Method and device for supplying water vapor to foreline

Abstract

The present invention is a method for supplying water vapor to a foreline (12) when an exhaust gas (E) to be detoxified, which is discharged from a semiconductor fabrication process, is decomposed by a plasma source (14) provided in the foreline (12), characterized by supplying, to a location along the foreline (12) where the pressure is 400 Pa or less, water vapor generated by adjusting water (W) to a water temperature between 10°C and 35°C, inclusive.

Description

Method and apparatus for supplying steam to a foreline

[0001] The present invention relates to a method and apparatus for supplying water vapor to a foreline in order to enable efficient foreline abatement, primarily in a semiconductor manufacturing process.

[0002] Many harmful gases, including toxic and flammable gases, are used in semiconductor manufacturing processes. Various abatement systems are used to safely treat these gases, and one type of system is the foreline abatement system, which uses plasma to decompose harmful gases in a vacuum environment upstream of the dry pump, i.e., in the reduced-pressure piping known as the foreline.

[0003] This foreline abatement method ４ PFCs (organofluorine compounds) gases such as SF ６ As a technology for decomposing and detoxifying such fluorinated greenhouse gases (F gases), for example, Patent Document 1 (Japanese Patent Publication No. 7021237) below discloses a technology in which a mixed gas of water vapor and oxygen is delivered to the plasma source via the foreline as a mitigating reactant when F gases are decomposed by plasma.

[0004] Patent No. 7021237

[0005] However, the above-mentioned conventional technology has the following problem. Specifically, the flow rate of water vapor supplied to the foreline is controlled by directly controlling the water vapor using a mass flow controller. In this method, an airtight container containing water is heated on the primary side of the mass flow controller. Water vapor generated in response to the temperature flows from the airtight container into a low-pressure chamber (secondary side). However, flow rate control is not possible unless the differential pressure between the internal pressure of the airtight container and the internal pressure of the chamber is equal to or greater than the operating pressure of the mass flow controller. For this reason, the water in the airtight container is typically heated to nearly 100°C, and the internal pressure of the airtight container is increased by utilizing the fact that the vapor pressure increases with temperature. However, when the water in the airtight container is heated as described above to achieve the required differential pressure of the mass flow controller, the temperature of the generated water vapor also increases. As a result, if there is a low-temperature location between the airtight container and the mass flow controller, the water vapor condenses (condenses) into water at that location, resulting in problems such as pipe clogging and mass flow controller failure. Furthermore, in order to avoid this problem, a new problem arises in that it is necessary to heat the piping, mass flow controllers, etc. along the way to prevent condensation of water vapor.

[0006] Therefore, the main object of the present invention is to provide a method and apparatus for supplying steam to a foreline that can stably supply steam to the foreline without the risk of clogging or failure of the flow control device when supplying steam to the foreline, thereby maximizing the decontamination efficiency of the foreline decontamination.

[0007] To achieve the above object, the present invention provides a method for supplying water vapor to a foreline, as shown in Figure 1. Specifically, the method supplies water vapor to a foreline 12 when exhaust gas E to be ablated, which is emitted from a semiconductor manufacturing process, is decomposed by a plasma source 14 provided in the foreline 12, and is characterized in that water W, generated by adjusting the temperature of the water to be 10°C or higher and 35°C or lower, is supplied to a portion of the foreline 12 where the pressure is 400 Pa or lower.

[0008] In this invention, the water W used as the steam supplied to the foreline 12 is generated at a temperature adjusted to 10° C. or higher and 35° C. or lower, so the temperature of the generated steam is also generally 10° C. or higher and 35° C. or lower. This prevents the steam from condensing and forming condensation before it is supplied to the foreline 12.

[0009] In the present invention, the amount of water vapor supplied to the foreline 12 is preferably 1.5 times or more and 6.0 times or less the flow rate of the exhaust gas to be ablated. More preferably, in the case of PFC gases, the number of O in the water vapor is 1.5 times the number of C, and SF ６ In this case, the number of O atoms in the water vapor is eight times that of S. In this case, the efficiency of abatement of the target exhaust gas E flowing through the foreline 12 by the plasma source 14 can be maximized.

