JP2008294257A - Semiconductor substrate detachment method and electrostatic chuck device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a separation method of a semiconductor substrate which can easily separate the semiconductor substrate from on a chucking stage without being influenced by existence of an insulating layer covering the rear of the semiconductor substrate and a variation of its film thickness, and an electrostatic chuck device. <P>SOLUTION: This method is one that separates a wafer W of which the rear is chucked and fixed to a surface of a chucking stage 1 by an electrostatic force from the chucking stage 1 concerned. This method contains the steps of: applying a voltage to the chucking stage 1 to remove electric charges electrified to the rear of the wafer W; detecting the remaining electric charges further remaining on the rear of the wafer W after the electric charges are removed; and applying a voltage negating the detected remaining electric charges to the chucking stage 1 to remove the remaining electric charges on the rear of the wafer W. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a semiconductor substrate detachment method and an electrostatic chuck device.

As this type of prior art, for example, Patent Documents 1 and 2 disclose that a semiconductor substrate (using electrostatic force)
For example, an electrostatic chuck device for attracting and fixing a wafer) on a stage is described. The electrostatic chuck device applies a voltage from the power supply circuit of the device to the electrostatic chuck to cause reverse polarization on the back surface of the semiconductor substrate and the surface of the electrostatic chuck, respectively, and electrostatic force (mainly Coulomb force) The semiconductor substrate is sucked and fixed on the stage. In addition, when the semiconductor substrate is detached from the stage, a voltage opposite in polarity to that at the time of adsorption (that is, reverse bias) is applied to the electrostatic chuck to remove the electric charge charged on the back surface of the semiconductor substrate, Thereafter, the semiconductor substrate was lifted up from the stage using pins or the like (hereinafter, this operation is also referred to as lift pinup).
JP-A-10-303287 JP-A-11-31737

By the way, when there is an insulating layer on the back surface of the semiconductor substrate, the thickness of the insulating layer on the back surface varies between the semiconductor substrates, the thickness of the insulating layer varies depending on the product type, Since the type of the insulating layer differs depending on the type, a case where the semiconductor substrate is easily detached from the stage and a case where the semiconductor substrate is difficult to remove are mixed in one detachment sequence. In particular, if a large amount of charge remains in the insulating layer even after reverse bias is applied, it is difficult to remove the semiconductor substrate, and if the lift pin-up is performed forcibly, the semiconductor substrate will jump or slip on the stage. There was a fear. In the worst case, the semiconductor substrate may fall off the stage.
Therefore, the present invention has been made in view of such a problem, and the semiconductor substrate can be easily removed from the suction stage without being affected by the presence of an insulating layer covering the back surface of the semiconductor substrate or variations in the film thickness. It is an object of the present invention to provide a method for detaching a semiconductor substrate and an electrostatic chuck device that can be detached.

In order to solve the above-mentioned problem, the semiconductor substrate desorption method according to the first aspect of the present invention is a method for desorbing a semiconductor substrate having its back surface adsorbed and fixed to the surface of the adsorption stage by electrostatic force from the adsorption stage, Applying a voltage to the adsorption stage to remove charges charged on the back surface of the semiconductor substrate; detecting residual charges remaining on the back surface of the semiconductor substrate even after removing the charges; Applying a voltage that cancels the detected residual charge to the suction stage to remove the residual charge on the back surface of the semiconductor substrate;
It is characterized by including. Here, the semiconductor substrate is, for example, a wafer. The wafer is made of, for example, silicon, and its back surface is often covered with an insulating film such as a silicon oxide film or a silicon nitride film.

The method for detaching a semiconductor substrate according to a second aspect is the method according to the first aspect, wherein the step of detecting the residual charge and the voltage that cancels the detected residual charge are applied to the adsorption stage to reduce the residual charge. The step of removing is repeatedly performed continuously.
The method for detaching a semiconductor substrate according to a third aspect is the method according to the first or second aspect, wherein in the step of previously providing a coil inside the adsorption stage and detecting the residual charge, the charged state of the back surface of the semiconductor substrate Inductive current generated in the coil in accordance with the change is measured, and the residual charge is calculated based on the measured value.

