The impossible machine
A lithography scanner prints each layer of a chip while the wafer moves. It has to be fast, because every wafer comes back to it layer after layer, and exact, because every layer has to land on the one below. Only ASML makes the extreme ultraviolet (EUV) scanners for the most intricate layers.
Fast or precise?
Anything heavy that moves fast overshoots and rings when it stops. Go slowly and land exactly, or go fast and wait for the ringing to die. The amber trace is the lens's path across the wafer.
A scanner prints while it moves, so the stage has to settle first. A Nikon patent application of 1997 works through settling times of 22 and 36 ms after accelerations of 3 and 4 g, and notes that a longer settling time leaves throughput "extremely deteriorated". 1 g is gravity's pull, 9.81 m/s².
Against the ringing, the makers name a counter mass (Nikon, 2005), learning control that keeps the 2 stages in step to 0.5 nm (Nikon, 2013), a neural-network stage control (Canon, 2022) and an EUV wafer stage that adjusts 20,000 times a second, to within a quarter of a nanometre (ASML).
Racing in opposite directions.
The optics shrink the reticle's image 4 times, or 8 times along the scan on ASML's High NA EXE, so the reticle travels 4 or 8 times as far as the wafer, the other way.
Nikon gives speeds: more than 500 mm a second for the wafer in 2005. ASML gives accelerations: the EXE's reticle stage at 32 g, 4 times the NXE's, in its words "the equivalent of a race car going from 0 to 100 km/h in 0.09 seconds".
Field by field.
A scanner prints a wafer field by field: a step, a scan, a stop. Nikon, Canon and ASML's NXE print fields of 26 × 33 mm; ASML's High NA EXE prints half fields, 26 × 16.5 mm, so a wafer takes "twice as many exposures" (ASML). How many depends on which edge fields count.
Wafers an hour, as stated: ASML EXE:5200B ≥ 175 and NXE:3800E ≥ 220, at 50 and 30 mJ/cm²; Nikon NSR-S636E ≥ 280 and Canon FPA-6300ES6a with Grade 10 300, at 96 fields.
Landing on the layer below.
Every layer has to land on the one printed before it, often by another scanner, days earlier. The error is called overlay. Between 2 machines, ASML specified 1.1 nm for its NXE:3600D EUV scanner in 2022; Nikon specifies 2.1 nm or better for its NSR-S636E. Canon gives 4 nm on a single KrF machine, a different measure. The readouts name each maker's tightest figure the error meets.
A wafer over 100 km across.
Blow everything up until a scanner's overlay figure becomes 1 mm, and keep its pace: every line still lands within about 1 mm of where the layer below expects it. Each machine is a composite of its maker's figures.
At Nikon's scale, its wafer speed of 2005, more than 500 mm a second, becomes 238 km a second. ASML states no scan speed.
A sprinter in a slow factory.
Semiconductor Engineering reported in 2017 that a fab takes 1 to 1.5 days a layer; Robert Leachman of UC Berkeley told it a wafer spends one minute under the scanner. Our arithmetic: 0.05 to 0.07% of its time. Nikon says the loop repeats several tens of times: pick the layers.
The SIA gives about 12 weeks a finished wafer, 14 to 20 for advanced processes. TSMC's 2009 contract set a target of 1.0 to 1.4 days a layer on 200 mm processes, with commercially reasonable efforts.
Fast, still, and exact.
Each figure on this page names its publisher in its card, or is our arithmetic. The machine drawn is a generic scanner, cut open, not any company's design; the figures beside it are ASML's, Nikon's and Canon's, each for its own machines.
Scanner makers on this record: ASML, Canon, Nikon and SMEE. ASML is the only one of them that makes EUV scanners.