基于离子切割技术制备的绝缘体上锗(GeOI)材料缺陷的去除方法研究

Ge with higher carrier mobility of electrons and holes can be used as the transistor channel. Ge has to integrate with silicon in order to sufficiently make use of the platform from the perfect silicon CMOS technology. Ge-on-insulator (GeOI), such as silicon-on-insulator (SOI) structure, should be employed to suppress the current leakage caused by narrow bandgap (0.66eV) as Ge is used as a transistor channel material. The technology in combination of wafer bonding and layer transfer (called as ion-cut technology) is important one of manufacturing approaches to achieve GeOI. The high defect (pin hole) density generated by some local unavailable layer transfer is blocking GeOI application up to now. However, the wafer bonding of Ge to silicon dioxide has to be carried out under a low temperature for avoiding the bonded pair crack thanks to the difference of thermal expansion coefficient between both materials and the demand of ion-cut kinetics. The annoying visible and invisible bubbles at the bonding interface are often caused during low temperature wafer bonding..In this proposal, the direct wafer bonding of Ge to silicon will be first employed to explore the Ge surface condition of bubble-free wafer bonding because Ge/Si wafer bonding is usually more sensitive to the interface bubbles than that of Ge to silicon dioxide. Afterwards, the low temperature wafer bonding of Ge to silicon dioxide will be conducted by the confirmed bubble-free Ge surface condition. Moreover, the germanium wafer of the bonded pair will be grinded to some 10μm to reveal the probably invisible bubbles (not to be viewed by infrared imaging or scanning acoustic microscopy) due to the collapse of the thin Ge layer. The process of low temperature wafer bonding will be further improved based on the previous research results to suppress bonding interface bubbles. Finally, the bubble-free low temperature wafer bonding of Ge to silicon dioxide will be used for ion-cut to perform GeOI fabrication by the H-implanted germanium wafer according to our investigation on the kinetics of H-implanted Ge (Ge-H platelets) blistering.

锗的高载流子迁移率特性使其成为将来CMOS晶体管沟道的理想材料。利用类似SOI结构的GeOI（Germanium-on-insulator）结构的氧化物埋层抑制其窄禁带导致的漏电成为业界追逐的目标。目前制作晶圆级GeOI材料最大的问题是锗层高缺陷密度。离子切割技术是制备GeOI的重要方法之一，但其中Ge/SiO2低温均匀键合问题导致高密度缺陷（即局部Ge层转移失效，在Ge层留下密集针孔）阻碍GeOI材料的应用。本研究主要创新是利用对低温键合界面气泡更加敏感的Ge/Si晶圆直接键合，探索去除界面可见气泡的锗表面条件，用此条件进行Ge/SiO2低温键合以去除界面可见气泡，又对键合后的锗单面减薄至10μm以下使可能的"隐形"气泡显露（锗薄层脱落），再调整键合工艺，使Ge/SiO2均匀键合。最后结合H离子注入锗后形成platelets（Ge-H小板块）的退火起泡动力学控制，实现无缺陷GeOI制作。

本项目主要研究了怎样通过控制晶圆直接键合和氢离子注入的工艺条件实现无缺陷的绝缘体上的锗（GeOI）晶圆的制备。通过研究我们不但实现了避免锗转移层缺陷的GeOI晶圆的制作方法，而且发现了至今国内外尚无报道的锗转移层缺陷产生机理。我们的研究表明：低温键合与氢离子注入的剂量和能量的选择是实现无缺陷GeOI晶圆材料的关键。大量实验观察发现转移锗层的缺陷密度与氢离子的注入剂量和能量密切相关，而这种关联主要与注入的氢在晶圆键合与锗层剥离转移的扩散行为有密切的联系。低注入剂量或者高注入能量（即氢在锗晶圆中的埋入深度）虽然能显著降低氢扩散进入晶圆键合界面，从而降低转移锗层的缺陷密度，但是将致氢离子切割退火发生层转移的时间增加甚至不能实现离子切割；如果提高注入剂量或降低氢离子的注入能量，能起到快速剥离的效果，但是将增加转移锗层的缺陷密度。因此本研究根据注入氢离子在锗中的扩散行为的研究，通过氢离子的注入剂量和注入能量工艺参数的合理组合，寻找出了一种能够快速实现锗层转移且同时避免转移锗层缺陷的发生，即通过高剂量和适当的低能量的氢离子注入，在埋入的氢离子未能在锗层剥离前到达键合界面（即避免氢离子对键合界面的破坏）前已实现锗的层转移，因此实现了无缺陷的GeOI晶圆材料制备。.本研究在不但发现了在氢离子智能剥离技术中国际上至今没有发现的氢离子扩散对层转移技术可能带来的负面影响，同时对氢离子注入剥离技术应用于其他半导体晶圆的层转移具有重要的指导作用，即氢的智能剥离（Smart-cut）技术中在关注其他条件（如表面预处理、键合温度等）方面外，还要关注氢在被注入晶圆材料中的扩散行为，因为氢对晶圆键合界面具有一定的破坏作用，因此本研究结果对所有应用氢离子实现层转移的材料具有重要的理论指导作用。