GB2163553A - Method and apparatus for chemiluminescence analysis - Google Patents

Abstract

Method and apparatus for chemiluminescent substances in which the radiant energy emitted as a result of a chemiluminescence reaction, in the presence of ozone, of a substance for example arsine or phosphine in the sample gas is detected by a sensor such as a photomultiplier, the time at which the radiant energy resulting from the chemiluminescence reaction is detected by a sensor is made slightly later than the time at which the sample gas is mixed with ozone to initiate the chemiluminescence reaction, to minimize interference from other short-lived chemiluminescent substances. In apparatus for use in carrying out the above-described method, reactants are mixed in a first chamber 3 and pass to a second chamber 4 where radiation is detected by a sensor 7. <IMAGE>

Description

SPECIFICATION Method and apparatus for chemiluminescence analysis This invention relates to an analytical method and apparatus utilizing chemiluminescence.

In electronics industries concerned in the manufacture of semiconductors and the like, toxic gases such as silane, arsine, phosphine, diborane, etc. are used in large amounts. The maximum allowable concentrations of these gases in a working environment are very low, i.e., for example in Japan, 5 ppm for silane, 0.05 ppm for arsine, 0.3 ppm for phosphine, and 0.1 ppm for diborane. As the semiconductor industry becomes more and more prosperous, the demand for a leak detector or analyzer capable of detecting and analyzing such toxic gases in a working environment with ease and accuracy has been growing.

Conventionally, such gases have been determined by a variety of well-known methods including infrared photometric analysis, chemical reaction/atomic absorption photometry, membrane galvanic cell method, controlled potential electrolysis, chemiluminescence analysis and the like.

Among the measuring principles above, the chemiluminescence is a radiation energy which generates when a substance (molecule) at an excited state being formed as a result of a chemical reaction falls into its ground state.

Although the chemiluminescent phenomenon has been known for long, recently the development of technologies of the measurement of weak light, such as photomultipliers and the like, an analytical method utilizing chemiluminescence has come to attract much attention. Since this analytical method is characterized not only by high sensitivity as the most distinctive feature but also by additional advantages such as a wide range of linear response, easy operation, rapid response, a simple construction of apparatus, and the like, its field of application has been expanding in recent years.

Among these chemiluminescence phenonema, chemiluminescence in the presence of ozone is known in connection with components (such as CO, THC, SO2, NO, etc.) of atmospheric air, flue gases and automobile exhaust gases, as well as inorganic hydrides as described above. With respect to apparatus utilizing the chemiluminescence method, Thermo Electron Corp. (U.S.A.) and other manufacturers have already achieved years of study and good commercial results in the supply of nitrogen oxide analyzers for atmospheric air, flue gases and automobile exhaust gases.

However, the chemiluminescence method had not been applied to the analysis of inorganic hydrides till quite recent.

Difficulties are encountered in applying the technology suited for nitrogen oxide analyzers to the detection of inorganic hydrides in a working environment. Usually, certain amounts of THC, CO, SO2, NO and the like exist in a working environment. Among others, NO poses a serious problem because it gives high chemiluminescence intensity and exists in high concentrations. As a result, NO exhibits chemiluminescence together with inorganic hydrides to be detected, and interferes with the measurement thereof. Thus, it is necessary to distinguish between the chemiluminescence arising from inorganic hydrides and the chemiluminescence arising from NO present in a working environment.

Japanese Patent Laid-Open No. 196138/'82 (applied in the name of L'AIR LIQUID SOCI ETE ANONYME, France, with the declaration of priority based on French Patent Application No. 8110316, filed May 25, 1981) discloses a method and apparatus for detecting inorganic hydrides by utilizing the difference in wavelength range between the chemiluminescence spectrum resulting from the reaction of NO with ozone and the chemiluminescence spectra resulting from the reactions of inorganic hydrides with ozone. Specifically, the light emitted as a result of the chemiluminescence reactions is passed through a filter transmitting light in the wavelength range from 495 to 650 nm and the resulting filtered light is detected, whereby inorganic hydrides can be detected with the elimination of interference from NO.The chemiluminescence spectrum of NO has a spectral distribution covering the infrared region from 600 nm to 3,000 nm, whereas that of arsine ranges from 300 to 900 nm and that of phosphine ranges from 350 to 750 nm. Accordingly, the interference from NO can be reasonably eliminated by using a suitable filter to restrict the wavelength range of the filtered light properly. However, this method has the disadvantage that the light absorption by the filter inevitably causes a loss of photometric intensity and, hence, a reduction in the detection sensitivity for inorganic hydrides.

