U.S. patent application number 11/438453 was filed with the patent office on 2006-09-21 for real-time component monitoring and replenishment system for multicomponent fluids.
Invention is credited to Todd Aycock, Joseph W. Evans, Thomas Kloffenstein, Russell Stevens.
Application Number | 20060211129 11/438453 |
Document ID | / |
Family ID | 26950525 |
Filed Date | 2006-09-21 |
United States Patent
Application |
20060211129 |
Kind Code |
A1 |
Stevens; Russell ; et
al. |
September 21, 2006 |
Real-time component monitoring and replenishment system for
multicomponent fluids
Abstract
A multicomponent fluid composition monitoring and compositional
control system, in which a component analysis is effected by
titration or other analytical procedure, for one or more components
of interest, and a computational means then is employed to
determine and responsively adjust the relative amount or proportion
of the one or more components in the multicomponent fluid
composition, to maintain a predetermined compositional character of
the multicomponent fluid composition. The system is usefully
employed in semiconductor manufacturing photoresist and post-etch
residue removal, in which the cleaning medium is a semi-aqueous
solvent composition, and water is the monitored and responsively
adjusted component.
Inventors: |
Stevens; Russell; (Austin,
TX) ; Kloffenstein; Thomas; (Morgan Hill, CA)
; Aycock; Todd; (Austin, TX) ; Evans; Joseph
W.; (Oak Park, IL) |
Correspondence
Address: |
INTELLECTUAL PROPERTY / TECHNOLOGY LAW
PO BOX 14329
RESEARCH TRIANGLE PARK
NC
27709
US
|
Family ID: |
26950525 |
Appl. No.: |
11/438453 |
Filed: |
May 22, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10264408 |
Oct 4, 2002 |
|
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11438453 |
May 22, 2006 |
|
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60328151 |
Oct 8, 2001 |
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Current U.S.
Class: |
436/173 |
Current CPC
Class: |
H01L 21/67253 20130101;
H01L 21/67017 20130101; Y10T 436/24 20150115; G05D 11/138 20130101;
Y10T 436/117497 20150115; G05D 21/02 20130101; Y10T 436/116664
20150115 |
Class at
Publication: |
436/173 |
International
Class: |
G01N 24/00 20060101
G01N024/00 |
Claims
1. A multicomponent fluid composition monitoring and compositional
control system, said monitoring and compositional control system
comprising: (a) a tank containing the multicomponent fluid
composition; (b) a recirculating system, wherein said
multicomponent fluid composition is withdrawn from the tank and
circulatingly flowed through at least a pump and a filter and
returned to the tank; (c) an analyzer unit comprising a sampling
system and a reagent dispensing system, wherein said analyzer unit
is constructed and arranged to monitor concentration of at least
one component of the multicomponent fluid using a real-time
methodology comprising spectroscopic analysis of near-infrared
frequency fluctuation; (d) a by-pass loop positioned downstream of
the pump and the filter, wherein the multicomponent fluid is bled
from the recirculating system to the analyzer unit for analysis
therein; and (e) a control unit, constructed and arranged to
compare the results of the real-time methodology to pre-programmed
specifications and responsively control dispensing of said at least
one component from a source of said component into the
multicomponent fluid using the reagent dispensing system to
maintain the concentration of said at least one component in the
multicomponent fluid, wherein the multicomponent fluid is utilized
in a fluid-using processing facility.
2. The system of claim 1, wherein said processing facility
comprises a semiconductor manufacturing facility.
3. The system of claim 2, wherein the semiconductor manufacturing
facility comprises a process selected from the group consisting of
etching, chemical mechanical planarization (CMP), photolithography,
chemical vapor deposition, spin-on coatings application,
supercritical fluids cleaning operations, wafer solvent drying
operations, and photoresist and post-etch residue removal.
4. The system of claim 1, wherein the multicomponent fluid
comprises a semi-aqueous solvent medium.
5. The system of claim 1, wherein the control unit includes
computational means and a display for visual observation of
outputted data of the unit.
6. A multicomponent fluid composition monitoring and compositional
control system, said monitoring and compositional control system
comprising: (a) an analyzer unit comprising a sampling system and a
reagent dispensing system, wherein said analyzer unit is
constructed and arranged to monitor concentration of water in the
multicomponent fluid using a real-time methodology selected from
the group consisting of a Karl Fischer titration, measurement of
multicomponent fluid conductivity, and ultrasonic energy response
of the multicomponent fluid; and (b) a control unit, constructed
and arranged to compare results of the real-time methodology to
pre-programmed specifications and responsively control dispensing
of water from a source of water into the multicomponent fluid using
the reagent dispensing system to maintain the concentration of
water in the multicomponent fluid, wherein: the multicomponent
fluid is utilized in a fluid-using processing facility; and the
sampling system is arranged to capture a sample deriving from a
flow stream of said multicomponent fluid.
7. The system of claim 6, wherein said processing facility
comprises a semiconductor manufacturing facility.
8. The system of claim 7, wherein the semiconductor manufacturing
facility is adapted to conduct a process selected from the group
consisting of etching, chemical mechanical planarization (CMP),
photolithography, chemical vapor deposition, spin-on coatings
application, supercritical fluids cleaning operations, wafer
solvent drying operations, and photoresist and post-etch residue
removal.
9. The system of claim 8, wherein the semiconductor manufacturing
facility is adapted to conduct a process for photoresist and
post-etch residue removal.
10. The system of claim 6, wherein the multicomponent fluid
comprises a semi-aqueous solvent medium.
11. The system of claim 6, wherein the multicomponent fluid
comprises water and organic solvent components.
12. The system of claim 6, wherein the semi-aqueous solvent medium
comprises water and a photoresist stripping solvent.
13. The system of claim 6, wherein the sampling system is arranged
to capture a sample from a by-pass loop of a flow stream of said
multicomponent fluid.
14. The system of claim 6, wherein the real-time methodology
comprises the measurement of multicomponent fluid conductivity.
15. The system of claim 6, wherein said analyzer unit further
comprises a bath of said multicomponent fluid from which sampling
is conducted using the analyzer unit, and from which fluid is
withdrawn from and flowed to the fluid-using processing
facility.
16. The system of claim 6, wherein the analyzer unit is constructed
and arranged to conduct a Karl Fischer titration of the fluid
withdrawn from the bath.
17. The system of claim 6, wherein the pre-programmed
specifications include volume of the bath being monitored,
frequency of monitoring and a titration calculation factor for
calibration.
18. The system of claim 6, comprising a source of titration
reagent(s) for conducting the Karl Fischer titration.
19. The system of claim 6, comprising a dryer adapted for
conducting pre-titration drying of at least one reagent for
conducting the Karl Fischer titration.
20. The system of claim 6, further comprising a constant-current
module adapted for detection of the endpoint of the Karl Fischer
titration.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates generally to a real-time fluid
monitoring and concentration control system for maintaining
concentration of one or more selected species in multicomponent
fluids at a desired level, e.g., in a range defining effective or
optimal operation.
[0003] 2. Description of the Related Art
[0004] In the field of semiconductor manufacturing, a number of
multicomponent fluids are employed to carry out process operations,
including etching, chemical mechanical planarization (CMP),
photolithography, chemical vapor deposition, spin-on coatings
application, supercritical fluids cleaning operations, wafer
solvent drying operations, to name a few.
[0005] In many of these process steps, the relative concentrations
or proportions of various components in the multicomponent process
fluid must be maintained at a predetermined value or within a
selected range, in order to achieve satisfactory results and avoid
the necessity of rework or discarding of defective semiconductor
device structures, including finished devices as well as precursor
structures thereof.
[0006] By way of specific example, in semiconductor manufacturing
operations of photolithography and etch processes, various solvents
are employed for photoresist and post-etch residue removal.
[0007] Photoresist compositions are solvent-based, light-sensitive
solutions, which are uniformly applied to a semiconductor wafer and
then processed to leave a selected pattern of cured photoresist on
the wafer after development. Etching then is carried out, wherein
reactive gases or liquids are used to remove undesired material
from the wafer surface, in the areas where the material is not
protected by the cured photoresist.
[0008] During etching, various chemical complexes are formed or
remain on horizontal and vertical surfaces of the structures being
delineated. At the completion of the etch process, these complexes
are no longer necessary and need to be removed, together with any
remaining cured or uncured photoresist. This is typically
accomplished using a mixture of fluids in gaseous, liquid or
supercritical state or a combination thereof. Solvent mixtures used
for the liquid removal of the cured photoresist and post-etch
residues from the wafer include both acidic as well as basic
solvent compositions.
[0009] The ability of the solvent chemistry to remove the cured
photoresist and post-etch residues is strongly dependent on the
ratios of its components. In addition, many solvent components
require an elevated operating temperature to be effective. However,
in solvent systems where water is a component, heating the solvent
causes the water to evaporate. If not enough water is present in
these solvent systems, then the solvent can become ineffective.
Conversely, if too much water is present, damage may occur to
exposed surfaces on the wafer. Therefore, an out-of-specification
solvent mixture can result in severe damage to the wafers and/or a
failure to remove undesired materials such as the photoresist or
etch-generated residues.
[0010] In addition to process instability, significant costs can be
incurred due to the limited lifetime of these solvent mixtures.
These can variously include: costs of the chemicals; costs
associated with equipment downtime reducing the production
efficiency of the manufacturing facility; costs associated with an
incremental and/or catastrophic yield loss due to device parametric
failures of defective wafers resulting from use of
out-of-specification chemicals, and disposal costs of the high
volumes of required chemicals.
[0011] The problems attendant the use of out-of-specification
multicomponent solvent compositions in removal of photoresist and
post-etch residues are illustrative of the difficulties encountered
in many industrial processes in which compositional uniformity of a
multicomponent fluid composition is critical to meeting process
objectives and commercial viability.
[0012] The foregoing provides a background to the advance of the
present invention, as described more fully hereinafter.
SUMMARY OF THE INVENTION
[0013] The present invention relates in one aspect to a
multicomponent fluid composition monitoring and compositional
control system, in which a component analysis is effected by
titration or other analytical procedure, for one or more components
of interest, and a computational means then is employed to
determine and responsively adjust the relative amount or proportion
of the one or more components in the multicomponent fluid
composition, in order to maintain a predetermined compositional
character of the multicomponent fluid composition.
[0014] In a further specific aspect, the multicomponent fluid
composition monitoring and compositional control system is utilized
in a fluid-using processing facility, and arranged for real-time
component analysis of the multicomponent fluid, with the
computational means determining and responsively adjusting the
relative amount or proportion of the component(s) in the
multicomponent fluid composition, in real time, to maintain the
predetermined compositional character of the multicomponent fluid
composition in the fluid-using processing facility.
[0015] A further aspect of the invention relates to a fluid
utilization and management system, comprising a fluid-using
processing facility using a multicomponent fluid, and a fluid
monitoring and concentration control system for maintaining
concentration of one or more selected species in the multicomponent
fluid at a desired level for use of the multicomponent fluid in the
fluid-using processing facility, wherein the fluid monitoring and
concentration control system comprises (i) an analyzer unit,
constructed and arranged to monitor the concentration of one or
more components of the multicomponent fluid using a real-time
methodology, and (ii) a control unit constructed and arranged to
compare the results of the analyzer unit to pre-programmed
specifications and responsively control dispensing of the
aforementioned one or more components into the multicomponent fluid
as required to maintain a predetermined concentration of the
aforementioned one or more components in the multicomponent fluid
used in the fluid-using processing facility.
[0016] A further aspect of the invention relates to a system for
generating hydrogen peroxide at a point of use comprising a
hydrogen peroxide-using processing facility, such system comprising
an electrochemical cell constructed and arranged for generating
hydrogen peroxide, and a hydrogen peroxide monitoring and
concentration control assembly including a Karl Fischer analysis
unit comprising means for sampling fluid from the electrochemical
cell and analyzing same by Karl Fischer analysis, wherein the
hydrogen peroxide monitoring and concentration control assembly
includes a source of titration agent for the Karl Fischer analysis,
and means for real-time determination of concentration of the
hydrogen peroxide based on the Karl Fischer analysis.
