Developing a Reliable Fluorinated Greenhouse Gas (F-GHG)
Destruction or Removal Efficiency (ORE) Measurement Method for
Electronics Manufacturing: A Cooperative Evaluation with Qimonda
March 2008
vvEPA
United States
Environmental Protection
Agency
Office of Air and Radiation
Office of Atmospheric Programs, Climate Change Division
EPA430-R-08-017
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Acknowledgements
The analytical measurements, data interpretation, and report preparations were funded by the
U.S. Environmental Protection Agency under contract GS-10F-0124J to ICF International and
Air Products and Chemicals, Inc. The authors wish to express their appreciation and thanks to
Qimonda, for their gracious support to this study by not only providing their facilities but also
their valuable assistance and advice. The U.S. EPA looks forward to continued collaborations
with Qimonda and other Partners in the PFC Reduction/Climate Change Partnership for
Semiconductors.
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Table of Contents
Page
Acknowledgements 2
1.0 Introduction 6
2.0 Experimental Setup 6
3.0 Data Analysis 8
3.1 Determination of Scrubber Dilution 8
3.2 Scrubber DRE Determinations 11
3.2.1 DRE Determination During Process Calibration Flows 11
3.2.2 Determination of DRE during Wafer Processing 14
4.0 Conclusion 21
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Table I
Table II
Table III
Table IV
Table V
Table VI
Table VII
List of Tables
Page
Data used to determine the total flow emitted from TPU systems on AMZ17 and AMZ18
Total chamber and process pump effluent flow from chamber B on AMZ17 and AMZ18
...9
.11
CF4 DRE values determined during process flow calibrations 13
CHF3 DRE for AMZ18 scrubber based on data shown in Figure 7 14
Process Utilization for etch gases used in contact etch 17
CF4 DRE determined for each scrubber by comparing inlet and outlet emission volumes
19
Comparison of two methods used to determine CF4 DRE on scrubbers for AMZ17 and
AMZ18 21
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List of Figures
Page
Figure 1 Sampling schematic used for testing TPU PFC DRE 8
Figure 2 QMS Response to 84Kr during calibration 8
Figure 3 Regression analysis of calibration data shown in Figure 2 9
Figure 4 Kr concentration determined for AMZ17 scrubber during spiking experiment 10
Figure 5 CF4 emission concentration determined from AMZ17 chamber B while CF4 was flowed
through chamber B with RF power off 11
Figure 6 CF4 emission profile from AMZ18 chamber B (top) and from TPU (bottom) during process
flow calibration 13
Figure 7 CHF3 emissions from process (top) and scrubber (bottom) during CHF3 process flow
calibration 15
Figure 8 FTIR spectra of emissions from arc etch (top) and contact main etch (bottom) 17
Figure 9 Emission profiles for PFC process gases (top) and plasma by-products (bottom) during
contact etching of test wafers on AMZ18 chamber B 19
Figure 10 FTIR spectrum of AMZ18 scrubber emissions during test wafer processing 20
Figure 11 CF4 emission profile from AMZ 18 scrubber during processing of test wafers on Chamber B,
and during processing of production wafers on multiple chambers 21
Figure 12 CF4 emission profile from AMZ 17 scrubber during processing of production wafers on
Chamber B, and during processing of production wafers on multiple chambers 21
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1.0 Introduction
The purpose of this study was to accurately determine the Destruction or Removal Efficiency
(DRE) of a Point Of Use (POU) abatement system or scrubber for process emissions containing
perfluorinated compounds. A key component in accurately determining DRE was to determine
the dilution of process exhaust occurring in the scrubber. This study used an experimental
approach to measure the dilution across the scrubber by injecting a chemical tracer that could not
react in the scrubber, or be produced as a by-product during scrubber operation. Krypton was
used as the chemical tracer as it met the requirements for this application.
Testing was conducted in a fully functional semiconductor manufacturing facility, owned and
operated by Qimonda in Richmond VA. Two tools, AMZ17 and AMZ18, each equipped with
POU scrubbers were tested. Both tools ran the same process and used the same model of
commercially available scrubber. The process evaluated was a contact etch process, which used
PFC gases CF4, CHF3 and C4F6.
