Centre for Emerging Device Technologies (CEDT)

Gas Source Molecular Beam Epitaxy (GSMBE) is a technique used to grow high purity, fine structure, crystalline materials. Since the founding of the CEDT in 1987, the Centre's GSMBE program, specializing in III-V semiconductor systems, has played a core role in the successful development of spin-off photonic and optoelectronic initiatives. 

The recent commissioning of a new GSMBE system has permitted the decommissioning of the Centre's original MBE system. The CEDT's material capability, previously limited to more traditional InGaAsPN compounds, has been vastly broadened by the new machine to include AlGaInNPAsSb containing compounds. Quantum structures as fine as 10 angstroms in the growth direction are easily produced. Many new research opportunities are anticipated. These include optoelectronic devices with a much broader wavelength range, as well as long wavelength devices for biophotonic applications.

The CEDT operates two plasma-enhanced chemical vapour deposition (PECVD) systems for the deposition of silicon-based thin films and other functionally doped dielectric layers. Films produced by our CVD group are tailored to meet highly specific optical, mechanical, and electrical requirements. Applications include anti-reflection coatings, optical amplification media, and electrical contact and diffusion barrier layers. 

CVD plasma generation is achieved via electron cylclotron resonance in the case of one system (ECR-CVD) and inductive coupling in the case of the second system (ICP-CVD). The ECR and ICP capabilities offer significant advantages and improvemnt in film quality when compared with conventional CVD techniques. Each CVD is also equipped with in-situ ellipsometry for monitoring the thickness and refractive index of films during the growth process.

•  Wet Benches
•  Metallization
•  ECR-Reactive Ion Etching
•  Silicon Reactive Ion Etching
•  SiON Chemical Vapour Deposition
•  Ellipsometry
•  Photolithography
•  Surface Profilometer
•  Stress Analysis
•  Holography
•  Plasma Asher
•  UV Ozone

The CEDT operates a Class 10000 cleanroom facility, available for the micro-processing of semiconductor and superconductor materials. The 1000 sqft work area is divided into two separate rooms.

The cleanroom facility is equipped for photolithographic processing and associated wet-chemistry, chemical vapour deposition, metallization, reactive ion etching, UV oxidation, and holography. This instrumentation is complemented with microscope stations, ellipsometry, surface profilometry, and additional related equipment.

The CEDT operates a variety of rapid thermal annealing furnaces and tube furnaces. The systems are useful in the study of diffusion and defect analysis in semiconductor materials, as well as for growing oxide film layers.

Rapid Thermal Annealing
The CEDT operates two Qualiflow Jipelec Jetfirst 100 rapid thermal annealing (RTA) furnaces. One is specific to III-V materials systems and the other is suitable for silicon-based materials.

Tube Furnaces
The CEDT operates a number of tube furnaces for annealing various systems. Each system can be purged with oxygen, nitrogen, or argon. 

A Lindberg Blue furnace is available for LiNbO3 materials.

A Lindberg and a Thermodyne 21100 are available for silicon-based material systems.

A Thermodyne 21100 is available for silicon-germanium materials.

Reactive ion etching (RIE) is a plasma-based process developed to physically imprint semiconductor circuit features into the surface of a wafer. The ionization of a controlled mixture of gases localized above a sample serves to remove any exposed portion of the sample's surface area via a combination of chemical reaction and physical bombardment. 

In addition, the electrical properties of the plasma can be exploited in order to produce extremely anisotropic etch characteristics. This offers certain advantages over more conventional wet chemical bath etching, which tends to etch isotropically or favour certain crystallographic directions. Thus, RIE can be well suited to the fabrication of features with extremely deep, vertical side walls, and highly consistent critical dimensions.

The quality of features etched by RIE depends on a number of process parameters, including:

• gas flow rates
• chamber pressure
• RF power
• chamber temperature
• pattern density

The CEDT owns and operates a Surface Technology Systems reactive ion etching system, model 320PC, located in TAB 110. The system is dedicated to silicon-based materials applications.

For etching III-V materials, an electron-cyclotron-resonance-RIE system (ECR-RIE) is located in the clean room, JHE A306.

The CEDT operates a Microace 3 dicing saw. Diamond impregnated resin blades are used for cutting materials ranging from semiconductors and glasses to multilayer laminate structures. 

The quality of the cut can be tailored to the requirements of the particular task. Quick, rough cuts can be used to dice wafers for packaging. The saw can also be used for applications requiring greater control and precision, such as the cutting of facets suitable for waveguide coupling. 

The dicing saw is located in TAB 205.

X-rays are electromagnetic radiation with characteristic wavelengths of a few Angstoms, comparable to the lattice constants of crystalline materials. As such, x-rays incident on the planes of semiconductor can exhibit wave interference phenomena, much like light reflected from a periodic grating. Given knowledge of the x-ray wavelength, measurement of the incident and reflected beam angles permits calculation of the spacing of the crystal's planes in accordance with Bragg's law.

The technique's precision makes x-ray diffraction analysis an invaluable tool in the determination of crystal structure, planar spacing, and material composition. Modelling of results can provide additional information indicative of crystal quality, layer mismatch and stress, defects and misorientation, mosaicity, surface curvature, and relaxation.

