Hirokuni Hiyama

Development of Prototype Pump Using a Vibrating Pipe With a Valve

Tests were conducted on a prototype pump which has an extremely simple structure and excellent controllability. Its structural and hydrodynamic features are different from those of previous conventional reciprocating pumps. The pump structure constitutes a leak-proof short vibrating pipe equipped with a nonreturn valve on the edge of its outlet. The authors developed a prototype pump which uses a 25 mm diameter vibration pipe and an electromagnetic excitation device. The pump performance, intentionally changed by adjusting the coil voltage or the coil current frequency, featured a maximum pressure of approximately 1.0 bars, a maximum flow rate of approximately 40 liters per minute, and a maximum efficiency of approximately 30 percent. Results of both a one-year test run, using water as the working medium, and a three-month durability test, using concentrated nitric acid as the working fluid, assuming application as a chemical pump, indicated favorable results

Shear Stress Analyses in Chemical Mechanical Planarization with Cu/Porous Low-k Structure

In current LSI devices, porous low-k films are adopted as interlayer dielectrics (ILDs). However, the extremely low Youngs moduli of these films result in defects such as delamination, which are sometimes induced during chemical mechanical planarization (CMP). The main cause of delamination is thought to be shear stress induced by CMP downward pressure. In this study, we demonstrated that finite element method (FEM) results could be used to predict dangerous stress fields during CMP. It was revealed that shear stress concentrated on the ILD boundary with a large modulus difference. Moreover, stresses at dense lines were always lower than those at isolated lines. Furthermore, shear stress was sensitive to frictional force. The effect of a plasma-damaged layer on shear stress was quite limited. Consequently, these considerations provide a useful suggestion for future work on Cu/porous low-k-film fabrication as well as on the CMP of LSI devices.

Stress Analyses during Chemical Mechanical Planarization Processing with Cu/Porous Low-k Structures of LSI Devices

Porous low-k materials are required for the construction of 45-nm-node LSI devices. However, the extremely low Youngs modulus values of these materials result in the stress corrosion cracking (SCC) of the Cu interconnects during chemical mechanical planarization (CMP). We performed finite element method analyses of the stress at each step during the CMP. The results showed that the horizontal tensile stress was especially concentrated at the edges of the isolated fine wiring, and that higher tensile stresses appeared at the step of the barrier CMP. Moreover, the maximum values of the tensile stress increased with a decrease in Youngs modulus in the low-k films. The cause of the horizontal tensile stress was the downward CMP pressure, which indented the low-k films. These results suggest that CMP with a lower downward pressure and an LSI structure with a Cu dummy pattern were effective for avoiding SCC.

An electromagnetically driven univalved artificial heart

A wide variety of clinical blood pumps including powering systems have been developed and evaluated for totally implantable support systems [1–6]. However, there are still several serious problems, such as thromboembolic episodes, size, and weight, affecting prolonged survival of a total system inside the body.

Effect of Viscoelasticity of PVA Brush on Friction during Post-CMP Cleaning: A Guideline for Nodule Configuration

The application of new materials and three-dimensional structures are being used to achieve next-generation semiconductor devices. Hence, the role of the chemical-mechanical planarization (CMP) process has gained importance. Polyvinyl acetal (PVA) brushes are widely used as scrubbers during post-CMP cleaning. However, the mechanisms of brush scrubber cleaning are still a matter of debate because direct observation is difficult. Many researchers have proposed the removal mechanisms that operate during brush cleaning based on investigations of the forces acting on particles, friction, and the lubrication characteristics. Hydrodynamic drag forces and direct contact between the brush and the particles have been proposed as cleaning mechanisms [1–5]. Philipossian et al. [6] and Sun et al. [7] focused on the brush design and suggested that the existence of nodules or eccentricity of the roller brush had a significant effect on the friction. The friction system between the roller brush and the surface is complex because of the collision of nodules with the surface. Hence, the shapes of the nodules have been designed through trial and error. In this study, we focus on the friction of a single nodule to investigate the role of nodules in roller brush cleaning. The normal and friction forces are measured during brush sliding. In particular, we focus on the viscoelastic properties of a PVA brush and discuss its effects on friction.

Frictional Analysis of PVA Brush for Post CMP Cleaning: Effects of Rotation Speed, Compression Distance, and Fluid Viscosity

Chemical mechanical polishing (CMP) is widely used in the surface planarization process of semiconductor fabrication. The planarization process produces a large amount of surface residue that must be removed before the next process is initiated. Typically, a combination of roll-and pen-type polyvinyl acetal (PVA) brushes is used for removing such contaminants. In the subsequent 450-mm wafer processing step, PVA brush cleaning is a viable candidate for post-CMP cleaning. However, given that the mechanisms of nanoscale particle cleaning are still under investigation [1-, the designs and operating conditions for brush cleaning are determined by trial and error. In this study, as a first step toward understanding the cleaning mechanisms, the tribological contact condition of the PVA roll brush (i.e., hydrodynamic, mixed, or boundary lubrication) is considered by measuring the frictional coefficients. In particular, the effects of rotation speed, compression distance, brush length, and fluid viscosity on the friction force are investigated.

Stress Analysis of Dielectrics Using FEM for Analyzing the Cause of Cracking Observed After W-CMP

This study examined the cause of the mechanical fracture (cracking) of dielectrics observed after chemical mechanical polishing (CMP) in the damascene interconnect process for W/oxide structures through the stress analysis of dielectrics with the finite element method (FEM). The analysis, performed considering polishing pressure during CMP and residual film stress, revealed that the stress in dielectrics generated by polishing pressure during CMP was approximately 2% of that generated through W film removal. This result suggests a high likelihood that the cracking of dielectrics observed after CMP is caused by the release of residual stress in W film through CMP. To prevent the mechanical fracture of dielectrics, it is thus important to reduce defects in the deposition of dielectrics and to decrease residual film stress.

Measurement of the Frictional Force between PVA Roller Brushes and Semiconductor Wafers with Various Films Immersed in Chemicals

To better understanding the lubrication condition between a polyvinyl acetal (PVA) brush and cleaning surfaces, we measured the frictional force between the PVA roller brushes and the semiconductor wafers with various films immersed in chemicals. The frictional force showed different tendencies depending on the combination of chemicals and surface films. Especially, the large fluctuation of friction force was observed under the combination of Cu and NH4OH.

Removal Rate Simulation of Dissolution-Type Electrochemical Mechanical Polishing

A new method for simulating the Cu removal rate in electrochemical mechanical polishing (ECMP) based on the dissolution-type polishing mechanism was developed. The effect of a protective layer on the Cu removal rate was considered in this method because the protective layer is a key element in the dissolution-type polishing mechanism. This method was used to simulate the removal rate in a rotary-type ECMP system. The simulations accurately provided the dependence of the Cu removal rate on the aperture ratio. Furthermore, the dependence of the Cu removal rate on the aperture ratio was described with respect to changes in the average protective layer amount with time. Regarding the dependence of the Cu removal rate on the aperture diameter, however, a discrepancy was observed between the simulation and experimental results because this method did not take into account the effect of the aperture diameter on the electrolyte-filling ratio in apertures.

An Observation Method of Real Contact Area during PVA Brush Scrubbing

In the post CMP cleaning, the contact condition between PVA brush and surface is very important. In this study, we observed the real contact area between a brush and surface using a collimating LED light and prism. As a result, we found that the real contact area increases with increasing the brush compression. In addition, we also found that the real contact area decreases when the brush starts to move, and the brush was locally compressed due to its deformation.