JP3025178B2 - Ultrapure water heating device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrapure water heating apparatus, and more particularly, to heat ultrapure water to obtain high-temperature ultrapure water required in the fields of the electronics industry such as semiconductor manufacturing and pharmaceutical manufacturing. Water heater for ultrapure water.

[0002]

2. Description of the Related Art In technical fields such as the electronics industry, high-temperature ultrapure water obtained by heating ultrapure water is used. For example, contamination is a major enemy in semiconductor manufacturing, and in a cleaning process in semiconductor manufacturing, a mixed solution of sulfuric acid and hydrogen peroxide water, ammonia for preventing organic matter contamination, particle contamination, heavy metal contamination, and removing a natural oxide film and the like. Chemical solutions such as a mixed solution of water and hydrogen peroxide, a mixed solution of hydrochloric acid and hydrogen peroxide, and a diluted hydrofluoric acid aqueous solution are used. Ultrapure water is used for preparing and washing away these cleaning chemicals. To increase the efficiency, ultrapure water heated to about 80 ° C. is generally used.

[0003] Ultrapure water has the ability to dissolve many substances, and is used in the cleaning process of semiconductor manufacturing by utilizing its properties. It is known that the capacity is improved and the cleaning effect is further improved, and therefore, ultrapure water having a higher temperature than before is used. However, on the other hand, since high-temperature ultrapure water has an extremely high ability to dissolve various substances, the constituent materials of the ultrapure water heater for obtaining high-temperature ultrapure water are hardly soluble in ultrapure water. In addition, it is necessary to have excellent heat resistance. Therefore, as a constituent material of the conventional ultrapure water heating apparatus, a metal material which can be a contamination source of heavy metals is avoided, and quartz glass has been widely used.

[0004] However, quartz glass, compared to metal materials,
The mechanical strength is low, and there is a high risk of breakage due to pressure fluctuation, mechanical shock, external compressive force or tensile force, and the like. Due to this damage, in addition to stopping the function of the ultrapure water heating device,
High-temperature ultrapure water not only scatters, causing serious damage to surrounding pipes and electrical components, but also impairs the safety of nearby workers and further affects the products themselves during the manufacturing process. The damage is severe and can lead to serious consequences.

Further, when the size is increased, the pressure resistance of the quartz glass is reduced, so that only a small device can be manufactured.
There is a drawback in that it is difficult to increase the size of the apparatus in response to the increase in the amount of high-temperature ultrapure water used with the increase in the diameter of the i-wafer.

Further, the ultrapure water heating apparatus having a heating section made of quartz glass has a drawback in that special consideration is required for transportation, for example, the quartz glass part must be specially packed and assembled on site. There is.

In this respect, ultrapure water is introduced into a resin pipe made of fluororesin (PFA) or polyetheretherketone (PEEK), which is widely used as ultrapure water piping, and is heated from the outside. Although a pure water heating device has been proposed, it has poor heat transfer characteristics and poor heat resistance, and thus lacks reliability as a heating device. In addition, since heating cannot be performed at a very high heating temperature, a large heat transfer area is required, and it is difficult to realize a practical and highly reliable ultrapure water heating apparatus such as an increase in the length of a resin pipe.

Further, the conventional ultrapure water heating apparatus does not employ a method in which ultrapure water is stored and heated in the apparatus in order to avoid elution from a high temperature ultrapure water contact part, as shown in FIG. To
This is a method of heating while flowing ultrapure water in the apparatus (see Japanese Patent Application Laid-Open No. 5-228465). Briefly describing the apparatus in FIG. 3, ultrapure water in an ultrapure water tank 21 for storing ultrapure water produced by the ultrapure water production apparatus is fed by a pump 22 to a stainless steel container 23, While heating the ultrapure water flowing in the container 23 continuously by the heater 25 covered with the heat transfer member operated by the thyristor power supply 24, the heated ultrapure water is sent to the high-temperature ultrapure water storage tank 26. It is a configuration to supply.

However, the method of heating ultra-pure water, which is used only intermittently in the actual washing process, in a short time while continuously circulating it requires a large-capacity heater, and therefore requires a large power equipment. For example, it is necessary to set up the equipment, and the equipment must be enlarged, which leads to an increase in equipment cost.

