Method of forming stepped contact trench for semiconductor devices

A method for forming a stepped contact trench for a semiconductor device, comprising the steps of:

• forming a cap layer on a semiconductor substrate;
• sequentially forming a first dielectric layer and a second dielectric layer on the cap layer;
• etching a preliminary contact hole through the second dielectric layer and the first dielectric layer;
• etching to remove the cap layer exposed by the preliminary contact hole;
• implanting first dopants in the substrate through the preliminary contact hole and then annealing to diffuse the dopants to form a first doped region;
• isotropically etching the sidewalls of the preliminary contact hole with an etching agent having a higher etch rate for the second dielectric layer than for the first dielectric layer, thereby forming a contact hole with a stepped sidewall;
• optionally implanting second dopants in the substrate through the stepped contact hole and then annealing to diffuse the dopants to form a second doped region;
• etching the substrate underneath the stepped contact hole to form a trench with the first doped region provided at the upper edges of the trench;
• and
• etching to remove the cap layer exposed by the stepped contact hole.