problems associated with W plasma etchback process are inherited in its chemistry and process design, it was difficult to resolve them [2-5]. Therefore, an alternative process - metal chemical mechanical polishing - has been proposed and studied extensively in the last several years [6-12]. With the maturing equipment and consumable sets, the W CMP process is proven to be better in terms of defectivity [6], controlling
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