대한전자공학회논문지SD (Journal of the Institute of Electronics Engineers of Korea SD)

대한전자공학회 (The Institute of Electronics and Information Engineers)
권호 표지

(Ba, Sr)TiO$_3$ 커패시터의 Thermally Stimulated Current분석

Thermally Stimulated Current Analysis of (Ba, Sr)TiO$_3$ Capacitor

  • 김용주 (한국과학기술원 전자전산학과 전기 및 전자) ;
  • 차선용 (한국과학기술원 전자전산학과 전기 및 전자) ;
  • 이희철 (한국과학기술원 전자전산학과 전기 및 전자) ;
  • 이기선 (충남대학교 물리학과) ;
  • 서광석 (고려대학교 재료금속공학부 재료공학과)
  • 발행 : 2001.05.01
PDF 다운로드
⟨ 이전 논문 다음 논문 ⟩

초록

고유전 (Ba, Sr)TiO/sub 3/ (BST) 박막을 이용한 DRAM storage capacitor의 저전계 영역에서의 전하손실을 발생시키는 커패시터의 누설전류는 유전완화전류와 진성 누설전류로 이루진다고 알려져 있다. 특히, 기가급 DRAM의 동작 전압(~IV)에서 유전완화전류가 진성 누설전류에 비해 훨씬 크기 때문에 이에 대한 심도 있는 연구가 필요하다. 본 연구에서는 thermally stimulated current (TSC) 측정법을 BST 박막에 처음으로 적용하여 트랩의 에너지 level 및 공정변화에 따른 트랩 밀도의 상대적 평가를 하였다. 그리고, 기존에 사용되던 전류-전압(I-V) 측정이나 전류-시간(I-t) 측정과 비교 및 분석함으로써 유전완화 전류의 원인을 규명하고 TSC 측정법의 신뢰성을 살펴보았다. 먼저 안정적인 TSC 측정을 위해 전계, 시간, 온도 및 승온속도에 따른 polarization condition을 알아보았다 이 조건을 이용한 TSC 측정으로부터 BST 박막에서의 트랩의 energy level이 0.20(±0.01) eV와 0.45(±0.02) eV임을 알 수 있었다. Rapid thermal annealing (RTA)을 이용한 후속 열처리에 따른 TSC 측정을 통하여 이 트랩들이 산소결핍(oxygen vacancy)에 기인함을 확인할 수 있었다. MIM BST 커패시터의 열처리에 대한 TSC 특성은 전류-전압(I-V) 및 전류-시간(I-t) 특성과 같은 경향성을 보인다. 이것은 TSC 측정이 BST 박막내의 트랩을 평가하는데 있어서 매우 효과적인 방법이라는 것을 보여준다.

It has been known that the leakage current in the low field region consists of the dielectric relaxation current and intrinsic leakage current, which cause the charge loss in dynamic random access memory (DRAM) storage capacitor using (Ba,Sr)TiO$_{3}$ (BST) thin film. Especially, the dielectric relaxation current should be seriously considered since its magnitude is much larger than that of the intrinsic leakage current in giga-bit DRAM operation voltage (~IY). In this study, thermally stimulated current (TSC) measurement was at first applied to investigate the activation energy of traps and relative evaluation of the density of traps according to process change. And, through comparing TSC to early methods of I-V or I-t measurement and analyzing, we identify the origin of the dielectric relaxation current and investigate the reliability of TSC measurement. First, the polarization condition such as electric field, time, temperature and heating rate was investigated for reliable TSC measurement. From the TSC measurement, the energy level of traps in the BST thin film has been investigated and evaluated to be 0.20($\pm$0.01) eV and 0.45($\pm$0.02) eV. Based on the TSC measurement results before and after rapid thermal annealing (RTA) process, oxygen vacancy is concluded to be the origin of the traps. TSC characteristics with thermal annealing in the MIM BST capacitor have shown the same trends with the current-voltage (I-V) and current-time (I-t) characteristics. This means that the TSC measurement is one of the effective methods to characterize the traps in the BST thin film.

