JPS5967629A - Electrostatic attracter - Google Patents

Abstract

PURPOSE:To bring attracting force in the case when an object to be attracted is taken away of an attracting base to approximately zero by measuring the attracting force of the object and generating erased charges corresponding to the measuring value in the attracting base. CONSTITUTION:A wafer 1 is placed on electrodes 4, 5, the surfaces thereof are coated with insulating layers 4a, 5a, and voltage is applied to the electrodes 4, 5 from a voltage generating section 10, thus attracting and fixing the wafer 1 to the electrodes 4, 5. Voltage applied to the electrodes 4, 5 is brought to zero when removing the wafer 1, and the attracting force of the wafer 1 is measured by an exfoliating-force generating section 13, a displacement member 12, a positional detector 14 and a chucking control section 15. Voltage of polarity reverse to one in case of attraction is applied to the electrodes 4, 5 so that attracting force is minimized in response to the measuring value. Accordingly, charges charged to an insulating layer 3 such as silicon oxide coating the surface of the wafer 1 are removed, and the wafer 1 is not subject to stress and can be removed. The wafer 1 is not attracted to an arm for carrying, etc. by residual charges.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus for electrostatically adhering an object, and more particularly to an electrostatic adsorbing apparatus for forcing a semiconductor wafer into a flat shape and adsorbing and fixing the object.

As a lithography system that can efficiently process submicron-sized patterns, an X-ray exposure system has been considered that places a mask and wafer in a vacuum and performs exposure at a position a finite distance away from an X-ray source. In this type of apparatus, it is necessary to fix and hold the surface of the wafer in a flat state in a vacuum, and chucking apparatuses that utilize electrostatic force have been proposed to meet this need. However, when a silicon wafer (hereinafter referred to as a wafer) is adsorbed using a chuck (adsorption stand) that uses electrostatic force, an insulating layer such as a silicon oxide film or nitride film is often formed on the surface, Even if the voltage applied to the suction table is later changed to O■, the suction force may continue to act between the wafer and the suction table.This may make it impossible to remove the wafer from the fixed state, or even if external force is applied. Even if it were removed, if the back side of the wafer was brought into contact with a conductive plate other than the suction table, the wafer would be attracted there, which prevented it from being put to practical use. The reason why this phenomenon occurs is that when the sea urchin is chucked, the electric charge induced in the wafer by the electric field applied from the electrode of the suction table enters the insulating layer such as the silicon oxide layer.
This is because even if the voltage applied to the electrode of the suction table is O2, the charge remains trapped in the insulating layer and cannot be moved, and this charge induces charges in other metal plates other than the suction table.

The present invention solves these drawbacks and reduces the applied voltage during adsorption to O
(2) The object of the present invention is to provide an electrostatic adsorption device that can reduce the attraction force acting between the object and the adsorption table or other conductor to a level that poses no problem in practice.

In other words, the electrostatic adsorption device of the present invention to achieve this purpose includes a suction table on which an object such as a conductor or semiconductor is placed and electrostatically adsorbed, and a measurement device that measures the adsorption force of the adsorbed object. Means and object? 1/ Erasing charge generating means for generating an electric charge on the suction table in an amount corresponding to the measured value of the measuring means so as to erase the electric charge, and the suction force is reduced when the object is removed from the suction table. It is characterized by being set to zero.

In one embodiment, the measuring means includes a peeling force generating means that comes into contact with an object to generate a peeling force from the adsorption table on the object and detects the peeling force as an adsorption force. In this case, the peeling force of the peeling force generating means is limited to a magnitude that does not damage the object.

Further, the erasing charge generating means intermittently applies a reverse voltage having a polarity opposite to that at the time of attraction and whose absolute value increases sequentially to the suction table, and after applying the reverse voltage, the peeling force generating means Detection of the peeling force is sequentially repeated, and the reverse voltage value when the detected peeling force becomes the minimum is set as the voltage for reducing the adsorption force to approximately zero.