[0017] Yet another aspect of the invention relates to a system for
generating hydroxylamine at a point of use comprising a
hydroxylamine-using processing facility, such system comprising an
electrochemical cell constructed and arranged for generating
hydroxylamine, and a hydroxylamine monitoring and concentration
control assembly including a Karl Fischer analysis unit comprising
means for sampling fluid from the electrochemical cell and
analyzing same by Karl Fischer analysis, wherein the hydroxylamine
monitoring and concentration control assembly includes a source of
titration agent for the Karl Fischer analysis, and means for
real-time determination of concentration of the hydroxylamine based
on the Karl Fischer analysis.
[0018] A still further aspect of the invention relates to a system
for generating an active reagent selected from hydroxylamine and
hydrazine at a point of use including a semiconductor manufacturing
facility arranged for use of the active reagent, in which the
system includes (i) means for electrochemical generation of the
active reagent at the point of use, (ii) means for simultaneous
real-time process monitoring of the concentration of these
chemicals both in the electrochemical cell and at the point of use,
such means (i) and (ii) including a Karl Fisher electrochemical
cell platform for both the generation and monitoring of the active
reagent.
[0019] In another aspect, the invention relates to a multicomponent
fluid composition monitoring and compositional control system,
including means for performing component analysis of the
multicomponent fluid by titration or other analytical procedure,
for one or more components of interest, and computational means
constructed and arranged to determine and responsively adjust the
relative amount or proportion of the one or more components in the
multicomponent fluid composition, to maintain a predetermined
compositional character of the multicomponent fluid
composition.
[0020] In another aspect, the invention relates to a process of
monitoring and compositionally controlling a multicomponent fluid
used in a processing facility, such process including conducting a
real-time component analysis of the multicomponent fluid by
titration or other analytical procedure, for one or more components
of interest, and computationally and responsively adjusting in real
time the relative amount or proportion of the one or more
components in the multicomponent fluid composition, to maintain a
predetermined compositional character of the multicomponent fluid
composition utilized in the fluid-using processing facility.
[0021] Another aspect of the invention relates to a fluid
utilization and management process, including providing a
fluid-using processing facility using a multicomponent fluid, and
maintaining concentration of one or more selected species in the
multicomponent fluid at a desired level for use of the
multicomponent fluid in the fluid-using processing facility, by
monitoring the concentration of one or more components of the
multicomponent fluid using a real-time methodology, and comparing
the results of the methodology to preestablished specifications and
responsively controlling dispensing of said one or more components
into the multicomponent fluid as required to maintain a
predetermined concentration of the aforementioned one or more
components in the multicomponent fluid used in the fluid-using
processing facility.
[0022] In yet another aspect, the invention relates to a process
for generating hydrogen peroxide at a point of use including a
hydrogen peroxide-using processing facility, such process including
generating hydrogen peroxide in an electrochemical cell, and
monitoring hydrogen peroxide in a Karl Fischer analysis unit
including sampling fluid from the electrochemical cell and
analyzing same by Karl Fischer analysis, titrating hydrogen
peroxide in the sampling fluid with titration agent in the Karl
Fischer analysis, and determining in real time the concentration of
the hydrogen peroxide based on the Karl Fischer analysis.
[0023] A further aspect of the invention relates to a process for
generating hydroxylamine at a point of use including a
hydroxylamine-using processing facility, such process including
generating hydroxylamine in an electrochemical cell, and monitoring
and controlling concentration of the hydroxylamine, including
sampling fluid from the electrochemical cell and analyzing same by
Karl Fischer analysis, wherein the hydroxylamine monitoring and
concentration control steps include real-time determination of
concentration of the hydroxylamine based on the Karl Fischer
analysis.
[0024] Yet a further aspect of the invention relates to a process
for generating an active reagent selected from hydroxylamine and
hydrazine at a point of use including a semiconductor manufacturing
facility arranged for use of the active reagent, such process
including (i) electrochemically generating the active reagent at
the point of use, (ii) simultaneously monitoring concentration of
the active reagent in real time, both in the electrochemical cell
and at the point of use, using a Karl Fisher electrochemical cell
platform for both the generation and monitoring of the active
reagent.
[0025] Another aspect of the invention relates to a multicomponent
fluid composition monitoring and compositional control process,
including performing component analysis of the multicomponent fluid
by titration or other analytical procedure, for one or more
components of interest, and computationally determining and
responsively adjusting the relative amount or proportion of the one
or more components in the multicomponent fluid composition, to
maintain a predetermined compositional character of the
multicomponent fluid composition.
[0026] Other aspects, features and embodiments of the invention
will be more fully apparent from the ensuing disclosure and
appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] FIG. 1 is a schematic representation of a fluid component
monitoring and concentration maintenance system according to one
embodiment of the invention.
[0028] FIG. 2A is a schematic representation of the fluid component
monitoring and concentration maintenance system of FIG. 1, as
wall-mounted in a semiconductor manufacturing facility utilizing
wall mounting brackets.
[0029] FIG. 2B is a schematic representation of a fluid component
monitoring and concentration maintenance system according to a
second embodiment of the invention utilizing a single,
self-contained cabinet for mounting the system, in which the
cabinet optionally may be equipped with wheels to facilitate
relocation as a mobile system within a semiconductor manufacturing
facility or alternatively the cabinet may be fabricated without
wheels to provide a semi-permanent installed system that is fixedly
positioned in the semiconductor manufacturing facility.
[0030] FIG. 3 shows an illustrative arrangement of the fluid
component monitoring and concentration maintenance system with a
fast loop recirculating bath arrangement utilizing the wall-mounted
embodiment of the invention.
[0031] FIG. 4 shows an illustrative arrangement of the fluid
component monitoring and concentration maintenance system deployed
in a non-recirculating bath configuration.
[0032] FIG. 5 shows the Wet Chemistry Module with respective fluid
lines.
[0033] FIG. 6 depicts the Sign-On Screen that appears when the
fluid component monitoring and concentration maintenance system is
turned on or after reset.
[0034] FIG. 7 depicts the Setup Screen 1, Analyzer
Sequencer/Methods for the fluid component monitoring and
concentration maintenance system.
[0035] FIG. 8 depicts a typical sequence section showing the use of
the conditional IF, for the fluid component monitoring and
concentration maintenance system.
[0036] FIG. 9 shows the Setup Screen 2, Analog Outputs and Relay
Set Points, for the fluid component monitoring and concentration
maintenance system.
[0037] FIG. 10 shows the Setup Screen 3, Calibration Data/Trigger,
for the fluid component monitoring and concentration maintenance
system.
[0038] FIG. 11 shows the Setup Screen 4, Analysis Timing, for the
fluid component monitoring and concentration maintenance
system.
[0039] FIG. 12 shows a screen representative of Setup Screens 5 and
7, Endpoint Parameters, for the fluid component monitoring and
concentration maintenance system.
[0040] FIG. 13 shows a screen representative of Setup Screens 6 and
8, Analysis Control, for the fluid component monitoring and
concentration maintenance system.
[0041] FIG. 14 shows a curve illustrating the values defined within
the Setup Screens 5-8 of FIGS. 12 and 13.
[0042] FIG. 15 shows Service Screen 1, for the fluid component
monitoring and concentration maintenance system.
[0043] FIG. 16 shows Service Screen 2, for the fluid component
monitoring and concentration maintenance system.
[0044] FIG. 17 shows the first Data Screen, for the fluid component
monitoring and concentration maintenance system.
[0045] FIG. 18 shows the second Data Screen, for the fluid
component monitoring and concentration maintenance system.
[0046] FIG. 19 shows the Run Screen, for the fluid component
monitoring and concentration maintenance system.
[0047] FIG. 20 shows a screen appearing after the analyzer has
started its analysis sequence, indicating the current step ("S1")
in the analysis sequence underneath the time.
[0048] FIG. 21 shows a screen appearing once the analysis is
completed, identifying a water concentration, as a number of
milliliters of titrant required to reach the endpoint.
[0049] FIG. 22 shows a real-time analysis curve 1, displaying a
rapid change in sensor mV suggesting a lack of sample.
[0050] FIG. 23 shows a real-time analysis curve 2, exhibiting a
"flat" sensor response whose cause, if the sensor mV is in an
unexpected range, may indicate a faulty sensor, connection, pre-amp
or other electronic fault, or, if the sensor mV remain in the
normal pre-endpoint range, may indicate that reagent is not
reaching the reaction vessel.
[0051] FIG. 24 shows a real-time analysis curve 3, reflecting a
scenario that usually occurs when the endpoint interpretation
parameters have been changed within the Setup Screens, but the
chemistry remains the same, indicating that the Setup parameters
should be carefully reviewed, or that a sensor that has drifted out
of the normal endpoint window and should be cleaned or replaced as
necessary.
[0052] FIG. 25 shows a Run Screen appearing after an analysis is
completed, displaying an [OPTIMIZE] menu option allowing for the
optimization of the endpoint and the minimum and maximum increments
used.
[0053] FIG. 26 shows an Optimize Screen, allowing the selection of
the endpoint with the greatest gradient (strongest point of
inflection), and thus optimization of the endpoint and increments
to invariably find this endpoint.
[0054] FIG. 27 shows an apparatus for the generation of hydrogen
peroxide and monitoring of same, utilizing a Karl Fischer analysis
tray.
[0055] FIG. 28 is a graph of titrant volume as a function of
titration cycles using ceric ammonium sulfate, and showing the
reproducibility of 2.5% peroxide determination.
DETAILED DESCRIPTION OF THE INVENTION, AND PREFERRED EMBODIMENTS
THEREOF
[0056] The present invention provides a multicomponent fluid
monitoring and replenishment system for measuring one or more
components of the multicomponent fluid, e.g., a solvent mixture,
and providing correlative quantitative feedback for on-line
chemistry control, to facilitate real-time correction of the
composition and stable control of the fluid process.
[0057] Although described primarily and illustratively hereafter
with reference to semiconductor manufacturing removal of
photoresist and post-etch residue from semiconductor device
structures by multicomponent solvent mixtures including water and
organic solvent(s) forming a semi-aqueous solvent composition, the
invention will be recognized as having broad applicability to a
wide variety of multicomponent fluid operations, in which it is
essential to maintain the compositional character of the
multicomponent fluid composition at a specific value or within a
specific range, in respect of the relative concentrations and
proportions of components in the fluid composition. Thus, the
invention may be employed in specific embodiments for monitoring
and compositionally controlling non-aqueous fluid compositions.
[0058] Accordingly, the ensuing discussion will be directed
illustratively to a solvent monitoring and replenishment system
according to the invention, which has been found to be particularly
suitable for controlling solvent processes such as photoresist and
post-etch residue removal, in which maintenance of water
concentration within specified limits is critical to the proper
operation of the process.
[0059] The illustrative solvent monitoring and replenishment system
of the invention in one embodiment thereof includes two primary
components: (i) an analyzer unit, which monitors the concentration
of the selected solvent mixture components using real-time
methodology, e.g., a Karl-Fischer titration methodology, and (ii) a
control unit which functions as the process controller. The control
unit compares the results of the analyzer unit to pre-programmed
specifications and controls the dispensing of one or more chemicals
into the solvent process system as required to maintain a desired
component ratio of solvent components. The solvent mixture in one
embodiment of the invention is provided in one or more baths in the
process system. In such case, the pre-programmed specifications
preferably include volume of each bath being monitored, frequency
of monitoring and a titration calculation factor for calibration.
The monitoring and control operations are carried out in real time,
i.e., the operations occur within a short period of time from the
beginning of the monitoring process and there is no substantial
time delay between the commencement of the sampling process and the
control operation.
[0060] In one embodiment of the invention, the analyzer unit
monitors the concentration of the water component of a sample using
a classic Karl Fischer titration methodology. The analyzer unit in
such embodiment incorporates a micro-size reaction vessel that
requires as little as 5 ml of KF titration solvent for each test.
While the titration is carried out in non-aqueous conditions, the
KF solvent can contain trace amounts of water. In addition, water
can originate from the methanol used to "shuttle" the sample as
well as from the internal surface of the analyzer's fluidics
system. This problem is solved by a technique of pre-titration of
the solvents in the enclosed reaction vessel. These two "pre-dry"
steps ensure maximum accuracy for the subsequent analysis. After
titration solvent has been dried, a small amount of the sample
(typically 1 ml) is extracted and its water content determined by
Karl Fischer titration using a dual-platinum sensor to detect the
titration end-point.
