Quality Assessment of Advanced Photomasks Using the Q-CAP Cluster Tool

摘要

The reduction of wavelength in optical lithography and the use of enhancement techniques like phase shift technology, optical proximity correction (OPC), or off-axis illumination, lead to new specifications for advanced photomasks - a challenge for cost effective mask qualification. "Q-CAP", the Qualification Cluster for Advanced Photomasks, comprising different inspection tools (a photomask defect inspection station, a CD metrology system, a photomask review station and a stepper simulation software tool) was developed to face these new requirements. This paper will show the performance and reliability of quality assessment using the Q-CAP cluster tool for inspection and qualification of photomasks. Special attention is paid to a key issue of mask qualification: the impact of CD deviations, loss of pattern fidelity - especially for OPC pattern and mask defects on wafer level. Photomasks were produced containing patterns with pre-programmed defects. Wafers were processed using these testmasks. Results from inspection of these wafers are compared to predictions of different cluster tools gained during inspection of the photomasks. One aspect covered in the paper is the comparison of CD-SEM images from wafers to software stepper simulation results: aerial image and printed wafer pattern using OPTISSIMO～R Client (without and with resist model respectively). The Q-CAP cluster concept allows the combination of hardware tools as well as software tools via network communication. It is designed to be open for any tool manufacturer and mask house. All mask relevant information created during processing a photomask is stored to a SQL database and is available for all tools connected to the cluster. The cluster can be seen as one single virtual tool that facilitates full qualification of photomasks. First results using a prototype of the Q-CAP cluster in production are presented.