In a method of detecting inhomogeneity of a layer, an incident light may be irradiated to at least two regions of the layer at a first incident angle position. First reflected lights reflected from the two regions of the layer may be sensed. The incident light may be irradiated to the at least two regions of the layer at a second incident angle position. Second reflected lights reflected from the two regions of the layer may be sensed. The first reflected lights and the second reflected lights may be compared with each other to obtain the inhomogeneity of the layer. Thus, the layer having a spot may be found.