JPH1050653A - Cleaning boundary layer in down-flow rectifying-type cleaning tank - Google Patents

Abstract

PROBLEM TO BE SOLVED: To quickly and effectively clean the boundary layer by temporarily stopping or reducing water feeding, according to the water draining to hold works, not exposed to the water surface for specified time and again increasing the water feed rate according to the water draining. SOLUTION: To clean the surface water, a drain pump is stopped with closing of a valve. This results in the rise of the water surface until the water overflows notches of the upper edge of an outer tank because no water drains. In this condition, the feed water flows down like a fall from the upper edge of an inner tank along its wall into this tank at a rate high enough to cause a circular flow which provides a stirring flow sufficient for cleaning works. When a water level L2 is reached at which the works are not exposed to the water surface after lowering about 20mm from upper edge of the inner tank, the water feed rate returns to a normal rate and feed value is controlled to stabilize at the level L2 .

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cleaning tank, and more particularly to a downward rectification type cleaning tank suitable for cleaning a wafer or the like.

[0002]

2. Description of the Related Art A downward rectification type cleaning tank used for cleaning a wafer or the like has been widely used. In a down-flow rectification type cleaning tank, cleaning of chemicals adhering to the surface of an object to be cleaned such as a wafer is more efficient than in an overflow type cleaning tank, and the same linear velocity (flow rate is determined by the cross-sectional area of the cleaning tank). If the value is a value obtained by division, the contaminated water can be removed and cleaned in about 1/2 time.

[0003]

At the same time, the linear velocity is in the range of 0.2 to 0.5 cm /
In addition, the chemical component remaining on the surface of the object to be cleaned is diluted and mixed into the cleaning solution only by diffusion. That is, even when the water in the cleaning tank is almost completely replaced by pure water, the chemical component remains in the boundary layer on the surface of the object to be cleaned, and gradually decreases as cleaning is continued. This can be determined by measuring the specific resistance of the drain water, and it can be seen that it takes a long time to return to the quality of the supply water.

As countermeasures against this, rocking, nitrogen bubbling,
While stirring is performed by various methods such as ultrasonic irradiation, there is a problem in that special equipment and parts are required.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for quickly removing boundary layer dirt in a descending rectifying type washing tank which solves the above-mentioned problems in the prior art.

[0006]

According to the present invention, the inner tank is used as a washing tank, and the supply water supplied to the outer tank surrounding the inner tank flows into the inner tank over the upper edge of the inner tank. In a descending rectification type washing tank designed to wash down the object to be washed contained in the inner tank by descending in the inner tank, cleaning is performed by temporarily stopping supply water or reducing supply water in comparison with discharge water. After the water level of the tank is lowered, the water level is kept lower than the upper edge of the inner tank by about 20 mm and the object to be cleaned is not exposed on the water surface for a predetermined time, the supply water is increased relative to the discharge water. There is provided a method for removing boundary layer dirt in a descending rectifying type washing tank in which the water level in the tank is raised and this operation is performed at least once so as to give a stirring effect to the water flow acting on the object to be washed.

[0007]

According to the present invention, it is possible to quickly and effectively remove boundary layer dirt without requiring special equipment and parts such as a swinging mechanism, nitrogen bubbling equipment, and an ultrasonic generator. it can.

According to the present invention, the rinsing action for completely removing the chemical component from the surface of the object to be cleaned can be performed in a short time.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to the accompanying drawings. FIG. 1 shows a water level in a normal cleaning state in a descending rectification type cleaning tank and a cleaning water in the cleaning tank as an embodiment of the present invention. FIG. 2 is a schematic cross-sectional view showing a flow, FIG. 2 is a schematic cross-sectional view showing a flow of washing water when the water level is lowered according to the present invention, and FIG. 3 shows an arrangement of a supply water control valve and a drainage pump. FIG.

The illustrated downward rectifying type washing tank has an inner tank for accommodating an object to be washed, an outer tank provided surrounding at least an upper portion of the inner tank, and a supply water inlet provided at a lower end of the outer tank. An outer tank straightening plate provided at an intermediate position of the outer tank height,
An inner tank straightening plate provided at a lower portion of the inner tank, and a pump suction drain port provided at a lower end of the inner tank are included.

