How Are Process Nodes Defined?

We talk a lot about process nodes at ExtremeTech, but we don’t often refer back to what a process node technically is. With Intel’s 10nm node now in production and TSMC + Samsung talking about future 5nm and 3nm nodes, it’s a good time to revisit the topic, particularly the question of how TSMC and Samsung compare to Intel.

Process nodes are typically named with a number followed by the abbreviation for nanometer: 32nm, 22nm, 14nm, etc. There is no fixed, objective relationship between any feature of the CPU and the name of the node. This was not always the case. From roughly the 1960s through the end of the 1990s, nodes were named based on their gate lengths. This chart from IEEE shows the relationship:

For a long time, gate length (the length of the transistor gate) and half-pitch (half the distance between two identical features on a chip) matched the process node name, but the last time this was true was 1997. The half-pitch continued to match the node name for several generations but is no longer related to it in any practical sense. In fact, it’s been a very long time since our geometric scaling of processor nodes actually matched with what the curve would look like if we’d been able to continue actually shrinking feature sizes.

If we’d hit the geometric scaling requirements to keep node names and actual feature sizes synchronized, we’d have plunged below 1nm manufacturing six years ago. The numbers that we use to signify each new node are just numbers that companies pick. Back in 2010, the ITRS (more on them in a moment) referred to the technology chum bucket dumped in at every node as enabling “equivalent scaling.” As we approach the end of the nanometer scale, companies may begin referring to angstroms instead of nanometers, or we may simply start using decimal points. When I started work in this industry it was much more common to see journalists refer to process nodes in microns instead of nanometers — 0.18-micron or 0.13-micron, for example, instead of 180nm or 130nm.

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