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The University of New South Wales

The Centre has three major research laboratories at the University of New South Wales: the Atomic Fabrication Facility (AFF), the National Magnet Laboratory (NML) and the Semiconductor Nanofabrication Facility (SNF). These facilities are located within close proximity to each other in the Newton building and offer a broad range of nanoscale device fabrication and measurement capabilities.

Consolidated within the Newton building, the Centre also has 700 m2 of office space with conference facilities supporting 50 staff, students and visitors. There is a Microsoft Windows based computer network of 70 personal computers (PC’s ) including 25 used for data collection, data processing and control of equipment in the laboratories. The backbone of the PC network is a cluster of Linux servers that perform file serving and web hosting duties. Three visualisation workstations are available for simulating semiconductor devices and electromagnetic and RF fields.

To complement the plant areas within and adjacent to the three facilities, there is a large services compound which supports all laboratories and several other areas within the School of Physics. This compound incorporates: a bulk liquid nitrogen vessel, large scale diesel generator to supply backup power via an uninterruptible power supply to crucial equipment in the AFF, helium recovery compressors with gas storage, gas bottle storage and outgoing chemical waste storage.

Semiconductor Nanofabrication Facility (SNF)
Now in its 11th year of operation, the SNF houses cleanroom laboratories containing a comprehensive collection of microelectronic and nano-electronic equipment for fabricating an array of silicon (Si) and gallium arsenide (GaAs) devices.

Extending over 300 m2 and three floors, the SNF contains four laboratory areas offering differing cleanroom environments. Each floor has 50 m2 of environmentally controlled class 3.5 cleanroom. This cleanroom environment is maintained by a vertical laminar air handling system. In addition, there is also approximately 135 m2 of class 350 cleanroom space. A further plant area accommodates the air conditioning units and the laboratory services including: ultrapure recirculating de-ionised water, high purity gaseous nitrogen, vacuum, cooling water and exhaust extraction.

The lower floor cleanroom houses equipment geared for nano-scale device fabrication. The key instruments within this laboratory are two electron beam lithography systems (EBL) which are used for nano-lithography and high resolution imaging. The systems (FEI XL30 and FEI Sirion) offer state-of-the-art resolution capabilities as well as high throughput. They have imaging resolution of better than 2 nm and are capable of producing line-widths below 10 nm. The Sirion system is a 30 kV Schottky emitter based FEG-SEM with an imaging resolution of 1.5 nm at > 10 kV. It is fitted with a fast, electrostatic beam blanker and Nabity Pattern Generator which enable ultra-high resolution electron beam lithography to be performed.

The lower floor class 3.5 area also holds systems and services for UV lithography, metal deposition, atomic force microscopy (DI3100) and wet chemical processing.

The upper floor cleanroom is furnished with an array of facilities for producing micro-scale silicon devices. Equipment and services include: high temperature silicon diffusion and oxidation furnaces, UV lithography facilities, a rapid thermal annealing station and wet chemical process lines.

The class 350 environments contain a collection of plasma processing and chemical vapour deposition systems, bonding stations and measurement tools complementing the class 3.5 facilities. The SNF laboratories are maintained by 4 full-time and 2 part-time professional and technical staff.


FIGURE 1 Operation of the Sirion and XL30 EBL systems at UNSW SNF.

FIGURE 2 Operation of evaporator for fabrication of single electron transistors.

FIGURE 3 High temperature silicon processing.

SPECIAL GASES SYSTEM
A suite of deposition, dopant and etching tools are served by the Special Gases System which distributes and stores the process gases to the laboratory. These gases include: PH3, SiH4 GeH4, B2H6, SF6, NH3, H2 and CH4. A rooftop gas shed houses gas cylinders, distribution pipes, exhaust extraction and environmental control items. Highly sophisticated gas monitoring and automatic safety equipment is used due to the hazardous nature of some of the gases.

