IE53060B1 - Process and device for continuous and direct analysis of traces of gaseous hydrides - Google Patents

Abstract

1. Method for the direct and continuous analysis of traces of gaseous hydrides selected from the group of arsine, phosphine, silane and diborane solely or in a mixture having very low contents in a carrier gas by chemiluminiscence emission of the said hydrides in presence of ozone, characterised in that the emitted spectra are optically filtered so that by optical filtration the signals of wave lengths between 495 and 650 nm are transmitted and that the transmitted optical signals are amplified by a photomultiplier tube the spectral response curve of which is adapted to the cited zone of wave lengths.

Description

This invention relates to the direct and continuous analysis of extremely low trace concentrations of gaseous hydrides.

Gaseous hydrides, particularly silane, arsine,: phosphine, and diborane, are used in increasing amounts in the electronics industry. Now, it is known that these gaseous hydrides are extremely, dangerous due to their toxicity and their tendency to flammability.

The maximum allowable concentrations (M.A.C.) in awork atmosphere for an exposure of eight hours a day and five days a week are: SiH^ 0.5 ppm volume, AsH^ 0.05 ppm volume, PH^ 0.3 ppm volume and 0.1 ppm volume.

Therefore, it is obvious that it is absolutely necessary and extremely important to place analyzers that are easily used, reliable and sensitive detection devices. Such devices should possess very short response time in workspaces for continuously 15 monitoring the atmosphere of the rooms where hydrides are used.

For at least the last fifteen years, various methods of analysis and detection have been studied and proposed. Among the detection devices, which are now available for sensing and analyzing these hydrides, are infrared spectrometers, colorimeters, photo20 ionization detectors and semiconductor detectors.

Infrared spectrometers, though of the most elaborate type, do not make it possible to detect arsine even at the level of the maximum allowable concentration, nor to perform the continuous detection of one of said four hydrides; therefore a system of data acquisition has to be included with such detection devices.

In the field of colorimeters there are colorimetric tubes and colorimeters having impregnated strips.

Colorimetric tubes function to detect with good reliability the maximum allowable concentration of arsine, phosphine and diborane, but exhibit the drawback of not being adapted to be coupled to a continuous automatic monitoring system including an alarm mechanism; moreover, no colorimetric tube can detect such maximum allowable concentration of silane.

Colorimeters having impregnated strips assure only the . detection of allowable concentrations of arsine and phosphine, but because of the necessity for periodically changing the reactive strip, which is impregnated with a toxic reagent and a response time greater than 5 min for the M.A.C., are unpopular for continuous automatic monitoring and for safety. Particularly because of the high toxicity of arsine, the lack of detection of a leakage of a few p.p.m, volume can cause irreversible lesions in a few minutes; thus in thirty minutes a leakage of 10 p.p.m. volume pollutes the atmosphere with concentrations corresponding to a lethal dose.

In using photoionization detectors in direct analysis, i.e., by directly analyzing the ambient air, the sensitivities obtained are not sufficient, being on the order of a few ppm, which makes them useless for monitoring the atmosphere of rooms where gaseous hydrides are used. Iu the case of chromatographic preseparation, photoionization detectors, which in principle operate at'an improved sensitivity, but exhibit a very long response time, i.e., the retention time of products in the column. Therefore, because of the very high toxicity of gaseous hydrides, this photoionization detection process cannot be considered satisfactory from the viewpoint of safety, more particularly as the transfer of said hydrides, in a very small amount in a chromatography column, is extremely delicate. Thus the possibility of not indicating a timely response increases the insecurity and the lack of reliability of this detection system.

With respect to semiconductor detectors, the types of apparatus now available are very sensitive to many compounds, particularly to gases, which are naturally present in the air, such as water vapor, carbon dioxide and carbon monoxide, and because of this such apparatus does not exhibit a specificity sufficient to analyze and to detect very low amounts of toxic hydrides.

