Method for increasing area of a trench capacitor

A method for increasing area of a trench capacitor, comprising:

• providing a substrate;
• forming a first oxide layer on the substrate;
• forming a first nitride layer on the first oxide layer;
• forming an opening through the first oxide layer and the first nitride layer into the substrate to expose the first oxide layer and the substrate, wherein the opening has a lower portion and an upper portion;
• removing a part of the first oxide layer exposed in the opening to form a first recess between the first nitride layer and the substrate;
• forming a second nitride layer in the first recess between the first nitride layer and the substrate;
• forming a second oxide layer on the first nitride layer and the opening;
• removing the second oxide layer from the upper portion of the opening;
• forming a third nitride layer on the upper portion of the opening;
• removing the second oxide layer from the lower portion of the opening;
• etching the substrate in the opening using the first nitride layer, the second nitride layer and the third nitride layer as a mask to form a second recess in the substrate in the lower portion of the opening;
• and
• removing the second nitride layer and the third nitride layer.