The present invention will be described below with reference to the illustrated embodiments.

FIG. 1 is a sectional view showing an embodiment of the present invention with a functional block attached thereto. It is assumed that a pattern 2 is formed on the top surface of the semiconductor wafer 1, and the back surface is covered with an insulating layer 6 such as silicon oxide. Reference numerals 4 and 5 are a pair of flat TA electrodes constituting a suction table (fixed base) for suctioning the wafer 1, and the surfaces of the electrodes 4 and 50 are covered with insulating layers 4a and 53. Furthermore, a voltage from a voltage generating section 10 is applied to the electrodes 4 and 5 through conductive wires 8 and 9 via a resistor 11 connected in series. The peeling force generating section 13 is connected to the deflection member 12
is deflected to generate a force of arbitrary magnitude in the direction of arrow Z, and this force is applied directly to the wafer 1 to move the wafer 1 to the electrodes 4,
A force that tries to move away from 5, that is, a peeling force is generated.

Further, the peeling force generating section 13 incorporates a strain gauge powder adsorption force measuring means for measuring the Z-direction stress of the deflection member 12, that is, the adsorption force of the wafer 1.

Needless to say, the magnitude of the peeling force can be controlled from the outside.

For example, the peeling force generating section 16 includes an L motor, an electromagnetic solenoid, etc.
The information is transmitted to the deflection member 12 using one structure or the like. Alternatively, the driving force may be transmitted to the phase 12 via a spring material (i41), and the adsorption force of the wafer 1 may be measured from the deflection 51 of the spring material.

The position detector 14 is specifically a photoelectric non-contact limit switch or the like, and detects the deflection of the deflection member 12.

The chucking control section 15 controls the output voltage of the voltage generation section 10, which also functions as an erase charge generation means, and controls the q1jlJj force generated by the peeling force generation section 13.
The position detection signal from the position detector 14 is input to centrally control the entire device.

Here, the operation of the peeling force generating section 16 including the adsorption force measuring means and the position detector 140 will be explained in detail using FIG. 2 (a and (b)). Fig. 2 (b) is a characteristic diagram in which the peeling force F of No. 13 is set on the vertical axis and the time t is set on the horizontal axis. It is a characteristic diagram of the position detector 14. This peeling force is measured by a stress sensor such as a strain gauge that measures the stress of the deflection member 12 as described above. It is assumed that the deflecting member 12 hits the wafer 1.The peeling force generating unit 13 monotonically deflects the deflecting member 12 in the direction in which the wafer 1 is lifted from tl[4,5] from time 0 to ts. The power is emitted 1'.

Then, at time t8, the peeling force reaches a value F■ larger than the adhesion force between the wafer 1 and the electrodes 4 and 5, and the wafer 1 is removed from the electrodes 4 and 5.
Stay away from 5. On the other hand, the deviation length detected by the position detector 14 is the position IZ during adsorption from time 0 to ts,
When wafer 1 leaves N-pole 4°5 at time ts, it is at position Z2. Therefore, the chucking control section 15 controls the time t.
In response to the detection signal from the position Z1 to the position Z2 output by the position detector 14 at S, the peeling force generating section 13 stops generating the peeling force. As a result, the peeling force sharply drops to zero,
The deflecting member 12 returns to its original position and the wafer 1 is again attracted to the electrodes 4 and 5 as shown in FIG. 2(b). Also, the peeling force generating part 1
3 is the maximum value Frn a of peeling force that causes damage to wafer 1
x, that is, Fv<Fmax. This can be easily detected and controlled using a stress sensor. In this way, the adsorption force of the wafer 1 can be determined by measuring the peeling force pv.

Next, the operation of sucking the wafer 1 and then removing it will be explained. During adsorption, the chucking control unit 15 controls the voltage generation unit 10 to output a DC voltage that makes the electrode 4 positive and the electrode 5 negative, for example. This voltage is on the order of several hundred ports.

