Method and apparatus for assessing a quality of a container for at least one semiconductor fabrication article

Abstract

The invention relates to a method (300) and an apparatus (200) for assessing a quality of a container (100) for at least one semiconductor fabrication article. The invention is based on the principle of providing a mild vacuum in an inner 5 volume (110) of the container (100) in order to create a driving force for an at- mosphere surrounding the container (100) to diffuse into the container (100) through any cracks or other insufficiently sealed openings. Constituents of the surrounding atmosphere (particularly, certain chemical compounds present in the surrounding atmosphere but not or less prominently present in the inner vol-0 ume (110) of the container (100)) are then used as an indicator for such insuffi- ciently sealed openings. (Figure 2)

Description

[0001] Brooks Automation (Germany) GmbH DG1.DG23.DD176329 / 01 IDF3180 11 September 2025

[0002] 1

[0003] Method and apparatus for assessing a quality of a container for at least one semiconductor fabrication article

[0004] Description

[0005] The present invention relates to a method of and an apparatus for assessing a quality of a container for at least one semiconductor fabrication article

[0006] Background of the invention

[0007] In semiconductor fabrication facilities, so-called Front Opening Unified Pod (FOUP=minienvironment) are used as an important wafer handling resource. A FOUP is essentially a plastics enclosure designed to hold e.g. silicon wafers securely and safely in a controlled environment during wafer transferring process between tools. While a FOUP is designed to enable process automation of large wafers and prevent contamination, wafer transfers into and out of such a mini-environment potentially lead to cross contamination, i.e. , airborne molecular contaminants (AMCs) outgassed from contaminated wafers remain inside a FOUP and cause contamination of the next batch of clean wafers in the same FOUP.

[0008] Therefore, it is essential to consider such mini-environments in semiconductormanufacturing, since the integrity of their materials of construction, and other critical components can significantly affect the quality of the end product of the semiconductor fabrication process.

[0009] One example of such a critical component of a FOUP is a lid gasket, typically made from polymeric materials Consequences of gasket damage because of natural wear and / or other reasons include:

[0010] - Compromised environment inside the FOUP because accelerated ingress of contaminants (for example, ambient particulates, moisture, and AMCs).

[0011] - Process flow interruption, leading to downtime and affecting production schedules.While the application refers to front opening unified pods (FOUR) as a preferred example, the invention is generally applicable to any kind of wafer or reticle container. As a further example, front opening shipping boxes (FOSB) are mentioned.

[0012] In semiconductor wafer processing, robotic mechanisms are constantly arranging, organizing and processing wafers and wafer containers, such as a front opening unified pod (FOUR). The FOIIP may be damaged in the process (e.g. scratch, break, crack, deform, etc.). Wafer containers such as FOUPs are also liable to contamination, by which for example a wafer manufacturing process is rendered less effective. This also applies to containers for other semiconductor fabrication articles, for example reticle containers. For this reason, it is for example of great importance that a gasket provided on a container body or lid has no defects, in order to be able to provide a controlled and uncontaminated atmosphere within the container. There exists a need to efficiently inspect the FOUPs for such damages and / or defects.

[0013] In the following, whenever the term container or component, i.e. a component of such a container, for example a container body or lid, is used, this shall refer to a wafer or reticle container and its components, i.e. a container configured and adapted to hold and / or transport wafers or reticles.

[0014] In order to avoid said negative consequences, regular visual inspections can help to detect signs of wear, for example. However, such a procedure may be purely subjective and / or not effective, particularly if defects are microscopic. Alternatively or additionally, following gasket manufacturing guidelines on scheduled replacement intervals can mitigate or avoid above mentioned consequences. However, this is a costly option, if a change of gasket is perhaps not yet necessary due to intact FOUP materials. Further, stringent quality control measures (ultra-sensitive, fully automated, and computerized), especially with respect to the end product of the semiconductor production process, can helpwith early issues detection to minimize risks and avoid costly downtime and / or faulty products.