SNF Extension
In November 2005, construction commenced on a large extension to the SNF adjacent to the upper level cleanrooms. The project involves 4 stages and will ultimately comprise 75 m2 of class 3.5 cleanroom, 100 m2 of class 350 cleanroom, 45 m2 of office and workshop space and 120 m2 of plant and service zones. Stages 1 and 2 are due for completion in April 2006 and incorporate the class 350 cleanroom, technical office, workshop and plantroom. Equipment to be installed includes: an inductively-coupled-plasma reactive ion etcher (ICP-RIE), low pressure chemical vapour deposition system (LPCVD), fumecupboards, UV mask aligners, two EBL platforms (EBL100 and a Leica S440 SEM which will be converted into an EBL) and vacuum deposition systems.






FIGURE 6
Floor plan and equipment layout of the Semiconductor Nanofabrication Facility.


FIGURE 7
Extension of the Semiconductor Nanofabrication Facility, to be completed in 2006.


FIGURE 4
Decanting liquid nitrogen from main vessel in the services compound.


FIGURE 5
Linux computer cluster at UNSW.


Atomic Fabrication Facility (AFF)
The Atomic Fabrication Facility (AFF) was established in 2001 and is situated on the ground floor of the Newton Building. It contains 5 interlinked laboratories all dedicated to the development of atomically precise devices in silicon with the ultimate goal of developing a scaleable quantum computer (QC) 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 an Omicron Variable Temperature STM (VT STM) and a combined STM-SEM/MBE system. This multi-chamber system has been designed in collaboration with Omicron NanoTechnology GmbH and MBE Komponenten GmbH in Germany to combine a high quality SiGe MBE system with a dual STM-SEM system. This unique ultra-high vacuum (UHV) microscope and crystal growth system will allow the atomic fabrication of the complete qubit architecture and occupies two of the rooms of the AFF laboratory.

VT-STM LABORATORY
The majority of work on understanding the phosphorus in silicon surface chemistry has been carried out on the Variable Temperature Scanning Tunnelling Microscope. This instrument was installed in 1998 and consists of a custom-configured, triple-chamber UHV STM/MBE system, also manufactured by Omicron NanoTechnology GmbH in Germany. In 2000, this facility was upgraded with the addition of a silicon sublimation source (SUSI) for high quality silicon MBE growth and in 2001, a second silicon evaporation source was directly attached to the STM stage. This silicon source deposits high-quality silicon films with monolayer or sub-monolayer thicknesses and allows for direct STM observation of the silicon growth dynamics. The first chamber of this system houses the STM which can be operated at temperatures ranging from 25 K to 1100 K in addition to the silicon evaporation source which is attached to the STM stage. Alternatively, this system can also be used as an Atomic Force Microscope (AFM). The STM/AFM tool is used to image the silicon surface and perform atom-scale lithography. The second UHV chamber houses a silicon evaporation source for the growth of thin epitaxial silicon films with thicknesses ranging from sub-monolayer to several tens of nanometers using an MBE process. The layer-by-layer epitaxial growth can be monitored by Reflection High-Energy Electron Diffraction (RHEED). 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).

  FIGURE 8 The VT-STM system for high resolution studies of the Si(100):phosphine surface chemistry.
 
MBE LABORATORY
A multi-chamber STM-SEM/MBE system is installed in the AFF which provides the necessary registration and high purity silicon growth capabilities required for multi- qubit fabrication. Specifically, the MBE component is capable of device quality 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, necessary to provide a continuous flow of liquid nitrogen at a constant pressure and a constant fill level in the MBE cryoshroud, was installed in 2004. 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. This system houses the RHEED, SUSI sublimation source and RF oxygen plasma facilities and will be used to develop our ability to build gated devices.

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 pre-patterned substrate. This system is where most of the pioneering device work has been developed and is due to be upgraded in 2006 with a newly designed manipulator for more accurate temperature control.

VACUUM TESTING LABORATORY
The AFF contains a general work area which houses a UHV test rig. The test rig is crucial for calibrating Knudsen cells and testing UHV components, ensuring that the cleanliness of the main MBE chambers is maintained. This laboratory also provides a workstation area for image manipulation and analysis. In 2006, this laboratory will be modified to accommodate the VT-STM, whilst the VT Laboratory will be reconfigured to house a new Omicron Nanoprobe system. This new four probe STM system is designed for in-situ electrical characterisation of nano, atomic-scale devices and is part of a separate, recently funded LIEF grant in collaboration with the Universities of Sydney (Crossley, Reimers, Hush, Stampfl) and Newcastle (Smith, Radny, King). This system will be 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.


