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- 주제어 : HfO_(2)-Al_(2)O_(3) thin film (검색결과 3 건)
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DC 마그네트론 스퍼터로 증착한 Al_(2)O_(3)/HfO_(2) 층형박막과 HfO_(2)-Al_(2)O_(3) 혼합박막의 물리적, 전기적 특성연구
HfO_(2)는 높은 유전상수와 Si기판 위에서 안정하게 생성되는 특성을 가지며, Al_(2)O_(3)는 결정화 온도가 높고, 산소확산계수가 낮으며, 높은 밴드갭의 특성을 가진다. 이러한 상호보완적인 HfO_(2)와 Al_(2)O_(3)의 특성을 이용하여 이를 소자의 게이트 유전막으로 적용하기 위해, 반응성 스퍼터링 방법으로 Al_(2)O_(3)/HfO_(2) 층형구조와 Al_(2)O_(3)-HfO_(2) 혼합구조의 박막을 증착하고, 이후 열처리 공정에 따른 물리적, 전기적 특성을 관찰하였다. Al_(2)O_(3)/HfO_(2) 층형구조 박막에서 열처리 온도에 따른 두 층의 구조변화는 거의 미미한 것으로 관찰되었으며, 증착 직후 상태에서는 비정질이 유지되다가 900℃의 온도로 열처리시 하부 HfO_(2)층의 부분결정화를 확인하였다. HfO_(2)-Al_(2)O_(3) 혼합구조 박막에서는 전체 HfO_(2)-Al_(2)O_(3) 박막내 Al_(2)O_(3)의 조성은 타겟파워로 조절하였으며, HfO_(2)-Al_(2)O_(3) 박막 내 Al_(2)O_(3)의 농도가 증가함에 따라 결정화 온도가 점차로 증가하는 것을 확인하였다. 그러므로, HfO_(2) 박막 내 Al_(2)O_(3)가 분포하게 되면 Al_(2)O_(3)의 농도증가에 따른 HfO_(2)-Al_(2)O_(3) 박막의 향상된 결정화 온도를 관찰할 수 있다. Al_(2)O_(3)/HfO_(2) 이중박막구조의 열처리에 따른 미세구조변화를 관찰한 결과, 열처리에 의한 Al_(2)O_(3)층과 HfO_(2)층의 계면을 통한 두 물질의 상호확산을 확인하였으나, 전체적인 이중 Al_(2)O_(3)/HfO_(2) 박막구조는 그대로 유지되었다. 그리고, 본 실험의 방법으로 증착한 Al_(2)O_(3) 박막은 산소확산장벽의 역할을 거의 하지 못하는 것으로 판단된다. HfO_(2)-Al_(2)O_(3) 혼합박막구조에서 전체 박막내의 HfO_(2)와 Al_(2)O_(3)는 어떠한 새로운 화합물을 형성하지 않고, 각각의 물질이 따로 mixture의 형태로 존재함을 확인하였다. 그리고, HfO_(2)-Al_(2)O_(3) 박막 내에 포함되어 있는 Al_(2)O_(3)가 산소확산 장벽 향상의 역할을 거의 하지 못하는 것으로 관찰되었다. HfO_(2)-Al_(2)O_(3) 혼합박막구조의 캐패시턴스-전압과 전류-전압을 측정한 결과, 약 ∼18의 k값을 산출하였으며, 열처리 온도가 상승함에 따라 중간계면층의 두께 증가에 기인하는 향상된 누설전류 값을 관찰하였다. Recently, high-k materials are under consideration as replacements for SiO_(2). Among some metal oxides, HfO_(2) is an attractive candidate due to their high dielectric constant and thermal stablity in contact with silicon. And Al_(2)O_(3) is an another attractive candidate because Al_(2)O_(3) can remain amorphous at temperature higher than 900℃. In this study, we investigated the thermal stability of the HfO_(2) based films with Al_(2)O_(3). HfO_(2)/Al_(2)O_(3) laminate and HfO_(2)-Al_(2)O_(3) thin films were grown on p-type Si(100) by DC magnetron sputtering, and composition of the HfO_(2)-Al_(2)O_(3) thin films was controlled by target power. After the annealing, HfO_(2)/Al_(2)O_(3) laminate structure was maintained, and Al_(2)O_(3) layer was not useful for blocking oxygen diffusion due to interfacial layer growth. Crystallization temperature of the HfO_(2)-Al_(2)O_(3) thin film which has 16% Al_(2)O_(3) was delayed up to 900℃, and as concentration of the Al_(2)O_(3) in Al_(2)O_(3)-HfO_(2) thin films increases, thermal stability improved. As an annealing temperature increases, HR-TEM analyses of the all the Al_(2)O_(3)-HfO_(2) films show the increased interfacial layer thickness. Therefore, our results show the addition of Al_(2)O_(3) is not useful for blocking oxygen diffusion through the HfO_(2)-Al_(2)O_(3) thin film. From the C-V and I-V measurements, calculated dielectric constant of the HfO_(2)-Al_(2)O_(3) thin films was ∼18, and as an annealing temperature increases, the leakage current of the films was improved.
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Device and Process Design Based on Functional Oxide Thin Films for Advanced Memory Applications
In this work, we present an integrated approach for implementing high-performance and high- reliability memory technology by precisely controlling the material-specific electrical properties of functional oxide thin films and applying them to the structural design of memory devices. In particular, representative oxide materials such as HfO2, Al2O3, and InGaZnO (IGZO) were applied to various roles such as ferroelectric layers, insulating layers, and channel layers, respectively, and the memory performance parameters such as charge storage characteristics, bias stability, and data retention characteristics of the devices were experimentally verified by controlling the process conditions and the stacked structure, and the possibility of applying them to memory devices was verified. First, the crystallization behavior and ferroelectric characteristic changes were analyzed by introducing an Al2O3 capping layer on an undoped HfO2 thin film. The crystal phase transition and polarization switching characteristics according to the temperature conditions of the HfO2 atomic layer deposition (ALD) process were evaluated, and it was confirmed that the polarization characteristics, leakage current, and endurance of the ferroelectric capacitor with the metal- insulator-ferroelectric-metal (MIFM) structure were significantly improved through the stabilization of the ferroelectric phase, which is the orthorhombic phase (o-phase). This suggests an effective methodology that can implement excellent ferroelectric characteristics only through interface control without separate doping. Second, by designing the IGZO thin film as a double-layer (DL) structure and depositing it with different oxygen partial pressures (PO2) during the sputtering process, we attempted to improve the performance in a 2-transistor-0-capacitor (2T0C) DRAM cell. The heterogeneous interface formed between the upper and lower IGZO layers served as an additional conduction path, and the storage efficiency and retention time were increased by advantageously utilizing the parasitic capacitance through geometric optimization of the active area. Through this, we propose a performance improvement method of 2T0C DRAM cells by combining structural design and material control. Finally, we designed a HfO2/Al2O3 nanolaminate gate insulator (GI) structure to secure electrical reliability while utilizing high-K dielectrics in the thin film transistor (TFT) constituting the 2T0C DRAM cell. By periodically laminating HfO2 and Al2O3 through a 150 °C ALD process, we simultaneously achieved crystallization suppression and interface defect reduction, which led to low-voltage operation and improved bias stress stability. When applied to an actual 2T0C DRAM cell, it was successfully verified by showing excellent long-term retention behavior. These results provide guidelines for the design of insulators for low-temperature oxide transistor- based memories.
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