In this paper, we have studied the effect of mechanical polishing to Ga-polar face for reducing the wafer bowing and strain in free-standing GaN. After the mechanical polishing to Ga-polar face, the bowing of the free-standing GaN substrate significantly decreased with increasing the size of diamond slurry, and eventually changed the bowing direction from concave to convex. Furthermore, the full width at half maximum (FWHM) of high-resolution X-ray diffraction (HR-XRD) were decreased, especially the FWHM of (1 0 2) reflection for 1.0 μm size of diamond slurry was significantly decreased from 630 to 203 arcsec. In the case, we confirmed that the compressive strain in Ga-polar face was fully released by Raman measurement.

We investigated the speed change of the diamond spherical abrasive during the substrate surface polishing under the pad compression by using classical molecular dynamics modeling. We performed three-dimensional molecular dynamics simulations using the Morse potential functions for the copper substrate and the Tersoff potential function for the diamond abrasive. As the compressive pressure increased, the indented depth of the diamond abrasive increased and then, the speed of the diamond abrasive along the direction of the pad moving was decreased. Molecular simulation result such as the abrasive speed decreasing due to the pad pressure increasing gave important information for the chemical mechanical polishing including the mechanical removal rate with both the pad speed and the pad compressive pressure.

Copper (Cu) had been attractive material due to its superior properties comparing to other metals such as aluminum or tungsten and considered as the best metal which can replace them as an interconnect metal in integrated circuits. CMP (Chemical Mechanical Polishing) technology enabled the production of excellent local and global planarization of microelectronic materials, which allow high resolution of photolithography process. Cu CMP is a complex removal process performed by chemical reaction and mechanical abrasion, which can make defects of its own such as a scratch, particle and dishing. The abrasive particles remain on the Cu surface, and become contaminations to make device yield and performance deteriorate. To remove the particle, buffing cleaning method used in post-CMP cleaning and buffing is the one of the most effective physical cleaning process. AE(Acoustic Emission) sensor was used to detect dynamic friction during the buffing process. When polishing is started, the sensor starts to be loaded and produces an electrical charge that is directly proportional to the applied force. Cleaning efficiency of Cu surface were measured by FE-SEM and AFM during the buffing process. The experimental result showed that particles removed with buffing process, it is possible to detect the particle removal efficiency through obtained signal by the AE sensor.