The Impact of Dielectric Films and Post-Metal Etch Wet Treatment on Charge-Induced Corrosion of Tungsten Vias
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The Impact of Dielectric Films and Post-Metal Etch Wet Treatment on Charge-Induced Corrosion of Tungsten Vias Szetsen Lee1, and Chi-Jung Ni2 1 Department of Chemistry, Center for Nano-technology, and R&D Center for Membrane Technology, Chung Yuan Christian University, 200 Jongbei Road, Chugli, 32023, Taiwan 2 Module Technology Development, Winbond Electronics Corporation, 9 Li Hsin Road, Hsinchu, 30078, Taiwan ABSTRACT The prevention of charge-induced corrosion of tungsten vias after metal etch has been studied with several types of commonly used wet chemical solutions and two kinds of dielectric film materials, silicon dioxide and silicon oxynitride. It was found that one of the solutions, leaving essentially no polymer residue on metal lines, could effectively prevent corrosion of tungsten vias. Other solutions either produced minor residues or severe sidewall erosion on metal lines. This study has shown that the combination of wet treatment with oxynitride as the dielectric charge shielding film was as effective as other conventional methods for preventing tungsten vias corrosion. However, for metal lines capped with silicon dioxide, significant sidewall erosion, surface roughness, and polymer residue were observed. Chemical reaction mechanisms are proposed for the preservation of tungsten vias after metal etch. INTRODUCTION Due to tighter design rules for higher pattern densities, the photolithographical misalignment between vias and metal lines can cause the corrosion of tungsten (W) vias after metal etch. As shown in figure 1, W is exposed because vias are not fully covered by overlying metal lines. Although copper damascene approaches can solve such a problem, aluminum technology is still widely adopted in memory products due to cost issues. In post-metal etch wet cleaning procedures, it is known that under high pH and high temperature conditions, even residues such as ñ chloride (Cl ), can enhance the W corrosion processes [1-4]. Wet treatment is a common remedy for metal corrosion problem [4-6]. For example, corrosion can be avoided by treating wafers with a low pH dilute HNO3 solution combined with electron beam to discharge metal lines prior to immersion in a polymer strip solvent [7].
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Figure 1. Corrosion of W in vias.
It has also been suggested that the antenna effect and the oxygen-stripping process are responsible for plasma charge-induced W corrosion [7,8]. Various techniques have been employed to prevent W corrosion [1,2,4,7]. Modifying the gas compositions in plasma is a common approach [5,8,9]. Downstream ozone (O3) ashing process has been adopted for photoresist strip after metal etch [9]. Addition of H2 or H2O in the photoresist stripping step is also found to be effective in preventing charge build-up [5]. Metal lines capped with dielectric materials such as silicon oxynitride (SiOxNy) is another option [10,11]. Dielectric materials can serve as chargeshielding layers to prevent plasma charge-induced damage during metal etch. In this study, several types of solutions were us
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