Line Edge Roughness Measurement Research Articles

Extreme ultraviolet laser-based table-top aerial image metrology of lithographic masks

We have realized the first demonstration of a table-top aerial imaging microscope capable of characterizing pattern and defect printability in extreme ultraviolet lithography masks. The microscope combines the output of a 13.2 nm wavelength, table-top, plasma-based, EUV laser with zone plate optics to mimic the imaging conditions of an EUV lithographic stepper. We have characterized the illumination of the system and performed line-edge roughness measurements on an EUVL mask. The results open a path for the development of a compact aerial imaging microscope for high-volume manufacturing.

Metrology Method of Line Edge Roughness with Nanometer Scale Precision Using Atomic Force Microscopes

This paper proposes a methodology method for line edge roughness (LER) measurement and characterization using atomic force microscope. The definition and origins of LER are discussed firstly. A LER quantificational method using image processing and threshold method is presented, which is used to analyze AFM images of Silicon lines and extract LER characteristics. Then the energy distribution of LER is determined by the multi-scale analysis based on wavelet transform and the parameters of multi-scale characterization were given. The experiment data shows that this method can offer an effective quantitative analysis of LER.

Line edge roughness metrology using atomic force microscopes

Line edge roughness (LER) measurements using two types of atomic force microscopes and three types of tips are compared. Measurements were made on specially prepared samples with inscribed edge roughness of different amplitudes and wavelengths. The spatial wavelengths and amplitudes each instrument was able to measure are compared. Techniques on checking the noise level of LER measuring instruments are highlighted.

Effect of a surface inhibition layer on line edge roughness

Line edge roughness (LER) is one of the most important issues in sub-100nm lithography. We have designed and implemented an experiment to study the coupled effect from acid depletion and percolation property of development process of Chemically Amplified Resist (CAR) on Line Edge Roughness (LER). The resist selected is UV-5 (a positive tone CAR from Shipley), known to be fairly sensitive to acid loss. After development, the resist is analyzed using high-resolution SEM (LEO 1550 VP), and an in-house made software is used for LER measurements. Our results indicate that the effect on LER and Critical Dimension (CD) variation depends on image modulation, and that aggressive lithography (low modulation image) will be more sensitive to the environment. In addition, it is shown that percolation development with stochastic energy deposition model can explain all the observed phenomena.

Line edge roughness investigation on chemically amplified resist materials with masked helium ion beam lithography

We conducted line edge roughness (LER) measurements on resists with various sensitivities, exposed with a 75 keV 1:1 masked ion beam lithography tool. The critical dimension measurement data were treated with an algorithm for separation of mask induced roughness from random LER. The scaling analysis approach provided the correlation length and the roughness exponent. The results indicate that for exposure doses >2.5 μC/cm2 LER is not governed by shot noise but by the resist material properties (sensitivity, molecular weight, acid diffusion length) and development conditions.

Line edge roughness investigation on chemically amplified resist materials with masked helium ion beam lithography

We conducted line edge roughness (LER) measurements on resists with various sensitivities, exposed with a 75 keV 1:1 masked ion beam lithography tool. The critical dimension measurement data were treated with an algorithm for separation of mask induced roughness from random LER. The scaling analysis approach provided the correlation length and the roughness exponent. The results indicate that for exposure doses >2.5 μC/cm 2 LER is not governed by shot noise but by the resist material properties (sensitivity, molecular weight, acid diffusion length) and development conditions.

Quantification of line-edge roughness of photoresists. I. A comparison between off-line and on-line analysis of top-down scanning electron microscopy images

An off-line image analysis algorithm and software is developed for the calculation of line-edge roughness (LER) of resist lines, and is successfully compared with the on-line LER measurements. The effect of several image-processing parameters affecting the fidelity of the off-line LER measurement is examined. The parameters studied include the scanning electron microscopy magnification, the image pixel size dimension, the Gaussian noise-smoothing filter parameters, and the line-edge determination algorithm. The issues of adequate statistics and appropriate sampling frequency are also investigated. The advantages of off-line LER quantification and recommendations for the on-line measurement are discussed. Having introduced a robust algorithm for edge-detection in Paper I, Paper II [V. Constantoudis et al., J. Vac. Sci. Technol. B 21, 1019 (2003)] of this series introduces the appropriate parameters to fully quantify LER.

Investigating Line-Edge Roughness in Calixarene Fine Patterns Using Fourier Analysis

The line-edge roughness (LER) of patterns of negative-tone electron-beam resists, methyl-acetoxy calix[n]arene (n=6–8), was investigated using Fourier analysis. LER measurements were carried out by determining the intensity peaks of the pattern edges in scanning electron micrographs. The Fourier analysis showed that the roughness of the resist materials produced large peaks in the 10 to 100 nm wavelength range. The total intensity of LER spectra clearly depended on the electron dose and the “n” number of the calixarene resists. The smallest LER was observed in the calix[7]arene films. In contrast, the calix[6]arene films had a relatively large intensity in their Fourier spectra. X-ray diffraction measurements (XRD) revealed crystallization in the calix[6]arene films and an amorphous phase in the calix[7]arene and calix[8]arene films.

Surface and line-edge roughness in plasma-developed resists

Silicon-containing, plasma-developed resists are characterised by surface (SR) and line-edge roughness (LER) measurements as functions of the exposure dose and plasma development conditions. Specifically, bilayer siloxane-based resists of different molecular weight distributions, and single-layer silylated chemically amplified resists are evaluated with measurements of SR and LER, while the results are compared with those of solution-developed chemically amplified resists. We show that plasma-developed systems can have low LER provided the resist material, the resist chemistry, and the processing conditions are chosen appropriately.

Correlation of atomic force microscopy sidewall roughness measurements with scanning electron microscopy line-edge roughness measurements on chemically amplified resists exposed by x-ray lithography

As critical dimensions of resist features shrink, roughness of the features may contribute significantly to the variation in critical dimension. Measuring and understanding the causes of this roughness will become increasingly important with smaller sizes. To date, mainly two techniques have been used to measure the roughness: atomic force microscopy (AFM) and scanning electron microscopy (SEM). Topdown SEM measurements provide an easy and expedient measure of the variation in the profile of the resist feature. These measurements are often called “line-edge roughness” (LER). AFM measurements are considerably more time consuming, but provide information on the entire sidewall surface of the resist, rather than just the profile in line-edge roughness. Our recent AFM measurements on the positive-tone resist APEX-E and UV5 have shown that the sidewall roughness of the resist is depth dependent; resist near the substrate is smoother than resist at the top surface of the resist. For instance, APEX-E may have a roughness on the order of 3 nm rms near the substrate, which may increase to 7 or so nm rms at the top of the resist line. This article will correlate measurements made by both AFM and SEM and explore how the depth-dependent roughness in AFM data may affect the magnitude of the roughness measured by topdown SEM.

Bilayer resists process for ArF lithography.

We evaluated three chemically amplified positive-tone resists for ArF bilayer process, which are mainly based on cyclo-hexyl-carboxylic-acid-silsesquioxane. The key of obtaining the good dissolution contrast is the improvement of resistance to aqueous base developer. The optimized resist had an excellent resolution capability of K1=0.404. It had a permissive sensitivity of 13mJ/cm2. The line edge roughness (LER) of the bilayer resist patterns was as good as conventional organic resist. The LER of bilayer pattern mainly depend on the roughness of upperlayer Si-containing resist pattern, . that was shown by the LER measurements before and after dry-development process.