Unbiased roughness measurements from low signal-to-noise ratio scanning electron microscope images

Mack, Chris A.; Severi, Joren; Zidan, Mohamed; Simone, Danilo De; Lorusso, Gian

doi:10.1117/1.jmm.22.2.021006

Cited by 2 publications

(2 citation statements)

References 13 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…6 shows that the SNR values are above 2, which is the threshold defined for reliable metrology. 12,14 Moreover, the SNR decreases with reducing the film thickness as expected and reported for other types of resists. 3,12…”

Section: Sem Image Visibility Using Imec Bkm Conditionssupporting

confidence: 83%

E-beam metrology and line local critical dimension uniformity of thin dry resist films for high numerical aperture extreme ultraviolet lithography

Zidan,

Lorusso,

De Simone

et al. 2023

J. Micro/Nanopattern. Mats. Metro.

Self Cite

View full text Add to dashboard Cite

.BackgroundLithography advancements require resist layer thickness reduction, essential to cope with the low depth of focus characteristic of high numerical aperture extreme ultraviolet lithography (High NA EUVL). However, such a requirement poses serious challenges in terms of resist process metrology and characterization, as patterns in thin resist suffer from low contrast, which may affect the performance of the edge detection algorithms used for image analysis, ultimately impacting metrology.AimWe aim to investigate the impact of reducing the film thickness of the dry photoresist on the E-beam metrology and line local critical dimension uniformity (LCDU).ApproachThin dry resist films from 10 to 30 nm are patterned at pitches 24, 28, and 32 nm using EUVL. A standard critical dimension scanning electron microscope (CDSEM) is used to perform E-beam metrology. The captured SEM images are analyzed using software to extract the parameters of interest, such as the critical dimension (CD), power spectral density (PSD), unbiased line width roughness (uLWR), LWR correlation length, signal-to-noise ratio (SNR), and line LCDU for a range of features with lengths from 12 to 50 nm. Furthermore, the experimental results of the line LCDU of a range of feature lengths and roughness parameters are plotted for different process conditions of thickness and pitch in a normalized way.ResultsThe results indicate that the dry resist shows good CDSEM imaging contrast and high SNR even at the thinnest resist thickness. This enables extracting a reliable uLWR measurement without the need to increase the number of frames to modulate the SNR. Moreover, it has LWR correlation length of around 2.5 nm. By thinning the resist thickness, the uLWR and line LCDU increase, and the SNR and the LWR correlation length decrease. Finally, when normalizing the line LCDU to uLWR and the feature length to the correlation length, the resulting curves of the different process conditions of the thickness and pitch overlap with each other, following an analytical model that relates the line LCDU to the resist roughness parameters.ConclusionWe showed the impact of reducing the dry resist thickness on E-beam metrology and line LCDU for features foreseen for High NA EUVL. The dry resist has good imaging contrast, LWR correlation length of around 2.5 nm, and the line LCDU depends on the resist thickness (uLWR and LWR correlation length for each particular thickness). With such a dataset, we demonstrated an overlap between the normalized curves of the line LCDU to the uLWR and the feature length to the correlation length for the different process conditions of thickness and pitch. The uLWR and correlation length are the knobs to achieve good patterning uniformity for a given feature length.

show abstract

Section: Sem Image Visibility Using Imec Bkm Conditionssupporting

confidence: 83%

E-beam metrology and line local critical dimension uniformity of thin dry resist films for high numerical aperture extreme ultraviolet lithography

Zidan,

Lorusso,

De Simone

et al. 2023

J. Micro/Nanopattern. Mats. Metro.

Self Cite

View full text Add to dashboard Cite

show abstract

“…For instance, they assume that 'in situations where white noise (that is, frequencyindependent noise) is added to the roughness profile, the error component due to that noise also appears in the PSD/HHCF as a frequency-independent plot called the flat noise floor'. This assumption ignores the correlation component [14][15][16] because the true roughness profile and noise are presumably independent. However, the validity of this assumption has not been checked, and the influence of the correlated component must be clarified for reliable assessment of noise errors.…”

Section: Introductionmentioning

confidence: 99%

Effect of white noise on roughness measurements of self-affine fractals

Kizu

Misumi

Hirai³

et al. 2023

Meas. Sci. Technol.

View full text Add to dashboard Cite

This study formulated and clarified the presentation of the noise-related error terms in the power spectral density (PSD) and height–height correlation function (HHCF) through a roughness analysis of self-affine fractals. Assuming the noise as white noise, this study simulated the PSD and HHCF of the noisy roughness profile in a typical situation: line-edge roughness measurements involved in semiconductor lithography technology. It was found that conventional noise-correction techniques can bias the PSD/HHCF from those of the true roughness profiles because they do not account for the residual noise-induced error. The findings obtained from the roughness analysis and simulation techniques are expected to benefit various applications, such as clarifying the quantitative residual error in specific situations, selecting the optimum analysis method (PSD or HHCF), estimating the required number of averaged profiles (measurements) that yields sufficiently small noise errors, and considering strategies for noise reduction.

show abstract

Unbiased roughness measurements from low signal-to-noise ratio scanning electron microscope images

Cited by 2 publications

References 13 publications

E-beam metrology and line local critical dimension uniformity of thin dry resist films for high numerical aperture extreme ultraviolet lithography

E-beam metrology and line local critical dimension uniformity of thin dry resist films for high numerical aperture extreme ultraviolet lithography

Effect of white noise on roughness measurements of self-affine fractals

Contact Info

Product

Resources

About