JPH06203993A - Static elimination control method for charged article by ionizer - Google Patents

Abstract

PURPOSE:To precisely perform static elimination regardless of a change of the environment by providing a vibrating type surface potential sensor in the flow of an ionized air, and applying a DC voltage to a counter electrode so that the detection value of the charge potential is within a determined range. CONSTITUTION:A number of discharge pairs consisting of a discharge electrode 1 and a counter electrode 2 are arranged in the direction crossing the flow of a purified air. An AC high voltage is applied to the discharge electrode by an AC power source device 5, and a DC voltage is applied to the counter electrode 2 by a DC power source device 7. When a vibrating surface potential sensor 8 is further placed in the flow of the ionized air, the sensor 8 is charged to the ion polarity to output an AC voltage corresponding to the field strength. Thus, when the negative ion concentration in the air is increased, the sensor 8 outputs the AC voltage according to this concentration, and when the positive ion concentration is increased, it outputs the AC voltage according to this concentration. Namely, the DC voltage applied to the counter electrode 2 is regulated by a controller 9 so that the AC voltage is within a determined range to control ion balance.

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 surface potential of a charged article (for example, a wafer being manufactured) by an ionizer.

[0002]

2. Description of the Related Art It has been proposed to remove charges generated on a wafer or a wafer carrier in a semiconductor manufacturing process by an ionizer. Various types of ionizers are known, but in the case of the Pulsed-DC type, the surface potential after static elimination is several tens of volts, and positive and negative are alternately repeated.
It has the drawback that smooth damping cannot be obtained.
With C (alternating current) type, there is a large deviation in the amount of positive and negative ions generated, so even after static elimination, it will be from tens of volts to 20
There was a problem that a potential of about 0 V remained.

On the other hand, semiconductor devices at the wafer stage are ESD
However, the surface potential of the wafer is constantly controlled to a value of several volts or less in, for example, a 4 Mbit DRAM or later in which the insulating oxide film has a thickness of several tens of angstroms or less. Will be needed. The above-mentioned conventional type cannot satisfy such requirements.

In order to meet such demands, the inventors of the present invention have disclosed Japanese Patent Application Laid-Open No. 3-230499, Japanese Patent Application Laid-Open No. 3-230500, Japanese Patent Application No. 2-222542, Japanese Patent Application No. 3-174807, and Japanese Patent Application No. 3-174807. In the AC type ionizer, such as Hira 3-94984, a controlled amount of bias voltage is applied to the discharge electrode side, or a direct current voltage of several hundred V is applied to the discharge counter electrode side (hereinafter, this voltage is called Ve). We have proposed various methods to balance the amount of positive and negative ions generated by applying them, and various improvements.

[0005]

In the AC type ionizer, even when a DC voltage Ve of an appropriate magnitude is applied to the discharge counter electrode side as previously proposed in order to balance the positive and negative ion generation amounts. It has been found that the magnitude of Ve necessary to balance the positive and negative ion generation amounts also changes due to changes in the environment in which this ionizer is installed, such as fluctuations in wind speed and humidity. Therefore, when the environment changes, it is necessary to properly control Ve according to the change. An object of the present invention is to simply solve this problem.

[0006]

According to the present invention, an AC ionizer for applying a high AC voltage to a needle-shaped discharge electrode to cause corona discharge is introduced into a flow of clean air passing through a filter. When neutralizing the static electricity of the charged object by installing and supplying the flow of air ionized by this ionizer to the charged article existing on the downstream side, a predetermined distance is set to the discharge end of the discharge electrode. In the static elimination method of a charged article, in which the counter electrode is arranged separately and the amount of positive and negative ions generated by applying a DC voltage of an appropriate magnitude to this counter electrode is balanced, the air ionized by the ionizer is used. An oscillating surface potential sensor is placed in the flow of electric current, and the DC voltage applied to the counter electrode is controlled so that the detected value of the charged potential of the surface potential sensor itself falls within a predetermined range. Providing neutralization control method of charging articles by ionizer according to claim. As a vibrating surface potential sensor to be used, it is preferable to use a vibration amplitude of a mechanical oscillator that vibrates by itself to convert the surrounding electric field strength into an AC voltage and output the AC voltage.

