Solver NEXT SPM. Instruction Manual
188
8.3. Electrical Lithography
There are two sorts of electrical lithography:
● Charge lithography. The probe-sample voltage is maintained constant during the
lithography process;
● Current lithography. The current through the sample is maintained constant during
the lithography process.
Charge lithography
Charge lithography is based on effects of electrical field at the contact between the probe
tip and the sample surface. When a sufficiently large voltage is applied between the tip and
the sample, exposure of electrical field can locally modify the surface. A number of
modification mechanisms are possible: local heating due to high current density; in a gas
environment, deposition of decomposition products that results from decomposing the gas
in the region of strong field close to the probe tip; electric-field evaporation of the sample
material or deposition of the tip material evaporated under strong electric field.
Current lithography
Current lithography operates with the sample-probe current maintained at a constant level.
During the lithography process, the feedback system maintains the predefined current by
controlling the applied electrical bias.
This technique uses the fact that electrochemical processes resulting to surface
modification of the sample depends, eventually, not on the applied voltage but on the
probe-sample current. Thus, controlling the current will provide much more stable results
because it is less sensitive to local properties of the sample and to quality of the sample-
probe contact.
When a sufficiently large voltage is applied between the tip and the sample, exposure of
electrical field can locally modify the surface. A number of modification mechanisms are
possible: local heating due to high current density; in a gas environment, deposition of
decomposition products that results from decomposing the gas in the region of strong field
close to the probe tip; electric-field evaporation of the sample material or deposition of the
tip material evaporated under strong electric field.
Requirements on the sample and on the probe
The sample must be a conductor or semiconductor. A substrate with the conducting contact
shall be used to mount the sample in order to enable the application of voltage between the
probe and the sample.
For electrical lithography probes with conducting coating shall be used. Typically,
semicontact probes with the coating of TiN, W
2
C and conducting diamond-like coating
(DCP) are used.
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