The present invention has been made with attention paid to the fact that the chemiluminescent reactions of various chemiluminescent components with ozone last for different periods of time. Specifically, the chemiluminescence of NO takes place upon contact with ozone and terminates in a moment (with a duration of several milliseconds or less), whereas the chemiluminescence of inorganic hydrides (such as silane, arsine, phosphine, diborane, etc.) in the presence of ozone lasts for an appreciable period of time (with a duration of several seconds). In order to utilize this phenomenon, the present inventors made intensive studies and perfected the present invention.

In accordance with one aspect of the pre sent invention, there is provided a method for the analysis of chemiluminescent substances in which the radiant energy emitted as a result of the chemiluminescence reaction, in the presence of ozone, of a chemiluminescent substance in a sample gas is detected by a sensor, the method being characterized in that the time at which the sample gas is mixed with ozone to initiate the chemiluminescence reaction precedes at least one of the times at which the radiant energy resulting from the chemiluminescence reaction is detected by the sensor.

In the method of the present invention, the steps of detecting the radiant energy resulting from the chemiluminescence reaction by a sensor need not be limited to only once, but may be carried out two or more times with proper intervals. Where this step is carried out at two or more different times, one of these times may coincide with the time at which the chemiluminescence reaction is initiated. However, it is necessary that the time at which a sample is mixed with ozone to initiate the chemiluminescence reaction precedes at least one of the times at which the radiant energy resulting from the chemiluminescence reaction is detected by a sensor.

The present invention also relates to apparatus for direct use in carrying out the abovedescribed method of the present invention.

Specifically, in accordance with another aspect of the present invention, there is provided apparatus for the analysis of chemiluminescent substances which comprises two or more chemiluminescence reaction chambers arranged in series, the apparatus being characterized in that (a) the first reaction chamber is provided with a conduit for introducing a sample gas thereinto, a conduit for introducing ozone thereinto, and an outlet for discharging the mixed gas into the second reaction chamber, the conduits for the introduction of a sample gas and ozone being option ally joined together just before the inlet of the first reaction chamber, and (b) the second or further chamber is provided with an inlet for introducing thereinto the mixed gas discharged from the preceding reaction chamber, an outlet for discharg ing the mixed gas into the succeeding re action chamber or to the outside of the apparatus, a sensor for detecting the radi ant energy resulting from the chemilumi nescence reaction in the chamber, and a window material transparent to light and disposed between the reaction chamber and the sensor.

In the apparatus of the present invention, it is not essential to provide the first reaction chamber with a sensor for detecting the radiant energy resulting from the chemiluminescence taking place in this reaction chamber.

However, it is to be understood that the provision of the first reaction chamber with a sensor is not precluded.

Brief Description of the Drawings Figure 1 is a schematic view illustrating an embodiment of the apparatus of the present invention; Figures 2A and 2B are sectional side and plan views illustrating the structure of the reaction chamber and its associated parts in another embodiment of the apparatus of the present invention; and Figure 3 is a schematic view illustrating still another embodiment of the apparatus of the present invention.

The chemiluminescent substances suitable for analysis by the method of the present invention are inorganic hydrides such as silane, arsine, phosphine, diborane and the like.

Among others, arsine and phosphine are the most suitable compounds. The chemiluminescence reactions of these substances in the presence of ozone last for several seconds, whereas the chemiluminescence reaction of NO takes place upon contact with ozone and terminates in a moment (with a duration of several milliseconds or less). Accordingly, if the time at which the sample gas is mixed with ozone to initiate the chemiluminescence reactions is made slightly earlier than the time at which the radiant energy emitted as a result of the chemiluminescence reactions is detected by a sensor, the chemiluminescence arising from the aforesaid inorganic hydrides can be selectively detected because the chemiluminescence arising from any NO present in the sample gas has thoroughly decayed.For example, in the case of NO present in atmospheric air, the radiant energy resulting from its chemiluminescence usually decays to a practically undetectable level at 2 to 5 milliseconds after the initiation of the chemiluminescent reaction by contact with ozone, though the duration may more or less vary according to the conditions at the time of contact. Since the radiant energy resulting from the long-duration chemiluminescence of inorganic hydrides decreases gradually, in order to selectively detect only the radiant energy resulting from the chemiluminescence of inorganic hydrides, the time at which the radiant energy is detected by the sensor should preferably be determined to be 2 to 5 milliseconds, most preferably about 3 milliseconds, after the time at which the chemiluminescence reactions are initiated.

In another embodiment, when a sample gas is mixed with ozone to initiate chemiluminescence reactions, the radiant energy resulting from the chemiluminescence reactions is detected by a sensor with a suitable interval of time, i.e., at the same time as the initiation of the chemiluminescence reactions and at a time slightly later than that. In this way, the radiant energy arising from all of the chemiluminescence substances is detected at the first time, and the radiant energy arising from only the substances whose chemiluminescence reaction is of long duration is detected at the second time. Thus, it is possible to analyze the respective chemiluminescence substances on the basis of the two measured values.

