미세 Cu 배선 적용을 위한 SiNx/Co/Cu 박막구조에서 Co층이 계면 신뢰성에 미치는 영향 분석
Effect of Co Interlayer on the Interfacial Reliability of SiNx/Co/Cu Thin Film Structure for Advanced Cu Interconnects
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비메모리 반도체 미세 Cu배선의 전기적 신뢰성 향상을 위해 SiNx 피복층(capping layer)과 Cu 배선 사이 50 nm 두께의 Co 박막층 삽입이 계면 신뢰성에 미치는 영향을 double-cantilever beam (DCB) 접착력 측정법으로 평가하였다. DCB 평가 결과 SiNx/Cu 구조는 계면접착에너지가 0.90 J/m2이었으나 SiNx/Co/Cu 구조에서는 9.59 J/m2으로 SiNx/ Cu 구조보다 약 10배 높게 측정되었다. 대기중에서 200oC, 24시간 동안 후속 열처리 진행한 결과 SiNx/Cu 구조는 0.93 J/m2으로 계면접착에너지의 변화가 거의 없는 것으로 확인되었으나 SiNx/Co/Cu 구조에서는 2.41 J/m2으로 열처리 전보다 크게 감소한 것을 확인하였다. X-선 광전자 분광법 분석 결과 SiNx/Cu 도금층 사이에 Co를 증착 시킴으로써 SiNx/Co 계면에 CoSi2 반응층이 형성되어 SiNx/Co/Cu 구조의 계면접착에너지가 매우 높은 것으로 판단된다. 또한 대기중 고온에서 장시간 후속 열처리에 의해 SiNx/Co 계면에 지속적으로 유입된 산소로 인한 Co 산화막 형성이 계면접착에너지 저하의 주요인으로 판단된다.
Abstract
The effect of Co interlayer on the interfacial reliability of SiNx/Co/Cu thin film structure for advanced Cu interconnects was systematically evaluated by using a double cantilever beam test. The interfacial adhesion energy of the SiNx/Cu thin film structure was 0.90 J/m2. This value of the SiNx/Co/Cu thin film structure increased to 9.59 J/m2. Measured interfacial adhesion energy of SiNx/Co/Cu structure was around 10 times higher than SiNx/Cu structure due to CoSi2 reaction layer formation at SiNx/Co interface, which was confirmed by X-ray photoelectron spectroscopy analysis. The interfacial adhesion energy of SiNx/Co/Cu structure decreased sharply after post-annealing at 200oC for 24 h due to Co oxidation at SiNx/Co interface. Therefore, it is required to control the CoO and Co3O4 formation during the environmental storage of the SiNx/Co/Cu thin film to achieve interfacial reliability for advanced Cu interconnections.
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