As a result, it is found that the analysis and detection apparatus presently available on the market, only partially satisfies the requirements for selectivity and safety, especially because of the slowness of their detection response. Despite much work which has been carried out over the years, there is still a search for a method that makes possible the reliable and timely quantitative detection and analysis of traces of hydrides, such as arsine, in very low amounts, under conditions which would satisfactorily respond to the criteria and need for safety required in the electronics and nonferrous metallurgy industries.

$ The phenomenon of chemiluminescence in the presence of ozone is known for various chemical substances, such as nitrous oxide, unsaturated hydrocarbons, sulfur products and even certain gaseous hydrides. This phenomenon is already in use for detecting even slight traces of nitrogen oxides in the atmosphere.

However, direct application of the technique suited to detect nitrous oxide does not lead to significant results with regard to the detection of certain gaseous hydrides because of interference between the emissions of the hydrides and those of other gases.

Actually, chemiluminescence of nitrous oxide in the presence of ozone produces a continuous emission spectrum, from a slight luminous intensity that begins at 6000 8 (l8 corresponds to 0.1 nm) to a maximum in the near infrared range at 12,000 8.

Also, ethylene hydrocarbons exhibit an emission band between 3000 and 6000 8, centered on 4,400 8.

Accordingly, the invention provides a process for continuous and direct analysis of traces of gaseous hydrides selected from arsine, phosphine, silane, diborane and mixtures thereof at very low concentration in a gas vector, by chemiluminescent emission of said hydrides in the presence of ozone, wherein the emitted spectra are optically filtered so that by optical filtration the signals of wavelengths between 495 and 650 nm are transmitted and the optical signals transmitted are amplified by a photomultiplier tube the spectral response curve of which is adapted to said range of wavelengths.

The chemiluminescent emission of the gaseous hydrides in the presence of ozone limits the maximum interference permitted with other gases, such as nitrous oxide, unsaturated hydrocarbons and sulfur products. Such a system makes possible the detection of a greater series of dangerous gases than by the commercial equipment, which is now being used, and also permits a more sensitive detection of arsine and phosphine.

The process according to the invention reduces the drawbacks of the known methods and uses a reliable, effective and very sensitive analysis and detection apparatus having a very short response time.

The apparatus according to the invention comprises an ozonizer, a reaction chamber containing the gaseous hydride(s) with ozone, a set of optical filters for transmitting by filtration the emitted spectra between 495 and 650 nm, a photomultiplier the spectral response curve of which is adapted to said range of wavelengths and alarm contacts. The apparatus according to the invention, which is simple to use for continuously and automatically monitoring the atmosphere of work areas possibly polluted by traces of gaseous hydrides by avoiding the detection of undesirable gases commonly used in the electronics industry.

In the process according to the invention, the spectra emitted by the gaseous hydrides are optically filtered so that by optical filtration the signals of wavelengths between 495 and 650 nm are transmitted and the optical signals trans20 mitted are amplified by a photomultiplier tube the spectral response curve of which is adapted to the aforementioned range of wavelengths.

This choice of a spectral range between 495 and 650 nm shows a favorable incidence for the detection of each of these gaseous hydrides at an improved sensitivity. Arsine, phosphine and silane are detected at very low amounts near the MAC and diborane at a content in the order of a few p.p.m. With arsine and phosphine the degree of interference can be considered to be negligible because of their very good sensitivity.

According to the method above described, the change in the content of said four gaseous hydrides can be continuously followed in a non-selective way in a working atmosphere. The slight sensitivity vis-a-vis the most common pollutants makes it possible to detect, in the aggregate, the presence of said gaseous hydrides.

The specificity of the technique can easily be achieved by a process of chromatographic detection of traces.of the gaseous hydrides at very low amounts according to which, in an initial stage, said gaseous hydrides are separated from one another by chromatography in a gaseous phase. In a second stage each of the hydrides is separately subjected to a chemiluminescent emission in the presence of ozone, the emitted spectra being optically filtered so that by optical filtration the signals of wavelengths between 495 and 650 nm are transmitted and the collected optical signals are amplified hy a photomultiplier tube the spectral response curve of which is adapted to said range of wavelengths.

