JP5481783B2 - Ozone supply method and apparatus - Google Patents

Description

  The present invention relates to a technique for supplying high-concentration ozone gas obtained by liquefying ozone gas.

In recent years, the use of ozone (element symbol: O ₂ ) has been developed in various fields including water and sewage treatment using its strong oxidizing power. In particular, in the field of manufacturing semiconductor devices, application to Si wafer cleaning and TEOS-CVD (Tetra Ethyl Ortho Silica-Chemical Vapor Deposition) is being studied. Si wafer cleaning uses ozone water in which ozone gas is dissolved in pure water as a cleaning solution, and it has been announced that heavy metals and organic substances on Si wafers can be removed by using in combination with dilute hydrofluoric acid aqueous solution (non-patent document) 1). TEOS-CVD is used to form an interlayer insulating film when a semiconductor element is formed into a multilayer wiring, and is characterized in that the unevenness of the wafer surface due to the electrodes can be planarized by the insulating film. It has been reported that the planarization performance is improved by adding ozone to the TEOS-CVD (Non-patent Document 2).

  These are examples using ozone gas with a relatively low concentration of about 10%, but by using ozone gas with a relatively high concentration of 80% or more, there is a possibility of a new application that could not be considered by conventional ozone gas usage. Has begun to be pointed out. As an example, there is an Si semiconductor oxide film forming method disclosed in Japanese Patent Laid-Open No. 8-335576. According to this publication, it is possible to form an oxide film at a relatively low temperature, which is impossible with the conventional thermal oxidation method, and to form a high-quality oxide film with less suboxide layer and defect structure. Has been.

  By the way, a silent discharge system is generally used to generate ozone gas. This generates a mixed gas of ozone and oxygen from oxygen gas by electric discharge. Due to the limit of generation efficiency and danger of explosion, it is difficult to generate ozone gas of about 10% by volume or more under normal temperature and pressure. It was. Therefore, Patent Document 1 (Japanese Patent Publication No. 5-17164) introduces a method of generating high-concentration ozone gas of 80% or more by once liquefying the generated ozone gas and then vaporizing it. This method will be described with reference to FIGS.

  The liquid ozone production apparatus shown in FIG. 5 includes an ozone gas generation and exhaust apparatus 1 and a liquid ozone generation apparatus 2 that liquefies ozone generated by the apparatus. Oxygen gas is sent from the oxygen cylinder 3 to the ozonizer 5 through the pressure adjustment valve 4. In the ozonizer 5, the oxygen gas becomes an ozone-containing oxygen gas mixed with ozone gas by silent discharge, and the ozone gas is passed through a mass flow controller 6 for controlling the flow rate and a particulate removal filter 7 for removing particulates in the ozone-containing gas. The liquefied liquid ozone generator 2 is supplied.

  In the liquid ozone generator, as shown in FIGS. 5 and 6, the ozone-containing oxygen gas in which the ozone gas is mixed with the oxygen gas introduced from the ozone gas generating and exhausting device 1 circulates in the ozone-containing oxygen gas introduction pipe 25. Then, it is introduced into the ozone chamber 9 through the flow rate adjusting valve 8. The ozone chamber 9 is thermally coupled to a cold head 19 that has been cooled by a refrigerator 21 that is driven in advance by a compressor 21, and is within 0.1 K by a temperature sensor 24, a heater 23, and a temperature control device 22. The temperature can be precisely controlled with temperature accuracy, and is kept at a low temperature of 80K to 100K.

  The principle of liquefaction of ozone gas is to liquefy only ozone gas by the difference in vapor pressure between ozone and oxygen. For example, at 1 atmosphere, the boiling point of ozone is 161K, but the boiling point of oxygen is 90K. Therefore, if it is cooled to a temperature of 90K or more and less than 161K, most of ozone is in a liquid state and most of oxygen is in a gaseous state, so that only ozone can be separated as a liquid. Actually, since it is handled under reduced pressure conditions for safety against explosive properties of high-concentration ozone, the separation conditions are determined by the difference between the vapor pressures of ozone and oxygen under the temperature and pressure conditions. For example, when considering a case where the temperature is 90K and the pressure is 10 mmHg (= 13.3 hPa), the vapor pressure of ozone is almost 0 mmHg (= 0 Pa) at 90K, but oxygen is about 690 mmHg (= 918 hPa), and only ozone is under this condition. Liquefied.

