Phases, polysilicon

It is not too surprising that vapor-phase HMDS also improves adhesion to this substrate. The native oxide has been shown on Y58 wafers to be easily treated and/or passivated. Actual resist image lift testing on vapor promoted polysilicon wafers produced superior results and no image lifting occurred even for first generation resists known to be susceptible to lifting . 

Krogh, O. Wicker, T. Chapman, B. The role of gas phase reactions, electron impact, and colli-sional energy transfer processes relevant to plasma etching of polysilicon with H2 and CI2. J. Vac. Sci. Technol. 1986, A4 (3), 1796. 

Next, the sacrificial layer is patterned and holes are etched into the oxide using established lithography and etching processes. These holes will be filled and thus act as anchor points on the left end of the two cantilevers formed later (Fig. 5.3.1 e). In the next step, the functional polysilicon layer is deposited (Fig. 5.3.1b). The thickness of this layer determines the mechanical properties of the movable beam. The thicker it is, the stiffer the beam will be in the z axis, which is desirable for structures intended to move only in the xy direction. But its thickness is limited by the capabilities of the deposition process used. The functional layer is next patterned and etched (Fig. 5.3.1c). Depending on the thickness of the polysilicon layer, specific trench etch processes (as described later on) may be required, especially when this layer is rather thick. Finally, the sacrificial layer is removed (Fig. 5.3.1 d). This is typically done with wet or vapor phase etches to dissolve the silicon dioxide and leave parts of the functional structures free-standing and movable. When using wet etching, special care has to be taken to prevent Stic-... 

Fig. 6.2. The basic MIS CCD structure illustrating charge transfer with three-phase dock voltage operation. In silicon devices overlapping polysilicon electrode gates are often used...

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