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dc.description☞ 이 논문은 저자가 원문공개에 동의하지 않은 논문으로, 도서관 내에서만 열람이 가능하며, 인쇄 및 저장은 불가합니다.-
dc.description.abstractAs the device dimension shrinks, the enhancement of carrier mobility by strain has been investigated to improve device performance. The strain changes the electronic band structure, such as the carrier repopulation and band splitting between sub-valleys, resulting in a change in carrier mobility. In a semiconductor, there are different scattering mechanisms such as Coulomb scattering, phonon scattering, and surface scattering and these scattering events influence the mobility of carrier. Matthiessen’s rule is widely used to determine the mobility associated to different scattering mechanisms. However, it is not exact and it results in large inaccuracies in the mobility extraction. Instead of Matthiessen’s rule, MRT (Momentum Relaxation Time) method should be used to calculate the phonon mobility more exactly. However, in the author’s knowledge, no MRT models suited for total mobility including Coulomb scattering, phonon scattering, and surface scattering have been presented in the literature until now. Also it has been known for a long time that deformation potential to calculate the components of the relaxation-time tensor is a constant. Recently, it has been reported that deformation potential should be dependent on surface electric field. The aim of this dissertation is to propose a physically based total mobility model using the new concept of effective deformation potential for device-simulation tools. Moreover, non-parabolic model for (110) orientation have been introduced, which are used to predict the electron mobility on (110) orientation more accurately. Analytical expressions for the strain-induced valley splitting and effective mass changes of the (100)/<110> also have been studied. Since then, various optimization technologies are investigated to enhance the electron mobility induced by uniaxial strain using our proposed total mobility model. Effects of strain on electron mobility are examined with one-dimensional Schrödinger-Poisson solver. In order to optimize the substrate doping concentration (Nsub) for strain-induced electron mobility enhancement of tri-gate nMOSFETs, the strain-induced electron mobility enhancement on the (100)/<110> which is used as top channel of tri-gate nMOSFETs can be increased at low Nsub, while the electron mobility enhancement on the (110)/<110> which is used as side channel of tri-gate nMOSFETs can be increased at high Nsub. Moreover, our calculated results suggest that vertical compressive stress is more efficient to maintain the strain-enhanced electron mobility than longitudinal tensile stress in high temperature condition. It is also revealed that, to optimize the combined effect of uniaxial and biaxial strain, the longitudinal tensile and transverse compressive uniaxial stresses are advantageous and vertical stress is not helpful for biaxially-strained n-MOSFET. Conclusively, our results should be helpful in understanding the strain-induced electron mobility characteristic and these optimization technologies should be advantageous for strain-induced high electron mobility of tri-gate nMOSFETs fabricated on a (100) wafer orientation.;소자의 집적도가 증가함에 따라, 소자의 성능을 개선시키기 위하여 strain을 이용한 carrier의 mobility 개선기술이 주목 받게 되었다. 소자에 strain을 인가하면 electron band 구조가 바뀌게 되면서 subband간 carrier 분포에 영향을 주어서 carrier의 mobility가 바뀌게 된다. 