A novel technique for micro profiling of slots

In this investigation, we describe a technique to obtain the 3D profile of surface, thickness and refractive index of an undoped double-side polished Si wafer at once. This technique is based on low coherence scanning interferometry (LCSI) and spectrally-resolved interferometry (SRI) using a NIR light, which is around 1 μm, for which transmission is non-zero for undoped silicon and also detectable by the typical visible CCD camera. LCSI allows for the measurements of surface, thickness and refractive index profiles of the Si wafer while SRI can determine their nominal values. For group refractive index measurements, the target which consists of a Si wafer segment and a mirror was designed. Consequently, the combination of these two techniques with the target enables to measure surface, thickness and refractive index profiles simultaneously and accurately. In the experiments, an undoped double sided polished (DSP) Si wafer with 475 μm thickness was measured and the 3D profiles of optical thickness, geometrical thickness, group refractive index were successfully obtained. Because of not using an expensive IR CCD camera and an optical source, the proposed technique is cost-effective.

Surface profiling and film thickness measurement play an important role for inspection in semi conductor industry. White light source had been used as scanning white light interferometry and spectrally resolved white light interferometry for determining surface and film thickness profile. These techniques however failed for thinner film. Recently, reflectometry and spectrally resolved white light interferometry was combined for the same. This technique used Fourier Transform for the calculation of phase in spectral domain with the use of Linnik interferometer. In this method a large amount of carrier offset (carrier fringes) is required to be effective. This carrier fringes in spectrally resolved white light interferometry was achieved by increasing the optical path difference between the test and the reference surface. But, Linnik interferometer cause defocusing problem to create these carrier fringes. We propose in this paper to combine reflectometry and spectrally resolved phase shifting interferometry for measurement of surface and film thickness profile with the use of Michelson objective. Michelson objective will be convenient to implement as compared to the Linnik type and the use of phase shifting interferometry does not necessarily need large number of fringes in the spectral domain.

In recent years, optical fringe-projection and other optical interferometric techniques for surface profiling have received much attention because they are whole-field and non-contacting; very high data processing speeds can be achieved using computer image-processing techniques. These advantages over many other mechanical probe-based techniques are particularly useful for the measurement of large surfaces as well as for micro-systems at the sub-micron level. In the fringe-projection technique, a reference optical grating is first generated and then projected onto the surface of interest. For a given optical set-up, the distribution of the reference grating is perturbed in accordance with the profile of the test surface, thereby enabling direct derivation of surface profiles from measurements of the perturbed fringe distribution. The reference gratings are readily generated with a Michelson interferometer, which uses a beam-splitting cube and mirrors - these optical elements are readily available in all laboratories. A major drawback of this technique is the need for good vibration isolation, as otherwise unstable fringes will be generated. Alternatively, beam-splitting cubes with coated reflective surfaces can be used, but this would not allow adjustment of the frequency of the generated fringes. This paper describes a very simple method of generating and projecting optical grating for surface profiling. The working principle is based on the reflection-refraction of a commercial beam-splitting cube. By carefully adjusting the orientation of the laser beam, the frequency of the grating can be varied. A distinct advantage of this method over the Michelson interferometer lies in its ability to generate stable carrier fringes under lax vibration isolation conditions.

As higher integration of semiconductor devices has progressed recently, mechano-chemical polishing process is playing a very important role. At the same time, cleaning and drying technologies after the polishing process have been more and more important in order to ensure the surface cleanliness of the wafer products. As a drying process after the cleaning, there is a method of supplying pure water and IPA (Iso-Propyl Alcohol) vapor simultaneously to the surface of the water meniscus region on a rotating wafer (which is called Rotagoni drying method). This technique causes a surface tension difference on the liquid surface and then gives rise to the convection by the Marangoni effect, which is thought to efficiently remove impure particles on the wafer surface. In this method, IPA vapor impinges on the vicinity of the liquid meniscus on the wafer. It is very difficult to measure the surface tension of the liquid surface in that part in situ, and the details about the convection are not well understood. As this technique further advances in near future in order to remove ultra-fine foreign particles on the wafer surface more efficiently, observation and understanding of the Marangoni convection in the meniscus region are necessary for the future progress of the technique. In this study, in order to consider the actual situation of the drying process, not only the measurement of the surface tension of the droplet of the IPA aqueous solution, but also the measurement by exposing pure water droplet to various concentrations of the IPA vapor were performed, and the relationship between the concentration of IPA vapor and the surface tension of the droplet was investigated. The latter situation is much closer to actual drying situation. Specifically, in measurements, a small pure water droplet was placed in a glass container, and the container was filled with a constant concentration of IPA vapor. At the time when it was judged that the IPA adsorption to the liquid surface had reached equilibrium by confirming that the shape of the droplet became unchanged, the image of the droplet shape was taken from the side of the container with digital camera. It is known that the static shape of a droplet which is flattened under the influence of gravity can be analytically expressed by a mathematical equation in consideration of surface tension and mechanical equilibrium. In this study, the surface tension was deduced by assuming that a uniform concentration of IPA and a uniform surface tension over the whole droplet surface. In another project of the authors’ group, physical simulation using a two-dimensional PDMS flow channel was performed to reproduce a situation of impinging IPA vapor to the meniscus region, and PIV (Particle Image Velocimetry) method was applied to obtain the flow velocity of the Marangoni convection. The measurement of IPA concentration on water surface during the actual drying process is very difficult, and moreover, the in-situ measurement of surface tension is almost impossible. From the data of surface tension as a function of IPA concentration and the measured velocity data with a simple analytical flow model, the estimation of surface tension and IPA concentration on the droplet surface will be discussed. END Figure 1

