Papers by Author: Tae Hyung Kim

Abstract: One of key processes in tungsten (W) CMP is to remove slurry particles inside W plug after CMP. In general, HF cleaning is well known to remove the slurry residue particles in W plugs. HF chemistry lifts off the particles by etching the plug during scrubbing and effectively removes particles. It is sometimes impossible to apply HF chemisty on W plug due to the degradation of electrical characteristics of a device. In this paper, a post W CMP cleaning process is proposed to remove residue particles without applying HF chemistry. After W CMP, recessed plugs are created, therefore they easily trap slurry particles during CMP process. These particles in recessed plug are not easy to remove by brush scrubbing when NH4OH chemistry is used for the cleaning because the brush surface can not reach the recessed area of plugs. Buffing with oxide slurry was followed by W CMP due to its high selectivity to W. The buffing polishes only oxide slightly which creates higher plug profiles than surrounding oxide. Higher profiles make the brush contact much more effectively and result in a similar particle removal efficiency even in NH4OH cleaning to that in HF brush scrubbing.

Abstract: This paper capitalizes on recent advances in the area of non-contact ultrasonic guided wave techniques. The present technique provides a decent method for nondestructive testing of defect thinning simulating a hidden corrosion or FAC(Flow Accelerated Corrosion) in a thin aluminum plate. The proposed approach is based on using EMAT(Electro-magnetic Acoustic Transducer) to generate guided waves and detect the wall thinning without any coupling. Interesting features in the dispersive behavior of selected guided modes are used for the detection of plate thinning. It is shown that mode cut-off measurement allows us to monitor a defect thinning level while a group velocity change can be used to quantify the thinning depth.

Abstract: In this paper the fatigue life of spur gear was investigated by changing the shot peening condition. From bending fatigue test depending on various shot peening intensity, fatigue characteristics were investigated. The causes of reduction in fatigue life were analyzed by observing the surface of gear with Scanning Electron Microscope(SEM), and impact of residual stress to fatigue characteristics was identified by measuring compressive residual stress depending peening intensity by depth. The results show that the optimum shot ball velocity is 65 m/s and optimum peening time is 8 minutes. From SEM image, the micro-crack was observed at the surface in case of over peening. This seems to be the factor which reduces fatigue life by decreasing compressive residual stress of surface.

Abstract: In this paper, study on evaluation of thickness reduction in a thin plate with guided waves is presented. Ultrasonic guided wave techniques have been widely studied and successfully applied to various non-destructive tests with the advantage of long range inspection. In addition to application of guided waves to NDT, non-contact methods for ultrasonic wave generation and detection have become very useful and well combined with guided wave techniques due to their capability of ultrasonic wave generation and reception in surface of high temperature or on rough surface. An advanced non-contact technique for detection of thickness reduction simulating hidden corrosion in thin plates using guided waves is proposed. The proposed approach uses EMAT(Electro-Magnetic Acoustic Transducer) for the non-contact generation and detection of guided waves in aluminum plates. Interesting features of the dispersive behavior in selected wave modes are used to detect plate thinning. The experimental results show that the mode cutoff measurements provide a qualitative measurement of thinning detects and change in the mode group velocity can be used as quantitative parameter of thinning depth measurement.