JPH11168133A - How to check the attachment / detachment of the electrostatic chuck - Google Patents

Abstract

(57) [Summary] [PROBLEMS] In a method of checking attachment / detachment based on the amount of electric charge accumulated in an electrostatic chuck, the attachment / detachment operation is correctly determined irrespective of the state of the bonding surface of a Si wafer or the like, so that it can be performed in a short time. Provide a method for confirming attachment / detachment. SOLUTION: An electrostatic chuck 1 includes a substrate 1c, an electrode 1
b, the insulating layer 1a. The amount of electric charge accumulated between the electrode 1b and the wafer 2 is measured, and it is detected that the current value that has increased at the beginning of the voltage application to the electrode has returned to substantially zero, and the attachment operation of the electrostatic chuck is confirmed. When the applied voltage drops to 1/10 or less of the fixed value, the de-operation is confirmed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for confirming the attachment / detachment of an electrostatic chuck for fixing a plate-like object such as a semiconductor wafer. In particular, the present invention relates to a method for confirming attachment / detachment of an electrostatic chuck, which has a high reliability of attachment / detachment confirmation, can reduce the time required for attachment / detachment confirmation of an electrostatic chuck, and can improve the throughput of process processing.

[0002]

2. Description of the Related Art The principle of an electrostatic chuck is that an electrode and an object to be fixed (wafer) are arranged to face each other via an insulating layer, and a high voltage (about 100 to 1,000 V) is applied to the electrode. This is to fix the wafer by generating static electricity of opposite polarity on the chuck side of the wafer. When the electrostatic chuck is put on, a voltage is applied to the electrodes. When the electrostatic chuck is put off, the voltage of the electrodes is dropped to the ground level.

[0003] After the electrostatic chucking operation is completed, the process equipment (exposure apparatus, CVD apparatus, etching apparatus, etc.) equipped with the electrostatic chuck is operated to perform exposure and etching on the wafer. . After the completion of the process, the electrostatic chuck is released, and after the completion of the process, the wafer handling apparatus is operated to take out the wafer out of the process equipment.

[0004] When such an attaching / detaching operation is performed by the electrostatic chuck, it is necessary to confirm the completion of attaching / detaching the wafer and then proceed to the next step. As a method of confirming the attachment / detachment of the electrostatic chuck, a method of calculating a charge amount by integrating a current flowing through the electrostatic chuck with respect to time, and determining that the wearing operation is completed when the charge amount exceeds a certain value, or the like. It is known (JP-A-61-270046, JP-A-7-21).
No. 1768).

[0005]

In such a method of confirming attachment / detachment based on the amount of charge accumulated in the electrostatic chuck,
When an oxide film or nitride film adheres to the back of the Si wafer,
Alternatively, when the thicknesses are different, the amount of charge accumulated between the electrostatic chuck and the wafer is different, and there is a problem that a correct determination cannot be made. Therefore, an object of the present invention is to provide a method capable of correctly determining a detaching operation regardless of the state of a bonding surface of a Si wafer or the like. Another object of the present invention is to provide a method capable of confirming attachment / detachment in a short time.

[0006]

In order to solve the above-mentioned problems, a method for confirming attachment and detachment of an electrostatic chuck according to a first aspect of the present invention is described.
When a voltage is applied to an electrostatic chuck composed of a base, electrodes formed on the base, and an insulating layer covering the electrodes, a current flowing through the electrostatic chuck when a wafer or the like is fixed on the electrostatic chuck. Is measured, and when the current value increased at the beginning of the voltage application is substantially returned to 0, the completion of the attaching operation of the electrostatic chuck is confirmed.

When a constant voltage is applied to the electrodes of the electrostatic chuck, a large current flows at first, as in the case of applying a constant voltage to the capacitor in a stepwise manner. The charging to the capacity between the wafers is completed and the current becomes 0. As described above, the capacitance between the electrostatic chuck and the wafer changes depending on the condition of the back surface of the wafer. However, when the current value becomes 0, the maximum charge is still stored. Therefore, at this time, it is determined that the wearing operation is completed.

According to a second aspect of the present invention, there is provided a method for confirming attachment / detachment of an electrostatic chuck, comprising: applying a voltage to an electrostatic chuck comprising a base, electrodes formed on the base, and an insulating layer covering the electrodes;
After the wafer or the like is fixed on the electrostatic chuck, when the application of the voltage is stopped to release the fixing of the wafer or the like, the voltage applied to the electrostatic chuck electrode is measured, and the voltage is measured. It is characterized in that it is determined that the removal operation of the chuck has been completed at the time when it has decreased to 1/10 or less of the fixed state.

