Focal Length Abnormalities Occur In The Lithography Process Cause Analysis And Solution

Driven by the Moore's Law, the minimum feature size has been scaled down from 0.35um to 0.25um and to 90nm at present, which have been applied in mass production in China, and the 65nm and 45nm technologies is under development as well. Meanwhile, Intel is currently leading the way to push the technology to 32nm and 22nm.For the IC manufacturing, the lithography is a key process because it defines patterns with precise dimensions and locations, as well as good overlay performance. The quality of the lithography process is also critical for subsequent etching and implantation processes.We will usually meet a kind of defect called defocus in the photo process. Defocus means that the focus on the specific location of the wafer is out of the DOR General speaking, defocus will make the profile/CD abnormal after the photo process, and then it will also impact the profile/CD after the etching process. Photo can detect only 20%～30% defocus in the photo area, other defocus wafer will be sent to next step and it will impact the product yield.This thesis work is dedicated to study the type of the defocus and the root cause of them in the lithography area. The thesis will give out some methods to detect the defocus inline ASAP through monitoring the proper parameter in the batch report, and we can modify some parameter in the scanner job in order to decrease the defocus possibility. Usually we will face three kinds of defocus in our photo process:1. Local defocusLocal defocus is a normal kind of defocus in the photo process. If it occurs, it will impact a lot of number of wafer and they will sent to rework. This thesis is working for the root cause of the local defocus. We found it is cause by some particle on the E-chuck, and we found some parameter in the batch report can detect the local defocus within the scanner process. Now we are using the IEMS system to monitor this parameter.2. Edge defocusEdge defocus is a kind of defocus occurs on the wafer edge area. Base on the statistics data, the edge defocus will impact the yield about 0.5%~2%. This thesis is working on the root cause of edge defocus and we have develop two methods to monitoring the machine E-chuck performance and how to solve it by fine tuning the scanner recipe. 3. Zero mark area defocusZero mark area defocus is a special kind of local defocus. Normally it is difficult for us to find the zero mark area defocus because there is no pattern on that area. Once it occurred, it will impact the overlay performance. If we deliver the impact lot to next step, the impact wafer need to be scrapped. My thesis is working on find a parameter in the batch report which can monitor the zero mark area defocus occurrence.Now we found the root cause of these three kinds of defocus. We have developed some methods to catch the defocus phenomenon by monitoring the suitable parameter in the batch report and we also can reduce the defocus possibility by fine tuning the scanner recipe.