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FBAR用AlN薄膜的MOCVD制备
【作者】 宁金叶；
【导师】 刘兴钊；
【作者基本信息】 电子科技大学 ， 电子信息材料与元器件， 2009， 硕士
【摘要】 与传统的介质滤波器和声表滤波器(SAW)相比,基于薄膜体声波谐振器(FBAR)技术的滤波器具有体积小、工作频率高、插入损耗低、带外抑制大、Q值高、功率容量大、温度系数低、抗静电冲击能力强以及与半导体工艺兼容等优点,作为GHz频段带通滤波器的一种解决方案, FBAR已显示出广阔的应用前景。压电薄膜是FBAR研制的关键,氮化铝(AlN)由于具有介电损耗小、机电耦合系数高、热膨胀系数与Si、GaAs等常用半导体材料相近等优异性质,而成为FBAR研制的首选材料。从目前的研究结果来看,AlN薄膜的质量极大地影响着FBAR及其滤波器的性能,其中,AlN薄膜的织构程度、结晶完整性对FBAR器件性能的影响最大,为此,人们围绕如何生长单一c轴取向的AlN薄膜开展了大量研究。本论文采用金属有机化学气相沉积(MOCVD)法,在蓝宝石衬底、Mo/Si衬底以及ZrN/Si衬底上沉积AlN薄膜,系统研究了工艺参数等对AlN薄膜晶体结构、微观组织、介电性能与压电特性的影响规律,主要研究成果如下:首先,本论文在蓝宝石(0001)衬底上采用MOCVD生长AlN薄膜,系统研究了衬底温度、三甲基铝(TMA)和氨气(NH3)的流量、反应室总压等工艺参数对AlN薄膜取向的影响规律,通过优化工艺参数,成功制备出了高度c轴取向、具有六方纤锌矿结构的AlN外延薄膜;其(0002)衍射峰的摇摆曲线半高宽(FWHM)达到了0.10°,AlN与Al2O3的面内关系为AlN[301?3]//Al2O3[33 2?9];椭圆偏振法测量出AlN薄膜的折射率介于2.0到2.4之间。其次,本论文采用直流磁控溅射法在Si(111)基片上生长Mo薄膜,在优化条件下成功制备出了(110)择优取向的Mo薄膜。在此基础上,本论文进一步在Mo/Si衬底上采用MOCVD生长AlN薄膜,在950℃到1050℃的温度范围内成功制备出了c轴择优取向的AlN薄膜;介电常数介于8.9到11.8之间;损耗介于1.0%到2.0%之间;压电系数介于2.1到2.9之间。最后,由于Mo电极上生长的AlN介电损耗过大,本论文选择ZrN作为新的底电极材料。通过优化射频磁控溅射工艺在Si基片上获得了(111)取向的ZrN薄膜。随后以ZrN/Si为衬底,在1000℃到1050℃的温度范围内采用MOCVD生长了c轴择优取向的AlN薄膜。研究结果显示:与在Mo/Si衬底上生长的AlN薄膜相比,由于AlN薄膜与ZrN之间的晶格失配度小,以ZrN为底电极所生长的AlN薄膜具有更加优良的介电性能与压电性能。AlN薄膜介电常数介于8.3到8.6之间;其损耗介于0.1%到0.6%之间;压电系数介于2.8到3.1之间。
【Abstract】 Thin film bulk acoustic wave resonators (FBAR) show considerable promise as an integrable solution for RF bandpass filters with center frequencies at GHz. It can replace conventional microwave ceramic filters and surface wave filters (SAW) because it provides several prominent advantages such as small size, high Q, high power handling capability, high operating frequency, good temperature stability, and the possibility of being integrated into semiconductor technology.Piezoelectric thin films are an essential component of FBAR. Aluminum Nitride (AlN) is one of the most attractive piezoelectric materials for FBAR application because of its low dielectric loss, high electromechanical coupling coefficient and similar thermal expansion coefficient with Si and GaAs. The quality of AlN thin films will strongly influence the performance of FBAR, and thus the bandwidth as well as the insertion loss of FBAR-based filters. So far, lots of researches have been done in order to obtain highly c-axis oriented AlN thin films.In this dissertation, the AlN thin films were grown on hexagonalα-Al2O3 (0001) substrates, Mo/Si substrates and ZrN/Si substrates by metalorganic chemical vapor deposition (MOCVD), respectively. The crystal microstructure, dielectric properties, and piezielectric properties of the deposited AlN thin films were systematically studied through the study on the effect of growth parameters, such as the substrate temperature, the flux flow of TMA and NH3, the total pressure in the reactor, and the kinds of substrates.The dissertation is mainly focous on the follows:Firstly, AlN thin films were grown on hexagonal Al2O3 (0001) substrates by MOCVD. The effect of growth parameters, such as the substrate temperature, the flux flow of TMA and NH3, and the total pressure in the reactor, on the crystallinestructure, texture, and microstructure, was systematically studied. It had been found that the AlN thin films were highly c axis oriented and extension films with hexagonal spiauterite structure. The full width at half maximum (FWHM) of the rocking curve around (0002) diffraction peak is only 0.10°and the inplane relation between AlN and Al2O3 was AlN[30 1?3]//Al2O3[33 2? 9]. The refractive index of the AlN thin films measured by elliptical polarimeter was between 2.0 and 2.4.Secondly, we deposited molybdenum (Mo) thin films on Si (111) substrates by DC magnetron sputtering. It showed that Mo thin films with (110) preferential orientation can be obtained after optimizing the deposition conditions. Then AlN thin films were grown on such Mo/Si substrates by MOCVD from the 950℃to 1050℃. It had been found that the AlN thin films were highly c axis oriented. The dielectric constant of the AlN thin films was between 8.9 and 11.8. The dielectric loss of the AlN thin films was between 1.0% and 2.0%. The piezoelectric coefficient of the AlN thin films was between 2.1 and 2.9.Finally, in order to decrease the high dielectric loss of AlN thin films prepared on Si substrates with Mo electrodes. So, we prepared zirconium nitride (ZrN) thin films on Si (111) substrates by reactive RF magnetron sputtering. It indicated the ZrN thin films with a (111) preferential orientation under optimized depositon condition. Then the AlN thin films were prepared on ZrN/Si substrates by MOCVD from the 1000℃to 1050℃. It had been found that the AlN thin films were highly c-axis oriented in this condition. The best microstructure and electrical properties can be obtained at 1025℃. In addition, the properties of dielectric loss and the piezoelectric properties of AlN thin films were enhanced on the ZrN/Si substrates, which can be interpreted by better crystal lattice match between AlN and ZrN compared to AlN and Mo. The dielectric constant of the AlN thin films on ZrN electrode was ranging from 8.3 to 8.6. The dielectric loss of the AlN thin films was between 0.1% and 0.6%. The piezoelectric coefficient of the AlN thin films was between 2.8 and 3.1.