Radiant energy – Radiation controlling means
Reexamination Certificate
1999-07-30
2001-12-04
Nguyen, Kiet T. (Department: 2881)
Radiant energy
Radiation controlling means
C250S310000
Reexamination Certificate
active
06326635
ABSTRACT:
BACKGROUND
1. Field of the Invention
This invention relates to electron beam lithography and particularly to reduction of electron double back scattering.
2. Description of Related Art
Electron beam lithography typically uses electrons accelerated in vacuum to expose a resist by penetrating the resist layer. These electrons are usually stopped by the resist or underlying substrate; however, some of them are scattered back by the resist or its substrate into the surrounding vacuum where they strike the accelerating column components, workchamber cover, or other components. Some of these scattered electrons then reflect back onto the resist where they degrade the image clarity by producing a fogging effect. Several known techniques minimize this fogging. One such technique utilizes materials with low densities and low atomic numbers in the construction of the components surrounding the resist and its substrate. These materials are usually effective in preventing electron “bounce-back” (reflection) by absorbing the scattered electrons. Another technique locates chambers above the resist and its substrate. A chamber has a window which allows electrons to enter and a deep interior from which a scattered electron has little probability of finding its way out of the window it entered. Electrons entering the chamber are usually absorbed by the chamber material. The chamber walls typically extend closely towards the point of where the electrons initially are incident on the resist. They are also formed by vanes such that the chambers have small openings. Although these chambers are effective in reducing the total energy of the fogging electrons, they can actually intensify the fogging effect close to the point of electron incidence on the resist due to back-scattered electrons reflecting off blunt edges of the vanes close to the resist. Therefore, there is a need not only to reduce the total energy of the fogging electrons, but to also reduce the intensified fogging effect produced by electrons reflecting off the blunt edges of the vanes of the chamber walls.
SUMMARY
In accordance with the invention, the above problem is overcome by use of an electron shield assembly having multiple vanes with sharp edges pointing towards the electron beam incident point on the resist. These vanes are in conically shaped assemblies and concentric about the electron beam path, which extends through the center of the assembly. The vanes have lower sharp edges due to oblique surfaces at the ends of the vanes angled between 10° and 20° relative to the outer vane surface and facing towards the electron beam path. Additionally, the shield assembly may also have the vanes angled towards the electron beam incident point such that the vertex of the cone-shaped vane assemblies is coincident with the beam incident point.
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Electron, ION and Photon Beam Technology and NanofabricationConference Sponsored by The American Vacuum Society, Marriott Resort Marco Island, Florida, Jun. 1-4, 1999 pp 59,60.
Babin Sergey
Hwa Chen
Innes Robert
Sagle Allan L.
Veneklasen Lee H.
Etec Systems, Inc.
Leitich Greg
Nguyen Kiet T.
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