JP2894464B2 - Static electricity removal control method for charged articles by using ionizer - Google Patents

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 in a manufacturing process) by using an ionizer.

[0002]

2. Description of the Related Art It has been proposed to remove an electric charge generated on a wafer or a wafer carrier in a semiconductor manufacturing process by using an ionizer. Various ionizers are known, but the pulsed-DC type has a surface potential of several tens of volts after static elimination and alternates between positive and negative.
There is a drawback that smooth attenuation cannot be obtained.
The C (AC) type has a large bias in the amount of positive and negative ions generated, so even after static elimination, several tens of volts to 20
There is a problem that a potential of about 0 V remains.

On the other hand, semiconductor elements at the wafer stage are ESD.
The surface potential of the wafer may be constantly controlled to a level of several volts or less in, for example, a 4Mbit DRAM or later, in which the insulating oxide film is several tens of Angstroms or less, because it is not protected or sensitive. Required. The conventional type described above cannot satisfy such requirements.

In order to satisfy such demands, the present inventors have disclosed JP-A-3-230499, JP-A-3-230500, Japanese Patent Application No. 2222542, Japanese Patent Application No. 3-174807, and Japanese Patent Application No. In the AC-type ionizer, a controlled amount of bias voltage is applied to the discharge electrode side, or a DC voltage of several hundred volts (hereinafter, this voltage is referred to as Ve) is applied to the discharge counter electrode side in Hei 3-94984. Various methods have been proposed to balance the amount of positive and negative ions generated by applying voltage, and also to improve them.

[0005]

In an 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 amount of generated positive and negative ions. It was also found that a change in the environment in which the ionizer was installed, such as a change in wind speed or a change in humidity, also changed the magnitude of Ve required to balance the amount of generated positive and negative ions. Therefore, when the environment changes, it is necessary to appropriately control Ve according to the change. An object of the present invention is to easily 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 perform a corona discharge is provided in a flow of clean air passing through a filter. In order to neutralize the static electricity of the charged object by supplying the flow of air ionized by the ionizer to a charged article present on the downstream side, a predetermined distance from the discharge end of the discharge electrode is set. In a method for neutralizing a charged article in which a counter electrode is arranged at a distance and a positive and a negative ions generated by applying an appropriate DC voltage to the counter electrode are balanced, air ionized by the ionizer is used. A surface potential sensor is arranged in the flow of the electric current, and the DC voltage applied to the counter electrode is controlled so that the detection 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 the vibration type surface potential sensor to be used, a sensor which converts the intensity of a surrounding electric field into an AC voltage by using the vibration amplitude of a mechanical vibrator which vibrates by itself and outputs the AC voltage is preferable.

[0007]

The surface potential sensor originally measures the surface potential of a charged article. A vibration-type surface potential sensor converts the strength of an electrostatic field formed by a charged article into an AC signal by using the vibration amplitude of a mechanical vibrator that self-oscillates. The change of the surface potential can be detected in a non-contact manner. Such a vibrating surface potential sensor itself is known, but it is not normally used to measure the deviation of the positive and negative ion concentrations in the flow of ion air.

However, when such a vibration-type surface potential sensor is placed in the flow of air ionized by the ionizer as in the present invention, when the positive or negative ion concentration is biased to one of the two, The sensor itself is charged to the biased side polarity, and the magnitude of the charged potential can be detected.

