Papers by Keyword: White Light Interferometry

Abstract: A white light, i.e., Fabry-Perot, interferometry was unprecedently applied to determine the rate change of the current density (J) of aluminum samples during the anodization processes of the samples in aqueous solutions. The current density(J) values were obtained by Fabry-Perot interferometry rather than the direct current (DC) or alternating current (AC), methods. Therefore, the abrupt rate change of the J was called electrochemical-emission spectroscopy. The anodization of the aluminum samples was conducted by an external DC source in 0.0,2,4,6,8,10% sulfuric acid (H₂SO₄) solutions at room temperature. In the meantime, the Fabry-Perot interferometry was used to determine the difference between the J of two subsequent values, dJ, as a function of the elapsed time of the DC experiment for the aluminum samples in 0.0,2,4,6,8,10% H₂SO₄ solutions. The Fabry-Perot interferometry was based on a fiber-optic sensor in order to make real time-white light interferometry possible at the aluminum surfaces in the sulfuric acid solutions. As a result, a new spectrometer was developed based on the combination of the Fabry-Perot, i.e., white light, interferometry and DC method for studying in situ the electrochemical behavior of metals in aqueous solutions.

Abstract: Thermo-responsive random copolymer poly (2-(2-methoxyethoxy) ethoxyethyl methacrylate-co-poly (ethylene glycol) methyl ether methacrylate), abbreviated as P(MEO₂MA-co-OEGMA₃₀₀) was synthesized by 2-(2-methoxyethoxy) ethoxyethyl methacrylate (MEO₂MA) and poly (ethylene glycol) methyl ether methacrylate (OEGMA₃₀₀) with a molar ratio of 1:1 via atom transfer radical polymerization (ATRP). The structure of P(MEO₂MA-co-OEGMA₃₀₀) was confirmed by ¹H NMR and GPC. The transition behaviors of P(MEO₂MA-co-OEGMA₃₀₀) in aqueous solution were investigated by UV-Vis and DLS. While the transition behaviors of P(MEO₂MA-co-OEGMA₃₀₀) thin films were probed by white light interferometry. Compared to the P(MEO₂MA-co-OEGMA₃₀₀) in solution, it shows a much broader transition region, which is a promising candidate for the slow release of drug in the field of medicine.

Abstract: The current research focuses on the characterization of the produced heat affected zone when laser heats AISI H13 steel, AISI 1045 steel and Ti6Al4V alloy workpieces via finite element simulations and experimental investigation. The surface roughness designedly varies on the surface of the samples and its influence on the absorption of laser light is investigated. Experiments are conducted at 1-4 W laser power and for two scanning speeds of 2 and 100 mm/min. A 3D transient thermo-structural finite element model for a moving Gaussian laser heat source is developed to simulate the micromachining process and predict the depth and width of the heat affected zone. The Johnson-Cook material model that takes into account the effect of plastic strain, strain rate and temperature, along with a fracture model, is adapted to the simulations. A good agreement between the experimental data and the simulation results is found. The depth and width of the heat affected zone strongly depend on the laser parameters and material properties of the irradiated samples. This study constitutes the basis to the optimization and improvement of the laser assisted micromachining process parameters and provides key insights on the roughness-absorptivity relation for the three metallic materials.

Abstract: Even though modern industrial robots have good repeatabilities, their positioning accuracies are still relatively poor. Moreover, in a complex process chain, involving several handling systems and diverse interdependent tasks, error propagation can make matters worse. In order to achieve the overall desired quality level, intelligent and highly adaptive methods are required to reduce individual errors and remove accuracy couplings as much as possible. This is especially true in high-risk applications, as found in the aviation MRO industry. Because of the difficulty to replicate existing manual MRO accuracy levels, automation in this area is still relatively scarce. For instance the inspection and repair of airplane combustion chamber liners are as yet performed fully manually. In this paper an automated version of the entire liner repair chain is introduced: from robot-guided white light interferometer inspection in a first cell, to part and data transfer to a second robot cell through to the automated repair steps. Particular consideration is given to individual error sources, such as robot and sensor inaccuracies, calibration deviations and the transfer of data between robot cells, as well as error propagation and prevention.

