Wet anisotropic etching based silicon micromachining is an important technique to fabricate freestanding (e.g. cantilever) and fixed (e.g. cavity) structures on different orientation silicon wafers for various applications in microelectromechanical systems (MEMS). {111} planes are the slowest etch rate plane in all kinds of anisotropic etchants and therefore, a prolonged etching always leads to the appearance of {111} facets at the sidewalls of the fabricated structures. In wet anisotropic etching, undercutting occurs at the extruded corners and the curved edges of the mask patterns on the wafer surface. The rate of undercutting depends upon the type of etchant and the shape of mask edges and corners. Furthermore, the undercutting takes place at the straight edges if they do not contain {111} planes. {100} and {110} silicon wafers are most widely used in MEMS as well as microelectronics fabrication. This paper reviews the fabrication techniques of convex corner on {100} and {110} silicon wafers using anisotropic wet chemical etching. Fabrication methods are classified mainly into two major categories: corner compensation method and two-steps etching technique. In corner compensation method, extra mask pattern is added at the corner. Due to extra geometry, etching is delayed at the convex corner and hence the technique relies on time delayed etching. The shape and size of the compensating design strongly depends on the type of etchant, etching depth and the orientation of wafer surface. In this paper, various kinds of compensating designs published so far are discussed. Two-step etching method is employed for the fabrication of perfect convex corners. Since the perfectly sharp convex corner is formed by the intersection of {111} planes, each step of etching defines one of the facets of convex corners. In this method, two different ways are employed to perform the etching process and therefore can be subdivided into two parts. In one case, lithography step is performed after the first step of etching, while in the second case, all lithography steps are carried out before the etching process, but local oxidation of silicon (LOCOS) process is done after the first step of etching. The pros and cons of all techniques are discussed.

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A comprehensive review on convex and concave corners in silicon bulk micromachining based on anisotropic wet chemical etching

A method for crystallizing an amorphous film by using an electric field and an ultraviolet (UV) ray, and method for fabricating an LCD by using the same. The method for crystallizing an amorphous film includes forming an amorphous film having a catalytic metal deposited thereon on a substrate, irradiating a UV ray on the amorphous film, and applying an electric field to the amorphous film.

Method for crystallizing amorphous film and method for fabricating LCD by using the same

The invention provides for a nanostructure, or an array of such nanostructures, each comprising a rough surface, and a doped or undoped semiconductor. The nanostructure is an one-dimensional (1-D) nanostructure, such a nanowire, or a two-dimensional (2-D) nanostructure. The nanostructure can be placed between two electrodes and used for thermoelectric power generation or thermoelectric cooling.

Nanostructures having high performance thermoelectric properties

Stress-assisted Cu-induced lateral growth of polycrystalline germanium (poly-Ge) at temperatures as low as 150 °C has been exploited to fabricate thin-film tunneling transistors on flexible plastic substrates. Applying external compressive stress during annealing, leads to the lateral growth of poly-Ge from Cu-seeded drain/source regions, progressing into the channel area. A potential barrier is formed midway in the channel where the two lateral growth frontiers, emanating from source and drain seeded areas, meet each other. As confirmed by electrical measurements, the barrier is controlled by the gate bias. An ON/OFF ratio of 104 has been measured for these transistors, which shows the potential of these devices for switching applications.

Thin-film tunneling transistors on flexible plastic substrates based on stress-assisted lateral growth of polycrystalline germanium

Three-dimensional vision has acquired great importance in the audiovisual industry in the past ten years. Despite this, the first generation of autostereoscopic displays failed to generate enough consumer excitement. Some reasons are little 3D content and performance issues. For this reason, an exponential increase in three-dimensional vision research has occurred in the last few years. In this review, a study of the historical impact of the most important technologies has been performed. This study is carried out in terms of research manuscripts per year. The results reveal that research on spatial multiplexing technique is increasing considerably and today is the most studied. For this reason, the state of the art of this technique is presented. The use of microlenses seems to be the most successful method to obtain autostereoscopic vision. When they are fabricated with liquid crystal materials, extended capabilities are produced. Among the numerous techniques for manufacturing liquid crystal microlenses, this review covers the most viable designs for its use in autostereoscopic displays. For this reason, some of the most important topologies and their relation with autostereoscopic displays are presented. Finally, the challenges in some recent applications, such as portable devices, and the future of three-dimensional displays based on liquid crystal microlenses are outlined.

