A study of the limited area scanning system in the mask CD-SEM

Measurement of resist critical dimensions (CDs) utilizing a scanning electron microscope (SEM) based metrology system causes the resist to change due to irradiation effects of the electrons. A new and novel scanning approach has been developed in an effort to minimize the effects electron irradiation and exposure during the measurement process. This technique is especially pertinent in view of the tightening requirements for process control to achieve single digit CD uniformity on leading edge photo masks being produced today. The measurement of OPC features necessitates utilization of SEM based metrology due to resolution requirements, but the effects of high magnification imaging presents unique challenges. By controlling the scanned region of interest (ROI) it is possible to reduce exposure and irradiation effects. This paper will detail this new approach as it is utilized on the LWM9045 SEM Metrology system. The LWM9000SEM mask CD SEM was introduced earlier.