반도체에는 Coulomb scattering, phonon scattering, surface roughness scattering과 같이 서로 다른 mechanism을 갖는 scattering들이 존재하고, 이러한 scattering의 특성을 결합 시켜 carrier의 total mobility를 계산하기 위하여 통상 Matthiessen’s rule이 많이 사용된다. 그러나 최근 Matthiessen’s rule의 부정확성에 대한 연구들이 진행되면서 그 대안으로 MRT (Momentum Relaxation Time) method가 제시되고 있다. 하지만 이러한 MRT method로 coulomb scattering, phonon scattering, surface roughness scattering을 모두 고려한 mobility model은 기존 연구에서 발표된 적이 없다. 또한 기존에는 deformation potential을 mobility 계산을 위한 단순 상수로 계산하였으나, 이것이 electric field와 연관이 있다는 사실이 알려졌음에도 불구하고 이를 mobility 계산에 model로 적용한 사례가 없었다. 본 논문에서는 MRT 방법을 이용하여 Coulomb scattering, phonon scattering, surface roughness scattering이 모두 고려된 total electron mobility를 계산할 수 있는 새로운 model을 제시하였다. 또한 electron mobility 특성을 더욱 정확하게 예측하기 위하여, deformation potential이 electric field 특성을 반영할 수 있는 effective deformation potential 특성을 modeling 하여 사용하였으며, (110) orientation 기판에서의 non-parabolic 특성 또한 modeling 하여 사용하였다. 이와 더불어, (100)/<110> 조건에서 strain에 의한 valley split energy 변화량 및 effective mass의 변화량을 계산할 수 있는 analytical 수식을 연구하였다. 이러한 model들을 1-D Poisson-Schrödinger equation solver에 접목시켜 strain에 의해 electron의 mobility 특성을 예측, 분석하였으며, 이러한 simulation tool을 이용하여 electron의 mobility 개선도를 극대화 하기 위한 여러 동작 조건 내에서 uniaxial strain 최적화 인가 방안을 제안하였다. 먼저, tri-gate nMOSFET의 substrate doping concentration (Nsub) 조건을 최적화 하기 위한 연구를 진행한 결과, tri-gate nMOSFET의 top channel 영역이 되는 (100)/<110> 조건의 경우 Nsub가 낮을수록 strain에 의한 electron mobility 개선도를 증가시킬 수 있다는 것을 확인하였다. 반면 tri-gate nMOSFET의 side channel 영역이 되는 (110)/<110> 조건의 경우 Nsub가 높을수록 strain에 의한 electron mobility 개선도를 증가시킬 수 있었다. 또한 (100)/<110> 조건의 경우, 고온에서도 strain effect를 유지하기 위해서는 longitudinal tensile stress 보다는 vertical compressive stress가 더 유리하다는 것을 확인할 수 있었다. 반면, uniaxial과 biaxial strain을 결합한 multi strain으로 electron mobility를 극대화 하기 위해서는 vertical stress보다는 longitudinal tensile stress와 transverse compressive와 같은 uniaxial stress가 더욱 효과적이라는 것을 확인할 수 있었다. 이상과 같은 연구 결과는 strain을 이용한 electron 이동도 개선 mechanism 이해에 도움을 줄 것이다. 또한 본 논문에서 제시한 strain 최적화 방안은 electron의 mobility 향상에 기여할 것으로 예상한다.-
dc.description.tableofcontentsI. INTRODUCTION 1 A. Mobility enhancement technology 1 B. Strained silicon technology 4 C. Organization 10 II. Electron scattering equation for simulation 13 A. MRT (Momentum relaxation time) Method 13 B. Coulomb scattering 16 C. Phonon scattering 17 D. Surface roughness scattering 21 E. Effective deformation potential 22 F. Non-parabolic characteristic of (110) orientation 25 III. Stress effects on the electronic structure 28 A. Sub-band engineering for electron mobility 31 B. Physics of strained Si 35 C. Transformation of coordinate system 42 D. Stress effect calculation 47 E. Stress effect simulation procedure 53 IV. Mobility enhancement via strain engineering 56 A. Substrate doping concentration effect 56 B. Temperature dependency 66 C. Multi stress 71 V. CONCLUSIONS 78 REFERENCES 81 APPENDIX : MATLAB Code 89 ABSTRACTS IN KOREAN 111-
dc.format.extent4050066 bytes-
dc.publisher이화여자대학교 대학원-
dc.titleAnalysis of Uniaxial Strain Technologies for Electron Mobility Enhancement using Self-Consistent Poisson-Schrödinger Equation Solver-
dc.typeDoctoral Thesis-
dc.title.translated1-D Poisson-Schrödinger Equation Solver를 이용한 uniaxial strain 기술의 Electron 이동도 개선에 관한 연구-
dc.format.pageviii, 113 p.-
dc.identifier.major대학원 전자공학과- 8-
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