Application Bulletin
ABG-100-1104a
Utilizing Pall Gaskleen® Purifiers for CO to Prevent
Metal Carbonyls and Moisture Contamination
in Dielectric Plasma Etch Processes
Anthony Ricci
Dielectric etch occurs in dry etch tools, typically
Inductively Coupled Plasma (ICP) or
Transformer Coupled Plasma (TCP) type
chambers. These types of plasma chambers
operate at low pressures, and high-density
plasmas are created by two independently
driven radio frequency sources.
react with the nickel and iron found in gas
delivery systems, resulting in metal carbonyl
formation. In addition, higher pressure and
moisture concentrations accelerate the
formation of metal carbonyls.2 Volatile metals
and moisture cannot be removed by particulate
filtration.
The process sequence before the dielectric
etch step is oxide deposition followed by a
series of photolithography steps. Dielectric
etch is an anisotropic etch process that removes
the dielectric (silicon oxide, silicon nitride)
and the overlying photoresist mask.
The CO process gas carries these volatile metal
carbonyls, along with moisture, into the
dielectric etch process chamber. This results in
deposition of the metals and moisture on the
wafer. Metallic contamination on wafers is
detrimental because it alters the electrical
characteristics of IC devices and can potentially
cause electrical shorts. Controlling metallic
contamination can prevent surface resistivity
changes and charge breakthrough, as well as
decrease minority carrier lifetime. Moisture
contamination can cause corrosion of
The dielectric etch recipe must provide the
critical dimension and profile control needed
to etch the high-aspect-ratio features that are
required in dense memory chips. The process
also must be capable of delivering the high
selectivity required to preserve the ultrathin
193 nm photoresist used for 90 nm and 65 nm
geometries in the industry's fastest logic chips.
Figure 1.
Ions
Carbon monoxide (CO) is used today in many
dielectric etch recipes because it provides
higher selectivity and greater profile control
than fluorocarbon- and oxygen-based etch
processes. The CO prevents loss of anisotropy
by forming sidewall passivating films, as
illustrated in Figure 1(d)1. With fluorocarbonbased recipes, the etch profiles are more
isotropic in nature, as illustrated in Figure
1(a)1 and Figure 1(b)1.
Metal Carbonyls and Moisture Are “Killer
Impurities” in Dry Etch Processes
Semiconductor grade (99.997%) CO may
contain upwards of 500 parts per billion (ppb)
of Fe(CO)5, 1 part per million (ppm) of Ni(CO)4
volatile metal carbonyl contamination, and 1
ppm of moisture contamination. Pure CO can
C
A
Ions
Passivating
film
D
B
Film removed
Plasma etching in integrated circuit manufacture:
(a) isotropic etch, (b) sidewall etching of the resist
mask, which leads to a loss of anisotropy in film
etch, (c) bombarding ions in anisotropic etch,
(d) sidewall passivating films in anisotropic etch.
Figure 2. Test Schematic Diagram
to less than 1 ppb levels from carbon
monoxide feedstock gas with much higher
concentrations (around a factor of 100) of
metal carbonyls than semiconductor grade
CO.4
The testing was performed using a gas
chromatograph equipped with an electron
capture detector (GC-ECD). The testing
apparatus consisted of cylinder sources of
purified and metal carbonyl-laden carbon
monoxide, a customized gas sampling system,
and precision mass flow controllers calibrated
in CO prior to testing. During the testing, GCECD instrument background levels fluctuated
between 0.72 ppb and 12.24 ppb for Ni(CO)4
impurity in the zero gas CO source. The test
system schematic diagram is depicted in Figure 2;
the Pall Gaskleen SIP purifier capacity curve
for metal carbonyls is shown in Figure 3.5
underlying metal layers 3 and can lead to
uncontrolled oxidation of the wafer’s surface
metal layers.
Testing Demonstrates That Gaskleen
Purifiers Are More Efficient at Removing
Metal Carbonyls
In independent laboratory testing, the Pall
Gaskleen SIP purifier has consistently
demonstrated the ability to remove metal
carbonyl (Fe(CO)5, Ni(CO)4) gaseous impurities
The graph in Figure 3 depicts removal
efficiency over purifier lifetime. The purifier
inlet challenge and effluent concentration
levels are used to calculate the removal
efficiency. For example, a removal efficiency
of 99.99% translates to an effluent
concentration of 10 ppb with a challenge of
100 ppm. The graph shows that the Gaskleen
SIP purifier removes metal carbonyl (Fe(CO)5,
Ni(CO)4) gaseous impurities from CO gas to
less than 1 ppb levels and that it has a large
capacity for metal carbonyls.
Figure 3.
