what do the nm or µm for a process technology refer to e.g 22nm process technology for device fabrication

Question

There are many "process technologies" that exist to fabricate circuits on silicon. They are mainly differentiated based on size of some feature. Here is the list of them:

10 µm – 1971
3 µm – 1975
1.5 µm – 1982
1 µm – 1985
800 nm – 1989
600 nm – 1994
350 nm – 1995
250 nm – 1997
180 nm – 1999
130 nm – 2002
90 nm – 2004
65 nm – 2006
45 nm – 2008
32 nm – 2010
22 nm – 2012
14 nm – 2014
10 nm – est. 2015
7 nm  – est. 2017
5 nm – est. 2019

What I wish to know is, what precisely do these numbers refer to e.g the 90nm that was reached in 2004, what does it precisely mean?

I think it has to do with some dimension of the transistor that is fabricated but do not know the details. So what does it mean?

Answer 1

The nanometer number on memory chips generally refers to the smallest "half-pitch" between identical features on the chip, as in this illustration from an IEEE article.

By this definition, a fairly fine-pitch PCB with 0.004" traces and spaces would be defined as 100 micron (100,000nm).

On microprocessors, it refers to the "node number" (the smallest feature). A CPU with a 32nm node might have a 50~56nm half-pitch, and a 22nm chip might have a 34nm half-pitch.

Answer 2

It refers to half the distance between neighbouring details on the die (ie between two CMOS)

Answer 3

Those are standard units, not specific to electronics or semiconductor manufacturing.

The "m" stands for meter, and the letter before it is one of the standard prefixes denoting a power of 1000. Here are some common prefixes:

Prefix  Name        Multiplier
------  ----------  ----------
     G  Giga        109
     M  Mega        106
     k  Kilo        103
     m  milli       10-3
     µ  micro       10-6
     n  nano        10-9
     p  pico        1012

So "22 nm", for example, means "22 nano-meters". This is the minimum feature size of that technology.