Sacrificial etching methods

A summary of the reported, selectively sacrificial diblock copol5miers and relevant etching methods used to produce porous materials is shown in Table 2.1. Rather few of these systems have yet been explored as electrochemical film templates, largely... 

The sacrificial layer techniques can be difficult to apply as they require a delicate choice of materials and etching methods that might not be compatible with the CPs. Also, the method introduces a step and thus a weak spot in the actuator (see Fig. 4A4). Therefore, a new method was developed that utilizes the poor adhesion between two materials, e.g., between Au and Si, the so-called differential adhesion method (Smela et al. 1995). First, an adhesive frame is patterned on the substrate that surrounds the actuator, except for an anchoring point (Fig. 4D). In the case of Si and... 

Polymer ashing is another process related method. This process is fairly complex and involves patterning of a polymer layer during the release. First, structures are partially released by a timed etch. Next, a polymer film is deposited onto the partially released structures. This film is patterned into support posts that hold the structure in position as the remainder of the sacrificial layer is etched away. Because the polymer support structures hold the devices in place, there is no concern for special drying techniques. Finally, the polymer supports are burned away, typically by ashing in an oxygen plasma.This leaves behind fully released and free-standing microstructures. 

There are a variety of materials that can be used as sacrificial cores. Inorganic sacrificial materials include Si02 and metals such as aluminum, " titanium, and nickel. Polymers such as PI, PMMA, PC, and photoresist have also been used as sacrificial materials. After deposition of the cover film, removal of the sacrificial layer can be achieved by dissolution, etching, or thermal degradation. These removal methods each have benefits and drawbacks selection of the optimal approach is specific to particular combinations of substrate, sacrificial layer, and cover film 73, 3 Recently Whitesides and coworkers " implemented a fabrication method using water-soluble sacrificial cores. Poly(acrylic acid) and dextran proved to be effective sacrificial layers that could be dissolved in water or aqueous NaCl, for making metallic microstructures by nickel electrodeposition. 

By using photoresist as a sacrificial layer or structure, further processes, etching, ion implantation, molding, lift-off, and so on, may be performed. When patterned photoresist finish its roles, it is better to be removed from substrate. There are two kinds of methods to remove photoresist layer, wet type and dry type. Wet type photoresist removal process requires the chemical, PR remover or PR stripper, which can dissolve photoresist. Alternatively, plasma ashing process may remove photoresist This process is called dry process and uses oxygen plasma which oxidizes photoresist layer. 

Another approach to fabrication of structures with vertical walls is by simultaneous electrochemical etching of pores and trenches first introduced by Geppert et al. (2006). Forming a closed contour, the trenches define the sacrificial parts of the structure, which fall out from a sample after the substrate is removed. Figure 9 shows a schematic of the method and a bar of a 2D photonic crystal, produced by removal of sacrificial parts of the sample. 

An alternative method to the yolk-shell structure is the use of a sacrificial intermediate layer, which is etched away to generate hollow spaces. This general scheme was realized by Schiith and his co-workers using the Au Zr02 yolk-shell NPs as an example (Fig. 5.11) [55]. They first synthesized 15-17 nm Au NPs using sodium citrate as the reductant, followed by coating a silica layer on the individual Au... 

---