Electron beam inspection systems based on a scanning electron microscopy (EBI-SEM) had been developed and used for the yield management in the semiconductor process because of its high resolution. However, they have the restriction of inspection speed due to the space charge effect of the electrons in the focused electron beam.
We have been developing the electron beam inspection system based on the projection electron microscopy (EBI-PEM), and reported the results which revealed the possibilities of detecting the defect size of less than 100nm and the data rate 600MPPS, last year. We have further improved the EBI-PEM on its secondary electron optical system (2'nd EO) for obtaining smaller aberrations and distortion. The aberrations and distortion of the improved EBI-PEM optical system have been estimated by calculation using conventional simulation program. Obtained aberration values were small enough than one necessary for attaining the spatial resolution of the target specification and a resolution has been confirmed by the experiments.
Optical inspection systems and/or electron beam inspection systems are quite useful tools for the yield management in the semiconductor process. However, they have some issues of difficulties for the application to the yield management after 100nm-technology node generation. Optical inspection systems have a resolution limit by diffraction phenomena. On the other hand, electron beam inspection systems based on scanning electron microscopy (EBI-SEM) have the limit of inspection speed. Both limits are serious matter for the application to yield management after 100nm-technology node generation. We have developed the electron beam inspection system based on projection electron microscopy (EBI-PEM), having both performances of inspection speed of optical types and spatial resolution of EBI-SEM. The system has been improved on the signal electron collection efficiency and transmittance of the electron optical system. We also have developed high rate and sensitive signal detection system. Then we considered that the inspection speed of several times faster than the conventional EBI-SEM is feasible at the spatial resolution less than 100nm.
The production prototype of an electron beam inspection system based on projection electron microscopy (EBI-PEM) has been developed. Inspection performances of the EBI-PEM were evaluated using the programmed defect standard wafer delivered by SELETE. We confirmed the EBI-PEM had the same inspection speed, 9 cm2/h, as the conventional electron beam inspection system based on scanning electron microscopy (EBI-SEM) under the following conditions: pixel size of 50 nm and defect capture rate of more than 80%. Furthermore, the EBI-PEM achieved an inspection speed of 36 cm2/h. This inspection speed is four times higher than that of the EBI-SEM.
The EBI-PEM would be an effective tool for inspection subsequent to the 90 nm technology node generation.