Moreover, among the chemical species whose chemiluminescence reaction last for several seconds, its duration varies with the particular compound. Accordingly, the chemical species contained in the sample gas can be more carefully discriminated and analyzed by detecting the radiant energy at three or more different times and examining the results of measurement comparatively.

The concentration of ozone required in the chemiluminescence reaction zone for the purpose of the present invention varies according to the sensitivity of the sensor used, the amount of the substance to be detected, and the like: However, it is preferable to use ozone at a concentration of 0.1% by volume or more. It is a matter of course that, if a sensor having higher sensitivity is used, the practice of the present invention is also posible at lower ozone concentrations.

In the practice of the present invention, the minimum detectable concentration of the substance to be detected depends not only on the type of the substance to be detected, but also on the measuring conditions such as the sensitivity of the sensor used, and the like.

Where the substance to be detected is an inorganic hydride and the sensor comprises a photomultiplier having high sensitivity, the minimum detectable concentration is 1 ppb or less for arsine, 18 ppb or less for phosphine, 100 ppb or less for diborane, and 500 ppb or less for silane.

The sensor used in the practice of the present invention may suitably comprise a photomultiplier, a photosensitive semiconductor or the like.

Now, several specific embodiments of the apparatus for carrying out the method of the present invention will be described hereinbelow with reference to the accompanying drawings.

Fig. 1 is a schematic view illustrating one embodiment of the apparatus of the present invention. In Fig. 1, reference numeral 3 indicates a first reaction chamber which is, so to speak, a pre-reaction chamber. The first reaction chamber 3 is provided with a conduit 2 for introducing a sample gas thereinto and a conduit 1 for introducing ozone thereinto, and these conduits are joined together just before the inlet of the first reaction chamber 3. As soon as both gases are introduced through the respective conduits and mixed in the first reaction chamber 3, the chemiluminescent substances present in the sample gas exhibit chemiluminescence. The chemiluminescence of short duration arising from NO in the sample gas has thoroughly decayed by the time at which the mixed gas enters a second reaction chamber 4.In contrast, the chemiluminescence or long duration arising from inorganic hydrides lasts even in the second reaction chamber 4. The resulting light passes through an optical window 5 made of quartz or quartz glass which is transparent in the full wavelength range of longer than 170 nm, and reaches to a sensor 7. Thus, the chemiluminescence analysis of inorganic hydrides in the sample gas can be carried out without suffering interference from NO.

In the apparatus of Fig. 1, the first reaction chamber 3 and the reaction chamber 4 are connected with a conduit 8 disposed therebetween. However, it is to be understood that an arrangement lacking the conduit 8 as shown in Figs. 2(A) and 2(B) is also possible.

Figs. 2(A) and 2(B) are sectional side and plan views illustrating the structure of the reaction chamber and its associated parts in another embodiment of the apparatus of the present invention. In this embodiment, the outlet of the first reaction chamber 3 is directly connected with the inlet of the second reaction chamber 4.

Fig. 3 is a schematic view illustrating still another embodiment of the apparatus of the present invention. In Fig. 3, there is shown a first reaction chamber 3 which is provided with a conduit 1 for introducing a sample gas thereinto, a conduit 2 for introducing ozone thereinto, and a conduit 8 for discharging the mixed gas into a second reaction chamber 4.

The light resulting from the chemiluminescence taking place in the first reaction chamber 3 passes through an optical window 5 and reaches to a sensor 7, which produces an electric signal 11. When the mixed gas is introduced into the second reaction chamber 4 through the conduit 8, the light resulting from the still continuing chemiluminescence of long duration passes through an optical window 9 and reaches to a sensor 10, which produces an electric signal 12. An electric signal 13 is obtained by subtracting the electric signal 12 from the electric signal 11. Such an arrangement permits the contents of long-duration chemiluminescent substances (such as inorganic hydrides) and short-duration chemiluminescent substances (such as NO) in the sample gas to be detected in the form of the electric signals 12 and 13, respectively.

In the apparatus of the present invention, no limitation is placed on the photometric spectrum for measurement and a window material (such as quartz or quartz glass) transparent in the full wavelength range may be used. This eliminates the loss of photometric intensity due to the light absorption by an optical filter as used in the invention of Japanese Patent Laid-Open No. 196138/'82, and brings about a marked improvement in detection sensitivity.

