【作者】 邝许平；

【导师】 韩杰才；

【作者基本信息】 哈尔滨工业大学 ， 材料学， 2014， 博士

【摘要】 纤锌矿结构氮化铝（AlN）薄膜作为一种重要的Ⅲ族氮化物半导体材料，具有许多优异的物理化学性能，使得AlN薄膜成为碳化硅基和蓝宝石基光电和声电器件领域的理想材料，广泛应用在声表面波器件、体声波器件、场发射显示和发光二极管领域。AlN薄膜的应用一般要求其具有高C轴取向或外延单晶结构。然而，高C轴取向和外延单晶AlN薄膜需要采用金属有机物气相沉积、分子束外延、氢化物气相外延等方法在高温下制备，其缺点是沉积温度高、毒性气体的排放、制膜设备昂贵，尤其是高温沉积还会给衬底和薄膜带来热损伤，这严重限制了AlN薄膜在微电子学领域的广泛应用。射频磁控反应溅射是沉积薄膜材料的一种重要方法，和其它制备技术相比，该技术具有简单、低温、价廉的优点。因此，研究磁控溅射低温制备高C轴取向AlN薄膜具有非常重要的意义。本文首次采用射频磁控反应溅射法在6H-SiC单晶衬底上成功制备了高度C轴取向及外延AlN薄膜，研究了工艺参数对AlN薄膜的形貌、组成、晶体结构以及光学性能的影响规律；采用更加廉价但晶格失配度较大的蓝宝石代替6H-SiC，同样实现了高度C轴取向的AlN薄膜生长，此外，探索了6H-SiC和蓝宝石衬底上AlN薄膜在300℃低温和室温条件下的生长。采用射频磁控反应溅射技术在6H-SiC和蓝宝石基体上制备了高C轴取向的AlN薄膜，采用扫描电子显微镜(SEM)、原子力显微镜(AFM)、X射线光电子能谱(XPS)和二维X射线衍射(2D-XRD)等多种表征手段，研究了反应气压、氮气浓度、射频功率等工艺参数对6H-SiC基体上的AlN薄膜的表面形貌、化学组成以及晶体结构的影响规律，获得了在6H-SiC单晶上生长高C轴取向AlN薄膜的最佳生长条件。发现所制备的AlN薄膜Al/N原子比可达1.09:1，薄膜中Al、N元素含量可达96%。薄膜晶粒尺寸随反应气压和氮气浓度的增加而减小，射频功率在250W表现出最优值，衬底温度增加到500℃后趋于稳定。表面粗糙度随反应气压、氮气浓度和射频功率的增加而降低。随氮气浓度和射频功率的增加，薄膜中Al原子浓度下降而N原子浓度升高， Al/N原子比减小。较低的反应气压有利于AlN薄膜的C轴取向生长，增加反应气压，薄膜的C轴取向生长变弱，当气压增加到1.0Pa时，生长的AlN薄膜呈非晶状态；随着氮气浓度由20%增加到60%，AlN薄膜由AlN（10-10）择优取向生长逐渐过渡到高C轴择优取向；射频功率增加到250W时，AlN薄膜的C轴取向达到最高，但射频功率太大，会诱导其它晶面的生长。采用射频磁控反应溅射技术，以更加廉价的蓝宝石取代昂贵的6H-SiC单晶作为薄膜生长基体，制备了高度C轴取向的AlN薄膜，克服了蓝宝石单晶衬底与AlN薄膜之间存在的较大晶格失配和热失配所引起的生长问题，并研究了生长温度对其形貌和结构的作用。发现在蓝宝石上生长高度C轴取向的AlN薄膜的温度窗口较窄，较高或较低的衬底温度都不利于高C轴取向的生长；另外，薄膜的表面粗糙度随衬底温度的升高而升高，较高的衬底温度可以降低薄膜中的O原子含量。首次探索了射频磁控反应溅射法在低温和室温条件下高C轴取向AlN薄膜的生长。在6H-SiC衬底上室温条件下制备了高C轴取向的AlN薄膜，并在衬底温度为300℃时成功获得了外延AlN薄膜。室温下在蓝宝石衬底上生长的AlN薄膜以C轴取向生长为主，同时出现少量其它晶面的微弱生长。采用椭偏仪研究了制备的AlN薄膜的折射率和消光系数，发现制备的AlN薄膜的折射率n都在1.83-2.15之间，AlN薄膜的折射率与其C轴取向性密切相关，薄膜的C轴择优取向性越好，其折射率越高，反之亦然。薄膜的消光系数受沉积条件的影响不明显，在波长大于300nm时其消光系数k值为零，薄膜在该波段内具有高透光性；而在波长低于300nm时k值迅速增大，在该波长光线范围内，薄膜表现出很强的吸收。更多还原

