In semiconductor manufacturing technology, copper has been widely used for BEOL process due to better conductivity than aluminum. TEM (Transmission Electron Microscopy) characterization has been played in key role to understand the process of semiconductor manufacturing. Gallium base Focused Ion Beam (FIB) is widely used on TEM sample preparation. The experiment to understand the impact of gallium which is from sample preparation process on Cu layer was performed. In-situ TEM studies have shown real time material characteristic of Cu at various temperature . We observed the gallium aggregation phenomenon on Cu layer at round the temperature of 400°C. This thermal aggregation of gallium on Cu layer has been confirmed by EDS analysis in the study. Detectable amount of gallium was found in whole area in the sample before heating the sample at in-situ TEM work. This paper also introduces alternative solutions to resolve this gallium aggregation in copper layer including the sample preparation technique using Xe Plasma Focused Ion Beam (PFIB) . This Xe PFIB showed the substantial improvement of specimen quality for the in-situ TEM experiment of sample preparation.