[0015] Disclosure of the invention

[0016] According to the invention, a method and an apparatus for assessing a quality or state of a container for at least one semiconductor fabrication article with the features as set out in the independent claims are provided. Advantageous embodiments are the subject-matter of the dependent claims as well as the following description. As an example, a front surface of a body of a container, comprising an opening through which wafers or reticles are inserted into the container body, and which interacts with a lid member adapted to sealingly close this opening, is usually provided with a seal or gasket. Also, for example, FOUPs must be regularly subjected to a purge, for example using N2 or other suitable gases with negligible moisture content, in order to remove contaminants and prevent contamination of the FOUR itself and / or its content. Suitable gases - apart from N2 - include Argon and / or any other noble gases as well as purified dry air or artificial dry air, but can be any other substantially pure gases with negligible humidity (and negligible content in other contaminants such as hydrocarbons, for example). A purge is effected by means of one or more valves typically provided in the base of a FOIIP. In order to prevent any contamination, the valve(s) may be provided in the form of check valve(s) preventing gas flow in an opposite direction such that an inlet and an outlet valve is clearly defined. Check valves typically require a certain surplus pressure in order to open which functions as an additional security mechanism since the inside of the FOIIP may be left at a slightly higher pressure than an atmosphere surrounding the FOIIP.

[0017] The invention is based on the principle of providing a mild vacuum in an inner volume of the container in order to create a driving force for an atmosphere surrounding the container to diffuse into the container through any cracks or other insufficiently sealed openings. Constituents of the surrounding atmosphere (particularly, certain chemical compounds present in the surrounding atmospherebut not or less prominently present in the inner volume of the container) are then used as an indicator for such insufficiently sealed openings.

[0018] In detail, according to the invention, a method of assessing a quality of a container for at least one semiconductor fabrication article, particularly a front opening unified pod (FOUR) as defined by SEMI standards (for example, SEMI E47.1 for a 300mm wafer FOUR), is provided. The container comprises an inner volume that is sealed against an atmosphere surrounding the container, (typically, naturally occurring air with other minor impurities which can be used as tracer gases, for example methane, noble gases and AMCs present in the fab environment), and at least one valve for supplying a fluid into the inner volume and / or withdrawing a fluid from the inner volume. The method comprises:

[0019] - a first withdrawing of a gas from the inner volume of the container through the at least one valve,

[0020] - a first determination of a content of at least one chemical compound within the first withdrawn gas,

[0021] - waiting for a predetermined amount of time,

[0022] - a further withdrawing of gas from the inner volume, thereby decreasing the pressure within the inner volume to a predetermined pressure level, which is lower than the pressure level of the atmosphere surrounding the container, - a second determination of the content of the at least one chemical compound within the further withdrawn gas, and

[0023] - assessing the quality of the container based on a comparison between the results of the first determination and the second determination of the content of the at least one chemical compound. By comparing the results of the first and second determination of content, it can be inferred, if the relevant chemical compounds changed their content in the inner volume of the container. If the container is properly sealed, no changes should be observed. Therefore, any changes in composition of the gas during the waiting time can be attributed to an already contaminated inner volume (e.g. adsorbed species on inner walls of the container) and / or to insufficiently sealed openings (e.g. gasket defect and / or cracks in outer walls of the container).Said first withdrawing may be effected by purging with a suitable dry gas and simultaneous application of a sensing tool used for the determination of the content of the at least one component with its own drawing flow, but not providing reduced pressure in the inner volume.

[0024] Said second or further withdrawing gas may be provided by a drawing flow of a sensing tool used for the determination of the content of the at least one component.

[0025] During said second withdrawing, a purge gas flow may be deactivated.

[0026] According to at least one embodiment, the method comprises, before and / or during the first withdrawing of gas, supplying a purge gas to the inner volume of the container, wherein the purge gas has a significantly lower concentration of the at least one chemical compound than the atmosphere surrounding the container. This enables discriminating between different origins of the at least one compound. Particularly, any species not contained in the purge gas will be purged out of the inner volume. Certain compounds, such as oxygen, methane or noble gases, for example, are known to poorly adsorb to the container material. Therefore, any increase in such compounds during the waiting time can be attributed to insufficient sealing.

