Mesoscale simulation of molecular resists: The effect of PAG distribution homogeneity on LER

Lawson, Richard A.; Henderson, Clifford L.

doi:10.1016/j.mee.2008.12.042

Cited by 22 publications

(14 citation statements)

References 11 publications

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“…Figure 2c shows the energetically favorable structure of the unit cell of size 9.12 nm × 3.01 nm × 8.20 nm divided into EUV-exposed and pristine domain. Because it has been known that the distribution of the PAG molecules significantly affect the final line edge morphology, 38 10−12 unit cells having different distributions of the PAGs were constructed for each PAG loading condition.…”

Section: Molecular Dynamicsmentioning

confidence: 99%

Multiscale Simulation Approach on Sub-10 nm Extreme Ultraviolet Photoresist Patterning: Insights from Nanoscale Heterogeneity of Polymer

Kim¹,

Moon²,

Choi³

et al. 2018

Macromolecules

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We developed a multiscale model that integrates density functional theory (DFT), molecular dynamics (MD), and the finite difference method (FDM) to reflect the heterogeneous spatial distribution of the material ingredients on sub-10 nm photoresist (PR) pattern fabrication using extreme ultraviolet lithography (EUVL). It allowed the exploration of phototriggered chemical reactions at the molecular level, including photoacid generator (PAG) dissociation, acid diffusion-coupled deprotection, and solubility switching of individual polymer chains. To quantify the progress of the deprotection, a protection ratio of each pendant group was tracked to distinguish the dissoluble PR chains from the developer as the process time elapsed. Deprotection was shown to preferentially occur in the pendant group adjacent to the acid molecule (<0.74 nm), which determined the chemical gradient and solubility switching trend of the PR chains. Based on the full description of the phototriggered chemical reaction, the morphology of the PR line pattern was predicted after wiping out the dissoluble chains. We particularly examined the PAG loading effect (5.68−30.12 wt %) on the line edge roughness (LER) of the PR pattern and predicted the LER inversion phenomenon at the critical threshold PAG concentration, which qualitatively agreed with the experimental observations. Such a LER trend due to PAG loading was explained by the reciprocal interaction between the homogeneous packing of the acid from the dissoluble PR chains and the acid clustering behavior. The variation of the homogeneity of the deprotection in each pendant group was verified as a function of PAG concentration, which rationalized the existence of the reciprocal interaction.

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Section: Molecular Dynamicsmentioning

confidence: 99%

Multiscale Simulation Approach on Sub-10 nm Extreme Ultraviolet Photoresist Patterning: Insights from Nanoscale Heterogeneity of Polymer

Kim¹,

Moon²,

Choi³

et al. 2018

Macromolecules

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“…The stochastic resist model is more fully described elsewhere for earlier 2D models [7][8] and the 3D model 6 used in the studies here, but a short description of the resist model is given. The resist simulation is based on three-dimensional lattice with 1 nm x 1 nm x 1 nm cells.…”

Section: Resist Modelmentioning

confidence: 99%

Investigating SEM metrology effects using a detailed SEM simulation and stochastic resist model

