A new dual bottom antireflectant consisting of an organic antireflectant and a SixOyNz:H (SiON) layer has been designed for metal layers to cover both 45nm and 32nm node logic devices. Simulations have been used to optimize the optical constants of the organic antireflectant. The new antireflectant system has been evaluated on a 1.2NA tool for metal layers. The same organic antireflectant has been successfully applied to via layers at a different thickness. The overall patterning performance including profiles, line width roughness (LWR), overlap depth of focus margin (ODOF) and critical dimension (CD) uniformity before and after etch has been evaluated. The new antireflectant system meets all the patterning requirements for a manufacturable process. An immersion tool at 1.2NA was used to perform lithography tests. Simulation was performed by using ProlithTM software.
It is well-known that the available depth of focus (DoF) tend to decrease for each advancing technology node.
Moreover the leveling control on wafer topography has become a challenge to affect the focus control on exposure tool
capability, especially for the critical hole-structure layer of the back end of line (BEoL). In this study, we used the via
layer from the real products as an example of optimizing the exposure tool's leveling system to reduce process-related
influences to improve the intra-field focus control range. First, the focus-exposure matrices (FEMs) were applied to a
wafer in different leveling modes. Then, patterns' critical dimension (CD) in different locations within the same field
were measured to produce the Bossung curves required to determine the best focus. The same steps were repeated on a
bare wafer to illustrate how the process reduced the common depth of focus range. We also introduced the non-optical
leveling sensor, which measured the wafer by the use of physical methods. Since it does not interact with the film stack
or the pattern density, the measurement accuracy will be insensitive to process variation. Therefore, it can be used to
compensate the optically induced errors from the optical leveling system and to expand the useful depth of focus for
improving CD uniformity. Finally, we briefly summarize the improvement ratio achieved of the common DoF using
these optical and non-optical leveling systems with different leveling modes.