  Thus, in the ozone chamber 9, only ozone gas is liquefied by the difference in vapor pressure between ozone and oxygen at the cooled temperature. When the ozone gas is liquefied, the valve 15 connected to the pipe connected to the oxidation treatment device 16 is closed, and the valve 10 connected to the pipe connected to the ozone killer 11 is opened. The non-liquefied oxygen gas that has circulated through the ozone discharge pipe 26 connected to the ozone chamber 9 is introduced into the ozone killer 11 through the valve 10. The ozone killer 11 is heated to change to oxygen so that the remaining ozone gas is not discharged to the outside. The heated oxygen gas supplied from the ozone killer 11 is supplied to the gas cooler 12 and cooled. The cooled oxygen gas is discharged out of the system by a vacuum pump 14 through a liquid nitrogen trap 13. The liquid nitrogen trap 13 prevents contamination and contamination of the ozone chamber 9 by carbides from the vacuum pump 14 and the like.

  When the liquid ozone 27 liquefied in the ozone chamber 9 is supplied to the oxidation treatment device 16 for the purpose of oxidation or the like, the flow rate adjusting valve 8 and the valve 10 are set to be closed while the valve 15 is set to be open. . Liquid ozone is vaporized by raising the temperature of the ozone chamber 9 thermally coupled to the cold head 19 by the heater 23, the temperature sensor 24, and the temperature control device 22. The ozone gas generated by the vaporization flows through the ozone discharge pipe 26 and is supplied to the oxidation treatment device 16 through the valve 15. Since liquid ozone 27 or high-concentration ozone gas has explosive properties, a safety valve 18 is installed in a piping system through which ozone gas flows in case of an explosion.

The oxygen gas of the raw material gas used for generating ozone by the silent discharge contains nitrogen gas as an impurity, and this nitrogen gas reacts with the oxygen gas in the ozonizer to generate nitrogen oxides. . The clean ozonizer used in the semiconductor industry (the ozonizer designed to minimize the generation of contaminants such as heavy metals) uses high-purity oxygen gas as the raw material gas. In this case, the ozone gas generated when the purity of the oxygen gas increases There is a known phenomenon that the concentration of oxygen decreases, and a method of adding some nitrogen to oxygen gas in order to obtain high-concentration ozone gas may be employed. For this reason, the generated ozone gas always contains a small amount of nitrogen oxides. Nitrogen oxides are likely to cause corrosion of equipment. Therefore, for example, a method of forcibly removing nitrogen oxides remaining in the ozone generator with an inert gas is employed, as in an ozone generator disclosed in Patent Document 2 (Japanese Patent Laid-Open No. 2003-283117).
Electronic Materials, March 1999, pp. 13-18 Jpn. J. et al. Appl. Phys. Vol. 32 (1993), pp. L110-L112 Japanese Patent Publication No. 5-17164 JP 2003-238117 A

  In the liquid ozone production apparatus 2, the ozone gas generated by the ozonizer 5 is cooled and liquefied to perform concentration. At this time, nitrogen oxides contained in the ozone gas supplied from the ozonizer 5 as shown in FIG. Liquefaction occurs in the ozone chamber 9.

  Since the boiling point of nitrogen oxides is much higher than ozone (23.1 ° C. in the case of nitrogen dioxide), nitrogen oxides in the ozone chamber 9 are not released to the outside when supplying high-purity ozone. When the supply is repeated, nitrogen oxides accumulate in the ozone chamber 9 as shown in FIG.

