Yoshitaro Sakata

Phosphorescence quenching by mechanical stimulus in CaZnOS:Cu

We have found that phosphorescence intensity of CaZnOS:Cu decreased visibly under an applied load. This mechanical quenching (MQ) of phosphorescence in CaZnOS:Cu corresponded to the mechanical stimuli. We have thus demonstrated that the MQ of CaZnOS:Cu could be used for visualizing stress distributions in practical applications. We propose that MQ arises from non-radiative recombination due to electron-transfer from trap levels to non-radiative centers as a result of the mechanical load.

Ellipsometry-like analysis of polarization state for micro cracks using stress-induced light scattering method

Fine polishing techniques, such as chemical mechanical polishing (CMP), are important to glass substrate manufacturing. When these techniques involve mechanical interaction in the form of friction between the abrasive and the substrate surface during polishing, latent flaws may form on the product. Fine polishing induced latent flaws in glass substrates may become obvious during a subsequent cleaning process if the glass surface is eroded away by chemical interaction with a cleaning liquid. Thus, latent flaws reduce product yield. A novel technique (the stress-induced light scattering method; SILSM) which was combined with light scattering method and stress effects was proposed for inspecting surface to detect polishing induced latent flaws. This method is able to distinguish between latent flaws and tiny particles on the surface. In this method, an actuator deforms a sample inducing stress effects around the tip of a latent flaw caused by the deformation, which in turn changes the refractive index of the material around the tip of the latent flaw because of the photoelastic effect. A CCD camera detects this changed refractive index as variations in light-scattering intensity. In this study, the changes in reflection coefficients and polarization states after application of stress to a glass substrate were calculated and evaluated qualitatively using Jones matrix-like ellipsometry. As the results, it was shown that change in the polarization states around the tip of latent flaw were evaluated between before and after applied stress, qualitatively.

Origin of light scattering variations of a latent flaw through light scattering measurement with applied stress effect

The stress-induced light scattering method (SILSM) was proposed for inspecting surface to detect polishing induced latent flaws. In this study, in order to clarify the mechanism of the light scattering intensity variation of latent flaws using SILSM, we have investigated stress effect of light scattering intensities using polarized light system and calculated the reflectance and the retardation using Jones matrix. As the results, we evaluated the change in the birefringence around a tip of a latent flaw between before and after stress were applied.

Inspection technique of latent flaws on fine polished glass substrates using stress-induced light scattering method

The fine polishing technique, e.g. Chemical Mechanical Polishing treatment (CMP), is one of the most important techniques in the glass substrate manufacturing. However, mechanical interaction, e.g. friction, occurs between the abrasive and the surface of substrates. Therefore, latent flaws are formed in the surfaces of glass substrates depending on the polishing condition. In the case of the cleaning process of the glass substrate in which the latent flaws existed, latent flaws become obvious because glass surfaces were eaten away by chemical interaction of cleaning liquid. Therefore, latent flaws are the cause of decrease the yield of products. In general, non-destructive inspection techniques, e.g. light scattering method, foreign matter on the surface of glass substrates. Though, it is difficult to detect the latent flaws by these method, because these are closed. The present authors propose a novel inspection technique of latent flaws which occurred by the fine polishing technique, using light scattering method with stress concentration (Stress-Induced Light scattering Method; SILSM). SILSM is possible to classify and separately detect latent flaws and particles on the surfaces. Samples are deformed by the actuator and stress concentrations are occurred around the tip of latent flaws. By photo-elastic effect, the refractive index of around the tip of latent flaws is changed. And then, changed refractive index is detected by cooled CCD camera as the light scattering intensity. In this report, applying SILSM to glass substrates, latent flaws on the surface of glass substrates are detected non-destructively, and the usefulness of SILSM is evaluated as novel inspection technique of latent flaws.

Visualization of crack propagation for assisting double cantilever beam test through mechanoluminescence

ABSTRACT Here, a mechanoluminescence-assisted double cantilever beam (DCB) test was proposed and its effectiveness was demonstrated. Based on mechanoluminescence, a crack tip was clearly distinguished and successfully tracked during crack propagation and delamination in the DCB test, which helped overcome the difficulty associated with the conventional DCB test. The crack length could be easily determined and used to evaluate the fracture toughness. In addition, mechanoluminescence sensing using the top image of the DCB specimen provided valuable information on the fracture and adhesive frontline to determine the distribution of fracture toughness and adhesive strength under the surface treatment and adhesion curing conditions in the DCB test.

A novel way to detect latent flaws

Semiconductors are widely used in electronic devices, often along with liquid crystal display panels based on glass substrates. For both semiconductors and glass substrates, fine polishing techniques are a very important part of the manufacturing process.1, 2 However, the mechanical friction used for fine polishing may induce micro/nanoscale cracks (latent flaws) on the surface of the polished products.1–3 If latent flaws are not detected before the washing process, they may become large dimples or visible cracks because of the erosive effect of the cleaning liquid. Glass substrates and the interlayer dielectric film of semiconductors are conventionally inspected by a light scattering method, which uses incident laser light and photodetectors, such as a photomultiplier tube, to detect light scattering from tiny particles (for instance, dust particles or pieces of foreign matter) and latent flaws with high sensitivity. However, this method detects both tiny particles and latent flaws on the surface as light scattering intensities, and so cannot distinguish between latent flaws and tiny particles. Additionally, ‘closed state’ latent flaws hide under the surface of products, and are thus difficult to detect by this method. We have proposed and evaluated a novel technique to detect latent flaws, which we name SILSM (stress-induced light scattering method). SILSM enables us to classify and separately detect latent flaws and particles nondestructively for both glass substrates and the dielectric interlayer of semiconductor surfaces.4, 5 SILSM detects the change in refractive index at the crack tips of latent flaws as a change in light scattering intensity before and after stress is applied (the photoelastic effect). It detects latent flaws only, and not particles, on which stress does not act and so the particles’ light scattering intensity does not change with stress and they are undetected. To test SILSM, we indented a glass substrate at a single point using a Vickers hardness tester. We fine polished away several micrometers of the sample surface so that only one latent flaw Figure 1. Optical microscopic image.