Provided are a thin film transistor substrate which include a substrate, a buffer layer and a thin film transistor, a display apparatus including the thin film transistor substrate, and a method of manufacturing the display apparatus including the thin film transistor substrate. The buffer layer includes an inorganic insulating layer. An area ratio of a peak corresponding to an N—H bond in the buffer layer is 0.5% or less based on a total peak area in a Fourier transform infrared spectroscopy (FTIR).