Patent Application
20130175161
The present application concerns a plant for fluorine production in the form of assembled skids and a process wherein it is applied.
During the manufacture of semiconductors, photovoltaic cells, thin film transistor (TFT) liquid crystal displays, and micro-electromechanical systems (MEMS), often consecutive steps of deposition of material and etching of the respective items are performed in suitable chambers; these processes are often plasma-assisted. During the deposition step, deposits are often not only formed on the item, but also on the walls and other interior parts of the chamber. It was observed that elemental fluorine is a very effective agent both for etching and for cleaning the chambers to remove undesired deposits. Processes of this kind are for example described in WO 2007/116033 (which describes the use of fluorine and certain mixtures as etchant and chamber cleaning agent), WO 2009/080615 (which describes the manufacture of MEMS), WO 2009/092453 (which describes the manufacture of solar cells), and in unpublished EP patent application 09174034.0 which concerns the manufacture of TFTs.
US patent application publication describes the generation and distribution of fluorine within a fabrication facility. Providing fluorine on-site reduces the risk connected to the transport of fluorine from a facility where it is generated to the point of use.
There are still problems to be solved in connection with the apparatus used in the on-site concept, for example, the destruction of greater amounts of pure fluorine (F2) and of HF in case of leakages, or the breakdown of equipment.
The present invention provides an improved plant suitable to produce fluorine on-site especially for the use as etchant and chamber cleaning agent in the manufacture of semiconductors, photovoltaic cells, thin film transistor liquid crystal displays and micro-electromechanical systems.
The plant of the present invention provides fluorine gas to a tool which applies fluorine gas as reactant to perform chemistry in this tool which apparatus comprises skid mounted modules including at least one skid mounted module selected from the group consisting of
The preferred plant of the present invention provides fluorine gas to a tool which applies fluorine gas as reactant to perform chemistry in this tool which apparatus comprises skid mounted modules including
The plant preferably also comprises skid modules which may be located close to the skid modules 1 to 8 but may be separated from them, namely
Further, the apparatus may comprise means to supply inert gas, e.g., means to supply liquid and gaseous nitrogen; means to supply compressed air and water; and ancillaries and amenities. At least, skids 1, 2, 3, 4, and 7, preferably all skids, comprise housings for safety reasons.
In the context of the present invention, the term “fluorine gas” denotes in particular molecular fluorine (F2) and mixtures thereof, in particular with inert gases. Inert gases are preferably selected for example from argon, nitrogen, oxygen and N2O. A preferred fluorine gas consists or consists essentially from F2.
In the following, a preferred plant as shown in
Such a plant comprising parts assembled in several skids has many advantages. For example, the skids can be pre-assembled and tested in a factory; thus, they are a kind of “off-shelf” product, and need only be mounted on-site. This saves time. It is also much easier to dismount specific skids for maintenance, repair or substitution by skids comprising parts with the same function but improved performance, or with lower or higher output. There are also improvements in safety: for example, as explained above, skid 2 comprises at least one electrolytic cell; preferably, all electrolytic cells are already filled with the electrolyte and then delivered to the site for being assembled in skid 2. Thus, the filling can be performed under respective safety considerations and must not be performed on a local site where such safety precautions may not be available. The capacity of the plant can be expanded by adding modules. Preferably, the skids have sea container size thus allowing for the easy transport of modules. A great advantage is a reliable production for 24 hours and 7 days a week of high purity F2.
The skids will now be explained in detail.
It is generally preferred that the cells are blocked and connected to the structure to avoid movements, e.g., as a seismic protection. It is also preferred that the plant comprises means which detect earthquakes and send a signal to the control room which causes the plant to shut down automatically or personnel to shut it down manually. Preferably, the plant includes at least one seismometer, e.g., a strong motion seismometer (accelerometer) which can detect vibration acceleration of the plant and, if a certain level is reached, e.g., 0.5 G, send a respective signal which triggers an alarm and/or an automatic shutdown of the plant.
All pipes connecting the cells and connected to the cells must be electrically isolated, e.g., by means of spacers between flanges. The floor must be electrically isolating, too.
Preferably, all process skids (skids 1 to 8) are comprised in an enclosed space.
Skid 1: The skid module for HF storage (skid 1) comprises at least one HF (hydrogen fluoride) storage tank which serves to store HF and to deliver it to the electrolytic cells. The storage tanks for HF are generally hollow bodies which optionally can be mounted on wheels or which can be transported e.g., by a forklift. Preferably, the skid comprises several storage tanks, more preferably, 2, 3, 4, 5, or 6 storage tanks. Preferably, the HF is stored in liquid form in the tank. Skid 1 is connectable to a tank comprising pressurized N2. The liquid HF is pressurized with N2 and delivered to an evaporator where it is evaporated. The resulting gaseous phase containing HF is delivered to the electrolytic cell or cells. If desired, for each electrolysis cell an evaporator can be installed.
The evaporator preferably contains a heating, e.g., an electrical heating or a heat exchanger using the heat of hot cooling water, to generate the evaporated HF. More preferably the HF storage containers can be isolated from the HF supply line by double isolation valves having a closed isolation space. In that case, skid 1 suitably further comprises at least one interspace vent valve in connection with one or more closed isolation space. The interspace vent valve is generally operable to remove optionally present hydrogen fluoride from the closed isolation space. Removal can be carried out, for example, by applying vacuum. In another aspect, removal can be carried out, for example, by flushing the closed isolation space with an inert gas and/or a pressurized purging gas such as for example anhydrous air or, preferably, nitrogen.
In one aspect, the removal is carried out continuously.
