Linewidth measurement in quarter micron devices involves some difficult problems, such as charging of photoresist films. Sample charging prevents not only accurate linewidth measurement but also inspection of high aspect ratio holes. Then we proposed the back scattered electron assisting LSI inspection (BEASTLI) method. In BEASTLI, a 200 keV scanning electron beam is used without being influenced by the charging of insulator. As BEASTLI is extremely useful for examining the shape and dimensions of devices, time and labor is saved when optimizing process conditions. However, owing to irradiation damage to semiconductor devices, BEASTLI could not be used as an in-line CD measurement system. In order to realize 'damage free inspection', we evaluated irradiation damage, such as VTH shift, increase of junction leak current, deterioration of oxide reliability, and hot carrier degradation. We evaluated these characteristics using MOS transistors. As a result of the investigation, we could apply the BEASTLI method for in-line CD measurement.