Thin Film Thickness Measurement Research Articles

Localized spin-wave excitation by the evanescent microwave scanning probe

We report a technique for the local contactless spin-wave excitation using the evanescent microwave scanning probe. Our probe is based on a dielectric resonator with the thin slit aperture. It operates at 8.8 GHz, has a spatial resolution of 10–100μm, and may be operated in the parallel and in the perpendicular magnetic field. The measurements can be performed in contact mode or by scanning the sample at constant probe-sample separation. Using 120–150 nm thick Permalloy films on a glass substrate as test samples, we show how our technique can be used for thickness measurements of thin magnetic films and for the mapping of their magnetic properties, such as magnetization and surface anisotropy.

On the thickness measurement of metallic thin films

Thickness is a key factor on the physical properties of the new miniaturized technology of thin film devices. Thin film physical properties depend on the thickness value and its control. This paper highlights the importance of the accurate determination of the thickness in thin films. Many efforts have been made through the years to develop reliable thickness measurement techniques. In this work, some of these techniques implemented to measure the thickness are briefly discussed. A theoretical model for film thickness determination was discussed. We proposed a simple method based on the variations of electrical resistance of a probe film to measure and control in situ the metallic film thickness with good resolution. Gold films were deposited by free evaporation and sputtering in order to apply the proposed method to measure and control the film thickness.

Multicavity Fabry-Pe/spl acute/rot interferometric thin-film sensor with built-in temperature compensation

A fiber-optic multicavity Fabry-Pe/spl acute/rot interferometric thin-film sensor with built-in temperature compensation has been constructed and demonstrated. Temperature information can be extracted from the multicavity structure to correct the temperature dependence of the optical thickness measurement of self-assembled thin-films. Experimental results demonstrate that the sensor is able to automatically compensate the temperature-induced optical-thickness error over the range from 0/spl deg/C to 100/spl deg/C.

Ultra-High-Sensitivity Measurement of Metal Thin Film Thickness by Photothermal Mirage Detection Method through Sample Surface Coating and Use of Semi-Cylindrical Lens

Methods to achieve ultra-high-sensitivity measurement of metal thin-film thickness by photothermal mirage detection are proposed. These methods apply 1) sample surface coating and 2) a semi-cylindrical lens for pumping beam focusing. Consequently, successful measurements are taken for thicknesses of less than several hundred nm. The semi-cylindrical lens plays a critical role in the measurements, and the sample surface coating significantly improves measurement sensitivity to about 2.5 times higher than the results for samples without coating.

Accounting for Secondary Extinction in Thickness Measurement of Thin Films by X-Ray Absorption

Allowing for secondary extinction (SE), a method is described for thickness measurement of thin films by x-ray absorption. The method is tested by employing Al foils and electrodeposited Cu films detached by the substrate. The thicknesses determined by the method were in fair agreement with that ones measured by the ordinary absorption method based on using incident beam intensities. Moreover, a dependence of the SE coefficient on the transmission factor of the films was experimentally shown, and thus additional light was thrown on the nature of SE.

Real time thickness measurement of thin film for end-point detector (EPD) of 12-inch spin etcher using the white light interferometry

A real time thickness measurement method based on the wide band white light interferometry for spin etcher is presented for the silicon-oxide and poly-silicon film deposited on 12-inch silicon wafer subject to a rotational vibration and chemical flow. Mathematical model for the vibration and chemical flow is described using a statistical method and analyzed to investigate their effects on the interference of reflected lights from the thin films. A white light interferometry system for the real time thickness measurement of thin films have been also developed to evaluate the performance of the method in experiment and determine the thickness of the films using signal processing techniques including curve-fitting and adaptive filtering. Experiments conducted for thin films ranging form 100 nm to 600 nm in thickness show that the method proposed in the paper is proved to be effective with a good accuracy of maximum 1.8% error.

