EUV mask inspection technologies with actinic tool for DRAM and logic lithography

As the design rule continues to shrink towards the EUV lithography and beyond, the EUV mask inspection is one of the most important technologies for HVM lithography. Until now, most of the EUV mask inspection was performed by the DUV inspection tools. However, due to the nature of 193nm source, the DUV inspection has resolution limit and is unable to perform through-pellicle inspection. To overcome these limitations, the actinic tool was proposed to achieve high-resolution pattern imaging performance and inspection sensitivity. As a result, the EUV imaging resolution of tested pattern such as DRAM and Logic design was improved by 4.7 times compared to DUV resolution and it can achieve the high-resolution inspection for the extreme OPC type pattern and SRAF pattern. While studies on EUV inspection algorithm was mainly focused on masks for logic devices, we developed the EUV mask inspection technology for DRAM and LOGIC devices with Lasertec ACTIS 150 tool. By using the 13.5nm EUV wavelength the APMI can selectively detect printable defects and reduce the detection of nuisance and false defects. Overall, the defect classification of APMI inspection can be easily done hence the higher-resolution imaging performance. We also applied machine-learning based DB inspection algorithm to overcome resolution limit and accuracy of conventional DB modeling based DUV mask inspection. Finally, by using the 13.5nm actinic source, we acquired the technology to detect phase defect and perform through-pellicle inspection.