Method and structure for determining an overlay error
A semiconductor structure includes a device area that includes a first structure in a first layer having a top surface above a top surface of the first layer, and a second structure in a second layer on top of the first layer, where the first structure is pinned in the second structure; an overlay metrology area for optically evaluating an overlay error between the second and first structure, including: a third structure in the first layer, having a top surface above the top surface of the first layer, a fourth structure in the second layer, where the combination of the third and fourth structures mimics the combination of the first structure and the second structures, and a fifth structure in the first layer, for use as a reference structure.
1 . A semiconductor structure comprising:
a first layer;
a second layer on top of and in contact with the first layer;
a device area comprising:
a first structure in the first layer having a top surface above a top surface of the first layer; and
a second structure formed of the second layer in contact with the first structure, such that the first structure is pinned in the second structure; and
an overlay metrology area comprising:
a third structure in the first layer formed of a material of which the first structure is formed and having a top surface above the top surface of the first layer;
a fourth structure formed of the second layer in contact with the third structure, such that the combination of the third structure and the fourth structure mimics the combination of the first structure and the second structure; and
a fifth structure in the first layer having a top surface above the top surface of the first layer.
2 . The semiconductor structure according to claim 1 , wherein the third structure is pinned in the fourth structure.
3 . The semiconductor structure according to claim 1 , wherein the first structure comprises a channel formed of a channel material, and wherein the second structure comprises an electrode formed of an electrically conductive material.
4 . The semiconductor structure according to claim 3 , wherein the second structure and the fourth structure are formed of a metal.
5 . The semiconductor structure according to claim 4 , wherein the metal is tungsten.
6 . The semiconductor structure according to claim 3 , wherein the device area comprises a gate structure formed of a gate material in the first layer wrapping the channel, and wherein the overlay metrology area comprises a structure formed of the gate material in the first layer wrapping the third structure.
7 . The semiconductor structure according to claim 3 , wherein the first structure and the second structure are part of a vertical field effect transistor.
8 . The semiconductor structure according to claim 1 , wherein the first structure and the third structure comprise nanowires.
9 . The semiconductor structure according to claim 1 , wherein the first structure and the third structure comprise arrays of nanowires.
10 . The semiconductor structure according to claim 9 , wherein the arrays are periodically spaced.
11 . The semiconductor structure according to claim 1 , wherein the third structure comprises an array of elements and wherein the fourth structure is in contact with each element of the third structure.
12 . The semiconductor structure according to claim 1 , further comprising, in the overlay metrology area and in the second layer, a sixth structure unpinned by any structure in the first layer.
13 . A method comprising:
obtaining an intermediate structure comprising:
a first layer;
a second layer on top of the first layer;
a masking layer over the second layer;
a device area comprising:
a first structure in the first layer having a top surface above a top surface of the first layer;
the second layer in contact with the first structure such that the first structure is pinned in the second layer; and
a first masking structure in the masking layer, overlapping the first structure; and
an overlay metrology area comprising:
a third structure in the first layer having a top surface above the top surface of the first layer;
the second layer, in contact with the third structure, such that the third structure is pinned in the second layer;
a second masking structure in the masking layer, overlapping the third structure; and
a fifth structure in the first layer having a top surface above the top surface of the first layer;
optically detecting a first distance between a feature of the second masking structure and a feature of the fifth structure;
etching the second layer, by using the first masking structure and the second masking structure, so as to form a second structure in contact with the first structure, and a fourth structure in contact with the third structure;
optically detecting a second distance between (1) a feature of the fourth structure that corresponds to the feature of the second masking structure and (2) the feature of the fifth structure; and
making a comparison of the first distance and the second distance.
14 . The method according to claim 13 , wherein obtaining the intermediate structure comprises:
obtaining the first layer comprising the third structure, having a top surface coplanar with the top surface of the first layer; and
epitaxially growing material of which the third structure is formed on the top surface of the third structure, thereby bringing the top surface of the third structure above the top surface of the first layer.
15 . The method according to claim 14 , further comprising depositing the second layer on the first layer.
16 . The method according to claim 13 , wherein obtaining the intermediate structure comprises obtaining, in the masking layer, a third masking structure, not overlapping with any structure for pinning in the first layer,
the method further comprising optically detecting a third distance between a feature of the third masking structure and a feature of the fifth structure or a feature of the second masking structure, wherein etching the second layer comprises using the third masking structure as a mask to form a sixth structure in the second layer, unpinned by any structure in the first layer,
optically detecting a fourth distance between the feature of the fifth structure or a feature of the fourth structure corresponding to the feature of the second masking structure, and a feature of the sixth structure corresponding to the feature of the third masking structure, and
comparing the third distance to the fourth distance to determine a lateral shift of the sixth structure in the second layer unpinned by the first layer.
17 . The method according to claim 16 , further comprising determining an overlay error for unpinned structures in the first layer and the second layer based on the comparison between the third distance and the fourth distance, and determining the lateral shift attributed to a stress release in the second layer from the comparison of the third distance and the fourth distance and the comparison of the first distance and the second distance.
18 . The method according to claim 13 , further comprising determining an overlay error for pinned structures in the first layer and the second layer.
19 . The method according to claim 18 , wherein determining the overlay error comprises determining the overlay error based on the comparison between the first distance and the second distance.
20 . The method according to claim 18 , further comprising applying the overlay error for pinned structures to reposition a mask pattern used for patterning the masking layer.