JPH07130827A - Electrostatic wafer chuck - Google Patents

Abstract

PURPOSE:To find whether a wafer is chucked or not positively and readily by providing a power supply part, and providing a detecting part, which detects the change in flowing AC current or AC voltage when the AC voltage is applied into an electrostatic chuck from the power supply. CONSTITUTION:A function, which outputs the AC voltage together with the high DC voltage in the overlapped pattern into a power supply part 1, is provided. The power supply part 1 applies the voltage into a means for measuring the capacitance of the gripper of an electrostatic chuck constituted of an electrode plate 2, a dielectric film 4 and a material 5, e.g., into the electrode plate 2. A detector 6, which detects the AC signal, i.e., the AC voltage or the AC current, outputted as a result of the application of the AC voltage into the gripper, is provided. When the frequency of the AC voltage is set at somewhat high frequency, the resistance R among the material 5, the dielectric film 4 and the electrode 2 can be disregarded, and only the capacitance C acts. When the AC current is detected with an ammeter 6 at this time, the capacitance C is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrostatic chucking device for holding and carrying a wafer in a vacuum, and more particularly to detecting whether or not a wafer is placed in the electrostatic chucking device. The present invention relates to necessary semiconductor manufacturing equipment and semiconductor evaluation equipment.

[0002]

2. Description of the Related Art Conventionally, as electrostatic attraction devices, there are, for example, JP-A-58-114437, JP-A-59-79545, and JP-A-4-308442.

[0003]

In a semiconductor manufacturing / evaluating apparatus, an electrostatic adsorption device is used to adsorb and hold or convey a wafer. In this case, it is confirmed whether or not the wafer is adsorbed with certainty. This is very important. If the wafer is not adsorbed correctly, the manufacturing apparatus cannot correct the warp of the wafer, resulting in defective processing dimensions, and the wafer is dropped in the transfer apparatus, resulting in damage. For this reason, a means for confirming the adsorption state is required.

However, in the disclosed example disclosed in Japanese Patent Application Laid-Open No. 58-114437, there is no consideration of means for confirming whether or not the wafer is surely sucked and held by the suction device.

Further, in the disclosed example disclosed in Japanese Patent Laid-Open No. 59-79545, the confirmation is made by the current value flowing in the power supply circuit constituting the electrostatic attraction device as the attraction confirmation means. Over time, an insulating film such as an oxide film is formed on the back surface of the wafer, which is the adsorption surface, and this insulating film causes a problem that the current value is extremely reduced and monitoring becomes impossible. Specifically, in an example of the inventor's experiment by this method, the current value was about 2 μA for a new bare wafer, but it was about 0.2 μA for a wafer having an oxide film on the back surface, and this value was It is almost equal to the current value when it is not mounted and cannot be monitored.

Further, in the disclosed example disclosed in Japanese Patent Application No. 4-308442, a plurality of distance sensors are embedded in the electrostatic adsorption device and the adsorption state is judged from the output value of each sensor. However, it has the drawback of being complicated and costly.

An object of the present invention is to provide an electrostatic chucking device which can surely and easily know whether or not a wafer has been sucked.

[0008]

Means for Solving the Problems The above-mentioned object is to measure the electrostatic capacity of an adsorption portion of an electrostatic adsorption device composed of an electrode plate, a dielectric and an object to be adsorbed, for example, applying a voltage to the electrode plate. The power supply unit is equipped with a function to superimpose and output the AC voltage together with the high-voltage DC voltage, and the AC signal (AC voltage or AC current) output as a result of this AC voltage being applied to the adsorption unit.
This is achieved by providing a detection device that detects

[0009]

The principle of the present invention is shown in FIG. This figure illustrates the principle of the present invention for a monopolar electrostatic adsorption device.

The electrostatic attraction device applies a high voltage between the object to be attracted and the electrode plate through an insulating dielectric film, and at this time, the electrostatic attraction force generated between the object to be attracted and the electrode plate is applied. This is a device that utilizes the adsorption target to adsorb and hold the adsorption target on the electrode plate.

