Method of making a semiconductor device
An improved method of making interconnect structures with self-aligned vias in semiconductor devices utilizes sidewall image transfer to define the trench pattern. The sidewall height acts as a sacrificial mask during etching of the via and subsequent etching of the trench, so that the underlying metal hard mask is protected. Thinner hard masks and/or a wider range of etch chemistries may thereby be utilized.
1. A method of forming a semiconductor device comprising:
forming a first mask having a first pattern defining a grooved area, said first mask overlying a metal film formed in an interconnect dielectric layer of said semiconductor device, wherein said first mask is formed by sidewall image transfer;
forming a second mask having at least one opening overlapping said first pattern to form a second pattern, said second mask overlying said first mask and said opening overlapping said grooved area in plan view;
etching the interconnect dielectric layer through said first and second masks, to transfer said first pattern to said interconnect dielectric layer; and
etching the interconnect dielectric layer through said second mask, to transfer said second pattern to said interconnect dielectric layer;
wherein said first pattern is formed in said interconnect dielectric layer to a different depth than said second pattern.
2. The method according to claim 1 , wherein said first pattern is transferred to the interconnect dielectric layer as a series of trenches extending part way into a thickness of the interconnect dielectric layer.
3. The method according to claim 1 , wherein said second pattern is transferred to the interconnect dielectric layer as a via extending through an entire thickness of the interconnect dielectric layer.
4. The method according to claim 1 , wherein said first mask is formed by forming a plurality of mandrels by lithography, applying a layer of insulating material to the mandrels, selectively removing the layer of insulating material to leave sidewalls of the insulating material on the mandrels, and removing the mandrels while retaining the sidewalls.
5. The method according to claim 1 , wherein said first and second patterns in said interconnect dielectric layer are filled with copper.
6. The method according to claim 1 , wherein said second mask comprises an overlying photoresist layer and an underlying organic planarization layer.
7. The method according to claim 1 , further comprising forming a third mask overlying said first mask before forming said second mask, said third mask exposing a region in which said first pattern is to be formed and covering a region in which said first pattern is not to be formed.
8. The method according to claim 1 , further comprising:
forming a third mask overlying an oxide layer from which said first mask will be formed before forming said first mask, said third mask exposing a region in which said first pattern is to be formed and covering a region in which said first pattern is not to be formed; and
forming said first mask by selective removal of said oxide layer through said third mask;
wherein said oxide layer is not removed in said region in which said first pattern is not to be formed.
9. The method according to claim 1 , wherein said second mask comprises plural openings, each defining with said first mask a single via pattern.
10. The method according to claim 1 , wherein said second mask comprises an elongated opening defining with said first mask a series of adjacent via patterns.
11. The method according to claim 4 , wherein said sidewalls have at least one of a thickness and spacing that is below a resolution of radiation used to perform said lithography.
12. The method according to claim 4 , wherein said mandrels are an organic material deposited by chemical vapor deposition or a spin-on technique.
13. The method according to claim 12 , wherein said mandrels are formed from amorphous carbon.