Etch Transfer

The SFIL process flow depicts etching steps which allow amplification of the imprinted feature aspect ratio by etching into a polymer underlayer. The etch barrier contains Si, C, O, and H, while the transfer layer contains C, O, and H. The existence of the Si in the etch barrier provides the etch resistance needed to etch into the transfer layer with O2 RIE, but also requires fluorocarbon etch chemistries in order to break through the residual imprint layer. This is shown pictorially in Figure 1.
Figure 1. Schematic diagram of post-imprint etch processing.
As a demonstration of the etch process, a sample wafer was processes using CHF3/O2 breakthrough etch, and O2 transfer etch, as described in Johnson (2003), and the results are shown in Figure 2. The imprinted features (Figure 2a) show fairly square feature profiles, while some faceting is observed throughout the breakthrough etch (Figures 2b and c). This faceting results from the anisotropic etch conditions, and is observed in conventional resist processing as well, as shown in Figure 3.
a) b) c)
d) e)
Figure 2. Etch transfer in action. a) Imprinted image with ~150 nm residual layer, b) part-way through breakthrough etch, c) after completion of breakthrough etch, d) part-way through transfer wtch, and e) after completion of the transfer etch. These are not from the same L/S array, since the samples had to be destroyed for SEM analysis. Figure 3e shows 40 nm lines approximately 400 nm tall.
a) b)
Figure 3. KrF resist images a) before and b) after ARC etch, showing the appearance of feature faceting arising from the anisotropic etch conditions.