According to the semiconductor substrate desorption method of the first to third aspects, when desorbing the semiconductor substrate from the adsorption stage, a voltage suitable for each semiconductor substrate can be applied to the adsorption stage, and the back surface of the semiconductor substrate is covered. The residual charge on the back surface of the semiconductor substrate can be brought close to 0 (zero) without being affected by the presence of the insulating layer and variations in the film thickness. Therefore, the semiconductor substrate can be smoothly detached. As a result, for example, it is possible to prevent problems such as the semiconductor substrate jumping or sliding on the suction stage during lift pin-up.

An electrostatic chuck device according to a fourth aspect of the present invention is an electrostatic chuck device that attracts and fixes the back surface of the semiconductor substrate to the front surface of the suction stage by electrostatic force, and includes a power source connected to the suction stage and the suction stage. A coil provided inside, and a control unit connected to the power source and the coil via wiring and operating the power source to apply a predetermined voltage to the suction stage, the control unit comprising: A function of measuring an induced current generated in the coil in accordance with a change in a charged state of the back surface of the semiconductor substrate, and a function of calculating a residual charge remaining on the back surface of the semiconductor substrate based on the measured value. Is.
With such a configuration, a voltage suitable for each semiconductor substrate can be applied to the adsorption stage based on the residual charge calculated by the control unit, and the residual charge on the back surface of the semiconductor substrate is set to 0 (zero). You can get closer. Therefore, the semiconductor substrate can be smoothly detached.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a diagram illustrating a configuration example of an electrostatic chuck device according to an embodiment of the present invention. Figure 1
FIG. 1A is a plan view showing an internal configuration example of the suction stage 1, and FIG. 1B is a conceptual diagram showing an overall configuration example of the electrostatic chuck device. The cross section of the suction stage 1 and the electrostatic chucks 3a and 3b shown in FIG. 1B corresponds to the XX ′ cross section of FIG.

As shown in FIGS. 1A and 1B, this electrostatic chuck device is, for example, a bipolar (Bi-Po).
lar) type apparatus, an adsorption stage 1, electrostatic chucks 3a and 3b provided in the adsorption stage 1, and a DC power source 5 connected to the electrostatic chucks 3a and 3b via wires, A coil 7 provided in the suction stage 1, a control unit 10 connected to the DC power source 5 and the coil 7 via wiring, a storage unit 13 connected to the control unit 10, and a switch 1
And 5.

Among these, the adsorption stage 1 is made of an insulator, and a stage surface on which the wafer W is placed is formed on the surface of the insulator. The electrostatic chucks 3a and 3b are provided at positions close to the stage surface (that is, the surface) inside the suction stage 1. These electrostatic chucks 3
A direct current power source 5 is connected to a and 3b through a switch 15 so that a direct current voltage can be applied for a required time, and the electrostatic chuck 3a has a positive voltage or a negative (including 0V). One of the voltages is applied to the other side of the electrostatic chuck 3b. The DC power source 5 is, for example, a variable constant voltage power source.

Further, as shown in FIGS. 1A and 1B, the coil 7 is provided at a position close to the surface inside the suction stage 1 and close to the outer peripheral portion thereof. The coil 7 is for detecting charges that are charged or remaining on the back surface of the wafer W. When the charged state of the wafer W changes, a change in the magnetic field occurs around it, and this change in the magnetic field can be grasped by the induced current generated in the coil 7.

More specifically, the wafer W is made of silicon, for example, and an insulating layer (not shown) (for example, a silicon oxide film or a silicon nitride film) is formed on the back surface thereof.
When such a wafer W is placed on the suction stage 1 and a negative voltage is applied to the electrostatic chuck 3a as shown in FIG. 2, positive (+) charges appear on the surface. Further, negative (−) charge appears on the surface of the stage located directly above the electrostatic chuck 3a, and positive (
+) A charge appears. That is, polarization occurs in the suction stage 1 and the wafer W.

