Manufacturing method of semiconductor device

A method of manufacturing a semiconductor device, the method comprising:

• forming a stack structure by alternately stacking interlayer insulating layers and sacrificial insulating layers on a lower structure, the stack structure including first regions spaced apart from one another and a second region disposed between the first regions;
• forming holes penetrating each of the first regions of the stack structure;
• forming pillars filling in the holes, the pillars being divided into first and second pillar groups by the second region, each of the first and second pillar groups including a center pillar and a slit-side pillar;
• forming a slit penetrating the second region to a depth to expose the lower structure;
• forming a protective layer on the lower structure which is exposed through the slit;
• removing only a portion of each of the sacrificial insulating layers which remains between the slit and the slit-side pillar through a first selective etching process by introducing a first etching material through the slit to form first openings between adjacent interlayer insulating layers;
• and
• performing a second selective etching process using a second etching material that is different from the first etching material for removing remaining portions of the sacrificial insulating layers adjacent to the slit which were not removed with the first selective etching process, and the sacrificial insulating layers between the pillars.