Method for fabricating semiconductor device

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

• preparing a substrate comprising a first surface and a second surface formed at a lower position than the first surface;
• forming an insulation layer over the substrate;
• etching the insulation layer to form a first contact hole exposing the first surface and a second contact hole having a larger depth than the first contact hole above the second surface;
• forming a first sacrificial layer over the insulation layer, the first contact hole, and the second contact hole;
• forming a second sacrificial layer over the substrate and filled in the first contact hole;
• exposing the first sacrificial layer at a bottom of the second contact hole while having the second sacrificial layer remain in the first contact hole;
• etching the first sacrificial layer at the bottom of the second contact hole the remaining second sacrificial layer formed over the first sacrificial layer in the first contact hole is partially etched such that the first sacrificial layer at a bottom of the first contact hole is not etched;
• and
• etching the remaining insulation layer to expose the second surface while the remaining second sacrificial layer in the first contact hole is etched but a portion of the first sacrificial layer under the remaining second sacrificial layer in the first contact hole is not etched.