氮化镓基高电子迁移率晶体管逆压电可靠性研究
发布时间：2018-08-17 18:23
【摘要】：由于GaN基高电子迁移率晶体管(HEMT)具有高击穿电压、高载流子密度、高载流子饱和速度等优势,目前已在高频大功率器件应用领域取得了广泛的关注。然而,目前可靠性问题仍然是阻碍GaN基HEMT器件进一步推广的主要原因。由于GaN基HEMT器件通常工作于高压大功率条件,逆压电效应成为影响器件可靠性的重要因素之一。本文首先结合理论分析以及软件仿真,建立了GaN基HEMT器件逆压电效应的物理模型;其次通过合理设计实验方法以及版图结构,对器件的逆压电效应进行了测试,并对逆压电效应引起器件退化的物理机制进行了分析;再次研究了SiN钝化介质对器件逆压电效应的影响,以及在正向栅压应力下器件特性的退化机制;最后研究了在机械应力作用下器件特性的变化规律。论文首先对GaN基HEMT器件做了简要介绍,包括GaN材料相对其他半导体材料的优势、GaN基HEMT器件适用于高频大功率应用的原因以及GaN材料外延生长技术和GaN基HEMT器件制造的发展历程。对GaN基HEMT器件目前存在的主要可靠性问题,包括热载流子效应、电流崩塌效应以及逆压电极化效应等进行了分析,并对GaN基HEMT器件可靠性的国际研究现状进行了讨论。论文对GaN基HEMT器件的逆压电效应理论进行了深入分析,并建立了GaN基HEMT器件逆压电效应的物理模型。在对GaN材料的极化特性,包括自发极化、压电极化以及逆压电极化效应理解的基础上,深入分析了AlGaN材料的逆压电极化效应理论,推导了AlGaN材料晶格应力以及弹性能密度与电场关系。通过Silvaco-ATLAS器件仿真软件,对GaN基HEMT器件的电场分布进行模拟,确定器件在任意工作模式下势垒层材料中任意一点的电场强度。结合逆压电效应的理论模型,计算出器件势垒层中的弹性能分布,并与势垒层材料所能承受的临界弹性能密度进行对比,从而确定器件可靠性工作的临界电压。制备出了特性优良的GaN基HEMT器件,并通过合理设计实验,对器件的逆压电效应进行了测试。通过对器件施加阶跃应力,同时检测应力过程中栅极应力电流随应力时间的变化,确定器件发生逆压电极化效应的临界电压。实验发现,超过临界电压器件栅极反向泄露电流急剧增大,本文结合GaN基HEMT器件漏电机制分析对该现象进行了解释。通过设计器件正反向测试实验,并对应力前后器件特性对比分析,证明了逆压电效应导致器件势垒层陷阱产生的位置位于源极一侧栅边缘。通过合理设计器件结构,系统的研究了逆压电效应对GaN基HEMT器件特性的影响,并对逆压电效应引起器件特性退化的物理机制进行了深入分析。通过设计对称结构GaN基HEMT器件,并对器件进行逆压电效应测试,证明了栅极边缘的高场峰值对逆压电效应的产生至关重要。通过湿法腐蚀的方法去除器件钝化介质以及金属接触,并通过扫描电子显微镜(SEM)对器件栅下材料形貌进行分析,证明了逆压电效并不一定会引起器件栅下材料的物理损伤。研究了逆压电效应的临界电压与器件偏置条件的关系,并结合不同偏置条件下器件势垒层中的电场分布对该现象进行了解释。采用能带理论以及陷阱产生理论,对逆压电效应引起器件退化的物理机制进行了详细阐述。研究了SiN钝化对器件逆压电效应的影响,并结合器件瞬态特性测试以及表面漏电理论对实验现象进行了深入的讨论。实验发现,去除SiN钝化介质后在阶跃应力测试过程中不会出现逆压电极化效应的临界电压。瞬态测试表明,SiN介质钝化会使得器件势垒层表面的慢态陷阱得到抑制,但同时也会引入大量的快态陷阱。结合器件表面漏电机制以及横向能带分析,我们认为表面慢态陷阱俘获电子并导致器件表面耗尽区的延伸,是导致上述实验现象的根本原因。论文还对器件在正向栅压下的退化规律进行了研究,并建立了应力作用下器件栅下界面氧化层消除理论。实验表明,正向阶跃应力后器件阈值电压正向漂移,栅极漏电显著增大。通过建立变频电容-电导模型对器件栅下界面陷阱进行表征,证明了应力作用后器件栅下氧施主浓度的降低。通过X射线光电谱(XPS)对栅下材料组分进行分析,发现应力作用后势垒层表面的Ga-O峰值显著减弱。我们认为在应力作用下栅极金属Ni会与界面氧发生反应,引起界面氧化层的消耗,从而导致器件特性的退化。发明了可以对芯片施加机械应力的测试装置,并利用该装置研究了GaN基HEMT器件在拉伸应力作用下特性的变化规律。实验发现,在晶格发生拉伸时,器件的输出电流密度和峰值跨导均出现增大趋势。结合GaN材料的极化模型我们认为,晶格拉伸会导致材料能带倾斜,使得更多的表面施主发生电离,从而引起沟道载流子浓度的增大以及沟道电阻的降低。
[Abstract]:GaN-based high electron mobility transistor (HEMT) has been widely used in high-frequency and high-power devices due to its high breakdown voltage, high carrier density and high carrier saturation speed. However, the reliability problem is still the main reason that hinders the further promotion of GaN-based HEMT devices. Inverse piezoelectric effect is one of the most important factors affecting the reliability of GaN-based HEMT devices. Firstly, the physical model of inverse piezoelectric effect is established by combining theoretical analysis and software simulation. Secondly, the inverse piezoelectric effect of GaN-based HEMT devices is carried out by reasonable design of experimental methods and layout structure. The physical mechanism of the device degradation caused by the inverse piezoelectric effect is analyzed. The influence of SiN passivation medium on the inverse piezoelectric effect and the degradation mechanism of the device characteristics under forward gate compressive stress are studied. Finally, the variation of the device characteristics under mechanical stress is studied. The advantages of GaN-based HEMT devices over other semiconductor materials, the reasons why GaN-based HEMT devices are suitable for high frequency and high power applications, and the development of GaN-based epitaxial growth technology and GaN-based HEMT devices manufacturing are briefly introduced. The inverse piezoelectric polarization effect of GaN-based HEMT devices is analyzed, and the research status of the reliability of GaN-based HEMT devices in the world is discussed. The inverse piezoelectric effect theory of GaN-based HEMT devices is analyzed in detail, and the physical model of inverse piezoelectric effect of GaN-based HEMT devices is established. Based on the understanding of piezoelectric polarization and inverse piezoelectric polarization effect, the theory of inverse piezoelectric polarization effect of AlGaN material is deeply analyzed, and