When a direct current high voltage is applied to the electrode plate 2 from the power source 1, a dielectric polarization is generated inside the dielectric film 4, and a polarity opposite to that of the voltage applied to the electrode plate side of the dielectric film 4 is generated. A charge distribution σ that has is generated. Along with this, a charge distribution −σ having the same capacity and opposite polarity is generated on the opposite surface of the dielectric film 4, and a charge distribution σ is generated on the surface of the adsorption target 5. At this time, an electrostatic attraction force (Johssen-Rahbeck effect) is generated due to the charge distribution generated in the dielectric film 4 and the attracted substance 5, and the attracted substance 5 is attracted to the dielectric film 4. The adsorption force f generated here per unit area can be calculated by dividing the dielectric constant of a vacuum by ε ₀ , the dielectric constant of a dielectric by ε ₁ , the potential difference between an object to be attracted and an electrode by V, and the thickness of the dielectric by d. If

[0012]

[Equation 1]

[0013]

FIG. 1B shows an equivalent circuit of the electrostatic attraction device. V is the voltage applied between the electrode plate and the object to be adsorbed, C
_a and _Ra are the capacitance value and resistance value between the adsorbent and the dielectric,
C _b and R _b are the capacitance value and resistance value between the dielectric and the electrode plate. In the conventional method, the current value flowing through the electrostatic adsorption device was monitored to confirm whether or not the wafer was adsorbed. If adsorbate is bare wafer, C _a since the resistivity of the wafer is negligible is R _a at most 10Ωcm, C _b,
Although it depends on R _b , in the steady state, the flow depends only on R _b which is the resistance value of the dielectric. If the adsorption state is insufficient or the wafer is tilted, the resistance value R _a between the wafer and the dielectric cannot be ignored and the current will not flow. However, in a wafer that has undergone a thermal diffusion oxide film generation process used in the fabrication of gate oxide films in the IC manufacturing process,
While on the back surface of the wafer oxide film of the insulating film is produced, the resistance value R _a between this wafer wafer and dielectric current does not flow very large, it becomes impossible to monitor by the current value.

There is also a method of monitoring the transient current value flowing at the moment when the applied voltage V is applied. However, this method also has a small current value, and the wafer with an oxide film has a lower current value, and the transient current Since it is difficult to detect because of the existence, it is difficult to determine the adsorption state. In one example, the peak value of the transient current is about 10 μA for a bare wafer and about 5 μA for a wafer with an oxide film.

In the electrostatic adsorption device of the present invention, the power source 1 for applying a voltage to the electrode plate 2 is provided with a function of superimposing an AC voltage together with a high-voltage DC voltage and outputting the same, and the AC voltage is applied to the adsorption portion. An ammeter (detection device) 6 for detecting an AC signal (AC voltage or AC current) output by is provided. In the equivalent circuit of FIG. 1B, even if there is an oxide film on the back surface of the wafer, the film thickness is from several tens of to several thousand.
Since it is Å, it can be regarded as shown in FIG. If the frequency of the AC voltage is set to a high frequency to some extent, the resistance R between the object to be adsorbed 5, the dielectric film 4, and the electrode plate 2 can be ignored, so it can be considered that only the electrostatic capacitance C acts. When i is detected, the electrostatic capacitance C can be obtained by C = i / (dV / dt). Therefore, if the applied AC voltage V is fixed and the AC current i is detected, the magnitude of the current value i can be used to determine the magnitude of the electrostatic capacity.
If the adsorption state is good, the electrostatic capacity is large, so the adsorption state can be monitored.

FIG. 2 shows an example of another detection method. Power supply 1
AC voltage V is applied to the adsorption portion of the electrostatic capacitance C. Assuming that the load impedance on the input side of the ammeter 6 is Z, the voltage detected by the ammeter 6 is the AC voltage V of the transfer function C · Z.
The voltage converted by s / (CZZs + 1). Figure 2
As shown in (b), the angular frequency ω (1
When an alternating current of (/ 2πf, f: frequency of alternating voltage) is input, the voltage value detected by the ammeter 6 increases as the electrostatic capacitance C of the adsorbing portion increases, and the presence or absence of a wafer can be monitored. .