  Nitrogen oxides also generate nitrate ions when combined with moisture contained in the gas from the ozonizer 5, causing corrosion of stainless steel, which is a constituent material of the apparatus, and generating heavy metal contaminants.

Then, the ozone supply method of Claim 1 is the ozone supply method which supplies the ozone vaporized by heating, after cooling the ozone gas generated with the ozonizer in the ozone chamber, liquefying and concentrating , After supplying the ozone outside the system, the temperature of the ozone chamber is controlled to a temperature at which only nitrogen oxides of the nitrogen oxide and water remaining in the chamber are vaporized , and only nitrogen oxides are discharged outside the system. And a step of controlling the temperature of the ozone chamber from which the nitrogen oxides have been discharged to a temperature at which water remaining in the chamber is vaporized to discharge water out of the system .

The ozone supply method of claim 2 is the ozone supply method of claim 1, wherein only the nitrogen oxide is vaporized and discharged based on the difference in vapor pressure of nitrogen oxide and water in the ozone chamber.

  The ozone supply method according to claim 3 is the ozone supply method according to claim 2, wherein only the nitrogen oxide in the ozone chamber is discharged by the vapor pressure when the temperature of the ozone chamber is 220K or less.

  The ozone supply method according to claim 4 is the ozone supply method according to claim 3, wherein after the nitrogen oxides are discharged, the water in the ozone chamber is discharged by a vapor pressure at a temperature of 220K or more in the ozone chamber.

  The ozone supply method according to claim 5 is the ozone supply method according to any one of claims 1 to 4, wherein a dilution gas is introduced into the ozone chamber in the step of discharging the nitrogen oxides.

  The ozone supply method of claim 6 is the ozone supply method of claim 5, wherein the temperature of the ozone chamber is adjusted to 260 K or more in the step of introducing the dilution gas.

The ozone supply device according to claim 7, wherein the ozone gas generated by an ozonizer is cooled in a ozone chamber, liquefied and concentrated, and then the ozone vaporized by heating is supplied outside the system. A temperature detecting means for detecting the temperature in the chamber; a pressure detecting means for detecting the pressure in the ozone chamber; and a temperature detection value of the temperature detecting means remains in the chamber after the ozone is supplied to the outside of the system. The temperature of the chamber is controlled so that only the nitrogen oxide of the nitrogen oxide and water is vaporized, and only the nitrogen oxide is discharged out of the system from the chamber, and the pressure of the pressure detecting means When it is detected that no nitrogen oxide remains in the chamber based on the detected value, the temperature of the chamber is vaporized from the water remaining in the chamber. That by controlling the temperature of the chamber so that the temperature and a cold head for discharging the water out of the system.

Ozone supply device according to claim 8, in the ozone supply device according to claim 7, the diluent gas in the process of the nitrogen oxide is discharged Ru provided with a piping system for supplying into the ozone chamber.

According to the first to eighth aspects of the invention, since nitrogen oxide and water in the ozone chamber are separately discharged, nitrate ions are not generated in the ozone supply device.

In particular, according to the inventions of claims 5 and 8 , the concentration of nitrogen oxides in the exhaust gas can be reduced and the exhaust rate of the gas is increased. According to the invention of claim 6, the vapor pressure of nitrogen oxide and water in the ozone chamber is increased.

According to the first to eighth aspects of the invention, since nitrate ions are not generated in the ozone supply device, nitrogen oxides can be discharged out of the system without corroding the ozone supply device. Thereby, generation | occurrence | production of the heavy metal contamination from an ozone supply apparatus is suppressed. Moreover, since the corrosion of the piping system is suppressed, the maintenance interval becomes longer, and the operating rate of the ozone supply device is improved.

In particular, according to the fifth and eighth aspects of the present invention, the concentration of nitrogen oxides in the exhaust gas can be reduced and the exhaust rate of the gas can be increased, so that the occurrence of corrosion in the ozone supply device can be efficiently suppressed. According to the invention of claim 6 , since the vapor pressure of nitrogen oxide and water in the ozone chamber is increased, the discharge time of nitrogen oxide and water can be shortened.

