Yuji Yamada

Evaluation of a mirror-polishing technique for fluorocarbon polymer surfaces for reduction of contamination from containers used in ultratrace analysis.

A mirror-polishing technique for fluorocarbon polymer surfaces using high-precision diamond cutting tools was developed. The goal of this technique was the reduction of ultratrace elemental analysis contamination levels of containers fabricated from such mirror-polished materials. Remarkably smooth inner surfaces with degrees of flatness of 0.1 μm peak-to-valley (PTV) for containers fabricated from mirror-polished PTFE materials were obtained, in contrast to degrees of surface flatness of more than 30 μm PTV for commercially available PTFE containers. (Here, PTV denotes the difference between the highest peak and deepest valley in a scanned area of 10 × 10 μm.) Extractable impurity levels for mirror-polished PTFE container surfaces were reduced by more than 1 order of magnitude relative to those of unpolished PTFE containers. The surface conditions of the PTFE containers were observed by atomic force and scanning electron microscopy. The microphotographs so obtained suggest that the degree of surface smoothness of the containers is proportional to their ultratrace metallic contamination levels.

Determination of ultratrace metallic impurities in fluorocarbon polymers by electrothermal atomic absorption spectrometry after decomposition with a combustion system

A combustion system method for determining ultra-trace impurities in fluorocarbon polymers was developed. 200 mg polytetrafluoroethylene (PTFE) material samples were inserted into a quartz combustion system and decomposed for 30 min in air. Sodium-, potassium-, calcium-, copper-, and iron-concentrations in the raw PTFE materials ranged between 2–96, 1–35, 4–18, <1 and 12–97 ng g−1, respectively, with blank levels of 0.3, 0.2, 0.4, 0.2, and 0.5 ng/analysis, respectively. The impurity profiles of the fluorocarbon polymers indicated that the polymers were contaminated as a result of the polymer processing procedures. The technique reported herein gives low blank concentrations and is a rapid and safe analytical method for fluorocarbon polymers.

Development of DAF (Die Attach Film) with functional gettering agent for metal impurities

Gettering effect which is to trap metal ions on the dangling-bonds located far from the device area is widely known as an inhibition way of this problem. Extrinsic Gettering (EG) method that is formed during back side grinding in the wafer thinning process is one of the most significant technologies considering of reducing cost. However the chip strength has been decreased with increasing the roughness derived from crystal defect. Under these circumstances, we focused on the DAF (Die Attach Film) which is commonly used as an adhesive sheet to stack thin chips and attempted to add a functional gettering agent in this film. We selected Inorganic Ion-Exchange materials as a gettering agent and prepared some samples which have Oxidized Sb for gettering agent. From the result based on this study, the main factor determining gettering effect is an amount of substance of Ion-Exchange materials in the DAF. Its also estimated the quantity of Cu ion adsorption was about 33~50% in the whole of trapped Cu ions in the DAF. And we obtained 38 % Cu ions were adsorbed in the DAF with 10um thickness, which is about 68 % compared to the value from #2000.

New FEOL Cleaning Technology for Advanced Devices beyond 45 nm Node

In FEOL (front-end-of-line) wet cleaning, acid-base chemicals have been employed to remove metallic contamination and oxide films. Ultrasonic irradiation under alkaline-base chemicals such as APM (NH4OH / H2O2 / DIW) is applied frequently to remove particles on silicon substrates. Recently, with scaling down below 50 nm, influence of pattern damage due to physical force such as ultrasonic irradiation has been reported. Hence, for the 3x and 4x nm devices, it will be very difficult to apply ultrasonic irradiation for particle removal process. APM chemical can prevent the re-adsorption of particles on substrates, because the particles-substrates interaction is retained repulsive. However, recently, it has become difficult to use alkaline cleaning for etching of ion-implantation-damaged silicon oxide film and silicon substrate. In this study, we tried to employ dispersant addition into acid-base chemicals and to prevent particles from adsorbing on substrates by controlling surface charge of particles and substrates. Although, according to reports, dispersant or surfactant agent in alkaline chemicals [1] or HF solution [2] was employed in some investigations, such techniques cannot be applied in view of the loss of silicon oxide and silicon substrate. We chose the dispersant agent that is the most effective in HCL acid-base chemicals without loss of silicon oxide and silicon substrate, and that is easy to decompose by subsequent ozone water rinse step.