Plan to Vertical Milling Technique By Focused Ion Beam
Tuesday, May 13, 2014
Grand Foyer, Lobby Level (Hilton Orlando Bonnet Creek)
The result revealed that vertical milling technique by Focused Ion Beam (FIB)   was very effective when analyzing a single bit or twin bits. However, in case of multi-bits, the cause of failure remains unknown. Vertical milling lamella by FIB was usually created approximately in the center of the multi-bits. In this case, the visualization success rate of a failure analysis has dropped. To improve the success rate, we, thus, made a new failure analysis technique. The first step was to create a lamella with a widely planned milling technique by FIB. Secondly, the lamella with Transmission Electron Microscopy (TEM)  was carefully observed to determine the cause of failure. Next, we made a specific target lamella as the center of a source with vertical milling technique by FIB and observed a specific target lamella with TEM. The fundamental concept was very simple. However, it is possible to make a new technique after several trial and errors. In this paper, we have introduced the new failure analysis technique step by step and each step’s precaution. At first, when making a plan lamella, milling and deposition should be simultaneously done. If we milled a lamella without a deposition, a part of the lamella’s pattern would often drop during the milling process. Creating a very thin lamella with a plan milling technique would often result in a bended or torn lamella. On the contrary, creating a thick lamella with a plan milling technique would result to an unknown cause of failure. Therefore, the proper thickness of the lamella is very crucial when using a plan milling technique. We arrived at a conclusion that the proper thickness was over 100 nanometer. After finding out the source of fault by observing a plan lamella through TEM, we marked a specific target in a plan lamella to make a vertical milling lamella by FIB. However, it is important to note that without a horizontal marking, the process would not allow us to make a vertical milling lamella as the end point will remain unknown. Therefore, it is very important to have a horizontal marking. Below summarizes the five major steps and its precautions:
1. Marking a plan milling lamella by FIB (Precaution : milling and deposition should be done simultaneously)
(Precaution : the thickness should be over 100 nanometer)
2. Observing a plan lamella with TEM
3. Marking a specific target in a plan lamella (Precaution: horizontal marking)
4. Making a vertical milling lamella by FIB
5. Observing a vertical lamella with TEM
Figure 3 is the result of the new failure analysis technique. We could determine the source of fault by observing a plan lamella with TEM. We could, then, create a specific target lamella by vertical milling. The result of the new failure analysis technique was very effective and was applied in a present mass production.
 Semiconductor Material and Device Characterization 3rd, by Dieter K. Schroder, Page 723
 Moon-Yee Wang, S.X. Lee, S. Peri, “The Effect of FIB Technology on Design Methodology”, Circuits and Systems, 1993, 725-728 vol1.
 Transmission Electron Microscopy, by David B. Williams and C. Barry Carter