Preferably, the removal is carried out discontinuously, in particular when an HF storage container is connected to and/or disconnected from the supply line. Gases recovered from the closed isolation space are suitably vented to an HF destruction unit, for example a scrubber in skid 6.
In the plant according to the invention, parts thereof which are supposed to be in contact with gas such as e.g., if appropriate, hollow bodies, valves and lines for charging and/or discharging gas are suitably made of or coated with material resistant to molecular fluorine. Examples of such materials include Monel metal, stainless steel, copper, and, preferably, nickel.
In a preferred aspect of skid 1, the hydrogen fluoride storage containers are contained in an enclosed space having at least a closeable gate allowing for entering into or removing from the enclosed space a hydrogen fluoride storage container. In one embodiment of this aspect the enclosed space contains the hydrogen fluoride storage containers and the connections to the hydrogen fluoride supply line. In another embodiment, the enclosed space contains in addition an evaporator for evaporation of liquid HF. In this preferred aspect and its embodiments, the enclosed space suitably comprises an HF sensor capable to trigger connection of the enclosed space to a scrubber described below.
Skid 1 generally has at least a liquid line and a gas line. In that case, the liquid line can be connected, if appropriate to the hydrogen fluoride supply line, for example by means of a flange connection. The gas line can additionally be connected to an inert gas (e.g., anhydrous air, nitrogen, etc.) supply line which allows to pressurize the hydrogen fluoride storage containers.
In skid 1, each hydrogen fluoride storage container has generally a capacity of from 10 to 5000 liters, often from 500 liters to 4000 liters, preferably from 500 to 3000 liters. Particular examples of hydrogen fluoride storage containers are tanks approved by RID/ADR-IMDG—of UN T22 or, preferably, UN T20 type. Such tanks are commercially available.
Each HF storage container in skid 1 can be suitably connected to the hydrogen fluoride supply line through a manifold.
Each HF storage container in skid 1 is preferably individually isolatable from the hydrogen fluoride supply line.
The HF storage containers in skid 1 can generally be isolated from the hydrogen fluoride supply line by a remotely controlled device, preferably a remotely controlled valve. More preferably each storage container is equipped with a remotely controlled device, preferably a remotely controlled valve, allowing isolating that container from the hydrogen fluoride supply line.
When remotely controlled valves are present, manual valves are suitably installed in addition. The remotely controlled valves allow for example to operate the HF-storage-containers from a remote control-room.
In a preferred embodiment, the HF storage containers comprise an automatic HF level sensor. In particular the HF storage containers can be installed on weighing scales. In that case, preferably, a process control system, in particular an automatic process control system is operable to closes the remotely controlled valve of a first, empty HF container and to open the remotely controlled valve of another second HF-containing hydrogen fluoride storage container. This embodiment is particularly effective to avoid manual handling of HF valves and to ensure a continuous HF supply.
In a preferred aspect, the valves are operable to close automatically in case of abnormal operation state, such as for example a process-interruption in a process-equipment connected to the HF supply line.
In another preferred aspect, the valves are operable to close automatically in case of an HF leakage in skid 1. Such HF leakage can for example be caused by a leakage of optional flange-connections inside the HF storage-container there is the possibility to close these valves via remote control. This avoids in particular the necessity to approach the hydrogen fluoride supply unit in this case.
The skid also contains valves to shut down the supply of HF and nitrogen. Preferably, skid 1 comprises from 3 to 10 HF containers; especially preferably, it comprises 4, 5, 6, 7, or 8 containers. 4 HF containers are suitable for a productivity of 150 tons F2/year. Tanks with smaller size, especially, if they can be closed via valves separately, improve the safety of the plants. The tanks must be made from or at least lined with material resistant to HF. The walls should be sufficiently thick; preferably, they have a 10 mm IMDG code (international maritime dangerous goods code) equivalent thickness.
In a particular embodiment, skid 1 comprises, preferably permanently, at least one HF emergency container. Such HF emergency container is preferably an empty HF storage container as described herein which is preferably connected to the HF supply line. The HF emergency container is generally operable to receive HF from a leaking HF storage container. The HF emergency container is suitably kept under pressure of an inert gas or under vacuum.
The tanks are preferably portable so that they can be transported by trucks and/or can be handled by a fork lift.
Skid 1 comprises a ventilation system, and the ambient air is preferably permanently ventilated to a scrubber, especially the ERS scrubber for HF and F2 removal (as described below).
Skid 2: The skid comprising the electrolytic cell or 2 or more cells (skid 2) is now described in detail. It contains at least one electrolytic cell. Preferably, it contains at least two electrolytic cells. More preferably, it contains at least 6 electrolytic cells. A skid 2 with 8 electrolytic cells is very suitable. The skid preferably is constructed such that if desired, additional electrolytic cells can be added if the demand for fluorine gas is rising. The cells comprise jackets through which cooling water can be circulated. If desired, skid 2 can be provided in the form of separate sub-skids 2A, 2B and so on. In these sub-skids, a certain number of electrolytic cells are assembled. The separate sub-skids 2A and 2B (and any other sub-skids) are attached together to form one cell room. Often, the cell room will contain 4, 6 or more cells, for example, 8 cells or even more. The advantage of providing several electrolytic cells is that the shut-off of one or even more cells for maintenance or repair can be compensated by raising the output other cells. To assemble several sub-skids has the advantage that dimensions can be kept within permissible maximum dimensions for usual road transport. The electrolytic cells are connected to collectors for the F2 and the H2 produced. It has to be noted that each cell may comprise 1 or more anodes. Typically, each cell comprises 20 to 30 anodes. In other embodiments, the number of anodes in each of the electrolytic cells may be greater than 30; each cell may, for example, have more than 60 anodes, up to 70 or even up to 80 anodes. A cable connects each of the anodes with the rectifier. Each cell cathode is connected through one copper or aluminium bus bar to the rectifier. One rectifier can supply current to one or more cells. It is preferred to apply one rectifier per anode. The advantage is that the intensity at each individual anode can be fine tuned depending on the specific anode characteristics, abnormal situations at a specific anode (e.g., overvoltage, short-circuit, or broken anode) can be immediately detected allowing the automatic shutdown of the faulty anode while all other anodes and cells continue to produce F2. Accordingly, skid 2 preferably comprises at least 4 electrolytic cells with a multitude of anodes wherein each of a multitude of rectifiers in skid 8 is allocated to a single anode, or wherein each of a multitude of dual rectifiers in skid 8 is allocated to two anodes.