[0027] According to at least one embodiment, the at least one valve comprises an outlet check valve and / or an inlet check valve, wherein the method during the first and / or further withdrawing of gas comprises determining a pressure and / or a gas flow downstream the outlet valve and / or upstream the inlet valve. In such embodiments, assessing the quality of the container comprises assessing an integrity of the outlet valve and / or the inlet valve based on the determined pressure and / or gas flow. Assessing the integrity of the outlet valve and / or the inlet valve comprises deeming the container inacceptable if the outlet valve and / or the inlet valve are deemed not intact. In the context of this invention, a check valve is considered to require a certain overpressure to open but does not need any other type of actuation. Particularly, a check valve may only be openable inone flow direction (i.e. for flow towards the inner volume or out of the inner volume, but not in both directions). Such a solution can streamline and simplify the assessment process by reducing the amount of hardware and making the inspection less ambiguous. Traditionally, separate tools are used for sealing functionality assessment and valve integrity assessment, whereas the present invention enables an integration of both assessments in one single method and tool.

[0028] According to at least one embodiment, the at least one chemical compound is selected from the group comprising oxygen, methane, ammonia, various saturated and unsaturated hydrocarbons and their respective derivatives These are particularly relevant and potentially harmful species which are typically present in atmospheres in semiconductor fabrication facilities but not in ultrapure purge gases. Therefore, they can be used as indicators (tracers) for leaks. Furthermore, for example oxygen, methane and noble gases are known to not adsorb to materials typically used for containers such as FOUPs. Therefore their presence or increase in the withdrawn gas can reliably indicate leaks in the containers.

[0029] According to at least one embodiment, the first determination and / or the second determination of the content of the at least one chemical compound comprises a measurement utilizing LASER-based spectroscopy, particularly cavity ringdown spectroscopy (CRDS). LASER-based spectrometers like cavity ring-down spectroscopy (CRDS) provide significant advantages over other methods, like FID (flame ionization), GC / MS (combined gas chromatography and mass spectrometry), PID (photo ionization) in terms of sensitivity, speed of response, simplicity, stability, and portability. Specifically, CRDS instruments based upon a broadband (BB) laser source with a span of more than hundred nanometers are available, thus enabling not only detection of simple molecules like oxygen, methane, ammonia and the like, but also various hydrocarbons, which are suspected to cause various damaging effects on wafers. CRDS has the additional advantage of not being vulnerable to fluctuations in LASER-intensity, due to its specific measurement principle.According to at least one embodiment, the first withdrawing of gas is carried out until the pressure within the inner volume of the container is decreased to the predetermined pressure level and / or, particularly when a purge gas is supplied to the inner volume, until the content of the at least one chemical compound is determined to be less than a predetermined threshold. This enables setting a predefined starting point for the assessment, i.e. a seal quality setpoint in the form of a predefined differential pressure from the surrounding atmosphere to the inner volume and / or a detection sensitivity in the form of a maximum starting concentration such that higher concentration changes are achieved by a given amount of ingress from the atmosphere surrounding the container.

[0030] According to at least one embodiment, assessing the quality of the container comprises deeming the container to be acceptable if the results of the first determination and the second determination differ by less than a difference threshold, and / or deeming the container to be inacceptable if the results differ by more than the difference threshold, particularly wherein the difference threshold pertains to a relative difference in concentration of the at least one compound in the first withdrawn gas and the further withdrawn gas, respectively, and is selected from the range between 10% and 500%, particularly between 50% and 200%. This is a relatively easily implementable assessment method and yields robust results. For example, a typical concentration of methane in the atmosphere surrounding the container is about 1900 ppb (or 1.9 ppm), whereas the concentration of methane in the FOUR after a purge may be about 0.5 ppb. This value of 0.5 ppb (result of the first determination) would then be used as a basis for the assessment explained here: a departure from 0.5 ppb over time is considered an indication of a leak. If the second determination yields a result of, for example, 1.0 ppb, this would be regarded as a relative increase by 100%:

[0031] second determination — first determination 1.0 ppb — 0.5 ppb 0.5 ppb first determination O.Sppb 0.5 ppb = 100%In other words, the term “relative difference” pertains to a difference between the result of the second determination and the result of the first determination relative to the result of the first determination, i.e. if the first determination yields a large result, the difference needs to exceed a higher (absolute) threshold to indicate a leak than in case where the first determination yields a low result.

[0032] Alternatively or additionally, a known flawless container can be used as a reference such that the mentioned threshold can be determined by an assessment of the quality of the reference container (and possibly applying an acceptable tolerance margin to the result of the assessment of the reference container) and defining the threshold based on this reference quality.