2.0 Experimental Setup
To carry out the objectives of this study it was necessary to monitor both process and scrubber
emissions simultaneously, and determine scrubber dilution using chemical spiking. Process and
scrubber emissions data were collected in parallel using Fourier Transform Infrared
Spectroscopy (FTIR). Data used to determine scrubber dilution were collected using Quadrupole
Mass Spectrometry (QMS). A schematic showing the experimental testing set up is shown in
Figure 1.
Two FTIRs were used to determine process and scrubber emissions. Both systems were MKS
2010 Multi Gas Analyzers equipped with liquid nitrogen cooled mercury cadmium telluride
(MCT) detectors. One FTIR was equipped with a 10 cm path length single pass gas cell, and
was used to sample process effluent. The other FTIR was equipped with a 5.6 m path length
multi pass gas cell, and was used to sample scrubber effluent. Both FTIR were operated at
0.5cm"1 resolution. Four scans were co-added for each data point yielding a sampling frequency
of 2.2 sec.
A Balzers QMS system was used to sample scrubber effluent during dilution determination. The
QMS was operated in Selective Ion Monitoring (SIM) mode and a secondary electron multiplier
was used to enhance sensitivity. A 1 sec sampling frequency was used for each data point. To
account for potential changes in QMS sensitivity, ion signals were normalized to the signal
obtained for the nitrogen fragment (N+), which is formed during electron impact ionization of
N2.
Sampling of effluent streams was done using metal bellows sampling pumps that were located
after the instruments. The sample flow rate was controlled using adjustable flow rate valves.
The sample line pressure for both FTIRs and the QMS were monitored using capacitance
manometers. A filter was installed in the sample line used for monitoring scrubber emissions to
ensure that particulate emissions from the scrubber would not coat the FTIR internal optics, or
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the pressure reducing orifice used for the QMS. Since the scrubber DRE determination and the
scrubber dilution determination were independent events, it was possible to use the same sample
line for both operations. This was accomplished by switching the instrument inlet sample fitting
from the FTIR to the QMS.
The QMS was calibrated to determine its response to Kr on site using a dynamic dilution
blending system. Test atmospheres containing Kr, were created by blending a calibration
standard containing 1% of Kr in N2 with N2 diluent. The QMS response to 84Kr during
calibration is shown in Figure 2. From regression analyses of these data a calibration curve was
generated and is shown in Figure 3. This calibration was repeated for both tools tested.
To Scrubbed Exhaust
Effluent front Process
Pump to Scirubber
\
N2 Purge
QMS
X
-^
I
X
^
,
X
V
Vacuum Pump
Sample Pump
Schematic for effluent analysis on
scrubbers at Qiinoiulii
Sample Pump
Figure 1: Sampling schematic used for testing TPU PFC DRE
QMS Response to Kr
O.OOE + OO
Figure 2: QMS Response to 84Kr during calibration.
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Regression Analysis of Kr Calibration
8.OOE-O4
2.OOE-O4
Y = 7.3e-6X •*• 2.5e-5
Figure 3: Regression analysis of calibration data shown in Figure 2
3.0 Data Analysis
3.1 Determination of Scrubber Dilution
One of the primary goals of this study was to accurately determine the dilution that occurs when
gas emitted from the process chamber passes through the scrubber. Dilution can occur from
many sources including effluents from other chambers, combustion gases and by-products added
to and generated within the scrubber, vapors added as the gas stream passes through the water
scrubber portion of the system, in-board leaks, and back diffusion from main headers. The
method of determining dilution in this study was to use a purely experimental approach where a
chemical was spiked into the gas stream entering the scrubber at a known flow rate, and
determined in the scrubber effluent stream. From the determined concentration and the
controlled flow rate added to the process exhaust duct, a total flow from the scrubber could be
calculated:
TF= Sf/(Ca
,X10"6)
(1)
Where Sf represents the spike gas flow and is reported in liters per minute, and Can represents the
analyte concentration reported in ppmv.