Skid 2 includes a cooling water circuit (fed by or connected to cooling water circuits of skid 5) supplying cooling water to the jackets of the cells.
Skid 2 also comprises settling boxes; preferably, a settling box for F2 and a settling box for H2 are connected with each of the cells. The settling boxes serve to reduce the gas velocity of the F2 and H2 produced in the cell to avoid electrolyte dust to be carried over. Preferably, the settling boxes comprise a vibrator and a heating to melt the separated electrolyte dust for easy removal.
The collectors collecting the produced F2 are connected by a pipe with skid 3, the collectors for produced H2 are connected by a pipe with a scrubber for H2 in skid 6B (this will be described in detail below). In a preferred embodiment, skid 2 also comprises a ventilation system to treat accidental releases of F2 and/or H2.
The ambient air of skid 2 is ventilated to a scrubber, especially the ERS scrubber for safety reasons (the scrubber is described below).
Skid 3: it comprises means for the purification of the produced F2. It comprises a cooler wherein the F2 is pre-cooled. Skid 3 also comprises an HF washer wherein the pre-cooled F2 is contacted with HF which is kept at a very low temperature. The HF washer contains a cooling jacket through which a coolant is circulating. Skid 3 further comprises a buffer tank, a compressor, e.g., a diaphragm compressor, an HF condenser operated at low temperature and at least one HF absorber column, preferably containing NaF as absorbent for HF. Preferably, at least two absorber columns are contained in the skid 3. If desired, the absorber columns are redundant so that one set is in absorption mode, the other set can be regenerated. The absorber columns comprise a heating. If desired, a further set of absorber columns may be present in skid 3 or on the site for reloading of absorbent. The HF condenser is connected via pipes to the electrolysis skid 2. Preferably, at least one set of columns is mounted on a wheeled trolley to keep them (re-)movable from the skid.
The HF condenser may be cooled to a temperature where HF condenses to form a liquid or even a solid. It is preferred if it is condensed to form liquid HF. Cooling the trap to a temperature of −60° C. to −80° C., preferably to about −70° is very suitable. As cooling medium, well-known cooling liquids operable at the desired low temperature are suitable. It is preferred to apply a N2 gas which was obtained by mixing liquid N2 and gaseous N2 in appropriate amounts. This way of cooling is very reliable. Thus, skid 3 comprises lines to deliver and to withdraw cooling medium.
The ambient air of skid 3 is ventilated to a scrubber, especially the ERS scrubber (described below) for safety reasons.
Skid 4: this skid serves for storage of fluorine gas and the delivery of fluorine gas to the point of use. Skid 4 comprises filters to remove any remaining entrained solids. For example, the F2 produced in the electrolytic cells may comprise entrained solid electrolyte from the cell, usually, adducts of KF and HF. The filter is preferably constructed from material resistant to HF and fluorine; stainless steel, copper, Monel metal and especially nickel are especially suitable. Filters made from sintered particles of these metals comprising a pore diameter in the nanometer range to provide semiconductor grade F2, e.g., with a pore diameter of equal to or less than 5 nm, and more preferably, with a pore diameter of equal to or smaller than 3 nm, are very suitable.
If desired, skid 4 comprises a pre-filter to remove from the F2 coarser particles with a pore diameter of equal to or less than 1 μm.
Skid 4 may also comprise a single-cell FT-IR. In this single-cell FT-IR, the purified F2 which is ready for storage or delivery to the point of use, may be analyzed. In this case, it is not necessary to provide the UV spectrometer and/or the multi-cell FT-IR in skid 7.
Skid 4 preferably comprises means for the storage of fluorine gas. It may, for example, contain a buffer tank for fluorine gas.
Additionally to, but preferably instead of the buffer tank, skid 4 may comprise a permanent or temporary fluorine gas storage unit in the form of a plurality of hollow bodies to store the F2. The storage unit is connectable to other skids.
“Permanent fluorine gas storage unit” is understood to denote in particular a fluorine gas storage unit which is integrated into the fluorine plant. For example, the fluorine gas storage unit can be a transportable or preferably fixed unit which is present in skid 4 throughout operation of the fluorine plant. Preferably, the permanent fluorine gas storage unit is designed to contain more than 90 wt % more preferably more than 95 wt %, most preferably about 100 wt % of the fluorine gas relative to the total weight of fluorine gas stored in the plant.
Skid 4 is further able to convey fluorine gas from skid 2 to the point of use. Possible components of skid 4 include but are not limited to supply lines, compressors, mixers and buffer tanks.
“Connectable” is understood to denote in particular that the permanent fluorine gas storage unit is equipped to be able to be connected to a component of skid 4. Preferably, the permanent fluorine gas storage unit is equipped to be able to be connected to a fluorine gas supply line. In a preferred aspect, the fluorine gas storage unit is connected to a component of skid 4, in particular a fluorine gas supply line throughout operation of the fluorine gas plant. In a further preferred aspect, the fluorine gas storage unit is directly connected to a component of skid 4.
