| CPC H01L 29/792 (2013.01) [H01L 29/40117 (2019.08); H01L 29/42344 (2013.01); H01L 29/66833 (2013.01)] | 9 Claims |
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1. A method for forming a semiconductor memory device, comprising:
providing a substrate;
forming a control gate on the substrate;
forming a source diffusion region in the substrate and on a first side of the control gate;
forming a select gate on the source diffusion region, wherein the select gate has a recessed top surface;
forming a charge storage structure under the control gate;
forming a first spacer between the select gate and the control gate and between the charge storage structure and the select gate;
forming a wordline gate on a second side of the control gate opposite to the select gate;
forming a second spacer between the wordline gate and the control gate; and
forming a drain diffusion region in the substrate and adjacent to the wordline gate, wherein the wordline gate has an inner sidewall, an outer sidewall, and a stepped top surface between the inner sidewall and the outer sidewall, wherein the stepped top surface comprises three sloped surface regions contiguous to one another, the three sloped surface regions include a first surface region descending from the inner sidewall to the outer sidewall, a second surface region between the first surface region and the outer sidewall, and a third surface region connecting the second surface region with the outer sidewall, wherein a slope of the first surface region is smaller than that of the second surface region, wherein the second surface region, the third surface region and the outer sidewall constitute a step structure.
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