Scatterometry metrology validation with respect to process control

Abstract

The scatterometry or OCD (Optical CD) metrology technique has in recent years moved from being a general purpose CD metrology technique to one that addresses the metrology needs of process monitoring and control, where its strengths can be fully utilized. With the significant advancements that have been made in both hardware and software design, the setup time required to build complex models and solutions has been significantly reduced. Whilst the application of scatterometry to process control has clearly shown its merits, the question still arises as to how accurately the process corrections to feed forward or feedback for process control can be extracted? In this work we critically examine the accuracy of scatterometry with respect to process control by comparing three hardware platforms, on a simple litho stack. The impact of hardware design is discussed as well as the 'setup' of the modeled parameters on the final measurement result. It will be shown that informations extracted based on scatterometry measurements must be true to process variation and independent of the hardware design. Our results will show that the ability to use scatterometry effectively for process control ultimately lies in the ability to accurately determine the changes that have occurred in the process and to be able to extract appropriate process corrections for feedback or feed forward control; allowing these changes to be accurately corrected. To do this the metrology validation extends beyond the typical metrology metrics such as precision and TMU; metrology validation with respect to process control must encompass accurate determination of process corrections to ensure a process tool and/or process stays at the set point.