the relationship between lattice stress, elastic energy density and electric field of AlGaN material is deduced. The elastic energy distribution in the barrier layer of GaN-based HEMT devices is calculated and compared with the critical elastic energy density that the barrier material can withstand to determine the critical voltage for the device reliability. The inverse piezoelectric effect of the device is tested by a reasonable design experiment. The critical voltage for the inverse piezoelectric polarization effect of the device is determined by applying step stress to the device and measuring the change of the grid stress and current with stress time. This phenomenon is explained by the leakage mechanism analysis of GaN-based HEMT devices. Through the forward and backward testing experiments of GaN-based HEMT devices and the comparative analysis of device characteristics before and after stress, it is proved that the position of barrier layer trap caused by inverse piezoelectric effect is located at the edge of the grid on the source side. By designing the device structure rationally, the system is designed. The influence of inverse piezoelectric effect on the characteristics of GaN-based HEMT devices is studied, and the physical mechanism of the degradation of GaN-based HEMT devices caused by inverse piezoelectric effect is analyzed. The passivation medium and metal contact were removed by wet etching and the morphology of the material under the gate was analyzed by scanning electron microscopy (SEM). It was proved that the inverse piezoelectric effect did not necessarily cause the physical damage of the material under the gate. The relationship between the critical voltage of the inverse piezoelectric effect and the bias condition of the device was studied. This phenomenon is explained by the electric field distribution in the barrier layer of the device under different bias conditions. The physical mechanism of the device degradation caused by the inverse piezoelectric effect is described in detail by using the energy band theory and the trap generation theory. The effect of SiN passivation on the inverse piezoelectric effect of the device is studied. The experimental phenomena are discussed in detail by the leakage theory. It is found that the critical voltage of inverse piezoelectric polarization will not occur during the step stress test after removal of SiN passivating medium. Based on the mechanism of surface leakage and the analysis of transverse band, we consider that the slow trapping of electrons on the surface leads to the extension of the depletion zone on the surface of the device, which is the fundamental cause of the above experimental phenomena. Experiments show that the threshold voltage drifts forward and the gate leakage increases significantly after the forward step stress. A variable frequency capacitance-conductance model is established to characterize the interface traps under the gate. It is proved that the oxygen donor concentration under the gate decreases after the stress action. The material components under the gate are fed by X-ray photoelectron spectroscopy (XPS). It is found that the Ga-O peak value on the barrier layer surface decreases remarkably after the stress action. We believe that the gate metal Ni will react with the interface oxygen under the stress action, resulting in the consumption of the interface oxide layer, which leads to the degradation of the device characteristics. The experimental results show that the output current density and peak transconductance of the HEMT devices increase with the tensile stress. Combined with the polarization model of GaN material, it is found that the crystal extension leads to the tilt of the energy band of the material, which leads to the ionization of more surface donors, and thus causes the groove. The increase of carrier concentration and the decrease of channel resistance.
