JP2007090174A - Used etching gas treating method and used etching gas treatment apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To greatly reduce an amount of drain by recycling water generated when treating used etching gas. <P>SOLUTION: This treatment apparatus 100 is provided with: a detoxifying facility 74 for burning used etching gas discharged from an etching apparatus 72; a scrubber 53 for producing hydrogen fluoride by bringing water into contact with gas discharged from the detoxifying facility 74 and causing a reaction; a reactor 20 for reacting hydrogen fluoride generated in the scrubber 53 with a calcium compound to form a calcium fluoride-containing treating solution 22; a treatment tank 30 for separating solid from liquid by membrane filtration of the calcium fluoride-containing treating solution 22 from the forming tank 20; a filter press 36 for recovering calcium fluoride precipitated in the treatment tank 30; a regeneration tank 40 forming hydrogen fluoride by adding an acid to the calcium fluoride recovered in the filter press 36 and causing a reaction; and a water recycling line for returning filtrate filtered in the treatment tank 30 to the scrubber 53. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a processing method and a processing apparatus for used etching gas generated in a back grinding process and an etching process particularly in a device manufacturing process.

For example, the manufacturing process of a semiconductor device includes an etching process, and this etching process is roughly divided into two types, a wet etching process and a dry etching process. In the wet etching process, waste water containing fluorine such as hydrogen fluoride (or hydrofluoric acid) is discharged, and in the dry etching process, an etching gas is used. For example, CF ₄ , NF ₃ , SF _{6 and the} like are used as the etching gas. It is used.

  The concentration of fluorine contained in the wastewater discharged from the etching process is specifically regulated to be 8 mg / L or less, and there is a possibility that the total amount of fluorine discharged will be regulated in the future. .

  Numerous removal methods have been proposed as the above-described fluorine removal method. As a method for removing fluorine contained in wastewater, a method of performing biological treatment and chemical treatment in separate treatment tanks has been proposed (see Patent Document 1 below). As another method for removing the fluorine content, after preparing a plurality of reaction tanks, calcium is added to the raw water stored in one reaction tank to form a seed containing a sol-like substance. There is also a method of treating the fluorine content by adding a seed agent to the raw water stored in the other storage tank (see Patent Document 2 below). Furthermore, there is a processing method for obtaining sludge by coagulating and precipitating fluorine contained in waste water using a polymer flocculant.

JP 2001-54792 A JP-A-6-312190

  However, the method for treating wastewater containing fluorine described in Patent Document 1 requires a plurality of wastewater treatment steps, which causes a problem that the facility becomes large. Therefore, the cost for wastewater treatment is high. Furthermore, since organic components are processed using living organisms, there is a problem that it is difficult to perform stable wastewater treatment.

  Furthermore, in the wastewater treatment method described in Patent Document 2, since the concentration of fluorine contained in the wastewater is extremely low, other treatment steps such as coagulation sedimentation treatment are performed in order to solidify the obtained fluorine. There was a problem that would be necessary.

  Furthermore, if the fluorine content in the wastewater is removed by a coagulation sedimentation method using a commercially available polymer flocculant, a large amount of sludge is generated as industrial waste. Furthermore, there is a problem that it is difficult to reuse sludge mixed with a large amount of a flocculant.

  Therefore, it is desired to remove fluorine from wastewater without using a flocculant and to regenerate the fluorine in the device manufacturing process so that it can be used as an etching agent.

  The features of the present invention are as follows.

  (1) A hydrogen fluoride generation process in which used etching gas discharged when dry etching the surface of a wafer is burned to react with water to generate hydrogen fluoride, and a fluorine gas generated in the hydrogen fluoride generation process. Generating a calcium fluoride-containing aqueous solution by reacting hydrogen fluoride with a calcium compound, and filtering the filtered water from the calcium fluoride-containing aqueous solution obtained in the generating step. This is a used etching gas treatment method that is reused as water.

  Since the filtered water obtained in the production process is reused in the hydrogen fluoride production process, the amount of drainage can be greatly reduced, and the water treatment piping system can be completed in the production process.

(2) In the used etching gas processing method according to (1), the used etching gas is CF ₄ .

  (3) An abatement facility that burns used etching gas discharged when the surface of the wafer is dry-etched, and hydrogen fluoride is generated by causing water to contact and react with the gas discharged from the abatement facility. A scrubber, a production tank for reacting hydrogen fluoride produced in the scrubber with a calcium compound to produce a calcium fluoride-containing aqueous solution, and a calcium fluoride-containing aqueous solution obtained in the production tank are separated by filtration. And a water recycling line for returning the water to the scrubber.

