Jon Wulff Petersen

ON THE NATURE OF CROSS-HATCH PATTERNS ON COMPOSITIONALLY GRADED SI1-XGEX ALLOY LAYERS

The effect of strain relaxation on the surface morphology of compositionally graded Si1−xGex layers grown at 550 °C has been investigated by a combination of transmission electron and atomic force microscopy. By annealing unrelaxed graded layers, we have found that shear displacements caused by dislocation glide roughen the surface dramatically. This effect is attributed to the formation of a network of dislocation clusters which give rise to the pronounced slip‐band pattern on the surface of the graded layers. It is shown that the surface plastic displacements produced by such a network during growth of the graded layer contribute significantly to the formation of the cross‐hatch patterns.

Silicon nanostructures produced by laser direct etching

A laser direct‐write process has been applied to structure silicon on a nanometer scale. In this process, a silicon substrate, placed in a chlorine ambience, is locally heated above its melting point by a continuous‐wave laser and translated by high‐resolution direct‐current motor stages. Only the molten silicon reacts spontaneously with the molecular chlorine, resulting in trenches with the width of the laser‐generated melt. Trenches have been etched with a width of less than 70 nm. To explain the functional dependence of the melt size on absorbed power, the calculations based on a two‐phase steady state heat model are presented, taking the temperature‐dependent thermal conductivities and optical parameters into account.

Fast three-dimensional laser micromachining of silicon for microsystems

Abstract The application of laser direct etching of silicon in developing and processing devices for microelectromechanical systems is discussed. The direct write system presented in this paper features high writing speed, high resolution and large access range. Direct micromachining of truly three-dimensional structures, rapid prototyping, processing on non-planar substrates, deep structuring such as drilling and cutting, and complementary processing and post-processing through laser direct etching are demonstrated. Examples include prototypes of micromachined diffuser/nozzle elements, illustrating the potential for microfluidic devices, lens arrays and structures cut out of a membrane, showing the high flexibility of this process.

Three-dimensional nanostructures by direct laser etching of Si

Abstract Nanostructures have been machined into Si by a high-resolution laser direct write system. The Si substrate is locally heated above its melting point by a continuous-wave laser and rapidly etched by dry Cl2 gas. If the solid-to-liquid transition is adjusted to occur only at the peak of the temperature profile, the melt size is significantly smaller than the diffraction-limited spot size. This can translate to extremely small etched features because of the high selectivity of the etching process for liquid Si compared to crystalline Si. By using objectives with a high numerical aperture, 488 nm as well as 351 nm light from an Ar ion laser, and X/Y/Z translation stages for moving the substrate instead of steering the beam, we have achieved line widths below 200 nm combined with very high scanning accuracy and speed. The resolution limit for Si machining is determined by the selectivity of the chemical reaction rather than the laser spot size. Interfacing to computer-aided design (CAD) software allows us to remove layer by layer of a truly three-dimensional nanostructure.

Growth and characterization of compositionally graded, relaxed Si1-xGex

Compositionally graded, relaxed, n-type, Si1-xGex alloy layers have been grown on (100) Si substrates; the main emphasis has been put on compositions with x = 0.25. It is found that for substrate growth-temperatures higher than similar 750°C and a grading rate of 10% Ge/μm relaxed Si0.75Ge0.25 epitaxial layers of high structural, optical, and electrical quality can be grown. The layers are characterized by channeling parameters close to expected bulk values, a threading dislocation density of similar 5 × 105 cm−2, and strong near-band gap luminescence. Electrical measurements have revealed Hall mobilities similar to published bulk values and concentrations of electrically active deep levels ≤2 × 1011 cm−3. The surface morphology is, however, strongly influenced by the grading procedure which produces a high degree of cross-hatching.

Fast 3d Laser Micromachining Of Silicon For Micromechanical And Microfluidic Applications

The application of laser direct etching of silicon in processing devices for microelectromechanical systems is discussed. The direct write system presented in this paper features high writing speed, high resolution, and large access range. The possibilities of micromachining truly three-dimensional structures, rapid prototyping, processing on non-planar substrates, complementary processing and post-processing through laser direct etching are demonstrated. Examples include prototypes of micromachined diffuser/nozzle elements illustrating the potential for microfluidic devices and structures cut out of a membrane, which both show the high flexibility of this process.

Cold-walled UHV/CVD batch reactor for the growth of Si1−xGex layers

Abstract A novel cold-walled, lamp-heated, ultrahigh vacuum chemical vapor deposition (UHV/CVD) batch system for the growth of SiGe layers is presented. This system combines the batch capability of the standard UHV/CVD furnace with the temperature processing available in rapid thermal processing (RTP) equipment. The first results are very encouraging: germanium contents up to 30% and boron doping levels up to 5×10 18 cm −3 have been obtained. The uniformity of the film thickness is around 10% both across a single wafer and through the boat load. Different surface passivation schemes were investigated using excess carrier lifetime measurements. These measurements show that diluted HF provides much better surface passivation than buffered HF.

Ordering of germanium islands in the Si1−xGexSi system pre-structured by misfit dislocations

Abstract We have investigated the ordering of germanium islands on a relaxed uniform Si0.84Ge0.16 buffer layer by atomic force microscopy and transmission electron microscopy. A pronounced ordering with the islands situated along dislocation slip band lines was observed. The resemblance of this ordering to the ordering obtained with compositionally graded buffer layers is discussed. Finally, the relaxed uniform Si0.84Ge0.16 buffer layer structures are used to investigate the kinetics of the ordering of the islands, either by changing the amount of deposited material or by changing the deposition temperature and exposing the islands to different annealing conditions.

Zero- and one-dimensional nanostructures on an surface

Zero- and one-dimensional nanostructures on the surface of compositionally graded, epitaxial layers on Si(100) single crystals produced by a self-organized relaxation process are reported. Post-growth atomically flat surfaces can be converted into ordered, long-range coherent networks of nanostructures by a simple heat treatment procedure. The choice of heat treatment leads to a range of structures from millimeter long, single plateaus to complex patterns with nanometer structures and spacings. The vertical dimensions can be controlled in the nanometer range by varying the thickness of the layer.