KR19980068982A - How to recover argon from silicon crystal furnace - Google Patents

Abstract

The present invention relates to two embodiments of a method for recycling argon mixed with impurities flowing out of a silicon crystal growth furnace using cryogenics. The first embodiment uses cryogenic distillation techniques and the second embodiment uses cryogenic adsorption techniques, both of which are pure argon for silicon crystal growth furnaces by utilizing catalytic treatment and adsorption in parallel with their cryogenic treatment steps. Provide a recycle stream.

Description

How to recover argon from silicon crystal furnace

The present invention relates to a method for recovering argon from an inert atmosphere used in connection with the growth of silicon crystals used in the semiconductor industry. In particular, the present invention relates to a method for recovering, cleaning and purifying argon from a silicon furnace into which silicon crystals are pulled for crystal growth and formation, and for recycling the argon into the furnace for inert environment composition.

The semiconductor industry uses large amounts of silicon crystals as substrates for manufacturing various electronic media, such as integrated circuits and memory devices. End use requires very uniform silicon crystals containing a minimum amount of impurities and modifications in the crystal lattice.

The Czochralski method is a reliable method for mass production of large diameter silicon single crystal ingots. The method consists in freezing the material from the molten pool on the end of the single crystal seed of the same material. The frozen material replicates the single crystal structure of the seed. As a result of the method, a small seed is actually a large crystal. The method is fundamentally quite simple and conforms to the laws of thermodynamics. The solid-liquid interface is formed by maintaining a temperature gradient that must be precisely controlled with the seed tension rate. In order to maintain the heat flux along the solid-liquid interface, the molten silicon contained in the quartz crucible must rise into the high temperature zone of the furnace because the liquid moves from the equilibrium point and crystals form. The above rise treatment helps to maintain accurate control of the three-dimensional temperature distribution, and therefore a mechanism is needed to precisely control both seed rise and crucible rise. The seeds and crucibles continue to rotate during the treatment to improve temperature uniformity as well as maintain a uniform dopant distribution in the axial and rotational directions. In order to obtain silicon crystals of manufacturing value, the process needs to control complex interactions and various processing variables.

These silicon ingots typically grow in a processing atmosphere that contains high purity argon to avoid deposition or incorporation of impurities into the growing silicon crystal lattice. These impurities can be present in the atmosphere present in the absence of a silicon bed or argon cleaning gas to decompose the quartz crucible.

As demand increases beyond supply as the use of argon increases, several attempts have been made to reuse argon, each of which attempts to take contaminated, impurity-containing argon from the silicon crystal and treat it. Efforts have been made to overcome the problems associated with the recycling of argon of acceptable purity for reuse in silicon crystal furnaces by removing particulates, dopants and other contaminating impurities in gaseous form. An important issue is whether the recovery and purification of argon is technically feasible and economically viable, as well as the cost of unused argon available in the industrial gas market.

The work of growing silicon crystals into and from typical silicon crystals is described in Papers 133-135, entitled Semiconductor Crystal Growth for the 90s and Beyond, published by Peter Disessa at Semiconductor Fabtech.

Japanese Patent Publication No. 4-89387 describes an inert gas recovery method for a single crystal tensioner, which includes recovering argon from a single crystal silicon furnace by vacuum pump with removal of fine particles. Argon mixed with compressed impurities is passed through a zeolite-filled pressure swing adsorption bed to remove nitrogen, carbon monoxide and carbon dioxide. It is then passed through a palladium catalyst bed, deoxo unit and adsorption tower to remove hydrogen, oxygen, carbon monoxide, water and carbon dioxide. The purified argon is then returned to the furnace to perform further tasks as inert gas during silicon crystal growth.

Japanese Patent Publication No. 7-33581 discloses a process for argon purification and recycling for silicon crystals, which converts impurities such as carbon monoxide, oxygen and hydrogen into carbon dioxide and water in a catalyst bed and removes them from the adsorption section of the purification apparatus. have. Argon mixed with impurities is recovered from the silicon furnace using a dry vacuum pump, and particulate silicon dioxide is captured by a bubble column apparatus.