Focus on Software

Focus on Software

Quantitative ellipsometric microscopy at the silicon–air interface

Ellipsometric microscopy is a technique that combines the merits of ellipsometry and light microscopy, i.e., it allows noninvasive, label-free measurements of thin film thickness and refractive index at high lateral resolution. Here we give a detailed description of the technique including a complete calibration scheme and a model to correct for the instrumental polarization of the imaging optics. The performance of the instrument was studied experimentally. We found a lateral resolution of 1μm and an absolute height accuracy of 3nm. The measured refractive indices were accurate to 2.3% and the height sensitivity of the instrument was smaller than 5Å. Another virtue of the instrument design besides its good performance is that it is in essence an extension of standard light microscopy and could be integrated into commercial microscopes.

Quantitative ellipsometric microscopy at the glass–water interface

Ellipsometric microscopy is a technique for simultaneous measurement of thin film thickness and index of refraction at a lateral resolution of approximately 1 μm. Up to now this technique has been used on silicon–air interfaces. However, biological processes take place often in aqueous solution and are studied at the glass–water interface. Due to the very low reflectivity of this interface we had to improve ellipsometric microscopy substantially. Here we present our approach to suppress the intensity of internal stray light by several orders of magnitude and show quantitative and laterally resolved ellipsometric measurements at the glass–water interface. When instrumental polarization was taken into account, an accuracy of δΨ = 0.41° and δΔ = 4.3° was achieved.

Focus on Spectroscopy

Focus on Spectroscopy

Measurement of thin film thickness by electronic speckle pattern interferometry

The surface profile of an Al thin film and its thickness have been observed by electronic speckle pattern interferometry (ESPI). The Michelson interferometer was used as our basic interferometric system to obtain interference fringes on a CCD camera. These interference fringes, arising from the path differences due to the surface contours of the thin film, were analyzed with three different techniques: fast Fourier transform (FFT), phase shifting, and digital image subtraction; and the results were compared with each other. We also derived a new formula for the image subtraction method, which is only valid in one-dimensional calculations. An unwrapping procedure was used to obtain a continuous phase in the FFT and phase shifting methods. Results on thickness measurements are presented and are found to be in good agreement with each other.

Ellipsometric microscopy: developments towards biophysics

Ellipsometric microscopy is a novel technique that combines the merits of ellipsometry and light microscopy, i.e. it allows noninvasive, label-free measurements of thin film thickness and refractive index at high lateral resolution. Ellipsometric microscopy has been successfully applied to silicon-air interfaces. However, typical biological systems require immersion in an aqueous buffer. Thus the authors have adapted the instrument for the observation of the interface between glass and water. In particular, the comparatively small differences in refractive indices between substrate and ambient media proved to be a challenge for instrument design. The first experiments with this new instrument are presented.

P1-38 Sensitivity enhancement by sample surface coatings on photothermal metal thin film thickness measurements

P1-38 Sensitivity enhancement by sample surface coatings on photothermal metal thin film thickness measurements

Focus on Laboratory Equipment

Focus on Laboratory Equipment

Fourier transform method for measurement of thin film thickness by speckle interferometry

The surface profile of an Al thin film and its thickness are observed by electronic speckle pattern interferometry (ESPI). The Michelson interferometer is used as our basic interferometric system to obtain interference fringes on a CCD camera. These interference fringes depend on the path differences due to the surface contours of the thin film. The interference fringes are analyzed with the fast Fourier transform method and a wrapped phase is obtained. An unwrapping procedure is used to obtain a continuous phase. Results on thickness measurement are presented.

Fixed-angle, energy-dispersive x-ray reflectivity measurement of thin tantalum film thickness

In this work, we employed a fixed-angle, energy-dispersive x-ray reflectivity technique to obtain the thickness of thin tantalum films (examples >9 nm) within seconds using a conventional, low-energy x-ray copper or chromium source (20 kV/20 mA/400 W). We compared this fixed-angle, energy-dispersive result with more conventional fixed-energy (monochromatic source), angular-dispersive x-ray reflectivity to establish the validity of the energy-dispersive method. This x-ray technique may be particularly useful for the metrology of growing thin-barrier layers, atomic-layer passivation, and seed-layer measurements in future microelectronics applications. Currently, thickness precision is limited by modeling assumptions and the energy discrimination available from x-ray detectors.