[0061] The process controller is used to accurately control the
automatic replenishment of the solvent components, in particular
water, guaranteeing optimum and stable processing over an extended
period of time. Once the component analyzer determines the relative
composition of the solvent system, the process controller can
restore the system to the correct component ratio. Specific limits
are pre-programmed into the process controller for the specific
component(s) being targeted for analysis. The results from the
component analyzer are compared to these specification limits and,
if determined to be below the minimum specification value, amounts
of the target component can be injected into the solvent solution
to restore the required component ratio. By maintaining the
component ratio of the solvent system within predetermined limits,
the effective bath life of the solvent mixture can be extended.
[0062] In many amine-based, alkaline solvent mixtures, such as the
ST-26S solvent mixture commercially available from ATMI, Inc.
(Danbury, Conn.), water constitutes an active and necessary
ingredient for the functioning of the solvent mixture. When the
water content is reduced below a particular value, it renders the
solvent incapable of performing the reactions required for
photoresist and post-etch residue removal in the semiconductor
manufacturing removal operation for which the solvent is
intended.
[0063] At an operating temperature of 60.degree. C., the water
content of such ST-26S solvent mixture decreases from an initial
value of .about.16.5% to a final value of .about.4.9% over 24 hours
due to evaporation. When coupled to the solvent monitoring and
replenishment system of the invention, the same solvent maintained
a water content of .about.16.5% for over 24 hours. By maintaining a
consistent water concentration in the solvent mixture, the
performance of the solvent will be stable over an extended period
of time. Maintaining chemical concentrations of the solvent
components of the solvent mixture at predetermined set-point levels
maximizes a solvent mixture's useful life and thus minimizes
production downtime due to re-pouring of solvents and
re-qualification of those chemical mixtures. In addition, more
stable solvent mixtures yield a more consistent process
performance, resulting in higher yield through reduced failure
rates.
[0064] The invention therefore provides in one embodiment a means
and method of in situ monitoring and H.sub.2O injection of aqueous
solvent mixtures used for the removal of bulk photoresists and post
plasma etch/ash residues, which achieve an unexpected level of
reduction, e.g., greater than 33%, and higher, of the overall
consumption of semi-aqueous solvent cleaning solution in such
semiconductor manufacturing operation.
[0065] The system and method of the invention are usefully applied
to the maintenance of semi-aqueous solvent mixtures that are
employed for wafer cleaning in semiconductor manufacturing
applications. Approximately 75% of all of the solvents used for
residue removal and photoresist "stripping" contain water. The
recommended operating temperature for these solutions is between
45-75.degree. C., and the typical bath life for these solutions is
between 8-24 hours. The bath life is primarily determined by the
loss of water due to evaporation. Using the concentration analysis
and solvent replenishment system of the invention to analyze the
solution and adjust the water level, the bath life can be increased
by at least 100%. This results in substantial savings in a)
chemicals, b) downtime for chemical changes, and c) chemical
disposal costs. The invention thereby achieves a substantial
advance in the art of cleaning semiconductor device structures.
[0066] Referring now to the drawings, FIG. 1 is a schematic
representation of a fluid component monitoring and concentration
maintenance system 10 according to one embodiment of the invention.
FIG. 2B, described more fully hereinafter, is a schematic
representation of the same system as mounted within a single
cabinet, as a unitary system assembly, wherein the cabinet is
fabricated of a chemically-resistant material, e.g., stainless
steel, Teflon.RTM. polytetrafluoroethylene, or polypropylene.
[0067] The fluid component monitoring and concentration maintenance
system 10 includes an Analytical Information Module 12. The
Analytical Information Module includes the user interface, display,
analysis control and data input/output functions for the system,
and functions as the concentration analysis and controller unit of
the apparatus. The Analytical Information Module also includes a
Wet Chemistry Module 14 as the solvent replenishment unit of the
apparatus.
[0068] The Analytical Information Module is mounted in a separate
enclosure from the Wet Chemistry Module in the embodiment
illustrated in FIG. 1. The Analytical Information Module is
provided with external connectors for coupling the Analytical
Information Module 12 to the Wet Chemistry Module 14, via an
interface cable harness 16. User-accessible input/output terminals
(not shown in FIG. 1) are provided at the upper portion of the
Analytical Information Module 12, under an access hatch on top of
the housing of such Analytical Information Module. The Analytical
Information Module is most advantageously mounted above or to the
side of the Wet Chemistry Module in the semiconductor manufacturing
facility.
[0069] The Wet Chemistry Module 14 of the apparatus is constructed
and arranged to perform highly accurate measurements and
comprises:
[0070] a sampling system;
[0071] sensor(s);
[0072] a reaction vessel with mixer; and
[0073] a reagent dispensing system,
each of which is described more fully below.
[0074] Sampling System
[0075] During analysis, the apparatus captures a small quantity of
sample from a by-pass loop connected to the process stream of the
semiconductor manufacturing operation. The process stream comprises
the cleaning solvent mixture that is used to remove unwanted
material from a wafer structure, e.g., a semiconductor device or
semiconductor device precursor structure on which material has been
deposited, or is otherwise present.
[0076] Once isolated, the solvent mixture sample is transferred to
the reaction vessel using a suitable solvent. After sample has been
transferred to the reaction vessel and analyzed, the reaction
vessel is rinsed with solvent to minimize the analyzer's exposure
to aggressive process chemistry that may alter or otherwise
adversely affect its operation in prolonged exposure.
[0077] The materials of construction of the sample system are
appropriately selected for optimal use in a clean-room environment.
The sample system is designed to ensure reliable isolation between
the process and the fluid component monitoring and concentration
maintenance system, so as to minimize the possibility of process
contamination. The sample system drain 18 (see FIG. 1) is most
advantageously located below the reaction vessel.
[0078] Sensors
[0079] One or more sensors is/are used by the fluid component
monitoring and concentration maintenance system to plot each
analysis curve, or for direct measurement of the sample.
[0080] Reaction Vessel
[0081] The micro-volume reaction vessel of the fluid component
monitoring and concentration maintenance system is constructed of a
suitable solvent-resistant material of construction. A preferred
material of such type is TPX engineering plastic, which is
transparent yet remains highly resistant to a wide variety of
solvents.
[0082] The reaction vessel in one embodiment of the invention
includes an integral mixing system, comprising a solid-state
magnetic stirrer and Teflon-coated stir bar, plus ports for up to
two standard 12 mm pH, oxidation-reduction potential (ORP) or ion
selective electrodes. The reaction vessel in such embodiment also
accommodates dual-platinum electrodes for following the Karl
Fischer reaction. This reaction vessel is sized and arranged to
accommodate one transfer solvent and up to three further analytical
reagents (e.g. titrant, cleaning solvent, etc.).
[0083] Reagent Dispensing System
[0084] The fluid component monitoring and concentration maintenance
system comprises a reagent dispensing system that in the
illustrative embodiment includes precision glass burettes, with
digital linear actuator control, to provide a highly accurate
reagent dispensing capability. Each burette in such embodiment has
a capacity of 5 ml/stroke, gives a resolution of 0.01 ml, and is
capable of theoretical accuracy of .+-.0.0015 ml.
[0085] In view of the deficiency of conventional syringe-pumps as
susceptible to damage caused by reagent leakage, the fluid
component monitoring and concentration maintenance system in the
reagent dispensing system uses an "inverted burette" design. Each
burette incorporates a solvent-resistant O-ring seal, e.g., a
Kalrez.RTM. O-ring seal providing an operational life of at least 3
months.
[0086] The fluid component monitoring and concentration maintenance
system in one embodiment is designed for double containment of both
the analyzer and the reagents, accommodating the sample
inlet/outlet lines, the reagent lines, and the drain lines. The
compressed air supply in such arrangement is not double contained.
The reagent enclosure also affords double containment of the
reagent lines.
[0087] The fluid component monitoring and concentration maintenance
system is preferably provided in a modular form to give a greater
degree of flexibility in locating the apparatus in the
semiconductor manufacturing facility. For example, the Wet
Chemistry Module, Analytical Information Module and reagents can be
located inside the associated process tool, in a service chase
adjacent to the process, or in the sub-fab area of the
semiconductor manufacturing plant, as may be necessary or desirable
in a given application of the present invention. Preferably, the
Wet Chemistry Module is located near the tool's pumps, piping and
drain, and the Analytical Information Module is mounted in a
convenient and accessible location either above or next to the Wet
Chemistry Module.
[0088] Installation of the fluid component monitoring and
concentration maintenance system can be effected on either a
recirculating bath/process or a non-recirculating bath/process, as
described more fully hereinafter.
[0089] The fluid component monitoring and concentration maintenance
system may optionally include a parallel display unit providing the
same functions as the Analytical Information Module, which is
remotely mountable from the Analytical Information Module and the
Wet Chemistry Module in the semiconductor manufacturing facility,
such as at a convenient location in the cleanroom. This arrangement
allows for a display unit of the Analytic Information System to be
positioned at its point of use in the semiconductor manufacturing
facility, e.g., for servicing and troubleshooting the analyzer,
while the remotely situated parallel display unit allows the
operator to manipulate the Analytical Information Module from
inside a cleanroom.
[0090] As an alternative to the use of double containment for
reagents, the fluid component monitoring and concentration
maintenance system may include a reagent enclosure designed to
contain an excess of the volume of all possible reagents, e.g., the
reagent enclosure may be sized and arranged to accommodate 110% of
all possible reagents. Such reagent enclosure is fabricated of any
suitable chemically compatible material(s) of construction.
[0091] The reagent enclosure (if provided) can be mounted below the
Wet Chemistry Module. The reagent enclosure can also be mounted to
the left or right of the Wet Chemistry Module, but it desirably is
not mounted above the Wet Chemistry Module, so as to eliminate the
possibility of a siphon effect. When mounting the reagent
enclosure, sufficient clearance should be maintained between the
Wet Chemistry Module and the reagent enclosure, in order to access
the Wet Chemistry Module drain and valve.
[0092] The fluid component monitoring and concentration maintenance
system 10 is shown in FIG. 2A as wall-mounted on wall 20 in a
semiconductor manufacturing facility, utilizing "UNI-STRUT" or
other wall mounting brackets 22, 24, 26 and 28. As mentioned
hereinabove, the fluid component monitoring and concentration
maintenance system 10 may also be integrated into a process tool
when the process tool contains sufficient space for such integrated
deployment of the fluid component monitoring and concentration
maintenance system.
[0093] The fluid component monitoring and concentration maintenance
system 10 as shown in FIG. 2A includes a sample system, sensor(s)
and mixed reaction vessel in the upper housing 30 of the Wet
Chemistry Module 14. The upper housing as shown is coupled with a
compressed air line 32, a sampling system including sample #1
inlet/return 34, and sample #2 inlet/return 36, drain 38, and
exhaust port 48. The double containment reagents line 40
interconnects the upper housing 30 with the lower housing 42
containing reagent supply means (not shown). The lower housing 42
is provided with an enclosure drain 18A, and exhaust 46.
[0094] Mounted on brackets 26 and 28 adjacent to the Wet Chemistry
Module 14 is the Analytical Information Module 12 including
computational means, such as a programmable general purpose
electronic computer, microprocessor, central processor unit (CPU),
or other suitable means, coupled to display 50 for visual
observation of the output of the Module 14. The Analytical
Information Module 14 is equipped with a power cord 44, for plug-in
to a plug receptacle of an electrical power system, for powering of
the computational means and other means disposed in the housing of
the Analytical Information Module 14.
[0095] The fluid component monitoring and concentration maintenance
system 10 is preferably arranged to sample the process solvent
mixture from a bath 68 in tank 66, equipped with a recirculating
pump 72, as is shown for example in FIG. 3. In such recirculating
bath arrangement, a proportion of the sample is bled from the
recirculation system in sample feed line 80 and fed by feed/return
line 56 to the fluid component monitoring and concentration
maintenance system 10. The sample enters the sample panel of the
fluid component monitoring and concentration maintenance system 10,
passes briefly through its 3/2-way sample valve, and then returns
to the process tool 58.
