Theoretical Calculation of Photoabsorption of Various Polymers in an Extreme Ultraviolet Region

Abstract

We have calculated the linear absorption coefficients of various resist polymers using the mass absorption coefficients at 13 nm and the density obtained from the graph-theoretical treatment derived by Bicerano. The values indicate that the transmittance at 13 nm of conventional resists used in 193-nm, 248-nm and 365-nm lithography is about 30% when the thickness is 3000 Å and 60–70% when it is 1000 Å. This shows that conventional resists are suitable for an EUVL (extreme ultraviolet lithography) thin-layer resist (TLR) process using a hard-mask layer, but their large photoabsorption makes them unsuitable for a single-layer resist (SLR) process. To design polymers that are suitable for an SLR process, we further calculated the absorption of about 150 polymers. The results suggest that the introduction of aromatic groups into a polymer not only reduces the absorption at 13 nm but also increases the etching resistance.

Comparison between the process windows calculated with full and simplified resist models

“…The relative concentration of photoacid, H, after exposure is related to the unreacted photoacid generator by the equation m H − = 1 (6) Next, the acid deblocks the polymer resin during PEB. This is described by a reaction-diffusion model, given by ( )…”

“…It is useful to examine a few examples of each of the different types of photoresist models commonly used by lithographers today. Molecular-scale models of the photoresist include dynamic Monte-Carlo [2], molecular dynamics [3,4], and ab initio quantum calculations [5][6][7]. These models are useful for developing a deeper understanding of resist chemistry and physics from a molecular standpoint, and these models can be used to examine new resist formulations.…”

Synthesis and Resist Properties of Hyperbranched Polyacetals

“…In these previous works, acetal moieties showed higher sensitivity. Furthermore, Matsuzawa et al [11] examined the relationships between the resist properties and physical properties of various resist materials based on polymers and reported that lower-density polymers are more transparent and would also show higher sensitivity in the photoresist system.…”

Relationship between Absorption Coefficient and Line Edge Roughness of Chemically Amplified Resists Used for Extreme Ultraviolet Lithography

“…The absorption coefficient of a typical chemically amplified resist used in KrF excimer lithography is approximately 4 m -1 for 13.5 nm EUV. [1,2] For their use for KrF excimer lithography, the absorption coefficient of resists has generally been adjusted to less than 1 m -1 . Therefore, the strong absorption of EUV has been a concern because it may cause severe degradation of the resist sidewall.…”