Contamination reduction in low voltage electron-beam microscopy for dimensional metrology

Contamination of structures to be analyzed in an electron microscope is a severe problem for dimensional metrology applications, especially for low voltage electron microscopy. Two methods for contamination reduction which do not use a temperature variation of the sample or its environment have been investigated in this article. First, injection of inert and reactive gases into the area of electron-beam impact to create a locally confined area of increased pressure which reduces the contamination growth by a factor of 2. Second, prescanning the surroundings of the area is intended for metrology measurements. This method effectively immobilizes contaminants on the specimen surface if the delay time between immobilization and measurement is short enough (approximately 40 ms), to avoid the replenishment of contaminants. A combination of the two techniques is recommended for a damage free low voltage electron-beam metrology. (C) 1997 American Vacuum Society.