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Abstract
Topography of tungsten should be assured at a minimum through chemical mechanical planarization (CMP) in the metal gate structures (e.g., buried gates, replacement metal gates) and via contact in the middle of line (MOL) process for sub−7 nm semiconductor applications. However, excessive tungsten dissolution during the CMP process that results from high oxidizer concentrations and acidic atmospheres results in poor tungsten topography. In this study, we report a novel strategy to improve the tungsten topography by suppressing tungsten dissolution via coordination complex formations between picolinic acid and tungsten oxide. With 1.5 wt% picolinic acid for the inhibitor, the dissolution rate of tungsten was dramatically attenuated, and improved topography with a Ra value of 7.8 nm were demonstrated while validating CMP removal rate.
Highlights
Tungsten has been used as a filling material for semiconductor structures such as buried metal gates and contact via holes in the semiconductor process due to its great conductivity and gap filling ability [1,2,3]
After tungsten deposition by chemical vapor deposition (CVD), a chemical mechanical planarization (CMP) process is necessary because the inherent characteristics of tungsten result in topographic features with widths of approximately 60 to 120 nm and heights of 50 to 80 nm [1,3]
As devices evolve from the planar DRAM structures to next-generation vertical structures and design rules shrink to sub 48 nm contact poly pitch (CPP) in logic devices, the number of tungsten CMP processes increased from four to six times, and topography removal should be controlled to below
Summary
Tungsten has been used as a filling material for semiconductor structures such as buried metal gates and contact via holes in the semiconductor process due to its great conductivity and gap filling ability [1,2,3]. In this regard, understanding the dissolution kinetics and modulating excessive dissolution of tungsten films are necessary to achieve high surface flatness with improved topography. In the tungsten CMP process, hydrogen peroxide (H2 O2 ) is used as an oxidant to oxidize the tungsten surface to enable a high removal rate [4,5,6,7]. Since there is a trade-off between the removal rate and dissolution of tungsten when using hydrogen peroxide, it is necessary to develop a new approach that can both suppress dissolution and secure a high tungsten removal rate [8]. The existing approaches have a limitation in preventing the tungsten dissolution because it is torn off by mechanical friction during the CMP process, and as a result, improving topography through modulating tungsten dissolution is insufficient
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