[0096] The process tool 58 is disposed in relation to wall 60
demarcating a boundary between cleanroom 62 and service chase 64,
as illustrated. The tank 66 containing bath 68 is coupled with a
fluid feed line 70 to the pump 72, from which the fluid is flowed
in discharge line 74 though filter 76 to recirculation line 78 for
return to the bath 68.
[0097] Sampled fluid is returned from fluid component monitoring
and concentration maintenance system 10 in feed/return line 56 from
return 36, and passes in sample return line 82 to join with the
fluid recirculated in recirculation line 78 for return to the bath
68. A portion of the fluid from the bath in recirculation line 78
is diverted in sample feed line 82 to the feed/return line 56 from
which it flows in the branched portion thereof to feed inlet
34.
[0098] The drains 38 and 18 from the Wet Chemistry Module 14
convergently join in drain line 54, which is connected in turn to
floor drain 57. The exhausts of the upper and lower housings 30 and
42 are coupled in closed flow communication with the exhaust
conduit 52, for fluid discharge of exhaust from the system.
[0099] This "fast loop" concept minimizes chemical wastage and the
possibility of process contamination, and lessens the criticality
of the distance between process and the fluid component monitoring
and concentration maintenance system, as a consequence of the zero
dead-volume of the fast loop arrangement.
[0100] FIG. 2B is a schematic representation of a fluid component
monitoring and concentration maintenance system 11 according to a
second embodiment of the invention utilizing a single,
self-contained cabinet 13 for mounting the system, in which the
cabinet optionally may be equipped with wheels 25 to facilitate
relocation as a mobile system within a semiconductor manufacturing
facility or alternatively the cabinet may be fabricated without
wheels to provide a semi-permanent installed system that is fixedly
positioned in the semiconductor manufacturing facility.
[0101] FIG. 2B shows the fluid component monitoring and
concentration maintenance system 11 in respective left-hand side
elevation, front elevation and right-hand side elevation views, as
viewed from left to right in the drawing figure.
[0102] The left-hand side elevation view shows the unitary cabinet
13 as including an upper housing member 31 that is arranged to be
swingably openable and closeable by means of the damped strut
connector 33. The upper portion of the housing includes a slidable
tray 27 on which is provided a display 29 which may comprise a
monitor that is coupled with a keyboard and CPU mounted on the
tray, for access to the programmable Analytical Information Module
embodied in the upper portion of the cabinet assembly.
[0103] The left-hand side elevation view of the unitary cabinet 13
as including a clean dry air (CDA) port 15, a sample #1 inlet and
return port 17, a sample #2 inlet and return port 19, and enclosure
drains 21 and 23. The wheels 25 are of any suitable type, e.g.,
castor or roller types, and enable to system to be portably
relocated in the semiconductor processing facility. In lieu of
providing the system shown in FIG. 2B as a mobile assembly, the
system may be deployed without wheels, to constitute a stationary
unit that is fixed positioned in the semiconductor manufacturing
facility.
[0104] The front elevation view of the system 11 shown in the
central view of FIG. 2B shows the cabinet doors 35 and 37 that
permit access to the componentry of the Wet Chemistry Module.
[0105] The right-hand side elevation view shown in the right-hand
portion of FIG. 2B depicts the unit in a mirror-image relationship
to the view of the system unit illustrated in the left-hand portion
of the FIG. 2B drawing, and shows the exhaust ports 41 and 43 of
the Wet Chemistry Module.
[0106] FIG. 3 shows an illustrative arrangement of the fluid
component monitoring and concentration maintenance system 10 with a
fast loop recirculating bath arrangement. The fluid component
monitoring and concentration maintenance system 10 as discussed is
located in a service chase adjacent to the process tool, and all
fluid lines are double contained, with a fluid drain free-flowing
with zero back-pressure. Flow of fluid through the recirculation
fast loop depends on there being sufficient pressure drop across
the loop, which may necessitate restriction or adjustment of the
flow through the main recirculation system, as appropriate.
[0107] Alternatively, the fluid component monitoring and
concentration maintenance system 10 may be deployed in a
non-recirculating bath configuration, as shown in FIG. 4, wherein
all parts and components are labeled for consistency and ease of
description, correspondingly as in FIG. 3. In this arrangement,
sampling from the non-recirculating bath 68 in tank 66 involves
sample being withdrawn from the top of the bath by a sampling pump
72, e.g., a pneumatic diaphragm-type pump, for flow of fluid from
the bath 68 to pump feed line 70, and from pump 72 in sample feed
line 80 to the feed/return line 56 from which it flows in the
branched portion thereof to feed inlet 34. The sample return fluid
flows from system 10 in feed/return line 56 from return 36, and
passes in sample return line 82 to the bath 68.
[0108] In the non-recirculating bath configuration, the fluid
component monitoring and concentration maintenance system 10 can be
located in the fab or in an adjacent service chase. There is a
greater possibility of entraining air in the sampling line in the
non-recirculating bath configuration than in the recirculating bath
mode, particularly when the bath is being drained. It therefore is
preferred to locate the tip of the sample extraction pipe as close
as possible to the bottom of the bath in the non-recirculating bath
configuration.
[0109] The fluid component monitoring and concentration maintenance
system 10 preferably is provided with suitable valving (not shown)
to allow the fluid component monitoring and concentration
maintenance system to be isolated from the associated process using
the solvent mixture being monitored by the apparatus. Such valving
may include automatic "fail closed" isolation valves, which close
if there is an interlock violation. Corresponding valves or
check-valves preferably are mounted in the sample return lines to
eliminate the chance of back-flow from the process in the event of
a leak.
[0110] The Wet Chemistry Module includes four 5 ml burette glasses
mounted on burette guide-posts. Tubing connects the respective
reagent bottles with the burette glasses in the Wet Chemistry
Module.
[0111] FIG. 5 shows the Wet Chemistry Module 14 with the respective
fluid lines, including compressed air line 32, a sampling system
including sample #1 inlet/return 34, and sample #2 inlet/return 36,
and drain 38. The reagent lines are fed through double containment
tubing of reagents line 40 to the reagent enclosure. An air source
(of clean dry air (CDA)) is connected outside the Wet Chemistry
Module by an appropriate coupling, e.g., a 1/4'' OD Flare-tek.TM.
fitting on line 32. The sample(s) inlet 34 and return 36 are
connected at the sample valves by appropriate couplings, which may
also comprise 1/4'' OD Flare-tek.TM. fittings. The drain 38 is
connected to the reaction vessel, and may for example comprise
3.times.1/8'' tubes.
[0112] The fluid component monitoring and concentration maintenance
system 10 in one embodiment is constructed and arranged to monitor
the concentration of water in a conventional n-methyl pyrrolidone
(NMP)-based photoresist stripping solvent. The apparatus may be
configured to allow multiple, e.g., two or more, process streams to
be independently analyzed.
[0113] The water content of the sample is measured by a suitable
analytical technique, e.g., Karl Fischer titration, following an
analyzer pre-dry phase, in which the endpoint is detected using a
double-platinum electrode pair driven by a constant current
module.
[0114] The fluid component monitoring and concentration maintenance
system 10 may thus be arranged to perform a water in NMP analysis
to determine sample water content by classical Karl Fischer
titration technique, performed in non-aqueous conditions. The
titration reaction requires three components: sulfur dioxide,
iodine and water. The sulfur dioxide is readily oxidized with
iodine--but only in the presence of water. A simple representation
of the chemistry is
SO.sub.2+I.sub.2+2H.sub.2O=H.sub.2SO.sub.4+2HI.
[0115] The sulfur dioxide and iodine, along with supporting
solvents, are combined in commercially available Karl Fischer
titrant/solvent packages such as those commercially available under
the Hydranal trademark.
[0116] In the sample titration, the sample is titrated against the
Karl Fischer titrant until any water contained in the sample has
been completely consumed. Once all the water has been removed, a
sharp endpoint is detected using a polarized (constant current)
double-platinum electrode.
[0117] The detection of the endpoint in the Karl Fischer titration
is accomplished by amperometric detection. Amperometry relies on
the measurement of an electric current flowing between two
polarized electrodes. The current flow is controlled by reactions
taking place at the electrodes (not by the conductivity of the
solution). These electrode reactions are: at the cathode
I.sub.2+2e.fwdarw.2I.sup.-, and at the anode
2I.sup.--2e.fwdarw.I.sub.2.
[0118] Before the endpoint of the titration, there is enough iodide
present from the reaction of the Karl Fischer reagent with the
sample water, so that there is no obstacle for the anode indicator
reaction to proceed. However, no iodine is available for the
cathode reaction, and this absence limits current flow between the
electrodes. Only at and after the endpoint are iodine and iodide
both present. Current then flows and the potential between the
polarized indicator electrode drops to give an exceptionally sharp
endpoint signal.
[0119] A very small (few micro-amp) current is imposed between the
two platinum indicator electrodes. The fluid component monitoring
and concentration maintenance system optionally may be provided
with an integral constant-current supply, which powers the platinum
indicator electrodes.
[0120] The Karl Fischer titration is carried out under
"non-aqueous" conditions, but in a typical two-component Karl
Fischer reagent set, the solvent usually contains considerable
amounts of water. Further water contamination can come from the
internal surfaces of the analyzer's fluidics system that come into
contact with the sample, as well as water contamination deriving
from atmospheric moisture.
[0121] The problem of obtaining a state of system dryness is solved
in the fluid component monitoring and concentration maintenance
system of the invention by a technique of pre-titration of the Karl
Fischer solvent, plus the use of completely enclosed titration
equipment with minimal unfilled volume. Thus the solvent used to
transfer the sample to the titration vessel is first dried in a
pre-titration step, using the Karl Fischer titrant itself. This
dried solvent can then be used to flush out the sample transfer
lines again prior to the sample capture step, where it again can
pick up water necessitating a further pre-titration to dryness.
Usually only two such "shuttle" drying steps are required, but it
will be recognized that greater or lesser numbers of drying steps
may be necessary or desirable in a given application of the
invention.
[0122] In the assembly of burettes provided in the fluid component
monitoring and concentration maintenance system of the invention,
the role of each burette is as follows:
[0123] Burette 1- Karl Fischer solvent K (solvent for water
determination in ketones);
[0124] Burette 2- methanol (optional flushing agent); and
[0125] Burette 3- Karl Fischer titrant K, 5 mg/ml (titrant for
water determination in ketones).
[0126] The burettes are primed with reagent in a flushing
procedure, carried out by the following sequence of steps: [0127]
Step 1. Power up the analyzer. [0128] Step 2. Have each of the
reagents ready in appropriate reagent bottles (e.g., the original
chemical manufacturer's bottles). [0129] Step 3. Unravel the
burette inlet lines. Take a first reagent line (reagent line #1)
and feed it through the reagent bottle cap, and slip the end of the
tube over a tube weight barb. [0130] Step 4. Drop the end of the
tube, with its tube weight, into the selected reagent bottle, and
secure the cap. [0131] Step 5. Repeat the above Steps 1-4 for the
second and third reagent lines (reagent lines #2 and 3). [0132]
Step 6. From the Sign-on Screen of the Analytical Information
Module (described hereinafter in greater detail), press [SERVICE],
then [NEXT]. Press [ENTER], and the number after "Flush Burette"
will be underlined by a flashing cursor. [0133] Step 7. Using the
[UP] or [DOWN] keys, select the number of the burette desired to be
flushed, then press [ENTER].
[0134] Following such steps, the burette will begin a standard
flushing routine; the burette's piston will cycle up and down three
times, during which any air and excess reagent will be expelled
into the reaction vessel. At the end of the cycle, the burette
should be full. If not, the routine is performed again, and the
procedure is repeated for the other burettes until each is
completely flushed. It is to be appreciated that Karl Fischer K
reagents are unusually viscous, and may require additional
flushing.
[0135] The Analytical Information Module is programmatically
arranged with software in a computational unit for operating the
system. The computer controlled fluid component monitoring and
concentration maintenance system will now be described with
reference to the software operation, and appertaining screen
displays.