The experiment conducted to determine dilution for the scrubbers on AMZ17 and AMZ18
consisted of using the calibration system shown in Figure 1 to add calibration gas into the
process effluent through the FTIR sample line where the process effluent was monitored. While
calibration gas was being added, the QMS was used to sample scrubber effluent. The flow of
calibration gas was controlled with a 0 - 5 slm Mass Flow Controller (MFC) that was calibrated
for nitrogen. Five flow rates were added to the scrubber: 1, 2, 3, 4 and 5 slm. The concentration
profile for Kr determined from QMS data during this experiment are shown in Figure 4 for
AMZ17.
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QMS Scan
Figure 4: Kr concentration determined for AMZ17 scrubber during spiking experiment.
Flow rates of calibration gas are indicated on the graph.
Applying Eq. 1 to the data obtained for the scrubbers on AMZ17 and AMZ 18 yielded the total
flows contained in Table 1. The average total flow for each scrubber is also contained in Table
1.
Table I: Data used to determine the total flow emitted from TPU systems on AMZ17 and
AMZ18.
AMZ 17 System
Total Cal Gas Flow
(slm)
1.0
2.0
3.0
4.0
5.0
AMZ 18 System
Total Cal Gas Flow
(slm)
1.0
2.0
3.0
4.0
5.0
Equivalent Kr
Flow (slm)
0.010
0.020
0.030
0.040
0.050
0.010
0.020
0.030
0.040
0.050
Kr Concentration
measured at TPU
Outlet (ppmv)
15.1 ±1.4
27.1 ± 2.7
40.8 ±1.8
55.5 ± 1.9
69.5 ± 2.0
14.1 ± 1.6
25.5 ± 1.7
38.8 ± 1.7
52.2 ± 1.9
65.8 ± 2.4
Total Flow
(slm)
662 ± 61
738 ± 74
735 ± 32
723 ± 25
719 ±21
Ave. Total Flow
for AMZ 17 System
721 ±2
709 ± 80
784 ± 52
773 ± 34
766 ± 28
760 ± 28
Ave. Total Flow
for AMZ 18 System
765 ±2
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The total scrubber flow data can be combined with the flow from the process chamber and pump,
which go into the scrubber and is referred to as the total process flow, to determine the dilution
that occurs as the process effluent passes through the scrubber. This calculation requires
measuring the dilution that occurs as gases from the etch chamber are pumped out of the
chamber and fore line and sent into the corrosive scrubber exhaust. The experiment to measure
the dilution of AMZ17 and AMZ18 chamber effluent consisted of flowing CF4 into the chamber
with the RF power in the chamber turned off at several flow rates. The determined CF4
concentration in the effluent could be used to calculate the total process flow entering the
scrubber from the following equation:
TPF= PGf/(CPGX106)
(2)
Here the total process flow (TPF) is determined from the ratio of the process gas flow (slm)
divided by the measured concentration (Cpo) in ppmv. The values obtained for CF4 on AMZ17
are shown in Figure 5. From these data the total process exhaust flows for both AMZ17 and
AMZ18 were calculated and are contained in Table II.
CF4 Emissions from ETCAMZ17 Chamber B during CF4 Chamber Flows
14000
12000
500
600
Figure 5: CF4 emission concentrations determined from AMZ17 chamber B while CF4 was
flowed through chamber B with RF power off.
10
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Table II: Total chamber and process pump effluent flow from chamber B on AMZ17 and
AMZ18. Values determined from the average concentration measured during each CF4
flow using Eq. 2
ETCAMZ17
CF4 Flow
(slm)
0.200
0.150
0.100
0.050
0.025
CF4 Cone.
(ppmv)
11,211 ±
183
8780 ± 55
5784 ± 109
3024 ± 43
1554 ± 48
Total
Effluent
Flow
(slm)
17.8 ± 0.3
17.1 ± 0.2
17.3 ± 0.3
16.5 ± 0.2
16.1 ± 0.5
ETCAMZ18
CF4 Flow
(slm)
0.200
0.150
0.100
0.050
0.025
CF4 Cone.