Lawson

Henderson

2015

SPIE Proceedings

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A Monte Carlo electron scattering simulation tool that can create SEM images of 3D features with arbitrary geometry has been developed. This is combined with both a stochastic resist model and synthetic 3D features to probe the effect of the effect of roughness on SEM measurements. Sidewall roughness makes it difficult to precisely identify the true feature width of a line because the roughness increases the SEM signal non-proportionally to the amount of material with which it is interacting. LER generally under predicts sidewall surface roughness because the SEM has an averaging effect as the electron beam interacts with a volume of material. LER becomes a better measure of surface roughness as the correlation length of the surface roughness increases. Decreasing film thickness causes a decrease in the linewidth and increase in LER measured by SEM, especially for features 35 nm thick and below. This occurs even if the true 3D feature width and roughness is approximately constant, meaning that the apparent change in linewidth and LER is a metrology effect. Threshold based estimations of line edges are difficult because the threshold choice that best matches the true feature width changes with the feature geometry. Model based library fits of linescans do not appear to provide a solution because sidewall roughness and sidewall angle have similar effects on the linescan meaning no unique linescan likely exists.Keywords: photoresists, scanning electron microscopy, electron scattering, sidewall roughness, line edge roughness, film thickness effects on LER, sidewall angle, stochastic photoresist model INTRODUCTIONScanning electron microscopes (SEMs) have long been and will likely remain the metrology tool of choice due to their ease of use, high resolution, and ability to easily image at a range of length scales. Despite often being treated as such, the image produced by an SEM is not identical to an optical image. This is because the SEM works by shooting a beam of electrons into a sample and then measuring the number of lower energy secondary electrons emitted by the sample for that incident location. This electron-material interaction means that there are certain biases or effects associated with the measurement that must be accounted for to correctly interpret the SEM image. One commonly known effect is the fact that the SEM signal is more sensitive to topography; this means that the signal is higher at the edges of features than in the middle. This fact is used to measure the width of features by identifying the edges where the signal is highest. Like many things in the semiconductor industry, SEM metrology of patterned features has become more difficult as the features sizes have shrank. The current length scales of features can potentially cause a whole new series of metrology effects that must be accounted for to correctly interpret the SEM images.One of the major issues is that the roughness length scale of current features is on the order of the feature size itself. This means there can be significant errors...

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“…Understanding LER is important for designing materials and processes, and the causes of LER have been intensively investigated over the past 20 years. 4,5 Consequently, to best decide on and develop more-robust acceptance criteria for alternatives to manufacturing existing CAR-based masks, it is important to carefully evaluate non-CAR photoresists that do not contain PAGs.…”

Section: Introductionmentioning

confidence: 99%

Fabricating a high-resolution mask with improved line-edge roughness by using a nonchemically amplified resist and a postexposure bake

Miyoshi¹,

Taniguchi

2015

Journal of Vacuum Science &Amp; Technology B, Nanotechnology and Microelectronics: Materials, Processing, Measurement, and Phen

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The authors have developed a high-resolution technique for fabricating photomasks at the 10-nm halfpitch logic nodes and beyond. Current mask-manufacturing techniques use a chemically amplified resist (CAR) that has a complex mechanism of acid generation, complicating the criteria for selecting the polymer and the quencher for industrial purposes. Thus, it is important to study fabricating masks with non-CARs. The authors exposed a non-CAR, diluted ZEP520A, to variable-shaped electronbeam lithography and used a postexposure bake (PEB) to modify the resist. Studying how the PEB temperature affected the non-CAR and resultant masks, the authors demonstrate that their technique can produce high-resolution structures. By measuring the critical dimensions (CDs), the authors show that the PEB shrunk, enlarged, and retained the size of 1:1 line-and-space, isolated space, and isolated line patterns, respectively. By optimizing the PEB temperature, the authors improved the line-edge roughness (LER) of the 1:1 line-and-space and isolated space CDs by $40%. To understand how the PEB affected the resultant structures, the authors measured the hardness of cured resists with and without a PEB at various temperatures. Optimizing the PEB temperature of the non-CAR increased the resist contrast, annealing the resist and improving the LER. As such, their technique is capable of high resolutions on the order of 20 nm. The insights the authors gained from optimizing the PEB might be useful when fabricating next-generation masks.

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Mesoscale simulation of molecular resists: The effect of PAG distribution homogeneity on LER

Cited by 22 publications

References 11 publications

Multiscale Simulation Approach on Sub-10 nm Extreme Ultraviolet Photoresist Patterning: Insights from Nanoscale Heterogeneity of Polymer

Multiscale Simulation Approach on Sub-10 nm Extreme Ultraviolet Photoresist Patterning: Insights from Nanoscale Heterogeneity of Polymer

Investigating SEM metrology effects using a detailed SEM simulation and stochastic resist model

Fabricating a high-resolution mask with improved line-edge roughness by using a nonchemically amplified resist and a postexposure bake

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