[0010] As described above, the flowing water type ultrapure water heating apparatus has a drawback that the equipment cannot be made compact. On the other hand, as shown in Fig. 4, the heated ultrapure water is stored. A storage-type ultrapure water heating apparatus that intermittently supplies a constant amount of ultrapure water from a storage tank to a use point has been proposed (see Japanese Patent Application Laid-Open No. 6-69174). Briefly describing the apparatus of FIG. 4, an ultrapure water heater 32 for heating ultrapure water 31 supplied from the ultrapure water production apparatus and high temperature ultrapure water storage / supply tanks 33 and 34 are connected by pipes. And the tank 3
An inert gas introduction pipe 35 is connected to the upper portions of the tanks 3 and 34, and the high temperature ultrapure water in the tank is sent to the use point via the pipe 36 by the pressure of the inert gas introduced into the tanks 33 and 34 from the pipe 35. It is a configuration to supply. However, the method shown in FIG. 4 requires the installation of an inert gas introduction pipe, which makes the apparatus and the control system complicated, resulting in an increase in equipment cost and operation cost.

The present invention has been made in view of the above-mentioned problems of the prior art, and the invention according to claim 1 is easy to mold, hard to break, and inexpensive. An object of the present invention is to provide an ultrapure water heating device capable of making the temperature distribution of water uniform and easily controlling the temperature of ultrapure water. Another object of the present invention is to provide an apparatus for heating ultrapure water in which the amount of elution into ultrapure water is extremely small.

[0012]

According to the present invention, an electric heater is provided in a lower portion of a metal container having an inlet at a lower portion and an outlet at an upper portion to prevent convection in the upper portion of the container. An ultrapure water heating apparatus having a baffle plate for performing the operation, the baffle plate being fixed to have a storage portion for storing high-temperature ultrapure water above the baffle plate, and the inside of the container detected by the temperature detection means. A first aspect of the present invention is an ultrapure water heating device including a control device for controlling the output to the electric heater according to the temperature of the pure water.

[0013] In the first aspect of the present invention, there is provided an ultrapure water heating apparatus characterized in that a passivation film formed by heating a cleaned stainless steel is formed on the inner surface of the container and the outer surface of the heater. Invention.

[0014]

[0015]

[0016]

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described.
This will be described together with the illustrated example. FIG. 1 is a sectional view of the ultrapure water heating apparatus of the present invention. In FIG. 1, a container 3 made of SUS316L having an inlet 1 and an outlet 2 (inner diameter = 259.
An electric heater 4 covered with a heat conductor is installed inside the container (4 mm, height inside the container = 1030 mm, internal volume = about 51.3 liters). The heat transfer body includes a lower layer 5 made of a metal (aluminum) having a larger heat transfer coefficient than stainless steel, and an upper layer 6 made of SUS316L coated thereon. On the inner surface of the container 3 and the outer surface of the upper layer 6 of the heat transfer body,
Passive film is formed. As this passive film,
Electrolytic polishing of the SUS316L surface, followed by cleaning and removal of surface deposits, followed by heat treatment in an oxidizing atmosphere, the use of an iron-based oxide film makes it resistant to elution in ultrapure water. Good nature. Furthermore, when the iron-based oxide layer of the iron-based oxide film is dissolved and removed with an acid, and an oxide film having a chromium-enriched oxide layer thereunder is used on the surface, the ultra-pure water can be further improved. Elution resistance is improved. The heating temperature is preferably 400 to 500 ° C., and the heating time is preferably about 1 to 8 hours. That is, if the heating time is shorter than 1 hour, a sufficient oxide film may not be surely formed. On the other hand, if the heating time exceeds 8 hours, the oxide film grows sufficiently. This is because there is a disadvantage that the manufacturing cost is increased due to the long time. If the heating time is extremely long, the oxide film grows too much and cracks the film,
It becomes difficult to form a desired oxide film.

The electric heater 4 has a heating element made of a nichrome wire covered with a stainless steel tube via magnesium oxide. Electric heater 4 temperature 7
Is controlled by controlling the output of Reference numeral 8 denotes a temperature indicating controller, which is connected to the power supply 7, and the level sensor 9 is also connected to the power supply 7. Reference numeral 10 denotes a temperature indicator. Reference numeral 11 denotes a disk-shaped baffle for preventing convection, and is supported on the top of the container 3 by a support 11a.

