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Defocused E-beam for Testing

IP.com Disclosure Number: IPCOM000060637D
Original Publication Date: 1986-Mar-01
Included in the Prior Art Database: 2005-Mar-09
Document File: 1 page(s) / 12K

Publishing Venue

IBM

Related People

Chiu, GLT: AUTHOR

Abstract

In the stroboscopic sampling mode of E-beam testing, a 1 nanosecond pulse window for the unblanked e-beam at 0.16 nanoam contains only 1 electron hitting the device under test. E-beam testing required long integration time to get a decent signal- to-noise ratio in this case. The operating temperature of the thermionic source can be increased, which increases the primary beam current at the expense of very short lifetime for the beam source. Alternatively field emission guns also have higher brightness. They need very high vacuum which is inconvenient to testing.

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Defocused E-beam for Testing

In the stroboscopic sampling mode of E-beam testing, a 1 nanosecond pulse window for the unblanked e-beam at 0.16 nanoam contains only 1 electron hitting the device under test. E-beam testing required long integration time to get a decent signal- to-noise ratio in this case. The operating temperature of the thermionic source can be increased, which increases the primary beam current at the expense of very short lifetime for the beam source. Alternatively field emission guns also have higher brightness. They need very high vacuum which is inconvenient to testing.

One way to solve this problem is to take advantage of the structure on the LSI/VLSI chips. Usually conductors are of minimum geometry in one dimension but quite lengthy in the other direction. Therefore, a focused line instead of a spot could increase the primary beam current hitting the target. There are several ways to achieve this. A line source can be used; however, this approach involves designing a special purpose scanning electron microscope from scratch. Wafer rotation on stage is needed to align with the line source. Rectangular final apertures can be used; however, at least three apertures are needed. One oriented in the x direction, one in y, and the third just a spot (for regular SEM spot mode). While this is conceptually very simple, these apertures must be switched in and ali to the wafer mechanically. This may lengthen the test time unless the orientation of the...