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edfas.org ELECTRONIC DEVICE FAILURE ANALYSIS | VOLUME 21 NO. 2 8 GUEST EDITORIAL CONTINUED FROM PAGE 2 In addition to the number of elements introduced, the molecular and stoichiometric compositions are increas- ing with six types of carbon, nine types of silicon nitride, and more than 10 types of silicon oxides forecast for the near future. This new revolution resulted in higher costs andmore complex manufacturing, which in turn diminished profit margins. New ways to control the process and speed up the yield ramp were needed. One approach focuses on materials metrology. Metrology now needs to keep track of material composition, stress/strain, doping levels, and in-depth species profiling—in addition to the usual lateral critical dimension (CD) and layer thicknessmeasurements. To meet these new material metrology challenges, tech- nologies that were well established in the lab to support process monitoring and solve yield problems have been adapted to the fab for in-line metrology. To be successful, metrology tools must focus on repeatability, resolution, stability, throughput, and fab automation. A lab tool may need to be redesigned from the ground up to become a metrology tool. The tradeoffs are often difficult andmay limit the tool to use in just one area. Accuracy, a key attribute of many lab tools, takes a back seat to resolution, flexibility to automation, and versatility to repeatability. The needs of the fabrication environment are fundamentally different from those in a lab. A metrology tool must be fast and repeatable to better than +/ − 1% 3 sigma relative standard deviation. These are the minimum requirements for metrology but are often not addressed in a lab tool. It is not enough to make a lab tool that can handle a full 300 mmwafer with an equipment front end module and expect it to become a metrology tool. The ultimate metrology measurement is made on a product wafer, in the die, and the wafer is returned to the line for further processing. For x-ray and other optical technologies, metrology is performed on product follow- ing the in-line model above. When high-k gate material (Hf oxide, for example) was introduced, there was no way to measure the thickness and composition of this film in line. XPS technology taken from the lab and adapted to in-line metrology bridged this gap successfully and has since been adopted inmanymore thin filmcompositional and thickness metrology steps. In some cases, the move from lab to fab is incremen- tal. The term near-fab or near-line refers to a lab that is supporting production either physically near the clean- room or in the cleanroom, although product wafers measured in such a tool are not returned to the line and are instead scrapped. Transmission electron microscopy (TEM) and the necessary TEM sample preparation using FIB-SEM have followed this incremental migration. TEM is used for critical measurements that are only available in cross-sectional views, althoughmodels are being used that correlate cross-sectional measurements to top-down optical responses. Some compositional information is also available in TEM imaging, but the process is slowand does not meet the in-line requirements. The proliferation of TEMusage, despite being slowand destructive, demonstrates the high value of this type of measurement but also opens up the door for other tech- nologies to potentially replace it. In conclusion, metrology is now used to monitor the composition of complex films that contain an increasing number of elements and complex integration schemes. It also continues to be challengedwith the lateral and verti- calmeasurement of critical dimensions. Solutions to these challenges present opportunities to create new metrol- ogy tools. The semiconductor lab is a breeding ground for some of the early implementations of such solutions. Advertise in Electronic Device Failure Analysis magazine! For information about advertising in Electronic Device Failure Analysis , contact advertise@asminternational.org or call 440.338.5151. Current rate card may be viewed online at asminternational.org/mediakit.