[0010] In the present invention, in addition to the water vapor, it is preferable to supply a second additive gas composed of at least one gas selected from the group consisting of argon, nitrogen, ammonia, and oxygen via a supply port separate from the water vapor supply port to the foreline 12. In this case, an appropriate second additive gas can be supplied depending on the type of exhaust gas E to be ablated, thereby making the decomposition reaction in the plasma source 14 even more efficient.

[0011] The second aspect of the present invention is a steam supplying device for carrying out the above-described methods, and is configured as follows: as shown in Fig. 1, the steam supplying device 10 supplies steam to a foreline 12 where foreline abatement is performed. That is, the steam supplying device 10 includes an evaporation tank 16 that generates steam by evaporating water W stored therein, a water level sensor 18 that measures the water level in the evaporation tank 16, a water supply means 20 that supplies water W to the evaporation tank 16, a liquid level control unit 24 that includes a water supply control means 22 that controls the operation of the water supply means 20 based on the liquid level data measured by the water level sensor 18 so that the liquid level in the evaporation tank 16 is within a predetermined range, a water thermometer 26 that measures the water temperature in the evaporation tank 16, and a water temperature sensor 26 that measures the water temperature in the evaporation tank 16. and a water temperature control unit 32 including a heater 28 for heating the water and heater control means 30 for controlling the operation of the heater 28 so that the water temperature measured by the water thermometer 26 is 10°C or higher and 35°C or lower, and a steam supply unit 38 including a steam supply pipe 34 connecting the upper part of the evaporation tank 16 with the foreline 12 and a flow rate adjustment means 36 for adjusting the amount of steam supplied from the evaporation tank 16 to the foreline 12 via the steam supply pipe 34.

[0012] In the present invention, the water surface area of ​​the evaporation tank 16 is 3 cm ２ Above 60cm ２ Since the water surface area of ​​the evaporation tank 16 is proportional to the amount of water vapor generated, it is preferable that the water surface area of ​​the evaporation tank 16 is 3 cm or less. ２ If the water surface area is less than 60 cm, it will be difficult to secure the required amount of water vapor. ２ If the temperature exceeds this value, it becomes difficult to control the water temperature uniformly over the entire water surface, and the amount of water vapor generated varies greatly.

[0013] In the present invention, the inner diameter of the steam supply pipe 34 is preferably 4 mm or more. If the inner diameter of the steam supply pipe 34 is less than 4 mm, the amount of steam supplied will be reduced due to pressure loss, and the steam may condense midway along the steam supply pipe 32, causing blockage.

[0014] In the present invention, it is also preferable to provide a reservoir tank 40 whose interior is in communication with the evaporation tank 16, as shown in Figure 2. In this case, the temperature and water level of the water in the evaporation tank 16 can be stabilized, making it possible to stably generate a predetermined amount of steam for a long period of time.

[0015] Furthermore, in the present invention, it is preferable that the inner surface of the evaporation tank 16 is formed to have an arithmetic mean surface roughness Ra of 25 μm or more, which increases the amount of water evaporation per unit area of ​​the water surface.

[0016] In the present invention, it is preferable that the conductivity of the water W supplied to the evaporation tank 16 is 10 μS / cm or less. In this case, the ion concentration in the water is low, so that the frequency of maintenance of the evaporation tank 16 and the like can be reduced.

[0017] According to the present invention, it is possible to provide a method and apparatus for supplying water vapor to a foreline that can stably supply water vapor to the foreline without the risk of clogging or failure of the flow control device when supplying water vapor to the foreline, thereby maximizing the decontamination efficiency in foreline decontamination.

[0018] 1 is an explanatory diagram showing an outline of an exhaust gas treatment device according to one embodiment of the present invention, and FIG. 2 is an explanatory diagram showing an outline of an exhaust gas treatment device according to another embodiment of the present invention.

[0019] An embodiment of the present invention will be described below with reference to Fig. 1. Fig. 1 is a diagram showing an overview of one embodiment (first embodiment) of a water vapor supply apparatus 10 for carrying out a method of supplying water vapor to a foreline 12 according to the present invention, i.e., a method of supplying water vapor to the foreline 12 when exhaust gas E to be ablated from a semiconductor manufacturing process is decomposed by a plasma source 14 provided in the foreline 12. As shown in this figure, the water vapor supply apparatus 10 of this embodiment is generally composed of an evaporation tank 16, a liquid level control unit 24, a water temperature control unit 32, a water vapor supply unit 38, and the like.