Reference numeral 12 denotes a pipe for feeding ultrapure water produced by an ultrapure water production apparatus (not shown). The pipe 12 communicates with the inlet 1 at the lower part of the apparatus. The outlet 2 at the upper part of the apparatus is connected to a pipe 13, and the pipe 13 further branches into pipes 14 and 15, and the pipe 14 leads to a use point (semiconductor cleaning apparatus). The pipe 15 is a pipe for discharging an excessive amount of the ultrapure water supplied to the container 3. In addition, the pipe 15 may have a problem in that the ultrapure water may be excessively heated by the heat accumulated in the heater while the high temperature ultrapure water is not supplied to the use point. It is also a pipe for discharging ultrapure water.

FIG. 2 is a plan view of the outlet of the container 3.

According to the ultrapure water heating apparatus of the present invention configured as described above, ultrapure water can be heated and supplied to the point of use as follows. That is, ultrapure water having a higher pressure than the atmospheric pressure sent from the ultrapure water production apparatus via the pipe 12 is supplied to the container 3 in a necessary amount by adjusting the opening of the valve 16. Then, the power supply 7 is turned on and the electric heater 4 (7.8 kW, 20
(0 V, 3 phases) to raise the temperature of the ultrapure water in the container. In the initial stage of the heating process, the temperature of the ultrapure water in the lower part of the container is relatively high, and the temperature of the ultrapure water in the upper part of the container is relatively low.
Eventually, "the ultrapure water in the lower part of the container where the temperature is high tends to rise toward the upper part of the container due to the specific gravity, while the ultrapure water with the lower temperature in the upper part of the container is pushed down to the lower part of the container" A convection phenomenon (see FIG. 1A) occurs. Since the ultrapure water in the lower part of the container is continuously heated by the electric heater 4, if the ultrapure water circulates between the upper part and the lower part in the container by the convection phenomenon, ideally the ultrapure water in the container The temperature should be uniform after a certain time.

However, unlike forced convection by mechanical means (for example, stirring blades), in the natural convection phenomenon, the ultrapure water in the container is not uniformly mixed, and some of the ultrapure water is not mixed. Only water convects inside the container, which may promote uneven temperature distribution of ultrapure water in the container, and in some cases,
The reverse phenomenon that the temperature of the ultrapure water in the upper part of the container is lower than the temperature of the ultrapure water in the lower part of the container may occur.

Therefore, by disposing the baffle plate 11 in the upper part of the container, the convection phenomenon at least in the upper part of the container is prevented, and high-temperature ultrapure water can be collected in the storage part in the upper part of the container.

In the process of raising the temperature of the ultrapure water, the temperature of the ultrapure water in the container is controlled to a predetermined temperature by controlling the output of the power supply 7 to the electric heater 4 in response to the instruction from the temperature indicating controller 8. Further, the presence of ultrapure water at the top of the container is confirmed by the level sensor 9, and the level sensor 9
Does not detect the presence of ultrapure water, it is possible to prevent empty cooking in advance by stopping the output of the power supply 7.

Thus, after a certain period of time, high-temperature and high-pressure ultrapure water is stored in the upper part of the container 3. This high-temperature and high-pressure ultrapure water can be supplied to the use point in a required amount by opening the valve 17 when the ultrapure water is required at the use point.

[0026]

The method for heating ultrapure water by the apparatus for heating ultrapure water according to the present invention will be described below based on specific numerical values.

The valve 16 of the ultrapure water heating apparatus shown in FIG. 1 was opened, and ultrapure water having a pressure of 4 kg / cm ² at 25 ° C. was introduced into the vessel 3 from the inlet 1 so as to fill the vessel 3. Then, the output of the power supply 7 to the electric heater 4 is turned ON-OF so that the indicated value on the temperature indicating controller 8 becomes 80 ° C.
When the ultrapure water was heated under the F control or the PID control, the temperature of the temperature indicator 10 showed about 82 ° C. after about 4 minutes, and the temperature of the temperature indicator controller 8 showed about 79 ° C. at this time. At this point, if the use point does not require ultrapure water, the output of the power supply 7 to the electric heater 4 is turned on.
The temperature of the ultrapure water in the container is maintained at about 80 ° C. while performing the OFF control or the PID control. If ultrapure water is required at the point of use, a valve 17
Was opened, and about 12 liters of high-temperature ultrapure water of about 80 ° C. above the baffle plate 11 was supplied to the semiconductor cleaning apparatus via the pipe 14.

