Product Briefing Outline: Entegris has introduced its
‘LiquidLens' ultrapure water (UPW) purification system that is designed
specifically for 193nm ArF immersion lithography systems. The
sub-system combines advanced technology and process expertise from both
Entegris and the former Mykrolis as a result of their merger in August
2005 to tackle high-purity issues associated with the needs of
immersion lithography.
Problem: Immersion is the newest lithography
technique for printing 45nm or smaller features on semiconductor
wafers, using ultra pure water between the optical lens and the wafer.
The UPW lens is utilized to significantly improve image resolution. The
water must be extremely pure as the smallest impurity can damage image
resolution, react with the photoresist. Ensuring ultrapure, consistent
water quality also preserves optic's life by controlling contaminants
at the point of use such as dissolved gases, micro bubbles and
particles.
Solution: Important factors in
designing an ultrapure water system for immersion lithography is the
selection of high purity, inert construction materials and the
integration of purification techniques in an optimal sequence. It is
important to deliver a stable DI flow precisely/repeatedly to the
illuminated area to prevent any bubble attachment on the wafer or the
lens during the filling process. The current flow rate control required
is in the range from 0.4 to 3 LPM at steady state with slower flow rate
at initial fill, to ensure complete filling under the lens, followed by
a faster rate during scanning to ensure byproduct removal and meniscus
integrity during stage movement. The contaminants to be removed from
the UPW system include dissolved gases and bubbles, particles, total
oxidizable carbon (TOC) and non-volatile residue (NVR), and ionic and
organic extractables that are added from the process materials and
piping components. Temperature control is also very important to ensure
constant optical properties (refractive index) and to ensure constant
physical properties (e.g. density, surface tension and gas solubility).
A ‘pHasor' II membrane contactor ensures the process water is free of
bubbles by delivering high dissolved gas concentrations with a low
pressure drop over the fluid path. Two UV lamps break down TOC levels
in the water while an ion exchange purifier removes the organics,
ensuring a high purity fluid stream. These elements are linked to an
advanced process control unit that monitors critical parameters,
providing 48-hour rolling trend data with configurable warning and
error alarms.
Applications: 193nm ArF immersion lithography systems.
Platform:
Incorporates a ‘Durapore' 0.02 µm filter in a ‘Chemlock housing'. The
high zeta potential PVDF membrane filter is ideally suited for water
applications and the Chemlock housing preserves space while reducing
cost of ownership, according to the company. LiquidLens UPW
purification systems are built to customer specifications and
individually quoted.
Availability: July 2006 onwards