Methods of forming nonvolatile memory devices using improved masking techniques

Methods of forming nonvolatile memory devices include the steps of forming a plurality of field oxide isolation regions on a semiconductor substrate. A thermal oxidation step may then be performed to define first gate insulating layers on active regions within the substrate. A blanket layer of polysilicon is then deposited as a first electrically conductive layer. Next, a blanket layer of an electrically insulating layer, is deposited. A blanket photoresist layer is then deposited on the electrically insulating layer. Conventional photolithography steps may then be performed to convert the blanket photoresist layer into a photoresist pattern on a memory cell array portion of the substrate. A dry etching step is then performed to define a floating gate electrode having an ONO electrically insulating cap thereon, on the memory cell array portion of the substrate. A wet etching step is then performed to remove the first gate insulating layer from the peripheral circuit portion of the substrate. This wet etching step is performed using the same mask (i.e., photoresist pattern) that was used during the dry etching step. Because this etching step causes portions of the floating gate electrodes to be undercut, a thermal oxidation step is then performed to grow sidewall insulating spacers on the sidewalls and undercut portions of the floating gate electrodes. Based on this thermal oxidation step, the floating gate electrodes become encapsulated by electrically insulating material.