(ppmv)
12,134 ±
195
9652 ± 121
6477 ± 48
3297 ± 32
1681 ±61
Total
Effluent
Flow
(slm)
16.5 ± 0.3
15.5 ± 0.2
15.4 ±0.1
15.2 ± 0.2
14.9 ±0.5
The data in Table II yielded an average total flow of 17.0 ± 0.7 slm for AMZ17 and 15.5 ± 0.6
slm for AMZ18. The process flow into the scrubber combined with the total flow from the
scrubber yielded the experimentally measured dilution for each scrubber:
System Dilution = TFout/TFin (3)
For AMZ17: Dilution = 721 ± 2/17.0 ± 0.1 = 42.4 ± 2
ForAMZIS:
Dilution = 765 ± 2/15.5 ± 0.1 = 49.4 ± 2
Equipped with these dilution factors and total flows into and out of the scrubbers it is now
possible to determine the scrubbers DRE for the gases used and by-products formed during wafer
processing.
3.2 Scrubber DRE Determinations
Determination of the scrubber performance was done using two different testing conditions. The
first was to measure the scrubber effluent of the etch process gases during the total process flow
calibrations and the second was to measure the scrubber effluent during wafer processing.
3.2.1. DRE Determination During Process Calibration Flows
The scrubber DRE for CF4, CHF3 and C4F6 was determined during total process flow
calibrations by comparing the steady-state inlet and outlet concentrations during the flow of each
gas, and adjusting for the scrubber dilution. From these data a direct calculation of the scrubber
DRE could be made. Figure 6 shows the scrubber inlet and outlet CF4 concentrations determined
for AMZ18 while CF4 was flowing through the chamber. (These were the data used to calculate
11
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the AMZ18 process dilution.) These data were used to calculate the scrubber DRE for CF4 using
the following equation:
DRE = 1 - ((CF4outX Dilution)/CF4in)
(4)
Here CF4out and CF4;n represent the average CF4 concentrations determined for each flow shown
in Figure 6. Using this method of comparing concentrations into and out of the scrubber, CF4
DRE values for AMZ17 and AMZ18 are tabulated and contained in Table III.
CF4 Emissions from ECTAMZ18 Chamber B During Process Flow Calibration
CF4 Emissions from TPU During Process Flow Calibration
Figure 6: CF4 emission profile from AMZ18 chamber B (top) and from TPU (bottom)
during process flow calibration. Each level of concentration is equivalent to a specific CF4
flow rate thru the process chamber.
Table III: CF4 DRE values determined during process flow calibrations.
12
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AMZ17
CF4 Flow
(slm)
0.200
0.150
0.100
0.050
0.025
Ave Process
Emiss. Cone.
(ppmv)
11,121 ± 183
8783 ± 55
5811 ± 109
3028 ± 43
1551 ± 48
AMZ18
0.200
0.150
0.100
0.050
0.025
12,134 ± 195
9652 ± 121
6477 ± 48
3297 ± 32
1681 ±61
Ave Scrubber
Emiss. Cone.
(ppmv)
191 ± 2.5
151 ± 1.5
104 ± 0.6
51 ± 0.4
27 ± 0.5
200 ± 2.0
162 ± 0.8
113 ±0.5
59 ± 0.3
30 ± 0.2
Dilution
Adjusted
Concentration
(ppmv)
8098
6402
4410
2162
1145
9880
8005
5582
2915
1482
DRE
(%)
27.8 ± 0.6
27.1 ± 0.4
23.6 ± 0.5
28.5 ± 0.5
26.3 ± 1.0
18.6 ± 0.4
17.1 ± 0.2
13.8 ± 0.2
11.6 ±0.2
11.8 ±0.5
From the data contained in Table III the scrubber CF4 DRE appears higher for the AMZ17
scrubber relative to the AMZ18 scrubber. Results for CHF3 indicated that AMZ17 abated CHF3
sufficiently to yield a concentration below the detection limit of the FTIR equipped with a 5.6m
cell, while relatively low emissions of CHF3 were detected from AMZ18 scrubber. The CHF3
inlet and outlet profiles determined during CHF3 flows through chamber B on AMZ18 are shown
in Figure 7. Both scrubbers abated C4F6 sufficiently to yield an outlet concentration not detected
by the FTIR.