Image plate X-ray diffraction and X-ray reflectivity characterization of protective coatings and thin films

Two-dimensional image plate applications in X-ray diffraction (XRD) and X-ray reflectivity (XRR) characterization, using a grazing incidence geometry and radiation from a conventional X-ray tube, were explored. XRD and XRR data obtained from a conventional diffractometer using a Si (Li) detector complement image plate results to give more complete phase and structure information. Protective chromium coatings, electrochemically deposited onto the bore of steel cylinders, were investigated. Retained austenite content in martinsitic steel was measured in simulated, inside-diameter, bore geometry. This approach demonstrates the versatility of the method for non-destructive chemical analysis and phase differentiation of interior bore surfaces in piping structures. MATLAB-based processing software was developed to facilitate quantitative image analysis, including multiple 2θ scans, χ-plots, and pole figure re-construction from multiple-ϕ images, where χ and φ designate, respectively, specimen tilt and rotation. For XRR applications, a 12-nm tantalum and an 82-nm tantalum oxide thin film sputtered on (100)-oriented silicon wafers were investigated. Density and thin film thickness were obtained from specular reflectivity modeling involving the periodicity of the interference fringes. Two-dimensional Kiessig interference-fringe images were analyzed and compared with conventional specular XRR for the measurement of thin film thickness and thickness uniformity over a sample.

Spectroscopic Fourier methods for thickness measurements of thick uniaxial wafers, with dispersive birefringence, using polarimetric techniques

This letter describes the measurement of the thickness of a thick uniaxial sample with a dispersive birefringence, using Fourier methods and standard polarimetric techniques. The formalism is also similar to, and easily adapted to, non-normal incidence thin-film thickness measurements. In a previous paper, a spectroscopic half-wave method for uniaxial wafer thickness measurements was investigated. A number of corrections for the dispersion had to be included in the analysis. It is demonstrated here that the fast Fourier transform over the recorded interval is a more robust measurement, with higher accuracy, and higher repeatability. The signal is treated as a standard frequency modulated signal. An undoped thick wafer of 4H-SiC and doped 4H-SiC are studied as examples.

Thickness and index measurement of transparent thin films using neural network processed reflectance data

Artificial neural networks and the Levenberg–Marquardt algorithm are combined to calculate the thickness and refractive index of transparent thin films from spectroscopic reflectometry data. A neural network is a set of simple, highly interconnected processing elements imitating the activity of the brain, which are capable of learning information presented to them. Reflectometry has been used by the semiconductor industry to measure thin film thickness for decades. Modeling the optical constants of a film in the visible region with a Cauchy dispersion model allows the determination of both thickness and refractive index of most transparent thin films from reflectance data. In this work, artificial neural networks are used to obtain good initial estimates for thickness and two Cauchy parameters An and Bn, these estimates are then used as the starting point for the Levenberg–Marquardt algorithm which converges to the final solution in a few iterations. This measurement program was implemented on a Nanometrics NanoSpec 8000XSE and will measure thickness and index of transparent films. The program works with a thickness range of 1000–16000 Å and index range of 1.36–2.35, and takes an average of 4 s.

Film thickness measurement and linear dichroism of organic thin films prepared by molecular beam deposition at oblique incidence

Linear dichroism – the in-plane optical anisotropy – is observed for organic thin films grown on fused silica and glass substrates. The films made of [4-pyrid-4-yl-ethynyl-benzoic acid] and [4-trans-2-(pyrid-4-yl-vinyl) benzoic acid] are deposited from an angle of about 30° with respect to the surface normal under ultra-high vacuum conditions. The film thickness measurements by alpha-step, atomic force microscopy in tapping mode, and in situ ellipsometry as well as transmission spectra are discussed in detail. Moreover, the optical constants of these novel materials are determined using ellipsometry and transmission spectroscopy. The remarkable optical asymmetry is found in the ultra-violet transmission spectra and attributed to oriented molecules which are connected by hydrogen bonds.