That is, by applying a DC voltage of an appropriate magnitude to the counter electrode, even if the amount of positive and negative ions generated from the ionizer is balanced, there is some external factor, especially a change in the speed of the air flow and a change in the humidity. The balance may be lost due to the change, but in this case, the detection value of the vibrating surface potential sensor arranged in the flow of the ionized air fluctuates, so that this detection value falls within a set range (for example, within ± 4 V). The balance can be controlled by adjusting the DC voltage applied to the counter electrode as described above. 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 traversed by a flow of clean air (indicated by an arrow 3). They are arranged in large numbers with a realistic spread. Each discharge electrode 1 is connected to a lead wire 4 covered with insulation, and since this lead wire 4 is connected to an AC power supply device 5, an AC high 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 at the center of the space surrounded by each frame. Thus, a pair of discharge pairs is formed for each frame. The shape of the frame does not need to be a square as shown in the figure, but may be a polygon, a circle or an ellipse. Each counter electrode of the large number of discharge pairs thus formed is connected to a DC power supply 7 through a lead wire 6.

As described in Japanese Patent Application Laid-Open No. 3-230500, this ionizer is capable of controlling the positive and negative ion concentrations, which is a drawback of the AC type ionizer, by appropriately adjusting the DC voltage applied to each counter electrode 2. The bias can be corrected, and the amount of positive and negative ions generated from each discharge pair can be balanced. However, if the air flow velocity or the humidity fluctuates, the ion balance will be lost. Unless this is prevented, the charge-removing effect of the charged article to be treated cannot be accurately achieved.

In this embodiment, automatic control is performed so that the positive and negative ion balances do not collapse even if the environment changes.
For this purpose, the oscillating surface potential sensor 8 is arranged in the flow of air ionized by the ionizer, and the DC voltage applied to the counter electrode 2 is manipulated using the detected value. Reference numeral 9 denotes a controller for this operation.

The vibration type surface potential sensor 8 of this embodiment uses a commercially available sensor element 81. As shown in an enlarged view, the sensor element 81 is housed in a grounded metal case 82. , Tenlon rubber insulation packing 83
And a metal lid 84 is placed over it and hermetically sealed. When such a surface potential sensor 8 is placed in the flow of ionized air, if either the positive or negative ion concentration increases, the sensor itself is charged to the ion polarity, and the electric field within the electric field formed by this charging is increased. When the vibrator in the chamber vibrates, an AC voltage corresponding to the electric field strength, which is the original mission, is output. Therefore, if the negative ion concentration in the air increases, the sensor 8 outputs an AC voltage corresponding to the concentration, and if the positive ion concentration increases, the sensor 8 outputs an AC voltage corresponding 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 certain threshold value range, the positive and negative ion balance can be controlled to an optimum state.

FIG. 2 shows the flow of the feedback control. As shown in the figure, the oscillating surface potential sensor 8 is controlled, and the DC voltage applied to the counter electrode so that the surface potential V detected thereby falls within a predetermined range (| V | ≦ 3.0 V in the example shown). 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 whether or not the voltage exceeds a set value of 3.0 V by an amplifier and a level detector. After determining whether or not the battery is negatively charged, the signal is amplified by an amplifier, and the amplified signal is used as a main feedback signal.
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 + 3.0V or more or -3.0V or less), If the polarity of the signal is negative, the DC applied voltage to the counter electrode is increased to the positive side, and if it is positive, it is increased to the negative side. In this example, this voltage operation amount is + 10V or -10V.

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

First, 100c below the counter electrode at the center of the ionizer
An ion concentration meter is installed at an air speed of 0.37 m / s and a temperature of 23 m.
Appropriate values of the voltage applied to the counter electrode of this ionizer under constant conditions of ° C and a relative humidity of 42% were obtained. The result is shown in FIG. As shown in Fig. 3, this equipment uses 50Hz
It can be understood that the positive and negative ion concentrations are balanced by setting the DC voltage Ve applied to the counter electrode to about -255 V while applying the AC high voltage of 11.5 kV.

