Yunwoo Lee

Measurement of the thickness profile of a transparent thin film deposited upon a pattern structure with an acousto-optic tunable filter

A simultaneous volumetric thickness-profile measurement method based on an acousto-optic tunable filter for transparent film deposited upon pattern structures is described. The nondestructive thickness profilometer prevents the destruction of samples such as one encounters in using a scanning-electron microscope and provides good accuracy. The information on the volumetric thickness profile is obtained through least-squares fitting with a phase model, ø(model)(k)=2kh+? (k, d)+(offset) , which has three unknowns: surface profile h, thickness d, and an indeterminate initial phase offset. Accurate phase information in the spectral domain can be obtained by introduction of the concept of spectral carrier frequency. Experimental results for a metal patterned sample show that the volumetric thickness profile can be determined within an error range of ~10 nm .

Fast thickness profile measurement using a peak detection method based on an acousto-optic tunable filter

In this communication, we describe a fast thickness profile measurement method for a transparent film, thinner than the white-light coherence length of 3-4 µm that is deposited on pattern structures. A visible acousto-optic tunable filter is employed for real-time wavelength scanning and the three-dimensional volumetric thin-film thickness profile information is obtained using a simple peak detection method in the spectral domain. The key idea is to divide the measurement into two states using a beam blocking mechanism to separately obtain the two unknowns of thickness and surface profile. Such separate measurements are required to compensate for the phase change effect caused by the multi-reflected beams from the thin film. The final thin-film surface profile information is measured by obtaining the number of peaks and phase deviations from the two separately scanned spectral intensity values.

Hydrostatic weighing at KRISS

To minimize the density correction of the transfer liquid in hydrostatic weighing, a new hydrostatic weighing machine with a single-step immersion pan was constructed. With this machine the volumes of two Zerodur? density-standard spheres (Z2, Z1), used as primary density standards at KRISS from 1992 to 2000, were measured against a silicon density-standard sphere that will be used as the new primary density standard. The relative measurement precision of the hydrostatic weighing was shown to be 7.7 ? 10?7, and the expanded uncertainty of the volume measurement was found to be 2.6 ? 10?5?cm3 for Z1 and Z2 with a confidence level of 95% and a coverage factor of 1.97, giving relative uncertainties of 6.7 ? 10?7 for Z2 and 7.9 ? 10?7 for Z1.

Automatic alignment method for calibration of hydrometers

This paper presents a new method to automatically align specific scale-marks for the calibration of hydrometers. A hydrometer calibration system adopting the new method consists of a vision system, a stepping motor, and software to control the system. The vision system is composed of a CCD camera and a frame grabber, and is used to acquire images. The stepping motor moves the camera, which is attached to the vessel containing a reference liquid, along the hydrometer. The operating program has two main functions: to process images from the camera to find the position of the horizontal plane and to control the stepping motor for the alignment of the horizontal plane with a particular scale-mark. Any system adopting this automatic alignment method is a convenient and precise means of calibrating a hydrometer. The performance of the proposed method is illustrated by comparing the calibration results using the automatic alignment method with those obtained using the manual method.

New weight-loading device for calibration of precise barometers

In order to calibrate highly accurate barometers, laser/ultrasonic mercury manometers have been used. However, the complexity and cost of mercury manometers have gradually taken them out of use in most calibration laboratories. As a substitute, a gas-operated pressure balance is used to calibrate precise barometers. In such a case, many commercially available pressure balances are not desirable because the consequent exposure of the piston, cylinder and masses to the atmosphere causes the problem of contamination and the ingress of dust particles to the gap between the piston and cylinder. In this paper, a novel weight-loading device for changing the masses in situ without breaking the vacuum is described. This device makes it possible to add or remove weights easily in the absolute mode, thereby greatly reducing the time between observations. Using this device we could easily calibrate a precise quartz resonance barometer (Paroscientific, Model 760-16B) from 940?hPa to 1050?hPa.

Mono-axial power spectrograph for a spectral imaging ellipsometer: design and experimental results

A novel mono-axial power spectrograph for spectral imaging ellipsometry is described in this paper. Spectral imaging ellipsometers employing the proposed mono-axial power spectrograph can measure information about thin films along the line of the entrance slit of the spectrograph. The mono-axial power spectrograph is simply composed of an entrance slit, a holographic transmission grating and a focusing cylindrical doublet. Several features of the proposed spectrograph give some benefits when used with an imaging ellipsometer. Above all, the holographic transmission grating guarantees polarization insensitivity of the incident wave to the spectrograph. Therefore, the polarization dependency and calibration factors in the spectral imaging ellipsometer can be minimized. Also, the simple structure of the spectrograph employing a cylindrical doublet allows optical compatibility with conventional ellipsometers and high adaptability to spectral imaging ellipsometers. The spectral resolution of the spectrograph is 5 nm and it has a spectral range from 400 to 800 nm. The focal length of the manufactured mono-axial power spectrograph is 25.4 mm and the total system dimension is less than 120 mm(L) × 100 mm(W) × 100 mm(H). The design procedure and the results of experiments to measure the spatial transmittance are discussed for some transmission samples.

