JPH06224286A - Attraction monitoring device of electrostatic attraction apparatus - Google Patents

Abstract

PURPOSE:To provide the monitoring device of an electrostatic attraction apparatus, wherein the warp of a wafer is corrected by the electrostatic attraction apparatus and it can be monitored whether the wafer is fixed surely or not. CONSTITUTION:A current detection means 6 is installed in an electric circuit which is formed of an object 1, to be held, mounted on an electrostatic attraction apparatus and of an electrode plate 3, and an operation means 8 which integrates and operates the time change of a detected current value is installed. Thereby, an attraction state is monitored. Thereby, it is possible to confirm that a wafer is attracted to a dielectric or that the wafer is flattened.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrostatic attraction device for fixedly holding a conductor or a sample such as a semiconductor such as a silicon wafer to be subjected to microfabrication, and particularly to a static adsorption device suitable for grasping the holding state. The present invention relates to an adsorption monitor device for an electroadsorption device.

[0002]

2. Description of the Related Art When a sample such as a semiconductor wafer is subjected to film formation such as etching, sputtering or CVD, it is necessary to fix and hold the sample at a predetermined position of an apparatus. Especially when processing a fine pattern on a semiconductor wafer, the pattern is printed on the wafer so that the warp is corrected and flattened, or the wafer is firmly adhered for the purpose of improving the thermal conductivity during spatter and film formation. It is required to be fixed. Conventionally, as a sample holding means for such an application, an electrostatic adsorption device that can be used even in a vacuum and that can generate an adsorption force on the entire back surface of a wafer has been used. Furthermore, since it can hold wafers in vacuum, it is also used as a holding device for high-speed transfer in vacuum. This electrostatic adsorption device is constructed by laminating a dielectric material on an electrode plate. A voltage is applied between the electrode plate and the sample to generate a potential difference, and the generated Coulomb force attracts the sample on the dielectric material. It is to hold it.

Examples of such an electrostatic attraction device are disclosed in, for example, JP-A-59-79545 and JP-A-63-142654.

[0004]

By the way, in the case of fine pattern processing on a semiconductor wafer such as etching, sputtering, or CVD in the semiconductor manufacturing process as described above, the warp of the wafer is corrected and flattened. Or, for the purpose of improving the thermal conductivity, it is required to securely fix the wafer tightly.

However, in the example disclosed in Japanese Patent Laid-Open No. 59-79545, means for confirming whether or not the wafer is reliably fixed and held after the warp of the wafer is corrected by the electrostatic attraction device is considered. There wasn't. In addition, JP-A-63-142654
In the example disclosed in the publication, whether or not the wafer is fixedly held is confirmed by the value of the current flowing through the circuit that constitutes the electrostatic adsorption device as the electrostatic adsorption confirmation means.
Since the dielectric of the electrostatic adsorption device is formed of a high resistance material, the current value in the circuit is often on the order of μA or less, and a micro ammeter is required, and this micro ammeter is expensive. The whole thing becomes very expensive. Further, different films are formed on the attracted surface of the wafer that has undergone the process depending on the type of the process, and the resistance value is different. Insufficient to make a judgment.

An object of the present invention is to provide a monitor device for an electrostatic chucking device which can confirm whether or not the warp of the wafer has been corrected by the electrostatic chucking device and whether the wafer is securely fixed by a simple method. .

[0007]

Means for Solving the Problems In an electrostatic adsorption type sample holding device, a current detecting means is provided in an electric circuit formed by a held object and an electrode plate, and a time change amount of the detected current value is integrated. This is achieved by providing a means and providing a device that determines the integrated value output by the means as the presence or absence of adsorption.

Further, a current detecting means is provided in the electric circuit formed by the held object and the electrode plate, and means for recognizing a current waveform generated when the held object is attracted and released as a pulse signal, for example, A / D. This is achieved by providing a converter and providing a device for determining the presence or absence of adsorption based on this pulse signal.

[0009]

When a voltage is applied to and cut off from the electrode plate of the electrostatic adsorption device and the object to be held, the current flowing between the two shows a pattern as shown in FIG. When a voltage is applied, that is, when adsorption is started, a relatively large current transiently flows because charges are accumulated between the held object and the electrode plate, and when the accumulation of charges ends, a minute current corresponding to the resistance value of the dielectric substance. Flows. Then, when the voltage is cut off, that is, when the held object is detached, the electric charge accumulated between the held object and the electrode plate is discharged, so that a current flows in the opposite direction.

The monitoring method of the electrostatic attraction device of the present invention is as follows.
A current detection means is provided in an electric circuit formed by the held object and the electrode plate, and the time change of the detected current value is integrated. As a result, the amount of charge accumulated between the held object and the electrode plate is calculated. Since the amount of charge accumulated between the held object and the electrode plate corresponds to the attraction force, the attraction force between the held object and the electrode plate can be monitored.