[0007]

Function The surface potential sensor originally measures the surface potential of the charged article. A vibrating surface potential sensor converts the intensity of an electrostatic field formed by a charged article into an AC signal by using the vibration amplitude of a mechanical oscillator that vibrates by itself, and the AC signal is used as a detection value for the charged article. The change in the surface potential of can be detected in a noncontact manner. Although such a vibration type surface potential sensor itself is known, it is not usually used for measuring the deviation of the positive and negative ion concentrations in the flow of ion air.

However, when such a vibrating surface potential sensor is placed in the flow of air ionized by the ionizer as in the present invention, when the positive and negative ion concentrations are deviated to either side, The sensor itself is charged to the polarity on one side, and the magnitude of this charged potential can be detected.

That is, by applying a DC voltage of an appropriate magnitude to the counter electrode, even if the positive and negative ion generation amounts generated from the ionizer are balanced, some external factors, especially changes in the velocity of the air flow and humidity The balance may be lost due to the change, but in this case, the detection value of the vibration type surface potential sensor arranged in the flow of ionized air fluctuates, so this detection value falls within the set range (for example, within ± 4 V). By adjusting the DC voltage applied to the counter electrode as described above, control can be performed to maintain balance. This feedback control can be automated.

[0010]

FIG. 1 shows an example of an AC ionizer according to the present invention, in which a large number of discharge pairs consisting of a discharge electrode 1 and a counter electrode 2 are two-dimensionally arranged in a direction crossing a flow of clean air (indicated by an arrow 3). Many are arranged with a wide space. Each discharge electrode 1 is connected to a lead wire 4 which is covered with insulation, and this lead wire 4 is connected to an AC power supply device 5, so that a high AC voltage is applied to each discharge electrode 1. On the other hand, the counter electrode 2 is configured as a grid-shaped frame, and the discharge end of each discharge electrode 1 is located on a substantially vertical line of the center of the space surrounded by each frame. As a result, a pair of discharge pairs is formed for each frame. The shape of this frame does not have to be rectangular as shown, but may be polygonal, circular, oval or the like. Each counter electrode of the multiple discharge pairs thus formed is connected to the DC power supply 7 through the lead wire 6.

As described in Japanese Patent Laid-Open No. 3-230500, this ionizer can adjust the DC voltage applied to each counter electrode 2 appropriately so that the positive and negative ion concentration, which is a drawback of the AC ionizer, can be reduced. The bias can be corrected, and the positive and negative ion generation amounts generated from each discharge pair can be balanced. However, if the airflow velocity or the humidity fluctuates, the ion balance is disturbed. Therefore, unless this is prevented, the static elimination effect of the charged article to be treated cannot be accurately achieved.

In this example, the positive and negative ion balance is automatically controlled so as not to be disturbed even when the environment changes,
For this purpose, the vibrating surface potential sensor 8 is arranged in the flow of air ionized by the ionizer, and the detected value is used to operate the DC voltage applied to the counter electrode 2. Reference numeral 9 indicates a controller for this operation.

The vibration type surface potential sensor 8 of this example uses a commercially available sensor element 81. As shown in an enlarged view of this sensor element 81, the sensor element 81 is housed in a grounded metal case 82. Insulated Tenron rubber packing 83
A metal lid 84 is put on the cover to be sealed. When such a surface potential sensor 8 is placed in the flow of ionized air, if either the positive or negative ion concentration becomes high, the sensor itself is charged to the ionic polarity, and within the electric field formed by this charging. By vibrating the vibrator inside the vessel, an AC voltage corresponding to the original mission of the electric field strength is output. Therefore, when the negative ion concentration in the air is high, the sensor 8 outputs an AC voltage according to the concentration, and when the positive ion concentration is high, the sensor 8 outputs an AC voltage according to the concentration. If the DC voltage applied to the counter electrode 2 is increased or decreased by the controller 9 so that the voltage falls within a range of a certain threshold value, the positive and negative ion balance can be controlled to the optimum state.