As a result, a negative charge is induced on the side of the wafer 1 that is in contact with the electrode 4, and a positive charge is induced on the side of the wafer 1 that is in contact with the electrode 5, and the wafer 1 is caused by the electrostatic force on the electrodes 4 and 5. It is adsorbed.

In order to remove the wafer 1, first the voltage applied to the electrode 4.degree. 5 is made zero. After that, the chucking control section 15
As described above, the adsorption force of the wafer 1 is measured using the peel force generator 16 and the position detector 14. In addition, by the peeling force generating part 13 and the deflection member 12, the wafer 1 'k electrode 4
, 5, the charge is still stored in the wafer 1.

Therefore, even if the deflecting member 12 is returned to its original position, the wafer 1 is attracted to the electrodes 4 and 5 due to the residual charge on the wafer 1.

Now, what happens when the adsorption force is measured? iL pressure generating part 10
A 'Tri circle with a polarity opposite to that at the time of attraction is applied between the electrodes 4 and 5 for a predetermined time so that the attraction force becomes minimum or koto. The magnitude and application time of this reverse polarity voltage are determined by the amount of charge when the wafer 1 is attracted. Of course, the amount of charge depends on the adsorption force).

In this way, according to this embodiment, the wafer 1 is placed at a pole of 4°5.
Since the band 11L load of the wafer 1 has been removed, the wafer 1 can be removed at 1" without any stress. Also, the wafer will not be attracted to the transfer arm or the like due to the wafer's residual charge. - Therefore, the wafer 1 can be immediately proceeded to the next processing step, which is extremely useful for automating the manufacturing process of semiconductor devices.

By the way, in the second embodiment, it is necessary to operate the peeling force generating section 13 every time the wafer 1 is removed, and if a voltage of opposite polarity is applied too much in terms of magnitude or time, the wafer 1 This is due to the fact that it becomes charged again and the adsorption force remains.

Generally, there are variations in the manufacturing process of integrated circuits, and the thickness and structure of the silicon oxide layer on the wafer surface also vary. However, in the process of manufacturing one type of integrated circuit, wafers within the same lot,
Variations in the thickness and physical properties of silicon oxide between wafers are kept small. As another embodiment of the present invention, a method of destaticizing a wafer in one loft after static N1 adsorption will be described.

31M(a) is a graph explaining the operation of the voltage generating section 10, and is a characteristic diagram in which time is plotted on the t+Q axis and generated voltage is plotted on the vertical axis.

When the wafer 1 is being attracted, the voltage generator 10 outputs a voltage of 0, but when the wafer 1 is being attracted, the voltage becomes O, and at time to, the above-described peeling force F (V) is generated. measurements are taken.

When the surface is a semiconductor such as silicon or a conductor, the measured value at this time is small, indicating that there is no need to release the charge. If there is a charge, the value at this time will exceed a certain value, so an operation to generate an erase charge, that is, to release the charge, is performed. First, the voltage at the time of adsorption ■0 and the opposite polarity nottHEVx (
After the peeling force is generated for a predetermined period of time between I vll < lVo l) and 5, the peeling force F (V) is measured as Pl at time t1. Next, voltage ■2, which has a larger absolute value than voltage ■1, is generated for a predetermined period of time and returned to O■, and at time t2, the peeling force F (
V) is measured as P2. In this way the voltage ■. By applying increasing voltages with opposite polarity and returning to O■ and measuring the peeling P1f force F (V), the relationship between the voltage of opposite polarity (reverse voltage) and the peeling force P (V) is The characteristics are as shown in FIG. 3(b). From this characteristic, the minimum value P of F(V),
Since the value of the reverse voltage {circle around (2)} that gives the voltage is known, the chucking control section 15 stores this value. When the voltage v8 is applied to this wafer after passing the minimum value P, it means that the electrification has been released. For other wafers of the same type (within the same lot) made in the same manufacturing process, there is no need to measure the appropriate voltage for charge release, and as shown in Figure 4, the m pressure during adsorption is It is only necessary to add the stored voltage value ■f immediately after the generation of ■o, and then return it to Ov. The application time is determined to be approximately equal to the application time of voltage v7 in FIG. 3(a).