How to reduce non-linearity in effective area caused by the O-ring seal in a high-pressure balance

The oil-operated pressure balance is standard equipment in the field of pressure metrology. A pressure balance is simply configured to measure a force acting on an area. This area is determined as the effective area of a piston-cylinder assembly, and the weight force as the product of masses acting on the piston and the acceleration due to gravity. The accuracy of the pressure balance depends largely on the effective area of the piston-cylinder assembly. Accurate determination of this value is required for accurate pressure measurement. Most commonly used pressure balances are in a simple piston-cylinder configuration where the piston and cylinder can deform freely under high pressure. The simple piston-cylinder assembly has an O-ring chamber on the cylinder bottom to seal it. The oil pressure acting on the bottom of the cylinder surrounded by the O-ring may thus deform the cylinder, causing non-linearity of the effective area, i.e. a change in the pressure distortion coefficient. Using a numerical analysis based on the finite element method (FEM), we predict that this non-linear effect could be significantly reduced by an appropriate change in cylinder configuration.

Design and Calibration of Acousto-Optic Tunable Filter(AOTF) for Near Infrared Spectral Analysis

In this paper, we proposed the design and calibration method for the near infrared Acousto-Optic Tunable Filter (AOTF). The theory and design principles of AOTF for the visible light are well known since I.C.Chang has developed the parallel tangent condition for the non-collinear AOTF. Deflection angle, frequency-wavelength relation, spectral resolution, etc. were calculated based on the theory of AOTF. From this result, important parameters - incident and acoustic angle - to fabricate AOTF were decided. We measured the spectral resolution and the relation between electrical driving frequency and the Optical wavelength of diffracted light to calibrate the near infrared AOTF. About 40 ∼ 80 MHz electrical frequency was required to get 1200 ∼ 2200 nm near infrared light. Spectral resolution was less than 10 nm in the near infrared region.

Non‐destructive surface profile measurement of a thin film deposited on a patterned sample

A novel non‐destructive method for volumetric thickness profile measurement of a transparent film, thinner than the white light coherence length of 3∼4 μm, that is deposited on a patterned structure is described in this paper. A visible acousto‐optic tunable filter (AOTF) for wavelength scanning is employed and the 3 dimensional thin film thickness profile information is obtained through 2 phase functions ψ(k) and φ(k) in the spectral domain. The first phase function ψ(k) compensates for the phase change effect caused by the multiple reflected beams from the thin film and the other is a total phase function φ(k) for the interference between a reference mirror plane and the film deposited patterned structure. Compensation for the phase change effect was achieved by measuring the 3 dimensional film thickness information separately prior to surface profile measurement. Then the final thin film surface profile information was measured by using the total phase function obtained through spectral frequency domai...

Effects of the O-ring used for sealing in high-pressure balances on measurements of pressure

An oil-operated pressure balance is standard equipment widely used in the field of pressure metrology. Most of the commonly used pressure balances are in a simple piston-cylinder configuration where the piston and the cylinder can deform freely under pressure. This simple piston-cylinder assembly has an O-ring chamber on the cylinder bottom to seal the cylinder. The effects of this O-ring seal on the effective area are not well known. This paper demonstrates by the numerical method using finite element method and the experimental method that, when performing precise measurements of pressure using a pressure balance, the cylinder will be deformed by the oil pressure exerted on the bottom of the cylinder surrounded by the O-ring, causing a non-linearity in the change of effective area, and that, when the piston-cylinder assembly is used in the body with different diameters of O-ring, the effective area, i.e. the pressure, can be significantly changed. The effects of O-ring seals on the effective area of a DH5306 oil-operated pressure balance were investigated using two piston-cylinder assemblies with nominal effective areas of 2 mm2 over the pressure range of 100-300 MPa. Three different sizes of O-ring, 4.8, 8.0 and 11.7 mm in diameter, were used. The maximum change of the effective area can reach 30 ppm at 300 MPa and 18 ppm at 100 MPa due to the change of O-ring. Therefore, for precise pressure measurement, the correct understanding of the O-ring under the cylinder is required along with checking of the size of the O-ring under the cylinder whenever calibrating the piston-cylinder assembly.