FR2873812A1 - Volatile organic compounds e.g. organic amide, sampling device for e.g. solid phase micro-extraction syringe, has tube defining volume between end parts, in which air flow is maintained constant and homogeneous, in direction and speed - Google Patents

Abstract

The device includes a cylindrical tube (12) with end parts (14, 18) respectively having an inlet orifice and an outlet orifice (16) and connected by walls. The tube defines a volume, between the two end parts (14, 18), where the air flows from the end part (14) to the outlet orifice (16) so that the flow of air is maintained constant and homogeneous, in direction and speed in the volume. Independent claims are also included for the following: (A) utilization of a sampling device with systems for sampling through solid phase micro-extraction (B) utilization of a sampling device for sampling volatile compounds in a clean room.

Description

2873812 1

  DEVICE FOR SAMPLING VOLATILE COMPOUNDS

TECHNICAL AREA

  The invention relates to a device for sampling volatile compounds, for example organic compounds.

  In particular, the invention relates to the controlled circulation of air in order to extract certain contaminants, in particular organic contaminants, and to determine their composition.

  The device according to the invention is particularly suitable for micro solid phase extraction, or to be associated with a portable gas chromatography device.

  STATE OF THE PRIOR ART In the semiconductor industry, the contamination comes largely from the gaseous species present in the air of the clean rooms; it can lead to a degradation of the performances of the processes or the quality of the integrated circuits realized. An example is contamination due to organic compounds such as organic amide (N-methyl-2-pyrrolidone) but many other organic compounds are known to generate condensation problems, for example on optics in photolithography rooms, but also to generate defects in integrated circuits: electrical faults, short circuits, delamination phenomena of successive layers. In addition, the engraving size becoming smaller and smaller, the contamination is all the more critical. In addition, lower levels of contaminants are required, of the order of ppb in volume or lower.

  To minimize the risks and monitor manufacturing, it is therefore necessary to analyze these contaminants that may be present in the air of the electronic clean rooms in trace amounts. Now the detectors of volatile organic compounds continuously have a detection limit of the order of 0.1 ppm by volume, much higher than the requirements of the field of semiconductors where the tolerated concentrations are less than 1 ppb by volume.

  Low contaminant concentrations typically require compound removal with a preconcentration method to achieve the detection limits required for assays in this area. For example, most equipment requires many hours of collection before samples can be analyzed; to this disadvantage of duration is added the risk of loss of the sample.

  For such compounds in the form of traces, a technique has been developed concerning solid phase micro extraction (SPME, for Solid Phase MicroExtraction). It consists in the adsorption of the volatile organic compounds on a porous material composed of a thin adsorbent layer: see for example WO 99/26063 or US 2002/0150504. In a short time, of the order of 10 min, a sufficient amount of compound can be removed by extraction in a porous material, usually in the form of fiber located inside a syringe. Desorption is then performed, and the analysis as such is performed. In particular, SPME may be associated with gas chromatography, for example followed by mass spectrometry (GC / MS) type detection for the identification of compounds.

  However, it turns out that this technique does not give reliable results at the quantitative level; in particular, tests carried out under actual clean-room sampling conditions showed variations of up to 100% in samples taken from two SPME fibers used simultaneously exposed directly to the air in the clean room. in supposed unidirectional flow.

  In fact, different parameters need to be optimized and controlled to allow the validation of sampling by SPME, or more generally by adsorption on porous material, as a possible method for a quantitative analysis of volatile organic contaminants in a clean room.

  DISCLOSURE OF THE INVENTION The main objective of the invention is to allow the use of adsorption techniques for quantification by overcoming some of the existing problems.

  More generally, the invention relates to a sampling device that allows a solid phase extraction in a reproducible manner.

  In particular, the sampling device makes it possible to control the flow reaching an extraction material both in speed and in speed.

