Sacrificial release

Figure 1.9 Bond pads that were not anchored are released after the sacrificial etch. Not only does this make electrical testing difficult, but the bond pads usually end up in places you do not want them. Your neighbors on a multiproject chip will be particularly annoyed if your parts land in their area The parts that do not get stuck to the chip are often observed as floaters in the etch bath that is used for the sacrificial release.

Figure 1.10 Stiction that can occur during the sacrificial release etch, (a) Before sacrificial etching, the sacrificial oxide is below the mechanical layer, (b) After the chip is removed from the etch bath it begins to dry and the remaining fluid forms a bridge between the substrate and the mechanical layer, (c) Capillary forces from the meniscus of the fluid exert a downward force on the cantilever and cause it to come into contact with the substrate, (d) The surface forces, such as Van der Waals attraction, that dominate at the microscale cause the cantilever to become stuck to the substrate. (Reprinted with permission from lOP Publishing Ltd.) [15].

If you use oxide, be sure that it is not completely etched away during the sacrificial release step or your structure will be released Use the cross-section tool in MEMS Pro to find a cross section of the structure including the anchor to the substrate. Make a solid model... 

These include the variations of sacrificial anode, sonication, and alternating polarity cell mentioned above, different solvent/co-solvent and electrolyte systems, monomer concentration, total current passed, and temperature. Best results appear to be obtained with THF and dimethyl ether (DME) as solvent and a perchlorate supporting electrolyte in some systems using fluorides, electrolyte decomposition occurred releasing fluoride anion which formed unreactive fluorosilanes.125... 

Most annulation procedures, which produce nitrogen heterocycles start from a tert-butvlimine, where the sacrificial organic moiety is released in the course of the process as isobutene. Ring closure of the 2-iodoveratraldehyde derivative shown in 4.34. and ethyl phenylpropiolate, for example, led to the formation of the appropriate isoquinoline derivative in excellent yield. Formation of the isomeric 4-phenylisoquinoline compound was also observed (5%).42... 

A 5.5 (xm photoresist layer was patterned as the sacrificial layer, followed by the deposition of a second 4.5 p,m parylene layer. The parylene/photoresist/ parylene sandwich structure formed the electrospray nozzle and channel when the photoresist was subsequently dissolved. A 1500 A sputtered aluminum layer was used as a mask for parylene etching to define the shape of the nozzle. Aluminum was removed by a wet etching process. After SU-8 developing, wafers were left inside the SU-8 developer for 2 days to release the photoresist. A serpentine channel (250 pan x 500 pm x 15 mm) extending from the junction of pump channels to the edge of the chip was patterned in the SU-8 layer. Platinum/titanium lines spaced 200 pm apart were patterned under the channel after the electrode deposition step. 

The vibrating ring/disk structure as well as the drive mechanism consists of 1 l- rm-thick poly-Si, which has been structured by deep RIE and released from the sacrificial oxide layer underneath by HE vapor phase etching. For the deposition of the thick poly-Si, a modified epitaxy deposition process (EPI poly) has been used [24]. However, as can be seen in Fig. 14.6, the deposition process leads to a rough poly-Si surface with Ra 100nm. For the removal of underlying topography, the surface has to be planarized by CMP in order to... 

FIGURE 14.7 The roughness of the EPI-poly layer can be planarized by using CMP. After removal of the sacrificial oxide layer by vapor phase etching, the sensor structures are released. 

Particulate soil is removed from fibres by a two-step process. First, a thin layer of wash liquid penetrates between the particle and the fibre surface, enabling surfactants to adsorb onto the particle surface (Fig. 7.1). Then, the particle becomes solvated and is transported away from the fibre and into the bulk of the wash liquid by mechanical action. Finishes that are hydrophilic (enhancing penetration of the fibre-soil interface) with low adhesion to soil under washing conditions should improve particulate soil release. Ablative or sacrificial finishes... 

Additional finish characteristics that should facilitate oily soil release include the ability of the finish to swell during the washing process and flexibility under mechanical action. As in particulate soil release, sacrificial finishes are expected to benefit oily soil release. 

One of the earliest soil-release materials was starch, which functioned as a sacrificial treatment. Other starch- and ceUulose-based products that have been... 

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