Tools for nanotechnology at the University of Glasgow
The University's strengths in the core technologies of Electron Beam Lithography, Molecular Beam Epitaxy, Plasma Processing Technologies and Nanocharacterisation are key to supporting the wide range of Nanotechnology actvities across the campus. These core capabilities have been developed over 30 years and the University's state of the art facilities enable the researchers to push the boundaries of Nanotechnology.
- Electron beam lithography
- Plasma processing technology
- MBE research – epitaxial growth and characterization of III-V semiconductors
- Nanocharacterisation
- Scanning capacitance microscopy
- Atomic force microscopy
Electron beam lithography
The University of Glasgow has more than 25 years of experience in electron beam lithography and has recently purchased and commissioned a Vistec VB6 UHR EWF lithography tool – one of the most advanced large area high resolution patterning tools in the world. It has a minimum spot size of 4 nm and can handle a range of different substrates up to eight inches in size.
Over the years a large and vibrant interdisciplinary lithography user group has grown at Glasgow and the boundaries of lithography tool performance are constantly being pushed. Early work on electron beam lithography was carried out on lithography tools constructed within the Department of Electronics & Electrical Engineering. In 1991 the university purchased a Vistec EBPG5 HR100 lithography tool capable of patterning substrates up to six inches in size with a 12 nm spot. The tool has been extensively used by many different research groups within the University including; nanoelectronics, optoelectronics, bioelectronics, cell engineering, and nanomagnetics. It has been used to pattern many thousands of substrates and over the years a wealth of processing experience has been established at Glasgow. The new VB6 tool has demonstrated excellent 10 nm lithography over 1.2 mm pattern writing fields and in the years ahead will allow Glasgow to continue to play a leading role in this core fabrication technology.
External users gain access to lithography facilities at Glasgow either through research collaboration or through Kelvin Nanotechnology, which handles commercial activities within the Department of Electronics & Electrical Engineering.
Contact: Dr Douglas Macintyre, Dr Stephen Thoms
Plasma processing technology
Glasgow has a comprehensive range of plasma processing facilities, which include:
- two plasma enhanced chemical vapour deposition (PECVD)
- one inductively coupled plasma-CVD (ICP-CVD) machines for plasma depositions
- four reactive ion etch (RIE)
- one ICP machine for dry etching
- optical interferometer and optical emission spectroscopy for in situ monitoring of plasmas and etch depth
- ellipsometer for film thickness and refractive index.
Glasgow has pioneered and established many novel research activities in original plasma processing technologies and their characterisations. As the absolute precision of pattern transfer and the process thermal budget are the dominant issues in realisation of nano-devices, our particular strength has been the studies of plasma-induced damage and low-temperature plasma depositions for high-performance nano-devices. These have lead to a fundamental understanding of the mechanisms of plasma processing and have been of great relevance to device design and fabrications.
In Glasgow dry etching tools have been routinely used to etch an extensive range of materials, which not only include III-V, II-VI and IV semiconductors, but also high-k dielectrics, metals, insulators and plastics. A number of specific processes have been developed for particular companies. PECVD tools have been routinely used to deposit conformal and uniform dielectric films of SiO2, SiNx as well as low stress SiNx at 300oC. Glasgow has also pioneered and successfully developed a novel room temperature ICP-CVD technology, which has produced high-quality SiN films with very low hydrogen content <3at. %, high breakdown electric field >3x106Vcm-1, low stress <1x109Dynes/cm2, and also very little plasma-induced damage.
Glasgow etching and plasma deposition facilities are in constant use by members of a wide range of multidisciplinary research groups within the university. We do collaborative research work with external organisations.
Contact: Dr Haiping Zhou
MBE research – epitaxial growth and characterization of III-V semiconductors
The Molecular Beam Epitaxy (MBE) Research Group in Glasgow has nearly 30 years experience with the MBE growth and characterisation of III-V semiconductors. The Group operates one Varian 3” Mod Gen II machine and has recently taken delivery of a new dual-chamber 4” Gen III, manufactured by Veeco Instruments Inc. The Gen II is equipped with In, Ga, Al, As2, Ge, Si and Be sources, and has been used to grow a wide variety of materials on both GaAs and InP substrates. The Gen III has been purchased to enable a new line of research into the growth of high-k dielectric stacks for the realisation of III-V MOSFETs, a project undertaken in collaboration with Freescale Semiconductors in Phoenix, Arizona. The Group routinely grows world-class epitaxial material and structures to support a wide range of projects in high speed devices and opto-electronics, including so-called third generation photo-voltaic (solar) cells.