At this time, as indicated by a solid line arrow in FIG.
Apparently, the current I flows. As is well known, when a current I flows, a magnetic field H is generated around it.
However, the arrangement position and the axial direction of the coil 7 are adjusted so that an induced current is generated by the change of the magnetic field H. For example, as shown in FIGS. 1A and 1B, the coil 7 is arranged so that the axial direction of the coil 7 is along the outer periphery of the electrostatic chuck 3a. Further, when 0V is applied to the electrostatic chucks 3a and 3b from the state shown in FIG. 2, most of the above polarization states are eliminated. At this time, an apparent current I flows from the electrostatic chuck 3 a toward the surface of the suction stage 1.

The control unit 10 is composed of, for example, a logic IC and a RAM. The induced current generated in the coil 7 is measured by the control unit 10. The storage unit 13 is configured by, for example, a nonvolatile memory or a hard disk. In the storage unit 13, an arithmetic expression for calculating the charge remaining on the back surface of the wafer W (that is, WF residual charge) from the magnitude of the induced current generated in the coil 7,
An arithmetic expression for calculating a reverse bias condition (for example, voltage magnitude, application time, etc.) necessary for canceling the F residual charge is stored. The storage unit 13 also stores a sequence for fixing the wafer W to the suction stage 1 and detaching it from the suction stage 1. The control unit 10 can read out the information from the storage unit 13 and can apply a voltage to the electrostatic chucks 3a and 3b based on the read out information.

Next, an operation example of the electrostatic chuck apparatus shown in FIGS.
FIGS. 3A and 3B are a diagram and a table (part 1) showing an example of the change over time of the ESC voltage and the WF residual charge. The horizontal axis of Fig.3 (a) shows the elapsed time t after starting the adsorption | suction process of the wafer W by an electrostatic chuck apparatus. Moreover, the vertical axis | shaft of Fig.3 (a) shows a voltage value.
In this example, the voltage applied to the electrostatic chuck 3a is referred to as an ESC voltage. ESC is an abbreviation for Electro Static Chuck. When the ESC voltage is applied to the electrostatic chuck 3a, a voltage having the same polarity as the ESC voltage and the same absolute value is applied to the electrostatic chuck 3b at the same timing. However, when the ESC voltage is 0V, the voltage applied to the electrostatic chuck 3b is also 0V. In this example, the charge charged or remaining on the back surface of the wafer W directly above the electrostatic chuck 3a is referred to as WF residual charge. The charge remaining on the back surface of the wafer W immediately above the electrostatic chuck 3b has a polarity opposite to that of the WF residual charge and has the same absolute value. However, when the WF residual charge is 0V, the charge remaining on the back surface of the wafer W immediately above the electrostatic chuck 3b is also 0V.

Based on the above, the wafer adsorption and desorption processes by the electrostatic chuck apparatus will be described.
As shown in FIGS. 3A and 3B, first, the ESC voltage is raised from 0V to 1500V to attract and fix the wafer W to the suction stage 1, and the bias application state is maintained for a certain period of time. (T = 0 to 3 seconds). Here, for example, the switch 15 is closed by a control signal from the control unit 10, and in this state, 1500 V is applied to the electrostatic chuck 3a and −1500 V is applied to the electrostatic chuck 3b. As a result, polarization occurs in the suction stage 1 and the wafer W, and the charged state of the back surface of the wafer W is as shown in FIG. An electrostatic force acts between the suction stage 1 and the wafer W. By this electrostatic force, the back surface of the wafer W is attracted and fixed to the surface of the suction stage 1.