Using the process, as described above, makes possible continuous and selective direct analysis of said gaseous hydrides.

The process, according to the invention, is used in a chemiluminescent detector in which a reaction chamber, a photomultiplier tube and alarm contacts are the essential parts of the apparatus. Furthermore, the apparatus comprises an ozonizer and a calibrating device having an injector of the standard arsine mixture in nitrogen. The circuits which monitor the atmosphere containing ozone are equipped with rotameters and flowmeters that assure the monitoring of the flows introduced into the reaction chamber. At the outlet of this chamber, a group of optical filters is inserted before the photomultiplier which is housed in a cooled chamber. The apparatus also includes an electronic unit that comprises an amplifier which assures the monitoring and regulating before the transmission of the signal to the alarm contacts and optionally to an alarm printer provided with several channels. These alarm contacts are used for detecting defects which trigger relayed signals which enhance the safety of the analyzer-detector apparatus. These alarm contacts prevent any possible malfunctioning of the apparatus, namely a failure of temperature regulation of the photomultiplier, the lack of circulation of the sample in the reaction chamber, the lack of ozone, etc.

Then the apparatus is calibrated by injecting a standard 5 arsine mixture the content of which is on the order of a few dozen p.p.m. in a dilution system, which makes it possible to send into the reaction chamber a known concentration of arsine near the M.A.C.

Then the response of the apparatus is checked.

The invention will be more easily understood with reference 10 to the accompanying drawings, in which: Fig. 1 is a schematic view of the apparatus of the invention.

Fig. 2 is a graphical representation showing the emission spectrum for arsine.

Fig. 3 is a graphical representation showing the emission spectrum for phosphine; and Fig. 4 is a graphical representation showing the emission spectrum for diborane.

In figure 1 of the accompanying drawings that represent 2o the apparatus of the invention, it is seen that the air to be monitored, taken from a working atmosphere, is carried by ducts (1) through a filter (2) that retains dust particles. The air is introduced into flowmeter (3), then into rotameter (4), then passes through sonic injector (5) and finally enters reaction chamber (6).

In calibrating position the arsine-nitrogen standard mixture is introduced through ducts (7) into standard diluter (8).

In measuring position, valve (9) located in the circuit including ducts (7) stops the flow of the standard mixture and lets only the ambient air penetrate into said reaction chamber (6).

The oxygen supply, which will be ozonized, circulates in ducts (10) passes through filter (11), which is intended to retain the dust particles. The oxygen then passes through valve 12, flow limiter (13), and flowmeter (14). Below the flowmeter is placed a T structure (15) intended to assure a light flow of escaping oxygen, which is monitored by rotameter (16) that makes It possible for the oxygen to enter the reaction chamber at atmospheric pressure. After having gone through the T structure, the oxygen passes into ozonizer (17) then through filter (18) and into sonic injector (19) before entering reaction chamber (6). The apparatus operates by suction and partial vacuum, and the flow of the air to be analyzed and of the oaonized oxygen are monitored by rotameters and flowmeters before entry into reaction chamber (6). The rotameter, I flowmeter, T structure (14, 15, 16) group makes it possible, in case of an oxygen supply failure, to suck the ambient air through the T structure to assure a continuity in the distribution of the oxygen in the ozonizer to prevent its deterioration.

The spectrum emitted by the chemiluminescence of the gaseous hydrides after passing through a set of optical filters 0 (20), that transmit wavelengths between 4,950 and 6,500 A, is transmicted to photomultiplier tube (21), located inside cooled chamber (22). Amplifier (23) receives the signal and transmits it to alarm contacts (24) and optionally to a printer provided with several channels. By way of example, a flow of 4 to 6 liters/hour for the ozonized oxygen can be shown, the flow of the air to be monitored that enters into the reaction chamber being on the order of 75 liters/hour.

