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本文提出了一种新的用于聚焦离子束的对准方法。使用质量标记而不使用几何形状标记,用通道电子倍增器接收和放大经质量分析后的二次离子作为对准信号而不使用二次电子或散射电子。新方法完全省掉了制作标记的附加工艺,因此标记和器件图形之间没有误差。所以这种方法对准精度最高、工艺过程最简化,还具有三维方向(x、y、z)的对准潜力。微聚焦离子束(FIB)是一种具有极其广泛用途的新工艺手段,但它存在两个突出的问题:对准问题和效率问题。在实际应用当中对于后续工艺来说对准技术特别重要,因为它限制了电路图形的位置精度。一般说来对准精度主要取决于对准信号的信噪比,标记相对器件图形的精度,初始束的束斑直径,扫描步距以及束原点随时间的漂移等等。目前聚焦离子束的对准方案大多是采用二次电子信号,也有用散射电子信号。二次电子法有如下缺点:(1)每次对准之前必须在基片上制作几何形状标记——凸台或凹槽,不仅工艺繁杂而且产生标记与器件图形之间的误差,(2)聚焦离子束腐蚀性极强,扫描几何形状标记时标记被破坏,(3)如果要保护台阶标记不被腐蚀就要增加附加工艺,而且信噪比大大降低。
This paper presents a new alignment method for focused ion beam. Using the mass markers instead of the geometric markers, the channelized electron multiplier receives and amplifies the mass-analyzed secondary ions as alignment signals without the use of secondary electrons or scattered electrons. The new method completely eliminates the need for an additional process for making marks, so there is no error between the mark and the device pattern. Therefore, this method has the highest alignment accuracy, the simplest process, and the alignment potential in the three-dimensional directions (x, y, z). Microfocus ion beam (FIB) is a new process with a very wide range of uses, but it has two outstanding problems: alignment problems and efficiency issues. Alignment technology is of particular importance for subsequent processes in practice because it limits the positional accuracy of the circuit pattern. In general, the alignment accuracy depends mainly on the signal-to-noise ratio of the alignment signal, the accuracy of the mark relative to the device pattern, the beam spot diameter of the initial beam, the scanning step, and the drifting of the beam origin over time. Currently focused ion beam alignment programs are mostly used by the secondary electronic signals, but also useful for scattering electronic signals. The secondary electron method has the following disadvantages: (1) A geometric mark, such as a boss or a groove, must be made on a substrate before each alignment, resulting in complicated processes and errors between the mark and the device pattern, (2) Ion beam is highly corrosive, marking is destroyed when scanning geometry marks, and (3) if additional steps are taken to protect the step marks from corrosion, the signal-to-noise ratio is greatly reduced.