Method for fabricating a trench structure which is electrically connected to a substrate on one side via a buried contact

1. A method for fabricating a trench capacitor with an insulation collar in a substrate, which is electrically connected to the substrate on one side via a buried contact, comprising:

providing a trench in the substrate using a hard mask with a corresponding mask opening;

providing an at least partial trench filling;

providing a liner comprising Al 2 O 3 on the resulting structure;

subjecting the liner to a heat treatment for increasing the crystallinity of the liner;

carrying out an oblique implantation of impurity ions onto the liner for the purpose of altering the etching properties of an implanted partial region of the liner;

selectively removing the implanted partial region of the liner by means of a first etching for the purpose of forming a liner mask from a complimentary partial region of the liner, which partially masks a top side of the trench filling;

removing a part of the trench filling by means of a second etching using the liner mask; and

replacing the removed part of the trench filling.

2. The method according to claim 1 , wherein for the trench filling,

provision is made of a capacitor dielectric in a lower and central trench region, an insulation collar in the central and upper trench region and an electrically conductive filling in the lower, central and upper trench region, the electrically conductive filling electrically contact-connecting the substrate in the upper trench region above the insulation collar and being sunk with respect to the top side of the substrate;

the liner mask defines a contact region on one side and an insulation region on a different side of a buried contact; and

the insulation region of the buried contact is formed by replacing the removed part of the trench filling by an insulation material.

3. The method according to claim 1 , wherein for the trench filling,

provision is made of a capacitor dielectric in a lower and central trench region, an insulation collar in the central and upper trench region and as far as a top side of the hard mask opening, and an electrically conductive filling in the trench, which filling reaches as far as at least into the upper trench region with the insulation collar;

the liner mask defines a contact region on one side and an insulation region on a different side of a buried contact; and

the contact region of the buried contact is formed by replacing the removed part of the trench filling by a further electrically conductive filling.

4. The method according to claim 1 , wherein the liner mask is removed before replacement of the removed part of the trench filling.

5. The method according to claim 4 , wherein, for removal, an oblique implantation of impurity ions onto the liner mask is performed for of altering the etching properties and the liner mask is subsequently removed by a third etching.

6. The method according to claim 1 , wherein the liner has a thickness of 15 to 25 nm.

7. The method according to claim 1 , wherein the implanted part of the liner is etched in an ammonia-containing etchant.

8. The method according to claim 1 , wherein the liner comprises Al 2 O 3 and the liner mask is removed before replacement of the removed part of the trench filling by means of the hot phosphoric acid.