A protection layer for use in fabrication of failure analysis (FA) sample is disclosed, which principally comprises a first thin film, a buffer thin film and a second thin film By forming the protection layer on a surface of a malfunction device die, a FA sample of the malfunction device die is obtained. As a result, in the case of treating the sample with a FIB thinning process, there are no cracks, distortion, and/or collapse resulted from inter-elemental isobaric interferences, stress effect or charge accumulation occurring on the surface layer of the malfunction device die because of the protection of the protection layer. On the other hand, this protection layer can also be applied to a microLED element or a VCSEL element, so as to make microLED element and the VCSEL element possess excellent stress withstanding capability.