Specimen Grating Research Articles

Phase shifting nano-moiré method with scanning tunneling microscope

In this paper, a new nano-moiré method using scanning tunneling microscope (STM) is proposed. This method is capable of measuring nanoscopic deformation of matter. The formation mechanism of the STM moiré fringe and the phase shifting technique used in STM moiré fringes are explained in details. Typical experiments are conducted with the crystal lattices of freshly cleaved highly oriented pyrolytic graphite, are used as specimen grating, to generate STM moiré fringe patterns. Phase shifting is realized in four steps from 0 to 2 π by controlling the PZT in the STM system to shift the specimen in the vertical direction. This method provides a new way for disposal of moiré fringes pattern in the nano-moiré measurement.

Phase shifting focused ion beam moiré method

In this article, a phase shifting technique for focused ion beam (FIB) moiré method is proposed, which is able to measure the full field in-plane deformation of an object in a micrometer scale. The FIB moiré is generated by the interference between a prepared specimen grating and FIB raster scan lines. The principle of phase shifting technique for FIB moiré is described in detail. With this method, phase shifting was realized in four steps from 0 to 2 π by shifting the focused ion beam controlled by a FIB system. This method is successfully used to measure the virtual deformation in a micro-electro-mechanical system structure with a 2500 lines/mm grating. The experiments prove the validity of this technique and show its ability of determine the full field strain with high accuracy.

Investigation of strain in microstructures by a novel moire method

A focused ion beam (FIB) moire method is proposed and demonstrated to measure the strain in microstructures. This technique is based on the advantages of the FIB system in nanofabrication, imaging, selective deposition, and fine adjustment. A nanograting is directly written on the top of the microstructures by ion milling without the requirement of an etch mask. The FIB moire pattern is formed by the interference between a prepared specimen grating and FIB raster scan lines. The strain of the microstructures is derived by calculating the average spacing of moire fringes. The sensitivity and accuracy of FIB moire in strain measurement is subsequently discussed. Since the local strain of a microstructure itself can be monitored during the process, the FIB moire technique has many potential applications in the mechanical metrology of microelectromechanical systems (MEMS). As an example, the strain distribution along the sticking microstructures and the contribution of surface oxidization and mass loading to the cantilever strain is determined by this FIB moire technique.

Focused ion beam Moiré method

A focused ion beam (FIB) Moiré method is proposed to measure the in-plane deformation of object in a micrometer scale. The FIB Moiré is generated by the interference between a prepared specimen grating and FIB raster scan lines. The principle of the FIB Moiré is described. The sensitivity and accuracy of deformation measurement are discussed in detail. Several specimen gratings with 0.14 and 0.20 μm spacing are used to generate FIB Moiré patterns. The FIB Moiré method is successfully used to measure the residual deformation in a micro-electro-mechanical system structure after removing the SiO 2 sacrificial layer with a 5000 lines/mm grating. The results demonstrate the feasibility of this method.

High resolution AFM scanning Moiré method and its application to the micro-deformation in the BGA electronic package

The formation mechanism of atomic force microscope (AFM) Moiré is explained using the transmittance function. The technique for preparing the AFM Moiré specimen grating is described. The sensitivity and accuracy of this method is analyzed. AFM Moiré method is used to measure the thermal deformation ball grid array (BGA) electronic package. The shear strain at the different solders in the BGA package is measured. The result is compared with that from electron beam Moiré method. The consistent comparison result verifies the AFM Moiré method is reliable and effective in the micro-deformation measurement in the electronic package.

Focused Ion Beam Nano-Machined Structures For Strain Analysis By A Moiré Technique

ABSTRACTThe accurate determination of residual stress/strain in thin films is especially important in the emerging field of MicroElectroMechanical Systems (MEMS). In this article, a focused ion beam (FIB) moiré method is proposed and demonstrated to measure the strain in MEMS structures. This technique is based on the advantages of the FIB system in nano-fabrication, imaging, in-situ deposition, and fine adjustment. Nano-grating lines with 70 nm width and 140 nm spacing are directly written on the top of the MEMS structures by ion milling without the requirement of an etch mask. The FIB moiré pattern is formed by the interference between a prepared specimen grating and FIB raster scan lines. The strain of the MEMS structures is derived by calculating the average spacing of moiré fringes. Since the local strain of a MEMS structure itself can be monitored during the process, the FIB moiré technique has many potential applications in the mechanical metrology of MEMS. As an example, the strain distribution along the sticking MEMS structures, and the contribution of surface oxidization and mass loading to the cantilever strain is determined by this FIB moiré technique.

