Installation C: UV Laser Material Processing Workstations

Installation C Task Force: D. Anglos

Installation C provides access to three excimer lasers with pulse energies up to 600mJ at 150Hz, resulting in focused intensities of 109-1010 W/cm2. They are used mainly for various material processing studies, in certain cases complemented by two low-power CO2 lasers as needed. The emphasis in Installation C is on the offering of workstations oriented to specific application areas of technological interest. In that respect Installation C also provides access to a wide range of material characterisation facilities for the evaluation of the results.

Excimer laser material processing workstations

Thin Film Deposition stations

The main technique employed for the deposition of thin films, the Pulsed Laser Deposition (PLD), is realized by experimental setups dedicated to the study of the principles involved and emphasis is placed on capability for growth of specific coatings. The workstations are modular in nature and allow for configurations to work on a variety of substrate geometries.

These capabilities are implemented in workstations equipped with rotating targets driven by either vacuum-compatible stepper-motors or external DC motors, double target arrangement for colliding plasmas deposition, large optical access for plume diagnostics, large area deposition by means of combined translational/rotational target/substrate movement, substrate heating by either tungsten wire or CO2 lasers. All stations are complemented by computer controlled flow metering and flow sequencing systems, if required.

Time-of-flight mass spectroscopy an intensified gated CCD camera and a streak camera are used to determine the plume characteristics. Profillometry, microhardness tester, scanning electron microscopy, transmission electron microscopy and electron probe X-ray analysis are employed for the ex-situ film characterization. An X-Ray Diffractometer provides more information on the thin film microstructure.

Films of a variety of materials can be grown on any substrate such as metals, ceramics, composites and fiber optics. Coatings of current interest include high-Tc superconductor thin films, epitaxial oxides on semiconductors, diamond-like carbon films, refractory materials, certain metals such as Pt, Ti, Au, ferroelectrics, polymers and biocompatible materials.

Micromachining centre

System description

The unit consists of a suitably modified UV microscope system and optics, in conjunction with a KrF excimer laser. The high power laser beam is used for imaging an arbitrary master mask on target. The target is placed on a system of high precision Burleigh x-y translation stages powered by piezoelectric motors offering 50 nm position measurement accuracy with 4 nm minimum step. Photoablation based etching of patterns with arbitrary morphology is possible via raster scanning. The system, which is enclosed in an environmentally stable cubicle, is capable of etching patterns of high resolution of the order of one micron and excellent etching quality.

Applications

Application Areas: Fabrication of microoptical components such as diffractive elements including Bragg gratings, microlenses, microlens arrays, computer generated holograms; additionally micromirrors, couplers, filters and distributed feedback lasers; Fabrication of micromechanical components such as microsensors, micromotors etc.

Holography and Optical Processing workstation

System description

The workstation consists of several cw lasers operating in the region from the UV to the near IR (e.g. HeCd, HeNe, AlGaAs) which can be used for the recording of volume holograms as well as holograms in waveguides. Depending on the material used, both static and dynamic holographic recording is possible. Real-time optical processing of images is also possible by exploiting the dynamic nature of holograms recorded in photorefractive materials such as BaTiO3, KNbO3, Bi12SiO3. Characterization of holographic gratings and other optical structures is available. Studies in optoelectronics and related devices can be undertaken. Writing constant and variable pitch (chirped) Bragg gratings in fibers, wave-guides, as well as holograms by using interferometric or holographic techniques. Interference patterns with minimum pitch of a few laser wavelengths can be holographically produced, complementing the micromachining facility.

Applications

Application Areas: Photorefractive optics in optical signal processing: phase conjugation; image amplification; optical detection; static and dynamic holography, including holographic recording and storage and optical interconnect systems. Fabrication and testing of optical waveguides, waveguide sensors etc. Study of new non-linear optical materials such as polymers, bacteriorhodopsin, fullerenes, chalcogenides etc. Development of new optical systems for biomedical applications. Fibre-sensors; Fibre-lasers; Fibre amplifiers; Gratings on conventional fibers; Fibre wavelength multiplexing.