FIG. 1 shows a cleaning state by normal downward rectification, and the water level is 2 L from the upper edge of the inner tank as shown by (L1).
It is set at a position higher by about 0 to 30 mm. At this time, pure water supplied from a supply water inlet provided at the lower end of the outer tank rises in the outer tank, flows into the inner tank beyond the upper edge of the inner tank, flows downward in the inner tank, The water is discharged from the bottom of the inner tank to the outside by the action of a drain pump (not shown) through an inner tank straightening plate provided below the object to be cleaned. Uniform downward rectification in the inner tank is mainly achieved by the action of the drainage pump and the inner tank rectifying plate.

At this time, the dirt detached from the object to be cleaned has a uniform flow velocity by the rectifying plate and is quickly discharged from the inner tank together with the descending water.

FIG. 2 shows a state in which the water level is lowered according to the present invention. For this purpose, the supply water valve is closed to temporarily stop the supply, or the supply water amount is made smaller than the discharge water amount of the drainage pump. The water level gradually drops, but when the water level drops to about 20 mm below the upper edge of the inner tank and the object to be cleaned reaches the water level (L2) where it is not exposed on the water surface, the supply water volume is returned to normal and the water level is stabilized at this level (L2). To control the supply water valve.

When cleaning the surface water, the drain pump is stopped, and at the same time, the valve (V2) is closed. The supply water is a valve (V
1), the entire flow is supplied from port (1) through (V3). Since no drainage is performed, the liquid level rises and overflows from the cutout provided at the upper edge of the outer tank.

In this state, the supply water from the outer tank falls from the upper edge of the inner tank along the inner surface of the tank wall like a waterfall, and flows into the inner tank. Since the inflow speed is high, a circulating flow as shown by an arrow in FIG. 2 is generated inside the tank, and a sufficient stirring flow is given to the object to be cleaned.

FIG. 4 is a diagram showing the specific resistance of the waste water in the washing tank with time on the horizontal axis, and shows that the waste water is pure water as an initial state. When the object to be cleaned is placed in the cleaning tank, the specific resistance decreases due to impurities separated from the object to be cleaned. As the washing proceeds, the amount of impurities in the wastewater decreases, and the specific resistance approaches the initial value. The effect of impurities remaining in the boundary layer is indicated by the radius at the end of cleaning, and it can be seen that this time can be significantly reduced by the present invention.

In a state where the water level is lowered, a stirring water flow state is established as shown in FIG. 2, so that the boundary layer is disturbed by this stirring effect, and impurities remaining in the boundary layer are quickly separated from the object to be cleaned. Thus, the separated impurities are transported to the outside of the cleaning tank together with the wastewater and discharged.

After washing is performed with the water level lowered for a predetermined time, the water surface is brought to the normal water level (L1) by temporarily stopping the drainage pump or temporarily increasing the supply water amount. Return and continue cleaning.

The above-mentioned lowering and rising of the water level is, for example, as shown in FIG.
It is possible by turning on / off the supply-side valve (V) and the discharge-side pump (P), or controlling the valve (V) and the pump (P) in two stages, respectively, and requires special equipment. And not. In this case, the set water level can be measured by an optical level sensor, a nitrogen gas pressure level sensor, or the like.

In this case, if the object to be cleaned is exposed from the surface of the water when cleaning is performed with the water level lowered, the cleaning effect is lost at a stroke. Therefore, it is important to determine the water level to prevent such a situation. It is.

[0021]

According to the present invention, it is possible to quickly and effectively remove boundary layer dirt without requiring special equipment and components.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing a normal cleaning state of a descending rectification type cleaning tank.

FIG. 2 is a schematic sectional view showing a cleaning state in which the water level is lowered according to the present invention.

FIG. 3 is a schematic diagram showing a water supply valve and a drain valve.

FIG. 4 is a schematic diagram showing the effect of dirt removal by a boundary layer.

[Explanation of symbols]

 (L1) Water level in a normal washing state (L2) Water level lowered by the present invention (V) Supply water valve (P) Drainage valve

Claims (1)

[Claims] 1. An inner tub is used as a washing tub, and supply water supplied to an outer tub surrounding the inner tub flows into the inner tub over the upper edge of the inner tub and descends in the inner tub to lower the inner tub. In the descending rectifying type washing tank designed to wash the object to be washed stored in the tank, the supply water is temporarily stopped or reduced in comparison with the discharge water to lower the water level of the inner tank, thereby reducing the level of the inner tank. After maintaining the state where the water level has decreased for a predetermined time, the supply water is increased in comparison with the discharge water to raise the water level of the inner tank,
A method for removing boundary layer contamination in a descending rectification type washing tank, wherein this operation is performed at least once to give a stirring action to a water stream acting on an object to be washed.