# Patent

## Title
System for securely dechucking wafers

## Abstract

A system for chucking and de-chucking a work piece comprises a wafer stage having a chuck support for supporting a chuck. The wafer stage further comprises a chuck mounted on the chuck support for receiving and attaching the work piece thereto; a support lift means for supporting the work piece; a driving means coupled to the support lift means for gradually raising the support lift means to contact the work piece in response to a variable quantity; a controller for receiving the variable quantity; and a regulating means coupled to the driving means and to the controller, the regulating means for controlling the variable quantity going to the driving means when a predetermined variable quantity is detected.

## Background
CROSS-REFERENCE TO RELATED APPLICATIONS
The present application is a Continuation-in-Part of and claims the priority of U.S. application Ser. No. 12/172,669, filed on Jul. 14, 2008, now U.S. Pat. No. 7,995,323, which is incorporated herein by reference in its entirety.


FIELD
The present invention relates generally to systems for de-chucking a work piece, such as a wafer from chucks, and more particularly, to systems for safely dechucking a wafer from electrostatic chucks.
BACKGROUND
Semiconductor devices are manufactured after performing many processes such as depositing a material layer on a wafer, patterning the deposited material layer, and removing unnecessary residuals on the wafer. To perform these processes repeatedly, a wafer is loaded on a wafer stage inside a chamber, the wafer is processed, and then unloaded.
In order to successively process a wafer, it is very important to chuck and fix the wafer in the chamber and to dechuck or remove the wafer so that the wafer will not be damaged after processing. As semiconductor devices become highly integrated, the design rule becomes smaller, and the process margin becomes narrower. As a result, there is a greater need to chuck and fix the wafer without damaging the wafer during dechucking.
Methods for fixing the wafer to the wafer stage in the process chamber when the wafer is loaded on the wafer stage include using hardware structures such as clamps, using a vacuum to suction the rear side of the wafer (a vacuum chuck), using gravity, and using a piezoelectric effect. Various methods are available for dechucking the fixed wafer on the wafer stage after processing the wafer. The dechucking method used is chosen in accordance with the method used for fixing the wafer.
The most widely used method for fixing a wafer is the piezoelectric effect. In this method, an electrostatic chuck is used to fix the wafer, and the electrostatic chuck and a lifting means are used to dechuck the fixed wafer.
FIG. 1 shows a sectional view of an electrostatic chuck and a wafer thereon in a process of chucking and dechucking the wafer according to the prior art. The electrostatic chuck 25 includes an upper insulating layer 5, an electrostatic electrode 10, a lower insulating layer 15, and a lower electrode 20. The lower electrode 20 controls the reaction speed of plasma when plasma is generated in the chamber (not shown). The electrostatic electrode 10 is connected to a DC generator (not shown), and positive charges or negative charges are distributed on the electrostatic electrode 10 by the DC generator. The electric charges on the electrostatic electrode 10 induce an electrostatic field such that the wafer 35 is chucked or dechucked. Wafer 35 and the electrostatic electrode 10 are insulated by the upper insulating layer 5.
In a method for chucking the wafer 35 according to the prior art, the wafer 35 is put on the electrostatic chuck 25, and an electrostatic field is induced by supplying power to the electrostatic electrode 10 under the upper insulating layer 5 on the upper surface of the electrostatic chuck 25. Positive charges accumulate on the electrostatic electrode 10 connected to the external DC generator (not shown), and negative charges accumulate on the lower surface of the wafer 35 by plasma generated on an upper portion of the wafer 35, thereby inducing an electrostatic field between the wafer 35 and the electrostatic electrode 10. When the upper surface of the electrostatic chuck 25 is completely in contact with the wafer 35, a clamping force is produced by the electrostatic field, and thus, the wafer is chucked.
In a process for dechucking the wafer 35, the voltage supplied to the electrostatic electrode 10 and the lower electrode 20 is turned off. As a result, the electric charges flow out and the clamping force is reduced. However, since a discharge time is necessary for the charges to flow when the clamping force is reduced, the wafer 35 becomes stuck to the electrostatic chuck 25.
When lift pins 30 are raised to dechuck wafer 35 that is stuck to the electrostatic chuck 25, the force applied to the wafer 35 can easily damage and/or break the wafer 35. It is often difficult to fully and efficiently dissipate the electric charge before the lift pins are raised to dechuck wafer 35.
For these reasons and other reasons that will become apparent upon reading the following detailed description, there is a need for an improved method and apparatus for safely dechucking wafers that avoids wafer breakage associated with conventional methods and apparatuses for dechucking wafers.