Suitable equipment for connecting the fluorine gas storage unit connected to a component of skid 4 includes a manifold connected to each hollow body of the fluorine gas storage unit through a line and preferably having a shut-off valve in each line allowing to individually isolate each hollow body and said manifold is further connected to a component of skid 4.
Skid 4 preferably comprises from 4 to 25 hollow bodies, more preferably from 5 to 8 hollow bodies. The hollow bodies are preferably of substantially identical shape and dimensions. Cylindrically shaped hollow bodies (tubes) are preferred. Each hollow body of the fluorine gas storage has preferably a shut-off valve.
The hollow bodies of the fluorine gas storage unit can be suitably fixed together by means of an appropriate frame. Particular frame geometries include triangular, square, and rectangular geometries.
In the fluorine gas plant according to the invention, the fluorine gas storage means are generally able to contain or contains fluorine gas at a pressure of at least 25 psig (about 1.72 barg). Often this pressure is equal to or greater than 35 psig (about 2.4 barg), preferably equal to or greater than 40 psig (about 2.8 barg). In the plant according to the invention, the fluorine gas storage means is generally able to contain or contains fluorine gas at a pressure of at most 400 psig (about 27.6 barg), preferably, equal to less than 75 psig (about 5.2 barg). Often, this pressure is equal to or lower than 65 psig (about 4.5 barg), preferably equal to or lower than 60 psig (about 4.1 barg). It is understood that the hollow bodies of the fluorine gas storage unit are generally able to contain or contain fluorine gas at the aforesaid pressures. It is particularly preferred that the hollow bodies contain fluorine gas at the aforesaid pressures.
In the fluorine gas plant according to the invention the ratio of the molecular F2 stored in the fluorine storage means to the daily molecular F2 producing capacity of the fluorine gas plant is generally from 0.1 to 1, preferably from 0.1 to 0.25.
Preferably, each of the hollow bodies can be shut off from the plant separately; this improves safety. The fluorine leaving skid 4 is transported preferably through double-walled pipes to the point of use. Fluorine gas is transported in the inner tube; the outer double wall envelope comprises nitrogen. The piping contains a pressure sensor to analyze the nitrogen pressure in the outer double wall envelope. Preferably, the walls of the pipes are thicker than commonly used for transporting gases, i.e. preferably, they are thicker than 1 mm, preferably, thicker than 4 mm; a wall thickness of equal to or greater than 5 mm is especially preferred; pipes classified as “schedule 80” are very suitable. This serves to improve the safety. Welded piping with radiographic inspection is very suitable.
The storage container or containers can be mounted on wheels or are transportable by a forklift.
The ambient air of skid 4 is ventilated to a scrubber, especially the ERS scrubber described below (for safety reasons).
In the fluorine gas plant according to the invention, the point of use can be connected to a further manufacturing plant, for example a chemical plant or, in particular, a plant using fluorine gas for surface treatment. The point of use is often connected to a semiconductor manufacturing plant, preferably a manufacture of photovoltaic devices or flat panel displays.
In a preferred embodiment of the fluorine gas plant according to the invention, skid 4 comprising the fluorine gas storage unit is an enclosed space. The enclosed space generally comprises a fluorine sensor capable to trigger connection of the enclosed space to skid 6. Suitably, the enclosed space is connected to skid 6 through a suction line connected to a fan which is operable to transport gas from the enclosed space of skid 4 to skid 6.
In a further embodiment, the fluorine gas plant according to the invention further comprises a mixer, preferably a static mixer, said mixer being preferably capable to receive fluorine from skid 4 and to receive inert gas, such as preferably argon and/or nitrogen, from an inert gas supply line.
In an optional embodiment, a pressure control loop adjusts, generally reduces the pressure of fluorine gas supplied to the point of use to a desired value.
Skid 5 provides for cooling or heating of parts of the plant by means of cooling water. It is preferably located close to the electrolytic skid 2 or sub-skids 2A and 2B or any additional sub-skids 2X, more preferably, it is located above the skids. Skid 5 comprises at least one circuit which serves to heat the electrolyte cells to melt the electrolyte salt when the reaction is started, and to cool the cells when the reaction is running. The circuit is filled with cooling water which may be tap water or distilled water. The circuit includes a buffer tank, a pump which is preferably redundant, and a dry cooler with fans with variable speed drives. The cooling water, during operation, is preferably kept at 75 to 95° C. to avoid solidification of the electrolyte in the cells.
Another circuit comprised in skid 5 serves to cool other heat exchangers of the apparatus. It contains a cooling liquid, preferably a mixture of water and ethylene glycol, more preferably, water comprising 40% by weight of ethylene glycol. Also this circuit comprises a buffer, a pump which preferably is redundant, and a dry cooler. The cooling circuits include detectors to measure the temperature of the cooling water, means to heat the cooling water, e.g., electric heating, heat exchangers to cool the circulating liquids. Optionally, the plant comprises a steam generator to provide steam or hot cleaning water. The steam generator may be a portable one. The hot steam may be, for example, used to provide hot water in which electrolyte salt may be dissolved, if necessary. Consequently, skid 5 preferably contains at least two cooling water circuits.
Skid 6 comprises at least one scrubber each for F2 and H2. Preferably, the scrubber pumps are redundant. The skids of the plant (especially skids 1, 2, 3, 4, and 7) include a ventilation system to ventilate the ambient air of the skid enclosures permanently through scrubbers in skid 6.