【Abstract】 As an important kind of Ⅲ-nitride semiconductor material, wurtzite aluminum nitride (AlN) has many outstanding properties. These properties make AlN a promising material for many applications including SiC-based and Sapphire-based optoelectronic and acoustic-electronic devices, such as surface acoustic wave and bulk acoustic wave devices, field-emission display, light-emitting diodes. Here it should be noted that the highly C-axis oriented films or single crystal AlN layer are needed to be grown for above-mentioned applications. However, the highly C-axis oriented films or single crystal AlN layers were prepared by metal organic chemical vapor deposition, molecular beam epitaxy and hydride vapor phase epitaxy techniques. There are many disadvantages such as high deposition temperature, toxic exhaust emission and expensive equipment, especially, high deposition-temperature has the disadvantage of the degradation of the substrate and AlN thin films during deposition due to thermal damage, which limits the wide applications of AlN layers in the field of microelectronics. Compared with these techniques above-mentioned, RF reactive magnetron sputtering method has some advantages of simple, low temperature and low price. Hence, low-temperature deposition of AlN thin films has become increasingly important and valuable. RF reactive magnetron sputtering is regard as an important method for the fabrication of thin films at low temperature. Therefore, the research on the preparation of high C-axis orientation aluminum nitride thin film by magnetron sputtering at low temperature has very important significance. In this thesis, high C-axis orientated and epitaxial AlN thin films were prepaed successfully by RF reactive magnetron sputtering on6H-SiC substrate. The surface micropholaogy, composition, crystal structure and optical properties were studied at different parameters. Further more, a lower cost and more lattice mismatch between sapphire and AlN film was used as the substrate instead of6H-SiC substrate. The same high C-axis orientated AlN thin films were achived. Finally, the low temperature growth of the AlN films was developed on both6H-SiC and sapphire substrates at the temperature of300℃and room temperature.AlN films with the high C-axis orientation were deposited on the6H-SiC substrate. The effects of the pressure, N2concentration and RF power on the surface microphology, composition and crystal structure were studied by scaning electrical microscopy (SEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and two dimensions x-ray diffraction (2D-XRD), etc. The best growth conditions of the AlN films with the high C-axis orientation were achived. The Al/N atom ratio of the prepared AlN films is up to1.09:1, and the Al, N atoms comcentration is close to96%. The size of crystal grain decreases with increasing the sputtering pressure and N2concentration, and have no obvious change when the substrate temperature higher than500℃. The surface roughness decreases with the increase of sputtering pressure, N2concentration and RF power. With the increase of N2comcentration and the RF power, the Al atom concentration decreases and N atom comcentation increases, thus the Al/N atom ratio decreases. The lower sputtering pressures is in favor of the growth of C-axis oriented AlN films, the C-axis oriention became weaker when increasing the sputtering preasure, and the films are amorphous state at the preassure of1.0Pa. The oriention of the film changed from AlN (10-10) to C-axis when increasing the N2concentration from20%to60%. The deposited AlN films present highest C-axis oriented when increasing the RF power to250W. If the RF power is too high, the growth of other crystal plane can be induced.With RF magnetron reaction sputtering technique, the high C-axis oriented AlN films were successful deposited on sapphire substrate which is a lower cost compared with6H-SiC substrate. The problem of serious lattice mismatch and thermal mismatch betwween the sapphire substrate and AlN film were solved, and the influence of growth temperature on the surface morphology and structure of the film were studied. It was suggested that the window of grown temperature is narrow for depositing high C-axis oriented AlN film. Both too high and too low substrate temperature are unfavorable to the growth of high C-axis oriented AlN film. In addition, the surface roughness increases with the increase of substrate temperature, and the oxygen atom concentration decreasesd a little at a higher substrate temperature.The growth of high C-axis oriented AlN films at low temperature and room temperature by RF magnetron reaction sputtering was fistly explored. The high C-axis oriented AlN films were deposited on6H-SiC at room temperature, and the AlN film with epitaxial structure were successful deposited on6H-SiC at the substrate temperature of300℃. The deposited AlN film presents C-axis oriented structure with some weak growth of other crystal plane when growing on sapphire substrate at room temperature.The optic performance of the deposited films was measured by spectroscopic ellipsometry. The result shows that the refractive index of the deposited AlN films is closely related to the crystalline structure of the AlN film, and the refractive index (n) between1.83and2.07. The better the C-axis orientated of the deposited films, the larger the value of refractive index, vice versa. The extinction coefficient of deposited AlN films is not affected by deposition conditions. The k value (extinction coefficient) is zero when the wavelength of the light greater than300 nm, so the deposited AlN films have a high light transmittance. When the wavelength less than300nm, k value increases rapidly, the deposited AlN films present a strong absorption.更多还原