[0020] The evaporation tank 16 is a sealed container that generates water vapor by evaporating the water W stored therein, and is made of a highly rigid material that is excellent in watertightness, airtightness, durability, etc., such as a metal such as stainless steel or a synthetic resin such as an acrylic resin. In the illustrated embodiment, the evaporation tank 16 is formed in a sealed cylindrical shape and is erected with its axis facing vertically.

[0021] In addition, when water W is stored in the evaporation tank 16, the water surface area (horizontal cross-sectional area of ​​the internal space) is 3 cm ２ Above 60cm ２ Preferably it is less than 30 cm ２ Above 50cm ２ The water surface area is 3 cm ２ If the water surface area is less than 60 cm, it will be difficult to secure the required amount of water vapor. ２ If the temperature exceeds this value, it becomes difficult to control the water temperature uniformly over the entire water surface, resulting in large variations in the amount of water vapor generated. Furthermore, it is preferable that the inner surface of the evaporation tank 16 be formed to have a roughness / density of arithmetic mean surface roughness Ra = 25 μm or more. If the inner surface of the evaporation tank 16 has an arithmetic mean surface roughness Ra = 25 μm or more, the effect of the surface tension of the water W at the contact point between the wall surface of the evaporation tank 16 and the water surface can be weakened, thereby increasing the amount of water W evaporated per unit area of ​​the water surface.

[0022] The liquid level control unit 24 is for controlling the liquid level in the evaporation tank 16 so that it remains within a certain range, and includes a water level sensor 18 , a water supply means 20 , and a water supply control means 22 .

[0023] The water level sensor 18 is used to measure the water level (liquid surface height) in the evaporation tank 16, and in the illustrated embodiment, a tubular level gauge 18x is attached to the side surface of the evaporation tank 16 as the water level sensor 18. Capacitive sensors such as a first level switch 18a, a second level switch 18b, and a third level switch 18c are attached to the tubular level gauge 18x in this order from the bottom in the vertical direction.

[0024] Of these, the first level switch 18a is for detecting the lower limit and is installed at a height near the upper end of the heater 28 (described later). The second level switch 18b is for detecting the upper limit and is installed slightly above the first level switch 18a. The installation height of this second level switch 18b is set to the upper limit height at which heat generated by the heater 28 is evenly applied to the entire water surface in the evaporation tank 16. The third level switch 18c is for detecting abnormalities and is installed at the top of the evaporation tank 16 to prevent the liquid level from rising too high and causing water W to infiltrate the steam supply unit 38 or the foreline 12 (described later). Therefore, during normal operation, the water level in the evaporation tank 16 is adjusted by the first level switch 18a and the second level switch 18b. The first level switch 18a, the second level switch 18b, and the third level switch 18c are each connected to the water supply control means 22 via a signal line L1.

[0025] In the illustrated embodiment, the water level sensor 18 is shown as being composed of a tubular level gauge 18x and capacitance-type level switches 18a to 18c, but this water level sensor 18 may be any sensor that can sense the water level (liquid surface height) in the evaporation tank 16 so as to control it within a predetermined range, and the water level sensor 18 may also be composed of, for example, a non-contact radio wave water level gauge or a contact float water level gauge.

[0026] The water supply means 20 is used to supply water W to the evaporation tank 16 and includes a water supply tank 20a, a water supply pipe 20b that connects the water supply tank 20a to the vicinity of the bottom of the evaporation tank 16, and a control valve 20c provided on the water supply pipe 20b. Of these, the control valve 20c is composed of a solenoid valve, and is connected to the water supply control means 22 via a signal line L2, and its opening and closing is controlled by the water supply control means 22. Note that reference numeral 20d in the drawing denotes a normally open manual valve that stops the flow of water through the water supply pipe 20b in an emergency.

[0027] Here, the water W supplied to the evaporation tank 16 by the water supply means 20 can be ordinary tap water or industrial water, but it is particularly preferable to use water with a conductivity of 10 μS / cm or less. When the conductivity of the water W is 10 μS / cm or less, the ion concentration in the water is low, which significantly delays the deposition of scale and the like on the evaporation tank 16, the water supply means 20, etc., thereby reducing the frequency of maintenance.