Japanese Patent Publication No. 6-24962 describes a method for recovering very pure argon from off-gases for producing silicon crystals. The method includes removing impurity mixed argon from a silicon crystal furnace and retaining impurity mixed argon in a storage container. Argon mixed with impurities passes through the venturi to remove particulates, retains oil from the compressed contaminants removed, and compresses oxygen through hydrogenation on the catalyst before passing argon mixed with impurities through the Deoxo catalyst tube. Remove it. Argon mixed with oxygen-depleted impurities is then passed through a catalyst bed of cuprous oxide to remove hydrogen and carbon monoxide, and the removed hydrogen and carbon monoxide are converted to carbon dioxide and water. The cuprous oxide catalyst bed is provided in tandem to switch between operating and regenerative modes. The water and carbon dioxide containing the argon mixed with impurities are then passed through a switching bed of suitable zeolite to remove water and carbon dioxide. Nitrogen is then removed from argon in an additional set of tandem type switching adsorption beds made of zeolite. Nitrogen adsorption is carried out on the zeolite bed at -50 ° C. The zeolite may be a mordenite adsorbent. Argon is then ready to be recycled for use.

U.S. Patent 5,106,399 describes an argon purification system. Argon mixed with impurities passes through a bed of molecular sieve adsorbent to adsorb water and carbon dioxide. The dehydrated argon then passes through the catalytic material to chemically absorb oxygen, hydrogen and carbon dioxide. Finally, argon is passed through an adsorptive bed at very low temperatures to adsorb nitrogen and hydrocarbons and then recover the purified argon stream for reuse.

Argon recovery and recirculation is also known as The Recovery and Recycling of High Purity Argon in the Semiconductor Industry, presented by JVO'Brien and JVSchurter at the AlChE 1988 Spring National Meeting, held March 6-10, 1988. It is also described in the following paper. The paper describes the pre-recirculation of argon for compression, catalysis of carbon monoxide and methane with oxygen, catalysis of excess oxygen and hydrogen in deoxo treatment, removal of carbon dioxide and water on molecular sieve beds and reuse in silicon crystal growth furnaces. A method for recycling contaminated argon from a silicon crystal growth furnace using removal of hydrogen and nitrogen by cryogenic distillation of argon is described.

The prior art has been trying to solve the high consumption rate of argon in the growth of silicon crystals for the semiconductor industry. However, previous argon recovery and purification methods for reusing argon in silicon crystal furnaces have been complicated, inefficient, expensive, and require expensive equipment. In addition, the prior art does not describe a method for removing volatile dopants that may be present in argon mixed with impurities. SUMMARY OF THE INVENTION An object of the present invention described below is to overcome the problems in the field of argon recycle and to provide an efficient and inexpensive recovery and purification method of argon for use in a silicon crystal growth furnace.

1 is a schematic diagram of a first embodiment of the process according to the invention for recovering, purifying and recycling argon to a silicon crystal growth furnace using cryogenic distillation techniques.

FIG. 2 is a diagram of a second embodiment of the method of the present invention for recovering, storing and recycling argon using cryogenic adsorption techniques for silicon crystal growth furnaces.

Description of the main parts of the drawing

18, 218; Silicon crystal growth furnace

23, 223; compressor

27, 37, 47, 80, 227, 237, 247, 262; heat transmitter

33, 233; Wet scrubber

43, 243; Deoxo catalytic unit

55a, 55b; 256a, 256b; A pair of tandem switching zeolite adsorbent beds

125; Double distillation column

128 (129); Bottom (top) distillation column

246a, 246b; A pair of tandem switching cupric oxide catalyst beds

267a, 267b; A pair of tandem switching calcium X-zeolite beds

The present invention utilizes cryogenic distillation or cryogenic adsorption in two separate methods for recovering and purifying argon and recycling it to the silicon crystal growth furnace. In the first method using cryogenic distillation, argon mixed with impurities is recovered, compressed, and mixed with argon mixed with impurities to a contaminant dopant by adsorption using a solvent or a liquid formulation. Argon is then passed through the deoxo unit with hydrogenation if necessary to reduce the oxygen content in the argon mixed with impurities on a suitable deoxo catalyst bed. The deoxygenated argon is then passed through a switching temperature swing adsorptive bed to remove carbon dioxide and water, and sent to a distillation column in a double column to rectify pure argon. In the high pressure or lower distillation zone, argon is separated from nitrogen, hydrogen or carbon monoxide. At low pressure or in the upper distillation zone, pure argon is recovered from residual hydrocarbons. Liquid argon replenishment, in addition to the recovered argon, is allowed as an intermediate stream in a low pressure rectification and purification upper distillation column. The pure argon is then heat exchanged for incoming argon mixed with the incoming impurities and sent to the furnace for further use as a pure acid argon stream in a silicon crystal furnace.

