Metal hard masks for reducing line bending

A method comprising:

• depositing a metal-containing hard mask layer over a dielectric layer;
• forming a plurality of mandrels over the metal-containing hard mask layer;
• forming a plurality of spacers on sidewalls of the plurality of mandrels;
• in a first etching process, etching the metal-containing hard mask layer using a first photo resist to form a first trench in the metal-containing hard mask layer, wherein the first trench is overlapped by a first space between two of the plurality of spacers;
• in a second etching process separate from the first etching process, etching a first mandrel of the plurality of mandrels using a second photo resist to leave a second space, wherein after the first mandrel is etched, a second mandrel of the plurality of mandrels remains;
• etching the metal-containing hard mask layer to form a second trench in the metal-containing hard mask layer, wherein the second trench is overlapped by the second space, and the second mandrel is used as a part of an etching mask for the etching;
• after both of the first etching process and the second etching process are performed, removing remaining portions of both of the plurality of mandrels and the plurality of spacers;
• and
• after the remaining portions of the plurality of mandrels and the plurality of spacers are removed, etching the dielectric layer to extend the first trench and the second trench into the dielectric layer, wherein the etching the dielectric layer comprises using a third photoresist.

A method comprising:

• depositing a low-k dielectric layer;
• depositing a first mask layer over the low-k dielectric layer;
• depositing a tungsten-containing hard mask layer over the first mask layer;
• depositing a second mask layer over the tungsten-containing hard mask layer;
• forming a plurality of mandrels over the second mask layer;
• forming a plurality of spacers on sidewalls of the plurality of mandrels;
• forming a first patterned photo resist over the second mask layer;
• using the first patterned photo resist to etch the second mask layer and the tungsten-containing hard mask layer, so that a first trench is formed in the tungsten-containing hard mask layer and between two neighboring ones of the plurality of spacers, and the first trench stops on a top surface of the first mask layer;
• forming a second patterned photo resist over the second mask layer;
• using the second patterned photo resist to etch one of the plurality of mandrels, so that a second trench is formed to extend into the tungsten-containing hard mask layer, wherein a top surface of the first mask layer is underlying and exposed to the first trench and the second trench, and the second trench stops on the top surface of the first mask layer;
• etching the low-k dielectric layer using a third photo resist to form a via opening, wherein the via opening is formed in the first trench, and extends from the top surface of the first mask layer to an intermediate level of the low-k dielectric layer;
• and
• transferring the first trench in the tungsten-containing hard mask layer into the low-k dielectric layer, wherein during the transferring, the via opening is extended to a bottom of the low-k dielectric layer.