Focused Ion Beam Nano-Machined Structures For Strain Analysis By A Moiré Technique

ABSTRACTThe accurate determination of residual stress/strain in thin films is especially important in the emerging field of MicroElectroMechanical Systems (MEMS). In this article, a focused ion beam (FIB) moiré method is proposed and demonstrated to measure the strain in MEMS structures. This technique is based on the advantages of the FIB system in nano-fabrication, imaging, in-situ deposition, and fine adjustment. Nano-grating lines with 70 nm width and 140 nm spacing are directly written on the top of the MEMS structures by ion milling without the requirement of an etch mask. The FIB moiré pattern is formed by the interference between a prepared specimen grating and FIB raster scan lines. The strain of the MEMS structures is derived by calculating the average spacing of moiré fringes. Since the local strain of a MEMS structure itself can be monitored during the process, the FIB moiré technique has many potential applications in the mechanical metrology of MEMS. As an example, the strain distribution along the sticking MEMS structures, and the contribution of surface oxidization and mass loading to the cantilever strain is determined by this FIB moiré technique.

Influence of object roughness on specimen gratings for moire´ interferometry

Moireinterferometry is a high-sensitivity method for whole- field, in-plane displacement measuring. This technique requires the sur- face under test to be mirror-like and prepared with a fine diffraction grat- ing (typically ;1200 lines/mm). Gratings are commonly made of photoresist. However, if we want to analyze engineering structures, to have a surface without preparation under polishing, the surface rough- ness is an important parameter to be characterized. We analyze the fringe visibility of moireduring the fabrication of specimen gratings in function of the surface object roughness. The surface object target is impregnated with photoresist Shipley S1822. Two beams from a He-Cd laser illuminating the surface target are used to record the specimen grating. With a similar optical system we use a He-Ne laser to obtain a virtual grating and consequently the interferometric moirefringes. Through the correlation length and basic statistical the surface rough- ness is characterized. © 2001 Society of Photo-Optical Instrumentation Engineers.

Advances in scanning electron microscope moiré

The scanning electron microscope (SEM) moire method for microscopic measurements based on electron beam lithography and an SEM has been well developed. Although it has been a reliable method, some drawbacks exist: reinforcement effects, complicated processing and low sensitivity. To improve the SEM moire method, new grating-casting techniques and a fringe-viewing technique must be developed. In this study, a carbonaceous grating technique and a total imaging technique are introduced. Accordingly, there are two techniques available for grating-casting (i.e., the carbonaceous grating technique and the existing lithography grating technique) and three techniques available for fringe viewing (i.e., the total imaging technique, the existing, monitor viewing technique and the existing photographic viewing technique). A total of six new imaging techniques of SEM moire methods are available for microscopic measurements by combining one technique from each of the two groups. This study demonstrates the feasibility of the individual techniques and discusses the characteristics and limitations of each. Based on the presented total imaging technique, the sensitivity of the moire method is only dependent on the frequency of specimen grating. Because it can be made as high as 10,000 lines/mm, the SEM moire method can achieve sensitivity as high as 0.01 percent.

A new moiré interferometer for measuring in-plane displacement

This paper proposes a new moire interferometer to be used for determining in-plane displacement of a body deformed with small strains and small surface slopes. With this interferometer, the grating not only diffracts the incoming beam but also rediffracts the two first orders, each of which is reflected by a mirror, back into the path of the incoming beam. The two rediffracted beams are then directed to the viewer to generate an interference fringe pattern that depends only on the in-plane displacement. Theoretical analysis of this new interferometer is presented. It was determined that the sensivity of the interferometer is twice that of conventional interferometers, and the slightly warped beam wave front coming from the laser source does not affect the measurement result. An experiment was performed by adopting the proposed and conventional interferometers to determine the displacement of a specimen grating. The results confirm the advantages of using this new interferometer.

