JPH1167885A - Substrate holding device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a substrate holding device, in which a circuit is simple, whose reliability and accuracy are high and which can detect the attraction state or the like of a substrate on an electrostatic chuck. SOLUTION: A device comprises a bridge circuit 20, which is provided with capacitors 21 to 26 which are electrically connected to be a rhomb, with a high-frequency power supply 30, which supplies a high frequency across two opposite corner parts (a), (b) in the rhomb and with a measuring instrument which measures a current or a voltage across two remaining opposite corner parts (c), (d) in the rhomb. Then, when an electrostatic chuck 6 is brought close to a substrate 4, a capacitance which is formed by electrode 10, 11 of the electrostatic chuck 6 and the substrate 4 is connected in parallel with the capacitor 24 on one side of the bridge circuit 20.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ion implantation apparatus, an ion beam etching apparatus, and a plasma CVD.
The present invention relates to a substrate holding apparatus that is used in an apparatus, a thin film forming apparatus, and the like, and includes an electrostatic chuck that attracts and holds a substrate to be processed by static electricity. The present invention relates to means for reliably detecting a state or the like with a simple circuit.

[0002]

2. Description of the Related Art FIG. 6 shows an example of a conventional substrate holding device. The substrate holding device includes an electrostatic chuck 6 for attracting and holding a substrate (for example, a semiconductor wafer) 4 by static electricity, and applying a voltage to the electrostatic chuck 6 (more specifically, to its electrodes 10 and 11). A suction power supply 14 for holding the substrate 4 by suction;

The electrostatic chuck 6 of this example is of a so-called bipolar type, in which two electrodes 10 and 11 are connected to an insulator 8.
Embedded near the inner surface. Electrodes 10 and 11
Are embedded in the insulator 8 such that both have a semicircular shape, and both face each other to form a circular shape.

In this example, the power supply 14 for suction is of a bipolar output type composed of two DC power supplies 14a and 14b, outputs DC voltages + V and -V of the same value and opposite polarities, and applies them to the electrostatic chuck. 6 can be applied to each of the electrodes 10 and 11.

When the substrate 4 is supplied onto the electrostatic chuck 6 and the above-mentioned voltage is applied to the electrostatic chuck 6 from the power supply 14 for suction, positive and negative charges are accumulated between the substrate 4 and the electrodes 10 and 11 and work during that time. The substrate 4 is attracted and held on the electrostatic chuck 6 by electrostatic force (or Johnson-Rahbek force). In this state, the substrate 4 can be subjected to a process such as ion implantation by irradiating the substrate 4 with the ion beam 2 or the like.

In such a substrate holding apparatus, the suction state of the substrate 4 on the electrostatic chuck 6 and the like, more specifically, the presence or absence of the substrate 4 and the suction state of the substrate 4 (the electrostatic chuck 6
How strongly the substrate 4 is attracted when a voltage is applied to the substrate 4), the detached state of the substrate 4 (how much the substrate 4 is attracted by residual charges after the voltage to the electrostatic chuck 6 is cut off) Is important from the viewpoints of transport of the substrate 4, prevention of overheating of the substrate 4 during processing, and the like.

As one of means for detecting such a suction state of the substrate 4, there is a technique for measuring a capacitance generated between the electrodes 10 and 11 of the electrostatic chuck 6 and the substrate 4. However, since the change in the capacitance due to the change in the suction state of the substrate 4 is very small (for example, about several pF to several tens of pF), it is necessary to devise to measure this with high sensitivity. Some proposals have already been made.

For example, as a first technology, Japanese Patent Publication No. 6-9
In Japanese Patent No. 1024, an inductance and a capacitor are inserted in series between the electrode of the electrostatic chuck and the high-frequency power supply to set the frequency of the high-frequency power supply close to the series resonance frequency, thereby reducing the output current from the high-frequency power supply. Techniques for increasing the change to improve the measurement sensitivity have been proposed.

A second technique is disclosed in Japanese Patent Application Laid-Open No. 63-1 / 1988.
Japanese Patent Application Laid-Open No. 69244 proposes a technique for improving the measurement sensitivity by providing a reactance oscillation circuit using the above-mentioned capacitance as a resonance circuit and measuring the oscillation frequency of the oscillation circuit.

