Automated photolithography critical dimension controls in a complex, mixed technology, manufacturing fab

Critical dimension (CD) control is one of the most difficult challenges in semiconductor manufacturing. In photolithography, factors associated with individual technologies, lithography tools, product levels, reticles, and product specifications dictate unique exposure conditions for each lithography tool set-up. In a multi-part number mixed technology environment, sophisticated controls are required to ensure that correct exposure conditions are used for each wafer processed. A process control system was developed by IBM Microelectronics using simple process rules and feedback to provide CD control. The system provides the control necessary to meet customization requirements in a highly automated low maintenance environment. It is driven by defined rules based on documented specifications of each technology. With documentation in place, new products can be introduced into the manufacturing facility without engineering assistance. The rules-based system eliminates traditional tool-setting tables by capturing engineering strategies for selecting relevant feedback information. A specific rule defines strategies for selecting the best available sample of historical tool setting and metrology data. CDs for each product are centered to their respective targets by the system's use of feedback algorithms which are integrated with a centralized specification database. Customized CD targets can be entered into the specification system for immediate customization of a particular part. A key feature of the system is its ability to learn the character of each reticle and the differences between each lithography tool.