[0033] It is to be noted that the leak rate (penetration through gasket defects) of the at least one compound is typically much faster in comparison to desorption of preexisting specimens of the at least one compound entrapped in container material. Therefore, with an adequately chosen waiting time, the result of the second determination can be attributed sufficiently exclusively to any leaks in the gasket.

[0034] According to the invention, an apparatus for assessing a quality of a container for at least one semiconductor fabrication article, particularly a front opening unified pod (FOUR) as defined by SEMI standards, is provided. The container comprises an inner volume that is sealed against an atmosphere surrounding the container, and at least one valve for supplying a fluid into the inner volume and / or withdrawing a fluid from the inner volume. The apparatus comprises: - a fluid connector for connecting the container to the apparatus via the at least one valve,

[0035] - a chemical compound detector in fluid communication with the fluid connector, and

[0036] - an evacuation device, particularly a vacuum pump downstream the detector. According to at least one embodiment, the apparatus is configured to perform a method according to any of the embodiments of the invention. As such, theapparatus enables performing the method according to the invention and, therefore, profits from the same advantages, respectively.

[0037] According to at least one embodiment, the detector comprises a LASER-based spectrometer, particularly a cavity ring-down spectrometer. As already mentioned, specifically, a CRDS instrument based upon a broadband (BB) laser source with a span of more than hundred nanometers may be used, thus enabling not only detection of simple molecules like oxygen, methane, ammonia and the like, but also various hydrocarbons, which are suspected to cause various damaging effects on wafers. CRDS has the additional advantage of not being vulnerable to fluctuations in LASER-intensity, due to its specific measurement principle.

[0038] According to at least one embodiment, the apparatus comprises a purge gas supply configured to supply a purge gas to the inner volume of the container via the at least one valve. This enables setting a defined starting point for the assessment by providing a defined inner atmosphere to the inner volume of the container.

[0039] According to at least one embodiment, the apparatus comprises at least one flowmeter and / or at least one pressure sensor upstream and / or downstream the container. This enables assessing an integrity of the at least one valve, for example by determining, at what overpressure the respective valve opens.

[0040] Further advantages and embodiments of the invention may be derived from the appended drawings and the description.

[0041] The invention is schematically illustrated in the drawings with reference to specific embodiments and, in the following, is described with reference to the drawings.

[0042] Brief description of the drawingsFigure 1 schematically depicts a container, which can be used in embodiments of the invention.

[0043] Figure 2 schematically depicts an embodiment of an apparatus according to the invention.

[0044] Figure 3 schematically depicts an embodiment of a method according to the invention

[0045] Figure 4 schematically illustrates exemplary detector data as observed during working the method according to Figure 3.

[0046] Exemplary embodiment(s) of the invention

[0047] In Figure 1, a container for at least one semiconductor fabrication article, specifically for at least one substrate such as a wafer, in this example in the form of a front opening unified pod (FOUR), usable in embodiments of the present invention is schematically depicted and generally referred to with 100.

[0048] In Figure 2, an embodiment of an apparatus according to the invention is schematically depicted and generally referred to with 200. In the apparatus 200 a FOUR 100 such as the one shown in Figure 1 is used.

[0049] In Figure 3, an embodiment of a method according to the invention is schematically illustrated in the form of a simplified process diagram and generally referred to with 300. The method 300 can particularly use the apparatus 200 to assess a quality of the FOIIP 100. Therefore, in the following, Figures 1, 2 and 3 are described together, wherein references to method steps particularly rely on Fig. 3, references to apparatus components particularly rely on Fig. 2 and references to features of a container, or more specifically a FOIIP, are based on Fig. 1.In Fig. 1 as a typical example of such a container, a container (FOUR) 100 is partly shown. The FOUR 100 comprises an inner volume 110, which is configured to hold a number of one or more, particularly a number of ten or more, articles for semiconductor fabrication, particularly semiconductor single crystal slices, generally known as wafers. Container 100 comprises a front surface 160 defining an opening of the container, through which wafers can be inserted into the inner volume 110 of the container 100. The FOIIP 100 further comprises a door or lid (not shown in Fig. 1 ) on its front side, interacting with a front surface or frame 160, permitting access to the articles stored within the FOIIP 100. The door of the FOIIP 100 is sealed with a gasket 170 around the frame 160 of the FOIIP body 140 in order to avoid any ingress of foreign matter, such as particles, oxygen or any airborne molecular contaminants (AMCs). In other words, the door or lid, when closed, enables provision of a controlled atmosphere in the inner volume or interior 110 within container 100. For example, ammonia (NH3), hydrocarbons such as methane (CH4) or more complex hydrocarbons, e.g. having more than one carbon atom per molecule and / or substituents other than hydrogen bound to at least one of the carbon atoms (i.e. derivatives) may be considered AMCs.

