JPH06216100A - Method for controlling liquid concentration - Google Patents

Abstract

PURPOSE:To clarify control performance at a designing stage by assembling a liquid concentration stable time to be set from a liquid quantity and circulating flow rate of a liquid tank with sequence, and further assembling pouring necessary amount to be set from a liquid concentration variable amount to a stock solution pouring amount with the sequence. CONSTITUTION:When a target value is larger than a sensor value, a valve 5 is opened, and stock solution is poured. After a predetermined time is elapsed, the valve 5 is closed, and the pouring is stopped. A liquid concentration stable time is calculated, the time is elapsed, the target value is compared with the sensor value, and then the pouring is repeated until the both coincide. The stable time is a value obtained by dividing a tank liquid amount by a circulating flow rate, i.e., a time required to circulate the liquid in the tank 2. If the pouring amount is sufficiently smaller than the flow rate, the liquid concentration is stabilized by one circulating time. Thus, since the stable time is assembled with a control sequence, the liquid concentration value does not exceed the target value.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling the concentration of a liquid used in a cleaning or wet etching process in a semiconductor or liquid crystal manufacturing process.

[0002]

2. Description of the Related Art As shown in FIG. 5, a liquid concentration control device comprises a sensor 3 for measuring the liquid concentration of a liquid tank 2 for immersing a substrate 1 for cleaning, etching or dyeing, and a valve 5 for injecting a stock solution 4. And a controller 6 that controls opening and closing of the valve 5 according to the liquid concentration value output from the sensor 3. Further, the liquid in the liquid tank 2 is sucked by the pump 7, the dust in the liquid is removed by the filter 8, and then the liquid is returned to the liquid tank 2. Conventionally, as shown in FIG. 6, when the target value is larger than the sensor value, the sequence for controlling the liquid concentration is to open the valve 5 to inject the stock solution, and after a predetermined time has elapsed, close the valve 5 to stop the injection. After the sensor sampling time has elapsed, the target value and the sensor value are compared again, and repeated injections are performed until they match.
In this method, there is only one injection amount and the control time is shortened. Therefore, as shown in FIG. 7, the difference between the target value and the sensor value is divided into, for example, three types, and the opening / closing time of the valve 5 is changed. There is a method of injecting three kinds of doses, and the control time is shortened as shown in FIG.

[0003]

However, in such a conventional liquid concentration control method, when the sampling time of the sensor is shorter than the liquid concentration stabilization time as shown in FIG. Will continue to rise and exceed the target value.

After manufacturing the liquid concentration control device,
If you measure the liquid concentration stabilization time and use that value as the sampling time for the sensor, the liquid concentration value will not exceed the target value, but the performance such as control time and accuracy will be known only after manufacturing. Therefore, there is a possibility that the required performance is not satisfied.

Therefore, it is an object of the present invention to provide a liquid concentration control method for clarifying the control performance at the design stage.

[0006]

In order to achieve this object, the liquid concentration control method of the present invention incorporates a liquid concentration stabilization time set from the liquid amount in the liquid tank and the circulation flow rate into a sequence.

Further, the required injection amount set from the change amount of the liquid concentration with respect to the injection amount of the original liquid is incorporated in the sequence.

[0008]

According to this method, the liquid concentration value does not exceed the target value, and the performance such as control time and accuracy is clarified at the design stage.

Further, the control time can be minimized by the second invention.

[0010]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows an embodiment of the first invention of the present invention. When the target value is larger than the sensor value, the valve 5 is opened to inject the stock solution, and after a lapse of a predetermined time, the valve 5 is closed to stop the injection. Then calculate the liquid concentration stabilization time,
After the lapse of that time, the target value and the sensor value are compared again, and repeated injection is performed until they match. The liquid concentration stabilization time is a value obtained by dividing the tank liquid amount by the circulation flow rate, that is, the time required for the liquid in the tank 2 to circulate by the pump 7. If the injection amount is sufficiently small with respect to the circulation flow rate, The liquid concentration stabilizes during the circulation time.

[0012]

[Table 1]

FIGS. 2, 3, and 4 (Table 1) show an embodiment of the second invention. If the target value is greater than the sensor value, the difference between the target value and the sensor value is divided by the liquid concentration change value for the minimum injectable amount, that is, the required number of injections is calculated, and the value is multiplied by the minimum injectable amount. That is, if the required injection amount is calculated, and the controller 6 controls the opening / closing time of the valve 5 in accordance with this amount, the control time can be minimized as shown in FIG. FIG. 4 (Table 1) is a specific example of controlling the concentration of the dyeing solution in the step of dyeing a semiconductor substrate.

[0014]

Since the liquid concentration stabilization time is incorporated in the control sequence, the liquid concentration value does not exceed the target value, the required performance can be satisfied, and the performance can be clarified at the design stage. .

Further, the control time can be minimized by the second aspect of the present invention in which a required amount up to the target value is injected.

[Brief description of drawings]

FIG. 1 is a flow chart of liquid concentration control in an embodiment of the first invention of the present invention.

FIG. 2 is a flow chart of liquid concentration control in the embodiment of the second invention.

FIG. 3 is a characteristic curve diagram showing the relationship between the liquid concentration value and the control time in the embodiment of the second invention.

FIG. 4 is a characteristic curve diagram showing a change in solution concentration of a dyeing solution in a step of dyeing a semiconductor substrate in an example of the second invention

FIG. 5 is a block diagram of a general liquid concentration control device.

FIG. 6 is a flowchart of a conventional liquid concentration control using the same device.

FIG. 7 is a flowchart of a conventional liquid concentration control using the same device.

FIG. 8 is a characteristic curve diagram showing the relationship between the liquid concentration value and control time when the same method is used.

FIG. 9 is a characteristic curve diagram showing the relationship between the liquid concentration value and control time when the same method is used.

[Explanation of symbols]

 1 substrate 2 liquid tank 3 sensor 4 stock solution 5 valve

Claims (2)

[Claims] 1. A method for controlling a liquid concentration, characterized in that a liquid concentration stabilization time set from a liquid amount in a liquid tank and a circulation flow rate is incorporated into a sequence. 2. The liquid concentration control method according to claim 1, wherein a required injection amount set from a liquid concentration change amount with respect to the original liquid injection amount is incorporated into the sequence.