Memory device with improved data retention

A method for forming a memory device, the method comprising:

• forming a source/drain region in a substrate;
• forming a gate structure on the substrate;
• forming a first spacer with an L-shaped cross-sectional profile in direct contact with a sidewall of the gate structure and in direct contact with a top surface of the source/drain region, wherein a sidewall of the first spacer is vertically coplanar with the sidewall of the gate structure and a sidewall of the source/drain region;
• forming a second spacer with an I-shaped cross-sectional profile in direct contact with a sidewall of the first spacer and with a dielectric constant greater than a dielectric constant of the first spacer;
• forming a third spacer in direct contact with a sidewall of the second spacer and in direct contact with a horizontal surface of the first spacer, wherein the third spacer comprises:
• an L-shaped cross-sectional profile;
• a horizontal spacer portion directly on a horizontal spacer portion of the first spacer, and
• a vertical spacer portion in direct contact with a sidewall of the second spacer;
• and
• forming a fourth spacer with a curved sidewall profile on the horizontal spacer portion of the third spacer using an anisotropic etching process and an isotropic etching process.

A method for forming a memory device, the method comprising:

• forming a gate structure on a substrate;
• forming a source/drain region on the substrate;
• depositing a first oxide layer, on the gate structure and the source/drain region, comprising depositing a sidewall of the first oxide layer in direct contact with a sidewall of the gate structure and on a same vertical plane as the sidewall of the gate structure and a sidewall of the source/drain region;
• depositing a first nitride layer with an I-shaped cross-sectional profile in direct contact with a sidewall of the first oxide layer and with a dielectric constant greater than a dielectric constant of the first oxide layer;
• etching the first nitride layer to expose a horizontal surface of the first oxide layer;
• depositing a second oxide layer on the horizontal surface of the first oxide layer and on a sidewall of the first nitride layer, wherein a bottom surface of the second oxide layer is coplanar with a bottom surface of the first nitride layer;
• depositing a second nitride layer in direct contact with a sidewall of the second oxide layer and in direct contact with a horizontal surface of the first oxide layer;
• etching the second nitride layer using an anisotropic etching process and an isotropic etching process to expose a horizontal surface of the second oxide layer;
• and
• etching the first and second oxide layers to form first and second dielectric structures with L-shaped cross-sectional profiles.