Further, the waveform of the current flowing at the start of adsorption and at the time of desorption takes a negative direction at the time of desorption when the direction of the current at the start of adsorption is positive. Therefore, if both current waveforms are recognized as a pulse signal, it can be determined that a positive pulse is adsorbed and a negative pulse is desorbed, and the presence or absence of adsorption can be monitored.

[0012]

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

FIG. 1 is a diagram showing a first embodiment of the present invention, and FIG. 2 is a time change of a current value flowing in a circuit formed by an electrode plate of an electrostatic adsorption device, a dielectric and a held object. It is the figure which showed typically.

In FIG. 1, 1 is a held object to be fixedly held, for example, a semiconductor wafer, 2 is a dielectric constituting an electrostatic chucking device, 3 is an electrode plate, 4 is a conducting portion that conducts with the wafer 1, Reference numeral 7 is a power source for generating a potential difference between the wafer 1 and the electrode plate 3. In addition, the conducting portion 4 is surely connected to the wafer 1
To contact the wafer 1 via a weak spring system 11 in order to establish electrical continuity with. The resistivity of the dielectric 2 is preferably 10 ⁹ Ωcm to 10 ¹¹ Ωcm at the operating temperature. 6 is a current monitor for measuring the current flowing in the circuit that constitutes the electrostatic adsorption device, 8 is a calculator for integrating the current waveform,
Reference numeral 9 is a control device for controlling the voltage applied by the power supply 7 according to the information of the integrated value sent from the integration calculator, and 10 is a device equipped with an electrostatic adsorption device,
For example, it is a control device that controls a semiconductor manufacturing device such as an etcher or a vacuum robot.

In the electrostatic chucking device thus constructed, first, the wafer 1 is placed on the chucking surface 2'of the electrostatic chucking device, and a predetermined voltage is supplied from the power source 7 to the electrode plate 3 and the wafer 1.
Applied between and. Then, the wafer 1 is adsorbed and held on the adsorption surface 2'by the electrostatic force generated at this time. When wafer transfer or predetermined processing is completed and the wafer is released from the electrostatic adsorption device, the voltage applied from the power supply 7 is cut off.

In this case, the current flowing between the circuits constituting the electrostatic attraction device has a pattern as shown in FIG. At the time of applying a voltage, that is, at the time of starting adsorption t1, a current 14 having a peak value V2 transiently flows because charges are accumulated between the wafer 1 and the electrode plate 3, and the dielectric 2 starts from t2 when the accumulation of charges ends. A minute current V1 corresponding to the resistance value of the current flows. Then, when the voltage is cut off, that is, when the wafer 1 is detached, at t3, the electric charge accumulated between the wafer 1 and the electrode plate 3 is discharged. It becomes zero.

The monitoring method of the electrostatic attraction device of the present invention is as follows:
A current detecting means 6 is provided in an electric circuit formed by the wafer 1 and the electrode plate 3, and a peak 1 of the detected current waveform is provided.
An arithmetic unit 8 is provided for 4 and 15 to perform integral calculation. For example, the peak 14 is integrated between the times t1 and t2, and the peak 15 is integrated between the times t3 and t4. Since the electric current is a change in electric charge with time, the accumulated electric charge amount or the discharged electric charge amount between the wafer 1 and the electrode plate 3 is calculated by integrating the electric current value. The electrostatic capacity is obtained by dividing this charge amount by the voltage.

The electrostatic attraction force is applied to the wafer 1 which is the object to be held.
Is proportional to the electrostatic capacitance between the electrode plate 3 and the electrode plate 3, and is further proportional to the amount of charge accumulated between the wafer 1 and the electrode plate 3. Therefore, the waveform of the current flowing in the circuit at the time of starting adsorption and desorption, when the applied voltage is increased, or when a gap is formed between the wafer 1 and the surface 2 of the adsorption surface for some reason, etc. Can be monitored and the amount of electric charge accumulated between the wafer 1 and the electrode 3 can be monitored, and thus the attraction force of the electrostatic attraction device can be monitored.

As the current detecting means, a minute ammeter may be installed in the circuit, or a known resistor having a value sufficiently smaller than the resistance value of the dielectric body 2 of the electrostatic attraction device may be installed in series. The current value may be detected simply by measuring the voltage across both ends. Further, the current detecting means in the present invention is not limited to these methods.

During adsorption, if a negative peak smaller than V3 appears, the sum of the negative charge amount calculated from this peak and the charge amount calculated from the peak value during adsorption is the wafer 1 and the electrode 3. Since it is the amount of electric charge between them, it means that the attraction force has decreased for some reason.

If for some reason, for example, the amount of deformation of the wafer 1 is too large, or a foreign substance is sandwiched between the wafer 1 and the suction surface 2 ′, and the gap is large and no suction force is generated, The current waveform does not appear and there is no charge accumulation, that is, it indicates that the adsorption force is not generated. Alternatively, when the accumulated charge amount is smaller than the charge amount calculated from the electrostatic capacity of the dielectric, it means that the adsorption force is reduced.