FIGURE 9
Loading a substrate with registration markers into the STM-SEM system.


FIGURE 10
Transfer of samples from the recently commissioned oxide chamber through to the STM-SEM system.
EBL/CL LABORATORY
The AFF laboratory also houses a Leica Stereoscan S440 Scanning Electron Microscope with a cryogenic stage. This system can be used for training students on Electron Microscopy and for studying defects in silicon by cathodoluminescence (CL). The Leica SEM is configured with an Oxford Instruments MonoCL2 Microanalysis System for cathodoluminescence imaging and spectroscopy. Cathodoluminescence microanalysis has the ability to detect with high sensitivity, diamagnetic as well as paramagnetic defects. The detected CL is used to modulate the display units of the SEM, thus providing an image or map of the spatial distribution of the dopant or defects present. There are currently only two of these specialist CL Microanalysis systems in Australia.

National Magnet Laboratory (NML)
Measurements and characterisation of quantum devices are performed in the National Magnet Laboratory. This 200 m2 laboratory houses sophisticated measurement facilities for performing experiments on nano-scale devices. Measurements of pico-Volt signals from DC to microwave frequencies can be made at temperatures ranging from 10 milliKelvin to room temperature, at constant magnetic fields up to 16 Tesla or pulsed magnetic fields up to 60 Tesla. In-house optical capabilities exist for spectroscopy, photoluminescence and photoconductivity measurements. These may be coupled to various low temperature platforms. The laboratory is at present equipped with four dilution refrigerators which are variously configured to enable a wide range of measurements. The ‘C’Dilution refrigerator is housed in an electrically screened room and is configured to allow highly sensitive measurements of two independent samples simultaneously using DC and low frequency AC measurements. Two ‘F’ dilution refrigerators have been custom designed and configured to allow ultra-high speed measurements on picosecond timescales using radio frequency (0-6 GHz), fast pulse (30 ps) and microwave (0-50 GHz) techniques. Supporting instrumentation includes: RF and microwave sources, cryogenic low noise amplifiers, two RF spectrum analysers, a network analyser, Anritsu pulse pattern generator and fast multi-channel oscilloscopes for data collection. RF fridge 1 is housed in a copper screened room.

Located in a new 30 m2 laboratory which was refurbished in mid 2005 is the fourth ‘lastic’ dilution refrigerator which provides for longer-term DC experiments down to 100 mK, in magnetic fields to 9 Tesla. This system can also be used in pulsed magnetic fields up to 60 Tesla.

Rapid characterisation of devices at liquid helium temperatures is achieved in seven device-dipping probes which may be coupled to either of two comprehensive electronics racks under the control of data acquisition PC’s enabling a variety of standard device tests to be performed. The tests include: DC transport, RF/Microwave measurements, magnetic studies and optical measurements.

Optical measurement systems which can be interfaced to the measurement platforms described above are housed in a purpose built optics laboratory within the NML. These facilities include a tuneable Ti-Sapphire ring laser pumped by an Argon laser and a triple-pass high resolution spectrometer fitted with CCD detectors. Experiments requiring large magnetic fields are conducted in a specially constructed blast-proof room capable of pulsed magnetic fields up to 60 Tesla (for 20 milli-seconds) or 30 Tesla (for 1 second).

The laboratory is supported by two full time professional staff with extensive experience in cryogenics and measurement systems.

  



FIGURE 11
‘Plastic’ dilution refrigerator in new NML annex.


FIGURE 12
Insert for radio-frequency equipped dilution fridge.

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FIGURE 13
Dilution fridge insert configured for low-frequency operation

FIGURE 14
RF1 – RF fridge insert being withdrawn from a helium dewar.

FIGURE 15
RF2 – dilution refrigerator platform and microwave electronics equipment.




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