CHF3 Emissions from AMZ18 Chamber B during Process Flow Calibration
1400
FTIR Scan
13
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CHF3 Emissions from Scrubber during CHF3 Process Flow Calibration
'• 5
Figure 7: CHF3 emissions from process (top) and scrubber (bottom) during CHF3 process
flow calibration.
From the data shown in Figure 7, the AMZ18 scrubber DRE was calculated for CHF?, during the
total process flow calibration and is contained in Table IV. These data indicate a relatively high
DRE for CHF3 on AMZ18 scrubber. The AMZ17 scrubber had a higher DRE as CHF3 was not
detected in the effluent during the CHF3 flow calibration.
Table IV: CHF3 DRE for AMZ18 scrubber based on data shown in Figure 7.
CHF3 Flow
(slm)
0.200
0.100
0.025
Ave Process
Emiss. Cone.
(ppmv)
12,820 ± 170
6538 ± 74
1601 ±15
Ave Scrubber
Emiss. Cone.
(ppmv)
3.1 ±0.1
1.4 ± 0.06
0.4 ± 0.01
Dilution
Adjusted
Concentration
(ppmv)
153
69
20
DRE
(%)
98.8
98.9
98.8
The DRE for C$6 was high for both AMZ17 and AMZ18 scrubbers. The estimated detection
limit for C$6 was 0.5 ppmv with the 5.6m gas cell based on a signal to noise ratio of 3. Thus,
based on a 0.100 slm process flow (0.100 slm was the maximum flow possible with the installed
MFC), which yielded an average process emission of 6474 ± 59 ppmv on AMZ18, the minimum
DRE would be 99.6 %.
3.2.2 Determination of DRE during Wafer Processing
Determining the scrubber DRE under wafer processing conditions can be much more
challenging, particularly if the PFC effluent concentration does not reach a steady state condition
(here a steady state condition is defined as dC/dt = 0, where the concentration (C) is not changing
over a relatively short period of time, as shown in Figure 6). Under these conditions it may be
14
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necessary to numerically integrate the PFC concentration over time to yield an emission volume,
which can be compared to the integrated process emission volume entering the scrubber for a
given analyte. To convert measured concentrations into volumes, the following equation was
used:
VEM = C,TfAt (5)
Where the total emission volume (VEM) is the summation of each FTIR data point where the
concentration of analyte C is determined during time interval At and multiplied by the total flow
(Tf). The summation of the entire emission profile provides an emission volume for a given
analyte during the process. During this study, these calculations were performed using standard
spreadsheet software (Microsoft Excel). Use of this technique reinforces the importance of
accurately determining the total process and scrubber flows as described in the sections above.
The process tested on AMZ17 and AMZ18 was a dielectric etch process that had two distinct
etch steps. The approximate process recipes were as follows:
Step 1 Arc Etch: 160 seem CF4; 100 seem CHF3; 150 seem Ar; 20 seem O2 35 sec
Step 2: Main Etch: 60 seem C4F6; 1000 seem Ar; 45 seem O2 65 sec
In addition to the etch times listed above, up to 5 sec of additional chamber stabilization time is
required to turn the process gases on and set the chamber pressure prior to turning on the process
plasma.
During the etch processes etch gases CF4, CHFs and C/tFe could be detected in the process
effluent. Many etch by-products were also detected. These included SiF4, HF, COF2, C2F4, C2F6
and CO. Figure 8 shows the FTIR spectrum of process emissions for each etch step.
