Download Application Note: Measurement of Dissolved Ozone in Flat Panel Display UPW Systems

THORNTON
Application Note
Leading Pure Water Analytics
Dissolved Ozone Measurement
In Flat Panel Display UPW Systems
Background
Ozonation of ultrapure water
Ozone (O3) is an unstable tri-atomic form of
oxygen. It is a very strongly oxidizing gas that is
injected into water to remove organics that may
contribute color, odor or taste. Most importantly,
ozone sanitizes the water, rapidly destroying any
microbiological contamination. Dissolved ozone
reverts back to harmless oxygen in a matter of
minutes, depending on the temperature and pH of
the water, so it must be generated and measured
right next to the process. Ozone leaves virtually
no harmful breakdown products.
Ozonation is used to disinfect and sanitize ultrapure water as it passes through final filtering and
distribution equipment. The goal is to control
bacteria levels of the ultrapure water transported
to the facility. Biological growth would generate
organics or particles that would detrimentally
affect product yields. Ozonation typically occurs
prior to the UPW storage tank, in the distribution
return piping, or may be diffused directly into the
storage vessel itself. Levels are typically maintained in the range 10 to 50 ppb but then must
be eliminated using ozone destructing UV light.
Ozone measurements are made to ensure proper
dosage control is maintained after injection and
then to ensure residual ozone is eliminated by UV
exposure. At this point any residual ozone
becomes an unwanted contaminant, which could
affect product yields. For this scenario, as
Figure A shows, there are two points of measurement required.
Ozone generators operate by passing dry air or
oxygen next to high voltage electrodes where a
corona discharge converts some of the oxygen to
ozone much as occurs in a lightning storm. That
gas mixture is then contacted with the water,
either in a tank diffusion system or in a pipe with
venturi injector. Intimate contact is made to maximize the dissolution. Other methods are designed
to prevent bubble formation during ozonation.
These methods have benefits in some flat panel
display applications, where the more conventional
methods for ozonating can cause artificially high
particulate counts or add excess oxygen. There
are also newer generation techniques that can
produce ozone directly in the water to reduce possible atmospheric losses.
Some wafer processes such as photoresist stripping and CMP (chemical mechanical polishing)
use dissolved ozone in the range of 10 to 30
ppm which is well above the range of measurement for Thornton’s dissolved ozone sensor. Other
technologies are more suitable.
Figure A - Flat panel display-grade ultrapure water system
Application Note
Feed
Water
Pump
Media
Filters
Activated
Carbon
2-Pass
Reverse
Osmosis
Break
Tank
Pump
PreFilters
Primary
Mixed Beds
UV
Sub-Micron
Filter
Ozone
Generator
Degassifier
To Points
of Use
Ultrafilter
Pump
UV
Dissolved Ozone
Sensor #2
Contact/Storage
Tank
Pump
Dissolved Ozone
Sensor #1
Dissolved Ozone Measurement
On-line monitoring and control of ozonation have
become standard practice where flat panel display
UPW systems have incorporated ozone treatment.
Dissolved ozone instrumentation is available
ranging from sophisticated high cost, maintenance-intensive equipment giving good performance to low cost, less reliable equipment with
flow sensitive readings. For measurements with
excellent performance, high reliability and infrequent simple maintenance at reasonable cost,
Mettler-Toledo Thornton offers dissolved ozone
measurement in a choice of multi-parameter
instrument platforms.
770MAX six-channel instrument
M300 two-channel instrument
The Mettler-Toledo Thornton 770MAX transmitter is a
well-accepted flat panel display industry standard. It
can measure from four sensors in any combination of
dissolved ozone, resistivity, flowrate, pH, ORP, dissolved
oxygen, TOC, pressure and level plus two additional
channels of flowrate. It provides unequaled flexibility
and value in satisfying measurement needs where multiple parameters and measurement points are required.
Mettler-Toledo Thornton M300 transmitters provide
two-channels of measurement of dissolved ozone,
resistivity, pH or ORP in any combination. This provides
a cost-effective choice where few measurement points
are required.
M800 multi-parameter transmitter
Mettler-Toledo Thornton M800 provides up to eight
measurements of pH/ORP, conductivity/resistivity, DO,
ozone and two for flow with touch-screen control and
predictive diagnostics capability.
www.mt.com/thornton
Visit for more information
Mettler-Toledo Thornton, Inc.
36 Middlesex Turnpike
Bedford, MA 01730 USA
Phone: +1-781-301-8600
Fax: +1-781-301-8701
Toll-Free: 1-800-510-PURE (US and Canada Only)
[email protected]
Subject to Technical Changes
© Mettler-Toledo Thornton, Inc.
AN-0128 Rev A 03/11