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Scanning Electron Microscope using Atomically Fine Field Emission Tip

IP.com Disclosure Number: IPCOM000113937D
Original Publication Date: 1994-Oct-01
Included in the Prior Art Database: 2005-Mar-27
Document File: 4 page(s) / 93K

Publishing Venue

IBM

Related People

Batson, PE: AUTHOR [+5]

Abstract

Disclosed is a subminiature scanning electron microscope which would work at low voltages with relatively long working distance.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Scanning Electron Microscope using Atomically Fine Field Emission Tip

      Disclosed is a subminiature scanning electron microscope which
would work at low voltages with relatively long working distance.

      (*) has shown that tungsten field emission tips can be
fabricated from oriented 111 tungsten so that the electrons are
emitted from a region of 6 or 3 or 1 atoms.  The effective dimensions
of these tips are in the region of 1 -10 A.  The divergence of the
electron beams emitted from these tips can be as low as a few tenths
degrees, and currents of 10 nanoamp at voltages of 5-15 volts can be
obtained.

      This invention uses typical micro lithography techniques to
make a miniature electron lens to focus this type of beam on to a
surface.  The spherical aberrations of an electrostatic lens scale as
the focal length, and if the dimensions of the beam electrodes are
reduced to the micron scale, the aberrations will be cut down
drastically, and the beam coming from a few angstroms on the field
emission tip can be focussed to small dimensions on the surface to be
investigated.  If the tip and lens are scanned mechanically, as in
the Scanning Tunneling Microscope (STM), the image spot on the
specimen will be scanned in a similar fashion.

      A cross section of the electrostatic lens is shown in Fig. 1.
The electron emitting tip 1 would have a negative potential of 5 to
100 volts, and the center electrode 2 made of metal or heavily doped
polysilicon would have a voltage near this value.  The electrode 3
nearest the tip would be made from p++ silicon and would be grounded,
as would the specimen 4.  The electrode 5 nearest the specimen 4
would have a few volts positive voltage to collect electrons emitted
from the surface to be investigated.  This current, or the specimen
current, would be used to form an image as t...