[0050] In order to provide such a controlled atmosphere in interior 110 after closing the opening with a lid member, valves 120, 130 are provided in a lower inner surface 150 of container 100. These valves 120, 130, in the example shown, are provided in inner surface 150 in the vicinity of front surface 160. One of the valves 120, 130 is configured as an inlet check valve 120 and one is configured as an outlet check valve 130. In interaction with apparatus 200, the closed FOIIP 100 (i.e. with the lid in place) is connected to an interface or fluid connector 240 of the apparatus 200. Particularly, the interface 240 connects to the valves 120, 130 of the FOIIP 100. The apparatus 200 comprises a purge gas supply 210, which provides a purge gas substantially void of any contaminants, particularly not comprising any AMCs. For example, nitrogen (N2), Argon (Ar), clean dry air (CDA) or extreme clean dry air XCDA). The purge gas supply 210 may be based on bottled purge gas or may comprise a device producing the purge gas.The purge gas supply 210 is connected to the interface 240 via a first controllable valve 231. In a fluid path 211 between the purge gas supply 210 and the inlet check valve 120, a first sensor 212 is provided. This first sensor 212 is configured to measure at least one of a pressure in and a flow rate through the fluid path 211.

[0051] The apparatus 200 further comprises a detector 220, configured to analyze a composition of a fluid, particularly a gas, at least in terms of a content of at least one chemical compound, wherein the at least one compound preferably comprises one or more AMC(s). In the example shown, the detector 220 is a LASER-based spectrometer, particularly a cavity ring-down spectrometer. The detector 220 is connected to the outlet check valve 130 of the FOUR 100 via the fluid connector or interface 240. A second sensor 222 is provided in a fluid path 221 from the outlet check valve 130 to the detector 220. This second sensor 222 is configured to measure at least one of a pressure in and a flow rate through the fluid path 221 and may be of an identical type as the first sensor 212.

[0052] In the example shown, a vacuum pump 225 is provided downstream of the detector 220. This vacuum pump 225, which may be provided in the form of a membrane pump or even a rather simple blower or any other device configured to produce a pressure of below 95%, 90%, 80% or below 50% of natural ambient pressure, is configured to withdraw gas from the detector 220 and, the detector 220 being connected to the fluid path 221 , through the detector 220 also from the fluid path 221. The fluid path 221 from the outlet check valve 130 to the detector 220 is closeable via a second controllable valve 232.

[0053] A third controllable valve 233 is provided between the purge gas supply 210 and the detector 220. And a fourth controllable valve 234 is provided in a path from the outlet check valve 130 to a waste gas outlet, bypassing the detector 220.In use of the apparatus 200, in a first step 310 of method 300, a purge gas is supplied from the purge gas supply 210 to the FOUR 100. During this supplying of purge gas, the sensor 212 in the fluid path 211 senses pressure and / or flow rate of the purge gas. Based on the data from sensor 212, an assessment 315 of the inlet check valve 120 is performed. If the inlet check valve 120 works properly, after opening the first controllable valve, an increase in pressure is expected until the inlet check valve 120 opens. Then, the pressure is expected to remain substantially unchanged, while the flow rate of purge gas into the inner volume 110 of the FOUR 100 is expected to increase (until the pressure difference is substantially equalized). If, however, the inlet check valve 120 was already open before the start of step 310, the pressure increase will be much slower, since the inner volume 110 of FOIIP 100 adds to the overall volume available to the supplied purge gas. If the inlet valve 120, however fails to open, the pressure increase will not stop at the expected pressure level but continue to increase, whereas the flow rate of the purge gas will not increase as expected or decrease after the volume of the fluid path 311 is essentially filled with purge gas.

