A thin film transistor (TFT) substrate comprises: a plastic insulation substrate; a first silicon nitride layer with a first refractive index, formed one surface of the plastic insulation substrate; and a TFT comprising a second silicon nitride layer formed with a second refractive index smaller than the first refractive index on the first silicon nitride layer. Thus, the present invention provides a TFT substrate wherein there is reduced a problem in that thin films are lifted from a plastic insulation substrate.