Radiant energy – Invisible radiant energy responsive electric signalling – Infrared responsive
Reexamination Certificate
2001-09-04
2003-11-04
Hannaher, Constantine (Department: 2878)
Radiant energy
Invisible radiant energy responsive electric signalling
Infrared responsive
C250S338100
Reexamination Certificate
active
06642521
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to a method for measuring greenhouse gases using an infrared absorption spectrometer. More particularly, the present invention relates to a method for measuring greenhouse gases using a Fourier-transform infrared spectroscope (FT-IR).
2. Description of Related Art
In recent years, problems relating to global warming are attracting more attention while greater concerns in environmental problems being raised. Global warming progresses in association with increases in the concentration of greenhouse effect gases (or greenhouse gases) in the atmosphere, such as CO
2
, NOx, methane, PFC (perfluorocarbon) and the like. These greenhouse gases have strong absorbance in an infrared region. When discharged into the atmosphere, they absorb energy irradiated from the earth's surface. The absorbed energy is radiated upward toward outer space and downward toward the earth's surface. In this instance, a part of the energy radiated from the earth's surface is returned again to the earth's surface by the greenhouse gases, such that the temperature on the earth's surface increases. By this system, the greenhouse gases are thought to bring about a global warming effect.
Global warming potential (GWP) is known as an indicator to compare degrees of the global warming effect caused by the greenhouse gases. The GWP represents how much warming effect one unit weight of a gas has compared to one unit of CO
2
. PFCs are counted as gases having a high global warming effect among the greenhouse gases. PFCs have an extremely high GWP value. For example, the GWP value of CF
4
is about 6,500 times higher than that of CO
2
. Also, PFC is stable compared to other gases, and have a very long life in the atmosphere. For example, the life of CF
4
in the atmosphere is about 50,000 years. Therefore, once discharged into the atmosphere, PFC would warm the earth for many years.
The PFCs are ordinarily used in a process of manufacturing semiconductor devices, and more particularly, they are frequently used in an apparatus using low-pressure plasma. For example, in a dry etching apparatus, PFCs, such as CF
4
, C
4
F
8
and the like, are used to etch SiO
2
and Si
3
N
4
. Also, in a CVD apparatus, gas plasma of C
2
F
6
or the like is often used to clean films of silicon compound or the like adhered to the apparatus. Furthermore, a liquid PFC is used as a medium to cool wafers. However, as described above, since the PFC has a high global warming effect, the reduction in the discharged amount of PFCs is purposefully being pursued. At the COP3 Kyoto Conference that was held in December 1997, an agreement was reached to reduce the discharged amount of PFCs and the like in Japan by 6% by the year 2010 compared to the level in the year 1995. Thereafter, at the ESH (environment·safety·health) task force in the WSC (World Semiconductor Conference) held in 1999, an agreement was reached to reduce the total discharged amount by 10% by the year 2010 compared to the level in the year 1995.
In order to verify the reduction of the discharged amount of PFCs, PFC gases that are emitted from factories need to be measured. At present, since it is difficult to measure PFC gases emitted from a factory, PFC gases discharged from a semiconductor manufacturing apparatus that uses PFCs are measured, and the discharged amount of PFCs is determined using an amount ratio (emission factor) of discharged gases to fed gases, and the amount of gases that are consumed in the factory. PFC gases that are actually discharged from a semiconductor manufacturing apparatus are measured to calculate the emission factor. Measurements of PFC gases that are actually discharged from semiconductor manufacturing apparatuses are conducted according to guidelines referred to as “Emissions Characterization Package Rev. 2.4 (generally referred to as “Intel Protocol”) (currently, “Equipment Environmental Characterization Guidelines Rev. 3.0”) by J. Mayers et al. of Intel Corporation, which was distributed at Global Semiconductor Industry Conference on Perfluorocompound Emissions Control that was held in Monterey, Calif., U.S. in April 1998. The Intel Protocol describes a method for measuring emitted PFC gases, using a quadrupole mass analyzing spectrometer (QMAS) and a Fourier-transform infrared spectroscope (FT-IR). However, since no detailed description is provided for the measurements using the FT-IR, measurement results may have great variations depending on measurement methods. Accordingly, to compensate for the Intel Protocol, methods of measuring PFCs in emitted gasses with simpler processes and good reproducibility have been sought.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a method for measuring components in emitted gases with ease and good reproducibility, using an infrared absorption spectrometer.
(A) A method for measuring greenhouse gases using an infrared absorption spectrometer in accordance with the present invention includes the steps of:
selecting a process chemical material;
selecting a measurement target chemical material corresponding to the process chemical material:
designating expected concentration ranges for the process chemical material and the measurement target chemical material;
selecting libraries for the respective expected concentration ranges for the process chemical material and the measurement target chemical material; and
analyzing data obtained by a gas infrared absorption spectrometry based on the libraries.
The process chemical material is a chemical material that is used in a process. Also, the measurement target chemical material is a chemical material that may possibly be included in the gas because the process chemical material is included in the gas.
Also, the library is absorbance data that is measured in advance for known concentration of the chemical material, which is used to perform an accurate concentration measurement, when data obtained by an infrared absorption spectrometry of the chemical material is analyzed.
By the method for measuring greenhouse gases in accordance with the present invention, concentrations of respective components in a mixed gas can be measured with a simplified method and with good accuracy.
For the method for measuring greenhouse gases in accordance with the present invention, the following description is provided of exemplary embodiments (1)~(3).
(1) A library formed of absorbance data for a plurality of known concentrations is made for each chemical material in the gas;
calibration curve data with respect to concentration-absorption area for a main peak region and an auxiliary peak region is made for the each chemical material in the gas based on the library; and
data obtained by the gas infrared absorption spectrometry is analyzed based on the calibration curve data.
When the expected concentration range of each composition among the gas is included in a region where a linearity of the calibration curve data for the main peak region is small, the concentration is determined using the calibration curve data for the auxiliary peak region.
Here, the “main peak region” is a region that includes the highest peak in the infrared absorption waveform of the gas. Also, the “auxiliary peak region” is a region that includes a peak located in a region that is different from the main peak region. Depending on compositions, two or more auxiliary peak regions may exist.
Also, the “calibration curve data” is data representing the relation between concentrations and absorption areas for each component in the gas. When an infrared absorption measurement is conducted, libraries are selected in accordance with the expected concentration ranges, and data analysis is conducted based on calibration curve data for the selected libraries.
Also, the “region where a linearity of the calibration curve data for the main peak region is small” is an area in the calibration curve data for the main peak region that has a smaller linearity in the relation between concentrations an
Namose Isamu
Sugiura Toshikazu
Gabor Otilia
Hannaher Constantine
Oliff & Berridg,e PLC
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