Details

Project TitleLaser Assisted Field Induced Oxide Nanopatterning
Track Code2007-096
Short Description

A system to effect field induced oxidation (FIO) nanopatterning of hydrogen passivated silicon surfaces with an atomic force microscope (AFM) controlled by laser irradiation.

#nanotechnology #fabrication #lithography

Abstract

Since the initial report of field induced oxidation (FIO) of silicon surfaces with a scanning tunneling microscope in 1990, numerous methods of silicon surface modification via scanning probe microscopy have been reported. The FIO process is generally thought to be limited by electrochemical reactions in the water meniscus that are initiated by charge injection from the probe into the meniscus. Thus schemes for influencing the charge injection rate may be exploited for control of FIO nanopatterning. This invention utilizes this principle by controlling FIO nanopatterning under a constant bias by toggling the on/off state of a visible laser that is focused on the AFM cantilever.

Patterning was performed on hydrogen passivated silicon surfaces, H:Si(111), employing a lightly doped n-type silicon AFM probe. The probe holder was electrically isolated from the AFM and connected to a variable gain current preamplifier to monitor current flow during both pattern formation on H:Si(111) and bias sweeps applied to the silicon probe while in contact with thermally deposited gold-on-silicon substrates. A diode laser (0.2 mW, 670 nm) served as the cantilever deflection laser. Contact mode AFM was performed in ambient conditions (35-45% relative humidity, 22-24°C) at a setpoint force of 10-30 nN, and patterns were created with a 10 V sample bias. A protocol to eliminate spurious light, maintain stable tip-sample contact force, and pattern with and without bias was developed. Under these conditions patterning only occurs when the laser is on consistent with the laser influencing the free carrier concentration in the doped silicon probe.

Laser assisted FIO oxide nanopatterns were generated by toggling the laser with a rate of 8 Hz while scanning a 4 m² region with a fast 1 Hz rate and 10 V sample bias. The resulting oxide nanopattern reflects the laser toggle rate, as patterning only occurs when the laser is on (Figure 1). Laser assisted FIO provides a novel and effective strategy for controlling oxide nanopatterning on hydrogen passivated silicon surfaces.

FIG. 1: AFM image of an FIO pattern created under a constant bias of 10 V with an 8 Hz toggle of the illumination (AFM fast scan speed is 1 Hz). The laser remained on (i.e., was not toggled) for the first and last 15 lines. In addition, the relative phase and frequency of the laser toggle signal compared to the fast scan signal was varied throughout the nanopatterning to demonstrate control over the linewidth.
 
TagsNANOTECHNOLOGY: lithography, NANOTECHNOLOGY: fabrication
 
Posted DateJul 4, 2011 2:42 PM

Inventor(s)

Mark C. Hersam

Liam Pingree

Advantages

Local oxidation on H:Si(111) surfaces can be fully suppressed or activated by toggling a laser luminating a lightly doped silicon AFM cantilever. Laser assisted FIO provides an alternative and flexible means for controlling oxide nanopatterning.

Status

Issued U.S. Patent No. 7,976,765

Contact Information

Arjan Quist, PhD
Invention Associate
(p) (847) 467-0305
(e) arjan.quist@northwestern.edu