H. Vanderwulp et al., SUBNANOMETER STABILITY OF NANOSTAGE SUPPORTS, Journal of vacuum science & technology. B, Microelectronics and nanometer structures processing, measurement and phenomena, 15(3), 1997, pp. 566-573
In order to obtain atomic resolution in a transmission electron micros
cope, a piezo-driven nanostage with subnanometer stability is under de
velopment. Inertial sliding motion is used to move the nanostage table
in the plane perpendicular to gravity. One of the most important para
meters on the way to such a nanostage is the design of the nanostage t
able supports. Through several experiments, the stability of two diffe
rent nanostage table supports is studied: a kinematic and a nonkinemat
ic support. In order to explain the submicrometer and nanometer stage
table drift measured in the direction parallel to gravity, a subnanome
ter contact theory is presented. This theory explains the stage table
drift by the following parameters: the size of the apparent contact ar
ea of the support, the gravity forces working on the support, the mult
imolecular layer of adsorbed water molecules on all contact surfaces,
creep in the contact points and settling of the contact through micros
liding at the contact points. For the initial placement of a nonkinema
tic support in ambient air with an apparent contact area size of 15x15
mm(2), a stage table drift of 100 nm over 30 min was measured, which
almost exactly followed a logarithmic curve. This drift reduced to abo
ut 45 nm when the support was placed in a low vacuum, where the number
of layers of adsorbed water molecules on the support surfaces is redu
ced to one or two. Filling the vacuum chamber with nitrogen gas result
ed in an even lower stage table drift (25 nm). Stage table drift after
single inertial sliding steps is about 25% of the initial amount of d
rift. In case of a kinematic support, the apparent contact area reduce
s significantly and stage table drifts after initial placement of 1 up
to 3 nm were found. The drift after single inertial sliding steps is
on the same order of magnitude. These drifts are attributed to contact
creep, which was minimized by optimization of the material selection
of both contact surfaces. A combination of two hard surfaces showed al
most no creep at the subnanometer level. Therefore, this highly stable
kinematic support suits the nanostage application very well. (C) 1997
American Vacuum Society.