Poly sacrificial oxidant

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. 

Yoshida et al. reported oxygen evolution by a soft material containing RUO2 nanoparticles dispersed by sodium dodecyl sulfate and embedded into a polymer of poly(N-isopropylacrylamide), cross-linked and sensitized with [Ru(bpy)3] derivatives, in the presence of [Co(NH3)5Cl] " " as the sacrificial oxidant [37]. 

Figure 18.12(a) shows the roughness of the epi-poly layer after deposition and Figure 18.12(b) shows a detail of the interdigital capacitors of the drive structure after poly-Si CMP, DRIB and vapour-phase HF release etch of the sacrificial oxide layer. Only the smooth surface after CMP allows the precision etch of the capacitor spaces <1 pm. 

Figure 18.15 shows the schematic of the fabrication process. After oxidation of the double-side polished silicon substrate wafer, a first lower poly-Si layer with a thickness of 45 pm is deposited by means of an epi-poly process. In order to remove spikes and obtain a smooth surface, 5 pm of poly-Si has to be removed by poly-Si CMP. This polishing is a two-step process, consisting of a 5 pm bulk removal by means of a fiimed-silica slurry and a subsequent final polish of several 10 nm with a haze-firee slurry. After deposition and stmcturing of some intermediate layers, a second upper poly-Si layer, again with a thickness of 45 pm, is deposited and subsequendy polished with the same two-step poly-Si CMP process. As this will be the surface of the evaporated silver mirror, a smooth as well as flat surface has to be achieved. After a backside silicon etch and the removal of the sacrificial layer, the scanning mirror device is released, see Figure 18.16(a) and (b). 

As an example, we consider a parallel plate actuator that is fabricated in the Poly MUMPS process using the first released polysilicon layer. Poly 1, as the structural layer and the first oxide. Oxide 1, as the sacrificial layer. We consider two configurations for the springs an X-beam configuration, as shown in Figure 3.5, and a Z-beam configuration, as shown in Figure 3.6. 

LB lithography for spatially controlled attachment of initiator to form regular stripes of PS and poly(n-butyl-acrylate) (PBA) brushes was reported by Studer and coworkers [16]. Mixed monolayers of L-adipalmytoyl-phosphatidylcholine (DPPC) and TEMPO-derived alkoxyamines 4 or 5 (Scheme 5) were transferred by the LB technique onto oxidized silicon wafer in regular stripes with submicrometer lateral dimensions. Physisorbed DPPC was removed by washing, and NMP of styrene from the surface of silicon wafer covalently bonded to 4 was performed at 125°C for 24 h in the presence of 6 as sacrificial polymerization regulator. NMP of n-butyl acrylate was conducted with a surface modified with 5 in the presence of 7 at 105°C for 24 h. Polymer stripe width was controlled by the concentration of alkoxyamine in the mixed phase and adjusted from about 0.2 to 1.3 pm. The height of the stripes increased to 8 0.2 nm for PS and 4.7 0.2 nm for PBA (Scheme 6). 

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