15
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;;J- ~~A~/
COF2 COSF4
CHF3
-JL
Arbitrary Y / Wavenumber (cm-1)
3000 3500 4000 4500
10/23/2007 1:39 PM Res=None
Arbitrary Y /Wavenumber (cm-1)
File#1 = QIMOND~1
Paged Y-Zoom CURSOR
10/23/2007 1:39 PM Res=None
Figure 8: FTIR spectra of emissions from arc etch (top) and contact main etch (bottom)
Typical emission profiles for the etch process are shown in Figure 9. These data were acquired
on AMZ18 chamber B during the etching of test wafers. The top graph shows PFC process gas
emissions during both etch steps for three wafers. The bottom graph shows the etch by-products
16
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formed in the plasma during the process. The spikes observed in the process gas emissions are
attributed to the stabilization flow at the beginning of the etch process, and the chamber purge of
residual gases after the plasma has been turned off at the conclusion of etching.
The PFC emissions data shown in Figure 9 (top) were integrated to determine the total emission
volume for each gas, and used to calculate the process utilization for each molecule. Using the
process recipe shown above the following PFC plasma utilization values were obtained for CF4,
CHF3 and
Table V: Process Utilization for etch gases used in contact etch. The volumes reported as
being used were calculated from the process recipe and assumed a stabilization flow of 5
seconds. Data reported per wafer processed.
CF4 Used for Process
(si)
0.107
CHF3 Used for Process
(si)
0.067
C4F6Used for Process
(si)
0.070
CF4 Emitted from process
(si)
0.088
CHF3 Emitted from
process
(si)
0.032
C4F6 Emitted from
process
(si)
0.005
CF4 Process Utilization
(%)
18
CHF3 Process Utilization
(%)
52
C4Fe Process Utilization
(%)
93
The data contained in Table V include emissions for both etch steps of the process.
Approximately 10% of the total CF4 emission was observed during the C$6 process step, where
CF4 was formed as a by-product.
PFC Emissions during Contact Etch on AMZ18
i
Arc Etch
^ \.
Uv»l
JUI
\ff*
,
Main
/
L/Jl
U*J
.
—
TRIFLUOROMET
HANE 1 5OC
CARBON
TETRAFLUORIDE
1 5OC
C4F6 Qimonda
AMZ18 Process
Flow 15OC
17
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By-product Emissions from Contact Etch on AMZ18
/I
-HF 15OC
-SiF4rp1OOC
-COF2 1O5C
C2F6 12OC
-C2F4
-CO LOW PPM 15OC
27OO 275O 28OO 285O 29OO 295O 3OOO 3O5O 31OO
FTIR Scan
Figure 9: Emission profiles for PFC process gases (top) and plasma by-products (bottom)
during contact etching of test wafers on AMZ18 chamber B. The ARC and Main etch
portions are labeled in the figures.
Emissions from the scrubber during wafer processing included primarily CF4. Figure 10 shows
an FTIR spectrum obtained during test wafer processing on AMZ18. Low level CHF3 and C2F6
emissions were detected. The CF4 emission profile from the scrubber is shown in Figure 11.
Only the data for the test wafers was used to calculate a DRE as emissions from multiple
chambers confound the DRE determination if the scrubber loading from other chambers is not
accounted for. CF4 emissions from the test wafers were integrated and used to calculate DRE by
comparing to the integrated process emissions reported above. Figure 12 shows CF4 emissions
from AMZ17 scrubber. Again multiple chambers were being used on the tool. CF4 emissions
for the last 9 wafers were integrated to yield total CF4 emission for 9 wafers and compared to the
integrated process emissions for the same 9 wafers. The results for both scrubbers are contained
in Table VI below:
18
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Table VI: CF4 DRE determined for each scrubber by comparing inlet and outlet emission
volumes.