CEDT X-Ray Analysis Systems
The CEDT operates two XRD systems.

The Bede D1 system's internal Si crystal monochromator makes the instrument suitable for diffraction measurement of most crystalline materials and wafers. Its 12 independently controlled motors also open up a range of additional measurement techniques, including powder diffraction analysis and glancing angle reflectometry.

The Bede QC1 is a dual-crystal rocking curve analysis system. The instrument is suitable for measuring the rocking curves from InP and GaAs based materials.

Booking x-ray time
The CEDT's x-ray facilities are available to CEDT members. Only trained operators are permitted to run the instruments. In cases where only a few samples are to be tested it may be far more efficient and cost-effective to have samples scanned by a CEDT staff Research Engineer, rather than participating directly in operator training.

The x-ray facilities are also available on a fee-for-service basis to McMaster University affiliates who are not CEDT members.

Subject to scheduling availability, the x-ray facilities may also be available on a fee-for-service basis to potential users unaffiliated with McMaster University.

Fees associated with the use of the CEDT's x-ray facilities are used to pay for the maintenance and up-keep costs associated with the systems; the x-ray tubes, power supply units, motors and control electronics all have a finite lifetime. Fees also reflect operator time committment.

Scheduling
Trained operators can book the Bede D1 XRD system via the sign-up form outside room TAB 110/B. However, it may be necessary to reschedule these sessions with little notice.

Training
X-ray operator training is available to CEDT members in cases where XRD analysis constitutes an integral aspect of thesis research. Operators must first attend an x-ray radiation safety seminar provided by McMaster Health Physics, after which a dosimeter is provided.

Specific XRD training on the Bede D1 system can be arranged through the CEDT. Typically, instrument training takes a few hours and requires some subsequent supervision before users become comfortable with independent system operation.

Photoluminescence (PL) describes light spontaneously emitted from a material under optical excitation. PL is studied to characterize a variety of semiconductor material parameters, including bandgap energy, surface quality, and defects. Experiments are reasonably simple to conduct; optical excitation is nondestructive, and samples therefore require minimal preparation or environmental control. The incorporation of temperature control capability or transient-sensitive detection capability can furthur enhance the wealth of information available experimentally.

Three PL systems are available to CEDT members, suiting a range of conditions. 

A low-temperature PL (LTPL) system with a Nd:YAG laser source is located in TAB 205. A low-temperature PL (FTIR-PL) system with FTIR spectrometer analyzer and Argon Ion laser source is located in TAB 110/A. A room-temperature PL (RTPL) system with a HeNe laser source is located in TAB 110/A.

The CEDT operates two FTIR spectroscopy systems. 

An ABB Bomem MB160 FTIR spectrometer with a quartz-halogen source and InGaAs or InAs detector option allows measurements from 1 to 3.3 microns. Figure 1 illustrates the instrument's spectral range. The spectrometer is located in TAB 110/A.

An ABB Bomem WorkIR FTIR spectrometer with a globar source can measure spectra from 2 to 28 microns. Figure 2 illustrates the instrument's spectral range. The spectrometer is located in TAB 205.

Scanning electron microscopy (SEM) uses a focussed electron beam to image the surface of a material. The focussed electrons cause the emission of secondary electrons, and by scanning the beam across the surface of the sample, a spatial image of surface morphology is generated as a function of this secondary electron intensity. Image resolution to 1 nm can be achieved under optimal conditions, and magnification to 500000 times is possible. Some SEM systems can also take advantage of back scattered electrons (BSE) and x-ray emission generated by the probe beam to perform material composition analysis.

The CEDT operates an Hitachi S-2150 SEM. The system is suitable for scans to sub-micron resolution.

Ellipsometry is a model-based measurement technique that can be used to determine certain physical and optical properties of semiconductor, dielectric, and metallic materials. Measurements of variations in the polarization of light reflected from a sample's surface are compared against values calculated based on the sample's composition. The model parameters are then tweaked until excellent agreement with the measured results is achieved. Characteristic sample properties that can ultimately be extracted from the model include:

• optical constants n and k
• thicknesses of single- or multi-layer films
• interface roughness
• doping concentrations
• crystallinity
• alloy ratio
• optical anisotropy
   

Ellipsometers available in the CEDT characterization lab

The CEDT maintains two ellipsometers that are located in the characterization lab.

These include:

• a Philips fixed wavelength, fixed angle ellipsometer with 632.8nm HeNe source
• a J.A. Woolam IR-VASE variable angle, spectroscopic ellipsometer suitable for measurements from 2 to 33 microns

The Hall Effect is used to determine the charge carrier, carrier densities (N), and resisitivities and mobilities of various materials. 

The CEDT operates a Nanometrics HL 5500PC Hall Effect Measurement system. The system includes a buffer amplifier for high resistivity measurements, as well as a cryostat providing temperature control from 77K to 500K. 

Measurements of luminescence, current, and voltage (LIV) are used to determine the properties of materials and devices fabricated by CEDT researchers. 

A probe station based on a Keithley 2400 LV SourceMeter with an Ando AO6317B Optical Spectrum Analyzer and Anritsu Optical Power Meter provide a versatile measurement system. LabView-based LIV software can be tailored to the requirements of various experiments.