Abstract: Thermo-responsive random copolymer poly (2-(2-methoxyethoxy) ethoxyethyl methacrylate-co-ethylene glycol methacrylate) P(MEO₂MA-co-EGMA) was investigated in thin film. By spin-coating, the obtained film thickness varied from 9 nm to 97 nm, which shows a linear relationship with tetrahydrofuran solution concentration. The swelling and transition behavior of P(MEO₂MA-co-EGMA) films were monitored by white-light interferometry under water vapor atmosphere. It is observed that the film rapidly swelled in the first 90 min. Afterwards it reached an equilibrium state. The film thickness did not show a prominent increase by further prolonging the swelling time. In addition, the swelling capability of P(MEO₂MA-co-EGMA) films was related to the film thickness. The thicker film possessed less swelling capability. Unlike the transition behavior in aqueous solution, P(MEO₂MA-co-EGMA) films showed a much broader transition region, which might be related to the influence of Si substrate.

Abstract: Leading edge lithography processes require silicon wafers of nearly perfect flatness. In order to improve wafer manufacturing processes as well as the wafer quality, already early manufacturing processes like grinding and lapping have to be monitored. Assessment of nanotopography (NT) is an established approach to analyze surface features in a spatial wavelength range of 0.2 to 20 mm on silicon wafers end of line. This paper presents a fully automated measurement tool to measure NT on wafers with low reflectivity and wafer sizes up to 300 mm, based on the FRT MicroProf^® MFE series. The system features a newly developed white-light interferometry sensor with a field of view of approximately 85 x 85 mm². 16 single measurements are stitched to cover the entire surface of a 300 mm wafer. An NT analysis optimized stitching algorithm was developed in order to combine the individual images to a complete wafer map. The stitched map of the non-polished wafer is subsequently high-pass filtered and analyzed to quantify NT. Measurement system analysis studies provided repeatability values below 1 nm at a throughput of > 20 wafer/h.

Abstract: The formation and the three-dimensional shape of slip bands in a fatigued dual phase steel were analyzed with the purpose of understanding the relation between fatigue crack initiation and the topography development on the specimen surface. Fatigue tests with small dog-bone-shaped specimens were conducted under fully reversed axial loading (R = -1) with a constant stress amplitude and were interrupted when the first slip bands occurred and at defined numbers of load cycles, respectively. Subsequently the surface topography of the specimen was investigated with a white light interferometer with hundredfold magnification and high numerical aperture (NA = 0.9) which allows analyzing the surface of individual grains. The results were confirmed by additional atomic force microscopy measurements. Based on this analysis the height, width and length of the slip bands are known at different stages of the fatigue process. The results obtained using white light interferometry and AFM, were checked by cutting individual slip bands with the help of focused ion beam thus revealing the true shape of the slip bands.

Abstract: A profilometer for micro-surface topography measurement is presented. The instrument is based on the scanning white-light microscopic interferometry (SWLMI). A Linnik type interference microscope is used and the interferograms which present changes of surface profile are recorded by a CCD camera. A developed nano-positioning work stage with integrated optical grating displacement measuring system realizes the precise vertical scanning motion during profile measurement. By white-light phase shifting algorism of arbitrary steps, frames of interferograms are processed by computer to rebuild and evaluate the measured profile. Because of the specialty of SWLMI, the profilometer is suitable for both smooth and rough surface measuring. It also can be used for the measurement of curved surface, dimension of MEMS etc. The vertical resolution of the profilometer is 0.5nm, lateral resolution 0.5+m.

Abstract: White-light interferometric technique has been widely applied in the measurement of three-dimensional profiles and roughness with high-precision. Based on the characteristic of interferometric technique, a new method combined with image location and a three-dimensional stage is proposed to achieve the non-contact absolute shape measurement for aspheric and spherical surface in a slarge range. The interference fringes vary with the horizontal displacement of the measured surface, the surface information was obtained by locating the transformation of the maximal intensity in the interferograms. Two main influence factors are discussed; they are performance of the inerferimetric microscope and the stage. Since the performance of the stage directly determines the measurement precision, a three-dimensional displacement stage with a large range and a high precision was developed. Some experiments were carried out to verify the performance of the three-dimensional displacement stage and the validity of the new measurement method with satisfactory results.

Abstract: In this initial phase of work, two methods of backside wafer thinning using ICP plasma etching of two-inch SiC substrates have been considered. Plasma processes were optimized for nonbonded and bonded wafers. The non-bonded process was used to etch 250μm thick substrates to a final thickness of 100μm. The bonded process was used to etch glass bonded SiC substrates mechanically ground to 130μm thick and plasma etched to a final thickness of 100μm. Etch rate measurements and surface analysis were performed using a profilometer and white light interferometry. Etch rates of 3.4μm/min were achieved for the bonded process and 2.0μm/min for the non-bonded process. The surface morphology for the non-bonded process was three to four times lower than the bonded process. The part mechanically ground samples showed evidence of surface damage from the grinding process after plasma etching.