Next, the valve 17 is closed, the valve 16 is opened, and ultrapure water corresponding to the amount of ultrapure water discharged from the valve 17 is introduced into the container 3. When the ultrapure water was heated while ON-OFF control or PID control of the output of was performed, the temperature of the temperature indicator 10 showed about 81 ° C and the temperature of the temperature indicator controller 8 showed 80 ° C after about 2 minutes. If ultrapure water is not required at the use point at this time, the temperature of the ultrapure water in the container is maintained at about 80 ° C. while the output of the power supply 7 to the electric heater 4 is ON-OFF controlled or PID controlled. . If ultrapure water is required at the point of use, the valve 17 immediately above the container is opened, and about 12 liters of high-temperature ultrapure water of about 80 ° C.
4 and supplied to the semiconductor cleaning apparatus.

Thereafter, similarly, the ultrapure water heating apparatus shown in FIG. 1 was continuously operated for about 10 hours. As a result, no damage was observed in the ultrapure water heating device, no elution of metal ions was observed in the obtained high-temperature ultrapure water, and high-purity high-temperature ultrapure water suitable for cleaning semiconductors was used. Could be washed.

In this embodiment, SUS316L is used as the stainless steel. However, the present invention is not limited to this. For example, other austenitic stainless steels such as SUS304, SUS304L, and SUS316 can be used.

[0031]

The ultrapure water heating apparatus according to the present invention is configured as described above, and has the following effects. According to the first aspect of the present invention, the ultrapure water heating which is easy to mold, hardly breaks, and is inexpensive, can make the temperature distribution of the resulting high-temperature ultrapure water uniform, and easily controls the temperature of the ultrapure water An apparatus can be provided. In particular, by fixing a baffle to prevent convection in the upper part of the container, the convection phenomenon in the storage part above the baffle is prevented, and the ultrapure water in the heating part below the baffle is heated by an electric heater. By heating, the ultrapure water in the heating section is heated to a substantially uniform temperature by the effect of convection, and high-temperature ultrapure water is obtained. Then, the high-temperature ultrapure water is collected in a storage section at an upper portion in the container. As described above, according to the present invention, high-temperature ultrapure water can be obtained both above and below the baffle plate, and the temperature of the ultrapure water in the container is not significantly different. Temperature uniformity of the ultrapure water in the container can be easily achieved.

According to the second aspect of the present invention, it is possible to provide an ultrapure water heating apparatus having an extremely small amount of elution into ultrapure water.

[Brief description of the drawings]

FIG. 1 is a sectional view of an ultrapure water heating apparatus according to the present invention.

FIG. 2 is a plan view of an outlet of a container 3 of the apparatus of FIG.

FIG. 3 is a diagram showing an outline of a configuration of a conventional ultrapure water heating device.

FIG. 4 is a diagram showing an outline of a configuration of another conventional ultrapure water heating device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Inlet 2 ... Outlet 3 ... Container 4 ... Electric heater 7 ... Power supply 8 ... Temperature indicating controller 9 ... Level sensor 11 ... Baffle plate

──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Mitsuru Shin-Oda 3-35-30 Kojidai, Nishi-ku, Kobe-shi, Hyogo (72) Inventor Hiroyuki Harada 2-6-3 Marunouchi, Chiyoda-ku, Tokyo Mitsubishi Corporation (56) References JP-A-3-294740 (JP, A) JP-A-61-256145 (JP, A) JP-A-5-228465 (JP, A) JP-A-6-60094 (JP, U) (58) Field surveyed (Int. Cl. ⁷ , DB name) C02F 1/02 F24H 1/00

Claims (2)

(57) [Claims] 1. An apparatus having an inlet at a lower part and an outlet at an upper part.
An electric heater is provided in the lower part of the metal container,
Water heater with baffle to prevent convection
In the above, the baffle plate is fixed by fixing the baffle plate.
The upper part has a storage part for storing high-temperature ultrapure water.
The above electricity is determined by the temperature of the ultrapure water in the container detected by the knowledge means.
Having a control device for controlling the output to the heater;
Characterized ultrapure water heating device . 2. The ultrapure water heating apparatus according to claim 1 , wherein a passivation film formed by heating a cleaned stainless steel is formed on the inner surface of the container and the outer surface of the heater.