Single VIA, VIA array, Stacked VIA

A via forms a connection between overlapping geometries on different layers through a cut layer, and is formed by geometries on all three layers.
Three types of vias:

1. a single via,
2. an array via,
3. and a stacked via.

1) Single VIA

Below diagram help you to understand how single VIA are placed between 2 metal and help them to connect them.
2D /Top view with different arrangement (also known as Layout View)

3D view (Help you to understand connection more closely).

Figure 3D_b is a transparent view of the 3D_a. It helps you to understand how different layers are connected with each other.

Side View of Via and Metal connection.

There are certain Design rules for VIAs also. I am not going to capture those in detail here but below figure give you a general idea.

Vias can be asymmetric, meaning the overhangs in the x and y directions are different. The overhang parameters refer to those of a via connecting preferred-direction wires. If the wires are in the nonpreferred direction, the via is rotated and the overhangs are reversed, meaning that the extensions in the x direction are given by the y overhang parameters.

2) VIA Array

Array vias are used for connecting wide wires where the required cut size would exceed the maximum cut size of the simple via. In an array via, the region of intersection of the wires is filled by a regular array of small cuts of fixed size and separation.

2D /Top view with and without preferred direction of Metal arrangement (also known as Layout View)

3D view (Help you to understand connection more closely).

Figure 3D_b is a transparent view of the 3D_a. It helps you to understand how different layers are connected with each other. you can also see that array size is 3x1 between M1 and M2. When it comes to M2 and M3, Single VIA connects both the wire. But dnt think that it will always be the case. It depends on design that and width of Metal wire, if you want to use VIA array or Single VIA. In the below figure, you can see that M1 and M2 are using 3x3 VIA array. Between M2 and M3 - it's 1x3 VIA array.

3) Stack VIA

3D view (Help you to understand connection more closely).

2D view of Stack via is not easy to understand. But if you want to try, you can do it in any tool to understand properly.

I can summarize this article with combined view of all 3 type of VIAs.