JPH0373355B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION In order to prevent discharge breakdown caused by static electricity while cleaning a wafer surface with ultra-pure water, the present invention aims to dissolve carbon dioxide by blowing carbon dioxide into the ultra-pure water. The amount of carbon dioxide gas injected into ultrapure water is adjusted using a solenoid valve, and this solenoid valve is controlled by a resistivity value sensor placed at the outlet of the filter that uniformly dissolves carbon dioxide gas. The present invention also relates to a method for producing ultrapure water and an apparatus therefor, which always maintains the resistivity value of ultrapure water jetted onto a wafer surface within a certain range.

Ultrapure water is used to manufacture IC wafers and other products. This ultrapure water does not contain any particulates, microorganisms, or ionic compounds, and has a specific resistance value of 16~
Exhibits high insulation properties of 18MΩ・cm (25℃). During the process of shredding a wafer with an ultra-thin grindstone, static electricity is generated on the wafer surface due to the friction, and when ultrapure water is jetted onto this surface during spinner cleaning (high-pressure water jet method), even dielectric materials can be damaged. Electrostatic discharge damage occurs when some ultrapure water passes through the water, causing some of the microcircuits on the wafer surface to melt and short-circuit. In order to prevent discharge damage, it is possible to lower the specific resistance of ultrapure water, but the incorporation of metal ions with free electrons can cause the IC to deteriorate due to diffusion.
This cannot be used because it damages the wafer itself, and discharge destruction is prevented as much as possible by adjusting the water pressure and spray angle of ultrapure water that is sprayed onto the wafer surface. However, adjustment of the injection angle, etc. did not significantly improve the yield, and separate discharge countermeasures have been considered. The present invention adopts a method of blowing highly pure water-soluble carbon dioxide gas into ultrapure water to significantly lower the resistivity, and uses ultrapure water that has a certain degree of conductivity to prevent discharge due to static electricity. , will be explained in detail below based on the drawings.

1 is a cylinder filled with highly pure carbon dioxide gas, 2
3 is a pressure reducing valve, and 3 is a solenoid valve which is repeatedly opened and closed by a resistivity regulator 4. 5 removes impurities from the gas using a filter. 6 is a manual control valve, 8 is a solenoid valve, 9
is a check valve, and the carbon dioxide gas from these carbon dioxide gas supply means is blown into the ultrapure water flow path 11 through the gas flow path 10. A check valve 12 that prevents the backflow of carbon dioxide gas is placed in front of the ultrapure water flow path 11, and downstream of the intersection with the gas flow path 10, the bubble-like carbon dioxide gas is atomized and the fine particles in the ultrapure water are disposed. A filter 13 is provided to remove bacteria and microorganisms. Further downstream of the ultrapure water channel 11, a resistivity value sensor 14 serving as an input to the resistivity regulator 4 and a resistivity value sensor 16 serving as an input to the resistivity alarm 15 are arranged. The solenoid valve 3 is opened when the output of the resistivity sensor 14 exceeds the upper limit of a certain range, and is closed when the output falls below the lower limit. 17 is a nozzle, and 18 is a wafer to be cleaned.

Next, the operation will be explained. Check valve 1 for ultrapure water
2, filter 13, specific resistance value sensor 14,1
6. The carbon dioxide gas in the cylinder 1 is flowing at a constant pressure through a channel system consisting of a nozzle 17, and the pressure is reduced to a predetermined pressure by the pressure reducing valve 2, and the carbon dioxide gas reaches the electromagnetic valve 3, which is closed. The specific resistance value of the ultrapure water passing through the nozzle 17 is approximately 18 MΩ·cm (25° C.) as shown in FIG.

Adjust the resistivity regulator 4 and set its upper limit value.
1.0MΩ・cm, lower limit set to 0.1MΩ・cm,
When the manual control valve 6 is opened, the resistivity value sensor 14
operates the resistivity regulator 4 and opens the solenoid valve 3.
After the carbon dioxide gas passes through the filter 5 to further increase its purity, it is blown into the ultrapure water flow path 11 through the gas flow path 10. The injected bubbly carbon dioxide gas is atomized by the filter 13 and uniformly dissolved in the ultrapure water. The ultrapure water that has passed through the filter 13 further removes fine particles and the like, and the dissolved carbon dioxide gas undergoes thermal equilibrium dissociation with water molecules to ionize hydrogen ions and lower the specific resistance. The specific resistance decreases depending on the proportion of carbon dioxide gas dissolved. When the resistivity value approaches 0.1 MΩ·cm, which is the lower limit value set by the resistivity regulator 4, the resistivity sensor 14 detects this, closes the solenoid valve 3, and stops blowing carbon dioxide gas. . At the same time, the solenoid valve 8 is opened for several seconds to discharge the ultrapure water that has entered the gas flow path 10 by the residual carbon dioxide gas pressure, and then closed again. When the blowing of carbon dioxide gas is stopped, the resistivity of the ultrapure water passing through the resistivity value sensor 14 gradually increases as shown in the waveform of FIG. 2.
The increased resistivity is the set upper limit of 1.0MΩ・cm
When reaching the vicinity, the resistivity regulator 4 again closes the solenoid valve 3.
is opened and carbon dioxide gas is pressurized into the ultrapure water flow path 11 to lower the specific resistance of the ultrapure water.