At the time when the voltage is lowered to this level, the chucking force of the electrostatic chuck is considerably weakened, and it can be removed from the chuck without any problem by a wafer handling apparatus. Therefore, the throughput can be improved by removing the wafer and starting processing of the next wafer without waiting until the applied voltage of the electrostatic chuck becomes zero.

In a third aspect of the present invention, there is provided a method for confirming attachment / detachment of an electrostatic chuck, comprising: applying a voltage to an electrostatic chuck comprising a base, electrodes formed on the base, and an insulating layer covering the electrodes;
When a wafer or the like is fixed on the electrostatic chuck, a current flowing through the electrostatic chuck is measured, and the amount of charge accumulated between the chuck and the wafer is calculated by integrating the current with time. Is determined to be a fixed value (saturated charge amount), it is determined that the attaching operation of the electrostatic chuck is completed. Here, (the thickness t of the insulating layer / the relative dielectric constant of the same layer) of the electrostatic chuck is 10 μm or more. It is characterized by doing.

With this configuration, it is possible to check the operation of attaching the electrostatic chuck irrespective of the state of the back surface of the wafer with high reliability.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing the overall configuration of an electrostatic chuck according to one embodiment of the present invention. The electrostatic chuck 1 has a base 1c made of alumina ceramics. The electrode 1b is formed on the upper surface of the base 1c. On the electrode 1b, an insulating layer 1a made of single crystal alumina is formed so as to cover the electrode 1b. The wafer 2 is mounted on the insulating layer 1a.

A power supply 5 is connected to the electrode 1b via a wiring 3a. A voltmeter 6 and an ammeter 7 are provided at the output terminal of the power supply.
Is connected. When a voltage is applied, a charging current for charging the capacitance created between the electrode 1b and the wafer 2 flows through the ammeter 7 and the wiring 3b.

Here, the amount of charge accumulated between the electrode 1b and the wafer 2 when the wafer 2 is chucked by the electrostatic chuck 1 is quantitatively predicted. The insulating layer 1a of the electrostatic chuck is made of alumina having a thickness of 100 microns, a relative dielectric constant ε ^* = 10, and an area of 100 cm ² . On the other hand, a 1 micron thick SiO ₂
Are formed, and the relative dielectric constant of SiO ₂ is set to 3.0.

The capacitance C at the time of adsorption is as follows: C = (8.85 × 10 ⁻¹² × 3 × 10 × 100 × 10 ⁻⁴ ) [mF] / {(10 × 1 + 3 × 100) × 10 ⁻⁶ } [M] = 8.56 × 10 ⁻⁹ [F] (three significant digits). The charge Q induced in the electrostatic chuck when the voltage V is applied is represented by Q = CV. When V is 1000 V, Q = 8.56 × 10 ⁻⁹ [F] × 10 ³ [V] = 8 .56 × 10 ^-6 [coulomb]. On the other hand, in the case of bare silicon, C = 8.85 × 10 ⁻¹² × 10 × 100 × 10 ⁻⁴ [mF] / (100 × 10 ⁻⁶ ) [m] = 8.85 × 10 ⁻⁹ [F] Similarly, the charge Q is as follows: Q = 8.85 × 10 ⁻⁶ [coulomb].

Therefore, the oxide film is 3% less than the wafer.
The charge changes only to the extent. This means that the thickness of the insulating layer of the electrostatic chuck is 100 microns, and the relative dielectric constant ε of the insulating material is
The value of 10 (the thickness of the insulating layer / relative permittivity) is 10 μm, which is a relatively large value. If the ratio is set to 10 μm or more, the difference in the charge amount becomes even smaller. Further, if the landing operation is completed because the current once rises and becomes almost zero, no erroneous judgment occurs because it does not depend on the condition of the wafer.

According to the result of actual measurement of the relationship between the electrostatic chucking force P and the voltage V, it was found that P was proportional to V ² within a range of a measurement error. It is also known that when the insulation resistance is sufficiently large as an insulating material, the electrostatic force becomes zero without delay within a measurable range when the voltage is cut off. Voltage is 1
If it becomes / 10 or less, the electrostatic force is 1/100 or less, so it can be determined that the device is detached.

