Phase-change semiconductor device and methods of manufacturing the same

A method of manufacturing a phase-change semiconductor device, comprising:

• forming a metal layer on a substrate;
• forming an etch stop layer on the metal layer, the etch stop layer having a thickness less than an upper thickness threshold;
• forming a photoresist pattern on the etch stop layer;
• etching the etch stop layer and the metal layer using the photoresist pattern to form an etch stop layer pattern and a metal layer pattern on the substrate and to form an opening exposing a portion of the substrate;
• reducing the photoresist pattern;
• forming an oxide layer pattern to at least partially fill the opening;
• forming an insulation layer on the etch stop layer pattern and the oxide layer pattern;
• forming a contact hole through the insulation layer and the etch stop layer, the contact hole exposing a portion of the metal layer pattern;
• forming a contact electrode to fill the contact hole, the contact electrode being electrically connected to the metal layer pattern;
• forming a phase-change layer on the insulation layer, the phase-change layer being electrically connected to the contact electrode;
• forming an upper electrode layer on the phase-change layer;
• and
• partially etching the upper electrode layer and the phase-change layer to form a phase-change layer pattern and an upper electrode.