  In a preferred embodiment, the device according to the invention may be repeatedly associated with a solid phase extraction system, in the form of an SPME syringe, for example. In particular, the flow direction is perpendicular to the orientation of the adsorption matrix. The sampling device then preferably comprises a cylindrical tube open at one end and connected to a pump at the other end. Advantageously, several extraction systems can be associated for simultaneous extractions.

  In another preferred embodiment, the device according to the invention is associated with an integrated desorption device, and for example a portable chromatography analysis system. In this case, advantageously, the sampling device comprises a reservoir in which the inlet and the gas outlet are through porous membranes which equalize the gas flow. Preferably, the air inlet is through a system of pipes provided with calibrated orifices to ensure a uniform flow between each of them.

  The device according to the invention is particularly suitable for use in a clean room. In particular, the speed of the flow is adjusted and controlled to be of the order of 0.4 m / s for example.

  Preferably, the device according to the invention is associated with measuring means, pressure and / or temperature and / or hygrometry.

  The device according to the invention can be portable in order to allow analyzes at different sites or different locations within the same site.

BRIEF DESCRIPTION OF THE DRAWINGS

  The appended figures will better understand the invention, but are given for information only and are not restrictive.

  Figure 1 schematically shows a syringe with a SPME fiber as marketed.

  Figure 2 shows a preferred embodiment of the invention.

  FIG. 3a shows the use of another preferred embodiment of the device of the invention, schematized in FIG. 3b, a detail of which is shown in FIG. 3c.

  DETAILED DESCRIPTION OF PARTICULAR EMBODIMENTS Solid phase microextraction (SPME) consists in the adsorption of volatile compounds, in particular organic compounds, onto a porous material, for example in a sampling syringe marketed and shown schematically in FIG. 1. A syringe 1 makes it possible to maintain an adsorbent fiber 2 protected from the ambient air and to take it out for sampling. The displacement of the fiber 2 is often carried out with the aid of a control system, for example by means of a spring 3. The fiber 2 is composed of a core 4, usually made of silica, surrounded on a part, for example over a length of 1 cm, of an adsorbent film to reach about 100 μm in diameter of the assembly formed by the core 4 and the film 5. Depending on the species that it is desired to extract, the film 5, for example with a thickness of 0.75 μm, may be composed of Carboxen ™ particles 6 of the order of 2 to 10 μm in diameter in a polymer 7 made of polydimethylsiloxane (PDMS).

  This method has been recently developed in the semiconductor industry by being coupled with gas chromatography mass spectrometry (GC / MS) to analyze organic contaminants in the clean room.

  However, it turns out that the reproducibility of the analyzes depends on various parameters. It was thus found that the ambient pressure and the temperature acted on the adsorption coefficient of the compound on the film 5.

  However, the usual conditions in the clean room, where the temperature is almost uniform and the variations of pressure very low, can be considered sufficiently reproducible and stable; otherwise, the temperature may be normalized to 20 C for example.

  Moreover, the competitive adsorption on the fibers 2 can modify the results. In particular, it is preferable, in order to obtain the best of the film 5, that the sampling time is between 5 and 15 min. Indeed, coadsorption phenomena can occur and cause competition between the various volatile compounds towards the fiber; Quantitative adsorption of the desired species then becomes impossible after a certain time, and the durations mentioned above have been optimized for the compounds of interest in the case of contamination in the clean room.

  It has also been found that the speed of the air flow coming on the fiber 2, in particular for the low speeds (that is to say less than 1 m / s) has an influence. Thus, the adsorption variation of decane on a CarboxenTM / PDMS fiber as defined above can reach 10% between 0.3 and 0.4 m / s (see for example Koziel et al., Anal Chem 2000, 72). ).

  Similarly, as shown diagrammatically in FIG. 1, a stream perpendicular to fiber 2, of type A, gives better results than a parallel stream, of type B: it is probable that, during parallel sampling B, the concentration of compound is different between the initial and final contact points between flux and film 5, which prevents a total exploitation of the performance of the fiber 2. In fact, the fiber used in a parallel flow B seems to act more like a chromatographic column only as a trapping reservoir for volatile compounds.