【学位授予单位】：西安电子科技大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TN386
本文编号：2188503
[Abstract]:GaN-based high electron mobility transistor (HEMT) has been widely used in high-frequency and high-power devices due to its high breakdown voltage, high carrier density and high carrier saturation speed. However, the reliability problem is still the main reason that hinders the further promotion of GaN-based HEMT devices. Inverse piezoelectric effect is one of the most important factors affecting the reliability of GaN-based HEMT devices. Firstly, the physical model of inverse piezoelectric effect is established by combining theoretical analysis and software simulation. Secondly, the inverse piezoelectric effect of GaN-based HEMT devices is carried out by reasonable design of experimental methods and layout structure. The physical mechanism of the device degradation caused by the inverse piezoelectric effect is analyzed. The influence of SiN passivation medium on the inverse piezoelectric effect and the degradation mechanism of the device characteristics under forward gate compressive stress are studied. Finally, the variation of the device characteristics under mechanical stress is studied. The advantages of GaN-based HEMT devices over other semiconductor materials, the reasons why GaN-based HEMT devices are suitable for high frequency and high power applications, and the development of GaN-based epitaxial growth technology and GaN-based HEMT devices manufacturing are briefly introduced. The inverse piezoelectric polarization effect of GaN-based HEMT devices is analyzed, and the research status of the reliability of GaN-based HEMT devices in the world is discussed. The inverse piezoelectric effect theory of GaN-based HEMT devices is analyzed in detail, and the physical model of inverse piezoelectric effect of GaN-based HEMT devices is established. Based on the understanding of piezoelectric polarization and inverse piezoelectric polarization effect, the theory of inverse piezoelectric polarization effect of AlGaN material is deeply analyzed, and the relationship between lattice stress, elastic energy density and electric field of AlGaN material is deduced. The elastic energy distribution in the barrier layer of GaN-based HEMT devices is calculated and compared with the critical elastic energy density that the barrier material can withstand to determine the critical voltage for the device reliability. The inverse piezoelectric effect of the device is tested by a reasonable design experiment. The critical voltage for the inverse piezoelectric polarization effect of the device is determined by applying step stress to the device and measuring the change of the grid stress and current with stress time. This phenomenon is explained by the leakage mechanism analysis of GaN-based HEMT devices. Through the forward and backward testing experiments of GaN-based HEMT devices and the comparative analysis of device characteristics before and after stress, it is proved that the position of barrier layer trap caused by inverse piezoelectric effect is located at the edge of the grid on the source side. By designing the device structure rationally, the system is designed. The influence of inverse piezoelectric effect on the characteristics of GaN-based HEMT devices is studied, and the physical mechanism of the degradation of GaN-based HEMT devices caused by inverse piezoelectric effect is analyzed. The passivation medium and metal contact were removed by wet etching and the morphology of the material under the gate was analyzed by scanning electron microscopy (SEM). It was proved that the inverse piezoelectric effect did not necessarily cause the physical damage of the material under the gate. The relationship between the critical voltage of the inverse piezoelectric effect and the bias condition of the device was studied. This phenomenon is explained by the electric field distribution in the barrier layer of the device under different bias conditions. The physical mechanism of the device degradation caused by the inverse piezoelectric effect is described in detail by using the energy band theory and the trap generation theory. The effect of SiN passivation on the inverse piezoelectric effect of the device is studied. The experimental phenomena are discussed in detail by the leakage theory. It is found that the critical voltage of inverse piezoelectric polarization will not occur during the step stress test after removal of SiN passivating medium. Based on the mechanism of surface leakage and the analysis of transverse band, we consider that the slow trapping of electrons on the surface leads to the extension of the depletion zone on the surface of the device, which is the fundamental cause of the above experimental phenomena. Experiments show that the threshold voltage drifts forward and the gate leakage increases significantly after the forward step stress. A variable frequency capacitance-conductance model is established to characterize the interface traps under the gate. It is proved that the oxygen donor concentration under the gate decreases after the stress action. The material components under the gate are fed by X-ray photoelectron spectroscopy (XPS). It is found that the Ga-O peak value on the barrier layer surface decreases remarkably after the stress action. We believe that the gate metal Ni will react with the interface oxygen under the stress action, resulting in the consumption of the interface oxide layer, which leads to the degradation of the device characteristics. The experimental results show that the output current density and peak transconductance of the HEMT devices increase with the tensile stress. Combined with the polarization model of GaN material, it is found that the crystal extension leads to the tilt of the energy band of the material, which leads to the ionization of more surface donors, and thus causes the groove. The increase of carrier concentration and the decrease of channel resistance.
【学位授予单位】：西安电子科技大学
【学位级别】：博士
【学位授予年份】：2016
【分类号】：TN386
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