[0010]

However, in both the first and second prior arts, the resonance of the inductance (L) and the capacitance (C) is used, so that the influence of the temperature change of the measurement system is obtained. In other words, when the temperature of the measurement system changes, the inductance value and the capacitance value change and appear as a change in the resonance frequency. There is a problem of low.

In the first prior art, the capacitance between the electrode of the electrostatic chuck and the substrate is very small (for example, about several tens pF to several hundred pF), and the value of the inductance connected in series to this is reduced. Because there is naturally a limit to increasing it,
In addition to requiring a high-frequency power supply having a high oscillation frequency (for example, 100 kHz or more), if the oscillation frequency of this high-frequency power supply changes and deviates from the series resonance frequency, it becomes a measurement error as it is. Requires a high frequency power supply. Such a high-frequency power supply having a high oscillation frequency and a very high frequency stability has a complicated circuit and is expensive.

In the second prior art, not only an oscillation circuit is required, but also a frequency measurement circuit for accurately measuring the oscillation frequency is required, so that the circuit becomes complicated and expensive. .

SUMMARY OF THE INVENTION Accordingly, it is a primary object of the present invention to provide a substrate holding apparatus capable of detecting the state of suction of a substrate on an electrostatic chuck with a simple circuit and with high reliability and accuracy.

[0014]

According to the present invention, there is provided a substrate holding apparatus comprising: a plurality of capacitors electrically connected in a diamond shape; a high frequency power supply for supplying a high frequency between two diagonal portions of the diamond; A measuring circuit for measuring the current or voltage between the remaining two diagonals of the bridge circuit,
And when a substrate is brought close to the electrostatic chuck, a capacitance formed between an electrode of the electrostatic chuck and the substrate is connected in parallel to a capacitor on one side of the bridge circuit. It is characterized by having.

According to the above configuration, the capacitance between the electrode of the electrostatic chuck and the substrate changes depending on the presence or absence of the substrate on the electrostatic chuck and the state of suction, and this change changes the equilibrium state of the bridge circuit. And the change appears in the measured value of the measuring instrument. Therefore, the presence or absence of the substrate on the electrostatic chuck and the state of suction of the substrate can be detected based on the measurement value of the measuring device.

Furthermore, since a bridge circuit is used in the measurement system, the bridge circuit is hardly affected by the temperature change because the equilibrium state of the bridge circuit hardly changes even if the temperature of the entire bridge changes. High reliability and accuracy of detection.

In addition, the bridge circuit is generally simple in circuit, and its high-frequency power source does not require high frequency and high frequency stability as in the prior art.
The circuit configuration is simplified and the cost is reduced.

[0018]

FIG. 1 is a diagram showing an example of a substrate holding device according to the present invention. Parts that are the same as or correspond to those in the conventional example of FIG. 6 are denoted by the same reference numerals, and differences from the conventional example will be mainly described below.

This substrate holding apparatus is a so-called capacitive or high-frequency bridge which uses a high-frequency power supply as a power source and forms a diamond-shaped four side with a plurality of capacitors in addition to the electrostatic chuck 6 as described above. The circuit 20 is provided.

As shown in FIG. 2, the bridge circuit 20 has four groups of capacitors: a capacitor 21, a capacitor 22, capacitors 23 and 24 connected in series with each other, and a capacitor 25 connected in series with each other. And 26 are electrically connected in a diamond shape, and a high-frequency power supply 30 is connected between two diagonal portions a and b of the diamond shape,
A measuring instrument 32 for measuring current or voltage is connected between the remaining two diagonal portions c and d.

The high frequency power supply 30 outputs a high frequency power and supplies it between the diagonal portions a and b. This bridge circuit 2
0 does not utilize the resonance of the LC as in the prior art, and the high frequency power supply 30 simply provides an appropriate impedance (capacitive reactance in this example) to the capacitors 21 to 26.
Therefore, the frequency of the high frequency output from the high frequency power supply 30 does not need to be as high as that of the prior art. For example, the frequency of the high frequency output from the high-frequency power supply 30 may be about several kHz to several tens kHz, more specifically, about 10 kHz. The capacitor 27 connected between the point b in FIG. 1 and the ground (that is, the high-frequency power supply 30 via the ground) passes the high frequency output from the high-frequency power supply 30, but is output from the suction power supply 14. And does not affect the essence of the bridge circuit 20. Therefore, it is omitted in the equivalent circuit of FIG.