  It would be possible to overcome these fluctuations by sampling from an air sample contained in a closed volume, as shown in WO 99/26063. This method has the first disadvantage that the quantity withdrawn is lower than in dynamic mode because there is no renewal of the atmosphere around the fiber. Secondly, a sample necessarily entails a depletion of the air which eliminates the possibility of a second sampling with the same initial sample and therefore any reproducibility.

  It therefore turns out that, for good reproducibility, and therefore possible quantification, a dynamic sample is used in a process according to the invention; it has furthermore been found that adsorption in dynamic mode makes it possible to obtain lower detection limits than in static mode. The adsorption is preferably carried out by a flow perpendicular to the adsorbent matrix, under a constant temperature, which can for example be normalized at 20 ° C., for a duration of the order of 8 minutes, and with a constant speed. circulating air.

  If some parameters are easy to control, it is not the same for the speed and direction of the flow. Indeed, the air renewal rate of a clean room can be fixed, often around 0.4 m / s, the presence of obstacles such as production tools inevitably generates turbulence. It is thus impossible to obtain a repeatable sampling if the fiber is exposed directly to the atmosphere.

  The invention proposes a sampling system comprising a reservoir in which the airflow is controlled and where the extraction system can be located.

  Advantageously, the sampling device according to the invention is easy to transport, for example of dimensions of the order of a suitcase (50 x 50 x 25 cm), so as to be used in different clean rooms. the same production unit, as well as in different places, even if they are not very accessible, in the same room.

  In a first embodiment, the device allows the use of standard SPME syringes, and the storage of samples before analysis. The configuration of the device can also be miniaturized, as for example in the second embodiment.

  In the embodiment shown schematically in Figure 2, the device 10 comprises a reservoir 12 in which syringes 1 as shown schematically in Figure 1 may for example be connected. The reservoir 12 is advantageously in the form of a glass tube of length 20 to 50 cm for a diameter of the order of 2 to 5 cm: the length to diameter ratio is determined so as to allow a laminar flow of a gas flow, that is to say having a flat speed profile inside the tank 12; advantageously, the length to diameter ratio is greater than 10.

  The air flows in the tube 12 between a first fully open end portion 14 and an outlet orifice 16 located in a second end portion 18. In the volume defined between the first and the second end portions 14, 18, the air flow is kept constant and homogeneous, both in speed and direction. For this purpose, a first duct 20 connects the outlet orifice 16 to a pump 22. On this first duct 20 there are means 24 for determining the flow rate of gas flowing in the tube 12, advantageously in the form of a calibrated orifice on which a differential pressure sensor makes it possible to recalculate the air flow in subsonic mode by reading the differential pressure.

  Preferably, the pump 22 is also connected by a second duct 26 directly to the ambient air, if possible via a control valve 28 which allows the flow rate inside the tank 12 to be regulated. sharing the total air flow between the one passing in the tank 12 and the one passing through the duct 26 on which it is mounted.

  Preferably, the pump 22 is connected to a filter 30 at the outlet to prevent rejection into the clean room of particles.

  The pump 22 generates a flow such that the speed in the tube 12 between the two end portions 14, 18 is constant. Preferably, for experiments in the clean room and for the device 10 to be of a size compatible with its transport, the speed may for example be set at about 0.4 m / s.

  The device 10 can also comprise means for determining other parameters of the circulating gas and in which the extracted compounds are present: a hygrometer H, a thermometer T,... Can be located on the first conduit 20, the second conduit. And / or in the atmosphere surrounding the device 10. Means 32 make it possible to display and / or record the various measured parameters.