The monitored air continuously leaves the reaction chamber through pipe (26) and passes through ozone filter (27) in which the destruction of the ozone is performed. The air is then taken by pump (28) and evacuated by pipe (29), to which is connected duct (30), that evacuates the excess of the standard mixture.

TABLE I Emission spectra picked up by the photomultiplier Kind of Gas Limits of the Recorded Spectrum Emission Maximum (X; lS =0.1nm) λ (A) ?h3 3,500 - 7,500 5,500 - 6,000B2H6 3,500 -6,500 4,700 - 5,700 AsHj 3,000 - 9,000 4,500 - 5,500 The spectra have been recorded by automatic passage of o the wavelengths, at 200 or 500 A per minute, from a mixture at 500 p.p.m. diluted in nitrogen.

The maxima of the emission spectra of the chemiluminescent reaction between the gaseous hydrides, arsine, phosphine, diborane and ozone are all located between 4,500 and 6,000 A. One may assume that the emission zone for silane will also be found between 4,500 and 6,000 S by analogy with the reaction of the other gases. w With respect to arsine and phosphine interference is negligible because of their great sensitivity.

AsHy 0.05 p.p.m. corresponding to a signal greater than 1000 mV.

PH.j: 0.3 p.p.m. corresponding to a signal on the order of 1000 mV.

SiH^: 0.5 p.p.m. corresponding to a signal on the order of 1000 mV. 152^: 3.8 p.p.m. corresponding to a signal on the order of 60 mV.

Figure 2 shows the emission spectrum of arsine, figure 3 that of phosphine and figure 4 that of diborane.

Claims (9)

CLAIMS:

1. A process for continuous and direct analysis of traces of gaseous hydrides selected from arsine, phosphine, silane, diborane and mixtures thereof at very low concentration in a 5 gas vector, by chemiluminescent emission of said hydrides in the presence of ozone, wherein the emitted spectra are optically filtered so that by optical filtration the signals of wavelengths between 495 and 650 nm are transmitted and the optical signals transmitted are amplified by a photomultiplier 10 tube the spectral response curve of which is adapted to said range of wavelengths.

2. A process for chromatographic detection of traces of gaseous hydrides selected from arsine, phosphine, silane, diborane and mixtures thereof at very low concentration 15 wherein, in an initial stage, said gaseous hydrides are separated from one another in a gaseous phase by chromatography, then in a second stage, each of the hydrides is subjected separately to a chemiluminescent emission in the presence of ozone, the emitted spectra being optically filtered so that 20 by optical filtration the signals of wavelengths between 495 and 650 nm are transmitted and the collected optional signals are amplified by a photomultiplier tube the spectral response curve of which is adapted to said range of wavelengths.

3. A process for continuous and selective direct analysis 25 of a gaseous hydride selected from arsine, phosphine, silane, diborane and mixtures thereof wherein the process according to claim 2 is used.

4. Use of the process according to any of the claims 1 to 3, to the selective quantitative analysis of slight traces of 30 gaseous hydrides selected from arsine, phosphine, silane, diborane and mixtures thereof in an atmosphere as a safety detector, and a control of atmospheric pollution and a detection of chromatography

5. Analyzing and detecting apparatus permitting the use of 35 the process according to claim 1, which comprises an ozonizer, a reaction chamber containing the gaseous hydride(s) with ozone, a set of optical filters for transmitting by filtration the emitted spectra between 495 and 650 nm, a photomultiplier the spectral response curve of which is adapted to said range of wavelengths and alarm contacts.

6. Analyzing and detecting apparatus according to claim 5, which further comprises an alarm printer. 57.

7.A process according to claim 1 for continuous and direct analysis of traces of gaseous hydrides, substantially as hereinbefore described.

8. A process according to claim 2 for chromatographic detection of traces of gaseous hydrides, substantially as 10 hereinbefore described.

9. Analysing and detecting apparatus according to claim 5, substantially as hereinbefore described with particular reference to Fig. 1 of the accompanying drawings.