Next, an integrated product in which 25 5-inch wafers are set on a Teflon carrier at 4.7 mm intervals and all 25 wafers are brought into contact with one conductive wire to make a conductive state (total capacity of wafers 17.5 pF) Is intentionally charged to + 3.3V or -3.3V, and placed at a distance L = 50cm, 100cm, 200cm from the counter electrode at the center of the ionizer to the downstream side. In other words, the applied voltage of the counter electrode is Ve =
Temperature of 22.6 to 23.8 ° C, relative humidity of 40.8 at −255V
We investigated how the surface potential of the wafer attenuated at ~ 45.1% and air velocity of 0.43m / s. The surface potential of the wafer is
The measurement was performed using Model 244 manufactured by Monroe Elect-ronics, Inc. The result is shown in FIG. 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 result of examining 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%
And how the surface potential Vs of the wafer at a position L = 100 cm downstream of the ionizer changes. The voltage applied to the counter electrode is -90 V in the example shown. As can be seen from the results in 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
It can be seen that there is a certain correlation between 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 50 cm downstream of the ionizer according to the present invention so that the value of the detection value falls within 4.0 V. Except for automatic control, the same experimental results as in FIG. 5 are shown. As a result, it can be seen that the surface potential Vs of the wafer was controlled within ± 3 V even when the airflow velocity changed.

FIG. 7 shows the result of examining how humidity affects the surface potential of a wafer. That is, temperature = 2
The relative humidity H was changed under the conditions of 3.0 ± 0.5 ° C. and the airflow velocity was 0.15 m / s, and the change in the surface potential Vs of the wafer at a position L = 100 cm downstream of the ionizer was observed. It is. The voltage applied to the counter electrode is -14 in the example shown.
2V. As can be seen from the results in FIG. 7, the surface potential Vs of the wafer tends to increase as the humidity H increases.

FIG. 8 shows the voltage applied to the counter electrode based on the detection value of the surface potential sensor at L = 50 cm downstream of the ionizer according to the present invention so that the magnitude of this detection value falls within 4.0 V. This is an experiment result similar to that of 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 when the humidity changed.

[0023]

As described in detail above, according to the present invention,
In static electricity removal equipment for charged articles that balances the positive and negative air ion concentrations by adjusting the DC applied voltage on the opposite electrode side of the AC ionizer, even if the balance is disrupted due to environmental changes such as humidity and airflow velocity. ， Automatic control can be performed so that the balance is not broken. Therefore, as a neutralization facility 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 the drawings]

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

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

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

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

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

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

FIG. 7 is an experimental result diagram for examining how a change in humidity affects a wafer surface potential when a wafer is neutralized by an ionizer.

FIG. 8 is an experimental result diagram similar to FIG. 7 , showing a change in a wafer surface potential when control according to the present invention is performed.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 discharge electrode 2 counter electrode 3 flow direction of clean air 4 lead wire to discharge electrode 5 AC power supply 6 lead wire to counter electrode 7 DC power supply 8 vibrating surface potential sensor 9 controller

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-3-230500 (JP, A) JP-A-51-67139 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H05F 3/04 H01T 19/04

Claims (3)

(57) [Claims] An AC ionizer for applying a high AC voltage to a needle-shaped discharge electrode to perform a corona discharge is installed in a flow of clean air that has passed through a filter, and air ionized by the ionizer is provided. When neutralizing the static electricity of the charged object by supplying the flow of electricity to the charged article existing on the downstream side, a counter electrode is arranged at a predetermined distance from the discharge end of the discharge electrode, and the counter electrode is placed on the counter electrode. In a method for neutralizing a charged article in which the amount of positive and negative ions generated is balanced by applying a DC voltage of an appropriate magnitude, an oscillating surface potential sensor is placed in the flow of air ionized by the ionizer. A charged object by the ionizer, wherein 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. Product static elimination control method. 2. The charged article according to claim 1, wherein the vibration-type surface potential sensor converts a surrounding electric field strength into an AC voltage using a vibration amplitude of a self-excited vibrator and outputs the AC voltage. Static elimination control method. 3. The charged article is a wafer or a wafer and a wafer carrier in a semiconductor manufacturing process.
3. The method for controlling static elimination of a charged article according to 1.