  Similarly to the above, according to the processing apparatus, since the water obtained by the generation tank is reused by the scrubber, the amount of drainage can be greatly reduced, and the apparatus is disposed in a clean room. Also, there is no risk of the fluorine content leaking outside.

(4) In the used etching gas processing apparatus according to (3), the used etching gas is CF ₄ .

  According to the present invention, in device manufacturing, the amount of waste water and waste can be greatly reduced, and the fluorine content in waste water can be reduced as much as possible.

  Hereinafter, preferred embodiments of the present invention will be described.

  FIG. 1 shows an example of a device manufacturing method, and a device manufacturing method will be described below by taking a manufacturing process of an FS type IGBT using an FZ wafer as an example.

  A silicon oxide film 8 (for example, a film thickness of 10 to 150 nm) is formed on the active layer 10 by using, for example, a thermal oxidation method using dry oxygen at 950 ° C., and then a CVD method (low pressure CVD method, plasma CVD) is formed thereon. The silicon nitride film 6 (for example, 200 nm) is formed using a method, a high-density plasma CVD method, or an atmospheric pressure CVD method.

  The silicon nitride film 6 and the silicon oxide film 8 are etched using a resist formed by photolithography as a mask corresponding to the element isolation region, thereby forming a hard mask for trench formation. This etching is usually performed by dry etching. After the etching is completed, the resist is removed.

  Thereafter, through a predetermined process of forming a semiconductor device, a gate oxide film is formed in the transistor formation region of the active layer 10 from which the silicon oxide film 8 as an insulating film is removed, and doped polysilicon or the like is formed on the gate oxide film. A conductive layer is formed, and the conductive layer is patterned to form a gate electrode.

Further, through a predetermined process, a surface side element structure comprising a base region, an emitter region, a gate oxide film, a gate electrode, an interlayer insulating film, an emitter electrode and a passivation film on the surface side of the n ⁻ FZ wafer to be the active layer 10 Part 12 is formed. The gate oxide film is made of, for example, SiO ₂ . The gate electrode is made of polysilicon, for example. The interlayer insulating film is made of, for example, BPSG. Further, the emitter electrode is made of, for example, an Al—Si film, and the Al—Si film is heat-treated at a low temperature of about 400 to 500 ° C. in order to realize a low-resistance wiring having a stable bonding property. The passivation film is made of, for example, a polyimide film.

  Next, the back surface of the wear is polished by back grinding and etching, so that the wafer has a desired thickness, for example, 70 μm. Here, the etching process may be either dry etching or wet etching.

  Next, for example, phosphorus, which is an n-type impurity, and boron, which is a p-type impurity, are ion-implanted from the back surface of the wafer, and heat treatment is performed at 350 to 500 ° C. in an electric furnace to form the buffer layer 14 and the collector layer 16.

  Next, a plurality of metals such as aluminum, titanium, nickel and gold are vapor-deposited on the surface of the collector layer 16 on the back surface of the wafer to form a collector electrode 18.

  After that, a dicing tape is attached to the collector electrode 18 side, and the wafer is cut into a plurality of chips. The collector electrode 18 of each chip is soldered to a fixing member of the device, and an aluminum wire electrode is fixed to a surface electrode such as an emitter electrode, whereby the device is mounted on various devices.

  FIG. 2 shows an example of a processing apparatus 100 for used etching gas discharged from the etching process in the device manufacturing method described above.

  In another example, the apparatuses used for the used etching gas processing apparatus 100 from the polishing process to the wastewater treatment process may all be disposed in a clean room, or may be disposed in separate facilities and connected by piping or the like. It may be.

As shown in FIG. 2, the processing apparatus 100 burns the etching apparatus 72 that performs dry etching on the surface of the wafer using the etching gas in the above-described device manufacturing process, and the used etching gas discharged from the etching apparatus 72. Detoxification facility 74, scrubber 53 that generates water by bringing water into contact with the gas discharged from the decontamination facility 74 and generating hydrogen fluoride (HF), and hydrogen fluoride produced in the scrubber 53 as a calcium compound And a treatment tank 30 for producing a calcium fluoride (CaF ₂ ) -containing treatment liquid by reacting with the solution, and a treatment tank 30 for filtering the calcium fluoride-containing treatment liquid 22 obtained by the production tank 20 into a solid liquid by membrane filtration A filter press 36 for recovering calcium fluoride precipitated in the treatment tank 30; and a fluoride fluoride recovered by the filter press 36. It includes a regeneration tank 40 which acid was added and the reaction to Siumu to produce hydrogen fluoride, and water recycling line for returning the filtered water which is filtered to the scrubber 53 in the processing vessel 30, a.