Liquid Crystal Microlenses for Autostereoscopic Displays.

Anisotropic etching of silicon is achieved in the presence of ultra-violet exposure in a solution containing hydrofluoric/nitric/acetic acids (HNA). The HNA solution is typically used for polishing silicon and etching polysilicon due to its isotropic etching property. In the technique proposed in this paper which is called UV-HNA, the etching of silicon is enhanced in the direction determined by UV exposure. A mixture of HF/HNO 3 /CH 3 COOH with a relative composition of 1:15:5 seems suitable for revealing 〈111〉 planes with an etch rate of 10  μ m/h at 35 °C. The bottom of the etched craters is hillock-free and etch rates as high as 60  μ m/h can be achieved using higher concentration of HF acid in HNA solution. In the latter case the etching is more isotropic and mask undercut is observed. Also membranes with a depth of 400  μ m are fabricated on n -type Si 〈100〉 with a thickness of 500  μ m by means of standard 34 wt% solution of KOH at temperature of 60 °C. Problems encountered during the experiment, and their solutions are discussed and results of these experiments are reported.

Study of bulk micromachining for 〈100〉 silicon

UV-assisted nickel-induced crystallization of amorphous silicon

The effect of an applied electric field during metal-induced lateral crystallization of a-Si is reported. Lateral growth of 300 μm is observed upon annealing the samples at 400 °C for 30 min while dc voltage of 100 V is applied between Ni silicide pads. The dependence of growth rate on the applied voltage is studied. The trapezoid test structure employed clearly reveals that the growth rate depends on the voltage applied rather than on the electric field intensity. In addition to field-enhanced diffusion of Ni atoms, which has been supposed to be responsible for the high growth rate, the role of the bombardment of Ni atoms by electrons flowing through the a-Si layer is considered.

Field-assisted metal-induced crystallization of amorphous silicon films

Effect of copper-induced recrystallization on the piezoresistivity of germanium films is reported. SEM and XRD are used to study the crystalline structure of the films, while RBS, PIXE, and EDX are utilized to investigate their composition. Significant grain growth is observed in Ge films, upon annealing a Cu/Ge bilayer at 400°C for 30 minutes. Also a dominant orientation of Ge(111) is observable when amorphous precursor films are used. Hall measurements and cantilever beam bending show a considerable increase in hole mobility and longitudinal gauge factor, respectively

Effect of Copper-Induced Recrystallization on the Piezoresistivity of Germanium Films

A novel method of UV-assisted metal-induced-crystallization is introduced to grow polysilicon films on ordinary glass at temperatures as low as 400°C. Annealing is accomplished in the presence of an ultra-violet exposure, leading to high crystallinity of the silicon film as confirmed by XRD, TEM and SEM analyses. A back-reflecting chromium layer is incorporated to further trap UV photons and enhance their absorption in the silicon film. This results in a significant increase in the crystallization rate as studied by XRD spectroscopy. A growth rate of 2 µm/hr is observed at 400 °C, when employing this method for lateral crystallization. Thin-film transistors fabricated using the proposed UV-assisted MILC show a threshold voltage of 1V and hole mobility of about 50 cm 2 /V.s.

Saber Haji

Papers

Study of bulk micromachining for 〈100〉 silicon

UV-assisted nickel-induced crystallization of amorphous silicon

Field-assisted metal-induced crystallization of amorphous silicon films

Effect of Copper-Induced Recrystallization on the Piezoresistivity of Germanium Films

A Novel Back-Reflecting UV-Assisted Metal-Induced Crystallization of Silicon on Glass