The present application provides a thin film transistor, a method of manufacturing a thin film transistor, and a manufacturing system. The thin film transistor includes a substrate, a buffer layer, an active layer, and a gate insulating layer. A side area of the active layer is doped and modified, so that a surface of the side area is formed as a high resistance area, and then the gate insulating layer is formed by a chemical deposition process, thereby to avoid a weak channel current produced by unintentional electrically conduction of a boundary of the active layer due to a thinner thickness of the gate insulating layer when operating, thereby increasing electrical reliability of the thin film transistor.