Next, the ESC voltage is lowered from 1500 V to 1000 V (t = 3 to 4 seconds). And
Wafer W sucked and held on suction stage 1 with ESC voltage held at 1000V
Is subjected to predetermined processing (t = 4 to 7 seconds). Here, the predetermined treatment is, for example, dry etching on the surface of the wafer W.
Next, the process proceeds to the step of detaching the wafer W from the suction stage 1. For example, ES
The C voltage is lowered from 1000 V to −500 V, −500 V is applied to the electrostatic chuck 3 a, and 500 V is applied to the electrostatic chuck 3 b (t = 7 to 8 seconds). That is, a reverse bias is applied to the electrostatic chucks 3a and 3b. And the application state of this reverse bias is maintained for a fixed time (t = 8-9 seconds). As a result, the polarization generated in the suction stage 1 and the wafer W is eliminated, and the electrostatic force is weakened. Next, the ESC voltage is returned to 0 V (t = 9 to 10 seconds).

Thereafter, the WF residual charge is detected. Based on the detection result, the suction stage 1
It is determined whether or not the desorption step of the wafer W from above is performed again (t = 10 to 11 seconds).
Here, if the WF residual charge when the ESC voltage is returned to 0 V is small enough to be regarded as 0 V or 0 V, it is determined that it is not necessary to perform the wafer W desorption step again. E
If the WF residual charge when the SC voltage is returned to 0V is larger or smaller than 0V, it is determined that the wafer W desorption step needs to be performed again. This determination is made, for example, by the control unit 10.
Do.

Incidentally, in the electrostatic chuck device shown in FIGS. 1 and 2, the WF residual charge can be grasped by the magnitude of the induced current flowing through the coil 7. That is, the ESC voltage is set to -500V, for example
When the voltage is returned to 0 V, the polarization between the front surface of the suction stage 1 and the back surface of the wafer W is eliminated, and the current I apparently flows from the electrostatic chuck 3 a toward the front surface of the suction stage 1. Where ES
The more the charge remaining on the back surface of the wafer W after the C voltage is returned to 0 V, the more the adsorption stage 1
Since the internal polarization is difficult to be eliminated, the current I becomes a small value. When the current I is small, the magnetic field H is small, and as a result, the induced current generated in the coil 7 is also small.
In this way, the magnitude of the WF residual charge can be grasped by the magnitude of the induced current.

For example, as shown in FIG. 5, when the ESC voltage is returned from −500 V to 0 V, the induced current when the WF residual charge becomes 0 V is Ia. Further, when the ESC voltage is returned from −500 V to 0 V, an induced current when positive charge remains on the back surface of the wafer W (that is, WF residual charge> 0 V) is defined as Ib. A difference between the maximum value of the induced current Ia and the maximum value of the induced current Ib is defined as ΔI.

Here, there is a correlation between ΔI and the WF residual charge, and the larger the ΔI, the larger the WF residual charge. When ΔI = 0V, the WF residual charge is 0V. Furthermore, since the values of the induced currents Ia and Ib are likely to increase as the reverse bias is higher, ΔI that is the difference between these values.
The value of tends to be large. For example, ΔI tends to be larger when the reverse bias is −1000 V than when the reverse bias is −500 V.

Therefore, the induced current Ia is obtained in advance by experiment or simulation for each reverse bias voltage value that is expected to be actually applied, and these values are stored in the storage unit 13, for example. Also, a relational expression indicating the relation between ΔI and WF residual charge is also obtained in advance by experiment or simulation for each reverse bias voltage value that is expected to be actually applied, and the relational expression is stored, for example, Stored in the unit 13.

