Integrated Metrology and Real-Time CD Control

Abstract

Lithography is the key technology driver in semiconductor manufacturing. In optical lithography, the most important variable to be controlled is critical dimension (CD) uniformity. As feature size miniaturization goes beyond the sub-micron technology node, the prevalence of optical lithography is only possible with state-of-the-art process equipment, in-situ metrology and efficient process control. This thesis presents a framework for lithography process monitoring and control which encompasses the development of an actuator, sensor and control methodology for post-exposure bake (PEB) in deep ultraviolet (DUV) lithography. As CD is very sensitive to wafer temperature during thermal processing steps in lithography, it is important to control the wafer spatial temperature uniformity for enhancing CD uniformity. A new programmable integrated bake-chill thermal processing module is designed and implemented to overcome limitations posed by conventional thermal processing module. By employing a set of thermoelectric devices (TEDs), resistance temperature detectors (RTDs) and model-based control method, the spatial wafer temperature non-uniformity can be well-controlled to within ?0.4?C and ?0.1?C during the transient and steady-state period of thermal cycle respectively. Metrology wise, a fixed angle scatterometer based on specular spectroscopic scatterometry is developed as an in-situ metrology system for patterned resist film monitoring during PEB. The rotating-polarizer configuration is adopted so that the detector does not need to be insensitive to polarization and parasitic light is suppressed. Calibration for sources of systematic errors is proposed. The effective spectral range recognized by the system ranged between 350nm to 850nm and measurement time during spectroscopic mode is 5 times faster than commercial ellipsometers which is critical for real-time monitoring and control. The scatterometer is integrated with a multi-zone bake-plate to form the advanced process control (APC) framework for PEB. Characterization on targeted DUV resist is performed to determine the temporal range for control during PEB. A control scheme based on merit function to match the measured and reference spectrums is proposed for real-time monitoring and control. Result shows CD non-uniformity can be significantly reduced to less than 10nm. With this system, real-time monitoring and control for CD uniformity is achieved, control resolution is further reduced from run-to-run control to across-wafer control.