Wet clean oxidation for optimal line width and LER

Abstract

Line Edge Roughness (LER) becomes increasingly critical to control at smaller dimensions. The LER also tends to become worse at smaller line widths and higher aspect ratios. We explored shrinking line width by litho dose, etch recipe, and wet cleans to meet the target line width for 42 nanometer pitch structures, while minimizing the impact to LER. We also demonstrated that for smaller aspect ratios, smaller line widths can be achieved without compromising LER. For small changes in dose, the litho LER was not impacted. Changes to either the litho dose or etch recipe had similar sharp increases to post-etch LER at smaller line widths. After wet cleans, the LER and line width were reduced. However, by observing the power spectral density (PSD), we can see that the wet cleans do not address the LER changes caused by small line width. Wet clean helped improve LER in mid to high frequencies, while the LER increase from smaller line width was observed at low frequencies. In order to pattern smaller line widths, the post-etch line width must be large, while using wet cleans to shrink to the target width. To shrink the line, a method of wet clean cycles was demonstrated. One chemistry was used to remove the outer oxide layer, while the second chemistry would oxidize the surface. Repeated cycles would further shrink the line, without negatively impacting LER.