Tungsten Corrosion during Wet Cleaning Process in Multilevel Metallization

(Journal of the Korean Institute of Chemical Engineers)

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Tungsten Corrosion during Wet Cleaning Process in Multilevel Metallization

Kang Sup Shin and Won Gyu Lee^†

System IC R&D Center, Hynix Semiconductor Inc., 1, Hyangjeong-dong, Hungduk-gu, Cheongju-si 361-725, Korea

JReceived 31 March 2001; accepted 5 July 2001)

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Abstract−In multilevel metallization process, when tungsten plugs have been exposed by misalignment between metal lines and via plugs, tungsten plug could be easily corroded in alkali solution due to positive charging into metal layers from ions generated by plasma. In this study, we have found that photoresist ashing process among several plasma processes was a main cause of positive charging. Here are results for reducing or eliminating tungsten corrosion: Choosing microwave-type plasma asher showed the better results than RF-type for reducing corrosion opportunity of tungsten. Oxygen in plasma ambient was highly ionized which leaded positively charging of metal lines during plasma photoresist ashing process. However, gas species containing hydrogen atoms, i.e. H₂, H₂O and N₂/H₂ mixture, showed the reducing effect of positive charging by capturing or neutralizing activity of hydrogen atom in oxygen ion rich environment. And also the effect of dielectric hard mask deposited over metal layer on the reduction of positive charging could be confirmed.

Key words: Tungsten Corrosion, Alkali Solution, Via, Positive Charging, Multilevel Metallization, Plasma Ashing Process, Tungsten Plug

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†To whom correspondence should be addressedP E-mail: leewk@hynix.com

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Fig. 9. Intact tungsten plug after solvent strip when adapting silicon oxide film of 1,500 Å thick on metal line to hard mask.

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