[0028] In addition, although the illustrated embodiment shows a case where the water supply tank 20a is used, it is also possible to directly connect the water supply pipe 20b to a water source (not shown) without using the water supply tank 20a, and to directly supply water W from the water source. When the water supply tank 20a is used as in the illustrated embodiment, a feed pump (not shown) can be installed as necessary.

[0029] The water supply control means 22 controls the water supply means 20 (particularly the control valve 20c) to adjust the water level in the evaporation tank 16 based on water level information in the evaporation tank 16 sensed by the water level sensor 18. Although not shown, the water supply control means 22 is generally composed of a CPU (Central Processing Unit), memory, an input device, a display device, and the like. The CPU executes programs stored in memory. Water level information in the evaporation tank 16 detected by the water level sensor 18 is input to its input side via signal line L1, and its output side is connected to the control valve 20c and, if necessary, a supply pump (not shown) via signal line L2. The memory stores multiple programs, including one for adjusting the opening of the control valve 20c so that the water level in the evaporation tank 16 is maintained within a predetermined height range.

[0030] The water temperature control unit 32 is for controlling the temperature of the water W in the evaporation tank 16 to be between 10°C and 35°C, and is equipped with a water thermometer 26, a heater 28, and a heater control means 30.

[0031] The water thermometer 26 is used to measure the water temperature in the evaporation tank 16 and is configured by, for example, a thermocouple. The water thermometer 26 is connected to the heater control means 30 via a signal line L3.

[0032] The heater 28 is used to heat all of the water in the evaporation tank 16, and in the illustrated embodiment, is an electric cylindrical heater that is erected from the bottom surface of the evaporation tank 16. The heater 28 is connected to heater control means 30 via a signal line L4.

[0033] The heater control means 30 controls the operation of the heater 28 based on water temperature information of the water W in the evaporation tank 16 detected by the water thermometer 26 to maintain the temperature of the water W in the evaporation tank 16 at 10°C or higher and 35°C or lower. Similar to the water supply control means 22 described above, the heater control means 30 is generally composed of a CPU (Central Processing Unit), memory, an input device, a display device, and the like, although not shown. The CPU is a device that executes programs stored in the memory. Information about the water temperature in the evaporation tank 16 detected by the water thermometer 26 is input to its input side via signal line L3, and the heater 28 (more specifically, a power supply device that supplies power to the heater 28, not shown) is connected to its output side via signal line L4. The memory stores a plurality of programs, including a program that adjusts the power supply to the heater 28 so that the water temperature in the evaporation tank 16 is maintained at 10°C or higher and 35°C or lower.

[0034] The water vapor supply unit 38 is designed to supply a predetermined amount of water vapor generated in the evaporation tank 16 to a location in the foreline 12 where the plasma source 14 is installed, where the pressure is 400 Pa or less, and is equipped with a water vapor supply pipe 34 and a flow rate control means 36.

[0035] The steam supply pipe 34 is a pipe that airtightly connects the upper part of the evaporation tank 16 with the foreline 12. As described above, the inner diameter of the steam supply pipe 34 is preferably 4 mm or more from the viewpoint of preventing clogging due to condensed steam. On the other hand, there is no particular upper limit to the inner diameter of the steam supply pipe 34, but from the viewpoints of workability and weight of the steam supply pipe 34, it is preferably 13 mm or less.

[0036] A flow meter 34a, which is an area flow meter, and a control valve 34b, which is a solenoid valve, are provided in this steam supply pipe 34, in this order from the downstream side. Of these, the flow meter 34a is connected to the flow rate adjustment means 36 via a signal line L5, and the control valve 34b is connected to the flow rate adjustment means 36 via a signal line L6.

[0037] The flow rate adjusting means 36 adjusts the amount of steam supplied from the evaporation tank 16 to the foreline 12 via the steam supply pipe 34. Similar to the water supply control means 22 and heater control means 30, the flow rate adjusting means 36 is generally composed of a CPU (Central Processing Unit), memory, an input device, a display device, and the like, although not shown. The CPU executes programs stored in memory. The steam flow rate detected by the flow meter 34a is input to its input side via signal line L5, and the control valve 34b is connected to its output side via signal line L6. The memory stores a number of programs, including one for adjusting the aperture of the control valve 34b so that the steam supplied to the foreline 12 reaches a predetermined flow rate.