AMZ17
Integrated CF4 Process
Emissions for 9 wafers
(si)
0.920
AMZ18
Integrated CF4 Process
Emissions for 5 test wafers
(si)
0.445
Integrated CF4 Scrubber
Emissions for 9 wafers
(si)
0.716
Integrated CF4 Scrubber
Emissions for 5 test wafers
(si)
0.425
Scrubber CF4 DRE
(%)
22
Scrubber CF4 DRE
(%)
4
Emissions of C2F6 and CHF3 from the AMZ18 scrubber during test wafer processing were
integrated and used to estimate minimum DRE values of > 98 % for C2p6 and > 98.7 % for
CHF3 Actual DRE values are presumed to be higher. The minimum DRE for C2p6 is based on
an integrated per wafer process emission of 0.010 si and an integrated scrubber emission of <
0.001 si. The minimum DRE for CHF3 is based on an integrated per wafer process emission of
0.033 si and an integrated scrubber emission of < 0.001 si. CHF3 and C2p6 were not detected in
the effluent of the scrubber on AMZ17.
Figure 10: FTIR spectrum of AMZ18 scrubber emissions during test wafer processing.
19
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CF4 Emissions from TPU During Process Flow Calibration
Multiple Chambers Processing Production Wafers
38OO
FTIR Scan
Figure 11: CF4 emission profile from AMZ18 scrubber during processing of test wafers on
Chamber B, and during processing of production wafers on multiple chambers.
CF4 Emissions from TPU During AMTZ17 Wafer Processing
Multiple Chambers Running
Chamber B Running
Figure 12: CF4 emission profile from AMZ17 scrubber during processing of production
wafers on Chamber B, and during processing of production wafers on multiple chambers.
Ill: Comparison of CFjDRE Determinations:
Both methods of determining the scrubber DRE for CF4 on AMZ17 and AMZ18 are compared in
Table VII. Both methods are in reasonable agreement and both indicate a relatively low DRE
for CF4 on the scrubbers tested. Higher DRE were obtained for etch gases CHF3 and C4p6, and
process by-product C2p6. The AMZ17 scrubber appears to be more effective at abating all PFCs.
It was noted during testing that the AMZ17 scrubber was operating at a higher reported
temperature than the AMZ18 scrubber, however, temperature data were not collected.1
1 Observations of temperature during the study indicated that AMZ17 was running at approximately 885 to 905 °C,
whereas, AMZ18 was running at approximately 800 to 815 °C. It is believed that the noted temperatures refer to the
external wall temperature of the combustion chamber within the abatement device.
20
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Table VII: Comparison of two methods used to determine CF4 DRE on scrubbers for
AMZ17 and AMZ18
Scrubber
ETCAMZ17
ETCAMZ18
CF4 DRE determined from
Process Gas flow Calibrations
(average of 5)
(%)
27
15
CF4 DRE from Integrated
Process Emissions
(%)
22
4
4.0 Conclusion
Determination of the DRE of PFCs by POU scrubbers has been conducted for a contact etch
process at Qimonda. Two scrubbers of the same make and model were tested. The processes
tested were the same on each tool. The results indicated very high DRE for most PFC process
gases and PFC by-products. Only CF4 was determined to have a low DRE on both systems.
One key element of this study was to accurately determine the dilution that occurs to process
effluent as it passes through the scrubber into the corrosive scrubber exhaust duct. In this study,
the dilution was determined by using a chemical tracer, Kr, which was injected into the scrubber
inlet of one process chamber, and subsequently determined in the scrubber effluent. The effluent
Kr concentration was determined by using a QMS, which was calibrated on-site for its response
to Kr. The choice of Kr for chemical spiking was dictated by the need for a tracer that would not
react in or be produced by the scrubber.
Two methods of determining process gas DRE were investigated. Use of a continuous flow of
PFC gases permitted a steady state emission of PFC from both the process chamber and scrubber
(provided the DRE was < 100%). This allowed direct comparison of emission concentrations
from tool and scrubber after scrubber effluent data were corrected for dilution. Wafer processing
emissions were also used to calculate DRE by integrating the emission concentrations over time
and total flow to yield emission volumes into and out of the scrubber. The comparison of these
methods yielded DRE values that were in reasonable agreement. The latter method could be
needed in cases where the effluent data do not appear to reach a steady state, particularly for the
scrubber effluent. The fundamental difference between the two methods is that etch by-products
would be present in method 2, whereas they would not present in method 1. This would include
any particulates that may be present in the etch effluent stream.
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