Mechanisms of Area-Selective Atomic Layer Deposition and Their Impact on Feature Sizes

As device feature sizes have decreased below 10 nm, area-selective deposition methods have become increasingly beneficial for self-aligned patterning. This study describes the mechanisms for area-selective atomic layer deposition of common oxide materials on poly(methyl methacrylate) (PMMA) and Si and the effects of these deposition mechanisms on feature size dimensions and film thickness. The mechanisms of deposition were studied by characterizing the extent of atomic layer deposition before and after PMMA removal. Atomic layer deposition of TiO2 is highly selective for Si in comparison to PMMA; however, the PMMA sidewalls inhibit deposition, so that the dimensions of the TiO2 feature are smaller than the original pattern. In contrast, HfO2 is less selective than TiO2 and demonstrates a mechanism combining selective deposition and lift-off. This deposition with lower selectivity limits possible HfO2 thicknesses before there is blanket coverage, but it also exhibits less sidewall inhibition. Significantly smaller feature sizes were obtained with HfO2 compared to TiO2. These results suggest that the deposition mechanism itself, whether it is a truly area-selective deposition or a combination of area selectivity and lift-off, will always affect possible feature sizes.