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In this study, we developed a methodology to evaluate scanning electron microscopy (SEM)-based line edge roughness (LER) metrology. In particular, we used a metrological tilting atomic force microscopy (tilting-mAFM) as LER reference metrology. We analyzed the height-height correlation function (HHCF) of SEM line-edge profiles combining averaging and unbiased correction methods. The direct comparison of our method with tilting-mAFM enabled a precise evaluation of the SEM-based LER metrology. We demonstrated that a combination of unbiased HHCF and averaging methods with appropriate condition enabled relatively precise measurement of three roughness parameters. We observed that, for precise roughness evaluation, reducing noise in the line-edge profiles is important before performing the HHCF analysis and unbiased correction.

Line edge roughness (LER) measurement of a nanoscale line pattern is a metrology challenge in the inspection of semiconductor devices. Conventional scanning electron microscopy (SEM), a classical LER measurement technique, is a top-view (2D) metrology and incapable of accurately measuring 3D structures. For LER measurements, SEM measurement generates a single line edge profile for the 3D sidewall roughness, although the line edge profile differs at each height in the 3D sidewall. In this study, we used atomic force microscopy (AFM) with the tip-tilting technique to measure the 3D sidewall roughness, as an LER reference metrology. An identical location of a line pattern measured by SEM and AFM was compared to evaluate the SEM’s performance. The line edge profile from the AFM measurement exhibited lower noise than that from SEM. The measured line edge profiles were analyzed using the power spectral density (PSD), height-height correlation function (HHCF), and autocorrelation function. The results demonstrate that the standard deviation (σ) and correlation length (ξ) are overestimated while the roughness exponent (α) is underestimated by SEM, considering the AFM results as reference values.

Line edge roughness (LER) measurement is one of the metrology challenges for 3D device structures, and LER reference metrology is important for reliable LER measurements. We developed an LER measurement technique, which is able to analyze LER distribution along height of a line pattern, with high accuracy, resolution, and reproducibility. Highly accurate atomic force microscopy (AFM) image of a vertical sidewall of a line pattern was obtained using a metrological tilting- AFM, which offers SI-traceable dimensional measurements. The tilting-tip was controlled with an inclined servo axis and scans the vertical sidewall along a line pattern with a high sampling density to enable an analysis of the LER height distribution at the sidewall. A horizontal cross-section of the sidewall shows sidewall roughness with sub-nm resolution. Power spectral density (PSD) analysis of the sidewall profile showed that the PSD noise in the high-frequency region was several orders of magnitude lower than the noise of typical scanning electron microscopy methods. AFM measurements were sequentially repeated three times to evaluate the reproducibility of the sidewall measurement and LER analysis; results indicated a high reproducibility of 0.07 nm evaluated as a standard deviation of LER at each height.

Editors:Prathan Buranasiri,Sarun Sumriddetchkajorn, We have studied a method to obtain both three-dimensional (3-D) spatial information and spectral information of a usual polychromatic object by a fully passive interferometric technique that is strongly coupled with digital signal processing. Our method can be used for a vast range of wavelengths, because no special imaging devices, such as lenses, are required. In addition, coherent light sources are not necessary. A hyperbolic-type volume interferogram is one type of the volume interferogram, which is used for retrieve the object information, and an interferometer to measure directly this volume interferogram has been introduced. This paper introduces a method to measure the hyperbolic-type volume interferogram with high sensitivity in fully interferometric 3-D imaging spectrometry. This is accomplished by coupling of interferometer to measure directly the hyperbolic-type volume interferogram and heterodyne detection system for broadband light. We also report a preliminary experimental result based on the interferometer to measure directly the hyperbolic-type volume interferogram.

Deep, stable starlight suppression is needed for the direct interferometric detection of Earth-like planets and requires careful control of the intensity and phase of the beams that are being combined. We have developed a novel compensator for the Terrestrial Planet Finder Interferometer based on a deformable mirror to correct the intensity and phase at each wavelength across the bandwidth of 8 to 12 microns wavelength. This paper will discuss the results of using the adaptive nuller to achieve deep broadband nulling in the mid-IR.

Deep, stable starlight nulls are needed for the direct detection of Earth-like planets and require careful control of the intensity and phase of the beams that are being combined. We have tested a novel compensator based on a deformable mirror to correct the intensity and phase at each wavelength across the bandwidth of 8 to 12 microns wavelength. This paper will cover the results of the adaptive nuller tests performed in the mid-IR.

Deep, stable starlight nulls are needed for the direct detection of Earth-like planets and require careful control of the intensity and phases of the beams that are being combined. We are testing a novel compensator based on a deformable mirror to correct the intensity and phase at each wavelength and polarization across the nulling bandwidth. We have successfully demonstrated intensity and phase control using a deformable mirror across a 100nm wide band in the near-IR, and are in the process of conducting experiments in the mid-IR wavelengths. This paper covers the current results and in the mid-IR.

Deep, stable starlight nulls are needed for the direct detection of Earth-like planets and require careful control of the intensity and phases of the beams that are being combined. We are testing a novel compensator based on a deformable mirror to correct the intensity and phase at each wavelength and polarization across the nulling bandwidth. We have successfully demonstrated intensity and phase control using a deformable mirror across a 100nm wide band in the near-IR, and are in the process of building the phase 2 experiment operating at mid-IR wavelengths. This paper covers the results of our demonstration in the near-IR, as well as our current progress in the mid-IR.