[0136] The Setup Screens displayed on the visual output display of
the Analytical Information Module contain parameters that the fluid
component monitoring and concentration maintenance system will use
in its operation. These parameters allow the fluid component
monitoring and concentration maintenance system to run a specific
analysis sequence, find the endpoint(s), calculate and report the
results.
[0137] The Calibration Screens are live read-outs of the electrode
signals. Although the Karl Fischer electrode pair does not require
routine calibration, these screens are still useful for
troubleshooting the electronics and the chemistry.
[0138] The Service Screens allow manipulation of the system.
Service Screen 1 allows the operator to force open any valve or
relay. Service Screen 2 allows the operator to flush the burettes,
set the analog outputs, and perform additional troubleshooting
operations. The Data Screens allow the operator to review the
stored analysis data. This data can be displayed either numerically
or graphically. The Data Screen also allows the operator to
download the data to a host computer for import into a spreadsheet
program. The Run Screen allows the operator to place the Analytical
Information Module into a single run or multiple runs operation.
This screen is displayed at all times during analysis.
[0139] The various screens associated with the operation of the
fluid component monitoring and concentration maintenance system
will now be described, as associated with an illustrative
embodiment of the invention.
[0140] The Sign-On Screen is shown in FIG. 6, and is the first
screen to appear when the fluid component monitoring and
concentration maintenance system is turned on or after reset. From
this screen all the features of the operating software can be
accessed.
[0141] The fluid component monitoring and concentration maintenance
system in one embodiment is operated through "softkeys." Data also
is enterable by the softkeys. The operation of the fluid component
monitoring and concentration maintenance system is simplified by
having a minimum number of keys. In the preferred arrangement of
the system, only the keys needed to perform a function for the
displayed screen are active.
[0142] Many modes accessible from the Sign-on Screen are actually
made up of several screens linked together. The "softkeys" are,
however, always clearly labeled and allow an unambiguous and simple
use of the many functions available.
[0143] The fluid component monitoring and concentration maintenance
system preferably is passcode-protected, whereby all parameters can
be protected from unauthorized programming. The passcode entry
routine is initiated by pressing the [SETUP] key for at least 2
seconds, and entering the passcode as instructed in the prompt
line.
[0144] The fluid component monitoring and concentration maintenance
system is arranged in one embodiment so that the first time the
apparatus is connected to a main power source, the passcode
"111111" is announced, and opportunity is afforded to customize the
passcode. Any passcode other than the original "111111" will not be
displayed, therefore the passcode remains a secret. If the
programming mode has not been entered with the passcode, viewing of
all screens is still possible, but the cursor and the keys [UP],
[DOWN], and [ENTER] which are necessary for programming the fluid
component monitoring and concentration maintenance system do not
appear.
[0145] The programming mode is cancelled in the Sign-on Screen when
any button is pressed for more than two seconds.
[0146] In the programming mode, the [SETUP] key has a double
function. A short press transfers the operator to the screen for
inspection of the data only. No programming is allowed. If,
however, the [SETUP] key is pressed for longer than two seconds,
the passcode input routine is accessed. On successful input of the
passcode, full programming is possible in the fluid component
monitoring and concentration maintenance system Setup Screens.
[0147] In such embodiment, the programming can be carried out by
individual parameters or by loading the default values. The default
values are loaded by pressing [CONTINUE] for longer than two
seconds. Otherwise, the data values remain intact until programmed
to another value individually.
[0148] If a reset occurs during the RUN mode, upon restarting, the
fluid component monitoring and concentration maintenance system
will return to the Sign-on Screen and remain idle until further
instructions are given. The Analytical Information Module cannot be
placed into any mode until the cause of the reset is corrected
(such as an open door).
[0149] The ensuing discussion is directed to programming of the
Analytical Information Module of the fluid component monitoring and
concentration maintenance system.
[0150] In the programming mode, the [UP] or [DOWN] keys are used to
move to the line required. The [ENTER] key is depressed, and the
[UP] or [DOWN] keys are utilized to change the currently selected
units. Pressing [ENTER] accepts the currently indicated data and
moves the cursor to the next data field for input of that
information. This process is repeated until all the data are
entered. The cursor will return to the beginning of the line where
the following steps are possible:
[0151] Re-entering the data by selecting this parameter with
[ENTER],
[0152] Moving the cursor with [UP] or [DOWN] to another parameter
on the screen,
[0153] Returning to the Sign-on Screen with [MAIN], and
[0154] Accessing the next Setup Screen with [NEXT].
[0155] Concerning the sequence parameters, all times preferably are
in decimal minutes (e.g., 0.3 minute (=18 seconds)), all volumes
are in milliliters, and the burettes are numbered 1-4 from left to
right.
[0156] The Setup Screen 1, Analyzer Sequencer/Methods, is shown in
FIG. 7. The analyzer sequencer/methods screens allow the analysis
routine to be defined. The FIG. 7 screen shows a routine that
allows the fluid component monitoring and concentration maintenance
system to take a sample (for 0.3 minute, or 18 seconds), titrate
the sample with titrant from burette 2, empty the reaction vessel,
and lastly re-fill the reaction vessel with methanol from burette
1.
[0157] In one embodiment, the Setup Screen 1 offers up to 32 steps,
allowing customization of the function of the fluid component
monitoring and concentration maintenance system. The available
commands are:
[0158] MS--Measure and Set [0159] Not required in the Water-in-NMP
application.
[0160] BUR--Burette [0161] Causes the selected burette to "draw
back" a specified amount of reagent from the burette's tip. This
feature is useful for eliminating the possibility of reagent
leakage contaminating a particular step in the analysis sequence.
The syntax is: [0162] BUR [0163] burette# [0164] volume
[0165] M1-M5--MACRO command
[0166] The MACRO commands, M1 through M5, allow custom valve
sequences to be introduced into the analysis scheme.
[0167] IF, FI--Logical branch
[0168] The conditional IF command allows a section of the
programmed sequence to be performed only when the given condition
is satisfied. The section subject to the IF condition is defined
between the IF command and the FI command. The syntax is: [0169] IF
[0170] Condition [0171] Value
[0172] The available tests are: [0173] pH>, pH<, mV>,
mV< . . . Tests based on sensor output [0174] ml>, ml< . .
. Tests based on endpoint volume [0175] x . . . A test based on
number of elapsed cycles [0176] Q2>, Q2< . . . Tests based on
the signal being fed into the specified level sensor (useful for
remote stream or method selection).
[0177] A typical sequence section showing the use of IF . . . FI is
shown in FIG. 8
[0178] In this example, the IF branch will be carried out only when
the previous titre was less than 0.50 mL. In this case, the
titration will be repeated using burette 2 (where presumably a more
dilute reagent is stored). The titrate command in the IF loop is
assigned the R tag to indicate that it is not a determination on a
new sample but a repeat of the previous. The second data field
indicates the degree of dilution or concentration of the reagent
over that used for the first titration.
[0179] A Ramp (RMP) command may be employed to automate validation
experiments common during analyzer startup and method development.
The RMP command functions like a C command, but adds reagent
(usually a standard or sample) from the specified burette to the
reaction vessel in amounts that increase by the specified volume
with each cycle. The syntax is: [0180] RMP [0181] burette# [0182]
volume increment
[0183] When the RMP command is used, a complete set of titration
curve data is automatically outputted via the RS232 interface after
each analysis.
[0184] The Blow (BLO) command is used as an "accelerated vessel
empty" command to initiate use of CDA to blow the contents of the
reaction vessel to the drain. The syntax is: [0185] BLO [0186]
Time
[0187] The Shuttle (STL) command follows the Td command,
manipulating the burette 1 to withdraw up to 5 mL of the reaction
vessel's contents and then force it back into the titration vessel
again. After the shuttling is completed, a further "polish"
dry-down of the solvent is automatically performed. This sequence
is designed to ensure a thoroughly dried sampling and analysis
system prior to introduction of the sample. The syntax is: [0188]
STL [0189] burette# [0190] volume
[0191] The Else branch (ELS) command is used with an IF . . . FI
loop; when the IF condition is not met, then whatever follows the
ELS command is performed.
[0192] The S1w or S2w commands (Sample from stream 1 or stream 2
prior to Karl Fischer (water) titration) trigger the preprogrammed
sampling sequence in preparation for titration of water in the
sample. The time is that allowed for purging the sample loop. The
syntax is: [0193] S1w [0194] Time
[0195] The Tw1 (Titrate water using method 1) command calls for the
titration of water in the sample, using the "method 1" parameters.
The titration parameters are defined in column "B3 H2O 1" in Setup
Screens 5 and 6.
[0196] The Tw2 (Titrate water using method 2) command calls for the
titration of water in the sample, using the "method 2" parameters.
The titration parameters are defined in column "B3 H2O 2" in Setup
Screens 7 and 8.
[0197] The Td (Titrate to dryness) command dries the Karl Fischer
solvent prior to capturing the sample. This command typically
precedes the STL command. The titration parameters are defined in
column "B3 dry" in Setup Screens 7 and 8.
[0198] The C1-C4 (Condition with reagent 1-4) command calls for a
defined volume of reagent to be dispensed into the reaction vessel
from the specified burette. The syntax is: [0199] C1 [0200]
volume
[0201] The W (Wait) command causes the analyzer to pause at this
point for the defined length of time. This command is typically
used to allow a sensor to stabilize prior to beginning a titration.
The stirrer operates throughout this time. The syntax is: [0202] W
[0203] Time
[0204] Setup Screen 2, Analog Outputs and Relay Set Points, is
shown in FIG. 9. In Setup Screen 2 the analog outputs and the relay
functions are set.
[0205] The fluid component monitoring and concentration maintenance
system has up to four analog outputs. The analog outputs are
standard 4 . . . 20 mA configuration. The assignment of the outputs
is given in the text input in the left data field. An output value
of 4 mA always represents a result (concentration) of zero. The
concentration corresponding to the end of the range may be
programmed freely, within the constraints of the input data format:
0.01 to 9999.99 in the right data field. For instance, if a typical
concentration is usually around 6%, the analog outputs can be
advantageously set to be 0 to 10%, so that the normal operating
range is in the middle of the analog output range.
[0206] In the Relay Assignments, the four/six alarm relays can be
assigned the following functions: [0207] 1>, 1<, 2<,
2>. . . relay closes if specified result is less than or greater
than the specified value [0208] err . . . relay closes if any error
condition is detected [0209] off . . . relay is disabled [0210] Q2,
Q3, Q4 . . . relay closes if the specified level sensor is
activated
[0211] The above assignments are made in the first field of the
relay set up line. The sample concentration that triggers an alarm
is set in the data fields to the right. The data is in decimal
format. If a relay has been assigned to a level sensor, then the
concentration data field is irrelevant.
[0212] The Setup Screen 3, Calibration Data/Trigger, is shown in
FIG. 10. This Setup Screen allows for process or factor calibration
data to be entered, which are used to convert the volume (ml) of
titrant used to reach the endpoint into units of concentration
(e.g. wt %).
[0213] The fluid component monitoring and concentration maintenance
system can manipulate the endpoint volume (or "titre") in one of
two ways: [0214] in a first approach, the analyzer's "factor" is
calculated from first principles, taking into account sample size,
reagent concentration, reaction stoichiometry and required result
units; and [0215] in a second approach of "process calibration,"
the analyzer is synchronized with a trusted laboratory analysis
result.
[0216] The parameter "calibration type" is used to define whether
the calculation of the concentrations is conducted according to
classical titration rules of balancing chemical equivalents
(factor) or using a parameter that has been determined from a
process calibration (process).
[0217] The analyzer's calculation factor can be derived from first
principles using the following equation: Calculation
Factor=(C.sub.tit.times.RR.times.U.times.MW)/V.sub.samp [0218]
where: C.sub.tit=Titrant Concentration (moles/liter) [0219]
RR=Reaction Ratio (moles of sample that will react with each mole
of titrant) [0220] U=Unit factor (typical values: "1" for g/l,
"0.1" for %, "1000" for mg/l etc.) [0221] MW=Molecular Weight of
sample species (e.g. HF=20) [0222] V.sub.samp=Volume of sample
taken (typically 0.25-1 ml)
[0223] Alternatively, a "process calibration" can be performed,
whereby the fluid component monitoring and concentration
maintenance system is adjusted to match results from a laboratory
analysis. This procedure may be required if the inflection point
seeking algorithm is used, but laboratory procedures takes an
endpoint (somewhat displaced) from the inflection point of the
titration curve.
