Gaseous backscattered electron detector for an environmental scanning electron microscope

摘要

An environmental scanning electron microscope is provided which is capable of only detecting backscattered electron signals emanating from the specimen with the detector assembly be positioned within the gaseous environment of the ESEM specimen chamber. This detector assembly includes a biased converter plate and a collection grid/collection plate/collector ring arrangement. The primary beam passes through the final pressure limiting aperture formed in the converter plate and then through a central aperture of the collection grid/plate/ring before striking the sample. The collection grid is held at ground potential and therefore does not collect secondary electron signals generated at the sample. The backscattered electrons are not collected by the collector grid/plate/ring and strike the converter plate creating converted backscattered electrons. The converted backscattered electrons are amplified in the gas by the electric field created between the converter plate and the collection grid. As a result, the collection grid/plate/ring will not collect secondary electron signals from the sample but will collect only an amplified converted backscattered electron signal. This dedicated gaseous backscattered electron detector can also be utilized to make a simple, low cost electron detector that can easily be switched between secondary electron detection, backscattered electron detection or both together.