FIG. 2 shows the flow of this feedback control. As shown in the drawing, the oscillating surface potential sensor 8 is the control target, and the DC voltage applied to the counter electrode so that the surface potential V detected by this is within a predetermined range (| V | ≦ 3.0V in the illustrated example). To control. This control is performed in the following procedure. The surface potential V detected by the sensor 8 is input to the input section 9a of the controller, where it is determined by an amplifier and a level detector whether or not it exceeds a set value of 3.0 V, and an ion polarity discriminator determines whether it is positive or negative. It is determined whether or not it is negatively charged and then amplified by an amplifier, and this is used as the main feedback signal, and the voltage control circuit section 9b of the controller is used.
Send to.

In the voltage control circuit section 9b, when the main feedback signal is sent (that is, when the surface potential of the surface potential sensor becomes +3.0 V or higher or −3.0 V or lower), When the signal polarity is negative, the DC voltage applied to the counter electrode is increased to the positive side, and when it is positive, it is increased to the negative side. In this example, this voltage operation amount is set to + 10V or -10V.

[Experimental Example] In the ionizer of FIG. 1, needle-shaped tungsten covered with thin quartz glass was used as each discharge electrode 1, and the HEPA filter outlet (1200 mm) of the clean room ceiling was used.
Each of the ionizers shown in Fig. 1 was attached to each of × 600 mm, area 0.72 m ² ).

First, 100c below the counter electrode at the center of the ionizer.
Ion densitometer installed at m, air velocity 0.37m / s, temperature 23
The optimum value of the counter electrode applied voltage of this ionizer under constant conditions of ℃ and relative humidity of 42% was obtained. The result is shown in FIG. As can be seen in Fig. 3, in this equipment, 50Hz is used for the discharge electrode.
It can be seen that the positive and negative ion concentrations are balanced by setting the DC voltage Ve applied to the counter electrode to approximately −255 V while applying the AC high voltage of 11.5 kV.

Next, 25 5-inch wafers were set on the Teflon carrier at 4.7 mm intervals, and all 25 wafers were brought into contact with each other by a single conductor to make them conductive (total wafer capacity 17.5 pF). Was charged intentionally to + 3.3V or −3.3V, and then it was placed at the distance L = 50cm, 100cm, 200cm from the counter electrode to the downstream side in the center of the ionizer, and the positive and negative ion balance in Fig. 3 was measured. Condition, that is, the counter applied voltage is Ve =
Temperature of 22.6 to 23.8 ° C, relative humidity of 40.8 with constant −255V
We investigated how the surface potential of a wafer decays at -45.1% and an air velocity of 0.43 m / s. The surface potential of the wafer is
It was measured using a Model 244 manufactured by Monroe Elect-ronics, Inc. The results are shown in Fig. 4. As can be seen from the results of FIG. 4, the surface potential of the wafer after static elimination was suppressed to within ± several volts.

FIG. 5 shows the results of an examination of how the wind speed affects the surface potential of the wafer. That is, temperature = 2
Air velocity U at 3.0 ± 0.5 ℃, relative humidity = 42.2 + 2%
By changing, the surface potential Vs of the wafer placed L = 100 cm on the downstream side of the ionizer changes. The voltage applied to the counter electrode is -90V in the illustrated example. As can be seen from the result of FIG. 5, when the airflow velocity U increases, the surface potential Vs of the wafer rises to the positive side accordingly, and when U decreases, Vs also decreases, and the airflow velocity U increases.
It can be seen that there is a constant correlation between the surface potential Vs and the surface potential Vs.

FIG. 6 shows the voltage Ve applied to the counter electrode based on the detection value of the surface potential sensor placed 50 cm downstream of the ionizer according to the present invention so that the magnitude of the detection value is within 4.0V. The experiment results are the same as those in FIG. 5 except that the automatic control is performed. As a result, it can be seen that the surface potential Vs of the wafer was controlled within ± 3 V even if the air velocity changed.