In the second method, contaminated dopants contained in argon mixed with impurities are removed from the silicon crystal growth furnace, compacted, cooled, and then cleaned in a wet scrubber using various caustics, liquid cleaners or solvents. Remove it. In addition, any solid particles present are also removed in the wet scrubber. The argon is then hydrogenated (if necessary), followed by deoxygenation on a catalyst bed containing a typical deoxo catalyst to remove oxygen, followed by deoxygenated argon mixed with impurities via a switched cupric oxide catalyst bed. Passage converts carbon monoxide and hydrogen into water and carbon dioxide. Argon mixed with impurities containing water and carbon dioxide is then passed through a switching zeolite bed to remove water and carbon dioxide by adsorption. Finally, anhydrous argon is passed through a calcium X-zeolite switching bed with any supplemental argon at cryogenic temperature conditions to remove nitrogen and methane, and then heat exchanged for incoming argon mixed with impurities and into the silicon crystal growth furnace. Recycle for use at

The present invention relates to a method for recovering argon mixed with impurities from a silicon crystal growth furnace for purification and recycling, and with reference to the following drawings, two embodiments of the present invention, namely a method using cryogenic distillation and a method using cryogenic adsorption. I would like to permanently

Embodiments of the invention relating to the recovery, purification and recycling of argon using cryogenic distillation are described with reference to FIG. 1.

The argon effluent gas 20 mixed with impurities is removed from the silicon crystal growth path 18 in which silicon crystals are grown using, for example, the Czochralski method. The stream 20 contains impurities such as nitrogen, oxygen, water, hydrogen, carbon dioxide, carbon monoxide, hydrocarbons and various dopants and particulates. Argon mixed with impurities is compressed to a pressure of 140 psia in the compressor (23) to form stream (25), followed by post-cooling to 90 ° F in heat exchanger (27) to form stream (30). Eggplant caustic solution, solvent or liquid detergent, for example, through stream 30 through liquid scrubber 33 using an aqueous sodium hydroxide or potassium hydroxide, wherein dopants such as arsenic, Oxides and hydrates of phosphorus, antimony, gallium and boron, and particulates such as silicon dioxide are removed. The impurity mixed argon 35 is then heated to about 350 ° F. in the heat exchanger 37 to form a stream 40, where the oxygen contained in the argon mixed hydrogen and impurities is a catalyst bed. Oxygen in the argon is removed when argon mixed with impurities is introduced into the deoxo catalyst unit 43 reacting with the phase 45 to the line 45. The deoxo catalyst can be any commercially available deoxo catalyst such as various forms of palladium, platinum / palladium mixtures. Deoxygenated, impurity mixed argon in line 45 is heat exchanged for pure cold argon reheatable in heat exchanger 47 and returns to 90 ° F., the temperature in stream 50. The stream may be further cooled in a cooling heat exchanger and then passed through switching zeolite adsorption beds 55a and 55b which are operated in a temperature swing adsorption process, where carbon dioxide and water are removed from the argon mixed with impurities. The zeolite can be any zeolite that selectively adsorbs water and carbon dioxide, such as 13X-zeolites, 4A-zeolites, 5A-zeolites and mixtures thereof. Stream 60 does not carry oxygen, water or carbon dioxide. The stream 60 is mixed with argon 70 exiting the downstream cryogenic distillation column and the mixed stream in line 100 is heat exchanged against the various process streams exiting from the cryogenic distillation column in heat exchanger 80. This is followed by input to stream 120 as a reheat stream to a high pressure or bottom column 128 of double distillation column 125. After performing the reheating, the mixed argon in the line 130 removes the vapor in the feed stream 140 and the low pressure or upper distillation column 129 for the high pressure or lower column 128 of the dual distillation column 125. Separated into reflux stream 150 for condensation. In the bottom or high pressure distillation column 128, nitrogen, hydrogen and / or carbon monoxide are separated from partially purified argon, where argon containing some hydrocarbons, for example 200 ppm of methane, is mixed with the supplemental liquid argon 205 While carbon dioxide is removed to line 210, which is used to reheat the incoming argon mixed argon in heat exchanger 80, and then into line 215. Removed. Supplemental liquid argon and partially purified argon in the stream 200 are introduced into the low or top distillation column 129 of the dual distillation column 125 where it is reheated to the top of the high pressure column and impurities in the stream line 150 It is refluxed by the mixed cold argon and rectified for further purification. The liquid in the wastewater treatment vessel of the low pressure distillation column 129 produces reflux for the high pressure column 128 by indirect heat exchange. The purified argon in line 230 is re-warmed to the mixed argon entering the heat exchanger 80 and 47 and recycled into line 240 and stream 15. Supplemental argon 10 may be added to argon 15. The temperature of argon in line 230 is about −261 ° F. and the pressure is 97 psia. A waste stream of hydrocarbon is removed into the line 220 from the bottom of the low pressure top distillation column 129 with liquid.