[0054] If the assessment 315 yields a positive result (i.e. the inlet check valve is deemed to work properly), the method continues with step 320, in which the second controllable valve 232 is open and the vacuum pump 225 is active, thereby withdrawing gas (for example about 1.5 to 5 liter per minute) from the fluid path 221 downstream the outlet check valve 130. Herein, this is also referred to as “first withdrawing” of gas. In this state, an assessment 325 of the outlet check valve 130 is performed, based on data from the sensor 222 in the fluid path 221 downstream the outlet check valve. This assessment 325 of the outlet check valve 130 is similar to the assessment 315 of the inlet check valve 120: If the outlet check valve 130 works properly, at first, a pressure decrease in the fluid path 221 is expected until a certain differential pressure over the outlet check valve is generated. Then, the pressure is expected to remain substantially constant while the flow rate in the fluid path 221 downstream the outlet check valve 130 is expected to increase (until it substantially matches the flow rate upstream the inlet check valve). If, however, the outlet check valve doesnot open, no increase in flow rate will be registered by the sensor 222, whereas in a case in which the outlet check valve was already open before the start of step 320, the flow rate will not increase (but remain on an already high level) and / or the pressure will not decrease.

[0055] If the assessment 325 of the outlet check valve 130 is also positive, the method continues with step 330, in which the detector 220 is active. During step 330, a first determination of a content of the gas first withdrawn from the inner volume 110 of FOUR 100 by the vacuum pump 225 in at least one chemical compound, for example one or more AMC(s) such as oxygen, ammonia or one or more hydrocarbons, is performed by the detector 220 (and / or, for example, a calculation unit such as a computer (not explicitly shown in the drawings) connected to or included in the detector 220. During step 330, the purge gas supply 210 may continue to supply the purge gas to the inner volume 110 of FOUR 100, such that the pressure within the inner volume 110 stays substantially constant. This serves as a purging step in order to provide a defined starting condition of the FOIIP 100 for the subsequent assessment of the sealing functionality of the FOIIP 100. Step 330 (the first determination of content of at least one chemical compound within the first withdrawn gas) may be performed for a predefined period of time (for example one or more seconds or up to one or two minutes), or may continue, until a predefined level of content of the at least one chemical compound is reached. Particularly, such a level may be considered reached, when the detector 220 is unable to detect any content of the at least one compound or when the detector 220 detects a content of this compound that is lower than a predefined threshold. In Fig. 3, this verification of setpoint is symbolized with a step 335.

[0056] When the predefined setpoint is reached, the method 300 continues with a step 340, in which the first controllable valve 331 is closed and after a predefined pressure level in the inner volume 110 is reached, the second controllable valve 332 is also closed. The predefined pressure level is lower than a pressure of an atmosphere surrounding the FOIIP 100. The arrival at the predefined pressure level can be monitored using sensor 222 downstream the outlet check valve, forexample. Then, in step 340 the FOUR is left for a predefined amount of time (for example several seconds or up to one minute) in a state of low pressure. During this waiting time, in a case in which the FOUR is insufficiently sealed against its surrounding atmosphere, AMCs are expected to be drawn into the inner volume of the FOIIP. This ingress might be too small to detect with a pressure sensor such as sensors 212 or 222, but may be large enough to detect with the sensitive detector 220, which analyzes the composition of the gas passing through it. Therefore, after the waiting time of step 340 has passed, the method 300 continues with a step 350, in which the first controllable valve 331 remains closed, but the second controllable valve is opened again and the vacuum pump is active and withdraws a sample of gas from the inner volume 110 of FOIIP 100. Herein, this is also referred to as “further withdrawing” of gas. The detector 220 performs a second determination of the content of the at least one chemical compound within the gas further withdrawn from the inner volume 110 of FOIIP 100. Step 340 may also be performed without a waiting time, during which the second controllable valve 332 is closed. Instead, vacuum pump 225 may continuously withdraw gas from the inner volume 110, thereby further decreasing the pressure inside the inner volume 110 of FOIIP 100.

