The Atomic Fabrication Facility (AFF) was established in 2001 and is a unique laboratory world-wide, dedicated to the development of atomically precise devices in silicon and germanium. The ultimate goal of this facility is to develop a scalable quantum computer prototype using a combination of Scanning Tunnelling Microscopy (STM), Scanning Electron Microscopy (SEM) and Molecular Beam Epitaxy (MBE). This facility has been constructed to house six state of the art scanning tunneling microscopes, including 3 Omicron Variable Temperature STMs (VT STM), a combined Multi-scan STM-SEM/MBE system, an Omicron Nanoprobe (4 point probe STM) and a low temperature STM. Each of these systems has been designed in collaboration with Omicron NanoTechnology GmbH and MBE Komponenten GmbH in Germany to combine high quality silicon growth with high resolution STM.

VT-STM Laboratory

The VT-STM combines high-resolution STM with a variable temperature stage.

The majority of work on understanding the phosphorus in silicon surface chemistry has been carried out on Variable Temperature Scanning Tunnelling Microscopes. An initial instrument was installed in 1998 and consists of a custom-configured, triple-chamber UHV STM/MBE system. The STM can be operated at temperatures ranging from 25 K to 1100 K and is used to image the silicon surface and perform atom-scale lithography. The second UHV chamber houses the SUSI silicon source for the MBE growth of thin epitaxial silicon films with thicknesses ranging from submonolayer to several tens of nanometers. Facilities to analyse surface structure and contaminants are provided in the third UHV chamber which incorporates both Low-Energy Electron Diffraction (LEED) and Auger Electron Spectroscopy (AES). Two further VT-STMs were installed in 2011.

STM-SEM Laboratory

Operating under UHV conditions, the STM-SEM and MBE chambers are physically connected even though they are housed in different, acoustically shielded laboratories in the AFF. A transfer line between the two systems (penetrating a dividing wall) is attached to a 3-tonne concrete block to prevent vibrations from the MBE reaching the STM. The STM system incorporates an SEM that allows registration markers to be easily found without damaging the STM tip. A specially designed optical position readout system is also incorporated to allow precise alignment of features during successive fabrication steps. Future plans for the SEM involve adapting it for Electron Beam Lithography, thus allowing registration of STM fabricated features with a prepatterned substrate.

MBE Laboratory

A multi-chamber STM-SEM/MBE system provides the necessary registration and high purity silicon growth capabilities required for multi-qubit fabrication. Specifically, the MBE component is capable of device quality Si and SiGe growth onto 4” wafers. Using liquid nitrogen cryoshrouds, this instrument achieves very low base pressures and low background doping levels. A liquid nitrogen gravity feed tank, provides a continuous flow of liquid nitrogen at a constant pressure and a constant fill level in the MBE. The MBE system has been designed with silicon and germanium beam flux control and a separate sample preparation chamber for outgassing of samples before introduction into the MBE system. The MBE system is also compatible with growth on 1 cm2 samples on small sample plates as required by the STM-SEM. To minimise vibrations from the crystal growth system affecting the atomic resolution of the STM, the MBE system is located on a separate concrete base. This is isolated from the main floor of the laboratory using piers drilled 10 m down into the foundation bed-rock. In addition, the two main chambers of the STM-SEM/MBE system are housed in separate rooms to reduce acoustic interference between them. A low temperature oxide chamber, for the development of high quality silicon dioxide barrier layers, is equipped with a RHEED, a resistive silicon sublimation source (SUSI) and a neutral atomic oxygen source extracted from a RF plasma. The oxide chamber liquid nitrogen cryoshrouds to achieve very low base pressures. The instrument is routinely used to deposit silicon dioxide at low temperatures for gating atomically precise devices in Si.

The MBE system has been designed with silicon and germanium beam flux control and a separate sample preparation chamber for outgassing of samples before introduction into the MBE system. The MBE system is also compatible with growth on 1 cm2 samples on small sample plates as required by the STM-SEM.

To minimise vibrations from the crystal growth system affecting the atomic resolution of the STM, the MBE system is located on a separate concrete base. This is isolated from the main floor of the laboratory using piers drilled 10 m down into the foundation bed-rock. In addition, the two main chambers of the STM-SEM/MBE system are housed in separate rooms to reduce acoustic interference between them.

In 2005, a low temperature oxide chamber, funded by the New South Wales Government, was installed onto the load lock of the MBE system for the development of high quality silicon dioxide barrier layers. The system is equipped with a RHEED, a resistive silicon sublimation source (SUSI) and a neutral atomic oxygen source extracted from a RF plasma. In 2006 the oxide chamber was upgraded with liquid nitrogen cryoshrouds to achieve very low base pressures. The instrument is routinely used to deposit silicon dioxide at low temperatures for gating atomically precise devices in Si.

Nanoprobe Laboratory

In 2006, an Omicron Nanoprobe system was installed. This new four probe STM system is designed for in-situ electrical characterisation of nano and atomic-scale devices.

This system is used for the development of new projects outside the Centre in quantum and molecular electronics as well as for fundamental characterisation of defect states of interest to qubit architectures.

Expansion of the Facility in 2012

At the end of 2011, the AFF was expanded to bring in 3 additional scanning probe microscopes. One of these microscopes, a new Omicron VT-STM, was purchased to meet the growing needs of the AFF team. This instrument was partly funded by the Federation Fellowship of Prof Simmons and strategic UNSW funds. The new VT-STM comprises of improved control electronics, along with a flexible tip preparation tool and a dosing source for both phosphorus and boron dopants. In 2011, the other two microscopes a Variable Temperatre (VT) STM and a Low Temperature (LT) STM were installed following the new academic hire of Prof Sven Rogge from Delft. The AFF now houses six STM systems, providing the highest concentration of STMs in the southern hemisphere.