For spot scanning dark-field scattering technology, the defocus caused by the change in wafer surface height decreases the defect detection rate and size measurement repeatability. The demand for accurately and rapidly measuring the wafer surface height online is becoming increasingly urgent. The defect detection system integrates scattering, reflection, film thickness, and topography defect detection channels. The integration of laser-triangulation-based defocus measurement into the bright-field optical path is proposed. The laser beam is directed onto the surface of the wafer, and the reflected light is transmitted through a lens onto the photosensitive surface of a four-quadrant detector. This detector captures both the strength and position of the reflected signal simultaneously. In this paper, a triangulation-modified model is established to obtain the height of each inspection spot on the wafer surface through the position signal of the reflected image. When the signal-to-noise ratio of the simulated reflection image position is 20 dB, the signal-to-noise ratio of the height measurement resolved by the triangulation-modified model is 41 dB, and the measurement error is less than 0.2 μm, indicating that the model has a noise suppression effect. The spot-scanning imaging system is established, and the height measurement results of the triangulation measurement model are verified using a laser interferometer. Within the travel range of 69 μm, the system has a measurement accuracy better than ±1 μm and a measurement repeatability better than ±0.2 μm, which meet the measurement requirements of the spot-scanning imaging system. The system is utilized for defect detection and defocus measurement of the wafer surface, along with the motion mechanism, to accurately and rapidly obtain the height distribution of the wafer surface.

A chemical mechanical planarization model for aluminum gate structures

Surface profiling and film thickness measurement play an important role for inspection. White light interferometry is widely used for engineering surfaces profiling, but its applications are limited primarily to opaque surfaces with relatively simple optical reflection behavior. The conventional bucket algorithm had given inaccurate surface profiles because of the phase error that occurs when a thin-film exists on the top of the surface. Recently, reflectometry and white light scanning interferometry were combined to measure the film thickness and surface profile. These techniques, however, have found that many local minima exist, so it is necessary to make proper initial guesses to reach the global minimum quickly. In this paper we propose combing reflectometry and white light scanning interferometry to measure the thin-film thickness and surface profile. The key idea is to divide the measurement into two states; reflectometry mode and interferometry mode to obtain the thickness and profile separately. Interferogram modeling, which considers transparent thin-film, was proposed to determine parameters such as height and thickness. With the proposed method, the ambiguity in determining the thickness and the surface has been eliminated. Standard thickness specimens were measured using the proposed method. Multi-layered film measurement results were compared with AFM measurement results. The comparison showed that surface profile and thin-film thickness can be measured successfully through the proposed method.

Thickness and surface profiling of optically transparent and reflecting samples using lens-less self-referencing digital holographic microscopy

As an optical focus detection technique, confocal microscopy has been received much attention in the last few years. It has not only the particular property of depth discrimination, but also the ability of enhancement of contrast by suppression of light scattered from defocused object location. Therefore, the techniques based on confocal microscopy have been developed as a powerful tool for surface profiling. However, in order to maintain the high resolution, it is difficult to make fiber-optic sensor as small as possible, and which restrict the measurement of small internal curve surface. For the purpose of uniting micromation and high-precision in profile, based on a fiber confocal microscopy theory, a new fiber optical scanning microscope made up of splitter and GRIN lens is presented. Compared with other confocal technique, it has smaller size, higher anti-jam, and higher axial resolution. Especially, it has the characteristic of absoluteness zero point, which can be used for 3D and super-glossy inner surface profile. Experiment results show that the axial resolution with 30nm and linearity range 40μm can be achieved. This linearity, high resolution and small cubage permit non-contacting surface profilometry to be readily obtained for specimens of uniform reflectivity and small internal curve surface profile.

