PC Gamer - UK 2020-04)

F

ormanydecadesnowwe’vebeenmelting

sandandmakingit think.Thecurrent

photolithography process for making

microchips, such as the CPU and GPU

inside your PC, dates back to around 1977,

and involves painting light-sensitive chemicals onto a

wafer of silicon, then shining UV lasers through a mask

so that they mark the chip’s pathways into the

chemical, then a bath in something nasty that dissolves

the top layer of silicon not protected by photoresist.

The process has been evolving, but now it’s starting to

reach the end of its useful life.

Why? Because chip pathways are, if you believe the PR

exhalations of chip manufacturers, now as small as 7nm

across. They’re not, of course, as the nanometre

measurements are more like marketing terms these days and

don’t represent any part of the chip size, they’re just a naming

convention that has stuck.

They are, however, really, really small, and 7nm represents

a shrinkage over the previous technology node, 10 or 14nm.

Gate sizes also differ between manufacturers, but for the

10nm process are usually in the range of 30-40nm.

The single crystal of silicon the chips are etched into is

another marvel, but its discovery dates back to 1916, when a

Polish chemist called Jan Czochralski, studying the

crystallisationratesofmetals,dippedhispenintoa crucibleof

moltentinratherthantheinkwellhewasaimingfor.Thepen

sucked up the tin, and the filament produced was shown to be

a single crystal. Later experiments showed that by doing

something similar you can create industrial quantities of

single-crystal semiconductors.

As technology nodes shrink, transistor gate density

increases, chip manufacture gets harder and new processes

are needed to keep up. Enter Extreme Ultraviolet Lithography,

the process being used for some 7nm chips as the current

Deep Ultraviolet Lithography process is wound up, and which

will become standard as we enter the worlds of 5nm and even

3nm. The wavelength of ultraviolet light runs from about

400nm down to 10nm, spanning the gap between visible light

and X-rays in the electromagnetic spectrum. The extreme

ultraviolet is considered to be anything with a wavelength less

than 124nm, and it’s a difficult type of light to emit.

Firstly, you need charged particles – ions – as neutral

matter cannot emit EUV light. Such ionised matter is

commonly known as a plasma, but there’s a catch – plasma

absorb EUV light and, due to electrons in the plasma

neutralising the ions, a great deal of other light is produced.

This means that the lasers used to create the plasmas need to

be much more intense than for previous processes.

From the laser-pumped tin plasma that is commonly used

to create the EUV light for chip manufacture, as little as two

One problem

with EUV light is

it’s readily

absorbed by just

about anything,

be it lenses,

mirrors, or

plasma.

Researchers at

Germany’s

Max-Born-

Institut think

they’ve cracked

it, by making a

lens out of jets of

helium or argon

that can focus

and bend the

light depending

on how dense

they are, without

absorbing it.

Gas

len se s

TO THE EXTREME!

Newchipmanufacturingmethodsgivesmallerandsmallerresults

A worker inspects a

wafer at one of

TMSC’s 12in wafer

fabrication plants.

Image credit: Taiwan Semiconductor Manufacturing Co.

TECH

REPORT