Wet-Chemical Etching

Silicon has a diamond cubic crystal structure. The Miller indices of the main crystallographic planes of silicon are (100), (110) and (111), respectively. In the wet bulk-micromachining, there are two silicon etching methods isotropic (direction-independent) and anisotropic (direction-dependent) etching. Wet chemical etching solutions are used in this bulk silicon micromachining technology. 

We prepared microchannel reactor employing stainless steel sheet 400tan thick patterned microchannel by a wet chemical etching. The microchannel shape and dimension were decided by computer simulation of flow distribution and pressure drop of the reactants in the microchaimel sheet. Two different types of patterned plates with mirror image were prepared [5]. The plate has 21 straight microchannels which are 550/an wide, 230/an deep and 34mi long as revealed in Fig. 1(b). 

Physical vapor deposition Electron-beam evaporation Electroplating Reactive ion etching Wet etching Molecular beam epitajty Chemical-mechanical polishing Rapid thermal processing Vacuum sealing... 

Wet chemical etching zero medium medium good... 

The micro channels were made by isotropic wet chemical etching of metal plates. The plates were tightened by various means they were either glued, stacked to-... 

The micro structured plates are made by wet-chemical etching. The platelet stack is bonded by laser welding. The inlet and outlet connectors are also laser welded. 

Microfabrication was made by wet-chemical glass etching [20]. Sealing was achieved by thermal bonding. 

D microfabricated reactor devices are typically made by fabrication techniques other than stemming from microelectronics, e.g. by modern precision engineering techniques, laser ablation, wet-chemical steel etching or pEDM techniques. Besides having this origin only, these devices may also be of hybrid nature, containing parts made by the above-mentioned techniques and by microelectronic methods. Typical materials are metals, stainless steel, ceramics and polymers or, in the hybrid case, combinations of these materials. 

This chip version is typically made in glass and has the great advantage that the flow can be directly visualized [40,44—46]. Fabrication is achieved by photolithography and wet-chemical etching followed by thermal bonding of the plates covered with a thin layer of solder [47]. 

The two plates were not manufactured via the same route and were not made of the same material [7]. Typically, rectangular channels in silicon are realized by sawing, whereas semi-circular channels are made in glass by wet-chemical etching. Such glass/silicon plates are joined by anodic bonding. 

The microstructure is part of a bottom plate a top plate serves as a cover [21]. Direct-write laser lithography and wet-chemical etching were employed for microfabrication of the bottom plate. Holes were drilled in the top plate to give conduits for the inlet and outlet ports. The top and bottom plates were bonded thermally. 

One problem with methods that produce polycrystalline or nanocrystalline material is that it is not feasible to characterize electrically dopants in such materials by the traditional four-point-probe contacts needed for Hall measurements. Other characterization methods such as optical absorption, photoluminescence (PL), Raman, X-ray and electron diffraction, X-ray rocking-curve widths to assess crystalline quality, secondary ion mass spectrometry (SIMS), scanning or transmission electron microscopy (SEM and TEM), cathodolumi-nescence (CL), and wet-chemical etching provide valuable information, but do not directly yield carrier concentrations. 

The membranes of the microhotplates were released by anisotropic, wet-chemical etching in KOH. In order to fabricate defined Si-islands that serve as heat spreaders of the microhotplate, an electrochemical etch stop (ECE) technique using a 4-electrode configuration was applied [109]. ECE on fully processed CMOS wafers requires, that aU reticles on the wafers are electrically interconnected to provide distributed biasing to the n-well regions and the substrate from two contact pads [1 lOj. The formation of the contact pads and the reticle interconnection requires a special photolithographic process flow in the CMOS process, but no additional non-standard processes. 

For a compound semiconductor to be useful as a substrate in studies of electrodeposition, it is desirable that clean, unreconstructed, stoichiometric surfaces be formed in solution prior to electrodeposition. For CdTe, the logical starting point is the standard wet chemical etch used in industry, a 1-5% Brj methanol solution. A CdTe(lll) crystal prepared in this way was transferred directly into the UHV-EC instrument (Fig. 39) and examined [391]. Figure 66B is an Auger spectrum of the CdTe surface after a 3-minute etch in a 1% Br2 methanol solution. Transitions for Cd and Te are clearly visible at 380 and 480 eV, respectively, as well as a small feature due to Br at 100 eV. No FEED pattern was visible, however. As described previously, a layer of solution is generally withdrawn with the crystal as it is dragged (emersed) from solution (the emersion layer). After all the solvent has evaporated, the surface is left with a coating composed of the... 

Once the resist has been patterned, the selected regions of material not protected by photoresist are removed by specially designed etchants, creating the resonator pattern in the wafer. Several isotropic (etching occurs in all directions at the same etch rate) and anisotropic (directional) etching processes are available. Wet chemical etching is an isotropic process that... 

Figure 13.1 Depiction of the glass-based lab-on-a-chip fabrication method. Shown in the figure is (a) the photoresist and chrome-coated glass substrate, (b) the coated substrate exposed to UV light through a mask (black rectangle), (c) removal of the exposed photoresist, (d) removal of the exposed chrome layer, (e) removal of glass by wet chemical etching, (f) removal of the bulk photoresist, and (g) removal of the bulk chrome layer.

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