A new method to characterize conformality of BARC coatings

In the semiconductor manufacturing industry, a bottom anti-reflective coating (BARC) is used to minimize thin film interference effects by reducing reflected light. As substrate topography becomes more complex with efforts to design more complex circuits, the effect of reflected radiation becomes more critical. The degree of conformality of the BARC coating plays an important role in lithography performance, which in turn affects the design of plasma etching processes. In this study, we propose a new method to measure the BARC coating conformality. The relationship between film thickness and horizontal distance from the step can be described by an exponential function. We found this profile is related to the properties of the coating material, such as molecular weight, the composition of formulation, the polymer structure, Tg of the polymer, thermal flow capability, and the crosslinking reaction, but is independent of step height, step width, and BARC thickness. The pitch affects the shape of the coating profile only when the spacing of features is smaler than a threshold that is related to coating material properties. The curvature of the profile indicates the uniformity of BARC thickness across the topography, which is a very good parameter to quantitatively describe the conformality of BARC coatings. Studies on Brewer Science BARC products confirm that the proposed conformality measuring method is in excellent agreement with observations. This method offers the option to separately consider the effects of coating processing, topography type, film thickness, and inherent material properties. It affords the predictability of BARC behavior for coatings that cover different topographies.