Feasibility study of non-topcoat resist for 22nm node devices

Subsequent to 45 nm node, immersion lithography using topcoat process is approaching its next step for mass production. However, microfabrication using immersion topcoat leads to increase in cost due to increase in process steps. In order to deal with this problem, high throughput scanners equipped with a wafer stage which moves at higher speed are under development. Furthermore, as resist process compatible with such high speed scanners, non-topcoat resist is available and seems promising in reducing costs of the resist process. Non-topcoat resist contains hydrophobic additives which are eccentrically located near the film surface. Because non-topcoat resist enables the formation of a more hydrophobic surface, non-topcoat resist process is more suitable for high-speed scanning than topcoat resist process. In the topcoat process, the function of topcoat material and resist material is separated. That is, the resist material and the topcoat material are responsible for lithographic performance and immersion scanning performance, respectively. However, the non-topcoat resist is expected both performances. That is, the non-topcoat resist are required a fine resist profile, small LWR, and low development defects at high speed immersion scanning. In this paper, we report the application of non-topcoat resist in 22 nm node devices. We investigate the influence of hydrophobic additives on imaging performance in several base polymers. Additionally, the influence of chemical species, molecular weight and amount of hydrophobic additive are investigated. Scan performance is also estimated by dynamic receding contact angle using pin scan tool. 22nm node imaging performance is evaluated using Nikon NSR-S610C. The surface characteristics and lithographic performance of non-topcoat resist for 22 nm node devices are discussed.