BRIEF DESCRIPTION OF THE DRAWINGS
The features, aspects, and advantages of the present invention will become more fully apparent from the following detailed description, appended claims, and accompanying drawings in which:
FIG. 1 shows a sectional view of an electrostatic chuck and a wafer thereon in a process of chucking and dechucking the wafer according to the prior art.
FIG. 2 is a sectional view of a wafer stage including an electrostatic chuck according to one embodiment of the present invention.
FIG. 3 is a flowchart showing a method for preventing wafer breakage according to one embodiment of the present invention.



DETAILED DESCRIPTION
In the following description, numerous specific details are set forth to provide a thorough understanding of the present invention. However, one having an ordinary skill in the art will recognize that the invention can be practiced without these specific details. In some instances, well-known structures and processes have not been described in detail to avoid unnecessarily obscuring the present invention.
Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, the appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. It should be appreciated that the following figures are not drawn to scale; rather, these figures are merely intended for illustration.
FIG. 2 is a sectional view of a wafer stage including an electrostatic chuck according to one embodiment of the present invention. A process chamber 40 includes an enclosed chamber 45 having an upper electrode 50 on an upper wall of the enclosed chamber 45, and a wafer stage 55 in the lower half of the enclosed chamber 45. A gas inlet 60 and a gas outlet 65 are located on the sidewalls of the enclosed chamber 45. During processing, a reactive gas and a plasma source gas, for example, are injected into the enclosed chamber 45 via the gas inlet 60, and waste gas is exhausted through the gas outlet 65 after processing a work piece or wafer 35. The upper electrode 50 is connected to an external radio frequency (RF) generator (not shown), and power is applied to the upper electrode 50 by the RF generator. When power is applied to the upper electrode 50, the plasma source gas injected through the gas inlet 60 reacts to form plasma in the enclosed chamber 45. The process chamber 40 may, in one embodiment be a device for processing a work piece or wafer 35 using plasma.
The wafer stage 55 includes an electrostatic chuck support 70 on the bottom of the process chamber 40, an electrostatic chuck 75 on the electrostatic chuck support 70, a lifting means 80, within the electrostatic chuck 75 and the electrostatic chuck support 70, and a grounding means (not shown) for electrically grounding the lifting means 80.
The electrostatic chuck support 70 supports the electrostatic chuck 75 and a guide ring 85 and has a space where the lifting means 80 can be installed.
The electrostatic chuck 75 includes: a lower electrode 20, which is installed on top of the electrostatic chuck support 70 and is connected to an RF generator (not shown) located outside the enclosed chamber 45; an insulating flat plate 90 on an upper portion of the lower electrode 20; and a plurality of electrostatic electrodes 10, which are connected to a DC generator (not shown) located outside the enclosed chamber 45, for generating static electricity. Also, a plurality of holes inside the electrostatic chuck 75 enable lift pins 30 of the lifting means 80 to be raised or lowered. The electrostatic chuck 75 can chuck the loaded wafer 35 and safely dechuck the wafer 35 after processing.
When power is supplied to the plurality of electrostatic electrodes 10, positive or negative charges can accumulate thereon. The positive or negative charges on the plurality of electrostatic electrodes 10 induce an electrostatic field to chuck or dechuck the wafer 35. That is, when the wafer 35 is chucked, the DC generator supplies power to the plurality of electrostatic electrodes 10 such that electric charges having a charge opposite to those in the wafer 35 flow into the electrostatic electrodes 10. When the wafer 35 is dechucked, electric charges having a charge opposite to those remaining in the plurality of electrostatic electrodes 10 flow into the electrostatic electrodes 10. A direct current (DC) voltage, which is used to chuck or dechuck the wafer 35, is applied to the plurality of electrostatic electrodes 10. The detailed method for safely dechucking the wafer 35 will be described later.
The lifting means 80 includes a plurality of lift pins 30 which move up and down the holes for passing the electrostatic chuck 75, a lift pin support 95 for supporting the lift pins 30 in the electrostatic chuck support 70, a connecting axis 100 for connecting the lift pin support 95 to a driving means 105 for lifting the connecting axis 100.
The lift pins 30 are formed such that the wafer 35 can be easily lifted and stress is not concentrated on any one spot of the wafer 35 when the wafer 35 is dechucked. Preferably, the lift pins 30 are formed of a conductive material such as aluminum (Al), so that electric charge on the wafer 35 can be easily grounded when the lift pins 30 are in contact with the wafer 35.
A power source for lifting the wafer 35 is necessary to dechuck the wafer 35 from chuck 75. The driving means 105 is the device for lifting the wafer 35. The driving means 105 is coupled to the lifting means 80 for gradually raising the lifting means 80 to contact the wafer 35 in response to a variable quantity, such as for example gas, liquid, oil, etc. A pneumatic motor, hydraulic motor, electric motor, spring device, screw device, a variable load applying device such as a weight and pulley system, or other types of servomechanisms may be used for the driving means 105.
Wafer stage 55 also includes a controller 110 that may act as an on-off switch or a variable control valve that regulates/controls the variable quantity that goes through controller 110 and to the driving means 105. In one embodiment, where the driving means 105 is a pneumatic motor, the controller 110 receives an inflow of gas and sends that amount of gas into the pneumatic motor. In another embodiment, where the driving means 105 is a hydraulic motor, the controller 110 receives an inflow of liquid and transmits that amount of liquid into the hydraulic motor.
After processing the work piece or wafer 35 and in a process of dechucking the work piece or wafer 35, plasma formation stops and power supply to the electrostatic electrodes 10 is turned off However, even though the power is cut to the electrostatic electrodes 10, residual charges remain on the wafer 35 and the upper portions of the electrostatic chuck 75 keeping the wafer 35 stuck to the chuck 75. In conventional processes, when the driving means 105 activate and raise the lift pins 30 to contact the underside of wafer 35, because the wafer 35 is stuck to the chuck 75, the wafer breaks or becomes damaged.
An aspect of the present disclosure provides a regulating means 115 that is coupled between the driving means 105 and the controller 110 for controlling the variable quantity going to the driving means 105. The regulating means 115 may be, for example a pressure regulator or a release valve. In one embodiment, the regulating means 115 controls the variable quantity going to the driving means 105 by shutting off the variable quantity from going to the driving means 105 when a certain variable quantity is detected by the regulating means 115. For instance, where the regulating means 115 is a pressure regulator, the pressure regulator can be pre-set to detect a maximum pressure at a predetermined time at which point the work piece or wafer 35 cannot be safely dechucked without damage thereto. When the maximum pressure is reached, the pressure regulator can be set to cut off the inflow of gas/fluid going into the driving means 105 (e.g., a pneumatic motor) and/or alert an operator. In another embodiment, the pressure regulator can act as a release valve, essentially allowing the variable quantity to escape and preventing it from going to the driving means 105, thereby lowering the lift pins 30. One of ordinary skill in the art understands that the regulating means 115 may be made by conventional means and be adapted to couple with the driving means 105 and to the controller 110.
Where the driving means 105 is a pneumatic or hydraulic motor, the pressure of the motor can be expressed by Equation 1.