[0057] In a step 355, the result of the second determination (step 350) is compared with a result of the first determination (step 330). If the sealing functionality is sufficient, no increase in the content of the at least one chemical compound is expected. If, however, the sealing functionality of FOIIP 100 is impaired, for example by a defect in the gasket 170 or a crack in the body 140 or lid of FOIIP 100, an increase in content of the at least one compound is expected. For example, the sealing functionality may be deemed satisfactory (and the quality of the respective FOIIP 100, therefore, acceptable), if an increase in the content of the at least one compound between the first determination 330 and the second determination 350 is lower than a predefined difference threshold. If the container 100 is deemed acceptable on this basis, the method ends in a step 360 returning a positive result (i.e. no failure of the container 100 determined). If, however, the assessment 315 of the inlet check valve 120, or the assessment 325 of the outlet check valve 130, or the comparison 355 between the first 330and second 350 determinations of the content of the at least one chemical compound, yielded a negative result, the method ends in a step 370 returning a negative result (i.e. a failure of the container 100 was determined). The negative result 370 may contain an information about the identity of the defect determined (i.e. defect of inlet check valve 120 and / or defect of outlet check valve 130 and / or defect of gasket 170 / body 140 / lid).

[0058] In a step prior to the first step 310 and / or after the last steps 360 / 370 of method 300, the apparatus 200 may be purged with purge gas supplied by the purge gas supply 210. To that end, controllable valves 231 and 232 may be closed and controllable valves 333 and optionally 334 may be opened in order to remove contaminants from the interior of the apparatus 200.

[0059] In Figure 4, exemplary detector data as observed during working the method 300 according to Figure 3 are schematically illustrated, wherein a diagram 410 illustrates a concentration of ammonia c(NH3) within gas withdrawn from the FOUR 100 over time and a diagram 420 illustrates the concentration of water c(H2O) within the gas over the same time scale as in diagram 410.

[0060] Arrow 1 indicates a time at which the FOUR 100 is in a fully purged state, i.e. the previously mentioned defined starting condition of the FOIIP 100. In this state at time 1 , the concentrations of both ammonia c(NH3) and water c(H2O) are low. For example, the concentration of ammonia c(NH3) at time 1 may be less than 0.3 ppb and the concentration of water c(H2O) may be less than 0.5% relative humidity.

[0061] Arrow 2 indicates a point in time, at which the vacuum pump 225 starts (further) withdrawing gas from the inner volume 110 of FOIIP 100 while the first controllable valve 331 is closed (i.e. the start of a period during which the inner volume 110 is under a lower pressure than the atmosphere surrounding the FOIIP 100. For example, a sampling rate of the vacuum pump 225 may be about 2.0 liters per minute (at ambient pressure). This sampling or further withdrawing of gas from the inner volume 110 creates a mild vacuum inside the FOIIP 100 with apressure in the inner volume 110 of about 90 kPa to 95 kPa, whereas the atmosphere surrounding the container may be under a pressure of about 99 kPa to 101 kPa. In other words, a differential pressure over the FOIIP body 140 and gasket 170 may be about 5 to 10 kPa.

[0062] This differential pressure puts more force on the sealing surface resulting in a generally better seal. As already explained, the quality of seal depends on the presence (or absence) of (micro)defects, which act as (micro-)conduits for ingress of ambient gasses, particularly AMCs). During the sampling time (between arrows 2 and 3), some increase in concentration of ammonia c(NH3) and water (c(H2O) inside of the FOIIP 100 is observed. AC indicates a difference in ammonia concentration over a sampling cycle. In the example shown, AC is about 0.2 ppb total over a sampling time of about two minutes. In this example, the atmosphere surrounding the FOIIP 100 contained about 1.5-2 ppb of ammonia. Similarly, in diagram 420, a water or moisture ingress is observed at about 0.04 mole% or about 1% RH / min. In the example shown, the atmosphere surrounding the FOIIP 100 exhibited a relative humidity of about 40%.

[0063] Arrow 3 marks a time, at which a new purge process is started (i.e. first controllable valve 331 is opened). In the example shown, such a purge comprises purging with CDA (about 5-20 liters per minute) to return to original base values. The diagrams 410 and 420 show two repetitions of the above following the first cycle.

