투명 산화물 박막 트랜지스터의 마스크 절감 및 특성 향상 방법에 관한 연구

Abstract

투명 산화물 반도체(transparent oxide semiconductors, TOSs)는 전기적 전도성과 광학적 투명성을 동시에 갖는 물질이다. 이들의 전통적인 응용분야는 평판 디스플레이, 발광 다이오드, 태양전지 및 이미지 센서 등의 투명 전도막 이었다. 최근 들어 이러한 물질을 투명 박막 트랜지스터(thin film transistors, TFTs)와 같은 전자소자의 박막재료로서 그 응용분야를 확대하기 위한 연구가 활발히 이뤄지고 있다. 본 연구의 목적은 미래 전자기기의 핵심화두로 떠오르고 있는 투명 산화물 반도체를 박막 트랜지스터의 활성 채널층(active channel layer)에 적용하고 상용화 측면에서 가장 중요한 요소인 마스크 절감을 통한 새로운 공정방법을 확보하는데 있다. 본 연구에서는 산화물 반도체를 증착하기 위해 마그네트론 스퍼터 장비를 이용하였다. 산화아연(zinc oxide, ZnO) 박막의 증착 시 수소 도핑 및 플라즈마 후처리를 통해 박막 내 캐리어 밀도(carrier concentration)를 조절하였으며, 전세계적으로 희소금속으로 잘 알려져 있는 인듐이 포함된 산화물 반도체를 대체하기 위해 실리콘이 도핑된 산화아연 박막에 대한 연구를 수행하였다. 증착된 박막들에 대하여 다양한 분석기법을 통해 전기적, 광학적, 구조적인 물성 분석을 수행하였다. 또한 그레이톤 마스크(gray-tone mask, GTM)를 적용한 투명 박막 트랜지스터 제작 방법에 대한 연구를 통해 두 개의 포토마스크 (photomask) 만으로도 소자제작이 가능하도록 하였으며, 소자 특성의 신뢰성을 확보하기 위하여 패시베이션층(passivation layer)을 고려한 단순화된 소자공정 방법을 도출하였다. 본 연구에서 제작한 산화물 기반 투명 박막 트랜지스터는 낮은 공정 온도에서도 우수한 소자 특성을 확보할 수 있기 때문에 LCD 및 OLED 등의 평판 디스플레이 패널의 구동소자로서 활용되어온 기존의 비정질 실리콘 박막 트랜지스터를 충분히 대체할 수 있을 것으로 사료된다. 또한, 본 연구에서는 비정질 실리콘 박막 트랜지스터 제작 시 적용되어온 복잡한 공정에 비해 혁신적으로 단순화된 새로운 소자 공정을 개발함으로써 제조 단가 및 시간을 획기적으로 개선하여 생산 효율 향상에 기여하는 바가 클 것으로 기대된다.| Transparent oxide semiconductors (TOSs) are materials that exhibit electrical conduction and optical transparency. The traditional applications of these materials are transparent conducting oxides (TCOs) in flat-panel displays, light-emitting diodes, solar cells, and imaging sensors. Significant research has been driven of late to extend the state-of-the-art applications of TOSs, such as thin-film transistors (TFTs).The purpose of this thesis was to obtain the ideal properties for the application of TOSs as active channel layers of transparent oxide TFTs, which is the core topic of the future transparent electronics. The RF magnetron sputter system was used to deposit oxide semiconductors. To control the carrier concentration of ZnO thin films, an experiment was conducted on in-situ hydrogen doping and plasma post-treatment. In addition, novel silicon-doped ZnO (SZO) thin films alternating the TOSs including indium, well known as a rare-earth element, were investigated. A detailed material analysis was carried out through various characterizations of the electrical properties, chemical composition, optical properties, crystal structure, and surface morphology. To simplify the complex process and to maximize the effectiveness of the mass production, a novel two-photomask process for the fabrication of transparent IGZO-based TFTs using a gray-tone mask (GTM) was successfully developed. A new GTM design was suggested, in which the PR on the active channel layer was formed in gray tone, and the drain electrode area was extended to the pixel electrode area. The measured electrical characteristics of the transparent IGZO-based TFTs fabricated using a GTM showed that they worked well functionally. Ultimately, the transparent oxide TFTs including ZnO, SZO, and IGZO-based TFTs were demonstrated to be promising devices applicable to future transparent electronics.; Transparent oxide semiconductors (TOSs) are materials that exhibit electrical conduction and optical transparency. The traditional applications of these materials are transparent conducting oxides (TCOs) in flat-panel displays, light-emitting diodes, solar cells, and imaging sensors. Significant research has been driven of late to extend the state-of-the-art applications of TOSs, such as thin-film transistors (TFTs).The purpose of this thesis was to obtain the ideal properties for the application of TOSs as active channel layers of transparent oxide TFTs, which is the core topic of the future transparent electronics. The RF magnetron sputter system was used to deposit oxide semiconductors. To control the carrier concentration of ZnO thin films, an experiment was conducted on in-situ hydrogen doping and plasma post-treatment. In addition, novel silicon-doped ZnO (SZO) thin films alternating the TOSs including indium, well known as a rare-earth element, were investigated. A detailed material analysis was carried out through various characterizations of the electrical properties, chemical composition, optical properties, crystal structure, and surface morphology. To simplify the complex process and to maximize the effectiveness of the mass production, a novel two-photomask process for the fabrication of transparent IGZO-based TFTs using a gray-tone mask (GTM) was successfully developed. A new GTM design was suggested, in which the PR on the active channel layer was formed in gray tone, and the drain electrode area was extended to the pixel electrode area. The measured electrical characteristics of the transparent IGZO-based TFTs fabricated using a GTM showed that they worked well functionally. Ultimately, the transparent oxide TFTs including ZnO, SZO, and IGZO-based TFTs were demonstrated to be promising devices applicable to future transparent electronics.