[0038] In the illustrated embodiment described above, the flow meter 34a is configured as an area flow meter, but this flow meter 34a may be any device, such as a differential pressure flow meter, that can accurately measure the amount of water vapor flowing through the water vapor supply pipe 34. In addition, in the illustrated embodiment described above, the control valve 34b is configured as a solenoid valve, but this control valve 34b may be any device, such as a differential pressure flow meter, that can accurately measure the amount of water vapor flowing through the water vapor supply pipe 34.

[0039] Furthermore, in the illustrated embodiment described above, the water supply control means 22, heater control means 30, and flow rate adjustment means 36 are shown as being configured as separate entities, but since these all consist of a CPU, memory, input device, display device, etc., the water supply control means 22, heater control means 30, and flow rate adjustment means 36 may also be configured as a single entity.

[0040] Furthermore, in the illustrated embodiment described above, an electric cylindrical heater erected from the bottom surface of the evaporation tank 16 is used as the heater 28, but this heater 28 may be of any type as long as it can heat the entire water W in the evaporation tank 16, particularly the entire water surface, and may, for example, be a band heater wrapped around the outer periphery of the evaporation tank 16.

[0041] Next, a method for supplying steam to the foreline 12 using the steam supply device 10 described above will be described. First, the power supply (not shown) for the steam supply device 10 is turned on to start operation of the device. This activates the liquid level control unit 24 and the water temperature control unit 32, and steam at a temperature of 10°C or higher and 35°C or lower is generated in the evaporation tank 16.

[0042] Here, it is preferable that the temperature of the generated water vapor be 10° C. or higher and 35° C. or lower, and also lower than the ambient temperature (room temperature) of the water vapor supply device 10. This makes it possible to more effectively prevent the water vapor from condensing and forming dew inside the water vapor supply unit 38.

[0043] Then, the water vapor supply unit 38 is operated to supply water vapor to the foreline 12 at a rate of 1.5 to 6.0 times the flow rate of the exhaust gas E to be ablated, which flows through the foreline 12 and has a pressure of 400 Pa or less. Then, in the plasma source 14, the plasma is stabilized by the following mechanism, and the efficiency of ablation of the exhaust gas E is improved. That is, the generation of plasma is maintained by giving energy to electrons in the plasma, and the PFCs and SF, which are the components to be ablated in the exhaust gas E, are ablated by the plasma. ６ When F gas is decomposed, the F atoms from the decomposed F gas bond with electrons to form F － The generation of ions reduces the electron density, making it difficult to provide energy to the plasma, which destabilizes the plasma and reduces the decomposition rate of F gas. Therefore, by supplying water vapor to the plasma in this state, F atoms from the decomposed F gas react with H (hydrogen) from the water vapor to form F. － Since the generation of ions is inhibited, the plasma can be stabilized, and the efficiency of detoxifying the exhaust gas E can be increased.

[0044] In the above embodiment, only water vapor is supplied to the foreline 12 at a pressure of 400 Pa or less. However, if necessary, a second additive gas composed of at least one selected from the group consisting of argon, nitrogen, ammonia, and oxygen may be supplied via a supply port (not shown) separate from the water vapor supply port. By doing so, for example, when argon (Ar) is added as the second additive gas, it is known that the plasma becomes more stable, and the efficiency of detoxifying the exhaust gas E also increases. In addition, when nitrogen (N ２ ) as a second additive gas, the pressure in the foreline 12 can be adjusted. ３ ) and hydrogen (H ２ ) is added, the added gas acts as a H source, and F － Since the generation of ions is inhibited, the plasma can be stabilized, and the efficiency of detoxifying the exhaust gas E can be improved. ２ ) is added, C, SF of PFC gas ６The S in the exhaust gas E reacts with the O in the oxygen to decompose the exhaust gas E, thereby increasing the efficiency of the exhaust gas E detoxification.

[0045] Next, a second embodiment of the steam supply device 10 will be described, as shown in Fig. 2. The difference from the steam supply device 10 of the first embodiment described above is that the inner diameter of the vertical portion of the tubular level gauge 18x that forms the water level sensor 18 is made thicker, and this portion serves as a reservoir tank 40 that stores the water W in the evaporation tank 16. Note that, in all other respects, the second embodiment is the same as the first embodiment described above, and therefore the description of the first embodiment will be used instead of the description of this embodiment.

