Constraints of the Corning on Plugs of W Film in W Chemical Mechanical Planarization

Abstract

The constraints of corning on the W plug in W chemical mechanical planarization ͑CMP͒ were investigated by controlling the corrosion behavior and static etch rate of the W film. Poly͑acrylic amide͒ ͑PAM͒ was used as an inhibitor to decrease the static etch rate of the W film. The interaction between PAM and the surface of the W film was determined by potentiostatic measurement using a potentiometer and by force measurement using an atomic force microscope ͑AFM͒. AFM results revealed that the adlayer of PAM formed on the W film, which prevented the oxidation of the W film. Consequently the addition of PAM suppressed the corning defect on the W plug in a W CMP test that used patterned wafers.According to memory device integration, pattern structures are becoming more and more complicated, and more than 10 layers of different metals, polymers, barriers, and oxides are stacked above the silicon. 1 Tungsten ͑W͒ is commonly used in contemporary memory devices as a wiring material for contact/via fill applications. 2 W is commonly deposited by chemical vapor deposition ͑CVD͒, 3 after which W plugs in metal interconnection are formed through chemical mechanical planarization ͑CMP͒. 4,5 In the W CMP process, W deposited by CVD should be polished to improve the lithography in multilevel device fabrication and to offer global planarization. 2,6 During CMP the tungsten-polishing mechanism is decided by both the formation of a passive oxide layer by slurry chemicals and the subsequent polishing by a slurry abrasive. 3 Kaufman et al. described the polishing mechanism of W CMP as the repeated formation and removal of the WO 3 layer. 2 The WO 3 layer is easily removed by the abrasive because the WO 3 layer is softer than the native W layer. 7 Therefore the oxidizer in the CMP slurry plays an important role in the high removal rate. 8 However when exposed tungsten is removed by CMP, the oxidizer in the CMP slurry attacks part of the seam on the W plug, 9 which is formed by CVD. The interaction between the oxidizer and the seam on the W plug results in the formation of a pit on the W plug, which is called a corning defect. Corning defects in memory devices have caused serious problems, such as electrical device degradation and leakage current in capacitor structures. This is true especially as the critical dimension of current semiconductor devices decreases below 70 nm. Therefore suppression of corning defects should be achieved to complete the formation of W plugs. Kishii et al. reported that W plugs could be formed without etching holes in seams by a MnO 2 slurry. 9 However the use of a MnO 2 slurry is improper for the formation of the W plug because the removal rate of the MnO 2 slurry is 10 times less than that of a commercial slurry based on fumed silica particles. Therefore a new approach is needed to suppress the corning defects. In this study, we considered the electrochemical properties of a W film as a critical factor to reduce its static etch rate and suppress the corning defects. Thus an attempt to control the potenti...

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