Laser-Integrated Molecular Beam Epitaxy (LIMBE) station

System description

A unique Molecular Beam Epitaxy (MBE) reactor which consists of two growth chambers with integrated laser processing capability, sharing the same entry-lock and preparation/analysis chambers, is installed in 40m2 of class 10.000 clean room space.

One growth chamber of the MBE reactor is for the epitaxy of III-V arsenide semiconductors using solid material sources. It contains 8 thermal sources (K-cells) that include Ga, As, Al and In for material structures, as well as Si and Be for n- and p-type doping. It is equipped with a Reflected High Energy Electron Diffraction (RHEED) system for in-situ monitoring of the epitaxial process and surface reconstructions, a Residual Gas Analyzer (RGA), a flux monitoring ion-gauge and a rotating holder capable for wafer diameters up to 3 inches. An excimer laser is available for the irradiation of the substrate surfaces, including a beam scan system, which in combination with substrate rotation allows for the uniform exposure of a growing 3 inch wafer.

The second growth chamber is dedicated to solid source epitaxy of Si and solid or gas source epitaxy of SiC. It is equipped with 2 electron-gun sources (one of Si and one for C), a gas source of C2H2 and 3-K cells for doping. It also includes a rotating substrate holder (up to 3 inches) , a RHEED system, a quartz oscillating thickness monitor and a movable flux monitoring ion-gauge. A laser beam scanning system is under construction.

The preparation/analysis chamber includes a heating stage for substrate outgasing up to 600-700oC and an Auger Electron Spectroscopy (AES) system for surface chemical analysis, which will be upgraded with capabilities for X-ray Electron Spectroscopy (XPS) in the near future.

Electrical and optical characterization of the epitaxial thin films is carried out by a Biorad fully automated 300K and 77K Hall mobility measurement station, a Biorad PN4300 fully automated Semiconductor CV Profiler, a BIORAD DL4600 automated DLTS system, and a Photoreflectance (300K)/Photoluminescence (12K) system.

Applications

Application Areas: Laser assisted MBE growth (GaAs, AlAs, AlGaAs, InGaAs, InAlAs, Si, SiC); In situ annealing, alloying, recrystallization; Laser cleaning of semiconductor grade wafers (GaAs, InP, Si, SiC, Al2O3, etc); Laser-induced etching of semiconductor layers with ablation (GaAs, InGaAs, InAlAs, AlGaAs, Si, SiC);

X-ray Scattering, Diffraction, and Reflectivity station

The application of x-ray scattering and diffraction methods to the investigation of the structure-morphology and phase transitions in self-assembled systems is an area of great scientific and technological interest. A common characteristic of the structure of complex systems is their organization in space over broad length scales ranging from A to mm and only scattering techniques produce information on the morphology on various length scales. At the same time, the investigation of the morphology and transitions in confined geometries and/or near surfaces/interfaces requires the use of reflection techniques.

The x-ray workstation includes a high flux Rigaku D/max-2400 generator capable of producing simultaneously two x-ray beams. The characteristics of the generator are: rotating anode with changeable target material capability; horizontal tube with 2 Be windows and electromagnetic shutters; Line and point focus; 12 kW maximum power output, 60 kV maximum voltage, and 200 mA maximum current; 0.5x10 mm2 focal spot size. Two instruments are attached to the generator: a small-angle x-ray scattering camera (2j range: -3° to +3°, slit collimation) with a position sensitive detector (100 mm effective length, 10 mm window height), and an x-ray diffractometer (2j range: -60° to +158°) which can be substituted with an x-ray reflectometer with a thin film attachment. The x-ray workstation can be combined with dynamic light scattering and rheo-optics.

Application Areas: Investigations of structure-morphology and phase transitions in self-assembled system; Kinetics of phase transitions and interfacial partitioning.

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