[0046] The reservoir tank 40 stores water W up to the same height as the water surface in the evaporation tank 16. This makes it possible to suppress and stabilize fluctuations in the temperature and water surface of the water W in the evaporation tank 16, and to stably generate a predetermined amount of water vapor for a long period of time.

[0047] In the above embodiment, the reservoir tank 40 is formed by increasing the inner diameter of the vertical part of the tubular level gauge 18x, but the reservoir tank 40 may be of any type as long as it can suppress and stabilize fluctuations in the water temperature and water surface of the water W in the evaporation tank 16. For example, the reservoir tank 40 may be a cylindrical or prismatic tank that is adjacent to the evaporation tank, has the same water surface area as the evaporation tank 16, and is wrapped in insulation.

[0048] Of course, various other modifications can be made within the scope of what a person skilled in the art can imagine.

[0049] 10: Steam supply device, 12: Foreline, 14: Plasma source, 16: Evaporation tank, 18: Water level sensor, 20: Water supply means, 22: Water supply control means, 24: Liquid level control unit, 26: Water thermometer, 28: Heater, 30: Heater control means, 32: Water temperature control unit, 34: Steam supply pipe, 36: Flow rate adjustment means, 38: Steam supply unit, 40: Reservoir tank, E: Exhaust gas, W: Water

Claims

1. A method for supplying water vapor to a foreline (12) when decomposing exhaust gas (E) to be ablated from a semiconductor manufacturing process using a plasma source (14) installed in the foreline (12), characterized in that water (W) is used to generate water vapor at a temperature between 10°C and 35°C, and the water is supplied to a portion of the foreline (12) where the pressure is 400 Pa or less.

2. A method for supplying water vapor to a foreline according to claim 1, characterized in that the amount of water vapor supplied to the foreline (12) is 1.5 times or more and 6.0 times or less the flow rate of the exhaust gas to be abatement.

3. A method for supplying water vapor to a foreline according to claim 1 or 2, characterized in that in addition to the water vapor, a second additive gas composed of at least one gas selected from the group consisting of argon, nitrogen, ammonia, and oxygen is supplied to the foreline (12) via a supply port separate from the water vapor supply port.

4. A water vapor supply device for supplying water vapor to a foreline (12) where foreline abatement is performed, comprising: an evaporation tank (16) for generating water vapor by evaporating water (W) stored therein; a water level sensor (18) for measuring the water level in the evaporation tank (16); a water supply means (20) for supplying water (W) into the evaporation tank (16); and a liquid level control unit (24) for controlling the operation of the water supply means (20) based on the liquid level data measured by the water level sensor (18) so that the liquid level in the evaporation tank (16) is within a predetermined range. a water temperature control unit (32) including a water thermometer (26) for measuring the water temperature in the evaporation tank (16), a heater (28) for heating the water in the evaporation tank (16), and heater control means (30) for controlling the operation of the heater (28) so that the water temperature measured by the water thermometer (26) is 10°C or higher and 35°C or lower; and a water vapor supply unit (38) including a water vapor supply pipe (34) connecting the upper part of the evaporation tank (16) to the foreline (12), and flow rate adjustment means (36) for adjusting the amount of water vapor supplied from the evaporation tank (16) to the foreline (12) via the water vapor supply pipe (34).

5. In the steam supply device of claim 4, the water surface area of ​​the evaporation tank (16) is 3 cm ２ Above 60cm ２ A water vapor supply device characterized by:

6. A steam supply device according to claim 4 or 5, characterized in that the inner diameter of the steam supply pipe (34) is 4 mm or more.

7. A steam supply device according to claim 4 or 5, characterized in that a reservoir tank (40) is provided whose interiors communicate with the evaporation tank (16).

8. A water vapor supply device according to claim 4 or 5, characterized in that the inner surface of the evaporation tank (16) is formed to have a roughness / density of arithmetic mean surface roughness Ra of 25 μm or more.

9. A water vapor supply device according to claim 4 or 5, characterized in that the conductivity of the water (W) supplied to the evaporation tank (16) is 10 μS / cm or less.

Images