20
FILTRATION
Breakthrough chemical analysis of
HMDS reveals a solution for the
prevention of lens hazing
One industry objective is to identify the most effective solution for lens hazing.
Donaldson discusses recent efforts in developing understanding of a comparison of
HMDS to TMS/HMDSO chemistry process in ambient air. Results suggest that
layering technology and BSMmax filters effectively remove TMS, NH
3
and HMDSO.
acid impregnated carbons are effective at removing
ammonia and also catalysing the dimerisation of
TMS to the less volatile and easily removed.
In recent years as the industry has moved from
248nm lithography tools to higher powered 193nm
tools, a new and costly problem emerged for
semiconductor processors: molecular
contamination on the optics (lens hazing). Because
progress in one area almost always prompts new
concerns in another, Donaldson has applied its
more than 90 years of filtration expertise to learn
about this challenge and discover a solution. With
so much at stake, costly lens replacement along
with lost time and productivity Donaldson’s
Figure 1: HMDS in air network of engineers delved into the problem to
at 25ºC and 50%
I
gain an understanding of the undefined chemistry
relative humidity issues involved with both ammonia and organics.
yields TMS and NH
3
t is necessary to focus on the hydrolysis
products of HMDS to ensure adequate While previous studies
1
have attempted to
removal of volatile siloxane compounds. unlock the mystery behind lens hazing, this
We have shown that the hydrolysis of HMDS Donaldson study is the first of its kind to reveal
predominantly creates TMS and ammonia, and analysis of the adsorption of HMDS, HMDSO and
layered adsorbents can effectively remove these TMS in semiconductor facilities. Through greater
compounds. Activated carbon or carbon understanding of the chemistry involved, Donaldson
impregnated with a base for the removal of acids creates superior processing environments with its
are very effective at removing hydrocarbons and advanced, cost effective filtration solution:
siloxanes such as TMS or HMDSO. Furthermore, BSMmax filters.
www.euroasiasemiconductor.com September 2008
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