The principle described above can be similarly applied to the bipolar type.

FIG. 3A shows a principle diagram of the bipolar type, and FIG. 3B shows an equivalent circuit diagram. C _a and R _a are the capacitance and resistance between the adsorbate and the dielectric, C _b and R _b are the capacitance and resistance between the dielectric and the electrode plate, and R _w is the adsorbate. The internal resistance value.

Regarding the method of monitoring the adsorption state by current detection, in the bipolar type, the steady current flowing due to the resistance of _Rb between the dielectrics and the charge generated by the dielectric polarization in the adsorption target flow inside the adsorption target. An electric current is generated, but when an oxide film is present on the back surface of the wafer, _Ra becomes large and no electric current flows inside the object to be adsorbed, so that it cannot be monitored. However, in the method of measuring capacitance,
Even if there is an oxide film on the back surface, it can be ignored because the oxide film thickness is thin, and it is possible to monitor like the monopolar type.

In the electrostatic attraction device described above, the dielectric film 4 is conventionally made of an insulating film such as Al ₂ O ₃ or S.
Although iO ₂ is used, if a semiconductor dielectric film such as SiC is used, the resistivity is low, the non-dielectric constant is high, and the dielectric strength is high, so the adsorption force can be increased, and the attachment / detachment time can be shortened. Therefore, there is an advantage that the mechanical strength can be increased.

[0022]

FIG. 4 shows an embodiment of the present invention, which is an example of a wafer holder using a bipolar electrostatic chuck.

In FIG. 4, 11 is a power source, 12 and 13 are bipolar electrode plates, 14 is a dielectric film, 15 is an ammeter, and 16
Is a wafer, 17 is an insulating spacer, and 18 is a holder base.

The power supply 11 comprises a DC voltage generator 31, an AC voltage generator 32, and a DC / AC voltage superimposing unit 33,
The DC / AC voltage superimposing unit 33 superimposes the DC voltage generated by the DC voltage generating unit 31 and the AC voltage generated by the AC voltage generating unit 32, and applies the superimposed voltage to the electrode plates 12 and 13. The DC voltage is a voltage applied to obtain the attraction force, and is usually several hundreds.
The voltage is set to about 1 kV from V. The voltage applied to the electrode plates 12 and 13 may be + or −, but if the same voltage of + and − is applied, the potential applied to the wafer becomes 0 V (GND potential) and it is safe in terms of electrostatic breakdown to the elements on the wafer. Therefore, + V and -V are usually applied to both electrodes. The attraction force depends on the potential difference applied between the electrodes, and the greater the potential difference, the greater the attraction force. When a semiconductor dielectric film is used as the dielectric film, an attracting force of about 100 g / cm ² is generated at an applied voltage of ± 200V. The AC voltage is a signal for measuring the electrostatic capacity, and is usually several kHz to several tens kHz and several V to several tens.
The AC voltage is V. The electrodes 12 and 13 are attached to a holder base 18 via an insulating spacer 17, and a dielectric film 14 is laminated thereon. A semiconductor dielectric film, for example, SiC having a specific resistance of 10 ⁹ to 10 ¹¹ is used as the dielectric film. The ammeter 15 is composed of a capacitor 34, a rectifier circuit unit 35, and a low-pass filter unit 36. The capacitor 34 takes out only the AC component of the voltage output from the adsorption unit, rectifies it into a DC pulsating flow by the rectifier circuit 35, and then the low-pass filter. The pulsating flow is smoothed by the filter unit 36 to obtain a DC voltage. This DC voltage value is a voltage value related to the electrostatic capacity of the adsorption unit, and the adsorption state is determined by comparing the voltage values. In an example of an experiment by the inventor, an output value of a bare silicon wafer is about 30 mV, an output value of about 10 mV without adsorbing the wafer, and an output value of about 30 mV on a silicon wafer having an oxide film on the back surface. It is possible to monitor regardless of the state.

FIG. 5 shows a second embodiment of the present invention, which is an example in which a monopolar adsorption device is used as a wafer transfer arm.