The measuring device 32 is a voltmeter or a voltage measuring circuit for measuring a voltage generated between the diagonal portions c and d, or an ammeter or a current measuring circuit for measuring a current flowing between the diagonal portions c and d. is there.

In this example, the electrostatic chuck 6 is of a bipolar type having two electrodes 10 and 11 as in FIG. 6, and these two electrodes 10 and 11 connect one side of the bridge circuit 20 to one side. The capacitor 24 is connected in parallel to both ends of the capacitor 24. When the substrate 4 is supplied to the electrostatic chuck 6 and brought into proximity (for example, by suction), as shown in FIG.
A capacitance C ₅ is generated between one electrode 10 and the substrate 4,
A capacitance C ₆ is generated between the other electrode 11 and the substrate 4. Therefore, when the electrostatic chuck 6 is connected as described above, the capacitances C ₅ and C ₆ connected in series to each other are connected.
Are connected in parallel to the capacitor 24. In addition,
Since both electrodes 10 and 11 usually have the same shape and the same area, C ₅ = C ₆ .

The electrostatic chuck 6 connected as described above
In order to supply the DC voltages + V and -V for suction from the power supply 14 for adsorption without disturbing the equilibrium state of the bridge circuit 20, one of the power supplies 14 for adsorption (in this example, ) The output is connected to the connection e between the capacitors 23 and 24 via the resistor 41 and the electrode 10 and the connection f between the capacitors 25 and 26 via the resistor 42 having the same value as the resistor 41. Also connected. The other output section (that is, the −V side in this example) of the suction power supply 14 is connected to the connection section b and the electrode 11 via a resistor 43. With this configuration, the suction power supply 14
Is connected symmetrically with respect to the bridge circuit 20, the power supply 14 for adsorption does not disturb the equilibrium state of the bridge circuit 20, so that the stability of the circuit with respect to a temperature change or the like is further improved. Since the circuit of the power supply 14 for suction does not affect the equilibrium state of the bridge circuit 20 as described above,
It is omitted in the equivalent circuit of FIG. Resistors 41-
43 is a power supply for suction 14
It also works to prevent leakage to the side. These resistors 41-
An inductor may be used instead of 43 (further, resistors 44 and 45 described later).

The bridge circuit 20 includes the electrostatic chuck 6
It is preferable that the equilibrium state is set when there is no substrate 4 above, and the value of the measuring instrument 32 is set to 0. The reason will be described later. Specifically, the substrate 4 is placed on the electrostatic chuck 6.
When there is no, since the magnitudes of the capacitances C ₅ and C ₆ are so small that they can be regarded as 0, as shown in FIG.
Assuming that the values of the capacitances of the combination of the capacitors 25 and 24 and the combination of the capacitors 25 and 26 are C _{1 to} C ₄ , respectively, as is well known as the equilibrium condition of the bridge circuit, Is set so that

[0026]

## EQU1 ## C ₁ = C ₂ and C ₃ = C ₄

The magnitudes of the capacitances C ₅ and C ₆ are as follows:
It changes depending on the presence or absence of the substrate 4 on the electrostatic chuck 6, the state of suction of the substrate 4, and the state of detachment of the substrate 4. In particular,
The magnitude of each of the capacitances C ₅ and C ₆ is C ₁₁ when the substrate 4 is not on the electrostatic chuck 6, and C ₁₁ when the substrate 4 is merely placed on the electrostatic chuck 6. ₁₂ ,
C ₁₃ those when adsorbed substrate 4 to the electrostatic chuck 6,
When those after turning off the voltage to the electrostatic chuck 6 after adsorbed C _14, typically, a _{C 11 <C 12 <C 14} <C 13. This is because the stronger the suction of the substrate 4 to the electrostatic chuck 6, the smaller the distance between the substrate 4 and the electrodes 10 and 11, and the larger the capacitance between them.
C ₁₁ can be regarded as 0, as described above. C ₁₄ is larger than C ₁₂ while the adsorption force due to the residual charge remains.