The circuit for confirming the attachment / detachment of the electrostatic chuck will be described again with reference to FIG. The ammeter 7 is provided with an integrating circuit 8. The integrating circuit 8 integrates the current with respect to time, and the comparing circuit 9 compares the current with the data 10 for each wafer. Here, the data 10 for each wafer includes data such as the charge amount calculated from the thickness of the insulator on the back surface of the wafer and its dielectric constant. 90% of the saturation charge for the wafer
, A preliminary arrival signal 13 is issued. Further, when the output of the ammeter 7 once becomes a large value and thereafter returns to 0, the arrival signal 12 is output. In order to obtain higher reliability, it is more preferable that the suction is completed only when both the signals 12 and 13 are output.

Next, the de-operation will be described. Before removing the wafer, the power supply 5 is turned off. At this time, since the charge described above is accumulated on the electrode 1b and the back surface of the wafer 2, the voltage does not immediately become 0, but becomes 0 by a time constant CR determined by the internal resistance R and the capacitance C of the power supply. Become. As described above, when the output of the voltmeter 6 becomes 1/10 or less of the initial voltage, the de-signal 11 can be issued.

When the power is turned off, the discharge current flows through the wiring 3b, so that the discharge current can be observed by the ammeter 7.
A de-signal may be output when this current once becomes a large negative value and returns to zero. To obtain a more reliable de-signal, de-signaling may be performed when both 11 and 12 de-signals are obtained.

[0021]

As is apparent from the above description, the method for confirming the attachment / detachment of the electrostatic chuck according to the first aspect of the present invention measures the current flowing through the electrostatic chuck, and when the current value becomes 0, the maximum charge is obtained. It is determined that the mounting operation has been completed assuming that the storage operation is completed, so that the attaching / detaching operation can be correctly determined regardless of the state of the bonding surface of the Si wafer or the like. In the method for confirming the attachment and detachment of the electrostatic chuck according to the second aspect of the present invention, the voltage applied to the electrostatic chuck electrode is measured, and when the voltage drops to 1/10 or less of the fixed value, the demounting operation of the chuck is completed. Therefore, the throughput can be improved by removing the wafer and starting the processing of the next wafer without waiting for the applied voltage of the electrostatic chuck to become zero. According to a third aspect of the present invention, there is provided a method for confirming attachment / detachment of an electrostatic chuck, which calculates an amount of electric charge accumulated between a chuck and a wafer, and when the amount of electric charge reaches a certain value (saturated electric charge), the attachment of the electrostatic chuck is determined. In the method for determining that the operation has been completed, the method of (thickness of insulating layer t /
Since the relative dielectric constant of the same layer is 10 μm or more, the attaching operation of the electrostatic chuck can be confirmed irrespective of the state of the back surface of the wafer, and can be confirmed with high reliability.

[Brief description of the drawings]

FIG. 1 is a diagram showing an overall configuration of an electrostatic chuck according to one embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Electrostatic chuck 1a Insulating layer 1b Electrode 1c Base 2 Wafer 3a Wiring 3b Wiring 5 Power supply 6 Voltmeter 7 Ammeter 8 Integrating circuit 9 Comparison circuit 10 Data for each wafer 11 De-signal 12 Landing signal 1 13 Landing signal 2

Claims (3)

[Claims] When applying a voltage to an electrostatic chuck composed of a base, an electrode formed on the base, and an insulating layer covering the electrode to fix a wafer or the like on the electrostatic chuck, Measuring the current flowing through the electrostatic chuck, detecting that the current value increased at the beginning of voltage application has returned to substantially zero, and confirming the completion of the mounting operation of the electrostatic chuck; How to check chuck attachment / detachment. 2. After applying a voltage to an electrostatic chuck composed of a base, electrodes formed on the base, and an insulating layer covering the electrodes to fix a wafer or the like on the electrostatic chuck, When the application of the voltage is stopped and the fixing of the wafer or the like is released, the voltage applied to the electrostatic chuck electrode is measured,
A method for confirming the attachment / detachment of the electrostatic chuck, wherein it is determined that the chuck demounting operation has been completed when the voltage drops to 1/10 or less of the fixed value. 3. When applying a voltage to an electrostatic chuck composed of a base, electrodes formed on the base, and an insulating layer covering the electrodes to fix a wafer or the like on the electrostatic chuck, The current flowing through the electrostatic chuck is measured, and the amount of charge accumulated between the chuck and the wafer is calculated by integrating the current over time. When the amount of charge reaches a certain value (saturated charge), the electrostatic charge is measured. It is determined that the attachment operation of the chuck has been completed, and (the thickness t of the insulating layer / the relative dielectric constant of the same layer) of the electrostatic chuck is 10 μm or more.