FIG. 7 shows the results of examining how humidity affects the surface potential of the wafer. That is, temperature = 2
Change of relative humidity H under 3.0 ± 0.5 ℃, air velocity = 0.15m / s, and how the surface potential Vs of the wafer on the downstream side L = 100cm of the ionizer changes. Is. The voltage applied to the counter electrode is -14 in the example shown.
It is 2V. As can be seen from the results of FIG. 7, the surface potential Vs of the wafer tends to rise as the humidity H rises.

FIG. 8 shows the voltage applied to the counter electrode based on the detected value of the surface potential sensor located at the downstream side L = 50 cm of the ionizer according to the present invention so that the detected value falls within 4.0V. 7 shows the same experimental results as in FIG. 7, except that Ve was automatically controlled. As a result, it can be seen that the surface potential Vs of the wafer was controlled within ± 3 V even if the humidity changed.

[0023]

As described in detail above, according to the present invention,
In a static elimination equipment for charged articles that balances the positive and negative air ion concentrations by adjusting the DC voltage applied to the opposite side of the AC ionizer, even if the balance is disrupted due to environmental changes such as humidity and air velocity. ， It can be controlled automatically so that the balance is not lost. Therefore, as static elimination equipment for wafers in a clean room in the semiconductor manufacturing process,
The surface potential can be accurately eliminated regardless of changes in the environment.

[Brief description of drawings]

FIG. 1 is a perspective view showing an example of an AC ionizer according to the present invention.

FIG. 2 is a flow chart of static elimination control according to the present invention.

FIG. 3 is a diagram showing the relationship between the applied voltage and the generated positive ion concentration and negative ion concentration when a DC voltage is applied to the counter electrode of the AC ionizer.

FIG. 4 is an experimental result diagram showing attenuation of the surface potential of a wafer.

FIG. 5 is an experimental result diagram for investigating how a change in airflow velocity affects a wafer surface potential when a wafer is destaticized by an ionizer.

FIG. 6 is an experimental result diagram similar to FIG. 5, showing a change in wafer surface potential when the control according to the present invention is performed.

FIG. 7 is an experimental result diagram for investigating how a change in humidity influences a wafer surface potential when a wafer is destaticized by an ionizer.

FIG. 8 is an experiment result diagram similar to FIG. 8 showing changes in the wafer surface potential when the control according to the present invention is performed.

[Explanation of symbols]

 1 Discharge electrode 2 Counter electrode 3 Flow direction of clean air 4 Lead wire to discharge electrode 5 AC power supply device 6 Lead wire to counter electrode 7 DC power supply device 8 Vibration type surface potential sensor 9 Controller

Claims (3)

[Claims] 1. An AC ionizer for applying a high AC voltage to a needle-shaped discharge electrode to perform corona discharge is installed in a stream of clean air passing through a filter, and air ionized by the ionizer is installed. In order to neutralize the static electricity of the charged object by supplying the flow of the electric current to the charged article existing on the downstream side, the counter electrode is arranged at a predetermined distance from the discharge end of the discharge electrode, and In a method of neutralizing a charged article in which positive and negative generated ion amounts are balanced by applying a DC voltage of an appropriate magnitude, a vibrating surface potential sensor is installed in the flow of air ionized by the ionizer. A charged object by an ionizer, which is arranged and controls the DC voltage applied to the counter electrode so that the detected value of the charged potential of the surface potential sensor itself falls within a predetermined range. Static elimination control method for products. 2. The charged article according to claim 1, wherein the vibrating surface potential sensor converts the surrounding electric field strength into an AC voltage and outputs it by utilizing the vibration amplitude of a mechanical vibrator that vibrates by itself. Static elimination control method. 3. The charged article is a wafer or a wafer and a wafer carrier in a semiconductor manufacturing process.
A method for controlling static elimination of a charged article according to item 1.