  In order to allow the extraction of the compounds, means 34 are provided in the walls of the tube 12 defining the volume within which the flow is controlled, that is to say between the two end portions 14, 18. These means are advantageously composed of at least one sealed port 34, sealed for example by a septum 36, which can be pierced by a syringe 1 such as that of Figure 1, while maintaining its seal. The ports 34 are such that the syringe 1 is directed perpendicularly to the axis of the tube 12, and therefore to the flow of air generated in the device 10. Advantageously, two ports 34, 34 'diametrically opposite allow for two simultaneous extractions: such a location makes it possible to ensure that the flux is the same on each fiber 2. The syringes 1 can be identical to check the reproducibility of the measurement, or of different natures, that is to say comprising different adsorbents, for extract different compounds. A greater number of ports 34 may be chosen, the ports then being advantageously located on the same circumference perpendicular to the axis of the tube 12. It is desirable for the diameter of the tube 12 to be greater than twice the length of the film 5 of the fiber 2 of the syringe 1 so as to avoid any problem of positioning.

  The device 10 can be used as follows: the device 10 is first positioned at a place where it is desired to measure the contamination. The pump 22 is then started. The various parameters, and in particular the stabilization of the flow rate, are verified by means of the control means 32 by means of the differential pressure sensor 24, which intervenes after a delay, for example of the order of 15 minutes. SPME syringes 1 are placed in the orifices 34.

  When the stabilization is established, the spring 3 is actuated to remove the fibers 2 and thus bring the air flow into contact with the adsorbent 6, 7.

  After the adsorption delay, for example 8 min, the spring 3 is actuated to enter and isolate the fiber 2.

  The extraction can be repeated by the successive introduction of other systems 1. The adsorbed compounds can then, in a conventional manner, be analyzed, for example by chromatography, after desorption out of the matrix 6, 7.

  The device according to the invention may be the subject of another embodiment, as shown diagrammatically in FIGS. 3, allowing direct adaptation to analytical equipment such as a gas chromatograph.

  In this other device 40, the volume of the reservoir 42 in which the flow is constant is delimited by two closed end portions 44, 46. The ambient air is preferably sampled using a Venturi 48 system, by suction by a carrier gas which can also be used for chromatographic analysis.

  The gas containing the compound of interest to be extracted feeds the sampling device 40 by a set of clarinets: the inlet 50 of the tank 42 is decoupled by a system comprising pipes 52 which line one of the end walls 54 of the device 40. Advantageously, four parallel pipes pass through the wall 54 of the tank 42. These pipes 52 are pierced with orifices 56 of gas outlet; the diameter of the orifices 56 is determined so that the gas has a speed identical to each: reference is made to the document FR-A-2713952 for more details on the dimensioning.

  For example, the reservoir 42 may be of dimensions 3 cm x 3 cm x 3 cm, with electropolished metal walls; the supply can be made by an inlet port 50 of 10 mm in diameter to which are coupled 4 pipes 52 2.8 cm long and each pierced with 10 orifices 56 of about 1 mm in diameter.

  The gas then passes through a porous wall 58 intended to create a piston effect making it possible to obtain an identical velocity profile over the entire surface of the porous wall 58. Plates 60 coated with adsorbent polymer, for example of the same type as the adsorbent phase which impregnates the aforementioned SPME fibers (CarboxenTM, polydimethylsiloxane PDMS, TenaxTM,

  .), will extract the compound of interest from the gas. Advantageously, a second porous wall 62 located before the outlet orifice 64 makes it possible to avoid turbulence within the volume delimited between the first end portion 44 and the second end 46. DTD: The plates 60 are preferably manufactured so as to be desorbed in situ, that is to say in the tank 42. Advantageously, the plates 60 are composed of two layers 66 of adsorbent material surrounding a support 68 comprising a heating filament 70, the desorption is done through at a rapid rise in temperature of the filament 70.

  At the outlet of the sampling device 40, a three-way valve 72 makes it possible to direct the gas: during the sampling phase, the output gas is directed to the atmosphere. During the desorption phase, the valve 72 is closed, just like the inlet valve 74 of the gas: the tank 42 is isolated. Then, the valve 72 is opened to direct the compound that has been extracted and then desorbed and mixed with the carrier gas to an analysis system 76, for example a GC / MS. Advantageously, the set composed of the device 40 and the analysis system 76 is portable.