Therefore, when the above configuration is adopted, the magnitudes of the capacitances C ₅ and C ₆ depend on the presence or absence of the substrate 4 on the electrostatic chuck 6, the state of suction of the substrate 4, and the state of separation of the substrate 4. This change changes the capacitance of one side of the bridge circuit 20 to change the equilibrium state of the bridge circuit 20, and the change appears as a large change in the measurement value of the measuring device 32. Therefore, according to the measurement value of the measuring device 32,
The presence / absence of the substrate 4 on the electrostatic chuck 6, the suction state of the substrate 4, and the detachment state of the substrate 4 can be detected. Substrate 4
In the adsorption state of strongly adsorbed, middle suction, there is a weak suction, the size of the electrostatic capacitance C ₅ and C ₆ are changed by these different, because it appears in the measured value of the measuring instrument 32 ,
These adsorption states can also be distinguished.

Moreover, in this substrate holding apparatus, the bridge circuit 20 is used in the measurement system. Even if the entire bridge circuit 20 changes in temperature, there is almost no change in its equilibrium state. Less susceptible to disturbances such as drift. Therefore, the reliability and accuracy of detecting the suction state of the substrate 4 and the like are high.

Further, since the bridge circuit 20 can basically be constituted by four or four groups of capacitors, the high-frequency power supply 30 and the measuring instrument 32, the circuit constitution is simpler than that of the prior art. In addition, the high frequency power supply 30 does not require a high frequency as in the prior art, and the fluctuation of the frequency of the high frequency power supply 30 causes almost no change in the equilibrium state of the bridge circuit 20 in principle. Does not require stability. Therefore, the circuit configuration of the bridge circuit 20 is simplified and the cost is reduced.

As described above, the bridge circuit 20
Is preferably set so that when the substrate 4 is not present on the electrostatic chuck 6, the equilibrium state is established and the value of the measuring instrument 32 becomes 0. In such a case, adjustment of the measuring instrument 32 and the like are performed. It will be easier. For example, even when the measuring device 32 is configured by a combination of an operational amplifier and the like, it is only necessary to adjust the output to zero when the substrate 4 is not present.
Is easy to adjust the zero point.

The display of the measuring instrument 32 is set to 0 when the substrate 4 is not on the electrostatic chuck 6 and set to the maximum scale (full scale) when the substrate 4 is attracted to the maximum, and the interval between the two is set to, for example, By allocating on the linear scale,
The various states of the electrostatic chuck 6 from the case where the substrate 4 is not on the electrostatic chuck 6 to the maximum suction state are measured by the measuring device 32.
Can be easily and accurately known.

In recent years, the surface of the substrate 4 is usually covered with an oxide film such as SiO ₂ having a thickness of, for example, about 1000 to 10000 °. Since the maximum output value of the measuring device 32 differs depending on the thickness of the oxide film, the thickness of the oxide film on the substrate 4 can be confirmed before the processing by the maximum output value of the measuring device 32. .

Further, as shown in FIG. 3, the substrate 4 adsorbed and held on the electrostatic chuck 6 is grounded by pins 50 and leaf springs 52 embedded in the electrostatic chuck 6 and ion-implanted. Processing is often performed. This is because grounding the substrate 4 is effective in preventing the substrate 4 from being charged (charged up) due to ion implantation or the like. Although the surface of the substrate 4 is covered with a thin oxide film (not shown) as described above, if the substrate 4 is normally adsorbed, the thin oxide film is usually broken at the tip of the pin 50.
The substrate 4 can be grounded by bringing the tip of the pin 50 into contact with the substrate 4.

In the above case, when the substrate 4 is properly grounded by the pins 50, the grounding path 5 indicated by a two-dot chain line in FIG.
4 is formed, thereby shorting the capacitance C _6, so that the capacitance inserted in parallel with the capacitor 24 is
Only becomes capacitance C _5, approximately doubles when the substrate 4 is not grounded. This is usually a C ₅
= C ₆ , and the capacitance inserted in parallel with the capacitor 24 is C ₅ C ₆ / (C ₅ +
C ₆₎ = C _5/2 next, if there is a ground path 54 C
_Because it becomes ₅ . When the substrate 4 is grounded when the substrate 4 is attracted to the electrostatic chuck 6 due to the sudden change in the capacitance, the measured value of the measuring instrument 32 rapidly increases, thereby detecting that the substrate 4 is correctly grounded. It is also possible. That is, the bridge circuit 20 can be used as a ground monitor for the substrate 4.

