JPS6312391A - Method and apparatus for controlling specific resistance of ultra-pure water - Google Patents

Abstract

PURPOSE:To improve the reliability of specific resistance control by subjecting the outputs of a flow rate sensor and specific resistance measuring instrument to parallel processing with a microcomputer so that a prescribed amt. of carbon dioxide can be exactly supplied to ultra-pure water. CONSTITUTION:The flow rate sensor 3, a carbon dioxide injector 2 and the specific resistance measuring instrument 4 are disposed in an ultra-pure water route 1. The outputs of the sensor 3 and the measuring instrument 4 are subjected to the parallel processing with the microcomputer 12. The prescribed mass of the carbon dioxide is then forced into the ultra-pure water by the injector 2 under the computer control. As a result, the excellent control of the specific resistance value is executed not only in the stationary stage but also when the pressure and flow rate fluctuate. The prescribed amt. of the carbon dioxide is thus exactly supplied to the ultra-pure water and the reliability of the specific resistance control is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a resistivity control device for ultrapure water, which controls the resistivity of ultrapure water used for manufacturing semiconductors, chemicals, etc. to a desired value by injecting carbon dioxide gas. In the ultrapure water path, a carbon dioxide gas injector, a flow rate sensor to measure the flow rate of ultrapure water in advance upstream, and a resistivity measuring device downstream are installed. The output of the device is processed in parallel by a microcomputer, and a predetermined mass of carbon dioxide gas is pressurized into ultrapure water.

In general, in order to adjust ultrapure water to a desired specific resistance, the solenoid valve method disclosed in Japanese Patent Application No. 60-876 and the method disclosed in Japanese Patent Application Laid-open No. 60-2760 are generally used.
The membrane system of No. 3 and the contact tower system of JP-A-60-153990 are adopted. The control method is feedback control from a resistivity measuring device placed after the carbon dioxide gas injection point. Nowadays, a plurality of various automated devices are connected to a single line of ultrapure water piping, and the flow rate and pressure of ultrapure water fluctuate depending on whether each automated device is turned on or off, making precise resistivity control difficult. In the dicing process, the specific resistance of ultrapure water is 1. O
It is said that MΩ/bo is optimal; if it is more than this, the product (chip) will be damaged by electrostatic discharge, and if it is less than this, the dicer blade will be severely worn out. Precise resistivity control is essential to improve product yield. The control method of the present invention performs excellent resistivity control even when the flow rate or pressure of ultrapure water changes, and will be explained in detail below with reference to the drawings.

A carbon dioxide injector (2) is placed in the ultrapure water path (1), a flow rate sensor (3) is placed in the upstream path m, and a resistivity measuring device (4) that sequentially measures the specific resistance value is placed downstream. do. The carbon dioxide injector (2) is powered by a pulse motor as shown in Figure 2.
Diaslam pulp (5) with excellent responsiveness and
It is formed by an injection nozzle α9 of the smallest possible diameter that guides the carbon dioxide gas pressure-fed through this pulp (5) to the path (1), and the secondary side from the tip of the injection nozzle α9 to the outlet end of the injection nozzle a9. The content is extremely small.

CO2 cylinder (6), pressure reducing valve (7), line filter (8), CO2 mass flow meter (9), solenoid valve α0
1t- sequentially arranged and connected to the next side of the carbon dioxide injector (2). The CO2 mass 70 meter (9) measures the mass flow rate using the specific heat of the passing gas, and the measured value is C
Input to O□ controller αυ. The CO2 controller αυ controls the amount of carbon dioxide gas injected as instructed by the microcomputer-02, measures the passing mass in real time, and opens and closes the diaphragm valve (5) of the carbon dioxide injector (2). The microcomputer a that controls the CO□ controller 〇υ is connected to a flow rate sensor (3), a resistivity measuring device (4), and a keyboard a3 for inputting desired resistivity values and coefficients. ) to determine the amount of carbon dioxide gas to be injected, and in parallel with this process, calculate the amount of carbon dioxide by calculating the difference between the input value from the resistivity measuring device (4) and the set value from the keyboard. The amount of gas to be injected is determined, and the data from this parallel processing is calculated to determine the final amount of gas to be injected.

Next, the effect will be explained. The ultrapure water used for cleaning and shredding semiconductor chips flows into the path (11) shown in Figure 1.
Flow rate sensor (3), injection nozzle α9 of carbon dioxide injector (2), cartridge filter selection specific resistance measuring device (4)
) and are used again for cleaning, etc. When the pulp (5) of the carbon dioxide gas injector (2) is opened, carbon dioxide gas from the CO2 cylinder (6) is injected into the ultrapure water path (1),
Dissolves in ultrapure water to lower specific resistance. If the flow rate and pressure of the ultrapure water flowing through the path (1) do not change, the microcomputer-a compares the measured value from the resistivity measuring device (4) with the setting value from the keyboard αJ, and calculates the value according to the difference. Decide the amount of carbon dioxide gas to be injected and instruct it to the CO□ controller aυ. The CO2 controller αυ processes the measured values from the CO□ mass flow meter (9) in real time, and sends the instructed gas injection amount to the carbon dioxide gas injector (2) and the channel (
1) Press fit inside.