Deep, stable nulling of starlight requires careful control of the amplitudes and phases of the beams that are being combined. The detection of earth-like planets using the interferometer architectures currently being considered require that the electric field amplitudes are balanced at the level of ~ 0.1% and the phases are controlled at the level of 1 mrad (corresponding to ~ 1.5 nm for a wavelength of 10 microns). These conditions must be met simultaneously at all wavelengths across the science band and for both polarization states, imposing unrealistic tolerances on the symmetry between the optical beamtrains. Lay et. al. proposed the concept of a compensator that is inserted into the beamtrain, which can adaptively correct for the mismatches across the spectrum enabling deep nulls with realistic, imperfect optics. This proposed design uses a deformable mirror to adjust the amplitude and phase of the electric field that couples into the single-mode spatial filter. We have demonstrated amplitude and phase control at a single wavelength in the near-IR. We are preparing to demonstrate control with our deformable mirror actuator in the near-IR and in parallel are preparing a demonstration in the mid-IR where the compensator will be required to operate.

A low-coherence tandem interferometer with a single-mode optical fiber is developed for remote-measurement of length. The optical path difference provided in the first low-coherence interferometer is transmitted through the optical fiber to the second low-coherence interferometer. Low-coherence interference fringes are generated when the optical path difference in the second interferometer, which correspond to the length being measured, compensates that of the first interferometer. A gauge block of 50 mm long has been calibrated remotely through the single-mode optical fiber of 3 km length with a stnadard deviation of 0.12 μm.

A new remote-measurement technique of length is developed, by using a low-coherence tandem interferometer and a single-mode optical fiber. The optical path length with a gauge block in the first low-coherence interferometer is transmitted through the optical fiber to the second interferometer. And then the interference fringes containing the length information are generated and detected with high accuracy.

A Novel setup for two-dimensional (2-D) parallel measurements of low-coherence heterodyne signal by using a tandem interferometer and a 2-D sensor has been developed. Generally speaking, it is difficult to obtain heterodyne signals whose frequencies are much higher than the frame rate of the coventional 2-D sensor. A mode-locked femtosecond laser (MLFL) is used as a light source.

A Fourier transform spectrometer with heterodyne modulation using a moving diffraction grating has been developed for the NIR region. The grating simultaneously acts as a beam splitter and a modulator, which realizes optical frequency shift of incident light for increasing the sensitivity of measurement by heterodyne modulation technique. The difference of diffraction angle is compensated by a collimating lens or a mirror and plane mirrors.

We have developed a gauge block measurement system that uses three frequency-stabilized lasers. The stabilized lasersare as follows: an 12-stabilized offset locked He-Ne laser (633 nm), an 12-stabilized Nd:YAG laser (532 nm), and a Rb-stabilized diode laser (780 nm). The 12-stabilized offset locked He-Ne laser is commercially available (NihonkagakuEngineering Co., Ltd.) and its relative wavelength uncertainty is 2.5 X 10' ' . An 12-stabilized Nd:YAG laser and a Rb-stabilized diode laser was developed in our institute and their relative wavelength uncertainties are 5 X 1 O12 and 1 X 1 O, respectively. In the measurement system, laser beams were introduced to the interferometer using an optical multimodefiber. An interferometric fringe pattern was taken using a CCD camera and the excess fraction parts were calculated from the fringe pattern using the Fourier transform method. The excess fraction part obtained from the Rb-stabilized semiconductor laser was used only to determine the integer part of the fringe order, because the accuracy and stability ofthe wavelength were not sufficient for the long gauge block measurements. This interferometer can measure gauge blocksofup to 1000 mm long and the standard uncertainty ofthe interferometer is about 75

The low-coherence interferometric technique is proposed for the in-situ measurement of the refractive index of dispersive samples with high accuracy. A tandem configuration of a Michelson interferometer and a triangular interferometer is used to compensate for the chirping effect which results from the broad spectrum of the light source. Thick samples can be successfully measured with the low- coherence interferometer, therefore the relative accuracy of the refractive index can be improved.

Heterodyne white-light interferometer that uses an optical grating to shift the optical frequency of the white light is proposed. By moving the optical grating, the diffracted lights undergo the frequency shift. The dependency of diffraction angle on wavelength can be resolved by using a spherical mirror, and then heterodyne detection of white-light can be realized with the combination of the optical grating and the spherical mirrors. In practical uses, a tandem-configuration interferometer is useful. The principle was demonstrated and the effect was confirmed experimentally for the first time The surface profile of a step-like object was measured. The signal-to-noise ratio of heterodyne signal is increased by thousand times from that of homodyne signal.

A novel low-coherence interferometer has been developed, based on the heterodyne technique for highly accurate and sensitive positioning of a three-dimensional (3-D) object, which uses two acousto-optic modulators (AOM's) and two spherical reflecting mirrors in a Michelson interferometer. By using this technique in a tandem interferometer, the profiles of diffusing and mirror-likes surfaces of the 3-D objects are measured with a high accuracy of 50 nm from the heterodyne signals of 200 kHz.© (1999) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

A multichannel spectral imaging system consisting of dichroic mirrors is proposed and evaluated. The system is expected to have the highest signal-to-noise ratio because of the largest optical throughput. The signal-to-noise ratio is studied and compared with that of another fast spectral imaging technique.