  When the ozone chamber of the ozone supply device stores ozone in a liquid state, both nitrogen oxide and water remaining in the ozone chamber are in a solid state. Therefore, corrosion of the ozone supply device is hardly caused by the residue. On the other hand, when the device is stopped due to maintenance or the like and the temperature of the ozone chamber rises to near room temperature, nitrogen oxides and water are mixed to generate nitrate ions, and the devices and piping system constituting the ozone supply device are It becomes easy to be corroded. That is, when nitrogen oxides and water are not mixed, nitrate ions are not generated, so that the ozone supply device does not corrode. The ozone supply apparatus described below prevents mixing of nitrogen oxide and water when discharging nitrogen oxide and water remaining in the ozone chamber.

  FIG. 1 is a schematic configuration diagram showing an ozone supply apparatus according to an embodiment of the present invention.

  The ozone supply device 30 includes a cold head 19, a thermometer 31, and a pressure gauge 32. The cold head 19 adjusts the temperature of the ozone chamber 9 in which the liquid ozone 27 is stored. The cold head 19 is provided with a refrigerator 20 and a heater 23. The thermometer 31 is a temperature detection means and detects the temperature in the ozone chamber 9. The pressure gauge 32 is a pressure detection means and detects the pressure in the ozone chamber 9. The cold head 19 changes the temperature of the ozone chamber 9 and exhausts the nitrogen oxide and water individually using the difference between the vapor pressures of nitrogen oxide and water staying in the ozone chamber 9. Table 1 shows the vapor pressure of nitrogen oxide (nitrogen dioxide) and water.

  An operation example of the ozone supply device 30 when discharging nitrogen oxides and water will be described with reference to FIGS. 1, 2, and 3.

  When exhausting the nitrogen oxide in the ozone chamber 9, the valve 15 shown in FIG. 1 is set to be closed, and the temperature of the ozone chamber 9 is set to a temperature at which the vapor pressure of water is sufficiently low by the cold head 19 (for example, 220K or less). ) Is maintained. At this time, as shown in FIG. 2, nitrogen oxides of the nitrogen oxides and water remaining in the ozone chamber 9 are vaporized. The vaporized nitrogen oxide is exhausted from the ozone chamber 9 by the vacuum pump 14. On the other hand, water remains in the ozone chamber 9. Thus, only nitrogen oxides in the ozone chamber 9 are selectively discharged out of the system.

  Next, when water remaining in the ozone chamber 9 is discharged, it is detected that nitrogen oxides in the ozone chamber 9 have disappeared based on the pressure in the ozone chamber 9 detected by the pressure gauge 32 shown in FIG. Then, as shown in FIG. 3, the temperature of the ozone chamber 9 is heated to 220 K or higher (for example, 320 K) by the cold head 19. At this time, water in the ozone chamber 9 is vaporized and exhausted from the ozone chamber 9 by the vacuum pump 14.

  As described above, nitrogen oxides and water in the ozone chamber 9 are individually discharged out of the system.

  Further, in order to dilute the concentration of nitrogen oxides in the gas discharged out of the system, a dilution gas composed of dry nitrogen or other inert gas may be supplied to the ozone chamber 9. That is, the ozone chamber 9 of the ozone supply device 30 is connected to a pipe 34 for introducing the dilution gas supplied from the dilution gas supply device 33 as shown in FIG. A valve 35 is installed in the pipe 34.

