Method of manufacturing a buried plate type DRAM having a widened trench structure

A method of manufacturing memory cells of a buried plate type semiconductor memory device, comprising the steps of:

• forming a mask for etching on a main surface of a semiconductor substrate;
• forming a plurality of trenches, each of which extends in a first direction perpendicular to the main surface of said semiconductor substrate, by performing a first anisotropic etch in said first direction using said mask;
• widening a bottom portion of each of said plurality of trenches by performing a second isotropic etch at an etching angle relative to said first direction, such that said bottom portion of each of said plurality of trenches is wider than an opening portion of each of said plurality of trenches;
• doping an impurity into said widened bottom portion of each of said plurality of trenches;
• connecting said widened bottom portions of said plurality of trenches by diffusing the doped impurity into said semiconductor substrate between said widened bottom portions by heat treatment, thereby forming a plate diffusion region;
• forming a first conductive layer on said plate diffusion region in each of said plurality of trenches;
• forming an insulating layer covering said first conductive layer;
• and
• forming a second conductive layer covering said insulating layer and buried into each of said plurality of trenches.

A method of manufacturing storage capacitors for a semiconductor memory device, the method comprising the steps of:

• forming trenches in a surface of a semiconductor substrate;
• forming a first insulating film on a sidewall of each trench;
• forming first impurity diffusion regions at a bottom portion of each trench;
• forming a widened bottom portion for each trench by removing said first impurity regions;
• doping an impurity into the widened bottom portion of each trench;
• diffusing the doped impurity to form second impurity diffusion regions which are connected to form a plate diffusion region;
• forming a first conductive layer in each trench on said first insulating film and on said plate diffusion region;
• forming a second insulating layer in each trench on said first conductive layer;
• and
• forming a second conductive layer in each trench on said second insulating layer.