키워드

참고문헌

  1. P. Bhattacharya, K. H. Park and Y. Nishioka, 'Control of Grain Structure of Laser-Deposited $(Ba,Sr)TiO_3$ Films to Reduce Leakage Current', Jpn. J. Appl. Phys. 33, pp. 5231-5234, 1994 https://doi.org/10.1143/JJAP.33.5231
  2. Y. P. Wang and T. Y. Tseng, 'Electronic defect and trap-related current of $(Ba_{0.4}Sr_{0.6})TiO_3$ thin films' J. Appl. Phys. 81, p.6762, 1997 https://doi.org/10.1063/1.365218
  3. Y. Fukuda, K. Aoki, K. Numata and A. Nishimura, 'Current-voltage characteristics of Electron-Resonance sputter-deposited $SrTiO_3$ tine films', Jpn. J. Appl. Phys. Vol.33, pp 5255-5258, 1994 https://doi.org/10.1143/JJAP.33.5255
  4. D. H. Kwak, B. T. Jang, S. Y. Cha and H. C. Lee, 'Calculation of Trap Densities between BST/Pt Interface From Capacitance-Voltage Characteristics and Rapid Thermal Annealing Effect for DRAM capacitor Application', The 4th Korean Conference on Semiconductors, pp, 347-349, 1997
  5. S. Y. Cha and H. C. Lee, 'Platinum Bottom Electrodes Formed by Electron-Beam Evaporation for High Dielectric Thin Films', Jpn. J. Appl. Phys. 34, pp. 5220-5223, 1995 https://doi.org/10.1143/JJAP.34.5220
  6. David E. Kotecki, 'Integrated Ferroelectrics', 16, pp. 1-19, 1997 https://doi.org/10.1080/10584589708013025
  7. H. M. Chen, J. M. Lan, J. L. Chen and J. Y. Lee, 'Time-dependent and trap-related current conduction mechanism in ferroelectric $Pb(ZrxTi1-x)O_3$ films', Appl. Phys. Lett. 69, p 1713, 1996 https://doi.org/10.1063/1.118006
  8. M. Meier, S. Karg, K. Zuleeg, W. Brutting and M. Schwoerer, 'Determination of trapping parameters in poly(p-phenylenevinylene) light-emitting devices using thermally stimulated currents', J. Appl. Phys. 84, pp. 87-92, 1998 https://doi.org/10.1063/1.368004
  9. Z. Wu and M. Sayer, 'Defect structurures and fatigue in ferroelectric PZT thin filmes', ISAF, pp. 244-247, 1992
  10. W. L. Warren, G. E. Pike, B. A. Tuttle and D. Dimos, 'Polarization-induced trapped charge in ferroelectrics', Appl. Phys. Lett. 70, pp. 2010-2012 https://doi.org/10.1063/1.118805
  11. P. Blood and J.W. Orton, 'The Electrical Characterization of Semiconductors : Majority Carriers and Electron States', Academic Press, pp. 466-473, 1992
  12. P. Braunlich, 'Thermally Stimulated Relaxation in Solids', Springer-Verlag, pp. 161-166, 1979
  13. H. Jang, B. T. Jang, S. Y. Cha and H. C. Lee, 'Electrical Conduction Mechanisim of $(Ba,Sr)TiO_3$ Thin Film Capacitor in Low Electric Field Region', 대한전자공학회논문지 제 36권 D편 제6호, pp. 522-529, 1999
  14. Y. Fukuda, K. Numata, K. Aoki and A. Nishimura, 'Origin of Dielectric Relaxation for $Ba_{0.5}Sr_{0.5}TiO_3$ Thin-Film Capacitor', Jpn. J. Appl. Phys. Vol. 35, pp. 5178-5180, 1996 https://doi.org/10.1143/JJAP.35.5178
  15. J. Gerblinger and H.Meixner, 'Electrical conductivity of sputtered films of strontium titanate', J.Appl.Phys. Vol. 67 (12), pp. 7453-7459, 1990 https://doi.org/10.1063/1.344535