The present invention may also use cryogenic techniques to purify the argon effluent stream exiting the silicon crystal growth furnace using adsorption rather than cryogenic rectification and distillation, which is one embodiment of the process of the present invention described above. A second embodiment of the invention is described with reference to FIG. The contaminated argon effluent stream in line 220 is removed from the silicon crystal growth furnace 218 where the contaminated argon stream may comprise nitrogen, oxygen, water, hydrogen, carbon dioxide, carbon monoxide, hydrocarbons, and arsenic Dopants such as oxides and hydrates of phosphorus, antimony, gallium and boric acid, and various particulates such as silicon dioxide. The stream is compressed at a pressure of about 110 psia in compressor 223 to form stream 225, which is then post-cooled through heat exchanger 227, resulting in a temperature of 90 ° F. and pressure This forms a stream in line 230 that is 108 psia. This stream is fed into a wet scrubber 233 using a caustic, solvent or liquid absorbent such as aqueous sodium hydroxide or aqueous potassium hydroxide, where the dopants and particulates contained are removed. The above is the same as the first specific example described above. Cleaned, impurity mixed argon collects in surge tank 234, which forms stream 235, which is lined from a temperature of 90 [deg.] F. of stream 235 in heat exchanger 237. Heat to 35 ° F-350 ° F in 240). The heated stream 240 is then introduced to a deoxo unit 243, where oxygen contained on the catalyst in the presence of hydrogen is removed. The deoxo catalyst can be any commercially available deoxo catalyst such as various forms of palladium, platinum / palladium mixtures, various forms of nickel and mixtures thereof. Argon mixed with deoxygenated impurities in line 245 is then introduced into one of the pair of tandem switching cupric oxide catalyst beds 246a and 246b, where carbon monoxide and hydrogen in the mixed argon stream are Converted to water and carbon dioxide. The off-line cupric oxide bed can be regenerated using a mixture of oxygen and nitrogen in line 251 and finally cleaned using a slipstream of the argon product of line 277. Thereafter, the mixed argon in the line 250 containing water and carbon dioxide is cooled against argon purified from downstream in the heat exchanger 247 to form a line 255 of 80 ° F., and then the formed line ( 255 is introduced into one of a pair of tandem switching zeolite adsorption beds 256a and 256b that remove water and carbon dioxide from the mixed argon with impurities. The zeolite can be any zeolite that selectively adsorbs water and carbon dioxide, for example 13X-zeolite, 4A-zeolite, 5A-zeolite and mixtures thereof. The non-operated bed can be regenerated using nitrogen cleaning gas 252 and finally cleaned by argon product reflux in line 278. Argon mixed with impurities in the dried, carbon dioxide-depleted line 60 still contain nitrogen and methane at a temperature of 80 ° F. and a pressure of 99 psia. The stream in line 60 is further cooled by heat exchange to a purified argon stream 270 for cooling impurity-argon to -220 ° F. in heat exchanger 262 and then supplemental argon in stream 265. Together with 280 a pair of tandem switching calcium X-zeolite beds 267a and 267b, where nitrogen and methane are removed by cryogenic adsorption. The unactivated calcium X-zeolite bed can be regenerated by warming to ambient temperature using a reflux of purified argon 279. Purified argon effluent from the internally contained nitrogen and methane depleted calcium X-zeolite beds 267a and 267b is removed into line 270 at a temperature of −220 ° F. and a pressure of 97 psia. 260 is re-heated for the mixed argon, and in line 275 is heated to a temperature of 70 [deg.] F. and a pressure of 95 psia for the mixed argon in line 250, followed by silicon to line 215. Recycle 276 with argon replenishment 210 to reintroduce into the crystal growth furnace. Alternatively, the supplemental argon in line 280 at −250 ° F. and 98 psia may remove nitrogen and methane-free calcium X-zeolite beds 267a and 267b while recycling impurity mixed argon before sending it into silicon colon growth furnace 218. Can pass).

So far two embodiments of cryogenic argon purification methods for silicon crystal growth in a furnace have been described. As can be seen from the above description, it is clear that the present invention utilizes cryogenic conditions to uniquely purify argon by distillation or adsorption using a simple method and a series of unique processing steps. The method of the present invention allows the most suitable removal of contaminants from argon to minimize the flow of gas through the catalyst, adsorption and distillation treatment stations, and to minimize the equipment for regeneration of these treatment stations that require regeneration. On the other hand, high purity argon can be recycled at minimal cost.