6 DOF 정합을 이용한 대 영역 실리콘 웨이퍼의 3차원 형상, 두께 측정 연구

Different diffusion barrier layers applied on the boron-doped surfaces of silicon wafers with sawdamage etched surfaces are investigated with respect to their applicability in the fabrication process of n-type silicon solar cells using sequential tube furnace diffusions with a first BBr3and a subsequent POCl3-diffusion. The barrier layers consist of silicon oxide and/or silicon nitride deposited either by plasma-enhanced chemical vapor deposition or sputter technology. The layer itself must act as barrier against phosphorus diffusion into the silicon wafer during POCl3-diffusion. Furthermore, it has to ensure that no substantial depletion of boron occurs at the wafer surface. The boron doping surface concentrations and profile depths measured after POCl3-diffusion depend on the applied diffusion barrier. If solely silicon oxide barrier layers are used, depletion of boron at the wafer surface and deeper profiles are observed, which we attribute to oxygen diffusion through the barrier and growth of a thin thermal oxide film at the silicon. With a thin silicon nitride layer incorporated into the diffusion barrier system, no significant change in the boron doping profile is detected. Numerical simulations of the boron diffusion during the POCl3process agree well with the measurements and support these findings.

A post-cell-removal surface morphology (PCRSM) profiling technique was used to identify the effects of targeted anticancer medicines on cancer cells. Living non-small lung cancer cells, A549 and H1299, were cultivated on a 3-aminopropyltriethoxysilane (γ-APTES) coated silicon wafer surface with and without targeted anticancer medicine added in the culture medium. Atomic force microscopy (AFM) was used to examine the surface morphology profile on the γ-APTES wafer surface after removing the cells. Two different targeted anticancer medicines, epidermal growth factor receptor (EGFR)-inhibitor Iressa (gefitinib) and protein kinase c (PKC)-inhibitor Staurosporine were examined. Our experimental results show that only the cancer cells treated with Staurosporine can have the PCRSM profiles resemble to those of normal cells, whereas those treated with Iressa reserve the PCRSM profiles of the pre-medicine treated cancer cells. This observation indicates that the PCRSM technique is able to detect the cell-traction force difference caused by EGFR-inhibitor and PKC-inhibitor, respectively and Staurosporine is more effective than Iressa in deactivating the cell-substrate interaction of the cancer cells.

Effect of sphere radius and bullet hitting location on the ballistic performance of alumina ceramic tile

With the growth of 3D packaging technology and the development of flexible, transparent electrodes, the use of multilayer thin-films is steadily increasing throughout high-tech industries including semiconductor, flat panel display, and solar photovoltaic industries. Also, this in turn leads to an increase in industrial demands for inspection of internal analysis. However, there still remain many technical limitations to overcome for measurement of the internal structure of the specimen without damage. In this paper, we propose an innovative optical inspection technique for simultaneous measurements of the surface and film thickness corresponding to each layer of multilayer film structures by computing the phase and reflectance over a wide range of wavelengths. For verification of our proposed method, the sample specimen of multilayer films was fabricated via photolithography process, and the surface profile and film thickness of each layer were measured by two different techniques of a stylus profilometer and an ellipsometer, respectively. Comparison results shows that our proposed technique enables simultaneous measurements of the top surface and its underlying film surfaces with high precision, which could not be measured by conventional non-destructive methods.

The traditional shadow moiré technique has been employed, using the fringe pattern information and numerical interpolation, to construct the wafer surface topology. In this paper, phase-shifting shadow moiré technique is discussed and applied to the measurement of wafer surface topology with high resolution. The phase-shifting technique takes advantage of the gray level information to increase the physical resolution of the measurement. A series of fringe patterns are recorded while they are shifted by moving the wafer along the direction perpendicular to wafer surface. The phase is encoded in the variations in the intensity pattern of the recorded fringe images, and a simple point-by-point calculation recovers the phase. The needs to locate the fringe centers and interpolation are eliminated. Since the depth variation of wafer surface is very small, usually within the range of 0.1 to 20 microns, very fine grating is required in order to capture the small depth variation. However, very fine grating will introduce strong diffraction effect which blurs the fringe patterns. In this study, the Talbot distance is applied to obtain images with good contrast. The phase shift is realized by moving the wafer to change the distance between the wafer surface and the reference grating. A four-step phase wrapping algorithm is used to calculate the phase. The phase pattern recovered from four fringes patterns is presented. Future work such as how to reduce the noise, how to do phase unwrapping and calibration is also discussed.