Methods of forming integrated circuit devices having gate oxide layers with different thicknesses and integrated circuit devices formed thereby

Abstract

An integrated circuit device, such as a merged device, is formed by forming a first gate oxide layer on a first region, such as a logic circuit region, of a substrate. A conductive layer is formed on the first gate oxide layer. A second gate oxide layer is formed on a second region, such as a cell array region, of the substrate. A first gate pattern is formed on the second gate oxide layer. The conductive layer and the first gate oxide layer are patterned to form a second gate pattern. A silicide layer is formed on the second gate pattern and in the substrate adjacent to the second gate pattern.