Journal of the Korean Crystal Growth and Crystal Technology (한국결정성장학회지)

The Korea Association of Crystal Growth (한국결정성장학회)
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Defect analysis of calcium fluoride single crystal substrates with (100) and (111) orientation

(100) 및 (111) 배향을 갖는 CaF2 단결정 기판의 결함 분석

  • Ye-Jin Choi (Department of Advanced Materials Engineering, Dong-Eui University) ;
  • Min-Gyu Kang (Department of Advanced Materials Engineering, Dong-Eui University) ;
  • Gi-Uk Lee (Department of Advanced Materials Engineering, Dong-Eui University) ;
  • Mi-Seon Park (Department of Advanced Materials Engineering, Dong-Eui University) ;
  • Kwang-Hee Jung (Department of Advanced Materials Engineering, Dong-Eui University) ;
  • Hea-Kyun Jung (SELIG) ;
  • Doo-Gun Kim (Korea Photonics Technology Institute) ;
  • Won-Jae Lee (Department of Advanced Materials Engineering, Dong-Eui University)
  • Received : 2024.01.26
  • Accepted : 2024.02.13
  • Published : 2024.02.29
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Abstract

The CaF2 single crystal has notable characteristics such as a large band gap (12 eV), excellent transparency over a wide wavelength range, low refractive index and dispersion. Due to these outstanding properties, CaF2 single crystal has considered as a promising material for short-wavelength light sources in recent lithography processes. However, there is an inherent birefringence of the material at 157 nm and the resulting aberration can be compensated for through the combination of the (100) plane and the (111) plane. Therefore, it is necessary to investigate the characteristics according to the plane. In this study, we analyzed crystallinity, optical properties of commercial CaF2 single crystal wafers grown by the Czochralski method. In particular, through chemical etching under various conditions, it was confirmed that the shape of etch pits appears differently depending on the plane and the shape and array of specific etch pits affected by dislocations and defects were examined.

다양한 광학 재료에 사용되는 CaF2 단결정은 밴드갭(12 eV)이 크고, 넓은 파장영역에서 투과율이 뛰어나며 낮은 굴절률과 분산을 가지는 특징이 있다. 이런 우수한 특성을 바탕으로 최근 리소그래피(Lithography) 공정에서 짧은 파장의 광원에서도 사용가능한 렌즈의 재료로 CaF2 단결정이 주목받고 있다. 다만 CaF2의 경우 157 nm에서 재료 고유의 복굴절이 존재하며, 이로 발생한 수차는 (100)면과 (111)면의 결합을 통해 보상할 수 있기 때문에 면 방향에 따른 특성을 조사하는 것이 필요하다. 이 연구에서는 초크랄스키(Czochralski) 방법으로 성장하여 상용화 된 CaF2 단결정 웨이퍼를 이용하여 면 방향에 따른 결정성, 광학적 특성을 분석하였다. 특히 chemical etching을 통해 etch pit의 형태가 면 방향에 따라 다르게 나타나는 것을 확인하였고, 결함 분석을 통해 결정 내 전위의 배열과 결함의 존재가 etch pit 형상에 영향을 주는 것을 확인하였다.

Keywords

Acknowledgement

이 연구는 2024년 정부(산업통상자원부)의 재원으로 한국산업기술평가관리원의 지원(20017105)과 교육부의 재원으로 한국기초과학지원연구원 국가연구시설장비진흥센터의 지원(No. 2019R1A6C1010045)과 2024년 정부(산업통상자원부)의 재원으로 한국산업기술진흥원의 지원(P0012451, 2024년 산업혁신인재성장지원사업)의 지원을 받아 수행된 연구입니다.

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