[0224] Having entered the laboratory-determined concentration, the
fluid component monitoring and concentration maintenance system
will calculate the conversion factor that relates concentration to
titre value, and display that value. If no valid data is available,
then an ERROR 32 will be generated.
[0225] The Analyzer Trigger Mode determines what controls the
analysis timing. If the fluid component monitoring and
concentration maintenance system is in LOCAL trigger mode, the
analyzer will be operated through the keypad and its own internal
timer.
[0226] If the fluid component monitoring and concentration
maintenance system is in REMOTE trigger mode, the analyzer will
await an external signal before beginning its analysis cycle.
Typically, this signal would be a relay closure performed by an
external programmable logic controller (PLC). After the analysis
cycle is completed, the analyzer sends a ready signal as a
handshake (via alarm relay). If the fluid component monitoring and
concentration maintenance system is in COMPUTER trigger mode, it is
fully controlled via its integral RS232 interface.
[0227] The Setup Screen 4, Analysis Timing, is shown in FIG. 11.
This screen sets the parameters for the timing of the fluid
component monitoring and concentration maintenance system. Inputs
for time, date, and analysis interval are provided on this
screen.
[0228] The Titre Frequency command sets the time interval between
analysis cycles. Units are decimal minutes. If the titration
actually takes longer than the programmed interval, the next
titration will commence 5 seconds after the finish of the previous
titration. In these 5 seconds the operator may abort a sequenced
titration by pressing the active [STOP] soft key. If the titre
frequency is less than or equal to one (1), then the fluid
component monitoring and concentration maintenance system will
perform mathematical models in a demonstration mode. If the value
is less than 0.3, then the burettes will be inactive. At the same
time the data bank will be loaded with computer generated data.
[0229] The Equilibration Time on the Setup Screen has a decisive
effect on the speed and accuracy of the titration. This is the time
allowed for the system to come to equilibrium after the dispensing
of titrant. After each titrant addition, there will be a certain
time required for the reagent to become perfectly mixed in the
whole solution, then time for the sensor to equilibrate to the new
mV value. An equilibration time of 6 seconds is typical for the
Karl Fischer titration method.
[0230] The Data Smoothing entry on the Setup Screen takes
cognizance of the fact that titration curves in non-aqueous solvent
are sometimes extremely "noisy". The Data Smoothing parameter
allows the titration curve to be smoothed mathematically, improving
the consistency of analysis results. This parameter typically
varies from 0.1 to 10. The Water-in-NMP application typically
requires little smoothing, so the default value of 1 is generally
adequate in such application.
[0231] The Setup Screens 5 and 7, Endpoint Parameters, are
representatively illustrated in FIG. 12. These Setup Screens
determine the parameters that will be used to define the shape of
the analysis curve and how the endpoints are interpreted. The data
fields are arranged in four columns (two on each screen)
representing parameters for the four titration procedures: [0232]
B2 acid (burette 2, acid analysis)--these parameters are associated
with the "Ta" command [0233] B3 H2O 1 (burette 3, water analysis
1)--these parameters are associated with the "Tw1" command [0234]
B3 H2O 2 (burette 3, water analysis 2)--these parameters are
associated with the "Tw2" command [0235] B3 dry (burette 3,
pre-dry)--these parameters are associated with the "Td" command
[0236] The End Point entry on this Setup Screen reflects the fact
that regardless of whether a fixed setpoint, seeking, or seek/set
inflection point algorithm is used, the expected endpoint value
(usually expressed in mV) must be given. In each case this value is
used to assign the endpoint/inflection points to a particular
parameter being measured.
[0237] The Sensor entry is set to KF for Karl Fischer
titration.
[0238] The Window/Smoothing entry defines the tolerance (either
side of the Endpoint parameter) in which the seeking algorithm will
search for the endpoint. Whenever the electrode signal resides in
this window, the titrant additions will be driven to their minimum
allowable value. Although the algorithms to detect the endpoints
are very robust, additional safety measures are provided by the
Window/Smoothing capability to unambiguously interpret the endpoint
data and to assign the appropriate results.
[0239] The "End" (Titre End) parameter defines the limit of the
titration experiment; when this value is exceeded, the analysis
will terminate. Using a fixed setpoint algorithm requires that the
titre end be set at or shortly after the endpoint point. The
self-seeking and seek/set inflection point algorithms, however,
require that reagent be added to the sample in excess such that a
symmetrical curve is obtained on both sides of the inflection
point.
[0240] In respect of the Algorithm entry on the Setup Screen, three
endpoint point algorithms are available: [0241] SEEK--titrate to an
inflection point ("self-seeking") [0242] SETPOINT--titrate to a
fixed setpoint value [0243] SEEK/SET--titrate to an inflection
point, then if failed to a fixed setpoint value
[0244] The first algorithm is an advanced curve fitting routine
that searches for the inflection point on the titration curve
("seeking" method).
[0245] The second algorithm is a "setpoint" method that finds the
titre value for the position of the theoretical/preset end point
programmed in the parameter list (i.e., the fluid component
monitoring and concentration maintenance system titrates to a
target electrode signal).
[0246] The third algorithm is a hybrid of the seeking and setpoint
algorithms. In the event there is an insufficient number of points
along the titration curve for the seeking method, the fluid
component monitoring and concentration maintenance system will
automatically shift to set-point analysis.
[0247] The seeking method will find the true inflection point
regardless of the mV electrode drift (provided the drift stays
within the defined endpoint window). This means that the electrode
does not have to be calibrated. On the other hand, the value of the
titre may differ from results obtained using a fixed set point
titration if the position of the set point does not exactly
correspond with the position of the inflection point on the
analysis curve. For this reason the process calibration feature has
been built into the fluid component monitoring and concentration
maintenance system to provide the option of using the advanced
inflection point seeking method, while allowing results to be
scaled to match those obtained in a well calibrated laboratory
setpoint determination.
[0248] The Titration Direction entry on the Setup Screen indicates
the direction the sensor signal is expected to move as the analysis
proceeds. If the sensor signal proceeds in the wrong direction, the
analysis is aborted and an error code is displayed on the liquid
crystal display (LCD) of the apparatus.
[0249] In addition to defining the expected sensor response, the
Direction_1 and _2 options allow further control of the titrant
addition mode. This can be particularly useful for titrations with
very unpredictable and abrupt titration curve profiles. When using
these modes, the expected endpoint volume is entered in the
corresponding "goal" field of Setup Screens 6 and 8.
[0250] Setup Screens 6 and 8, Analysis Control, are
representatively shown in FIG. 13. The analysis control screens
determine how titrant is added and how the result is
calculated/displayed.
[0251] Minimum and Maximum Increments (ml) entries are shown on the
representative Setup Screen in FIG. 13. The minimum and maximum
titre increments have a large influence on the speed and accuracy
of the titration.
[0252] In principal, the smaller the minimum increment value the
greater will be the accuracy. A small minimum increment will,
however, result in a slow titration, since many more points will be
measured. A maximum of measurement points is allowed per titration
curve, to ensure that the minimum increment enables a complete
curve will be taken with less than 201 points.
[0253] The maximum value defines the upper speed of the titre when
far from the endpoint point. Care should be taken with large values
in case the first few additions of reagent shoot the curve past the
endpoint point.
[0254] All fluid component monitoring and concentration maintenance
system titration endpoint determination algorithms interpolate
between data points, thereby giving resolutions that are higher
than the minimum reagent dispense volume.
[0255] The Pretitre/Goal entry reflects the fact that if sample
concentration remains reasonably stable relative to the frequency
of analysis, then it is likely that sequential analysis will yield
similar endpoint volumes. Under these circumstances, it is possible
to perform part of the next titration very rapidly by adding a
proportion of the last titre in one "slug", thus coming close to
the end point almost instantaneously. Such a "predose" will allow
the titration to be performed with the maximum speed without
sacrificing accuracy.
[0256] The pretitre parameter can be set to any value between 0 and
1; "0" represents no predose at all (i.e. titration proceeds
normally) while "1" represents adding 100% of the last endpoint.
Typical pretitre values are in the 0.2-0.7 range, depending on how
predictable and stable the sample concentration proves to be.
[0257] When the UP/DOWN_1 or UP/DOWN_2 addition modes are selected
in Setup Screens 5 and 7, then the pretitre fields becomes "goal"
fields; in this case, the expected endpoint volume in ml. Is
entered.
[0258] The Calculation Formula is selected on the Setup Screen, and
in the FIG. 13 embodiment, is "normal." The conversion of the
titration endpoint volume to a concentration reading (see
discussion herein concerning Setup Screen 3, Calculation Factors)
can be performed in several ways. The most common and simple is the
"normal" calculation, in which the endpoint volume is directly
multiplied by the calculation factor. However, a number of
alternative calculations are available that permit more advanced
titration techniques such as back titration to be exploited.
[0259] The Mix Correction entry on the Setup Screen is usually left
at 0.00 for the Water-in-NMP application.
[0260] Although the fluid component monitoring and concentration
maintenance system is typically provided for use with the default
parameters pre-loaded, so that the apparatus is suitable for
running the analysis quickly and accurately from the initial
operation of the operation of the apparatus, the apparatus
nonetheless may require adjustment to the default values during the
operational life of the apparatus, to accommodate changes in
process conditions, sensor response or new user requirements.
[0261] The curve in FIG. 14 illustrates the values defined within
the aforementioned Setup Screens 5-8. The endpoint is shown at 800
mV, but a 100 mV tolerance has been established by the Window
setting. Therefore, the fluid component monitoring and
concentration maintenance system will look between 700 and 900 mV
for the point of inflection. The titre end is set at 1100 mV,
allowing the curve to be drawn symmetrically, as required by the
seeking algorithm. The maximum increments allow the analysis to be
speedy, but once the fluid component monitoring and concentration
maintenance system detects a change in the slope it will slow down
the analysis to the minimum increment.
[0262] In the circled portion of the curve in the graph of FIG. 14,
the data points are much closer together to give the fluid
component monitoring and concentration maintenance system the best
chance at finding the most accurate endpoint. This allows for a
quick measurement, yet still maintains a high degree of
accuracy.
[0263] The Service Screens 1 and 2 shown in FIGS. 15 and 16,
respectively, allow testing of major functions of the fluid
component monitoring and concentration maintenance system hardware,
including all of the outputs, dispensers, relays and valves, by
manually actuating them. They also allow programming of Macros.
[0264] In Service Screen 1, any item can be actuated by simply
scrolling the cursor down to the chosen item and pressing [ENTER].
The digit to the right of the item will change from 0 to 1, and the
operator will be able to observe the item actuating correctly.
[0265] Upon exiting the Service Screens, any actuated items will be
automatically deactivated.
[0266] Up to 16 valve/relay selected operations can be custom
programmed to create a custom operation such as switching on
external pumps or customizing sampling operations. Up to five
macros can be saved in the memory of the fluid component monitoring
and concentration maintenance system.
[0267] To program a Macro, the [MAIN/MAC] button is first pressed
and held for 10 seconds. Once in the Macro Screen, [START] is
pressed and then the chosen valves were operated before [STOP] is
pressed to save the sequence. When recalled, via the M command in
Setup Screen 1, the Macro is repeated in exactly the same sequence
(including timing).
[0268] Service Screen 2 (FIG. 16) features additional controls that
flushing of the burettes, setting of the analog outputs etc.
[0269] The data screens of the fluid component monitoring and
concentration maintenance system provide access to all of the
stored data of the apparatus. The fluid component monitoring and
concentration maintenance system stores up to 1400 measurements,
with the most recent measurement replacing the oldest
measurement.
