Provided are a method for manufacturing a memory device and a memory device manufactured by the method. The memory device may be a flash memory device. The method for manufacturing the memory device may include sequentially stacking a tunnel dielectric, a floating gate conductive layer, an inter-gate dielectric, and a control gate conductive layer on a semiconductor substrate; anisotropically etching the floating gate conductive layer, the inter-gate dielectric, and the control gate conductive layer to form gate structures. The gate structures may be separated by regions where top surfaces of the tunnel dielectric are exposed, the exposed top surfaces being damaged during formation of the gate structures. The method includes reacting the exposed top surfaces of the tunnel dielectric damaged during the formation of the gate structures with a reaction gas comprising ammonium fluoride to form a reaction by-product on the exposed top surfaces of the tunnel dielectric, and removing the reaction by-product.