PLASMA INTERACTIONS WITH MASKING MATERIALS FOR NANOFABRICATION

Abstract

Plasma-based transfer of patterns into other materials is a key process for production of nano-scale devices used in micro-electronic technology. With the continuously decreasing feature-size of integrated circuits, manufacturing tolerances are becoming increasingly smaller and complex interactions of plasmas and patterned mask materials require an atomistic understanding to meet future processing tolerances. In this work, we investigated how plasma-material interactions in typical low-k pattern transfer processes depend on individual plasma components and properties of polymeric and metallic masks. First, we studied modifications of 193nm and 248nm photoresist (PR) by plasma ultraviolet/vacuum ultraviolet (UV) radiation, quantifying contributions of plasma radiation to the overall material modifications for direct interaction with plasma. Energetic ions (~125 eV) led to rapid (~3-5 s) formation of a graphitic ion-crust (~1.8 nm) and introduced together with simultaneous UV modifications of the material bulk significantly higher roughness for 193nm PR (~6 nm) than for 248nm PR (~1 nm).

During ion-crust formation, 193nm PR softened by chain-scissioning and pendant group detachment in a depth of ~60 nm by UV radiation, while 248nm PR was radiation stable showing surface-close cross-linking (~4 nm). Pretreating 193nm PR with a radiationdominated

He plasma and introducing UV modifications before ion-crust formation in the subsequent plasma etch reduces synergistic roughness formation as explained by wrinkling theory. Second, we studied interactions of fluorocarbon (FC) plasmas with Ti and TiN and compared these with organosilicate glass (OSG). Metal hardmasks are expected to provide improved etching selectivity (ES) and low-k damage compared to PR

during pattern transfer. Erosion stages and dependencies of etch rates (ER) on FC layer thickness and energy deposition by ions were identified. ES were low (~4-8) in the diffusion-limited regime (thick FC layers) where OSG experienced strong reduction in ER, but high (up to 15) in the chemical sputtering regime (thin FC layers) at low ion energies where removal of Ti etch products was limited. TiN exhibited higher ER and lower ES than Ti due to increased surface reactivity after rapid removal of N. Overall, findings give directions for rational design of masking materials and plasma discharges for future nanofabrication pattern transfer processes.