Papers by Author: Yasuhiro Takaya

Abstract: Surface with nanometer accuracy is required to manufacturing process of integrated circuit (IC) devices. One of the most promising techniques for surface planarization is chemical mechanical polishing (CMP). CMP is a high efficiency process, both due to the varied chemical and physical properties of the surface materials. Conventional CMP uses the slurry, which is composed of abrasive particles suspended in a chemical solution. The abrasive particle is effective for surface planarization by a chemical mechanism with little mechanical abrasion. So chemical reactivity appears to be an essential factor of CMP process. In our conventional study, fullerenols have been proposed as suitable abrasives for copper CMP. The chemical reactivity of fullerenol is suggested by the fact that high removal rate (150 nm/min) and surface flatness (0.6 nm RMS) have been confirmed using fullerenol slurry. In this study, we analyzed the chemical reactivity between fullerenol molecule and copper surface, which is important to understand the material removal mechanism. Using the intrinsic Raman spectroscopic signal of interaction between fullerenol and copper with surface plasmon resonance (SPR), the chemical reactivity over a period of the reaction process was analyzed. Raman spectroscopy is commonly used in chemical analysis, since vibrational information is specific to the chemical bonds and symmetry of molecules. Therefore, it provides a fingerprint by which the molecule can be identified. However, spontaneous Raman spectroscopic signal is typically very weak, and as a result the main difficulty of Raman spectroscopy is separating the weak inelastically scattered light from the intense Rayleigh scattered laser light. Then Raman spectroscopic signal in this study is further enhanced by the SPR, also known as surface enhanced Raman scattering (SERS). The increase in intensity of the Raman spectroscopic signal for adsorbates on copper surface occurs because of an enhancement in the electric field provided by the surface. This technique enables high-sensitive analysis in the near-surface region. The signature of copper-oxygen bond was measured by Raman spectroscopy for fullerenol/copper system by in-process SERS analysis. It is thought to be caused by the hydroxyls of fullerenol molecule adsorbed on the copper surface. This result suggests that fullerenol molecules absorbing onto the copper surface affect the high efficient material removal.

Abstract: This paper presents a laser-assisted Cu-CMP (Chemical Mechanical Polishing) method for obtaining higher planarized surface by forming laser aggregation particles on recessed areas of uneven copper surface before polishing. At first, the laser trapping of fine particles in slurry and the formation of aggregated marks on the copper wafer surface were investigated by fundamental experiments based on optical radiation pressure. Next, proposed planarization method for uneven surface of copper wafer was attempted. As the polishing processed, the height of aggregated marks was reduced. Then, it was confirmed that the aggregated marks played a role of masks, and no material removal at the bottom surface of recessed areas took place during polishing. This process made it possible to realize high planarity on copper wafer surface.

Abstract: In order to reduce and control yield loss in the fabrication process of next generation ULSI devices, nano-defects inspection technique for polished Silicon (Si) wafer surface becomes more essential. This paper discusses a new optical nano-defects detection method, which is applicable to silicon wafer surface inspection for next-generation semiconductors. In our proposed method, the evanescent light is emerged on the wafer surface with total internal reflection (TIR) of infrared (IR) laser at the Si-air interface. By scanning the surface where the evanescent light is emerging with a very shaped fiber probe, it enables to detect nanometer scale defects in the vicinity of Si wafer surface without diffraction limit to resolution. To experimentally verify the feasibility of this method, an evanescent light measurement system was developed and several fundamental experiments were performed. The results show that the proposed Si wafer microdefects detection method can detect the microdefect with 10nm scale on and beneath the surface based on evanescent light distribution.

Abstract: Laser scattering characteristics of typical CMP-induced defects such as particles and microscratches with the size of sub-micron order are investigated using a developed automated scattered light measurement system. The measurement system has an ability to detect three-dimensional distribution of scattered light from the defects with high sensitivity. The angular distributions of scattered light from the standard PSL (Polystyrene latex) spheres and microscratches reveal that scattering characteristics of microscratches are quite different from those of Particles. The scattered light from the PSL sphere is detected mainly ahead. In contrast, the scattered light from the microscratches only exists in the direction perpendicular to its length dimension at an oblique incidence maintaining the sheet-shaped pattern, even if its orientation relative to the incident direction is changed. Optical arrangement for defect detection and classification is suggested based on the experimental results.