Preferably, skid 6 comprises an F2 scrubber for destruction of any F2 or HF vent required for safety reasons or maintenance operations. F2 and HF from the ventilated air from the skids are treated in a scrubber for emergency response (ERS). The scrubbers are preferably jet scrubbers and provide the suction. The scrubbers may be mounted on sub-skids, e.g., a sub-skid 6A which comprises at least one scrubber for emergency response (ERS), a sub-skid 6B which serves to scrub produced H2 with the purpose to remove HF entrained therein, and a scrubber to remove HF and/or F2 in waste gas originating from ventilating the ambient atmosphere from skids as explained below.
The capacity of the regular F2 scrubber (optionally mounted in sub-skid 6B) corresponds at least to the expected amount of F2 to be removed during regular operation. F2 is removed by contact with an abatement solution. This scrubber preferably comprises a jet scrubber and a packed column to provide a high contact area between the abatement solution and F2. Preferably, the gas leaving the regular F2 scrubber is passed through the back-up scrubber of the ERS scrubber.
The ERS scrubber serves as back-up of the regular F2 scrubber used for removal of F2 or HF from ventilated air, and for the emergency treatment of ventilated air which contains HF and/or F2 after a leakage. The capacity of the ERS scrubber (optionally mounted in sub-skid 6A) corresponds preferably at least to the amount of fluorine and HF to be removed in cases for emergency, for example, in the very improbably case of pipe breaking, an accident with one of the tubes containing fluorine or an HF storage tank. It is advisable to select the capacity of the ERS scrubber according to a worst-case scenario; for example, if HF tanks with 2 m3 capacity and F2 storage tubes with a capacity of 8 kg F2 are present, the ERS should be able to abate the respective amounts of HF and F2 and the plant-holdup. Preferably, the ERS scrubber comprises 2 units for scrubbing to achieve a high destruction and removal efficiency; redundant pumps are fed by normal and emergency power supply. It preferably comprises a jet scrubber and a packed column to achieve a good contact between the gas to be treated and the abatement solution. The other unit serving for emergency treatment may comprise a packed column, but preferably, it comprises two jet scrubbers in series. The F2 removal can be performed with agents known to remove F2. Preferably, a KOH solution or NaOH optionally comprising an alkali metal thiosulfate, e.g., sodium thiosulfate or potassium thiosulfate is used as abatement solution and is pumped through the scrubber or scrubbers and the column, if present, as decomposing agent for F2. A cooler may be foreseen to cool the KOH solution. Of course, it is an advantage of the concept that one emergency scrubber serves to treat HF and F2.
The scrubber of skid 6 serving for the HF abatement of the H2 gas stream may be mounted in sub-skid 6B. Sub-skid 6B includes preferably a jet scrubber operated with aqueous HF solution to reduce the content of HF in the H2. The concentration of HF may be in a range between 1 and 10% by weight. The scrubber further comprises a packed column wherein fresh water is given on top of the column to reduce the HF content. Skid 6B also includes a line which allows the dilution of H2 by nitrogen which was used as cooling medium in skid 3.
The reliability of the scrubbers in skid 6, or in skids 6A and 6B respectively, is very important. Thus, essential parts like fans or pumps to circulate the abatement solution through the scrubbers may be redundant. From time to time, fresh abatement agent, for example, KOH solution, and/or thiosulfate or its solution, e.g., provided by a truck, is added to the circulating abatement solution.
Skid 6 preferably comprises also one or more retention pits for liquid in case of accidental leakages.
Skid 7 concerns the apparatus used for the analysis of the produced F2. It is preferably installed near skids 2A and 2B; very preferably, it is located above the skids 2A and 2B. Skid 7 is, for example, an analyzer shelter. The ambient atmosphere around it is preferably ventilated to the ERS. The analyzer contains analyzing means suitable to determine the content of the main impurities of the produced F2.
In one embodiment, a UV spectrometer (which analyses the UV spectrum) and multi-input, multi-cell FT-IR spectrometer (Fourier-Transform Infra-Red spectrum) analyzers are very suitable. Preferably, both raw F2 taken from the cells and purified F2 may be sent to a single-cell FT-IR or a multi-cell FT-IR. In a multi-cell FT-IR, one channel is analyzed at a given time. The amount of HF, CF4, C2F6 and COF2 can, for example, be measured by FT-IR while the content of F2 is analyzed by UV. It has been found that UV spectroscopy can be used as a direct measurement tool for fluorine which shows a sharp decrease in fluorine concentration when an anode burn occurs; an enormous increase of CF4 is observed at the same time in the FT-IR. Therefore the burn can be detected easily by the sharp decrease of the F2 concentration during the burn, during which impurities are formed (mainly CF4 and C2F6). The result of this burn (the produced F2 contains more CF4, C2F6, COF2, HF than when working regularly) is not only the alteration of impurities' contents but also a sharp decrease in the content of fluorine monitored by a detector system, especially, in the present invention, by UV spectroscopy. During the measurements using UV spectroscopy, the whole UV spectrum can be used. Preferably, not the whole spectrum but only the absorption at this particular wavelength, particular UV spectroscopy between 200 and 400 nm, more preferred between 250 and 330 nm, most preferred between 270 to 290 nm, even at about 280 nm is used for measuring, because it is more or less the maximum of the UV absorption of F2. The FTIR and UV measurements are also used to control the purity of the purified F2. Thus, the analysis serves to detect anode burns by measuring the raw F2 by UV and CF4 by FT-IR and to document and control the purity of the purified F2.
The raw F2 of all cells and the purified F2 are continuously sampled and analyzed. Current FT-IR can accept up to 9 samples. Thus, the purified F2 and the raw F2 of up to 8 electrolysis cells can be analyzed with one multi-cell FTIR of the current generation of apparatus.
According to another embodiment, the analysis of the fluorine produced is performed only with a single-cell FT-IR; a UV spectrometer is not applied. The single-cell FT-IR is used for the analysis of the purified F2 (final analysis).