  This second technique has the advantage of being fully automatable which avoids human errors. It also eliminates the problem of the fragility of the SPME fiber 2 of FIG. 1. Finally, the coupling of the sampling device 40 to an analysis system 76, for example portable, makes it possible to carry out on-site analyzes without risk of deterioration. some samples.

  Experiments have shown that the variation of the levels measured on samples taken on two SPME fibers used simultaneously was less than 15%, compared to 100% of the systems tested by SPME fibers exposed directly to the supposed unidirectional flow.

  For example, for N-methyl-2-pyrrolidone NMP, a compound known to be difficult to quantify by the conventional method of adsorption on TenaxTM tubes since a two-stage thermal desorption is necessary after sampling, variations less than 10 % were measured. It should be noted that, moreover, the usual method also requires a cryogenic trap for refocusing the compounds on a cold trap, which greatly increases the possibility of sample loss, a disadvantage eliminated by the method according to the invention.

  Of course, it is possible to combine the embodiments, and for example to have plates 60 removable in the second embodiment.

Claims (20)

  A device for collecting compounds present in a gas comprising: - a reservoir (12, 42) which comprises a first end portion (14, 44) and a second end portion (18, 46), respectively provided with an inlet (14, 50) and an outlet (16, 64) of gas, and connected by walls, the reservoir (12, 42) defining a first volume between the walls and the two parts end (14, 18; 44, 46), and - means for moving gas from the inlet port (14, 50) to the outlet port (16, 64) adapted so that the flow of the gas is controlled and homogeneous, in direction and speed in the first volume.   2. Device according to claim 1 wherein the means for moving the gas comprises a pump (22) and further comprising a first conduit (20) which connects the outlet port (16) to the pump (22).   3. Device according to claim 2 wherein the reservoir (12) is a cylinder of circular section whose length to diameter ratio is greater than 10.   4. Device according to claim 3 wherein the inlet port is composed of the end of the tube (12) at the first end portion (14).   5. Device according to one of claims 2 to 4 wherein the reservoir (12) further comprises access means (34) on the walls which are sealingly sealed by means (36) may be pierced or a septum.   6. Device according to one of claims 3 and 4 comprising two means (34, 34 ') access sealed diametrically opposite the walls.   7. Device according to one of claims 2 to 6 comprising a second conduit (26) of gas supply connected to the pump (22).   8. Device according to claim 7 comprising a control valve (28) on the second conduit (26).   9. Device according to one of claims 2 to 8 comprising means (24) for determining the air flow in the first conduit (20).   10. Device according to one of claims 1 to 9 comprising means for measuring temperature and / or hygrometry.   The device of claim 1 or 10 wherein the first and second end portions (44, 46) are connected to the walls through a porous membrane (58, 62).   12. Device according to claim 11 wherein the orifice (50) of gas inlet comprises a pipe system (52) provided with openings (56) calibrated so that the flow of gas leaving each opening (56) is identical.   13. Device according to one of claims 11 to 12 comprising means (60) for adsorbing compounds in the first volume.   The device of claim 13 wherein the means (60) for adsorbing comprises porous layers (66) associated with a heatable support (68,70).   15. Device according to one of claims 11 to 14 comprising a valve (72) associated with the outlet (64).   16. Device according to claim 15 comprising analysis means (76) coupled to the three-way valve (72).   17. Device according to one of claims 11 to 16 comprising a Venturi system (48) associated with the inlet port (50).   18. Device according to one of claims 1 to 17, the dimensions and materials are chosen so that it is portable.   19. Use of a device (10) according to one of claims 1 to 10 with systems (1) of solid phase extraction by micro extraction.   20. Use of a device (10, 40) according to one of claims 1 to 18 for taking volatile compounds in a clean room.