Contact hole shrink by directed self-assembly: Process integration and stability monitored on 300 mm pilot line

Abstract

The semiconductor devices dimensions continue to shrink to keep up with the ITRS roadmap. Due to delay and extensive cost of EUV for 14 nm technology node and beyond, the directed self assembly (DSA) process has great potential for extending optical lithography, and enables to reduce the critical dimension (CD) and pitch of the final feature. After the recent implementation of DSA processes in 300 mm clean room environment, it is now time to move to the forward maturity step and demonstrate process stability through time. This study investigates the potential of DSA for contact hole shrink patterning using poly(styrene-block-methyl methacrylate) (PS-b-PMMA) di-block copolymers to target contact holes CD down to 15 nm. Based on the 300 mm pilot line available at LETI, the DSA manufacturability is considered through different criteria to achieve high resolution and pattern density multiplication, at a low cost in fully 300 mm wafers production line. The DSA process flow performance based on grapho-epitaxy approach is controlled after each step to follow the thicknesses of random and BCP materials supplied by ARKEMA. Moreover, the natural period of block copolymers and CD uniformity on free surface are also measured and defectivity is evaluated after etch transfer by image treatment. The thermal budget of DSA of both random and block copolymers have been evaluated to define optimum conditions. The paper has shown that UV exposure prior to PMMA wet development improves PMMA degradation to enable complete removal by wet development in acetic acid. DSA process for contact hole shrink patterning has shown final contact holes with an average CD of 21 nm and intra-wafer CD uniformity of 1.1 nm with an open yield of more than 99.9%.