Semiconductor manufacture: A “battle with contamination”
Did you ever wonder why semiconductors and liquid crystal are made in cleanrooms? Theanswer is that the microscopic particles shed not only by people and manufacturing materials,
but by seemingly innocuous items such as notepads and pencils, interfere at the molecular levelwith the manufacture of liquid crystal and semiconductors, resulting in defective products.
For that reason, the process used for cleaning devices to remove particles and organic matterthat accrete during semiconductor or liquid crystal manufacturing is one of great importance.
However, wet cleaning with water or solvents cannot remove all organic matter at the molecularlevel, and cleaning by atmospheric-plasma jet entails risk of electrically damaging products. This
is where Ushio’s method of using ultraviolet for “cleaning by light” enters the equation.

PHOTOLEX UV cleaning system
Developed in 1983 as the world’s first
optical cleaning system. At the time, it
used a low-pressure UV lamp.

Cleaning by light?!
With light, energy capable of inducing chemical change increases in proportion to theshortness of the wavelength of light. This energy has the ability to disrupt the bonds between
molecules. It follows that VUV (vacuum ultraviolet), which has a wavelength even shorter than UV(ultraviolet) should be able to neutralize and remove organic contaminants by breaking themdown into harmless CO2 and H2O. This is the idea behind optical cleaning. This method makes it
possible to clean substrates without the possible effects of using water or solvents. Furthermore,since ultraviolet light carries no heat, it can be used without fear of harming heat-sensitive filmsor glass.

CExcimer VUV cleaning system
Introduced in 1994, the year following
development of the excimer lamp. Made it
possible to clean 10 times faster thanwith low-pressure UV lamps at a lowtemperature and consuming 1/3 thepower. Now made in lengths of up to 3meters.

In 1993, Ushio created an excimer lamp (a dielectric barrier discharge excimer lamp) that
became the world’s first commercial VUV lamp. Efficiently producing energy with a wavelength of172 nm, it was the first lamp capable of producing high speed photochemical reactions, Today, it
not only supports the quality and performance of many leading semiconductor and liquid crystal
production lines, but finds use in medicine and environmental applications.
* Excimer lamps are also used in the following applications.
Curing and Bonding (see page 26)
Healing with Light (see page 74)
Protecting with Light (see page 78)

leaning

Contamination at the molecular level can affect productperformance and quality. Consequently, with microfabrication ofsemiconductors at the micron and nano level, cleaning cancomprise up to a third of the overall production process.
Removing invisible contaminants with invisible light:
This is a cleaning process that is possible thanks to Ushio’s
optical technology.

“Cleaning with light” The Mechanism
VUV radiation is applied with an excimer lamp. As
the result:

Excimer VUV/O3
cleaning system(excimer lamp)① Ozone and active oxygen are generated.
② The direct action of VUV radiation breaks themolecular bonds of organic matter on thesubstrate.
These effects take place simultaneously,
breaking organic matter (contaminants) down
into water vapor and carbon dioxide, which isreleased to the atmosphere. This leaves thesurface of the substrate completely free ofcontaminants.

Atoms of oxygenO2 (oxygen)
H (hydrogen) Organicmatter
C (carbon)

172-nm VUV(vacuum ultraviolet)
irradiation acts directlyon oxygen
O3
Ozone generation
Adsorption anddecomposition ofCO2
organic matter onsubstrate

Organic matteron substrate(contamination)

Dispersion asgas and water vapor
H2O
CO2

Substrate

Oxidation of matter on substrate* Concept illustration of optical cleaning