Method of forming semiconductor memory device
A method of forming a semiconductor memory device includes the following steps. First of all, a substrate is provided, and a plurality of gates is formed in the substrate, along a first direction. Next, a semiconductor layer is formed on the substrate, covering the gates, and a plug is then in the semiconductor layer, between two of the gates. Then, a deposition process is performed to from a stacked structure on the semiconductor layer. Finally, the stacked structure is patterned to form a plurality of bit lines, with one of the bit lines directly in contact with the plug.
1. A method of forming a semiconductor memory device, comprising: providing a substrate;
forming a plurality of gates in the substrate, extending along a first direction;
forming a semiconductor layer on the substrate, covering the plurality of gates;
forming a protection layer on the semiconductor layer;
forming a plug in the semiconductor layer, between two adjacent gates of the plurality of gates,
wherein the forming of the plug comprises:
forming a plug-hole in the semiconductor layer;
forming a conductive layer on the semiconductor layer to fill in the plug-hole; and
forming a sacrificial layer entirely covering on the conductive layer and the plug-hole; and
performing an etching process to remove the sacrificial layer and the conductive layer on the semiconductor layer to form an arched top surface of the conductive layer;
performing a deposition process to from a stacked structure on the semiconductor layer; and
patterning the stacked structure to form a plurality of bit lines, with one of the bit lines directly in contact with the plug;
wherein the etching process comprises:
a first etching process, removing a portion of the sacrificial layer to expose a top surface of the conductive layer, to remain a rest portion of the sacrificial layer with a coplanar surface with the top surface of the conductive layer;
a second etching process, completely removing the sacrificial layer and the conductive layer on the semiconductor layer to expose the arched top surface of the conductive layer; and
a third etching process to remove the protection layer and the arched top surface of the conductive layer to form a planar top surface of the conductive layer coplanar with a top surface of the semiconductor layer.
2. The method of forming a semiconductor memory device according to claim 1 , wherein the etching process is performed by using an etchant which has a same etching selectivity related to the sacrificial layer and the conductive layer.