In a method, a first opening is formed in a first insulating interlayer on a first substrate. A first conductive pattern structure contacting a first diffusion prevention insulation pattern and having a planarized top surface is formed in the first opening. Likewise, a second conductive pattern structure contacting a second diffusion prevention insulation pattern is formed in a second insulating interlayer on a second substrate. A plasma treatment process is performed on at least one of the first and second substrates having the first and second conductive pattern structures thereon, respectively. The first and second conductive pattern structures are contacted to each other to bond the first and second substrates.