More specifically, although CF ₄ , NF ₃ , SF _6, etc. are used as the etching gas, CF ₄ is preferable from the viewpoint of green chemicals. The used etching gas discharged from the etching apparatus 72 is burned in the abatement facility 74 and becomes exhaust gas containing CO ₂ , SO _x , NO _x , and F. Normally, CO ₂ , SO _x , and NO _x are removed from the scrubber 53 and only F is supplied. Water 62 is stored in the water storage tank 60, and water is supplied to the injection nozzle 54 of the scrubber 53 via the pump 68. In the scrubber 53, the water sprayed from the spray nozzle 54 reacts with the supplied F to generate a hydrogen fluoride-containing aqueous solution 56.

A hydrogen fluoride-containing aqueous solution 56 is transported from the scrubber 53 to the production tank 20, and a calcium compound-containing aqueous solution 26 is transported from the calcium content storage tank 24 by a pump 28. As a result, a calcium fluoride-containing treatment liquid (or calcium fluoride-containing aqueous solution) 22 is generated. Here, as the calcium compound, for example, calcium chloride (CaCl ₂ ) can be used, and the calcium compound-containing aqueous solution 26 is preferably an aqueous solution containing 30% by weight of calcium chloride. Since calcium chloride has a very high solubility product, it can be supplied in large quantities to the water to be treated in the production tank 20. For example, by adding calcium chloride to the water to be treated in the generation tank 20 so that the calcium ions (Ca ²⁺ ) become 200 mg / L or more, fluorine ions ( The concentration of F ⁻ ) can be 8 mg / L or less. This fluorine ion concentration satisfies the general discharge standard.

  The treatment tank 30 is provided with a filtration membrane 32 immersed therein, and a certain amount of filtered water 52 filtered from the filtration membrane 32 is stored in the filtered water tank 50, part of which is discharged, and part of the water is recycled. The water is returned to the water storage tank 60 through the use line and reused as water for the scrubber 53.

  In the present embodiment, the filtration membrane 32 performs filtration using a self-forming membrane. Here, the self-forming film may be a self-forming film made of an object to be removed containing calcium fluoride.

  Further, an air diffuser 34 is provided below the filter membrane 32 of the treatment tank 30, and a self-forming film formed on the surface of the filter membrane 32 by supplying bubbles from the air diffuser 34 to the filter membrane 32. Filtration is performed while keeping the thickness below a certain level, suppressing clogging of the self-forming film, and securing a certain amount of flux. As the gas generated from the air diffuser 34, for example, an inert gas such as helium, neon, argon, or nitrogen is used.

  The high calcium fluoride content to be removed precipitated in the lower part of the treatment tank 30 and the high calcium fluoride content to be removed which is deposited on the surface of the filtration membrane 32 are transported to the filter press 36, and the water is removed by the filter press 36. Concentrated.

  The calcium fluoride-rich material to be removed concentrated by the filter press 36 is transported to the regeneration tank 40, and the acid 42 is supplied from the acid storage tank 42 by the pump 38. Here, examples of the acid include hydrochloric acid, sulfuric acid, and nitric acid, and sulfuric acid is preferable.

  In the regeneration tank 40, calcium fluoride and acid react to produce hydrogen fluoride and a calcium salt of acid, and the obtained hydrogen fluoride is reused as an etching agent in the etching apparatus 72.

  Next, the waste water treatment after the etching treatment step in the treatment apparatus 100 of the present embodiment will be described below.