P=F/A  [Equation 1]

    P: pressure of the motor
    F: force of the motor to raise the lift pins
    A: area of the cylinder of the motor

Referring to Equation 1, the pressure is proportional to the force over the area. Given a certain clamping force produced by the electrostatic field (i.e., wafer is chucked), the force of the motor and the therefore the pressure necessary to raise the lift pins can be determined to, for example, safely dechuck the wafer or to damage and/or break the wafer.



Where pressure Pmax1 represents the maximum pressure at a time T1 at which the wafer may be safely dechucked without damage thereto, if the regulating means 115 detects a pressure P1 (the pressure at time T1), where P1 is greater than Pmax1, the regulating means 115 can either cut off the inflow of gas/fluid to the motor or release the gas/fluid from going to the motor.
Where P1 is less than or equal to Pmax1, the regulating means 115 may allow an inflow of gas/fluid to the motor. At a later time T2 greater than T1, if the regulating means 115 detects a pressure P2 (the pressure at time T2) less than or equal to Pmax2 (the maximum pressure at time T2 at which the wafer may be safely dechucked without damage thereto), the regulating means 115 may continue to allow the inflow of gas/fluid to the motor. Where the higher pressure, and therefore force eventually overcomes the clamping force that exits between the wafer and the chuck, the wafer may then be dechucked safely. Where P2 is greater than Pmax2, the regulating means 115 can either cut off the inflow of gas/fluid to the motor or release the gas/fluid from going to the motor. This process may be repeated for subsequent pressures and times.
FIG. 3 is a flowchart showing a method for preventing wafer breakage according to one embodiment of the present invention. The method 200 begins at step 202 by placing a work piece or a wafer on a chuck. At step 204 the wafer is attached to the chuck using an attachment force. At step 206, a support lift means is provided for supporting the wafer. At step 208, a driving means is provided to couple to the support lift means for gradually raising the support lift means to contact the wafer in response to a variable quantity. At step 210, a variable quantity is received. At step 212, the variable quantity to the driving means is controlled when a predetermined variable quantity is detected. Various changes, substitutions and alterations can be made in this method without departing from the spirit and scope of the present disclosure.
According to one embodiment, a process chamber comprises a wafer stage having a chuck support for supporting a chuck. The wafer stage further comprises a chuck mounted on the chuck support for receiving and attaching a work piece thereto; a support lift means for supporting the work piece; a driving means coupled to the support lift means for gradually raising the support lift means to contact the work piece in response to a variable quantity; a controller for receiving the variable quantity; and a regulating means coupled to the driving means and to the controller, the regulating means for controlling the variable quantity going to the driving means when a predetermined variable quantity is detected.
According to another embodiment, a system for chucking and de-chucking a work piece comprises a wafer stage having a chuck support for supporting a chuck. The wafer stage further comprises a chuck mounted on the chuck support for receiving and attaching the work piece thereto; a support lift means for supporting the work piece; a driving means coupled to the support lift means for gradually raising the support lift means to contact the work piece in response to a variable quantity; a controller for receiving the variable quantity; and a regulating means coupled to the driving means and to the controller, the regulating means for controlling the variable quantity going to the driving means when a predetermined variable quantity is detected.
The present disclosure has described apparatuses and methods for safely dechucking work pieces or wafers from electrostatic chucks. However, the apparatuses and methods may be utilized with other types of chucks, such as for example a vacuum chuck, and for dechucking wafers from chucks due to forces other than electrostatic forces, such as for example a vacuum force. The present disclosure has described specific exemplary embodiments. It will, however, be evident that various modifications, structures, processes, and changes may be made thereto without departing from the broader spirit and scope of the present invention, as set forth in the claims. The specification and drawings are, accordingly, to be regarded as illustrative and not restrictive. It is understood that the present invention is capable of using various other combinations and environments and is capable of changes or modifications within the scope of the inventive concept as expressed herein.

