Semiconductor devices

1 . A method of manufacturing a semiconductor device, the method comprising:

forming an alignment key through a portion of a substrate including first and second surfaces opposite to each other, the portion being adjacent to the second surface;

forming a transistor on the second surface of the substrate, the transistor including a gate structure and a source/drain layer;

removing a portion of the substrate adjacent to the first surface of the substrate to expose the alignment key;

forming a contact plug through a portion of the substrate adjacent to the first surface of the substrate, the contact plug being electrically connected to the source/drain layer; and

forming a power rail on the first surface of the substrate, the power rail being electrically connected to the contact plug.

2 . The method as claimed in claim 1 , wherein forming the alignment key includes:

removing a portion of the substrate adjacent to the second surface of the substrate to form a first trench; and

forming an insulation layer in the first trench.

3 . The method as claimed in claim 2 , wherein the substrate includes a chip region and a scribe lane region, and the first trench is formed in the scribe lane region of the substrate, and

wherein the method further comprises:

removing a portion of the substrate adjacent to the second surface of the substrate in the chip region to form a second trench; and

forming an isolation pattern in the second trench.

4 . The method as claimed in claim 3 , wherein the second trench defines an active pattern in the chip region of the substrate, and

wherein the isolation pattern is formed in a lower portion of the second trench, and covers a lower sidewall of the active pattern.

5 . The method as claimed in claim 1 , wherein forming the alignment key includes:

alternately and repeatedly stacking a sacrificial layer and a semiconductor layer on the second surface of the substrate, the sacrificial layer including silicon-germanium and the semiconductor layer including silicon;

partially removing the sacrificial layers, the semiconductor layers and a portion of the substrate adjacent to the second surface of the substrate to form a first trench; and

forming an insulation layer in the first trench.

6 . The method as claimed in claim 5 , wherein the substrate includes a chip region and a scribe lane region, the first trench is formed in the scribe lane region of the substrate, and

wherein the method further comprises:

partially removing the sacrificial layers, the semiconductor layers and a portion of the substrate adjacent to the second surface of the substrate in the chip region to form a second trench; and

forming an isolation pattern in the second trench.

7 . The method as claimed in claim 1 , wherein forming the alignment key includes:

removing a portion of the substrate adjacent to the second surface of the substrate to form a first trench;

alternately and repeatedly stacking a sacrificial layer and a semiconductor layer on the second surface of the substrate having the first trench thereon; and

forming an insulation layer on a portion of an uppermost one of the semiconductor layers on the first trench.

8 . The method as claimed in claim 7 , wherein the substrate includes a chip region and a scribe lane region, the first trench is formed in the scribe lane region of the substrate, and

wherein the method further comprises:

partially removing the sacrificial layers, the semiconductor layers and a portion of the substrate adjacent to the second surface of the substrate in the chip region to form a second trench; and

forming an isolation pattern in the second trench.

9 . The method as claimed in claim 1 , wherein forming the transistor includes:

forming a dummy gate structure on the second surface of the substrate;

forming the source/drain layer on a portion of the substrate adjacent to the dummy gate structure; and

replacing the dummy gate structure with the gate structure.

10 . The method as claimed in claim 1 , wherein forming the contact plug includes:

removing a portion of the substrate adjacent to the first surface of the substrate to form an opening exposing the source/drain layer; and

forming the contact plug in the opening.

11 . A method of manufacturing a semiconductor device, the method comprising:

removing portions of a substrate in a chip region and a scribe lane region to form first and second trenches, respectively, the substrate including first and second surfaces opposite to each other, and the portions being adjacent to the second surface of the substrate;

forming an isolation pattern and an alignment key in the first and second trenches, respectively;

forming a dummy gate structure on the second surface of the substrate;

forming a source/drain layer on a portion of the substrate adjacent to the dummy gate structure;

replacing the dummy gate structure with a gate structure;

removing a portion of the substrate adjacent to the first surface of the substrate to expose the alignment key;

forming a contact plug through a portion of the substrate adjacent to the first surface of the substrate, the contact plug being electrically connected to the source/drain layer; and

forming a power rail on the first surface of the substrate, the power rail being electrically connected to the contact plug.

12 . The method as claimed in claim 11 , wherein the isolation pattern and the alignment key include substantially the same material.

13 . The method as claimed in claim 11 , wherein the first trench defines an active pattern in the chip region of the substrate, and

wherein the isolation pattern is formed in a lower portion of the first trench, and covers a lower sidewall of the active pattern.

14 . The method as claimed in claim 11 , further comprising, prior to forming the first and second trenches, alternately and repeatedly stacking a sacrificial layer and a semiconductor layer on the second surface of the substrate,

wherein forming the first and second trenches in the chip region and the scribe lane region, respectively, includes partially removing the sacrificial layers, the semiconductor layers and portions of the substrate adjacent to the second surface of the substrate.

15 . The method as claimed in claim 14 , wherein replacing the dummy gate structure with the gate structure includes:

removing the sacrificial layers to form an opening; and

forming a gate insulation pattern and a gate electrode in the opening.