A semiconductor apparatus and its manufacturing method are presented. The method entails providing a substrate structure comprising a substrate, one or more fins positioned along a first direction on the substrate, and a separation region surrounding the fins. The separation region comprises a first separation region neighboring a first side of the fins and a second separation region neighboring a second side of the fins; forming a first and a second insulation layers on the substrate structure; forming a barrier layer; performing a first etching process using the barrier layer as a mask; removing the barrier layer; performing a second etching process using the remaining second insulation layer as a mask; forming a third insulation layer on side surfaces of the remaining first and second insulation layers; and performing a third etching process using the remaining second insulation layer and the third insulation layer as a mask.