Study of barrier coats for protection against airborne contamination in 157-nm lithography

Abstract

Keywords: 157 nm lithography, 157 nm photoresist, amine barrier coat ABSTRACTWe summarize our work on devising protective barrier coats for use against airborne contamination when using tertbutoxycarbonylmethyl (BOCME) capped fluoroalcohol resist resins as part of our strategy to develop a 157 nm resist platform. We will describe how a barrier coat (AZ® EXP FX Coating 145) consisting of a fluoroc-yclopolymer formulation, soluble in aqueous developer, can improve the post-exposure delay (PED) latitude of 157 nm resist resists exposed under conditions or airborne contamination. Specifically, a 20 nm thick coating of AZ® EXP FX Coating 145 gives a PED latitude for L/S features of at least 10 min under condition of airborne amine contamination (10 ppb amine contamination). The barrier coat, AZ® EXP FX coating 145 is formulated in a solvent which is compatible with resist film coated from typical 193 nm resist spin casting solvents. Moreover, it can be easily removed as part of the normal aqueous base development scheme, no extra post-apply bake or stripping step is required.

Fluid-photoresist interactions and imaging in high-index immersion lithography

“…The maximum amount of PAG leaching into the immersion fluid has been set based on this concern ͑ASML= 1.6 ϫ 10 −12 mol/ cm 2 -sec, Nikon= 5.0ϫ 10 −12 mol/ cm 2 -sec͒. Others have quantified the amount of PAG leaching into water [18][19][20][21] and even shown the contamination pattern formed on a test lens after laser exposure of water doped with ppm levels of PAG. Here, our interest is to determine the levels of PAG leaching seen in second-generation immersion fluids, from the concern of both lens contamination and the reduction of active recycle efficiency, since these fluids need to be cleaned before being recirculated back to the exposure area.…”

Advances in Patterning Materials for 193 nm Immersion Lithography

“…Protective topcoat layers enable the continued use of resists designed for dry lithography while protecting the immersion scanner from contamination by resist components (especially PAG) leached into the immersion fluid. Protective polymeric topcoats had been previously used in 193 nm dry imaging to provide reflectivity control as well as to protect the resist against environmental contamination. − …”

“…The detrimental impact of water on the KRS resist is not surprising given its acid-catalyzed hydrolysis mechanism. , There was little change in the intrinsic image blur of several 193 nm resists with or without topcoat under immersion conditions, presumably due to the aforementioned lower water uptake of 193 nm resists relative to 248 nm materials . In addition, a topcoat was observed to suppress outgassing of deprotection fragments from the resist film , as well as to reduce the effects of airborne environmental contamination. , …”

“…The structure and formulation of alkali-developable topcoat materials are frequently tailored to control the profiles of the final photoresist features formed during development. For example, it has been shown that ethereal or hydrocarbon topcoat casting solvents cause less topcoat-resist interdiffusion and extract less PAG than alcoholic casting solvents. ,, The addition of free sulfonic acid species or thermal acid generators into the topcoat formulation has been reported to induce some resist top-loss, eliminate t-topping, and improve profiles. ,,, Remarkably, the addition of photoacid generators into the topcoat formulation has been shown to alleviate profile issues (via the generation of additional photoacid above the exposed regions of the resist) without significantly increasing the amount of PAG leaching into the immersion fluid. ,, Alternatively, small amounts of strongly acidic groups can be incorporated into the topcoat polymer itself as a polymer-bound PAG ( 47 , Figure ) or as a polymer-bound acid ( 48 − 50 ) to alleviate profile issues. ,, …”