In this way, when processing a large number of wafers in the same lot, the peeling force F (V, ) is applied to only the first wafer.
, and subsequent wafers can be removed from charge at an extremely high speed based on the memorized appropriate voltage.

In FIG. 1, a resistor 11 connected in series between the voltage generator 10 and the electrode 4.5 determines the responsiveness (the feeding speed of the banding line) when the wafer 1 is attracted or removed. be. Also, since the state in which the wafer 1 is placed on the electrode 4.5 is electrically equivalent to a capacitor, the resistance 11
The series connection of this and this capacitor forms a so-called time constant circuit. Therefore, the value of the resistor 11 may be set small when it is to be attracted, and the value of the resistor 11 may be set to be larger when it is to be removed than when it is attracted. In this way, the wafer 1 can be quickly attracted and removed, and when removing the wafer 1, the control of applying a reverse voltage to measure the minimum value of the attraction force will not be strict, as shown in 3rd ffl (a). There are advantages. Specifically, the time for applying the reverse voltage should not be extremely short.

Therefore, the minimum value of the adsorption force can be measured accurately and reproducibly.

As described above, according to the present invention, the charge on the wafer as a target object after electrostatic adsorption can be released, and the wafer can not only be easily separated from the adsorption/fixation part, but also be able to separate the wafer 1 and other conductive materials. The suction force that acts on it also decreases. Further, according to the embodiments of the present invention, since an upper limit is set for applying the peeling force, unnecessary stress is not applied to the semiconductor wafer, and there is an advantage that generation of crystal defects due to stress can be suppressed.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a functional block showing an embodiment of the present invention viewed from the male side, FIG. 2(a) is a peeling force characteristic diagram of the peeling force generating part, and FIG. 2(b) is a position detector σ] Characteristic diagram, Figure 6 (a
) is a time chart showing the operating waveform of the voltage generator, FIG. 6(b) is a characteristic line showing the relationship between 514H separation force and reverse voltage when erase charge is generated, and FIG. 4 is a voltage diagram of another example. FIG. 6 is a time chart diagram showing operation waveforms of the generator. DESCRIPTION OF SYMBOLS 1... Silicon Ueno, 4, 5... Electrode (suction table), 4a, 5a... Insulating layer, 10... Voltage generating part (erase charge generating means), 12... Deflection member , 13...
- Peeling force generating section, 14... position detector, 15... chucking control section. Agent Sanro Kimura Figure 3 Figure 4 Figure 129-

Claims (3)

[Claims] (1) A suction table on which an object such as a conductor or a semiconductor is placed and electrostatically adsorbed; a measuring means for measuring the adsorption force of the adsorbed object; and erase charge generation means for generating an electric charge on the suction table in an amount corresponding to the measured value of the measuring means, so that the suction force is reduced to approximately zero when the object is removed from the suction table. Electrostatic adsorption device. (2) The measuring means includes a peeling force generating means that comes into contact with the target object and detects the peeling force from the suction table as an adsorption force on the target object, and the peeling force of the peeling force generating means is applied to the target object. 2. The device according to claim 1, wherein the device is limited in size so as not to damage the device. (3) The erasing charge generating means intermittently applies a reverse voltage to the suction table whose polarity is opposite to that at the time of suction and whose absolute value increases sequentially, and after applying the reverse voltage, the amount of the charge (
Detecting the peeling force using the force generating means is repeated sequentially, and the reverse voltage value when the detected peeling force becomes the minimum is calculated as follows:
3. The device according to claim 2, wherein the voltage is set to make the adsorption force approximately zero.