Use of multiple lithography monitors in a defect control strategy for high volume manufacturing

As I-line and deep ultraviolet (DUV) photolithography processes grow more complex, yield improvement has become more challenging and critical. With the advent of smaller sub-micron geometries using newer chemically amplified photoresists, a high sensitivity, easy to review and trouble-shoot monitor is essential. In order to fully understand what defects may be generated by a process or process tool, it is necessary to fully duplicate the given process on the test wafer used to monitor the defect level. That concept is called: Process Induced Defects Per Wafer Pass (PIDPWP). PIDPWP requires the real and exact product process to be used in creating the defect test monitor. To monitor a photolithography process using the concept of PIDPWP, typically, a coat, expose, and develop sequence is used with a selected and simplified mask, such as a diffraction grating. In a manufacturing area with multiple technologies, each step of the process may require different resist/developer combinations. Each resist/developer combination requires constant monitoring to insure adequately low levels of defects. Our solution to this problem is to use multiple integrated monitors to verify each process. This allows for better response time and defect density control when the defects are due to the chemicals or chemical delivery systems, and not just the mechanical aspects of the tool. In addition, we have designed our system to have minimal impact on production, yet still allow for statistical process control, analysis, and defect reduction. The Photo Track Monitor (PTM) methods and results of this control strategy as applied in a high volume manufacturing environment are discussed.