When the WF residual charge is detected, the reverse bias actually applied (for example, −5
The value of the induced current Ia corresponding to 00V) is read from the storage unit 13. In parallel with this, the above relational expression corresponding to the actually applied reverse bias (for example, −500 V) is stored in the storage unit 1.
Read from 3. Next, the induced current Ib is actually measured, and the measured value Ib and the read I
ΔI is calculated from the value of a. By substituting the calculated ΔI into the above relational expression, the WF residual charge can be calculated. As described above, for example, the control unit 10 performs the process of calculating the WF residual charge from the value of the induced current Ia and the process of determining whether or not to perform the desorption step again based on the calculation result.
In this embodiment, as shown in FIGS. 3A and 3B, the charge on the back surface of the wafer W cannot be sufficiently canceled by the first reverse bias application, and the WF residual charge is, for example, 2
Assume a case of 00V. In such a case, since the reverse bias is unpredictable, it is determined that the desorption step of the control unit wafer W needs to be performed again.

FIGS. 4A and 4B are a diagram and a table (part 2) illustrating an example of the temporal change of the ESC voltage and the WF residual charge. FIG. 4 is a continuation of FIG. 3, and the horizontal axis of FIG. 4A indicates the elapsed time t from the start of the wafer W desorption process, and the vertical axis indicates the voltage value.
As described above, when it is determined that the desorption step needs to be performed again, FIG.
And as shown in (b), the ESC voltage is lowered from 0V to -200V, and the electrostatic chuck 3a
-200V is applied to the electrostatic chuck 3b, and 200V is applied to the electrostatic chuck 3b (t = 11 to 1).
2 seconds). Then, the ESC voltage is maintained at −200 V for a certain time (t = 12 to 13 seconds). Thereby, the polarization remaining on the suction stage 1 and the wafer W is canceled out, and the electrostatic force acting between the suction stage 1 and the wafer W is further weakened.

Next, the ESC voltage is returned to 0 V (t = 13 to 14 seconds). Thereafter, the WF residual charge is detected. Then, based on the detection result, it is determined whether or not the desorption step of the wafer W from the suction stage 1 is performed again (t = 14 to 15 seconds). Here, when the WF residual charge when the ESC voltage is returned to 0V is small enough to be regarded as 0V or 0V, it is determined that it is not necessary to perform the desorption step again. If the WF residual charge when the ESC voltage is returned to 0 V is still large, it is determined that the desorption step needs to be performed again.

In this embodiment, as shown in FIGS. 4A and 4B, it is assumed that the WF residual charge cannot be set to 0V even after the second reverse bias application, and the value is −100V. To do.
In such a case, it is determined that the desorption step needs to be performed again, and this time, the -100V W
The reverse bias is applied so as to cancel the F residual charge.
Thereafter, the third reverse bias application (t = 15 to 18 seconds) and the fourth reverse bias application (t = 19 to 22 seconds) are performed. The procedure is the same as the second reverse bias application, for example. is there. In addition, the absolute value of the applied voltage (that is, the ESC voltage) may be gradually reduced each time the number of reverse biases is increased. Since the WF residual charge has a smaller absolute value than the voltage applied immediately before, the WF residual charge is finally reduced to 0V or 0V by gradually decreasing the reverse bias applied voltage. It can be made as small as possible.

As described above, according to the embodiment of the present invention, when the wafer W is desorbed from the suction stage 1, a voltage suitable for each wafer W can be applied to the suction stage 1. The residual charge on the back surface of the wafer W can be brought close to 0 (zero) without being affected by the presence of the insulating layer to be covered or variations in the film thickness. Accordingly, the wafer W can be smoothly detached from the suction stage 1, and problems such as the wafer W jumping or sliding on the suction stage 1 during lift pin up can be prevented.

In the above embodiment, the case where the induced current Ia when the WF residual charge becomes 0 (zero) is obtained in advance by experiment or simulation and this value is stored in, for example, the storage unit 13 has been described. Then, when detecting the WF residual charge, from the value of ΔI that is the difference between the value of the induced current Ia stored in the storage unit 13 and the actually measured induced current Ib,
The calculation of the WF residual charge has been described.