A moiré microscope for finite deformation micro-mechanical studies

A new version of a moire microscope is presented that embodies the theory of optical moire interferometry. To interrogate the deformed specimen grating, the device uses a transmission diffraction grating that allows for a simple and quick change of the virtual reference grating vector without disturbing the optical alignment of the other components in the optical train. To analyze deformation from the acquired moire interference fringe patterns, the displacement light-itensity moire optical law introduced by Sciammarella is revisited. The analysis of deformation is consistent with the continuum principles of finite deformation and can readily be used to obtain micro-mechanical quantities of interest such as the local strains, stretches and rotations.

In situ deformed specimen grating replication technique in moiré interferometry

High-sensitivity moiré interferometry with the in situ deformed grating replication technique is adopted to investigate the deformations of a nickel-based polycrystal superalloy under uniaxial tensile loading. By multiple replication of several desired loading levels and observing them in moiré interferometry, nearly real time deformation measurements can be conducted flexibly even when the testing machine is far away from the optical set-up. As an alternative to deformed specimen grating replication caused by mechanical loading, a thermally induced deformed specimen grating can also be replicated at an elevated temperature and deformation fields can be obtained by observing the replicated pieces in moiré interferometry at room temperature. Thermally induced deformations of a microelectronic assembly are given as an example.

Study of thermal deformation of microelectronics packaging product by interferometric technique

In this paper, the out-of-plane deformation of silicon surface of Direct Chip Attachment (DCA) assembly, under thermal loading, was measured in real-time by Twyman/Green interferometry. The contour maps of the out-of-plane displacement fields of silicon surface under thermal loading and cycling of various temperature were obtained. Experimental results show that the relation between the out-of-plane displacement and temperature is nonlinear and varies with temperature cycling, due to nonlinear mechanical behavior of the materials used in electronic packaging. A comparison of the out-of-plane displacement fields of silicon surface measured by T/G interferometry in real-time and replicating technique of high temperature specimen grating of moire interferometry was made.

Ultra-thin packaging versus the Known Good Die : Keith Gurnett. Microelectronics Journal, 25, 8, xxiii (1994)

An AFM (atomic force microscope) moiré method has been developed to measure surface deformations and strains. The scanning lines in the AFM monitor are used as the reference grating. The reference grating interferes with the specimen grating and forms a moiré pattern on the monitor. The condition of forming scanning moiré with an AFM is described. The deformation measurement principle using AFM moiré is discussed in detail. The AFM moiré method was used to measure the thermal deformations in QFP (quad flat pack) and BGA (ball grid array) packages. The experiment results verify the feasibility of the AFM moiré method and show its ability to measure the in-plane deformations and strains.

Theory of Electron Beam Moiré.

When a specimen surface carrying a high-frequency line grating is examined under a scanning electron microscope (SEM), moiré fringes are observed at several different magnifications. The fringes are characterized by their spatial frequency, orientation, and contrast. These features of the moiré pattern depend on the spatial frequency mismatch between the specimen grating and the raster scan lines, the diameter of the electron beam, and the detailed topography of the lines on the specimen.A mathematical model of e-beam moiré is developed that expresses the spatial dependence of the SEM image brightness as a product of the local intensity of the scanning beam and the local scattering function from the specimen grating. Equations are derived that give the spatial frequency of the moiré fringes as functions of the microscope settings and the spatial frequency of the specimen grating. The model also describes the contrast of several different types of moiré fringes that are observed at different magnifications. We analyze the formation of these different fringe patterns, and divide them into different categories including natural fringes, fringes of multiplication, fringes of division, and fringes of rotation.