Next, when the flow rate or pressure of the ultrapure water flowing through the path (1) changes, the flow rate sensor (3) detects this change and transmits the change to the IT microcomputer-α2. The computer (13) determines the amount of gas to be injected based on the coefficients etc. entered in advance through the keyboard (13), and determines the amount of gas to be injected based on the measured value of the resistivity measuring device (4) processed in parallel. It performs arithmetic processing and instructs the CO2 controller αυ to determine the amount of gas to be injected.This instructed amount of gas is injected into the ultrapure water path (1) via the carbon dioxide gas injector (2).The flow rate sensor (3) ), the flow rate fluctuation is detected in advance, the gas injection amount is calculated according to the amount of change, and the specific resistance value amplitude during the transient response is extremely small. Since the gas is pressurized into the path (1) from the injection nozzle α9, the specific resistance value of the ultrapure water passing through this is approximately equal to the value set from the keyboard 03, but the specific resistance value of the specific resistance measuring device (4 ), it is compared with the set value in the computer, and if there is a difference, the gas injection amount is calculated and instructed to the CO2 controller 0υ.Such a flow rate sensor (3) and a resistivity measuring device (4) ), the actual measured value at the outlet of path (1) when the set value is set to IMΩ・1 is shown by the dotted line in Figure 3, and the dot-dashed line of the conventional method. It is possible to obtain a specific resistance value with an extremely small transient response to fluctuations in flow rate and pressure compared to ultrapure water with a specific resistance value of 18 MΩ・2 at the inlet of path (1). In a line where the specific resistance value is set to , even if the pressure of ultrapure water changes from the initial setting #) IK9/Cm2, the change in specific resistance value is within ±15%, and the flow rate of ultrapure water When the pressure or flow rate fluctuated or did not fluctuate, it could be controlled within ±10%.

When the pressure of ultrapure water fluctuates, as shown in Figure 2, the carbon dioxide flow path (secondary side) between the diaphragm valve (5) and the tip of injection nozzle a9 also fluctuates, making resistivity control unstable. Easy to use. In the present invention, the carbon dioxide injector (2) is integrated with the path (1), a diaphragm valve (5) is adopted, and the injection nozzle 09 is also made as small as possible, so the influence of this unstable factor is reduced. It became smaller.

As described above, the present invention includes a carbon dioxide gas injection means consisting of a CO2 cylinder (6), a CO2 mass flow meter (9), and a carbon dioxide gas injector (2), and a carbon dioxide gas injection means located upstream of the carbon dioxide gas injector (2) and controlled. A flow rate sensor (3) that measures the flow rate of ultrapure water in advance, and a resistivity measurement device that is located downstream of the carbon dioxide gas injector (2) and sequentially measures the specific resistance of ultrapure water with dissolved carbon dioxide gas. (4) and a processing means that appropriately selects the amount of carbon dioxide gas to be injected according to changes in the pressure and flow rate in the ultrapure water path (1), so it can be It also allows for excellent control of resistivity. In particular, CO2
Controller 〇〇 and CO□ mass flow meter (9),
A carbon dioxide injector with a smaller internal capacity (flow path) on the secondary side (
2) The carbon dioxide injection system with excellent responsiveness can accurately supply a predetermined amount of carbon dioxide to ultrapure water, increasing the reliability of resistivity control.

[Brief explanation of the drawing]

The drawings show an example of the implementation of the present invention. Fig. 1 is a flow sheet, Fig. 2 is an explanatory diagram of a carbon dioxide injector, and Fig. 3 is an illustration of actual measured values when IMΩ・I is taken as the set value. It is a graph diagram.

Claims (5)

[Claims] (1) A flow rate sensor, a carbon dioxide gas injector, and a resistivity measuring device are installed in the ultrapure water path, and the outputs of the flow rate sensor and resistivity measuring device are processed in parallel by a microcomputer, and a predetermined mass of carbon dioxide gas is collected by the computer. A resistivity control method for ultrapure water that is injected into ultrapure water using a controlled gas injector. (2) The specific resistance of ultrapure water according to claim 1, wherein a flow rate sensor is arranged upstream of the ultrapure water path to which the carbon dioxide gas injector is attached, and a specific resistance measuring device is arranged downstream. Control method. (3) C between the CO_2 cylinder and the carbon dioxide injector
The ultrapure water system according to claim 2, wherein a predetermined mass of carbon dioxide gas is injected into the ultrapure water path by a CO_2 controller which is equipped with an O_2 mass flow meter and is connected to the mass flow meter and manages a gas injector. Method for controlling resistivity of pure water. (4) A carbon dioxide gas injection means consisting of a CO_2 cylinder, a CO_2 mass flow meter, and a carbon dioxide gas injector, and a flow rate sensor located upstream of the carbon dioxide gas injector to measure in advance the flow rate of ultrapure water to be controlled. , a resistivity measuring device located downstream of the carbon dioxide gas injector that sequentially measures the resistivity of ultrapure water with carbon dioxide dissolved in it, and a resistivity measuring device that measures the specific resistance of ultrapure water in which carbon dioxide gas is dissolved, and the amount of carbon dioxide gas injected according to changes in pressure and flow rate in the ultrapure water path. A resistivity control device for ultrapure water, comprising a treatment means for appropriately selecting (5) A carbon dioxide gas injector is formed by a diaphragm valve with excellent responsiveness and an injection nozzle with a diameter as small as possible that guides carbon dioxide gas pumped through this valve to an ultrapure water path. Ultrapure water resistivity control device as described in .