Extreme Ultraviolet Resists Research Articles

Effects of Rate Constant for Deprotection on Latent Image Formation in Chemically Amplified Extreme Ultraviolet Resists

The resolution of chemically amplified extreme ultraviolet (EUV) resists has reached sub-30 nm. However, the sensitivity and the reduction in the line edge roughness of such resists is still inadequate for the realization of EUV lithography. The pattern formation of chemically amplified resists is based on chemical reactions, which start with energy deposition from exposure tools and are terminated by quenchers or by cutting the heat supply for chemical reactions. In this study, the effects of rate constant for deprotection on latent image formation in chemically amplified EUV resists were investigated from the viewpoint of the difference between high- and low-activation-energy (Ea)-type resists. In chemically amplified resists, neutralization and deprotection competitively proceed. In high-Ea-type resists, in which neutralization proceeds before deprotection, the contrast of pattern edges is improved by suppressing deprotection in the low-dose region. In low-Ea-type resists, in which a fast deprotection is expected, the difference in the extent of deprotection between the high- and low-dose regions can be enhanced by promoting deprotection over neutralization. For the improvement in high- or low-Ea-resist performance, it is effective to enhance or balance all advantages of chemical reactions.

Outgassing Quantification Analysis of Extreme Ultraviolet Resists

Extreme ultraviolet (EUV) resist outgassing quantification analysis using the pressure rise method with a modified ideal gas equation is discussed. The use of the outgassing amounts based on the E0 and/or multiples of E0 is recommended as this information may be crucial in understanding the behavior of resist outgassing at various exposure or patterning doses. Furthermore, this method is effective in representing resist outgassing release mechanisms which were found to differ greatly depending on the resist formulation. Applying this method with quadrupole mass spectrometry (QMS), analysis of the resist outgassing obtained from a model poly(hydroxystyrene) (PHS) resist with varied quencher concentrations showed that the decrease and shift of the maximum pressure rise peak of the pressure rise curve as quencher concentration was increased was found to be due to the suppression of photo acid production which, in effect controls the amount of protecting group released as resist outgassing.

Reaction Mechanism of Extreme Ultraviolet Resists

Molecular resist of polyphenol was evaluated as an extreme-ultraviolet resist compared with a polymer resist of poly(tert-butoxycarbonylhydroxystyrene). X-ray reflectometry was used to determine the resist-film density and measurement accuracy was improved. The molecular resist shows higher sensitivity of 3 mJ/cm2 than the polymer resist of 4 mJ/cm2. The deprotection mechanism was approximated by simple reaction equations and Fourier-transform infrared spectra was interpreted to give the products of a quantum yield and a deprotection rate constant as 9.7×10-8 and 8.1×10-8 cm3 molecule-1 s-1 for molecular and polymer resists. The higher sensitivity of the molecular resist is due to the larger efficiency of the reaction mechanism.

Resolution degradation caused by multispur effect in chemically amplified extreme ultraviolet resists

Extreme ultraviolet (EUV) (92.5 eV) radiation is expected as a next-generation exposure source. When EUV photons enter resists, they are absorbed by resist molecules and photoelectrons are emitted. Photoelectrons with the initial energy of approximately 80 eV further induce ionization and generate ion pairs. Because the inelastic mean free path of these electrons is less than 1 nm, ion pairs are so narrowly distributed that they interact with each other through Coulomb forces. In this study, the details in the interaction among ion pairs were investigated by using a Monte Carlo simulation. It was found that the electric interaction between ion pairs significantly degrade the initial acid distribution. The dependence of resolution degradation and multispur effect on acid generator concentration was clarified. The acid generator loading of >10 wt % is effective for the suppression of resolution degradation.

Impact of Nonconstant Diffusion Coefficient on Latent Image Quality in 22 nm Fabrication using Extreme Ultraviolet Lithography

In chemically amplified resists, acids catalyze pattern formation reactions with acid diffusion in the presence of quenchers, starting with the initial acid distribution as a boundary condition. Diffusion coefficients have been intensively investigated and reported to depend on the condition of the matrix. In this study, the effect of nonconstant diffusion coefficients was investigated using a simulation based on the reaction mechanisms of chemically amplified extreme ultraviolet resists. It was found that nonconstant diffusion coefficients have a significant impact on the resolution, sensitivity, and image quality (line edge roughness) in 22 nm fabrication.

Microfield exposure tool enables important advances in extreme ultraviolet resists

Microfield exposure tool enables important advances in extreme ultraviolet resists

Characterization of extreme ultraviolet resists with interference lithography

This paper describes extreme ultraviolet (EUV) resist screening results that have been obtained on an interference printer at the Swiss Light Source. Imaging performance of a variety of chemically amplified resists has been studied. The main focus of the work has been on evaluating ultimate resolution and exposure latitudes of various materials and on improving their process parameters. The chemically amplified resists have also been compared with non-chemically amplified PMMA. The resolution of the latter is clearly superior to that of the chemically amplified materials. Below 40–35 nm half-pitch all chemically amplified materials at best show modulation in resist, a limitation that is attributed to acid diffusion. However, PMMA shows clean profiles on the interference printer down to about 20 nm.

Molecular Challenges of Immersion and Extreme Ultraviolet (EUV) Resists

This paper outlines the major challenges for the development of 193 nm immersion and extreme ultraviolet (EUV) resists. The major issues for the implementation of 193 nm immersion are developing high index immersion fluids and high index lens materials to enable 32 nm half-pitch imaging. For EUV resists, reaction mechanisms are not well understood. In addition, the many constraints placed on EUV resists, such as needing low photospeed, low line width roughness, and low outgassing while achieving the desired resolution, make resist design very difficult.

Resist effects at small pitches

The ITRS roadmap and Moore’s law are driving us to print ever smaller features and ever tighter pitches. For these ultrasmall features and pitches, resist effects are expected to play a dominant role in limiting the overall lithographic process capability. To study the impact of resist parameters such as acid diffusion and quencher level on the lithographic performance, we have designed and formulated a matrix of 14 extreme ultraviolet (EUV) resists. In this article, we discuss results that we have obtained from EUV exposures of those resists on the 0.3 numerical aperture EUV Micro Exposure Tool at the Advanced Light Source at Lawrence Berkeley National Laboratories. In addition to exposure latitude and line edge roughness, acid diffusion lengths were characterized using a modification of the extended Nijboer–Zernike theory for each photoresist. A simple theory for the drop in resist contrast as function of the diffusion length is tested and leads to a verified correlation between exposure latitude and diffusion length. This theory gives guidelines to predict what acid diffusion lengths should be used for a certain lithography node. Line edge roughness analysis showed that shot noise statistics are present, and also points out that acid diffusion effects come into play. From the experimentally observed tendencies in this unique matrix of EUV photoresists, fundamental understanding was gained about prominent resist effects that will determine the lithographic performance of resist processes in future lithography nodes.