Methods of forming wiring structures

A method of forming a wiring structure, the method comprising:

• forming, on a substrate, a first insulation layer that includes a plurality of trenches therein;
• forming a barrier layer in the plurality of trenches and on an upper surface of the first insulation layer;
• forming a metal layer on the barrier layer to fill the plurality of trenches;
• planarizing upper portions of the metal layer and the barrier layer until the upper surface of the first insulation layer is exposed to form a metal layer pattern having a first oxide layer thereon and a barrier layer pattern having a second oxide layer thereon;
• performing an ultraviolet (UV) pre-treatment process using UV and a reducing gas on the metal layer pattern and the barrier layer pattern to remove the first and second oxide layers thereon, respectively, so as to form a plurality of wiring patterns, wherein the plurality of wiring patterns include the barrier layer pattern and the metal layer pattern;
• forming a protection layer pattern directly on top surfaces of the plurality of wiring patterns, the protection layer pattern including a material having a high reactivity with respect to oxygen;
• partially removing the first insulation layer to form recesses between the plurality of wiring patterns;
• and
• forming a second insulation layer on the protection layer pattern and the first insulation layer to form an air gap between the plurality of wiring patterns.