Skid 8 contains the rectifiers, the BPCS (basic process control system), the ESD (emergency shutdown system), the F&G (fire and gas system) panel which registers fire alarms and gas alarms, small motor starters, lighting distribution and other means to provide electricity and to control electric means of the plant. Skid 8 is installed near skids 2A and 2B; preferably, it is located above them. Each electrolytic cell, as mentioned above, usually has at least one, but often a multitude of anodes, e.g., 26 anodes. The term “multitude of anodes” may denote any figure which is equal to or greater than 2. The number of anodes is limited only by practical considerations, e.g., the cell or cell unit (constituted of several cells) should not be unreasonably large. Often, the number of anodes is equal to or lower than 80, preferably, equal to or lower than 70. One rectifier could provide current to one, two or more anodes. Preferably, each anode is supplied by a rectifier. Rectifiers are available on the market which can provide current separately to several anodes. For example, if 26 anodes are present in a cell, it is preferred to provide 26 rectifiers or 13 dual rectifiers which separately provide current to 2 anodes. The rectifiers are preferably assembled in rectifier cabinets installed in air-conditioned enclosure.
It is preferred to provide a slight overpressure in this skid 8 to protect from gas ingress. All cables and cathode bus bars should be carefully sealed.
It is preferred that the rectifier cabinets are bolted on a fixed frame for seismic protection.
Skid 8 comprises walls and a roof. It includes preferably also a fire detection system, especially a VESDA (very early smoke detection apparatus) and a fire extinguishing system operating, e.g., with HFC-227ea or with Inergen®, a mixture of inert gases (nitrogen, argon, and carbon dioxide).
Skid 9 is preferably a pre-fabricated room with concrete walls or similar to a container, made from metal shields. It contains means for connection to electric current and to transform it from medium to low voltage. Preferably, it contains the “electric sub-stations” sub-skids 9A and 9B. Skid 9A preferably contains the MV (medium voltage) cells for incoming and outgoing current and bypass current and the transformers to transform the medium voltage current into low voltage current. It is adaptable to the local network; for example, the transformers are selected such that they fit to the local voltage which may, for example, be 380 V or 400 V (50 Hz) or 440 V (60 Hz). Skid 9 includes preferably also a fire detection system, especially a VESDA (very early smoke detection apparatus) and a fire extinguishing system operating, e.g., with HFC-227ea or with Inergen®, a mixture of inert gases (nitrogen, argon, and carbon dioxide).
Skid 9B also is preferably a pre-fabricated concrete room having walls and a roof. This substation houses the low voltage switchgears (LVCS) and a diesel generator. It is interconnected by cables to the skids which need a low voltage power supply, e.g., via a cable trench. It includes preferably also a fire detection system, especially a VESDA (very early smoke detection apparatus) and a fire extinguishing system operating, e.g., with HFC-227ea or with Inergen®, a mixture of inert gases (nitrogen, argon, and carbon dioxide).
Skid 9B preferably also comprises a battery charger station for a forklift.
Skid 9B must be interconnected to the process skids, especially with the rectifiers in skid 8.
Skid 10 comprises utilities for the personal, for example, a control room, a laboratory, and a rest room. Preferably, it is divided into sub-skid 10A and sub-skid 10B. Sub-skid 10A contains the control room and the laboratory. The laboratory which may be small includes a fume hood with good ventilation, e.g., up to 500 m3/h and even more, which hood is preferably made from acid-resistant materials and can be used for analytical titrations, a safety cabinet for reagents and samples, a wash basin and a chemical sink wherein chemical waste can be collected, preferably in a drum made from acid resistant material. The laboratory preferably has a gas detector installed in a fresh air intake and a closing mechanism which closes the air intake in case of a gas alarm. Sub-skid 10A preferably is kept under a slight overpressure to prevent gas ingress. Skid 10A preferably comprises air-conditioning.
The control board of the control room is preferably connected online to a remote control board which may be located on another facility. This allows operating several fluorine gas production plants remotely from one single control room.
Sub-skid 10B contains the rest room. It contains installations useful for the control room personal. It preferably includes lockers, a changing room, a toilet, a shower, and cabinets for chemical gowning (gloves, capes etc). The plant safety shower includes eye-shower systems and is preferably located close to the outside of sub-skid 10B because it must be fed with warm potable water. Skid 10 preferably comprises ventilation and heating.
The plant will include further equipment useful to operate it.
Compressors are needed to provide pressurized fluorine gas. They must be resistant to fluorine gas. Compressors which are used for fluorine gas handling in the nuclear industry are very suitable. They are preferably diaphragm type compressors.
Such compressors are available on the market. The diaphragms are made from F2 resistant material, especially from Monel metal, stainless steel, copper or nickel. The membranes are 3-layer membranes so in case of a membrane break the break will be detected by pressure measurement, and no F2 will leave the compressor membrane to the outside area.
The plant also will need instruments and valves for operation.
For example, if a mixer is present to provide mixtures of F2 and inert gases or other gases, the process step of mixing the gases includes mass flow meters for F2 and the gas or gases to be mixed with it, installed control valves with dedicated programmed control loops and interlocks to ensure an appropriate and safe mixing of the gases, e.g., the inert gas or inert gases, with F2.
