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The semiconductor community is well aware of the challenges that exist in developing lithographic methods that can pattern features at sub-20 nm periodic feature spacing (pitch, L0). Optical lithography already utilizes complex multiple patterning schemes to overcome diffraction limitations at 193-nm exposure wavelengths, and the delayed insertion of EUV lithography will likely require the use of multiple patterning or other assistive processes to further reduce the achievable feature sizes. An alternative to these techniques employs the directed self-assembly (DSA) of block copolymers. Block copolymers (BCPs) can naturally micro-phase separate into morphologies such as lamellae, cylinders, spheres, and gyroids at length scales down to sub-10 nm dimensions. Using the ability of BCPs to micro-phase separate in conjunction with alignment methods such as graphoepitaxy and chemoepitaxy to produce well-ordered structures, a process referred to as DSA, offers a possible method for producing sub-20 nm features in conjunction with optical patterning processes at greatly reduced cost and complexity. One of the many challenges in implementing line-space type DSA processes is the lack of methods for effective modulation and tuning of the pattern pitch (L0) produced by a given BCP. Previous studies have shown that blending homopolymer into the BCP thin films can allow for tuning of both: (1) L0 to be larger than that provided naturally by the BCP's molecular weight (MW) and (2) the relative size line-space size ratio. However, this tuning ability comes at the expense of increased line edge roughness (LER) and line width roughness (LWR). It has also been shown that either higher or lower MW BCP can be blended into a primary BCP in order to modulate and tune the pattern pitch produced from the BCP mixture, but the effects of this BCP blending on pattern LER and LWR have not been explored or reported in detail. In this study, coarse-grained molecular dynamics simulations of BCP DSA on a chemoepitaxial underlayer were implemented to characterize the impacts that blending controlled amounts of two different MW BCPs together have on DSA pattern LER and LWR. The blends shown here had LER and LWR values as much as 20% higher than those of pure, monodisperse BCPs; however, reducing the MW difference between the 2 BCPs could reduce this effect. |
