Browse Prior Art Database

Secondary Electron Detection Device

IP.com Disclosure Number: IPCOM000074180D
Original Publication Date: 1971-Mar-01
Included in the Prior Art Database: 2005-Feb-23
Document File: 2 page(s) / 40K

Publishing Venue

IBM

Related People

Thompson, FD: AUTHOR [+2]

Abstract

Uniform collection efficiency of secondary electrons for large target areas is attained by using multiple detectors and locating the detectors above the target so that the collector opening is effectively enlarged as the beam moves away from the detector.

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 72% of the total text.

Page 1 of 2

Secondary Electron Detection Device

Uniform collection efficiency of secondary electrons for large target areas is attained by using multiple detectors and locating the detectors above the target so that the collector opening is effectively enlarged as the beam moves away from the detector.

In A, target 1, impinged by electron beam 2, is surrounded by a plurality of secondary electron detectors 3. Each detector comprises a diode 4 on an insulated rod 5 held in support 6. The number of electrons reaching the detectors is limited with the annular collector opening formed by collector screen 7, top 8, and bottom 9. The screen is held at target potential allowing electrons to reach the opening with line-of-sight trajectories, while the diodes are held at positive potential to capture all electrons that pass through the opening.

Selection of the collector dimensions can be understood from sketch B, which shows electrons collected by a typical element of the screen from two different points on the target. Assuming secondary electron emission to follow a cosine distribution, this element of the screen opening presents a smaller effective aperture for electrons from point 10 at the target edge than for electrons from point 11 at the target center. Although electrons from the edge come from a portion of the distribution that is more intense than that at the target center, the smaller admission angle counteracts the greater density. By integrating this affect over the enti...