The plant, as described above, has means to analyze certain parameters (e.g., mass flow control of fluorine gas or inert gas) for its operation. For this purpose, mass flow controllers are preferably used. With such mass flow controllers, the amount of fluorine gas can be controlled which passes through lines carrying it for example, to the FTIR and UV analyzers. The mass flow controllers ought to be “low ΔP type” controllers causing only a low pressure drop. Such flow meters, as well as tubes, pipes, and fittings used to transport gas to the analyzers which must be suitable for fluorine gas transport, are also available on the market. Valves should be bellow sealed heavy duty valves. A PLC (programmable logic controller) manages the movements of the FTIR mirrors, collects malfunction alarms and transmits results to the BPRS (basic process control system). To analyze pure F2, windows made from AgCl are preferably applied, for the analysis of raw F2, e.g., raw F2 from the sampling lines of the electrolytic cells, Al2O3 windows can be applied.
From the description above, it becomes clear that several alternatives can be applied concerning the analysis of F2.
According to a first alternative, a single cell FT-IR is located in skid 4. It serves to perform a final analysis of the F2.
According to a second alternative, a multi-cell FT-IR and optionally, a UV analyzer is located in skid 7.
According to a third alternative, a single-cell FT-IR is located in skid 4, and a multi-cell FT-IR and optionally, a UV analyzer is located in skid 7.
The first alternative is the cheapest solution. The second alternative is more expensive than the first alternative; but it allows a quick reaction if the F2 production in one or more cells is disturbed. It also allows to identify the cell operating irregularly. The third alternative is the most expensive one; it allows, at the same time, a quick reaction and to identify faulty cells, and it allows to check the purity of the final F2.
Which alternatives are chosen depends on the expectations or demands of the customer, the experience of personnel, the inclination of the plant to run into faulty conditions etc. It would also be possible to provide analyzers in skid 4 and 7 but to operate one of them or both not continuously, but intermittently.
Safety equipment: It is well known that especially F2 and HF are compounds which need cautious handling. H2 is, of course, flammable. Accordingly, the plant includes safety installations. For example, the plant comprises a safety panel with switches for an emergency shutdown (ESD), for alarms, and for overriding automatic processing.
Detectors for F2, HF and, where appropriate, H2, are installed, for example, in ventilation ducts to the ERS scrubber and at the emission points. Gas alarm signals are sent to the ESD for safety functions. The plant includes warning lights which are activated, i.e., if gas alarm signals are sent to the ESD. The alarms must also be detectable in the control room of skid 10. Gas measurements must be given in the control room, e.g., in ppm. It is very advantageous if the plant comprises a Fire & Gas panel in the control room of skid 10 to show all fire and gas alarms, and failure of ventilation.
As mentioned above, the plant includes smoke detectors and VESDA detectors. Especially the process skids, e.g., skids 1, 2, 3, 4, and 7, comprise means to stop the F2 production manually, e.g., emergency push buttons, and/or to actuate fire extinction apparatus. CC TV (closed circuit television) can be used to supervise the plant. It can be used to monitor access to the plant, unloading of materials (e.g., of HF portable tanks or KOH solution).
Safety Instrument Systems (SIS) comprising sensors, ESD system and safety actuators are included in this plant. The SIS are designed to achieve a Safety Integrity Level “2”. In particular, where electrical motors or electrical loads were needed to be included as a part of a safety instrumented function, alternate and independent means of tripping these motors/loads are considered, e.g., by tripping the upstream breaker if the contactor or circuit breaker dedicated to the motor/electric load fails to open.
An emergency generator, preferably a diesel generator supplying 100 kVA is preferably contained in the plant if external power supply is interrupted.
It is also preferred if the control room comprises a “dead man” detection for the operator working alone.
Further, it is preferred that the control room provides data for wind direction and wind speed.
The footprint of the assembled process skids for a plant with a capacity of 150 t/year is 30 m by 9.2 m. With skids for utilities, personnel areas and access clearance for maintenance and servicing, the overall size is about 39 m by 23 m. The height of the skids may be higher than standard (standard height is 64 inches). Skid 6A comprising the emergency scrubber has often not the standard footprint but must be adapted to the specific need of the respective plant.
Often, the skid structure is a painted steel frame on which all equipments are fixed; they are designed for outdoor installation. Panels, doors and roofs, if fixed on the external structure of the skid, imply that the external skid dimensions exceed the standard sea container dimensions. If necessary, such skids are prefabricated and panels, doors and the roof, respectively, are assembled to the skids on site. The skids are anchored on an existing concrete slab or by or on specific foundations.
The advantage of skids is, for example, that they are manufactured, piped, wired and assembled together before shop testing. It is preferred if they are constructed such that the interfaces between the skids are minimized and that all parts in the respective skid are accessible as easily as possible for maintenance, inspection or repair.
The advantage of the skids is the safety aspect, a reliable F2 production for 24 hours and 7 days a week of high purity F2.
In the following, the assembly and operation of a plant constructed of skids is described.
The skids as described above are assembled in a workshop; in one embodiment, the electrolytic cells of skid 2 already are supplied filled with the electrolyte salt. This improves safety. The skids are preliminarily tested in the workshop and then shipped to the facility where the F2 produced by them is needed. On the facility, it is preferred if a concrete slab had been built sufficiently beforehand upon which the F2 production plant can be erected.
The skids are assembled and connected. Skid 2 comprises 6 electrolytic cells forming one cell room. Each electrolytic cell, in this case, comprises 26 anodes; other multitudes, e.g., up to 80 anodes and even more, would be possible, if desired.
Before connection or thereafter, they are blocked to the ground as an earth quake or bad weather precaution measure.
Skid 13 serves as storage room for chemicals needed, e.g., thiosulfate, hydroxide and/or electrolyte salt.
Operability of the built-in parts is preferably tested then.
The operation of the plant is now described in detail.
