ABSTRACT
Another mechanism that can be utilized in pattern transfer that can extend its capability and plays a central role in current state-of-the-art nanoscale pattern transfer technologies is anisotropy enhancement via
selective surface passivation. For example, if the hypothetical problem illustrated in Figure 5.2 is maintained at a temperature that is low enough to make reactive by-products nonvolatile, and energy is directionally deposited on surface A only, one could theoretically passivate surface B with residual by-product while providing a constant reactive surface on A. One or both of these mechanisms can promote anisotropic material removal, and are the key elements in current
state-of-the-art pattern transfer, such as is illustrated in Figure 5.3b. More advanced etch processes that utilize a bimodal etch/dep process, such as Bosch processing, rely heavily on this passivation technique, and promising results have been demonstrated using this technique to etch features down to <40 nm and over 1.6 µm deep.3
