Quantifying acid generation efficiency for photoresist applications

Abstract

A direct analytical technique for measuring the solution quantum efficiencies of photoacid generators (PAGs) is presented. The technique is based on the nonaqueous potentiometric titration of the photogenerated acid and does not require separate calibrations, or the addition of sensing materials such as dyes or bases. Solutions of PAGs in acetonitrile were irradiated at 248 nm and subsequently titrated with known concentrations of triethanolamine base. The only quantities required for an accurate determination of the quantum efficiency are the incident radiation energy and the titration equivalence point. A mathematical analysis that enables this calculation is derived, and a table with calculated quantum efficiency values for three classes of PAGs having a variety of counterions is presented. The method is simple, accurate, and applicable to any class of PAG molecules.

The Control of Shrinkage and Thermal Instability in SU‐8 Photoresists for Holographic Lithography

“…The quantum effi ciency of photofragmentation of triarylsulfonium PAG is ≈ 0.5, [ 27 ] implying that at threshold, where N p = 4-5 × 10 18 cm − 3 , approximately 5% of the PAG, the concentration of which is 4.47 × 10 19 cm − 3 , has been destroyed. Because the fragmentation effi ciency in this medium has not been measured and the correction for it is small, it is ignored in Figure 3 .…”

“…At the absorbed dose needed to exceed the insolubility threshold ( N p ≈ 5 × 10 18 cm − 3 ), the measured conversion level, after baking at 55 ° C, corresponds to the polymerization of ≈ 5% of the epoxy groups (2 × 10 20 cm − 3 ). Assuming a photoacid generation effi ciency of ≈ 0.5, [ 27 ] the concentration of carbonium ion initiators is ≈ 2.5 × 10 18 cm − 3 , so the ratio of the number of reacted epoxy groups to the number of initiations, which can be interpreted as an average chemical chain length (or amplifi cation factor), is ≈ 80. After a 95 ° C bake, the chain length increases slightly to ≈ 110 indicating that, at this level of initiation, further polymerization is not primarily limited by diffusion, but rather by chain termination.…”

Nonionic photoacid generator behavior under high-energy exposure sources

“…Multiple different methods have been developed to quantify the amount of photogenerated acid, but they all have drawbacks. Some methods use PAG solutions, 11 but this is different from the way that PAGs are typically used in lithography in a solid state film. The standard addition technique that consists of the addition of known amounts of base to effectively titrate the photogenerated acid in a film has been used for many different CAR acid generation studies, but is limited to use in materials that can be patterned, and requires multiple resist formulations with different base loadings.…”

Review of methods for the mitigation of plasma‐induced damage to low‐dielectric‐constant interlayer dielectrics used for semiconductor logic device interconnects

“…The generated NH 3 starts to be desorbed in the thermal annealing process in photoresist development. The desorbed NH 3 penetrates the SiOC film again and is evacuated from the sidewalls of via‐hole to via‐hole and partially deactivates photo‐generated acids in the photoresists . The amount of desorbed NH 3 from a via is determined by accumulation in the surroundings of the via‐free areas.…”