Optical fringe multiplication in moiré interferometry

An optical method for multiplication of moiré fringes is proposed to increase the sensitivity of moireé interferometry. The process involves two recording steps. In the first step, a traditional moiré interferometry setup is used. The moiré pattern containing carrier fringes and load fringes is recorded onto a glass-based holographic plate. The carrier frequency is much lower than that of the original specimen grating. The plate is then developed. In the second step, the holographic plate, regarded as a distorted specimen grating, is further examined by a similar moiré interferometry system. The frequency of the second virtual grating is arranged to be 2n times that of the carrier fringes contained in the recorded plate. As a result, the load fringes are revealed with a multiplication factor of 2n. The interpretation of the optical multiplication method from wave-front interference theory is given and an experiment is conducted.

The optimization of three-mirror illuminating system for the four-beam Moiré interferometer

The three-mirror illuminating system for moiré interferometry consists of a Lloyds mirror and two additional mirrors at right angles to each other. This arrangement makes possible the design of a four-beam moiré interferometer system for a cross-lined specimen grating, to determine the u and v displacement components of the object under test. The design problems, including optimization of dimensions of the optical elements and adjustment by a user, are discussed and analytically solved. The analysis was verified by the construction and laboratory use of the interferometer.

Toward Measurement of Thin Film Properties by Enhanced Moire Interferometry

ABSTRACTGrowing use of thin films in encapsulated integrated circuits(IC's) necessitated new developments in measurement of their mechanical properties in-situ. This can be done by a hybrid analytical experimental approach. The films are approximated by orthotropic membranes and the substrate is assumed to be an elastic continuum. It can be shown that power of stress singularity is a function of geometry and film/substrate material properties. By loading the sample and measuring actual displacement field in the close proximity to the crack or edge, one can evaluate the needed properties.The technique used to measure full field displacements is enhanced moire' interferometry. It is based on the formation of fringes by the coexistence of light wave fronts diffracted from a specimen grating of high frequency. These specimen gratings are created on the specimen surface using a replication technique from a specially prepared mold. Two beams of coherent laser light illuminate the specimen grating obliquely to create a virtual reference grating in front of the specimen. The frequency f of this grating is chosen to be 2400 lines/ mm, this corresponds to a sensitivity of 0.417 µk per fringe order. When the specimen is deformed the interference pattern (moire' fringes) is formed and collected by a video camera connected to a PC-based digital image processor. Analysis of the moire pattern results in full field displacement.

High sensitivity moiré interferometry with compact achromatic interferometry

Experimental observations and measurements are the sources of information essential for correct development of mathematical models of real structural materials. Moiré interferometry offers high sensitivity in full-field measurements of in-plane displacements on the surface of a specimen. Although it is a powerful method in experimental stress analysis, it has some shortcomings. One is that existing systems require highly coherent light. The only sufficient source of light for this application is a long cavity laser, which is relatively expensive and at best cumbersome. Another shortcoming is that measurements must be performed in a vibration-free environment, such as that found on a holographic table. These requirements limit the use of existing moiré interferometers to a holographic laboratory. In this paper a modified concept of compensation is presented, which permits the use of a chromatic source of light in a compact moiré system. The compensator provides order in the angles of incident light for each separate wavelength, so that the virtual reference grating created by each wavelength in a continuous spectrum is identical in frequency and spatial position. The result is a virtual reference grating that behaves exactly like that created in coherent light. With this development the use of a laser diode, which is a non-coherent light source of tiny dimensions, becomes practical. The special configuration of the optics that create the virtual grating allows its synchronization with the specimen grating and leads to an interferometer design that is relatively insensitive to the vibrations found in a mechanical testing laboratory. Sensitivity to relative motion is analyzed theoretically. This development provides the oppurtunity to apply moiré interferometry to solid mechanics problems that cannot be studied in an optics laboratory. Experimental verification of the optical concepts is provided. A compact moiré interferometer based on the presented idea was developed for measurements of deformation on a testing machine. Its application in both coherent and temporally non-coherent light is demonstrated.

A new real-time method of moiré interferometry for displacement derivative fringe patterns

A new method of moiré interferometry is proposed in this paper to obtain the strain fringe pattern in real time. The specimen grating is illuminated by dual beams whose optical path-difference is larger than the coherence length of the laser. The diffractions of the grating are sheared by a glass wedge to fulfil the optical differentiation. The principles based on wavefront analysis are shown and an experimental verification is reported.