A plant with 6 cells is provided. The nominal capacity of this plant, if run 24 hours for 7 days a week, is about 100 tons/year of pure F2 (12 kg/h, peak 20 kg/h). The capacity could be expanded by adding two further electrolysis cells and rectifiers or rectifier racks. The expansion of capacity to 300 t/year would be possible by adding further skids (additional cell room and rectifiers, additional cooling skid, additional analyzers). Tanks, preferably with an inner volume of from 1 to 20 m3, most preferably in a size of from 1 to 3 m3, filled with HF, are assembled in skid 1 and connected to the electrolytic cells. Electrolyte salt of the rough composition KF.2HF had already been filled into the cells before the final assembly of the plant. The content of the electrolytic cells is heated to about 80-120° C. to be molten therein. HF coming from the evaporator from skid 1 is fed into the electrolytic cell. From skid 9A, medium voltage is supplied to skid 9B, transformed to low voltage direct current with a voltage in the range of from 8 to 12 V, and current is passed through the molten composition of HF and the molten electrolyte salt which is kept in a temperature range between 80 and 120° C. One rectifier may be allocated to each cell; preferably, one rectifier is allocated to each anode. It is especially preferred to apply dual rectifiers; such a dual rectifier can serve two anodes. If 26 anodes are present in each cell, then 13 dual rectifiers may be applied to provide electric current to the anodes. The cells are operated at as pressure higher than ambient pressure (e.g., at 7 to 10 mbarg). Elemental fluorine (F2) and elemental hydrogen (H2) form in the respective electrode compartments in skid 2.
HF is advantageously supplied such that the level of electrolyte salt and HF in the respective cell does not exceed specific upper and lower levels. Preferably, the skid containing the electrolytic cell or cells also includes sensors which determine the temperature in the cell, the level of liquid in the cell or cells, the pressures and pressure differences, the anode currents and voltages and gas temperatures. The cells are cooled with cooling water having a temperature of about 75 to 95° C., preferably from 75 to 85° C.
H2 formed is passed to skid 6B and is contacted in a jet scrubber with an aqueous solution comprising 0 up to about 5% by weight of HF in water. Gas leaving the scrubber is passed to the bottom of a packed column and contacted therein with fresh water sprayed on top of the column. Gas leaving the packed column is diluted with nitrogen and passed into the atmosphere.
The plant produces about 415 kg/day of F2.
F2 produced in the cells is first pre-purified by removing particles (mainly, entrained re-solidified electrolyte salt). The stream of raw F2 is then cooled down whereby a part of entrained HF condenses and can be removed. Then, the raw F2 is compressed with a diaphragm compressor to a pressure of about 3.5 barg. The redundant pairs of NaF towers are installed on trolleys to keep them movable, especially for the case that the NaF pellets need to be exchanged completely (when further regeneration is not possible any longer). The compressed F2 is then passed through a trap and cooled therein to about −70° C. by means of evaporated liquid N2 and gaseous N2. Residual HF is removed in this trap by condensation. Any remaining traces of HF are then removed by passing the F2 through one line of two lines of two absorption towers containing NaF pellets; the lines are redundant because from time to time, the NaF towers are heated to about 350 to 400° C., and N2 is passed through them to remove absorbed HF and to regenerate the respective towers. The pressure in the NaF towers in absorption mode is about 3.5 barg. The F2 gas stream leaving the two NaF towers is passed through two filters to remove any solids, especially NaF; the filters are preferably made from Monel metal, and the second filter has a pore diameter of 3 nm. The temperature of the first tower is about 100° C., the temperature of the second tower is about 30-40° C. The purified F2 is continuously sampled.
According to one embodiment, samples are sent to a multi-cell FT-IR and to a UV analyzer, as described above. According to another embodiment, a single-cell FT-IR is applied for the analysis selectively of the purified F2. Analytical data are sent online to a control board in the control room in skid 10A.
If the analysis of the samples shows that one or more of the cells produces F2 too impure to be useful for semiconductor manufacturing purposes, for example, containing too much CF4 or higher homologues which indicates a cell failure, the respective sample or samples and the F2 produced by the electrolytic cell are passed to the F2 scrubber in skid 5 and the emergency scrubber for destruction by means of a KOH solution including sodium thiosulfate. Alternatively, the impure F2 could be collected to be used for purposes for which the degree of purity is sufficient. If the samples show that the F2 produced corresponds to the desired purity, the samples are returned to the F2 product line. The F2 is then passed to a storage means which includes 6 identically shaped containers each having an internal volume of 1.3 m3. Each of the cylinders can be opened and shut off individually by shut-off valves. Alternatively, the pressure of the produced F2 is lowered to about 1.5 barg by a pressure control loop and is then passed to the point of use, a flat panel display manufacturing plant using F2 for chamber cleaning. A double-walled pipe is used, wherein the space between the inner and the outer tube contains nitrogen, and the F2 is passed through the inner tube of it.
In normal operation, the shut-off valves are open and the pressure difference between the F2 storage unit and the point of use provides a buffer allowing a smooth control of the delivered fluorine gas flow, even for variable consumption patterns at the point of use or during interruption of the production of the F2 generating unit.
Should the disclosure of any patents, patent applications, and publications which are incorporated herein by reference conflict with the description of the present application to the extent that it may render a term unclear, the present description shall take precedence.
The present application is a U.S. national stage entry under 35 U.S.C. §371 of International Application No. PCT/EP2011/065773 filed Sep. 12, 2011, which claims priority to U.S. provisional patent applications No. 61/383,204 filed Sep. 15, 2010 and N° 61/383,533 filed Sep. 16, 2010, the whole content of each of these applications being incorporated herein by reference for all purposes.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2011/065773 | 9/12/2011 | WO | 00 | 3/12/2013 |
| Number | Date | Country | |
|---|---|---|---|
| 61383204 | Sep 2010 | US | |
| 61383533 | Sep 2010 | US |
