Relative importance of various stochastic terms and EUV patterning

Abstract

An error propagation stochastic model is described and used to study the impact of both photon and photoresist material sources of line-width roughness (LWR). Based on typical chemically amplified resist parameters, material sources of LWR are shown to be of equal importance to photon sources. Of the material sources, quencher is shown to be the most important input noise term. The results show that it is not the relative quencher noise that ultimately matters but rather the absolute quencher noise relative to the mean produced acid count. The results also show that chemical yield is critical and that benefiting from increased absorptivity also requires the chemical yield to be maintained.

Modeling of novel resist technologies

“…We will begin the discussion with the conventional base resist data (blue). Consistent with previous modeling [3][4], as well as experiment [12], an increase in base loading initially leads to a reduction in LWR, bottoming out at a value of about 3.6 nm at 55% base loading for the parameter set used in this study. After this point, increasing the base loading leads to an increase in LWR.…”

“…This imposes a material limit on the noise performance of the resist given a set of blurs and reaction rates that cannot be improved upon even in the limit of zero photon shot noise. This material limit is discussed in [3]. In PDB, the absolute noise from base alone is similar to that in NPDB.…”

“…A previously published model [3] of relative noise is useful in understanding stochastics in the deprotection image. In summary, this simplified model treats the net acid (A) as the sum over the number of absorbed photons (P) of the yield (Y) of each photon, minus the amount of base quencher (Q).…”

“…Fundamentally, these challenges make it difficult to simultaneously achieve the resolution (R) required for continued device scaling, features smooth and predictable enough to meet device requirements (L), and sensitivity (S) required for the process to be economical. It has been shown that these challenges are fundamentally a result of the quantum nature of light and matter [1] [2] [3]. In order to smooth out the naturally grainy images produced by these quantized interactions, CAR utilizes incoming radiation to produce photoacid that, in effect, spatially averages the exposure energy by catalytically reacting with its host polymer environment.…”

“…One strategy to limit acid diffusion is the addition of basic quencher molecules (referenced interchangeably as "base" and "quencher" in this paper) to neutralize the generated photo-acid. While this has proven an effective way to limit the acid blur, previous work has shown that it comes at a cost in terms of resist stochastics [3] [4]. In order to mitigate the negative stochastic effects of quencher and to increase the photospeed of the resist, some resists have been engineered with photodecomposable base (PDB), a photoactive base that self-quenches when activated by EUV light.…”