Application Note
Nitrous Oxide (N2O)
Contaminant Detection Using
MultiGas™ Purity Analyzer
Note #01/03
CUSTOMER PROBLEM
• Detection of H2O, NH3, NO, NO2, CO2, CO and CH4 to low ppb levels in high purity bulk N2O gas
• Improve quality of high purity bulk N2O gas production
• Increase product yield and performance
BACKGROUND
High purity bulk N2O is used as an oxygen source for chemical vapor deposition (CVD) of silicon dioxide layers in semiconductor
processing, as well as in LCD production. It has been proven that trace impurities in N2O have detrimental effects on device
performance. To monitor trace impurities in N2O, methods such as gas chromatography with discharge ionization detection have
been used to quantify CO, CO2, CH4 and H2O. However, this method is difficult to incorporate into production environments
since different columns and oven temperature programs are required to complete the analysis. For polar gas impurities such as NOx
and NH3 the chromatography is difficult, thus leading to higher detection limits than desired. One added disadvantage to gas
chromatography is that it cannot sample the gas stream continuously and cannot provide real-time analysis.
SOLUTION
The MKS MultiGas Purity Analyzer is a real-time, fully calibrated system for monitoring trace impurities in bulk gases, such as
N2O. The Purity Analyzer has been proven to monitor trace levels of H2O, NH3, NO, NO2, CO2, CO and CH4 in 100% N2O
gas, all in real-time and in production environments. The typical detection limits of selected contaminants in N2O are as follows:
Contaminant
H2O
Typical Detection Limit
10 ppb
NH3
NO
NO2
5 ppb
20 ppb
10 ppb
CO2
CO
CH4
2 ppb
10 ppb
15 ppb
Figure 2 shows standard additions of NO in high purity N2O at 4.1, 3.7 and 1.87 ppm to demonstrate the accuracy and minimum
detection limit for the MultiGas Purity Analyzer. All the measurements were recorded to be within 2% of the set points. Figure 2
also illustrates the fast response time of the Purity Analyzer - all of set points were reached within a couple of minutes.
The MultiGas Purity Analyzer has been demonstrated to be the most accurate and reproducible impurity analyzer available. Its
detection limits are significantly below process requirements to enable accurate impurity monitoring. The MultiGas Purity
Analyzer can monitor purifier performance continuously and in real-time to allow purifiers to be switched or replaced only when
required, saving significant time and money. Process risk is also reduced through the ability to observe gas purity excursions as they
occur. Designed for continuous, real-time high purity gas monitoring, the MultiGas Purity Analyzer can improve the quality of
bulk gas production and the yield of subsequent semiconductor and LCD based devices.
Page 2
Application Note
SOLUTION (CONT'D)
Multiple NO Additions in N2O
MultiGas Purity
5
NO Generator Setpoints
4.5
NO Concentration (ppm)
4
3.5
3
2.5
2
1.5
1
0.5
0
-0.5
8:52 PM
10:48 PM
12:43 AM
2:38 AM
4:33 AM
Time
Figure 1: Spectral analysis of NO (blue) in 100% N2O (yellow)
illustrates the MultiGas Purity differentiation capabilities.
Figure 2: Chart of NO additions to high purity N2O. Figure used
with permission from BOC Edwards, Phoenix, AZ.
BENEFITS
The MultiGas Purity analyzer provides numerous benefits to high purity gas manufacturers, semiconductor manufacturers, and
LCD manufacturers:
• Improved product yield and performance at fabs
— Purifiers switched or replaced only when needed, not before
— Greater use of bulk cylinders
— Early warning of process gas purity upset
• Continuous measurement of N2O purity in real-time, in production environments - no lab analysis required
• ppb level impurity detection limits that are significantly below process requirements for accurate impurity detection
REFERENCE MATERIALS
MKS Publications:
MultiGas Purity datasheet
For further information, call your local MKS Sales Engineer or contact the MKS Applications Engineering Group at 800-227-8766.
MultiGas™ is a trademark of MKS Instruments, Inc., Wilmington, MA.
App. Note #01/03 - 4/03
© 2003 MKS Instruments, Inc.
All rights reserved.
Gas Analysis/FTIR
651 Lowell Street
Methuen, MA 01844
978.682.4567
MKS Global Headquarters
90 Industrial Way
Wilmington, MA 01887-4610
978.284.4000
800.227.8766 (in U.S.A.)
www.mksinst.com