基于薄膜晶体管应用的功能薄膜AIN和ZnO的生长与特性研究

【作者】 梁俊华；

【导师】 刘旭； 郭冰；

【作者基本信息】 浙江大学 ， 光学工程， 2006， 硕士

【摘要】 作为下一代光电子器件,透明电子器件正在国际上引起广泛的关注。透明的薄膜晶体管（TFT）作为当前最具有商业价值的透明电子器件,即将成为有源矩阵液晶显示（AMLCD）和有机发光显示（OLED）的关键技术。目前硅基TFT（特别是非晶硅TFT）正面临一系列性能瓶颈:光敏性强、场效应迁移率低以及材料的不透明性。利用透明的氧化物半导体材料—氧化锌（ZnO）制备的TFT可以在一定程度上克服这些困难。ZnO是一种多功能的宽禁带直接带隙半导体材料,具有六角纤锌矿型的晶格结构,室温下禁带宽度约为3.37eV,对可见光的透射率很高。此外,利用磁控溅射法可以在较低的衬底温度下制备高质量的多晶ZnO薄膜,这对于电子驱动的响应速度是十分有利的。氮化铝（AlN）是一类重要的宽带隙Ⅲ—Ⅴ族化合物半导体材料,电阻率高,击穿场强大,适合作为绝缘材料应用于TFT结构。此外,由于AlN的晶格结构与ZnO相同,所以也可作为生长高质量ZnO薄膜的缓冲层,并改善ZnO/AlN界面结构。 本论文中利用射频磁控反应溅射技术在不同的衬底上制备出高质量的AlN和ZnO薄膜,用X射线衍射仪（XRD）、场发射扫描电子显微镜（FESEM）、原子力显微镜（AFM）、傅立叶变换红外光谱仪（FTIR）、喇曼光谱仪和紫外—可见分光光度计等测试手段对沉积薄膜的结构和光学性能进行了表征。结果发现,AlN薄膜的择优取向与氮氩气压比P_N2/P_Ar、溅射气压P_s、衬底温度T_s和射频功率P有很大关系。在P_N2/P_Ar=3∶1,P=300W,T_s=300℃,P_s=0.5Pa的条件下,AlN薄膜c轴择优取向达到最佳;通过引入低温AlN缓冲层,显著增强了ITO玻璃衬底上沉积AlN薄膜的c轴择优取向,在晶粒增大的同时降低了表面平均粗糙度,为生长高质量的AlN薄膜提供了实验依据;此外,根据包络线法理论,利用透射率曲线的极值点计算得到可见光波段内AlN薄膜的折射率n和消光系数κ。当λ=554nm时,n=2.0187,κ=0.0077。 通过对ZnO薄膜的研究发现,工艺参数是影响薄膜结晶性能的关键因素。随着衬底温度的上升和射频功率的提高,ZnO薄膜（002）面衍射峰显著增强,晶粒尺寸进一步增大;溅射气压升高,（002）面衍射峰先增强后减弱,这主要是由更多还原

【Abstract】 Transparent electronics are nowadays an emerging technology for the next generation of optoelectronic devices. The most commercially important application for transparent electronics seems to be as a transparent thin film transistor (TFT) for active-matrix liquid crystal display (AMLCD) and organic light emitting display (OLED). TFT based on Si technology (especially the amorphous silicon) actually present some limitations like: light sensitivity, low field effect mobility and opacity. One possible way to overcome such problem is the utilization of transparent oxide semiconductor based transistors, which have recently been proposed using as active channel intrinsic zinc oxied (ZnO). ZnO is a wide direct band gap (3.37eV at room temperature) semiconductor with a hexagonal wurtzite structure. It is transparent in the visible region of the spectra. The main advantage of using ZnO deals with the fact that it is possible to grow at relative low temperature high quality polycrystalline ZnO films by magnetron sputtering, which is a particular advantage for electronic drivers, where the response speed is of major importance. Aluminum nitride (A1N) is an important wide band gap III- V compound semiconductor. The wide band gap of 6.2eV, high resistivity as well as the large dielectric strength of A1N films make them more suitable as insulating layers in TFT structures. In addition, A1N has the same structure as ZnO, which makes it as the buffer layer to grow high-quality ZnO thin film and improve the interface structure.In this paper, A1N and ZnO thin films with high quality have been deposited on various substrates by radio frequency (RF) reactive magnetron sputtering. The microstructural and optical properties of the deposited films were characterized by x-ray diffractometer (XRD), field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), fourier transform infrared spectroscopy (FTIR), raman spectroscopy and spectrophotometer. The results indicated that the preferred orientation of A1N films was influenced by many depositon parameters such as P_N2/P_Ar, sputtering pressure P_s, substrate temperature T_s and RF power P. At the condition of P_N2/P_Ar=3/1, P_s =0.5Pa, T_S =300℃ and P =300W, the A1N films showed an excellent preferred orientation along the c axis. With the introduction of low-temperature A1N buffer layers, the microstructure of A1N films deposited on ITO glass substrates was significantly improved with enhanced c-axis preferred orientation, increased grain size and smoothened morphology. Additionally, according to theenvelope method, the refractive index and the extinction coefficient were calculated by several extrema in the transimission spectrum of AIN film deposited on K9 glass substrate, which were respectively 2.0187 and 0.0077 at the wavelength of 554 nm.It was found that the crystalline quality of ZnO films was affected greatly by the deposition parameters. The (002) diffraction peak of ZnO films was obviously enhanced with the elevation of substrate temperature and the increase in RF power, which also resulted in largened grains. The best fabrication condition of ZnO films was:P=200W, Ps=1.0Pa, Ts=300°C, PO2/PAr=l/2. It can be seen from theAFM images that the ZnO films presented a densely-packed, pebble or cell-like surface appearance with columnar growth crystals perpendicular to the substrate surface. In addition, the transmission curve was fitted with the dispersive model proposed by Forouhi and Bloomer to determine the refractive index of ZnO film. The results indicated that the refractive index at the wavelength of 633nm was about 1.989, which was in good agreement with that previously reported in the literature.更多还原