Publications
The MRG has extensive facilities for semiconductor fabrication from substrate development with molecular beam epitaxy (MBE) to device fabrication in a class 1000 clean-room to measurement and analysis. To further investigate group capabilities choose a sub area of interest:
Cleanroom (A. G. Nassibian Nanofabrication Facility)
The Microelectronics research group operates a class 1000 clean-room facility, where all device fabrication processes are carried out. The equipment available in the cleanroom are shown below.
Thermal deposition system used for ZnS passivation layers on MCT detectors
BOC Edwards Ebeam system with Ar sputter pre-clean capability and Temescal 6 Pocket crucible used for materials such Ti,Pt,Pd,Au,SiO,Si,Ge.
Dual chamber thermal evaporation system used for metals and dielectrics, Standard materials include Al,Cr,Au,Ni,SiO,Ge and In
Oxford instruments ICPECVD system for low temperature (<100C) Si based films such as SiO2, SiOxNy, SiNx, SiC.
Oxford Instruments PlasmaLab80 system, dual RIE and PECVD system.
Rapid thermal processing system, can heat (upto 900C) in ambient, vacuum or selected gas environments.
Dektak surface profilometer for measuring film heights or etch depths after processing.
One of four chemical fume cupboards for liquid based processing of materials and devices.
SPI critical point drying system for releasing MEMS devices in a surface tension free environment. Also known as the “lab bomb” as it contains supercritical carbon dioxide at pressures in excess of 80 atmospheres.
Headway photoresist spinner and hotplate.
A MJ3B mask aligner system using for optical lithography.
Vacuum ovens for curing photoresists and polyimide.
Molecular Beam Epitaxy Laboratory (MBE)
Molecular Beam Epitaxy (MBE) is a method of depositing thin, single crystal semiconductor layers onto a suitable crystalline substrate. In its basic form, polycrystalline source materials are thermally evaporated in an ultra high vacuum (UHV) environment, so that the molecular beams may travel across the vacuum and crystallise onto a heated substrate also within the vacuum. In a carefully controlled system it is possible to create conditions where the molecular beams from the source materials condense as single crystal semiconductor material, in a layer by layer or two dimensional (epitaxial) growth mode. Due to the relatively low temperature of MBE growth and the two dimensional nature of the growth, very abrupt changes in composition may be achieved with MBE, which is of particular use in realising many optoelectronic and high speed electronic device structures.
Measurement
Hall measurement system
Automatic, variable magnetic field (0-2T) Hall system allowing for magnetic field dependent Hall data measurement and analysis.
Responsivity measurement system.
The spectral response of photosensitive devices is obtained from responsivity measurements. These are performed on an Optronic Laboratories Detector Spectral Response Measurement System, which is controlled by a computer. In this system, infrared radiation from a ceramic glow bar is directed through a monochromator and chopper which illuminates the device. The device converts the incident radiation into an electrical signal, which is then amplified and measured using a lock-in amplifier. Responsivity can then be calculated from the calibrated input power and measured signal.
This spectral response system is an integral part of the characterisation of the HgCdTe and MEMS devices that are fabricated here at MRG.
Scanning Laser Microscope/ Laser-Beam Induced Current
The Waterloo Scientific model ICM-200 scanning laser microscope (SLM) is used for optical characterization of HgCdTe materials and devices. The tool is equipped with both HeNe (633nm) and Nd:YLF (1047nm) lasers, and samples are mounted in a cryostat to enable variable temperature measurements under vacuum. Laser beam induced current (LBIC) testing is performed using the SLM to create a 2D map of the electrical response of samples to the incident laser which can be used to map features such as electrically active material defects and also for qualitative investigation of junction devices. The SLM is also used to map spatial photoresponse of devices and for transient lifetime measurements.
Above is a LBIC image of a n-on-p junction fabricated in vacancy doped HgCdTe. As measured through remote ohmic strip contacts outside the scan area to the left and right. At each sample point the induced current is measured as a function of position - the so called LBIC arises as photoinduced electron-hole pairs are able to diffuse to and be swept apart by an electric field (in this case the built-in field of the junction) and seek to recombine.
Mask making for photolithography (“The rocket”)
A mask making facility is available to transferring mask-designs, from overhead transparencies, to emulsion masks, with a reduction ratio of 1:20.
View of emulsion mask placed at the top of the rocket, to receive reduced image from transparency.
Optica
Optics lab basic equipment
- 3 optical measurement laboratories
- 3 optical benches
- Monochromators:
- SPEX 270M
- SPEX 750
- Oriel Cornerstone
- 3 Lock-in amplifiers (Stanford Research Systems SR-830-DSP
- Choppers with controllers (Stanford Research Systems SR-540)
- 3 Current pre-amplifiers (Stanford Research Systems SR-560/570)
- 1 Voltage pre-amplifier (Stanford Research Systems SR-560)
- Current sources
- Lasers
- Hewlett Packard 54522A digitizing storage oscilloscope
- Agilent 33220A Arbitrary function generator
- Various optics and optomechanics
Setups in the optics labs
R&T Setup for the shortwave and midwave range
A reflection & transmission measurement setup is available in the optics lab, primarily used for the MEMS research thrust of the group. It consists of:
- A Quartz-Tungsten Halogen optical source
- a SPEX 270M monochromator
- a Stanford Research Systems SR-830-DSP lock-in amplifier
- Stanford Research Systems SR-560/570 preamplifiers
- a Stanford Research Systems SR-540 chopper and controller
Spectral measurements over both the shortwave, and the midwave spectral regions is facilitated by switching a grating. The source and the optical elements function from the visible, up to the midwave spectral range.
Source side of R&T Setup
Shortwave arm of R&T setup
Midwave arm of R&T setup
Optical surface profilometer
The optical profilometer available in the optics lab is a model A22 unit, made by Zygo Corporation. It uses the principles of interferometery, and phase unmapping, to reconstruct the surface profile of a sample, from a series of interferometric images.
Originally a 2.5x Michelson mode interferometric objective was provided with this unit. A new 20x Mirau objective has since been purchased for this system to allow measurements of more lateral detail.
The depth range of the system is 160nm, with a resolution of 5nm. However, with the use of two filters closely spaced in wavelength, and a the “synthetic wavelength” obtained by the effect of these two filters, The depth scan range extends to 2.5 microns.
UV Lifetime measurement setup
This technique is used to determine the minority carrier recombination lifetime of GaN. The phase difference, φ between a sine-modulated optical excitation signal and the photoluminescence signal emerging from the sample is measured and used to calculate lifetime using Tr = -(1/ϖ)tanφ. The intensity of the excitation signal is modulated sinusoidally at about 100MHz using a UV-optimised electro-optic modulator, which utilises the Pockels effect.
Absolute Photocurrent Technique
This technique is used to determine the minority carrier diffusion length in GaN. Minority carriers are generated within a Schottky diode and collected via the Schottky contact. Carriers are generated by UV light of varying wavelengths and the diffusion length is extracted from the short-circuit photocurrent measured. The wavelength of the incident light is varied using a monochromator with a 1200 lines/mm holographic grating. The light source is a 150W Xenon arc lamp with a high UV output.