However, in the present invention, it is possible to calculate the WF residual charge after applying the reverse bias even by other methods. For example, in steps S1 to S4 in FIG.
The integral value (that is, the amount of moving charges) of the induced current generated in the coil 7 when the C voltage changes is measured in advance. For example, as shown in FIG. 6B, the integrated value of the induced current measured in step S1 is c1, the integrated value of the induced current measured in step S2 is c2, and the integrated value of the induced current measured in step S3. Is c3, and the integrated value of the induced current measured in step S4 is c4.
c1 and c4 can be represented by positive values, and c2 and c3 can be represented by negative values.

Here, the sum of c1 to c4 (that is, the amount of charge remaining after canceling the positive / negative) has a correlation with the WF residual charge, and when the sum of c1 to c4 is 0, the residual charge on the back surface of the wafer W is 0. . C1
The reverse bias is insufficient when the sum of .about.c4 is a positive value, and the reverse bias is excessive when the sum of c1 to c5 is a negative value. Therefore, by measuring the induced currents c1 to c4 generated in the coil 7 in steps S1 to S4, and adding these c1 to c4 after completing step c4, it is possible to determine whether the reverse bias is excessive or insufficient.

Further, the relationship between the reverse bias applied voltage (ie, ESC voltage) in step S4 and the integrated value c4 of the induced current generated by this applied voltage is obtained in advance by experiment or simulation, and an equation indicating this relationship is stored in the storage unit. 13. And step S4
Then, the applied voltage is set so that the sum of c1 to c4 becomes zero. According to this method,
Since the sum of the induced currents c1 to c4 is substantially zero, the WF residual charge can be brought close to 0 (zero) with high accuracy.

The figure which shows the structural example of the electrostatic chuck apparatus which concerns on embodiment. The figure which shows the generation | occurrence | production mechanism of the induction current in the electric current I, the magnetic field H, and the coil 7. FIG. The figure which shows an example of a time-dependent change of an ESC voltage and WF residual charge (the 1). FIG. 2 is a diagram illustrating an example of changes over time in an ESC voltage and a WF residual charge (part 2); The figure which shows typically the magnitude | size of the induced currents Ia and Ib. The figure which shows step s1-s4 which an induced current produces, and the integrated value c1-c4 of an induced current.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Adsorption stage, 3a, 3b Electrostatic chuck, 5 DC power supply, 7 Coil, 10 Control part, 13 Memory | storage part, 15 Switch, c1-c4 Integral value of induced current

Claims (4)

A method of detaching a semiconductor substrate having its back surface adsorbed and fixed to the surface of an adsorption stage by electrostatic force from the adsorption stage,
Applying a voltage to the suction stage to remove the electric charge charged on the back surface of the semiconductor substrate;
Detecting residual charge remaining on the back surface of the semiconductor substrate even after the charge is removed;
Applying a voltage that cancels the detected residual charge to the adsorption stage, and removing the residual charge on the back surface of the semiconductor substrate. The step of detecting the residual charge and the step of applying the voltage that cancels the detected residual charge to the adsorption stage to remove the residual charge are repeated in succession. Item 2. A method for detaching a semiconductor substrate according to Item 1. A coil is provided in advance inside the suction stage,
In the step of detecting the residual charge,
3. The residual charge is calculated based on a measured value of an induced current generated in the coil in accordance with a change in a charging state on the back surface of the semiconductor substrate.
2. A method for detaching a semiconductor substrate according to 1. An electrostatic chuck device that attracts and fixes the back surface of the semiconductor substrate to the surface of the suction stage by electrostatic force,
A power source connected to the suction stage;
A coil provided inside the suction stage;
A controller that is connected to the power source and the coil via wiring, and operates the power source to apply a predetermined voltage to the suction stage; and
The control unit calculates a residual charge remaining on the back surface of the semiconductor substrate based on a function of measuring an induced current generated in the coil in accordance with a change in a charging state on the back surface of the semiconductor substrate, and the measured value. An electrostatic chuck device having a function of

Images