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극자외선 리소그라피용 마스크의 습식 및 건식 세정 공정 중 오염 입자의 흡착 및 제거 메커니즘
Researcher who has been awarded a research grant by Humanities and Social Studies Support Program of NRF has to submit an end product within 6 months(* depend on the form of business)
  • Researchers have entered the information directly to the NRF of Korea research support system
Project Number D00035
Year(selected) 2004 Year
the present condition of Project 종료
State of proposition 재단승인
Completion Date 2006년 07월 28일
Year type 결과보고
Year(final report) 2006년
Research Summary
  • Korean
  • EUV 리소그라피 마스크 표면의 세정에서의 나노 입자 흡착과 제거 거동에 대한 연구가 수행되었다. EUV 리소그라피는 차세대 리소그라피 공정 중의 가장 중요한 공정 중 하나로 인식되고 있다. 일반적으로 투과형 마스크가 리소그라피 공정에 사용되지만 EUV 리소그라피에서는 EUV 빛이 흡수되는 성질 때문에 반사형 마스크를 사용하게 된다. 또한 반사도를 유지시키기 위하여 pellicle을 사용하지 못하고 매 공정마다 마스크를 EUV 빛에 노출시켜야 하므로 마스크 세정 또한 중요한 공정 중의 하나로 이해되고 있다.
    종래에 사용되는 습식 화학액 세정 공정을 EUVL 마스크 세정에 적용할 수 있으나 습식 세정 화학액과 EUVL 마스크 박막 간의 화학 작용으로 인한 표면 손상이 발생할 수 있는 어려움이 있다. 이를 해결하기 위하여 본 연구에서는 새로운 건식 세정 방법 중 하나인 레이저 충격파 세정 공정을 적용하였다.
    실제 세정 공정을 수행하기 이전, 오염 입자와 EUV 마스크 표면 간의 interaction force를 계산함으로써 세정 효율을 예측해 볼 수 있다. 습식 조건에서는 DLVO 이론을, 그리고 일반 공기 중에서는 전통적인 van der Waals force와 JKR, 그리고 DMT 모델을 적용하여 전체 interaction force를 계산하였다. 계산 결과 Cr absorber layer가 분위기와 관계없이 가장 입자를 제거하기 어려울 것으로 예상되었으나 SiO2 buffer layer의 경우 Hamaker 상수와 상대적으로 negative한 제타포텐셜 때문에 가장 쉽게 세정이 이루어 질 것으로 계산되었다. 계산 결과를 검증하기 위하여 AFM의 cantilever에 silica, alumina 입자를 흡착시켜 각각의 EUV 리소그라피 마스크 표면과의 입자 부착력을 측정하였다. 측정 결과 측정한 입자 부착력과 계산 결과가 잘 일치함을 알 수 있었다.
    EUV 리소그라피 마스크 표면에서의 나노 입자 세정을 위해 레이저 충격파 세정 공정이 적용되었으며 세정 효율을 증가시키기 위하여 UV 레이저 또한 EUV 리소그라피 마스크 표면에 조사되었다. UV 레이저의 에너지와 레이저 충격파와 세정 표면간의 gap distance가 레이저에 의한 표면 손상을 일으키는 주된 요소로 밝혀졌으며 표면 손상을 최소화하기 위한 5 mJ UV 레이저 에너지, 5.5 mm gap distance가 최적 공정 변수로 도출되었다. 최적 공정 조건에서 Si capping, SiO2 buffer, 그리고 Cr absorber layer에 대한 나노 입자 제거 실험이 수행되었다. 50 nm 유기 오염 입자가 각각의 표면에서 성공적으로 제거되었으며 가장 높은 제거 효율은 SiO2 buffer layer에서 그리고 가장 낮은 제거 효율은 Cr absorber layer에서 각각 관찰되었다. 이 실험 결과는 앞선 입자 부착력의 결과에서 기인한 것으로 판단된다.
    EUV 리소그라피 마스크 표면에서의 나노 입자 제거 메커니즘은 UV 레이저는 photo chemical 효과에 의해 레이저 충격파 세정은 기계적인 효과에 의해 각각 설명될 수 있다. 유기 오염 입자는 photo chemical 효과 중 bond breaking 모델에 의해 입자 제거가 설명될 수 있으며 rolling removal mechanism이 레이저 충격파 세정의 중요 메커니즘으로 판단된다.
    Ru capping layer에 대한 EUV 빔의 reflectivity 측정이 실시되었다. 초기 63.9%의 reflectivity가 Ru capping layer에 조사되었으며 높은 표면 roughness를 갖는 Ru capping layer에서도 크게 변하지 않은 값이 관찰되었다. 이는 interfacial roughness 모델로는 설명할 수 없으며 removed multi layer에서 reflectivity가 크게 감소하지 않는 시뮬레이션 결과와 잘 일치하는 것을 알 수 있다.
  • English
  • The adhesion and removal behaviors of nano particles on the cleaning process of extreme ultraviolet lithography (EUVL) mask surfaces was investigated. EUVL has been one of the most promising techniques for the next generation lithography process. Reflective EUVL mask has no pellicle to maintain the high reflectivity even after EUV light irradiation. The various EUVL mask layer can be easily contaminated and the EUVL mask surface has to be cleaned every exposure level.
    Conventional wet chemical cleaning has been widely used in semiconductor process. However, the wet chemical including H2O2 can damage the thin EUVL mask surfaces. In this study, a new dry cleaning method, laser shock cleaning (LSC) was used to clean the each EUVL mask layers to prevent the surface damage induced from chemical reaction during convention wet chemical cleaning process.
