Chiemi Ishiyama

Uniform Ni – P Film Using an Electroless Plating Method with an Emulsion of Supercritical Carbon Dioxide

This paper proposes a method for electroless plating by combining supercritical fluid technology and electroless plating in a hybrid technique. The electroless plating reactions are carried out in an emulsion of supercritical carbon dioxide and an electroless plating solution with surfactant. The Ni-P film obtained by this proposed technique was a uniform and conformal film without the pinholes that form from the hydrogen bubbles produced by the electrolysis of water, and without the nodules that form from the nuclear growth on the electroless plating reaction. The dissolution of the hydrogen bubbles in the dense CO 2 particles of the emulsion prevented the pinholes from forming. The formation of nodules might have been prevented by the transport properties of the emulsion with the diffusive dense CO 2 and the suppression of the dissolved oxygen concentration when the oxygen dissolved in the dense CO 2 particles of the emulsion. The Ni-P film fabricated by our technique was smoother and more uniform than the substrate. The roughness of the plated film was constant during film growth, whereas the surface of the film fabricated by conventional electroless plating tended to roughen as the reaction time increased.

Development of New Evaluation Method for Adhesive Strength between Microsized Photoresist and Si Substrate of MEMS Devices

An evaluation method for adhesive bending and shear strengths between microsized components and silicon substrate were developed to quantitively determine micro-sized adhesive strength for micro-electro mechanical system (MEMS) devices. Cylindrical shape is employed as a micro-sized adhesive specimen to simply analyze adhesive stresses of both shear and bending. Micro-sized adhesive tests between micro-sized SU-8 cylindrical specimen and Si substrate were performed using a mechamical testing machine for micro-sized material that has developed by our group. Delamination of all the specimens occurred within the SU-8 near by the substrate in a brittle manner under both bending and shear loading conditions. The adhesive bending stress is 57 % lower than the bend strength of the SU-8 material. The adhesive shear strength under bend loading is 15 % lower than the adhesive strength under shear loading and the delamination surface is different in each loading mode. All the results suggest that some defects at the interface must induce the stress concentration, which may make the apparent strength of SU-8 decrease.

Effects of Aspect Ratio of Photoresist Patterns on Adhesive Strength between Microsized SU-8 Columns and Silicon Substrate under Bend Loading Condition

The adhesive strength between microsized SU-8 columns and a silicon substrate under the bend loading condition has been studied to clarify effects of the columnar aspect ratio. The maximum tensile stresses at the root are almost the same within the range of high aspect ratios (1.4–2.1) of the SU-8 columns, in which delamination cracks are opened by bend loading (mode I). This result shows that the delamination is induced by the maximum tensile stress at the root. On the other hand, the maximum tensile stress irregularly changes within the range of low aspect ratios (0.8–1.1) of the specimens and features of the delamination surfaces differ from those within the range of high aspect ratios. This result suggests that the delamination mode must change from mode I to mode II or the complex mode. All the results show that the adhesive strength of a SU-8 column with the range of high aspect ratios of 1.4 and more obtained from the adhesive bend test can be analyzed as the maximum tensile stress at the root (the adhesive bend strength) in this study.

Effects of heat curing on adhesive strength between microsized SU-8 and Si substrate

Adhesive strength between microsized SU-8 components and Si substrate is evaluated to clarify effects of heat curing. Micro-sized cylindrical shape is employed as a micro-sized adhesive test specimen to properly apply the load onto the specimen and to simply convert applied load to stress. Micro-sized cylindrical specimens of epoxy type photoresist, SU- 8, were fabricated on a silicon wafer using a photolithographic technique. All the load-displacement curves behave in brittle manner and all the specimens were failed from the edge of SU-8 near by the bonding interface at the maximum load. Maximum load of heat treated specimens are much higher than no heat-treated ones. Adhesive strength decreases with increasing aspect ratio of SU-8 cylinder. The decrease of adhesive strength is stronger in heat cured specimens than that without heat curing. Form the obtained results we discussed the relationship between effects of heat curing on the adhesive strength in micro-sized SU-8, Yield stress of SU-8 and the residual stress.

Effects of Humidity History on the Tensile Deformation Behaviour of Poly(methyl –methacrylate) (PMMA) Films

Tensile testing of Poly(methyl methacrylate)(PMMA) films has been conducted to clarify the effects of humidity history upon their tensile properties. Prior to testing, PMMA film specimens were kept under three different humidity conditions for 3 days to adjust the water content to each condition. The conditions used in this study were 11%, 54% and 98% relative humidity (RH) respectively. The tensile strength of PMMA films at these storage humidities tends to decrease with increasing humidity. The tensile deformation behaviour is ductile at 11% and 54% RH although brittle at 98% RH. When tensile tests were performed for different storage terms at 98% RH using specimens which had been equilibrated to 11% RH before testing, the tensile strength decreased within a short storage term. The tensile deformation behaviour, however, remains ductile. The tensile deformation behaviour drastically changes to a brittle mode after a 3 day storage term at 98% RH. This suggests that the tensile strength is affected by moisture around the specimen surfaces. This is attributed to a reduction in the crazing stress as a result of surface moisture. Brittle failure, however, occurs after a long storage term at the high humidity levels tested. This suggests that the ductile manner is caused by both absorbed water and the moisture around the specimen surfaces.

