CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to International Application No. PCT/JP2017/040878 filed on Nov. 14, 2017, which claims priority to Japanese Application No. 2017-012138, filed on Jan. 26, 2017, the contents of which are incorporated herein in their entirety.

TECHNICAL FIELD

The present invention relates to a fluid heating device.

BACKGROUND ART

Typically, a front-end process of a semiconductor manufacturing process includes many steps of cleaning a semiconductor wafer with deionized water heated to a high temperature.

Patent Literature 1 discloses a typical heating method of deionized water in which deionized water supplied at a room temperature is delivered through a heating source to be heated to a target temperature and the heated deionized water is supplied to a cleaning tank.

Patent Literature 1 discloses that a water discharge valve is provided to a pipe for supplying the heated deionized water to the cleaning tank, thereby keeping discharging the heated deionized water.

This method requires the high-temperature deionized water to be kept being supplied even at a non-cleaning period of a semiconductor wafer, for the following reasons.

The first reason is that, if the heating is interrupted, re-heating is required at a next cleaning process, which requires extra time and energy for increasing the temperature.

The second reason is that, if the flow of the deionized water is halted for a long time, live bacteria may be generated in a pipe to cause contamination.

Since the heated deionized water must be discharged in the technique disclosed in Patent Literature 1, energy loss is caused. In order to recover and improve the energy loss, Patent Literature 2 discloses heat exchange between a pipe for a waste liquid after a cleaning process and a deionized water supply pipe.

However, in the technique disclosed in Patent Literature 2, an energy recovery efficiency is low and the unused deionized water for cleaning is also discharged as a waste liquid.

Recently, a lot of high-temperature deionized water have been used for cleaning in many steps of a semiconductor manufacturing process due to an increase in diameter of a semiconductor wafer, an increase in size of a processing tank, and an increase in number of a single wafer cleaner. Accordingly, energy saving and water saving in the steps requiring the high-temperature deionized water have been increasingly demanded.

In response to this demand, there has been proposed a method, which is the same as a cleaning method using chemicals disclosed in Patent Literature 3, including: circulating deionized water while heating the deionized water; storing the deionized water in a tank; and separating only a part of the deionized water required for cleaning from a circulation circuit to draw the part of the deionized water for use. In this method, a non-cleaning period requires the deionized water only to circulate and energy required for heating is smaller than that in a typical method.

CITATION LIST

Patent Literature(S)

Patent Literature 1: JP 2003-42548 A

Patent Literature 2: JP 2000-266496 A

Patent Literature 3: JP 2010-67636 A

SUMMARY OF THE INVENTION

Problem(s) to be Solved by the Invention

However, in the cleaning using the deionized water unlike the cleaning using chemicals, a temperature of the deionized water is sometimes changed depending on usage. In changing the temperature of the deionized water, the technique disclosed in Patent Literature 3 can change a temperature setpoint of the deionized water from a low temperature to a high temperature, but faces difficulty in changing the temperature setpoint of the deionized water from a high temperature to a low temperature since a heat source has no cooling function. The technique disclosed in Patent Literature 3 requires that all the heated deionized water in the tank is disposed and again deionized water at a normal temperature is supplied into the tank and heated. Accordingly, energy saving and water saving cannot be achieved.

An object of the invention is to provide a fluid heating device capable of achieving energy saving and water saving.

Means for Solving the Problem(s)

According to an aspect of the invention, a fluid heating device includes: a tank configured to store a fluid; a pump configured to deliver the fluid stored in the tank; a heater configured to heat the delivered fluid to a predetermined temperature; a return pipe configured to return the fluid heated by the heater to the tank; a fluid supply valve configured to supply an unheated fluid into the tank; a fluid discharge valve configured to discharge the heated fluid from the tank; a temperature sensor configured to detect a temperature of the heated fluid; and a temperature controller configured to control an opening degree of each of the fluid supply valve and the fluid discharge valve to control a temperature of the fluid stored in the tank, in which the temperature controller further includes a discharge opening-degree controller configured to control the opening degree of the fluid discharge valve on a basis of the temperature detected by the temperature sensor; and a supply opening-degree controller configured to control the opening degree of the fluid supply valve on a basis of the temperature detected by the temperature sensor.

In the above aspect of the invention, since the temperature sensor detects the temperature of the heated fluid, the temperature of the heated fluid stored in the tank can be checked when unheated fluid is supplied from the fluid supply valve. Accordingly, unlike a typical method, it is unnecessary to discharge all the heated fluid from the tank, newly store unheated fluid, and heat all the unheated fluid by the heater. Accordingly, energy saving and water saving are achievable.

Moreover, by detecting the temperature of the heated fluid, a decrease in the temperature of the fluid caused by the supply and mix of the unheated fluid to the heated fluid can be checked. Accordingly, the heating by the heater and the discharge amount of the heated fluid can be minimized. Consequently, energy saving and water saving are achievable.

In the above aspect of the invention, the temperature controller preferably includes a supply calculator configured to calculate a supply amount of the unheated fluid for decreasing the temperature of the heated fluid stored in the tank to a temperature setpoint.

In the above aspect of the invention, the fluid discharge valve is preferably provided in the return pipe located downstream of the heater.

In the above aspect of the invention, the fluid heating device preferably includes: a first circulation loop provided with the pump, the heater, and the return pipe; and a second circulation loop independent of the first circulation loop and configured to supply a part of the heated fluid to a cleaner of a semiconductor wafer and return the rest of the part of the heated fluid to the tank, and the fluid discharge valve is preferably provided in the second circulation loop.