Claims

Claims1. Method (300) of assessing a quality or state of a container (100) for at least one semiconductor fabrication article, particularly a front opening unified pod (FOUR) as defined by SEMI standards, wherein the container (100) comprises an inner volume (110) that is sealed against an atmosphere surrounding the container (100), and at least one valve (120, 130) for supplying a fluid into the inner volume (110) and / or for withdrawing a fluid from the inner volume (110), the method (300) comprising- a first withdrawing (320) of gas from the inner volume (110) of the container (100) through the at least one valve (130),- a first determination (330) of a content of at least one chemical compound within the first withdrawn gas,- waiting for a predetermined amount of time (340),- a further withdrawing of gas from the inner volume (110), thereby decreasing the pressure within the inner volume (110) to a predetermined pressure level, which is lower than the pressure level of the atmosphere surrounding the container (100),- a second determination (350) of the content of the at least one chemical compound within the further withdrawn gas, and- assessing the quality or state of the container (100) based on a comparison (355) between the results of the first determination (330) and the second determination (350) of the content of the at least one chemical compound.

2. Method (300) according to claim 1 , comprising, before and / or during the first withdrawing (320) of gas, supplying (310) a purge gas to the inner volume (110) of the container (100), wherein the purge gas has a smaller concentration of the at least one chemical compound than the atmosphere surrounding the container (100).

3. Method (300) according to claim 1 or 2, wherein the at least one valve (120, 130) comprises an outlet check valve (130) and / or an inlet check valve(120), wherein the method (300) comprises, during the first (320) and / or further withdrawing of gas, determining a pressure and / or a gas flow downstream of the outlet valve (130) and / or upstream of the inlet valve (120), andwherein assessing the quality of the container comprises assessing (315, 325) an integrity of the outlet valve (130) and / or the inlet valve (120) based on the determined pressure and / or gas flow, wherein assessing (315, 325) the integrity of the outlet valve (130) and / or the inlet valve (120) comprises deeming the container inacceptable (370) if the outlet valve (130) and / or the inlet valve (120) are deemed not intact.

4. Method (300) according to any one of the preceding claims, wherein the at least one chemical compound is selected from the group comprising oxygen, methane, ammonia, saturated and unsaturated hydrocarbons with a maximum of four carbon atoms per molecule, and their respective derivatives.

5. Method (300) according to any one of the preceding claims, wherein the first determination (330) and / or the second determination (350) of the content of the at least one chemical compound comprises a measurement utilizing LASER-based spectroscopy, particularly cavity ring-down spectroscopy (CRDS).

6. Method (300) according to any one of the preceding claims, wherein the first withdrawing (320) of gas is carried out until the pressure within the inner volume of the container is decreased to the predetermined pressure level and / or, particularly when at least supplying (310) a purge gas according to claim 2, until the content of the at least one chemical compound is determined (330) to be less than a predetermined threshold (335).

7. Method (300) according to any one of the preceding claims, wherein assessing (355) the quality of the container comprises deeming the container (100) to be acceptable (360) if the results of the first determination (330)and the second determination (350) differ by less than a difference threshold, and / or deeming the container (100) to be inacceptable (370) if the results differ by more than the difference threshold, particularly wherein the difference threshold pertains to a relative difference in concentration of the at least one compound in the first withdrawn gas and the further withdrawn gas, respectively, and is selected from the range between 10% and 500%, particularly between 50% and 200%.

8. Apparatus (200) for assessing a quality of a container (100) for at least one semiconductor fabrication article, particularly a front opening unified pod (FOUR) as defined by SEMI standards, wherein the container (100) comprises an inner volume (110) that is sealed against an atmosphere surrounding the container (100), and at least one valve (120, 130) for supplying a fluid into the inner volume (110) and / or withdrawing a fluid from the inner volume (110), the apparatus (200) comprising- a fluid connector (240) for connecting the container (100) to the apparatus (200) via the at least one valve (120, 130),- a chemical compound detector (220) in fluid communication with the fluid connector (240), and- an evacuation device (225), particularly a vacuum pump, downstream the detector (220).

9. Apparatus (200) according to claim 8, wherein the detector (220) comprises a LASER-based spectrometer, particularly a cavity ring-down spectrometer.

10. Apparatus (200) according to claim 8 or 9 comprising a purge gas supply (210) configured to supply a purge gas to the inner volume (110) of the container (100) via the at least one valve (120, 130).

11. Apparatus (200) according to any one of claims 8 to 10 comprising at least one flowmeter (212, 222) and / or at least one pressure sensor (212, 222) upstream and / or downstream the container (100).

12. Apparatus (200) according to any one of claims 8 to 11 configured to perform a method (300) according to any one of claims 1 to 7.

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