标题: | 氧化锡薄膜与P型氧化亚锡电晶体之研制与分析 Study on the Preparation of Tin-Oxides Films and Fabrication of P-type Tin-Monoxide Thin-Films Transistors |
作者: | 钟嘉文 林鸿志 黄调元 Zhong, Chia-Wen Lin, Horng-Chih Huang, Tiao-Yuan 电子研究所 |
关键字: | 氧化物半导体;薄膜电晶体;氧分压;氧化锡;二氧化锡;累积式退火;保护层;元件操作寿命;双闸极结构;oxide semiconductor;thin-film transistors;oxygen partial pressure;SnO;SnO2;cumulative annealing;passivation layer;long-term durability;double-gated structure |
公开日期: | 2017 |
摘要: | 在本论文中,我们成功地利用反应式直流磁控溅镀系统在改变氧分压条件制备三种类型的氧化锡薄膜,接着在低氧环境中对薄膜进行300度退火30分钟,在低氧分压(0.23 mTorr)的沉积条件中,退火后,从N型锡主导(Sn-dominant)转变成P型锡化亚锡主导(SnO-dominant)的氧化锡薄膜;在中氧分压区(0.33~0.51 mTorr)的沉积条件中,薄膜的成分皆为高阻态;在高氧分压(0.60 mTorr)的沉积条件中,薄膜的成分则为N型二氧化锡。本论文着重于P型氧化亚锡薄膜电晶体的制作与特性分析,因此我们选用上述低氧分压(0.23 mTorr)沉积条件来制备P型锡化亚锡薄膜,并采用背电极结构来制作薄膜电晶体。首先,探讨在低氧或真空环境退火对薄膜电晶体的电性影响,这两种退火条件下,都获得不错的元件特性,包括大于103的电流开关比、场效载子迁移率分别为3.97和4.66 cm2/V-s,这些初步结果相当接近过去文献中最好的成果。 为了更加瞭解退火时薄膜的转态过程,我们把刚完成制作的氧化锡薄膜电晶体进行累积式退火(cumulative annealing)的实验,每次15分钟的退火后进行元件电性与物性量测分析。元件特性从N型载子过多导致无法有效地闸控的状态,转变成高阻值通道,再转成P型的开关特性。藉由光学显微镜下观察通道层的变化,我们提出薄膜结晶过程的示意图来解释上述结构的转换。我们也探讨不同闸极氧化层(SiO2, HfO2, and Al2O3)对氧化锡薄膜结晶过程的影响。氧化锡薄膜电晶体使用SiO2作为闸极氧化层最先获得P型开关特性,接着是HfO2¬,Al2O3需要最长的退火时间。 此论文也探讨以二氧化矽与氮化矽作为P型氧化亚锡薄膜电晶体保护层的影响。电晶体之临界电压(threshold voltage, VTH) 在沉积保护层后往负的方向偏移,表示通道层的电洞浓度下降,我们归咎于电浆中氧或氮自由基与氧化亚锡之间的化学反应而生成些许N型二氧化锡。保护层也使得薄膜电晶体的次临界摆幅(subthreshold swing, S.S.)变好并延长元件操作的寿命。在保护层沉积温度为300度时,薄膜电晶体的开启电流较其他低温沉积的元件变小很多,我们认为P型氧化亚锡薄膜电晶体不能承受过多的热效应,要不然将生成N型二氧化锡导致元件特性劣化。 最后,我们建构独立双闸极P型氧化亚锡薄膜电晶体。当元件在双闸极(double gate, DG)操作下,对比于元件在单闸极操作下的饱和总电流其饱和电流提升25%,其原因为载子导通于通道中间区域,较远离通道介面处,载子受到较少的表面散射(surface scattering)。另外,双闸元件临界电压的调控性也获得证实。在波长370奈米照光测试下,此元件的上电极能有效地反射入射光,元件特性因此未受到照光影响。 In this dissertation, we’ve successfully prepared three types of SnOx films deposited at various oxygen partial pressures (PO) by a reactive DC sputtering system. After being annealed in a low O2-containing ambience at 300oC for 30 minutes, the state of the SnOx films deposited at low PO (0.23 mTorr) is changed from n-type Sn-dominant to p-type SnO-dominant, while the SnOx films deposited at medium (0.33~0.51 mTorr) and high PO (0.60 mTorr) are high-resistivity and n-type SnO2, respectively. From the above results, the films deposited at low PO (0.23 mTorr) were adopted for fabricating p-type TFTs with bottom-gated configuration. The impact of annealing ambiences on electrical characteristics of the SnOx TFTs is studied first. The devices annealed in either O2 or vacuum ambience show decent performance in terms of high Ion/Ioff (>103) and good field-effect mobility (3.96 and 4.66 cm2/V-s). These results are comparable to the best values ever reported in the literature. To gain more insights into the transformation in the structure of the SnOx channel films, the as-fabricated SnOx TFTs were treated with a series of cumulative annealing (CA) steps in O2 ambience. Duration of each CA step was 15 minutes. After being annealed for CA time of 45 minutes, operation of the annealed device is changed from non-gated, to high channel resistance, and finally to p-type. The channel region of the device is inspected by an optical microscopy (OM). Based on the observations, we propose a schematic model which describes the nucleation and crystallization processes of the channel film during the annealing. The model is also supported by the results of several material analyses which reveal that the film is gradually changed from n-type Sn-dominant to p-type SnO-dominant with increasing annealing. We also investigate the impact of different gate dielectrics (SiO2, HfO2, and Al2O3) on the nucleation and crystallization processes in the SnOx channel. As compared with the case of SiO2, the processes are retarded with the gate oxide of HfO2 and Al2O3. The latter case needs the longest annealing time to transform the channel into p-type. The influences of depositing a passivation layer (SiOx or a SiNx) on the characteristics of p-type SnOx TFTs are also studied. The VTH of the passivated devices is shifted and becomes more negative. This is owing to the interactions of O and N radicals in the plasma with the channel film which result in a reduction in hole concentration. The subthreshold swing of the passivated devices and the long-term durability are improved apparently. However, the on-state current is degraded significantly when the annealed devices were passivated at 300oC as compared to those passivated at lower temperatures. This implies excessive thermal budget would degrade the p-type SnOx film. Lastly, we’ve fabricated p-type SnOx TFTs with a double-gated structure. The result shows 25% improvement in saturation current of the device measured under the DG mode as compared with the sum of two individual single-gate modes is achieved. For DG-mode operation the carriers accumulating in the middle of the channel may suffer less from the surface scattering. Furthermore, effective tuning capability of VTH is demonstrated with the DG scheme. Under a light stressing test at 370 nm of wavelength, the electrical characteristics are not affected as the top gate effectively blocks the incident light. |
URI: | http://etd.lib.nctu.edu.tw/cdrfb3/record/nctu/#GT079811520 http://hdl.handle.net/11536/141626 |
显示于类别: | Thesis |