The electrostatic chuck 6 is not limited to the bipolar type as in the above example, but may have one electrode or three or more electrodes. For example, FIG. 4 shows an example in which a three-electrode type electrostatic chuck 6 having three electrodes 10 to 12 having a 円 circle shape is used. Also in this example, similarly to the example of FIG. 1, in order not to disturb the equilibrium state of the bridge circuit 20, a DC voltage -V from the DC power supply 14c of the power supply 14 for adsorption to the third electrode 12 is applied. Is supplied using resistors 44 and 45 having the same value. The operation of detecting the suction state or the like of the substrate 4 by the bridge circuit 20 is the same as in the example of FIG. When the electrostatic chuck 6 is of a three-pole type as described above, the suction power supply 14 may be a symmetric three-phase AC power supply.

In the case of a multipolar electrostatic chuck 6 having four or more electrodes, the number of capacitors, DC power supplies, resistors and the like can be increased in the same way as the circuit is increased from FIG. 1 to FIG. Good.

FIG. 5 shows an example in which a monopolar electrostatic chuck 6 having one circular electrode 10 is used.
Shown in Also in this example, in order not to disturb the equilibrium state of the bridge circuit 20, the supply of the DC voltage + V from the DC power supply 14a of the suction power supply 14 to the electrode 10 is performed by using resistors 41 and 42 having the same value as each other. I am using it. Even when the electrostatic chuck 6 is of such a monopolar type, the substrate 4 on the electrostatic chuck 6 is formed by the grounding pins 50 as described above, plasma formed near the surface of the substrate 4 during processing, and the like. A ground path 56 is formed as shown by a two-dot chain line in FIG. 5, and a capacitance formed between the electrode 10 and the substrate 4 passes through the ground path 56 and Since it is connected in parallel with the capacitor 24, the state of suction of the substrate 4 can be detected by the bridge circuit 20 in the same manner as in the example of FIG.

[0039]

As described above, according to the present invention, the presence / absence of the substrate on the electrostatic chuck and the suction state thereof can be detected based on the measurement value of the measuring device constituting the bridge circuit. In addition, since the bridge circuit is less susceptible to disturbances such as temperature changes, detection reliability and accuracy are high. In addition, the bridge circuit generally has a simple circuit configuration, and its high-frequency power supply does not require a high frequency and a high frequency stability as in the related art, so that the circuit configuration is simplified and the cost is reduced. Become cheap.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of a substrate holding device according to the present invention.

FIG. 2 is an equivalent circuit diagram around a bridge circuit in FIG.

FIG. 3 is a sectional view partially showing an example of an electrostatic chuck having a grounding pin;

FIG. 4 is a diagram showing another example of the substrate holding device according to the present invention.

FIG. 5 is a view showing still another example of the substrate holding device according to the present invention.

FIG. 6 is a diagram illustrating an example of a conventional substrate holding device.

[Explanation of symbols]

 Reference Signs List 4 substrate 6 electrostatic chuck 8 insulator 10 to 12 electrode 14 power supply for adsorption 20 bridge circuit 21 to 29 capacitor 30 high frequency power supply 32 measuring instrument

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI H01J 37/20 H01J 37/20 A H02N 13/00 H02N 13/00 D

Claims (1)

[Claims] 1. An electrostatic chuck having one or more electrodes in an insulator and holding a substrate by electrostatic attraction, a suction power supply for applying a voltage to the electrodes of the electrostatic chuck to suck and hold the substrate, and In the substrate holding device comprising: a plurality of capacitors electrically connected in a diamond shape; a high-frequency power supply for supplying a high frequency between two diagonal portions of the diamond shape; and a current between the remaining two diagonal portions of the diamond shape. Or a bridge circuit having a measuring device for measuring voltage, and when a substrate is brought close to the electrostatic chuck, the capacitance formed between the electrode of the electrostatic chuck and the substrate is the capacitance. A substrate holding device configured to be connected in parallel to a capacitor on one side of a bridge circuit.