Effects of Specimen Dimensions on Adhesive Shear Strength between a Microsized SU-8 Column and a Silicon Substrate

The adhesive shear strength between a microsized SU-8 columnar specimen and a Si substrate has been evaluated, especially focusing on the effects of the bonded specimen dimensions using Weibull analysis. The adhesive shear strength complicatedly changed with changing dimensions of the SU-8 column. The m value for the adhesive shear strength is much smaller in SU-8 specimens with smaller columnar lengths, because the effective factor on the delamination, such as natural defects at the interface, should be widely scattered at the smaller columnar length. In contrast, the m value is much larger in the longest columns, which suggests that the dispersion of the natural defect should less affect the adhesive strength. This may be because that the longest SU-8 column should be softer than the others owing to the lower degree of cross-linking. All the results show that the adhesive shear stress is strongly affected by the bonded film thickness, because the effects of natural defects and/or mechanical properties of bonded SU-8 may change by the thickness.

Effects of Supercritical Carbon Dioxide on Adhesive Strength between Micro-sized Photoresist Patterns and Silicon Substrates

Adhesive bend testing for micro-sized photoresist components has been performed to clarify the effects of supercritical CO 2 (ScCO 2 ) treatment. Multiple microsized cylindrical specimens were fabricated on a silicon substrate using epoxy-type photoresist. The specimens were ScCO 2 treated at a temperature of 323K at a pressure of 15MPa for 30 min, and then, decompressed to atmospheric pressure at two different rates. Double refraction appeared in the SU-8 specimens near by the interface between the SU-8 specimens and a substrate after ScCO 2 treatment. Adhesive bend strength of ScCO 2 treated specimen with slow decompression process is approximately 60% higher than that of non- ScCO 2 treated specimens, however, the strength of the microsized photoresist was slightly degraded by ScCO 2 treatment with quick decompression process. All the results suggest that ScCO 2 treatment improves the adhesive strength between microsized photoresist components and a silicon substrate by control of the decompression process.

84 Development and implementation of the comprehensive scheme for exposure assessment of chemicals in industrial/academic research facilities

Introduction It is often difficult to conduct exposure assessment of chemicals in research facilities of chemical industries or universities, because of the characteristics of laboratory tasks – variety of chemicals handled, relatively short task duration, and irregularity. The comprehensive scheme of exposure assessment for such laboratories was developed, where laboratory staff are engaged in the risk screening stage, and implemented in the large science/engineering university in Japan. Methods The first part of the scheme is risk screening in respective laboratories. Laboratory staff identifies major chemical handling tasks in their laboratory rooms at first. They perform exposure assessment for each tasks in three ordered steps; qualitative judgment, ‘revised control banding’ (a qualitative risk assumption scheme developed by Japan Industrial Safety and Health Association and the University–A), and detector tube measurements. During this process, the staff finishes the assessment of a task when the identified risk is ‘low’, or they proceed to the next step or take risk mitigation measures when the identified risk is ‘medium/high’. The result of this process is then collected and examined by a few occupational hygienists who oversee the whole research facility. The hygienists preform personal exposure assessments for tasks having residual risk, as the second part of the scheme. Result This scheme was implemented in Tokyo Institute of Technology (with 14 000 faculties/staff and students) for about one year. Exposure screening was smoothly performed by ab. 220 laboratory groups for ab. 2100 chemical handling tasks. The numbers of conducted assessments in steps (1,2), and (3) were; 2100, 1300, and 170 respectively. Tasks with medium/high risk were effectively squeezed out throughout the process. The number of high-risk tasks finally identified was quite small. Discussion It has been demonstrated that the developed scheme is very effective and practical for exposure assessment in chemical research facilities.

Intact Ultrathin Ni Films Fabricated by Electroplating with Supercritical CO2 Emulsion

Ultrathin (2 emulsion (SCE). Incomplete coverage of the Cu plate, the working electrode, by electroplated Ni and non-uniform Ni films with defects were obtained when conventional electroplating at 1 A/dm2 with 30 sec of deposition time was used. When electroplating with SCE (ESCE) was applied, complete coverage, defect-free and uniform UTNFs were obtained. SEM and AFM showed surface morphology of the UTNFs was covered by spherical-shaped particles with ~10 nm in diameter, which was expected to be individual Ni grains because the size was consistent with grain size of Ni films reported when ESCE was applied. High H2 solubility in CO2, periodic-plating-characteristic after applying ESCE, and improved transport efficiency of the reactive species are believed to be the main reasons to cause effects of grain refinement and suppression in formation of the defects. Thickness of the UTNFs was 11.97±1.82 nm when the deposition time was 15 sec, and the thickness increased to 38.45±1.71 nm when the deposition time was increased to 45 sec.

Influence of Heat-Treatment on the Adhesive Strength between a Micro-Sized Bonded Component and a Silicon Substrate under Bend and Shear Loading Conditions

Adhesive bend and shear tests of micro-sized bonded component have been performed to clarify the relationship between effects of heat-treatment on the adhesive strength and the bonded specimen shape using Weibull analysis. Multiple micro-sized SU-8 columns with four different diameters were fabricated on a Si substrate under the same fabrication condition. Heat-treatment can improve both of the adhesive bend and shear strength. The improvement rate of the adhesive shear strength is much larger than that of the adhesive bend strength, because the residual stress, which must change by heat-treatment, should effect more strongly on the shear loading. In case of bend type test, the adhesive bend strength in the smaller diameters (50 and 75 ㎛) widely vary, because the critical size of the natural defect (micro-crack) should vary more widely in the smaller diameters. In contrast, in case of shear type test, the adhesive shear strengths in each diameter of the columns little vary. This suggests that the size of the natural defects may not strongly influence on the adhesive shear strength. All the result suggests that both of the adhesive bend and shear strengths should be complicatedly affected by heat-treatment and the bonded columnar diameter.