    Before the cleaning process, the total interaction force was calculated between a particle and EUVL mask layers to expect the cleaning efficiency on each EUV mask layers in air and liquid atmosphere. Among the various EUV mask layers, Cr absorber layer was expected to be most difficult to remove the particles on surface in both air and liquid atmosphere. However, SiO2 buffer layer was considered to be easily cleaned due to its low Hamaker constant and relatively more negative zeta potentials. In order to confirm the calculated interaction force, the adhesion force between particle and EUVL mask layers was measured with AFM for silica and alumina particles. Measured adhesion forces and calculated interaction forces were well equivalent to each other.
    During the LSC of EUVL mask surface, the UV laser was used to enhance the removal efficiency. The 5 mJ UV laser and the 5.5 mm gap distance between the laser shock focus and EUVL mask surface were optimized to eliminate the surface damage. 4 nm Si capping, 100 nm SiO2 buffer and 70 nm Cr absorber layers were cleaned with LSC and UV laser irradiation. 50 nm organic PSL particles were successfully removed on the EUVL mask layers. The particle removal efficiency increased when LSC combined with UV exposure. The high cleaning efficiency over 98% was observed in SiO2 buffer layer due to its lower Hamaker constant. However, Cr absorber layer showed the lowest cleaning efficiency. It was noted that the highest adhesion force between particle and Cr absorber layer caused the lowest particle removal efficiency.
    Particle removal mechanism of UV laser and LSC were explained by photochemical effect and rolling removal mechanism, respectively. The bond breaking model of photochemical effect could explain the organic PSL particle removal on EUVL mask surfaces during UV laser irradiation. Modified rolling removal mechanism could explain the high removal efficiency on LSC.
    The reflectivity of EUV light on damaged Ru capping layer was not significantly reduced from initial 63.9 % in spite of the increased roughness after UV exposure. The maintenance of reflectivity could not explain by interfacial roughness model between Si and Mo layer. It was equivalent with the simulated reflectivity results as a function of removed multi layer.
Research result report
  • Abstract
  • The adhesion and removal behaviors of nano particles on the cleaning process of extreme ultraviolet lithography (EUVL) mask surfaces was investigated. EUVL has been one of the most promising techniques for the next generation lithography process. Reflective EUVL mask has no pellicle to maintain the high reflectivity even after EUV light irradiation. The various EUVL mask layer can be easily contaminated and the EUVL mask surface has to be cleaned every exposure level.
    Conventional wet chemical cleaning has been widely used in semiconductor process. However, the wet chemical including H2O2 can damage the thin EUVL mask surfaces. In this study, a new dry cleaning method, laser shock cleaning (LSC) was used to clean the each EUVL mask layers to prevent the surface damage induced from chemical reaction during convention wet chemical cleaning process.
    Before the cleaning process, the total interaction force was calculated between a particle and EUVL mask layers to expect the cleaning efficiency on each EUV mask layers in air and liquid atmosphere. Among the various EUV mask layers, Cr absorber layer was expected to be most difficult to remove the particles on surface in both air and liquid atmosphere. However, SiO2 buffer layer was considered to be easily cleaned due to its low Hamaker constant and relatively more negative zeta potentials. In order to confirm the calculated interaction force, the adhesion force between particle and EUVL mask layers was measured with AFM for silica and alumina particles. Measured adhesion forces and calculated interaction forces were well equivalent to each other.
    During the LSC of EUVL mask surface, the UV laser was used to enhance the removal efficiency. The 5 mJ UV laser and the 5.5 mm gap distance between the laser shock focus and EUVL mask surface were optimized to eliminate the surface damage. 4 nm Si capping, 100 nm SiO2 buffer and 70 nm Cr absorber layers were cleaned with LSC and UV laser irradiation. 50 nm organic PSL particles were successfully removed on the EUVL mask layers. The particle removal efficiency increased when LSC combined with UV exposure. The high cleaning efficiency over 98% was observed in SiO2 buffer layer due to its lower Hamaker constant. However, Cr absorber layer showed the lowest cleaning efficiency. It was noted that the highest adhesion force between particle and Cr absorber layer caused the lowest particle removal efficiency.
    Particle removal mechanism of UV laser and LSC were explained by photochemical effect and rolling removal mechanism, respectively. The bond breaking model of photochemical effect could explain the organic PSL particle removal on EUVL mask surfaces during UV laser irradiation. Modified rolling removal mechanism could explain the high removal efficiency on LSC.
    The reflectivity of EUV light on damaged Ru capping layer was not significantly reduced from initial 63.9 % in spite of the increased roughness after UV exposure. The maintenance of reflectivity could not explain by interfacial roughness model between Si and Mo layer. It was equivalent with the simulated reflectivity results as a function of removed multi layer.
  • Research result and Utilization method
  • 본 연구를 통한 연구 결과
    1. EUVL 마스크 세정에 대한 기초 연구
    2. 건식 레이저 세정 공정의 적용 및 우수한 제거 성능의 확인
    3. 실제 공정의 적용 가능성 확보
    연구실적
    1. SCI 저널 투고 2편
    2. 학술발표 4편
    활용방안
    1. 추후 개발될 다른 종류의 박막에 대한 기초 세정 성능 지표로 활용 가능
    2. 기존의 투과형 마스크 세정 공정에의 적용
  • Index terms
  • EUVL, Mask Cleaning, Particle Adhesion, Laser Cleaning
  • List of digital content of this reports
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