Apparatus for characterising the electrical, optical and structural properties of MBE samples includes a 4-300 K Hall effect apparatus; a high resolution 10 K photoluminescence spectrometer for studies from ~600 nm out to ~1.6 µm; a fast Fourier transform infrared (FTIR) spectrometer to measure material and devices properties in the wavelength range from ~900 nm to ~ 18 ?m; C-V and I-V measuring equipment, and a bench-top double crystal X-ray diffractometer for determining the composition of epitaxial layers. The Group collaborates with colleagues in the Department of Physics and Astronomy on high resolution transmission electron microscopy (TEM) and quantum transport measurements at 1.2 K, and makes extensive use of AFM equipment located in the James Watt Nanofabrication Centre.
The MBE Research Group is located in a purpose-built facility known as Photonix, off-campus on the West of Scotland Science Park.
Contact: Prof Colin Stanley
Nanocharacterisation
Understanding the properties of new and exciting materials at the nanoscale is at the core of the research activity within the Physical Sciences Faculty. Research concerns the characterisation, development and application of advanced functional materials - the aim is to understand at a microscopic level, how various physical properties relate to material nanostructure and how the former can be improved by the ways in which materials are grown and processed. With this understanding we hope to enable the development of devices of the future by using new materials.
Work also focuses on the development and application of techniques of nanoanalysis combined with transmission electron microscopy - allowing the characterisation of the structure and chemistry of materials down to atomic scales. Physicists have developed an understanding of electron energy loss near edge structure and have used this to extract information about local composition and chemistry on a nanometre scale.
Researchers are pushing the capabilities of techniques available to understand what’s going on within materials such as semiconductor materials, silicon III-V, metal alloys, steel, hard coatings for cutting tools, composites and ceramics, amongst others, to provide information on the materials.
Contact: Prof Alan Craven
Scanning capacitance microscopy
Two of the most important challenges to semiconductor metrology as identified in the International Technology Roadmap for Semiconductors are measurement of the equivalent oxide thickness of high-k dielectric stacks and dopant profiling in 2-d and 3-d. Scanning Capacitance Microscopy provides a potential Solution to these problems.
An SCM consists of a tip situated at the end of a resonant line which is detuned by changes in the capacitance between tip and surface. Dopant concentration may be measured by measuring the change in capacitance as carriers are depleted (C-C profiling).
The three problems associated with commercial SCM instruments are stray capacitance, low intrinsic sensitivity and illumination of the sample by the laser associated with AFM Force–Distance measurement. These problems are solved by the approach here. The SCM project concerns the development of a system for the local measurement of capacitance in Ics using a micromachined 0.35mm SiGe BiCMOS die. The use of a high operating frequency (8GHz) will allow the use of a monolithic resonator, eliminating stray capacitance drift. The use of foundry silicon allows for the use of complex on-chip signal processing and force sensing by the use of integrated piezoresistors. System targets include zeptoFarad sensitivity, corresponding to 0.1% change in Equivalient Oxide Thickness in a 10nm square measured in unit bandwidth.
Contact: Prof John Weaver
Atomic force microscopy
With around 15 years experience in the development of technologies for the integration of ultra-high resolution lithography with micromachining, the AFM group have developed new reproducible processes to enable commercial production of functionalised microscope probes. By using photolithography and reducing the reliance on expensive Electron Beam Lithography, the group can produce passive microscope probes faster, more simply, at reduced cost and with better yield. The group has developed thermal probes that can be used for analysis of forensics and pharmaceuticals, and these products are available commercially.
Probes are produced in batches of 240 for production probes and 60 for research probes. Photolithography and potassium hydroxide etching are used to pattern the probe bases then, using etched through alignment markers, we begin the electron beam lithography levels on the other side of the wafer. Multiple levels of e-beam are performed to make the sensor devices and then the cantilevers are released in a final KOH etch.
Scanning Near-Field Optical Microscopy (SNOM) has applications in the Bio field as sensors. The team researching SNOM are developing multiple parallel SNOM probes as part of the SNOMIPEDE consortium which will greatly increase the speed of this technique and aid its application in the areas of microscopy materials modification and lithography.
Contact: Prof John Weaver