Claims (15)

(1) contacting argon mixed with impurities with a deoxygenation catalyst and hydrogen to remove any contained oxygen; (2) removing any water and carbon dioxide from argon mixed with impurities by contacting zeolite that selectively adsorbs water and carbon dioxide from argon mixed with impurities and argon mixed with impurities; and (3) cryogenic separation further purifying the mixed argon mixed with impurities to remove impurities from the mixed argon and producing an argon product stream having a purity of at least 99.5% by volume; and mixing the mixed argon with the impurities Removing the dopant from the impurity mixed argon prior to step (1) by contacting a liquid absorbent for removing the dopant from argon, wherein the impurity containing argon containing residual dopant from the silicon crystal growth furnace is mixed. Method of recovery and purification. The method of claim 1, wherein the ultra low temperature separation is a high temperature distillation column separation consisting of a high pressure distillation column separation separating nitrogen and carbon monoxide from argon mixed with impurities and a low pressure distillation column separation separating hydrocarbons from argon mixed with impurities. The method of claim 1, wherein the impurity mixed argon is brought into contact with the deoxygenation catalyst, followed by contact with the cupric oxide catalyst to convert carbon monoxide and hydrogen into water and carbon dioxide. 4. The process according to claim 3, wherein the cryogenic separation is cryogenic selective adsorption of nitrogen and hydrocarbons from argon mixed with impurities on a calcium X-zeolite adsorbent. The process of claim 1 wherein said argon product stream is recycled to a silicon crystal growth furnace. The method of claim 1 wherein said liquid adsorbent is selected from the group consisting of sodium hydroxide, potassium hydroxide and mixtures thereof. The method of claim 1, wherein the cryogenic temperature is no greater than −220 ° F. 7. The method of claim 4, wherein the cryogenic temperature is no greater than −220 ° F. 6. The method of claim 2, wherein the cryogenic temperature is no greater than −260 ° F. 4. 4. The method of claim 3, wherein the cuprous oxide catalyst is contained in two parallel switching adsorbent beds, one of which contacts the argon mixed with impurities, while the other contains a portion of the inert gas and argon product stream. How to play. (1) contacting argon mixed with impurities with a deoxygenation catalyst and hydrogen to remove any contained oxygen; (2) removing any water and carbon dioxide from argon mixed with impurities by contacting argon mixed with impurities and zeolite which selectively adsorbs water and carbon dioxide from the mixed argon with impurities; (3) introducing argon with impurity into a cryogenic distillation column to separate nitrogen from the impurity with argon and producing an argon product stream having a purity of at least 99.5% by volume; And (4) recycling the argon product stream to a silicon crystal growth furnace, removing the dopant from the impurity mixed argon prior to step (1) and separating nitrogen and carbon monoxide from the impurity mixed argon. Containing a residual dopant from the silicon crystal growth furnace, comprising performing step (3) in a cryogenic double column distillation separation consisting of a high pressure distillation column separation and a low pressure distillation column separation separating a hydrocarbon from argon mixed with impurities. A method for recovering and purifying argon mixed with impurities. (1) contacting argon mixed with impurities with a deoxygenation catalyst and hydrogen to remove any contained oxygen; (2) converting carbon monoxide and hydrogen into water and carbon dioxide by contacting an impurity mixed argon and a cuprous oxide catalyst; (3) removing any water and carbon dioxide from the argon mixed with impurities by contacting argon mixed with impurities and a zeolite that selectively adsorbs water and carbon dioxide from the mixed argon with the impurities; (4) contacting the impurity-argon with calcium X-zeolite adsorbent at cryogenic temperatures to remove nitrogen and hydrocarbons from the impurity-argon and producing an argon product stream having a purity of 99.5% by volume; And (5) recycling the argon product stream to a silicon crystal growth furnace, and impurity prior to step (1) by contacting argon with impurity mixed with aqueous sodium hydroxide to remove a dopant from the insoluble argon. A method for recovering and purifying argon mixed with impurities containing a residual dopant from a silicon crystal growth furnace, comprising removing a dopant from the mixed argon. 13. The method of claim 12, wherein the calcium X-zeolite adsorbent is contained in two parallel switching adsorbent beds, one of which contacts the argon mixed with impurities, while the other utilizes a portion of the argon product stream. How to play. 12. The method of claim 11, wherein the zeolite adsorbent is contained in two parallel switching adsorbent beds, one of which contacts the argon mixed with impurities while the other is regenerated by elevated temperature. 13. The method of claim 12, wherein the zeolite adsorbent is contained in two parallel switching adsorbent beds, one of which is in contact with argon mixed with impurities, while the other is regenerated by the original nitrogen gas, after which the argon product How to play using part of a stream.