  When nitrogen oxide in the ozone chamber 9 is exhausted by the vacuum pump 14, the valve 35 is set to open, and the dilution gas is supplied from the dilution gas supply device 33 into the ozone chamber 9. At this time, the concentration of nitrogen oxides in the gas discharged from the ozone chamber 9 decreases and the gas discharge rate increases. In this case, even if the temperature of the ozone chamber 9 is a temperature at which water is slightly mixed into the exhaust gas, the occurrence of corrosion of the apparatus is suppressed by the effect of dilution. Therefore, if the temperature of the ozone chamber 9 is increased to about 260 K, the vapor pressure of nitrogen oxide and water in the ozone chamber 9 is increased, and nitrogen oxide and water can be discharged rapidly. In addition, what is necessary is just to discharge | emit the water in the ozone chamber 9 in the procedure demonstrated with reference to FIG.

The schematic block diagram of the ozone supply apparatus which concerns on embodiment of invention. Schematic explanatory drawing explaining discharge | emission of the nitrogen oxide by the said ozone supply apparatus. The schematic explanatory drawing explaining discharge of the water by the said ozone supply apparatus. Schematic explanatory drawing explaining introduction of dilution gas by the ozone supply device. The schematic block diagram of an ozone manufacturing apparatus. The detailed block diagram of a liquid ozone production | generation apparatus. Schematic explanatory drawing explaining operation | movement of the ozone chamber when accumulating liquid ozone. Schematic explanatory drawing explaining operation | movement of the ozone chamber when supplying liquid ozone.

Explanation of symbols

DESCRIPTION OF SYMBOLS 9 ... Ozone chamber 10, 15, 35 ... Valve 14 ... Ozone killer 16 ... Oxidation processing device 19 ... Cold head 23 ... Heater 26 ... Ozone discharge pipe 30 ... Ozone supply device 31 ... Thermometer 32 ... Pressure gauge

Claims (8)

In an ozone supply method for supplying ozone gas generated by heating after liquefying and concentrating ozone gas generated by an ozonizer by cooling in an ozone chamber ,
After supplying the ozone outside the system, the temperature of the ozone chamber is controlled to a temperature at which only nitrogen oxides of the nitrogen oxide and water remaining in the chamber are vaporized , and only nitrogen oxides are discharged outside the system. A process of
A step of controlling the temperature of the ozone chamber from which the nitrogen oxides have been discharged to a temperature at which water remaining in the chamber is vaporized to discharge water out of the system. Ozone supply method. 2. The ozone supply method according to claim 1, wherein only the nitrogen oxide is vaporized and discharged based on a difference in vapor pressure between nitrogen oxide and water in the ozone chamber.   3. The ozone supply method according to claim 2, wherein only the nitrogen oxide in the ozone chamber is discharged by a vapor pressure at a temperature of 220 K or less in the ozone chamber. 4. The ozone supply method according to claim 3, wherein after the nitrogen oxide is discharged, water in the ozone chamber is discharged by a vapor pressure at a temperature of 220 K or more in the ozone chamber.   The ozone supply method according to any one of claims 1 to 4, wherein a dilution gas is introduced into the ozone chamber in the step of discharging the nitrogen oxides.   6. The ozone supply method according to claim 5, wherein in the step of introducing the dilution gas, the temperature of the ozone chamber is adjusted to 260 K or higher. In an ozone supply device that supplies ozone gas generated by heating after liquefying and concentrating ozone gas generated by an ozonizer by cooling in an ozone chamber ,
Temperature detecting means for detecting the temperature in the ozone chamber;
Pressure detecting means for detecting the pressure in the ozone chamber;
The temperature of the chamber is set so that the temperature detection value of the temperature detection means after the ozone is supplied to the outside of the system is a temperature at which only nitrogen oxides of water and nitrogen oxides remaining in the chamber are vaporized. , And only nitrogen oxides are discharged from the system, and when it is detected that no nitrogen oxides remain in the chamber based on the pressure detection value of the pressure detection means, An ozone supply device comprising: a cold head that controls the temperature of the chamber so that the water remaining in the chamber becomes a temperature at which the water remaining in the chamber is vaporized, and discharges water out of the system. The ozone supply device according to claim 7, further comprising a piping system for supplying a dilution gas into the ozone chamber in the process of exhausting the nitrogen oxides .

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