  For example, in the above-described device manufacturing process, the silicon oxide film or the like is dry-etched by the etching apparatus 72, or after the back surface of the wafer is back-ground, the back surface of the wafer is dry-etched and polished. The used etching gas discharged by the etching apparatus 72 is transported to the abatement facility 74 and burned. Exhaust gas discharged from the detoxification facility 74 is sent to the scrubber 53, where it is brought into contact with water and reacted to generate hydrogen fluoride (HF). The hydrogen fluoride produced by the scrubber 53 is transported to the production tank 20. In the generation tank 20, the calcium compound-containing aqueous solution 26 is transported from the calcium content storage tank 24 via the pump 28. Thereby, in the production tank 20, hydrogen fluoride in the wastewater reacts with the calcium compound to produce a calcium fluoride-containing treatment liquid 22. The calcium fluoride-containing treatment liquid 22 produced in the production tank 20 is transported to the treatment tank 30. In the treatment tank 30, the calcium fluoride-containing treatment liquid 22 is separated into filtered water and a high calcium fluoride content to be removed by the filtration membrane 32 while supplying gas from the air diffuser 34 to the information. The filtered water 52 filtered by the filtration membrane 32 is stored in the filtered water tank 50, and a part is returned to the water storage tank 60 through the water reuse line and reused as water for the scrubber 53. On the other hand, the high calcium fluoride content to be removed, which is a solid content separated by the filtration membrane 32, is transported to the filter press 36, where the moisture is removed and concentrated. The filtrate filtered by the filter press 36 is returned to the production tank 20. On the other hand, the high calcium fluoride content to be removed concentrated by the filter press 36 is transported to the regeneration tank 40. On the other hand, the acid 42 is supplied to the regeneration tank 40 from the acid storage tank 42 by the pump 38. Thereby, calcium fluoride and an acid react to produce hydrogen fluoride and a calcium salt of the acid, and the obtained hydrogen fluoride is separately reused as an etchant for wet etching.

  Since the water obtained from the generation tank 20 is reused by the scrubber 53, the amount of drainage can be greatly reduced. Further, by disposing the processing apparatus 100 in a clean room, there is no possibility that the fluorine content leaks to the outside.

  The filtration membrane 32 mentioned above is further demonstrated in detail using FIG.

  The fluid mixed with the object to be removed, which is calcium fluoride, is removed with a filter made of a self-forming film formed from the object to be removed.

  More specifically, in the filter membrane 32 of the present embodiment, a self-forming membrane to be the second filter 82 formed from calcium fluoride as a removal object is formed on the surface of the organic polymer first filter 81. It will be. Using the second filter 82 which is this self-forming film, the water to be treated containing the material to be removed is filtered.

  The first filter 81 can be either organic polymer type or ceramic type in principle if a self-forming film can be attached. Here, a polyolefin polymer film having an average pore diameter of 0.25 μm and a thickness of 0.1 mm was employed.

  The first filter 81 has a flat membrane structure provided on both sides of the frame 84 and is immersed so as to be perpendicular to the fluid. The filtrate can be taken out from the film hollow portion 85 by being sucked by the pump 86 from the hollow portion 85 of the frame 84.

  Next, the second filter 82 is a self-forming film that is attached to the entire surface of the first filter 81 and solidified by sucking the aggregated particles of the object to be removed. This self-forming film may be agglomerated in a gel or cake form.

  Filtration for forming the second filter 82, which is a self-forming film of the object to be removed, and removing the object to be removed will be described. The fluid (treated water) mixed with calcium fluoride is diffused in the treated water in the form of fine particles.

  The first filter 81 has a large number of filter holes, and the second filter 82 is a self-forming film of an object to be removed formed in a layered manner on the opening of the filter hole 81A and the surface of the first filter 81. is there. The surface of the first filter 81 has agglomerated particles of the object to be removed made of calcium fluoride. The agglomerated particles are sucked through the first filter 81 by the suction pressure from the pump, and the moisture of the fluid is sucked. For this reason, the second filter 82 is formed on the surface of the first filter 81 by solidifying immediately after drying (dehydration).

  Since the second filter 82 is formed from the aggregated particles of the object to be removed, it immediately has a predetermined film thickness, and the filtration of the aggregated particles of the object to be removed is started using the second filter 82. Therefore, if the filtration of the hollow portion 85 between the first filters 81 is continued while sucking with the pump 86, a self-forming film of aggregated particles is laminated on the surface of the second filter 82 to become thicker. The second filter 82 is clogged and cannot continue filtration. During this time, the calcium fluoride as the object to be removed is solidified, adheres to the surface of the second filter 82, and the water to be treated passes through the first filter 81 and is taken out as filtered water.

  On one side of the first filter 81 is water to be treated mixed with a material to be removed, and on the opposite side of the first filter 81, filtered water that has passed through the first filter 81 is generated. The water to be treated is sucked into the hollow portion 85 between the first filters 81 and flows, and the agglomerated particles in the water to be treated are solidified as they approach the first filter 81 by this suction. Further, the self-forming film to which some aggregated particles are bonded is adsorbed on the surface of the first filter 81 to form the second filter 82. The object to be removed in the solution is solidified by the action of the second filter 82 and the water to be treated is filtered.