Further, the result of the present monitoring method is fed back to control the voltage from the power source, or fed back to the entire apparatus equipped with the electrostatic chuck, for example, a semiconductor manufacturing apparatus such as an etcher or a control apparatus such as a vacuum robot. It can also be used as a safety device for the entire device or as an operation monitor.

In the present embodiment, the so-called monopolar type electrostatic attraction device of the type in which each circuit has one electrode plate and which conducts electricity from the wafer has been described, but the same applies to a bipolar type electrostatic attraction device. The effect of is obtained.

Next, a second embodiment of the present invention will be described with reference to FIGS. FIG. 3 is a diagram showing a second embodiment of the present invention, and FIG. 4 is a schematic diagram showing a time change of a current value flowing in a circuit formed by an electrode plate of an electrostatic adsorption device, a dielectric and a held object. 2 is a diagram shown in FIG. 2 and a diagram obtained by converting it into a digital signal.

In this embodiment, the time t
1, and the currents 14 and 15 flowing with a transient peak between the wafer 1 and the electrode plate 3 at the time of wafer detachment t3 are captured as pulse signals. That is, the waveform of the current flowing at the start of adsorption and at the time of desorption takes a negative direction at the time of desorption, with the positive direction at the start of adsorption. Therefore, the current waveforms of both can be converted into a pulse signal by means of a pulse counter or a digital meter relay, for example, and it can be determined that a positive pulse is adsorbed and a negative pulse is desorbed. You can monitor. In this embodiment, the current waveform is converted into a digital signal via the A / D converter 12, and the pulse signal is taken into the control device 13.

Since the magnitude of the pulse signal corresponds to the amount of charges accumulated between the wafer 1 and the electrode plate 3, the magnitude of the attraction force can be indirectly monitored. That is, if a negative pulse signal is input during suction and this signal is smaller than the pulse signal 13 at the time of suction, it indicates that the suction force has decreased for some reason, and this signal is the pulse signal at the time of suction. If the value is the same as 13, it means that the adsorption force has disappeared. And pulse signal 1
If 1 is smaller than usual, it means that the adsorption force is lowered for some reason.

Further, if the sum of the magnitudes of the pulses during the operation of the electrostatic attraction device is sequentially obtained, the amount of charge accumulated between the wafer 1 and the electrode 3 is monitored, and the attraction force can be monitored. When the rectangular waveform is converted by the A / D converter 12 as in the present embodiment, it is also possible to monitor the magnitude of the attraction force by the area.

Further, as in the first embodiment, the result of this monitoring method is fed back to control the voltage from the power source, or fed back to the control device of the entire device equipped with the electrostatic chuck to feed back the entire device. It can also be used as a safety device or an operation monitor.

In the present embodiment, the so-called unipolar type electrostatic attraction device of the type in which the electrode plate of the electrostatic attraction device is one and the conduction is obtained from the wafer has been described. The same effect can be obtained in the device.

[0030]

According to the present invention, since the change in current between the held body and the electrode plate is integrated and detected, it is determined whether or not the wafer is securely held by the electrostatic chuck and whether or not the wafer is flattened. Can be monitored. Also, it is possible to monitor how much suction force is applied, and the processing device can surely process the wafer surface.

[0031]

[Brief description of drawings]

FIG. 1 is a sectional view showing a first embodiment of the present invention.

FIG. 2 is a diagram showing a waveform of a current flowing through a circuit of the electrostatic attraction device.

FIG. 3 is a diagram showing a second embodiment of the present invention.

FIG. 4 is a diagram showing a waveform of a current flowing through a circuit of the electrostatic attraction device.

[Explanation of symbols]

1 ... Wafer, 2 ... Dielectric, 3 ... Electrode plate, 4 ... Conducting part, 5 ... Insulator, ...
・ Current detector, 7 ... Power supply, 8 ... Integral calculator, 9 ... Control device, 10 ... Control device, 11,
12 ... peak value of current, 13, 14 ... pulse signal.

Claims (2)

[Claims] 1. A dielectric is laminated on an electrode plate, an object to be held is placed on the upper surface of the dielectric, and a voltage is applied between the electrode plate and the object to be held to hold the object to be held on the dielectric. In an electrostatic attraction device for attracting an object, current detection means is provided in an electric circuit formed by including the held object and the electrode plate, and a time change amount of the current value detected by the current detection means is integrated. An adsorption monitor device for an electrostatic adsorption device, characterized in that the arithmetic means for performing the operation is connected to the electric circuit. 2. A dielectric is laminated on an electrode plate, an object to be held is placed on the upper surface of the dielectric, and a voltage is applied between the electrode plate and the object to be held to hold the object to be held on the dielectric. In an electrostatic attraction device for attracting an object, current detection means is provided in an electric circuit formed by including the held object and the electrode plate, and when the held object is attracted to the dielectric, or An adsorption monitor device for an electrostatic adsorption device, comprising input signal converting means for converting a current waveform generated when desorbing from a dielectric into a pulse signal.