In FIG. 5, 11 is a power source, 12 is a unipolar electrode plate, 14 is a dielectric film, 15 is an ammeter, 16 is a wafer, 19 is a needle electrode for conducting to the wafer, 2
Reference numeral 0 is an arm drive unit, 21 is a CPU, and 37 is an arm base.

The voltage generated by the power source 11 is applied to the electrode plate 12. Normally, in the unipolar electrostatic adsorption, a voltage of several 100 V to 1 kV is applied to the electrode plate 12, and the wafer 16 is set to the GND potential by the needle electrode 19. The needle electrode 19 is fixed to the arm base 37 via a leaf spring 38.

When the wafer is placed on the transfer arm, the CPU 21 applies a voltage obtained by superimposing an AC voltage on a DC voltage from the power supply 11. The alternating current is measured by the ammeter 15 and it is confirmed whether or not the wafer is adsorbed. If there is no wafer or if there is a wafer and it is placed diagonally, the current value is low, so it is judged as an error and the processing is stopped. When it is determined that there is a wafer, the CPU 21 controls the arm drive unit 20 to drive the arm. After driving, the output of the ammeter 15 is confirmed again to confirm that the wafer is on the arm, the voltage of the power supply 11 is cut off, and the process is ended.

In the automatic recovery process after the transfer arm is stopped due to a power failure or the like, a voltage is applied from the power supply 11 and an alternating current is measured by the ammeter 15 to confirm whether or not the wafer is on the arm. When the wafer is on the arm, the return processing operation is performed and the automatic return is completed.

[0030]

According to the present invention, whether or not a wafer is adsorbed and held on the electrostatic adsorption device can be detected reliably and simply regardless of the condition of the back surface of the wafer.

[Brief description of drawings]

FIG. 1 is a principle diagram of the present invention.

FIG. 2 is a second principle diagram of the present invention.

FIG. 3 is a third principle diagram of the present invention.

FIG. 4 is a diagram showing an example of the present invention.

FIG. 5 is a diagram showing a second embodiment of the present invention.

[Explanation of symbols]

1, 11 ... Power source, 2, 3, 12, 13 ... Electrode plate, 4, 1
4 ... Dielectric film, 5 ... Object to be adsorbed, 6, 15 ... Ammeter, 14
... Dielectric film, 16 ... Wafer, 17 ... Insulating spacer, 1
8 ... Holder base, 19 ... Needle electrode, 20 ... Arm drive part, 21 ... CPU, 31 ... DC voltage generation part, 32 ... AC voltage generation part, 33 ... DC / AC voltage superposition part, 35 ... Rectifier circuit, 36 ... Low-pass filter, 38 ... Leaf spring.

Claims (4)

[Claims] 1. An electrostatic attraction device comprising an electrode plate and a dielectric film laminated on the surface of the electrode plate, wherein a voltage is applied to the electrode plate to adsorb non-adsorbed substances. A power supply including a DC power supply unit and an AC power supply unit so that voltages can be superimposed and applied, and detection for detecting a change in an AC current or an AC voltage flowing when the AC voltage is applied from the power supply to the electrostatic adsorption device. An electrostatic adsorption device for wafers, characterized by being provided with a container. 2. A wafer electrostatic device according to claim 1, wherein the electrode plate is divided into two or more parts, and a potential difference is applied between the divided electrode plates to adsorb the dielectric substance and an object to be adsorbed. Adsorption device. 3. The electrode plate according to claim 1, wherein the electrode plate is a single flat plate, and a needle-like electrode for conducting a non-adsorbed substance to an arbitrary potential is provided, thereby providing a space between the electrode plate and the attracted substance. An electrostatic chucking device for a wafer, wherein a dielectric potential and an object to be attracted are attracted to each other by causing a potential difference between the electrodes. 4. The method according to any one of claims 1 to 3, wherein the dielectric film is made of a semiconductor dielectric material, and a large attractive force can be generated and a non-adsorbed material can be instantly attached / detached. Wafer electrostatic adsorption device characterized in that