  In this way, by slowly sucking the water to be treated through the second filter 82, the water in the water to be treated can be taken out as filtered water, and the object to be removed is dried and solidified. The aggregated particles of the object to be removed are trapped as a self-forming film.

  The first filter 81 is immersed vertically in the water to be treated, and the water to be treated is in a state where the objects to be removed are dispersed. When the water to be treated is sucked by the pump 86 through the first filter 81 with a weak suction pressure, the aggregated particles of the objects to be removed are bonded to the surface of the first filter 81, and the first filter 81 Adsorbed on the surface. Aggregated particles having a diameter smaller than that of the filter hole pass through the first filter 81, but there is no problem in the process of forming the second filter 82 because the filtered water is circulated again to the water to be treated. In this film forming step, since the particles are sucked with a very weak suction pressure, the aggregated particles are stacked while forming gaps of various shapes, and the second filter 82 of a soft self-forming film having a very high degree of swelling is formed. Become. The water in the water to be treated permeates and sucks the self-forming film having a high degree of swelling, passes through the first filter 81 and is taken out as filtered water, and finally the water to be treated is filtered.

  Moreover, a parallel flow is formed in the to-be-processed water along the surface of the 1st filter 81 by sending a bubble from the bottom face of to-be-processed water with the diffuser 34. FIG. This is because the second filter 82 adheres uniformly to the entire surface of the first filter 81 and also forms a gap in the second filter 82 so that it adheres softly. Specifically, the air flow rate is set to 1.8 liters / minute, but it is selected depending on the film quality of the second filter.

  Next, in the filtration step, the aggregated particles made of calcium fluoride are gradually laminated on the surface of the second filter 82 while being adsorbed by a weak suction pressure. At this time, the second filter 8222 and the further agglomerated particles are permeated and taken out from the first filter 81 as filtered water.

  However, if the filtration is continued for a long time, a thick self-forming film adheres to the surface of the second filter 82, so that the above-mentioned gap eventually becomes clogged, and filtered water cannot be taken out. For this reason, in order to regenerate the filtration capacity, it is necessary to remove the laminated self-forming film as needed.

  In particular, it is useful for the processing of an etching agent and an etching gas in the semiconductor manufacturing field, but the processing apparatus can be suitably used in other etching processing fields.

It is a figure explaining the process of the device manufacturing method of this invention. It is a figure explaining the structure of an example of the used etching gas processing apparatus of this invention. It is a figure explaining filtration operation by a filtration membrane.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 Active layer, 12 Surface side element structure part, 14 Buffer layer, 16 Collector layer, 18 Collector electrode, 20 Generation tank, 22 Calcium fluoride containing processing liquid, 24 Calcium content storage tank, 26 Calcium compound containing aqueous solution, 28, 38 , 48 Pump, 30 Treatment tank, 32 Filtration membrane, 34 Air diffuser, 36 Filter press, 40 Regeneration tank, 42 Acid, 42 Acid storage tank, 50 Filtration water tank, 52 Filtration water, 53 Scrubber, 54 Injection nozzle, 56 Foot Hydrogen fluoride-containing aqueous solution, 60 water storage tank, 62 water, 70 back grinding apparatus, 72 etching apparatus, 74 abatement facility, 100 treatment apparatus.

Claims (4)

A hydrogen fluoride generating step for burning hydrogen used when dry etching the surface of the wafer and reacting with water to generate hydrogen fluoride;
Reacting hydrogen fluoride produced in the hydrogen fluoride production step with a calcium compound to produce a calcium fluoride-containing aqueous solution,
A used etching gas treatment method, wherein the calcium fluoride-containing aqueous solution obtained in the production step is separated by filtration and the filtered water is reused as water in the hydrogen fluoride production step. The used etching gas treatment method according to claim 1,
The used etching gas processing method, wherein the used etching gas is CF ₄ . A detoxification facility that burns used etching gas discharged when dry etching the wafer surface;
A scrubber for generating hydrogen fluoride by bringing water into contact with and reacting with the gas discharged from the abatement facility;
A production tank for reacting hydrogen fluoride produced in the scrubber with a calcium compound to produce an aqueous solution containing calcium fluoride;
A used etching gas processing apparatus comprising: a water recycling line for filtering the calcium fluoride-containing aqueous solution obtained in the generation tank and returning filtered water to the scrubber. In the used etching gas processing apparatus according to claim 3,
The used etching gas processing apparatus, wherein the used etching gas is CF ₄ .

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