A fast QC method for testing contact hole roughness by defect review SEM image analysis

We propose a new and fast method for monitoring contact hole roughness (CHR), which can be a major yield-loss factor for advanced SRAMs. The method, defect-review scanning electron microscopy (SEM) image processing, can monitor CHR 100 times faster than the conventional method by critical dimension (CD)-SEM. The speed can facilitate faster identification of process countermeasures by, for example, making detailed monitoring of CHR variation within a wafer practicable. Results for CHR obtained by both new and conventional methods show similar trends for differences in process conditions. Also, we experimentally confirmed the new method's measuring variation of the rate of deformed contact holes. Through evaluation by the new method, we demonstrate that the standby electric current of advanced SRAM depends not only on overlay error but also on CHR. We believe that the new method will be very useful in the evaluation of process countermeasures and their stability. Index Terms--Electron beams, inspection, integrated circuit manufacture, logic devices, SRAM chips.