다층금속배선공정에서 금속배선과 하부의 비아 플러그의 오정렬로 텅스텐이 노출되는 경우에 앞선 플라즈마 공정에서 발생하는 양이온에 의한 전하축적으로 금속배선층의 전위가 상승되어 플러그 텅스텐이 알칼리 용액에서 부식이 된다. 이와 같은 플라즈마 공정수행에서 기인되는 전하축적에 의한 부식은 금속식각 후 감광막 제거공정이 주원인이었다. 전하축적에 의한 비아 플러그내의 텅스텐의 부식현상은 전하축적의 주요 단계로 확인된 감광막 제거공정에서 RF형 보다 마이크로웨이브형 플라즈마 감광막 제거장치를 사용하는 것과 플라즈마 발생 시 기체조성 조절에서 산소에 수소성분이 함유된 기체를 첨가하여 사용하는 경우에 부식감소 효과를 나타냈다. 또한 비아 플러그 상부의 금속배선막 상부에 절연막인 실리콘산화막을 하드마스크(hard mask)로 사용하는 경우도 텅스텐 부식 방지효과가 있었다.

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.

Tungsten Corrosion Alkali Solution Via Positive Charging Multilevel Metallization Plasma Ashing Process Tungsten Plug

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