Method of forming metal interconnection

A method comprising:

• forming a dielectric layer over a first conductive feature disposed in a semiconductor substrate, wherein the first conductive feature is surrounded by a first barrier layer in the semiconductor substrate;
• forming a trench in the dielectric layer, wherein a portion of the first conductive feature and a portion of the first barrier layer are exposed within the trench;
• forming a second barrier layer in the trench directly on the dielectric layer, the portion of the first barrier layer and the portion of the first conductive feature, wherein a first portion of the second barrier layer is formed along a sidewall surface of the trench defined by the dielectric layer and a second portion of the second barrier layer is formed along a bottom surface of the trench defined by the first conductive feature, the second barrier layer comprising manganese nitride;
• converting the first portion of the second barrier layer into a third barrier layer, wherein the third barrier layer and manganese nitride have different etching selectivity;
• exposing the first conductive feature in the trench by removing the second portion of the second barrier layer while a portion of the third barrier layer is disposed over the dielectric layer;
• and
• forming a second conductive feature in the trench directly on the third barrier layer and the first conductive feature such that an interface between the first and second conductive features is free of manganese nitride.

A method comprising:

• forming a via through a dielectric layer to a conductive feature disposed in a semiconductor substrate, wherein the conductive feature has a first sidewall and an opposing second sidewall and a first barrier layer is disposed along the first and second sidewalls such that the first conductive feature is separated from the semiconductor substrate by the first barrier layer;
• forming a second barrier layer in the via and directly on the conductive feature and the first barrier layer, the second barrier layer being formed of manganese nitride;
• performing a thermal treatment on the second barrier layer to form a third barrier layer by reacting with the dielectric layer and a fourth barrier layer by reacting with the conductive feature, wherein the third barrier layer is different from the fourth barrier layer, and wherein the third barrier layer and manganese nitride have different etching selectivity;
• selectively removing the fourth barrier layer to expose the conductive feature;
• and
• forming a second conductive layer to fill in the via such that an interface between the second conductive layer and the conductive feature is free of manganese nitride and the second conductive layer is in direct contact with the second barrier layer.