Example Using two types of apparatus as illustrated in Figs. 2(A) and 2(B), nitrogen gas containing 0.5 ppm of phosphine, nitrogen gas containing 3.74 ppm of NO, and nitrogen gas containing 0.5 ppm of phosphine and 3.74 ppm of NO were subjected to chemiluminescence analysis.

The dimensions shown in Figs. 2(A) and 2(B) were chosen so that a=10 mm, b=30 mm, and c=13 mm. The value of I was 0 mm in one apparatus (i.e., the first reaction chamber was eliminated) and 52.5 mm in the other.

The sensor 7 comprised a photomultiplier and its output was passed through a current-tovoltage converter to obtain a voltage output.

First, using the apparatus from which the first reaction chamber was eliminated, a sample gas was introduced into the reaction chamber through the conduit 1 at a flow rate of 155 cc/min, and air containing 0.3 vol.% of ozone was introduced thereinto through the conduit 2 at a flow rate of 120 cc/min. The absolute pressure within the reaction chamber was about 210 mmHg. Under these conditions, the radiant energy resulting from chemiluminescence was detected by the sensor 7.

When the sensor output for the sample gas containing 0.5 ppm of phosphine was taken to be 100 (the voltage applied to the photomultiplier was adjusted so that this output became equal to be 1.0 V), the sample gas containing 3.74 ppm of NO gave an output of 93.5 and the sample gas containing both phosphine and NO gave an output of 193.

This indicated that the presence of NO seriously interfered with the detection of phosphine.

Next, using the apparatus having the first reaction chamber (1=52.5 mm), experiments were carried out at the same flow rates and under the same pressure within the reaction chambers. The sensor output for the sample gas containing 0.5 ppm of phosphine was 59.5, indicating that the chemiluminescence was still continuing in the second reaction chamber. However, the chemiluminescence of the sample gas containing 3.74 ppm of NO had thoroughly decayed and gave a sensor output of as low as 0.6. The sample gas containing both phosphine and NO gave a sensor output almost equivalent to that of the sample gas containing phosphine alone. This indicated that, if measurements are made under these conditions, phosphine alone can be analyzed without suffering interference from NO.

Similar experiments were carried out under the same conditions as described above, except that air containing 0.3 vol.% of ozone was introduced through the conduit 1 at a flow rate of 120 cc/min and a sample gas was introduced through the conduit 2 at a flow rate of 155 cc/min. Also in this case, the results indicated that, if measurements are made using the apparatus having the first reaction chamber (1=52.5 mm), phosphine alone can be selectively detected and analyzed without suffering interference from NO.

Claims (9)

1. A method for the analysis of chemiluminescent substances in which the radiant energy emitted as a result of the chemiluminescence reaction, in the presence of ozone, of a chemiluminescent substance in a sample gas is detected by a sensor, the method being characterized in that the time is which the sample gas is mixed with ozone to initiate the chemiluminescence reaction precedes at least one of the times at which the radiant energy resulting from the chemiluminescence reaction is detected by the sensor.

2. A method as claimed in claim 1 wherein the chemiluminescent substance is an inorganic hydride.

3. A method as claimed in claim 2 wherein the inorganic hydride is arsine.

4. A method as claimed in claim 2 wherein the inorganic hydride is phosphine.

5. A method as claimed in claim 1 wherein the time at which the radiant energy is detected by the sensor is 2 to 5 milliseconds later than the time at which the chemiluminescence reaction is initiated.

6. Apparatus for the analysis of chemiluminescent substances which comprises two or more chemiluminescence reaction chambers arranged in series, the apparatus being characterized in that (a) the first reaction chamber is provided with a conduit for introducing a sample gas thereinto, a conduit for introducing ozone thereinto, and an outlet for discharging the mixed gas into the second reaction chamber, the conduits for the introduction of a sample gas and ozone being option ally joined together just before the inlet of the first reaction chamber, and (b) the second or further chamber is provided with an inlet for introducing thereinto the mixed gas discharged from the preceding reaction chamber, an outlet for discharg ing the mixed gas into the succeeding re action chamber or to the outside of the apparatus, a sensor for detecting the radi ant energy resulting from the chemilumi nescence reaction taking place in the re action chamber, and a window material transparent to light and disposed between the reaction chamber and the sensor.

7. Apparatus as claimed in claim 6 wherein the window material is quartz or quartz glass.

8. Apparatus as claimed in claim 6 wherein the first reaction chamber is also provided with a sensor for detecting the radiant energy resulting from the chemiluminescence reaction taking place in the reaction chamber, and a window material transparent to light and disposed between the reaction chamber and the sensor.

9. A method or apparatus for the analysis of chemiluminescent substances substantially as any herein described with reference to and as iilustrated in the accompanying drawings.