[0270] The first Data Screen in FIG. 17 shows the data in numeric
form. Pressing [UP] or [DOWN] moves the data one place. If these
buttons are pressed for longer than 3 seconds, the display moves up
or down one whole day to the first measurement of that day (first
after midnight). Pressing [PRINT] will give access to the soft keys
[RESULTS] or [CURVE]. Pressing [RESULTS] briefly will download, via
the RS232 output of the Analytical Information Module, the data of
the day currently shown in the display. Pressing for longer than 3
seconds will download all the data held in the memory. Pressing
[CURVE] will download the last titration curve.
[0271] The second Data Screen in FIG. 18 shows the results in a
graphical format, displayed in 24 hour blocks. To move between days
the [BACK] and [FORWARD] softkeys are used. The [DISPLAY] key is
used to move between components. The scale of the graph is
determined by the analog outputs defined in Setup Screen 2.
[0272] The graphical display feature enables a quick glance at the
process over a short time period. For a higher resolution, the data
is downloaded to be imported into a spreadsheet. The downloading
procedure using Windows 95/98 operating system software is set out
below. [0273] In Windows, click on the "Start" button. Move to
"Programs," select "Accessories," and choose the "HyperTerminal"
icon. [0274] Click on the HyperTerminal icon. [0275] Create a
HyperTerminal icon, by giving the HyperTerminal directory an
appropriate name such as "SemiChem." Now select an icon for the new
"SemiChem" directory. [0276] When done, click "OK". [0277] The
Phone Number Window will be displayed next. Verify which COM port
the RS232 cable is connected to on the computer. In most cases this
will be COM 2. To select COM 2, move the cursor until "Direct to
COM 2" is displayed. Click on "OK." [0278] The Port Setting Window
will be displayed next. The following setting must be selected:
[0279] Bits per second: 2400 [0280] Data bits: 8 [0281] Parity:
none [0282] Stop Bits: 1 [0283] Flow Control: Hardware [0284] When
this is done click "OK." [0285] The apparatus is now ready to
download data. From the HyperTerminal window click on the icon just
created. [0286] Next select "Transfer" from the menu bar. The
Capture Text Window should now be displayed, and it should read:
Folder C:\Program Files\Accessories\Hyperterminal\Capture.txt
[0287] At this time rename the file with an appropriate name
followed by the .txt extension. [0288] On the Analytical
Information Module, press the [DATA] softkey [0289] On the
Analytical Information Module, press the [PRINT] softkey [0290] On
the Analytical Information Module, press the [RESULTS] softkey for
the analysis data, and press [CURVE] softkey for the most recent
electrode response data. [0291] The data from the fluid component
monitoring and concentration maintenance system will be sent to the
computer and displayed on the computer screen. [0292] Once the Text
Capture has stopped, the data can be imported into any spreadsheet
program (as comma delimited text).
[0293] The following Setup Screens are typical of parameters
suitable for analysis of water in NMP-type photoresist stripping
solvent. In this example, solvent is analyzed only on stream 1, the
sample size is 0.5 ml and the expected sample composition is 2 wt %
water in NMP. TABLE-US-00001 Setup Screen 1 BLO C1 Td STL W S1w Tw1
BLO W BLO C2 0.50 5.00 1 0.30 0.40 0.40 0.20 0.20 5.00 3.00 Setup
Screen 2 Output 1 = Conc.1 Max . . . 2 Output 2 = Conc.2 Max . . .
2 Output 3 = Conc.3 Max . . . 2 Output 4 = Conc.4 Max . . . 2
Relays 1-6 = off Setup Screen 3 Calibration Type = Factor
Calculation Factor 1 = 1.000 Calculation Factor 2 = 1.000
Calculation Factor 3 = 1.000 Calculation Factor 4 = 1.000 Analyzer
Trigger = Local Setup Screen 4 Titration Frequency (min.) = 30
Equilibration Time (sec.) = 6 Data smoothing = 1.00 Acid Cal = 4.00
Water Cal = 1.00 Setup Screen 5 Endpoint (pH/mV) = -- 200.00
Endpoint Window = -- 10.00 Titre End = -- 190.00 Sensor = -- KF
Algorithm = -- Setpoint Titrate up/down = -- down Setup Screen 6
Min.Increment (ml) = -- 0.01 Max.Increment (ml) = -- 0.05
Pre-titre/Goal = -- 0.00 Calculation Formula = -- Normal Units = --
% Mix Corr. = -- 0.00 Setup Screen 7 Endpoint (pH/mV) = -- 200.00
Endpoint Window = -- 10.00 Titre End = -- 190.00 Sensor = -- KF
Algorithm = -- Setpoint Titrate up/down = -- down Setup Screen 8
Min.Increment (ml) = -- 0.01 Max.Increment (ml) = -- 0.03
Pre-titre/Goal = -- 0.00 Calculation Formula = -- Normal Units = --
% Mix Corr. = -- 0.00
[0294] After the fluid component monitoring and concentration
maintenance system has been installed, the reagents have been
flushed and the system software reviewed, the fluid component
monitoring and concentration maintenance system is ready for
analysis service.
[0295] The Run Screen is shown in FIG. 19, and contains all data
related to the current analysis. This screen displays the
concentration for samples number 1 through 4 (if provided). It also
displays the current/last analysis curve, which is generated in
real-time during analysis.
[0296] Upon pressing [RUN], the analyzer will start its first
analysis, then repeat at the interval specified in Setup Screen 4.
If [SINGLE] is pressed, the analyzer will start a single analysis
and, once finished, will remain idle until it receives a further
command.
[0297] When the analyzer has started its analysis sequence, the
upper right corner of the display, as illustratively shown in FIG.
20, indicates the current step ("S1") in the analysis sequence
underneath the time. During the analysis sequence, the [MAIN],
[RUN], and [SINGLE] buttons are gone. At this time the analysis can
only be interrupted by pressing the [RESET] button, which abruptly
stops the analysis and returns the operator to the Run Screen.
[0298] Underneath the sample concentration, which at this point
reads 0.000, a line of text is displayed, indicating the function
currently being performed. In this case "Taking Sample One" is
displayed. The fluid component monitoring and concentration
maintenance system will go through the default sampling sequence
and begin the titration.
[0299] Once the analysis is completed, the screen shown in FIG. 21
is displayed, identifying a water concentration of 2.343, which is
the number of milliliters of titrant required to reach the
endpoint. In this illustrative example, no calculation factor has
previously been entered in Setup Screen 3.
[0300] Subsequent to display of numeric information as shown in
FIG. 21, the fluid component monitoring and concentration
maintenance system is ready to be calibrated to the associated
semiconductor manufacturing process. The calibration process may
comprise a "factor" calibration method, whereby the Calculation
Factor is calculated from first principles, as previously discussed
herein. Alternatively, a "process" calibration may be performed, in
which the analyzer is re-scaled to correlate with a laboratory
analysis result.
[0301] A process calibration may be carried out in a "stop" mode.
This is the simplest way to perform a process calibration, but
requires the fluid component monitoring and concentration
maintenance system to remain off-line for the duration of the
reference laboratory test procedure. The procedure is as follows:
[0302] Verify that the fluid component monitoring and concentration
maintenance system is running under normal process conditions, and
functioning correctly. If the process is not operating (i.e. there
is no sample flow), do not proceed with the calibration. [0303]
Press [SINGLE]. [0304] Take a grab sample during or immediately
after the fluid component monitoring and concentration maintenance
system has captured its sample for analysis. This ensures that the
samples are the same. [0305] While the fluid component monitoring
and concentration maintenance system is completing its analysis
procedure, subject the grab sample to analysis using a reliable
reference laboratory method. [0306] Once the fluid component
monitoring and concentration maintenance system has completed its
analysis, advance to the Sign-on Screen by pressing [MAIN]. Press
[SETUP], then [NEXT] until Setup Screen 3 is reached. [0307] Set
the Calibration Type parameter to "Process". [0308] Scroll [DOWN]
to the appropriate Calculation Factor line (e.g., factor #1 for
analysis #1, etc.). Press [ENTER], and dial in the result of the
laboratory analysis (in the appropriate units, e.g. %, g/l, etc.).
Once the last digit is entered, pressing [ENTER] again will cause
the fluid component monitoring and concentration maintenance system
to re-calculate the Calculation Factor. Thus will be used in all
subsequent measurements. [0309] Exit the Setup Screens by pressing
the [MAIN] key once. Press the [RUN] key to return to the Run
Screen. The displayed result should now match the laboratory result
previously entered.
[0310] An alternative procedure is to perform the process
calibration in "run" mode, calibrating against a laboratory test
performed while the fluid component monitoring and concentration
maintenance system remains on-line. This is particularly useful if
the sample has to be sent to another department or external
laboratory for analysis. The procedure is as follows: [0311] Verify
that the fluid component monitoring and concentration maintenance
system is running under normal process conditions, and functioning
correctly. If the process is not operating (i.e., there is no
sample flow), do not proceed with the calibration. [0312] The fluid
component monitoring and concentration maintenance system will
likely be in Run mode, so wait until the next analysis cycle
begins. [0313] Take a grab sample during or immediately after the
fluid component monitoring and concentration maintenance system has
captured its sample for analysis. This ensures that the samples are
the same. [0314] Once the fluid component monitoring and
concentration maintenance system has completed its analysis, record
the displayed result, as displayed result "C1". [0315] Analyze the
grab sample using a reliable reference laboratory method. Record
the laboratory test result, as result "A1." [0316] Exit the fluid
component monitoring and concentration maintenance system Run mode
by pressing the [STOP] key (visible between analysis cycles).
Record the fluid component monitoring and concentration maintenance
system's currently displayed result, as displayed result "C2".
[0317] Advance to the Sign-on Screen by pressing [MAIN]. [0318]
Advance to Setup Screen 3 by pressing [SETUP] then [NEXT] twice.
[0319] Calculate the "adjusted calibration value" (CAL) as follows:
CAL=(A1/C1).times.C2 [0320] Set the Calibration Type parameter to
"Process". [0321] Scroll [DOWN] to the appropriate Calculation
Factor line (e.g., factor #1 for analysis #1, etc.). Press [ENTER],
and dial in the CAL value. Once the last digit has been entered,
pressing [ENTER] again will cause the fluid component monitoring
and concentration maintenance system to re-calculate the
Calculation Factor. This will be used in all subsequent
measurements. [0322] Exit the Setup Screens by pressing the [MAIN]
key once. Press the [RUN] key to return to the Run Screen. The
displayed result should now match the CAL value previously
entered.
[0323] This calculation protocol is intended to compensate for
possible changes in the process chemistry between the time the grab
sample was taken and when the Calculation Factor is updated.
[0324] An illustrative example is set out below.
EXAMPLE
[0325] The analyzer's displayed result at the time of the grab
sample was 3.863 wt % (C1).
[0326] Laboratory analysis reports the concentration of the grab
sample to be 4.101 wt % (A1).
[0327] The analyzer's displayed result at the time of updating the
calibration is 3.422 wt % (C2)
CAL=(4.101/3.863).times.3.422=3.633
[0328] Therefore, the adjusted calibration value (CAL) is 3.633 wt
%.
[0329] Set out below is an identification of error codes of the
Analytical Information Module of the fluid component monitoring and
concentration maintenance system, such as may be encountered in the
operation of the apparatus, together with a tabulation of the
meanings and severity of such error codes. TABLE-US-00002 error
code meaning severity 1 The sample is already neutral (detection in
single Fatal: Analyzer will not proceed with endpoint inflection
point mode) analysis until problem is corrected 2 The sample is
already neutral (detection of first endpoint Fatal: Analyzer will
not proceed with in dual inflection point mode) analysis until
problem is corrected 4 The sample is already neutral (detection of
second endpoint Fatal: Analyzer will not proceed with in
dual-inflection point mode) analysis until problem is corrected 8
Too many data points (increments too small) Warning: Accurate
detection of endpoint may not be possible 16 Calculation of results
impossible (incompatible output Fatal: Analyzer will not proceed
with assignments) analysis until problem is corrected 32 Process
calibration received invalid concentration data Warning: Analysis
proceeds using old data
[0330] In one embodiment of the invention, multiple error-states
are indicated by a composite error code. To decode, simply subtract
the highest error code possible and keep doing so until 0 is
reached. For example, E40=E32+E8.