The resistivity value sensor 14 detects the set upper and lower limit values, and the resistivity adjuster 4 repeatedly opens and closes the solenoid valve 3, so that the resistivity of the ultrapure water jetted from the nozzle 17 becomes as shown in Figure 2. It takes a repetitive waveform and is controlled to always have a specific resistance value within a certain range. When the jetted ultrapure water deviates from the set allowable range, the resistivity alarm 15 issues an alarm when the resistivity value sensor 16 is input.

High-pressure ultrapure water is sprayed onto the electrostatically charged wafer 18 to clean it, but since this ultrapure water has a low resistivity and a certain degree of conductivity, the static electricity on the surface is absorbed through the flowing ultrapure water and disappears. do. When conventional ultrapure water has an extremely high resistivity and functions as a dielectric (insulator), submerged discharge breakdown tends to occur and the wafer 18 is damaged by fusing, but the ultrapure water of the present invention, which has a low resistivity, When using pure water, such discharge due to static electricity does not occur.
The permissible range of resistivity value due to carbon dioxide gas blowing is the range within which the static electricity on the wafer 18 surface is maintained at a low resistivity value without dissipating due to discharge when ultrapure water is jetted onto the wafer 18 surface. This is the range that can be eliminated by the conductivity of , and is not limited to the range shown in FIG. This range is appropriately determined depending on the electrode pattern of the wafer 18, the amount of electrostatic charge on its surface, and the like.

Further, as a means for uniformly dissolving carbon dioxide gas in ultrapure water, a well-known vortex or turbulent flow generating mechanism may be used instead of the filter 13. Although the wafer 18 has been described as an object to be cleaned, the present invention is naturally applied to cleaning a mask substrate by electron beam writing.

In short, the present invention directly blows carbon dioxide whose flow rate is controlled by the solenoid valve 3 into the ultrapure water channel 11 that is supplied onto the wafer surface, and filters the bubbles into ultrapure water by making the filter 13 fine. In order to quantitatively control the amount of carbon dioxide gas blown into the wafer surface by controlling the electromagnetic valve based on the resistivity sensor 14 disposed at the outlet of the filter 13 so as not to cause discharge damage due to static electricity on the wafer surface. , the surface of the wafer 18 can be cleaned without causing damage due to static electricity.

[Brief explanation of drawings]

The drawings show an example of the implementation of the present invention. Fig. 1 is an explanatory diagram of a block circuit for blowing carbon dioxide gas into ultrapure water, and Fig. 2 shows actual measurement results in which the vertical axis indicates the specific resistance value of ultrapure water. It is a graph diagram. 1... Cylinder, 3... Solenoid valve, 4... Specific resistance regulator, 10... Gas flow path, 11... Ultrapure water flow path,
13... Filter, 14... Specific resistance value sensor.

Claims (1)

[Claims] 1. Ultrapure water channel 1 supplied onto the wafer surface, etc.
1. Carbon dioxide gas whose flow rate is controlled by a solenoid valve is directly blown in, and the blown bubbles are atomized by a filter and dissolved in ultrapure water, and the above-mentioned solenoid valve is based on a resistivity value sensor placed at the outlet of the filter. A method for producing ultrapure water with low resistivity for use in cleaning wafers, etc., which quantitatively controls the amount of carbon dioxide gas blown into the wafer surface to prevent electrostatic discharge damage from occurring on the wafer surface. 2. A carbon dioxide supply source that blows carbon dioxide directly into the ultrapure water in the main flow path, a solenoid valve that adjusts the amount of this blowing, and a filter that atomizes the carbon dioxide gas bubbles blown into the ultrapure water in the main flow path. A resistivity value sensor is placed on the outlet side of the filter, and the electromagnetic valve is opened and closed by the resistivity value sensor so that the ultrapure water sprayed onto the wafer surface has a resistivity value within a certain range. Ultrapure water production equipment with low resistivity used for cleaning wafers, etc.