Taro Sugihara

Outlier rejection with mixture models in alignment

Outliers in measurement often interfere with alignment. They are caused by sudden damages in the alignment mark, and existence of particles, resist damages and so on. In a conventional way to identify outliers, the observations that have larger residual than previously determined threshold are identified as outlier. It works well only with the operator’s labor of adjusting the threshold according to the deviation of ordinaries (non-outliers). However, labor is a problem especially in Small-Quantity Large-Variation fabrication such as for ASIC, System-LSI and so on. A novel method for elimination of the labor has been developed. It utilizes normal mixture models whose number of components is determined based on the Maximum Penalized Likelihood (MPL) method. It can be regarded as an identification method that determines threshold adaptively using ordinaries’ deviation. Simulation results show that the penalty coefficient, the only parameter of the method, can be a constant in the variation of ordinaries deviation. It also shows that in the absence of outliers, the accuracy of the method is comparable with the maximum likelihood estimation that is commonly considered to be the best method when the observations follow the normal distribution. The method performs better than conventional ones when there are a sufficient number of observations (no less than ten) in the standard Enhanced Global Alignment (EGA). Superiority of the adaptive method is dependent upon the probability of outlier occurrence, variation of the situation, the number of observations and the complexity of the model fitted to the observations.

Total lithography system based on a new application software platform enabling smart scanner management

Along with device shrinkage, higher accuracy will continuously be required from photo-lithography tools in order to enhance on-product yield. In order to achieve higher yield, the advanced photo-lithography tools must be equipped with sophisticated tuning knobs on the tool and with software that is flexible enough to be applied per layer. This means photo-lithography tools must be capable of handling many types of sub-recipes and parameters simultaneously. To enable managing such a large amount of data easily and to setup lithography tools smoothly, we have developed a total lithography system called Litho Turnkey Solution based on a new software application platform, which we call Plug and Play Manager (PPM). PPM has its own graphical user interface, which enables total management of various data. Here various data means recipes, sub-recipes, tuning-parameters, measurement results, and so on. Through PPM, parameter making by intelligent applications such as CDU/Overlay tuning tools can easily be implemented. In addition, PPM is also linked to metrology tools and the customer’s host computer, which enables data flow automation. Based on measurement data received from the metrology tools, PPM calculates correction parameters and sends them to the scanners automatically. This scheme can make calibration feedback loops possible. It should be noted that the abovementioned functions are running on the same platform through a user-friendly interface. This leads to smart scanner management and usability improvement. In this paper, we will demonstrate the latest development status of Nikon’s total lithography solution based on PPM; describe details of each application; and provide supporting data for the accuracy and usability of the system. Keywords: exposure