[0331] The correlation of real-time analysis curves and error codes
provides a conjoint analytical approach to analysis of the fluid
component monitoring and concentration maintenance system
performance.
[0332] The real-time analysis curves can be utilized as a
"fingerprint" for a particular analysis. Interpretation of error
codes should be done in conjunction with an evaluation of the curve
shape. The ensuing discussion is directed to the relationship
between the error codes and the curve shape.
[0333] Curve 1 is shown in FIG. 22. This rapid change in sensor mV
suggests a lack of sample.
[0334] The first small amount of titrant, when added to the pure
solvent, causes the sensor response to jump immediately to the
titre end. This may be accompanied by an E1 error code. The
calculated results would most likely be very low (or even 0).
[0335] In this case, check that the sample is being delivered from
the process to the reaction vessel correctly.
[0336] Curve 2 is shown in FIG. 23. A "flat" sensor response like
this can have two causes.
[0337] First, if the sensor mV is in an unexpected range, then this
may indicate a faulty sensor, connection, pre-amp or other
electronic fault.
[0338] On the other hand, if the sensor mV remains in the normal
pre-endpoint range, then reagent may not be reaching the reaction
vessel. This would typically be accompanied by an E8 error code.
The level of reagents should be checked, and it should be verified
that the burette is filled and functioning properly.
[0339] Curve 3 is shown in FIG. 24. This scenario usually occurs
when the endpoint interpretation parameters have been changed
within the Setup Screens, but the chemistry remains the same.
[0340] In this case, the Setup parameters should be carefully
reviewed, and the passcode feature is desirably employed to
safeguard Setup parameters from unauthorized access.
[0341] Another cause can be a sensor that has drifted out of the
normal endpoint window. If the Setup parameters are correct, the
sensor should be cleaned or replaced as necessary.
[0342] After an analysis is finished, the analyzer will display an
[OPTIMIZE] menu option in the Run Screen, as shown in FIG. 25. This
feature allows for the optimization of the endpoint and the minimum
and maximum increments used.
[0343] To use the Optimize Screen, press [OPTIMIZE]. This will
generate the screen shown in FIG. 26.
[0344] This screen allows selection of the endpoint with the
greatest gradient (strongest point of inflection), and thus
optimization of the endpoint and increments to find this endpoint
every time. In the above case, [UP] is pressed until the
0.36/750/265.30 line is at the top, then [SELECT] is pressed. The
Setup parameters then are automatically optimized to the selected
point. Care should be exercise with this procedure, since if an
inappropriate endpoint is selected, the Setup parameters will be
inadvertently changed, and will adversely impact the analysis
accuracy.
[0345] The fluid component monitoring and concentration maintenance
system is preferably maintained on a regular maintenance schedule,
involving replenishment of reagents, replacement of burette
O-rings, updating of Analytical Information Module software,
refurbishing/replacement of electrodes, etc.
[0346] While the invention has been described herein with primary
reference to the use of Karl Fischer titration techniques in
respect of monitoring and control of water in semi-aqueous solvent
media, it will be appreciated that the invention is susceptible of
use with other analytical techniques and chemistries, and/or for
monitoring and control of other fluids than semi-aqueous solvent
media, and/or for monitoring and control of other fluid components
than water.
[0347] In lieu of the specifically described methodology for
monitoring and controlling the concentration of the water component
of a sample using the classic Karl Fischer titration methodology,
alternative methods of analysis that can also be used include
spectroscopic analysis of infrared and near infrared frequency
fluctuations, measurement of variations in the multicomponent
solution conductivity, and the use of ultrasonic wave generation,
e.g., involving impingement of ultrasonic energy on the sample
liquid, and measurement of the response of the sample thereto.
[0348] By way of further specific examples, the method of the
invention may be practiced with ultraviolet-visible detection and
monitoring of liquid species in liquid multicomponent compositions,
or with microelectromechanical devices (MEMs) for detection and
monitoring of gas species of multicomponent gas compositions,
thermopile device-based detection and monitoring of gaseous species
in a multicomponent gas composition, and electrochemical cells of
varied types for detection and monitoring of liquid species of
multicomponent liquid compositions.
[0349] The invention in application to water monitoring and control
of semi-aqueous solvent media thus provides an apparatus and method
for extracting small amounts of the clean chemistry, such as
solvent mixtures used for photoresist and post-etch residue
removal, measuring the water content of the clean chemistry, and
responsively injecting additional water as necessary to maintain
water concentration within appropriate levels. In solvent
compositions based on NPM, the amount of water in the chemistry is
a critical feature in determining bathlife. If the water level in
the solvent composition is too low, the cleaning efficiency will be
reduced. If the water level is too high, there is a strong risk of
metal corrosion. It therefore is critical to maintain water level
within a strict range of concentration. When the water level is
appropriately maintained, the bathlife can be extended
substantially, e.g., 2-3 times, beyond the level achievable without
monitoring and water control concentration maintenance. The
increased bathlife reduces chemical usage and chemical waste, as
well as the need for downtime to facilitate chemical changeouts.
Additionally, the increased bathlife and associated maintenance of
the value of the water concentration in the solvent composition
enables tight process control and higher yields to be realized.
[0350] The water monitoring and control apparatus and method of the
invention thus effects injection of water into semi-aqueous solvent
mixtures as needed to maintain a predetermined level of water
concentration in the solvent composition for maximizing its
efficiency.
[0351] The invention embodies a real-time chemical bath monitoring
and replenishment system, which may be usefully employed in a wide
variety of applications, including semiconductor manufacturing
operations such as photoresist and post-etch residue removal from
semiconductor device structures and precursor articles,
chemical-mechanical planarization in which solvent components
ratios in the CMP composition are critical to the material removal
operation, as well as other applications in which one or more
solvent components of a multi-component composition are susceptible
to analytical assessment and monitoring.
[0352] In another aspect of the invention, there is provided a
means and method of generating and monitoring species such as
H.sub.2O.sub.2.
[0353] Hydrogen peroxide (H.sub.2O.sub.2) used in semiconductor
processes is typically of unknown concentration due its spontaneous
decomposition into water over time.
[0354] The present invention in a specific embodiment resolves such
problem, by carrying out electrochemical generation of high purity
peroxide at the point of use, and performing real time quantitative
analysis of the peroxide as it is generated and in the process in
which it is being used.
[0355] The generation of hydrogen peroxide in accordance with such
aspect of the invention is carried out by electrochemical means.
Such electrochemical generation of hydrogen peroxide is extremely
efficient. For example, hydrogen peroxide can be generated in an
electrochemical cell, e.g., to produce at least 0.054 mol of
peroxide in a basic medium of sodium hydroxide using only 150
mA.
[0356] A Karl Fisher dual electrochemical cell (e-cell) arrangement
may be used as the platform in conjunction with a constant current
source with a Ag/AgCl reference electrode. The working electrode
(cathode in this case) connected to the current source can be
constituted by a sintered carbon/PTFE composite disk in intimate
contact with a nichrome screen. This electrode is highly porous and
as such allows oxygen to diffuse through at a rapid rate to promote
the formation of peroxide at the cathode. The anode material can be
graphite or Pb/PbO.sub.2 prepared as described in Brillas, E., J.
Electrochem Soc., 142 (1995) 1733, the disclosure of which hereby
is incorporated herein by reference in its entirety. In basic
solution this cathode configuration will catalyze a two-electron
reduction of oxygen to peroxide via the hydroperoxide anion:
O.sub.2+H.sub.2O+2e=HO2.sup.-+HO.sup.-.
[0357] Transition metal catalysts may also be added to facilitate
the reduction process and to increase peroxide yield or improve the
reaction efficiency.
[0358] The equipment configuration for this generation of hydrogen
peroxide and monitoring of same may be advantageously carried out
in the equipment configuration shown in FIG. 27, utilizing a Karl
Fischer analysis tray. The top cell is used for the generation of
the peroxide and a small aliquot is removed using the syringe pumps
and shuttled to the cell below where it can be tested using
permanganate or ceric ammonium sulfate. The bulk of the peroxide
generated can be shuttled to a holding vessel by pressurizing the
cell.
[0359] The top cell uses two platinum electrodes that are easily
modified to hold a Pb/PbO.sub.2 electrode and a composite
graphite/Teflon electrode.
[0360] Peroxide concentration, e.g., in chemical mechanical
planarization (CMP) slurries employed in semiconductor
manufacturing processes for polishing of semiconductor devices and
device precursor structures, can be easily monitored by titrating
with permanganate or ceric ammonium sulfate. Other transition metal
salts may be used with corresponding advantage, e.g., Fe complexes
such as NH.sub.4Fe(oxalate), NH.sub.4Fe(sulfate) or
NH.sub.4Fe(nitrate), to carry out the following reactions:
2Fe+2e.sup.-=2Fe.sup.+2 2Fe.sup.+2+2O.sup.-=O.sub.2+2Fe.sup.+3
[0361] FIG. 28 is a graph of titrant volume as a function of
titration cycles using ceric ammonium sulfate, and showing the
reproducibility of 2.5% peroxide determination.
[0362] The half reactions for the titration of H.sub.2O.sub.2 with
standard Ce.sup.+4 are: 2Ce.sup.+4+2e.sup.-.fwdarw.2Ce.sup.+3
2O.sup.-.fwdarw.O.sub.2+2e.sup.-
[0363] The complete reaction for this titration is:
2Ce.sup.+4+2O.sup.-.fwdarw.O.sub.2+2Ce.sup.+3.
[0364] The invention in another aspect relates to the generation
and monitoring of hydrazine and hydroxylamine.
[0365] Hydroxylamine and hydrazine are used as active reagents in
several semiconductor processing operations. However, both
chemicals present a transport and storage problem due to their
explosive nature and high reactivity. In-situ generation is highly
advantageous as solid hydroxylamine is known to rapidly detonate
when dried.
[0366] The present invention resolves the aforementioned
difficulties by (i) electrochemical generation of these compounds
at their point of use, (ii) simultaneous real-time process
monitoring of the concentration of these chemicals both in the
electrochemical cell and at the point of use, and (iii) use of a
modified Karl Fisher electrochemical cell platform for both the
generation and monitoring of these compounds. While described below
in reference to hydroxylamine, it will be appreciated that
corresponding procedures may be employed for the generation and
monitoring of hydrazine in accordance with the invention.
[0367] The electrosynthesis of hydroxylamine by be effected by
reduction reaction in mild nitric acid solutions at a mercury
amalgam electrode:
NO.sub.3.sup.-+7H.sup.++6e.sup.-=H.sub.2NOH+2H.sub.2O
[0368] Alternatively, glassy carbon electrodes with a thin polymer
membrane, formed from polyphenylenediamine in nitric acid, can be
used to promote this reaction and suppress further reduction to
ammonia. Typical current densities are under 1 A/cm.sup.2.
[0369] Using a Karl Fisher platform or a similar electrochemical
cell platform, hydroxylamine can be generated in one cell, a small
aliquot shuttled to the second cell, and an analysis performed to
detect the presence and concentration of hydroxylamine. Likewise,
sample from the process (utilizing the hydroxylamine) can be taken
on board the analysis tool via a six port valve and analyzed in a
similar manner, preferably in an automated manner.
[0370] Since hydroxylamine is reducible to ammonia at a platinum
electrode, subsequent titration with an oxidizer such as
permanganate can be monitored with an oxidation-reduction potential
(ORP) electrode.
[0371] Another potential synthetic method for generating
hydroxylamine bubbles both NH.sub.3 and O.sub.2 gas into an aqueous
solution in an electrochemical cell, as described herein.
Transition metal catalysts may also be added to enhance the
reaction efficiency and to increase the overall yield of
formation.
[0372] A dual cell apparatus of the type as shown in FIG. 28 may be
employed wherein the top cell is utilized to monitor sample from
the process bath or the lower cell for hydroxylamine
concentration.
[0373] Although the invention has been variously disclosed herein
with reference to illustrative embodiments and features, it will be
appreciated that the embodiments and features described hereinabove
are not intended to limit the invention, and that other variations,
modifications and other embodiments will suggest themselves to
those of ordinary skill in the art. The invention therefore is to
be broadly construed, consistent with the claims hereafter set
forth.
* * * * *