铜/氮化镓界面应力状态及相关失效机理研究

Gallium nitride has the advantages of large band-gap width, wide wavelength range and good performance at high temperature, which could be widely used in the light-emitting diode, semiconductor laser and others in the future. However, there are still some theoretical and technical problems which restrict the performance improvement and product marketization of gallium nitride device, stress is one of them. Transfer process and working status will affect the stress of substrate/gallium nitride interface, cause the change of band-gap width, energy gap tilt status and surface charge distribution, and further result in the change of wavelength, luminous efficiency and reliability of the devices. The spatial resolution and stress resolution of electron backscatter diffraction based stress measurement method are very high. This method can flexibly measure stress by point, line and plane scanning modes; it can obtain information such as morphology, size, orientations and dislocation density at one time. Therefore, this method is very suitable for the study of microstructure and stress state of substrate/film interface. In this project we will establish a measuring method of interfacial stress based on electron backscatter diffraction and cross correlation algorithm; study the effect of metallic bonding parameters on the element distribution, microstructure and stress states of copper/gallium nitride interface; reveal the relationships of the element distribution-microstructure-stress states of the interface; ascertain the interfacial failure mechanism caused by stress. Finally, we hope to provide theoretical and technological foundations for the design and manufacture of gallium nitride devices with outstanding photo-electronic properties.

氮化镓具有禁带宽度大，波长覆盖范围广，高温性能好等优点，未来可能被广泛应用于发光二极管和半导体激光器等领域。但是，目前仍有一些理论和技术问题制约着氮化镓器件的性能提升和产品市场化，应力就是其中之一。转移工艺和工作状态会影响基体/氮化镓界面应力，导致其禁带宽度、能带倾斜和表面电荷分布发生变化，导致器件的波长、发光效率和可靠性等变化。电子背散射衍射应力测量方法的空间分辨率和应力分辨率非常高，能灵活地进行点、线、面扫描应力测量，能同时获得形貌、尺寸、取向和位错密度等信息，非常适用于基体/薄膜界面微观组织结构和应力状态研究。本项目拟建立基于电子背散射衍射和相关联算法的界面应力测量方法，研究金属键合工艺对铜/氮化镓界面元素分布、微观组织结构和应力状态的影响，构建界面元素分布-微观组织结构-应力状态之间的关系，探明界面的应力失效机理，为设计和生产具有优异光电性能的氮化镓器件提供技术基础和理论依据。

应力/应变状态及其演变是氮化镓生长和应用过程中的一个重要问题，应力在材料或器件承受范围内时，会影响其性能；超出承受极限时，将导致失效。本项目围绕Cu/GaN界面应力/应变分布及结构缺陷开展研究，主要研究结果有：.采用X射线衍射技术对铜/氮化镓进行2θ扫描与ω扫描，计算了应力大小与位错密度，未掺杂GaN层的拉伸应力随沉积铜膜厚度的增加而减小，50 nm Cu/Si掺杂GaN所受拉伸应力最大（0.48 GPa），螺位错密度为7.01×107cm-2。.Ga缓冲层/GaN界面Ga侧的5个EBSD应变分量图中，均存在显著的应变和应变分布。一部分是正负应变交替混杂分布，一部分是纯正应变或纯负应变。位于中间的GaN层不存在显著应变。GaN/Cu界面GaN侧受铜薄膜厚度和Mg掺杂影响，产生了小范围的应变，可见GaN掺杂种类和铜薄膜厚度会影响GaN/薄膜界面的应变状态。.采用高分辨晶格成像和几何相位分析法研究了Cu/GaN界面的应变分布和结构缺陷类型。GaN中Mg元素与Si元素浓度分别在（0-9.4） nm和（0-19.0）nm的深度范围内显著降低。在未掺杂GaN中，存在柏氏矢量为1/2<0001>的螺位错和柏氏矢量为1/3<112 ̅0>的刃位错。Mg掺杂GaN存在I1 型堆垛层错，总位移矢量为1/6<202 ̅3>，堆垛层错是由周围的Mg受体产生的，附近的应变主要是由Mg掺杂原子的聚集和相关位错引起的。Si掺杂GaN中的位错类型与未掺杂GaN中的位错类型相同，Si在位错附近形成杂质气氛阻碍位错运动。 .Cu/GaN的半共格界面会导致晶格失配。GaN上Cu薄膜的生长机制属于扩展原子失配模型。Cu和GaN之间的晶格失配不会在界面线附近产生大量位错，因此保持应变状态。GaN生长过程中产生的大量不全位错存在于远离界面线的区域。.本项目研究了铜/氮化镓界面元素分布、微观组织和应力/应变状态的演变机制及铜薄膜沉积生长工艺参数对它们的影响规律；构建了铜/氮化镓界面元素-微观组织-应力状态之间的关系，揭示了铜/氮化镓界面的应力失效机理，为设计和生产具有优异光电性能的氮化镓材料和器件提供了技术基础和理论依据。