Patterning method and overlay measurement method

1. A method, comprising:

forming a target layer on a substrate;

forming a hard mask layer over the target layer;

performing a first patterning process on the hard mask layer by using a photomask having a first pattern with a first pitch;

shifting the photomask along a first direction by a first distance;

performing a second patterning process on the hard mask layer by using the photomask that has been shifted, so as to form a patterned hard mask; and

patterning the target layer using the patterned hard mask, so as to form a patterned target layer, wherein the patterned target layer has a second pattern with a second pitch less than the first pitch,

wherein shifting the photomask further comprises:

shifting the photomask along a second direction by a second distance, wherein the second direction is perpendicular to the first direction.

2. The method of claim 1 , wherein the first distance is half of the first pitch, and the second pitch is half of the first pitch.

3. The method of claim 1 , wherein performing the first patterning process comprises:

forming a first photoresist on the hard mask layer;

exposing the first photoresist to a patterned irradiation through the photomask, such that the first pattern of the photomask is transferred into the first photoresist to form a first patterned photoresist; and

etching the hard mask layer using the first patterned photoresist as an etching mask, such that the first pattern is transferred into the hard mask layer.

4. The method of claim 3 , further comprising:

removing the first patterned photoresist before performing the second patterning process.

5. The method of claim 3 , wherein performing the second patterning process comprises:

forming a second photoresist over the hard mask layer having the first pattern;

exposing the second photoresist to a patterned irradiation through the photomask that has been shifted, such that a shifted first pattern is transferred into the second photoresist to form a second patterned photoresist; and

etching the hard mask layer using the second patterned photoresist as an etching mask, such that the shifted first pattern is transferred into the hard mask layer.

6. The method of claim 5 , further comprising:

forming a first bottom anti-reflection coating (BARC) layer between the hard mask layer and the first photoresist;

removing the first BARC layer before performing the second patterning process; and

forming a second BARC layer on the hard mask layer before forming the second photoresist.

7. The method of claim 1 , further comprising:

forming a first pair of overlay marks over the substrate, wherein forming each of the first pair of overlay marks comprises:

forming a lower patterned layer that is patterned using the photomask, the lower patterned layer has a lower pattern including lines extending in the first direction and arranged along the second direction; and

forming an upper patterned layer over the lower patterned layer using the photomask that has been shifted along the second direction, the upper patterned layer has an upper pattern including lines extending in the first direction and arranged along the second direction;

wherein the first pair of overlay marks both have a first shift of the upper pattern with respect to the lower pattern, and the first shift is along the second direction.

8. The method of claim 7 , wherein the first pair of overlay marks are formed in a first wafer, and the method further comprising:

forming a second pair of overlay marks over an additional substrate of a second wafer, wherein forming each of the second pair of overlay marks comprises:

forming an additional lower patterned layer that is patterned using the photomask, the additional lower patterned layer has an additional lower pattern including lines extending in the first direction and arranged along the second direction; and

forming an additional upper patterned layer over the additional lower patterned layer using the photomask that has been shifted along a third direction opposite to the second direction, the additional upper patterned layer has an additional upper pattern including lines extending in the first direction and arranged along the second direction;

wherein the second pair of overlay marks both have a second shift of the additional upper pattern with respect to the additional lower pattern, and the second shift is along the third direction.

9. The method of claim 7 , wherein the first pair of overlay marks are formed in a first exposure region of a wafer, and the method further comprising:

forming a second pair of overlay marks over the substrate in a second exposure region of the wafer that is adjacent to the first exposure region, wherein forming each of the second pair of overlay marks comprises:

forming an additional lower patterned layer that is patterned using the photomask, the additional lower patterned layer has an additional lower pattern including lines extending in the first direction and arranged along the second direction; and

forming an additional upper patterned layer over the additional lower patterned layer using the photomask that has been shifted along a third direction opposite to the second direction, the additional upper patterned layer has an additional upper pattern including lines extending in the first direction and arranged along the second direction;

wherein the second pair of overlay marks both have a second shift of the additional upper pattern with respect to the additional lower pattern, and the second shift is along the third direction.