Capacity Testing for Metal Carbonyl Removal
Pall Sample A080 with 1.0 slpm CO Flow
Challenge Concentrations: Ni(CO)4 = 96.9 ppmv, Fe(CO)5 = 96.9 ppmv
Ni(CO)4
Fe(CO)5
100.00%
Removal Efficiency
99.95%
99.90%
99.85%
99.80%
99.75%
0
5
10
15
20
25
30
35
40
Time (hrs)
During testing, the Pall Gaskleen® 11⁄8 ˝ C-seal Top Mount CO Purifier (part number GTMP3SIPCC4)
demonstrated a removal efficiency of 96.9 ppm for both Fe(CO)5 and Ni(CO)4.
Figure 4.
Metal Carbonyl Capacity and DesorptionTesting
Pall Sample A083 with 1.0 slpm of Carbon Monoxide Flow
Challenge Concentrations: Ni(CO)4 = 45.9 ppmv, Fe(CO)5 = 90.2 ppmv
Ni(CO)4
Fe(CO)5
Metal Carbonyl Concentration (ppb)
100000.0
Metal Carbonyl Challenge
At High Concentrations
For 18.6 Hours (1116 liters CO)
10000.0
1000.0
100.0
10.0
1.0
0.1
0
3
6
9
12
15
18
21
24
27
30
33
36
39
42
Time (hrs)
Pall Gaskleen® 11⁄8 ˝ C-seal Top Mount CO Purifier (part number GTMP3SIPCC4)
metal carbonyls desorption test results.
A purification medium’s metal carbonyl
removal efficiency and capacity are clearly
critical. However, it is equally important that
the medium not release metal carbonyls during
changeout at the end of the purifier’s life. The
release of toxic metal carbonyls into the
atmosphere is a safety hazard for the operator
performing the changeout.
Desorption testing was also performed as part
of the independent lab testing. The test
consisted of challenging a Pall Gaskleen® 11⁄8˝
C-seal top mount CO purifier (part number
GTMP3SIPCC4) with 45.9 ppm Ni(CO)4 and
90.2 ppm Fe(CO)5 impurity-laden CO gas at 1
standard liter per minute (slpm). After this
challenge, ultra-high purity CO gas (metal
carbonyl levels < 13 ppb) was passed through
the same Pall purifier at 1 slpm for 20 hours.
The effluent CO gas was monitored throughout
the testing on the GC-ECD. Results show levels
of CO effluent metal carbonyl below 13 ppb
(see Figure 4), indicating that the Pall Gaskleen
SIP purifier did not release any metal carbonyls
into the clean CO gas stream.
Gaskleen Purifier Reduces Nickel
Contamination by More Than 50% for
Semiconductor Manufacturer
A European semiconductor manufacturer found
nickel contamination on a silicon wafer. The
cause was the CO gas used in the oxide etch
process to remove silicon dioxide on the wafer.
The customer had a Pall Mini-Gaskleen™ HiFlow filter assembly installed on the CO gas
line, but the nickel passed through the filter
because it was in a vapor state (Ni(CO)4). By
replacing the Mini-Gaskleen filter assembly
with a Mini-Gaskleen™ purifier assembly, nickel
contamination on the wafer was reduced by
a minimum of 50%.
References
1. Lieberman and Lichtenberg. Principles of Plasma
Discharges And Materials Processing. WileyInterscience, 1994.
2. Braker and Mossman. Gas Data Handbook.
Matheson, 1980.
3. John Rosato. “Critical Cleaning Challenges for
Copper/Low-k Interconnect Systems,” Future Fab
Intl., Volume 8, July 2000.
4. Analysis performed by APCI, Allentown, PA, 2003.
5. P. Connor and K. Brown. “Pall Gaskleen® 1.125 CSeal Top Mount Purifier Testing Report: Metal Carbonyl
Removal from Carbon Monoxide,” Pall internal STR,
December 2003.
6. R. Chakraborty, K. Brown, and M. Horikoshi.
“Comprehensive Performance Testing and
Characterization of Various Point-Of-Use (POU) Inert
Gas Purification Technologies Used in Microelectronics
Fabrication Processes,” Gases and Technology,
July/August 2004.
Gas Filtration Purifiers Data Sheet A79a
Mini-Gaskleen™ Purifier
Gas Filtration Purifiers Data Sheet A88
Gaskleen® II Purifier
Gas Filtration Purifiers Data Sheet A87a
Gaskleen® ST Purifier
Gas Filtration Purifiers Data Sheet A81a
Maxi-Gaskleen™ Purifier
Gas Filtration Purifiers Data Sheet A86a
Gaskleen® 11⁄8” C-seal Purifier
25 Harbor Park Drive
Port Washington, New York 11050 USA
1.800.360.7255 toll free (Only in US)
1.516.484.5400 phone
1.516.625.3610 fax
Visit us on the Web at www.pall.com
Pall Corporation has offices and plants throughout the world.
To learn more, please contact your local Pall Microelectronics representative. Contact
information for your region is available at www.pall.com/microelectronics_contact.asp.
© Copyright 2006, Pall Corporation. Pall,
trademark registered in the USA.
ABG-100-1104a
, are trademarks of Pall Corporation. ® Indicates a Pall
is a service mark of Pall Corporation.