## Claims

1. A process chamber, comprising:
a wafer stage having:
a chuck support for supporting a chuck;
chuck mounted on the chuck support for receiving and attaching a work piece thereto;
a support lift means for supporting the work piece;
a driving means coupled to the support lift means for gradually raising the support lift means to contact the work piece in response to a variable quantity;
a controller for receiving the variable quantity; and
a regulating means coupled to the driving means and to the controller, the regulating means for controlling the variable quantity going to the driving means when a predetermined variable quantity is detected.

2. The process chamber of claim 1, wherein the chuck is an electrostatic chuck.

3. The process chamber of claim 1, wherein the support lift means comprises at least one lift pin that vertically moves through at least one corresponding opening provided in the chuck.

4. The process chamber of claim 1, wherein the driving means is a pneumatic motor.

5. The process chamber of claim 1, wherein the driving means is a hydraulic motor.

6. The process chamber of claim 1, wherein the driving means is an electric motor.

7. The process chamber of claim 1, wherein the driving means is a servomechanism.

8. The process chamber of claim 1, wherein the controller is an on-off switch.

9. The process chamber of claim 1, wherein the regulating means is a pressure regulator.

10. The process chamber of claim 1, wherein the regulating means is a release valve.

11. The process chamber of claim 1, wherein the regulating means shuts off the variable quantity to the driving means when the predetermined variable quantity is detected.

12. A process chamber, comprising:
a wafer stage having:
a chuck support for supporting a chuck;
a chuck mounted on the chuck support for receiving and attaching a work piece thereto;
a support lift means for supporting the work piece;
a pneumatic driver coupled to the support lift means for gradually raising the support lift means to contact the work piece in response to an inflow of gas;
a controller for receiving an inflow of gas; and
a pressure regulator coupled to the pneumatic driver and to the controller, the pressure regulator for controlling the inflow of gas going to the pneumatic driver when a predetermined pressure is detected.

13. The process chamber of claim 12, wherein the chuck is an electrostatic chuck.

14. The process chamber of claim 12, wherein the support lift means comprises at least one lift pin that vertically moves through at least one corresponding opening provided in the chuck.

15. The process chamber of claim 12, wherein the controller is an on-off switch.

16. The process chamber of claim 12, wherein the pressure regulator shuts off the inflow of gas to the pneumatic driver when the predetermined pressure is detected.

17. The process chamber of claim 12, wherein the pressure regulator is a release valve.

18. A system for chucking and de-chucking a work piece, comprising:
a wafer stage having:
a chuck support for supporting a chuck;
a chuck mounted on the chuck support for receiving and attaching the work piece thereto;
a support lift means for supporting the work piece;
a driving means coupled to the support lift means for gradually raising the support lift means to contact the work piece in response to a variable quantity;
a controller for receiving the variable quantity; and
a regulating means coupled to the driving means and to the controller, the regulating means for controlling the variable quantity going to the driving means when a predetermined variable quantity is detected.

19. The system of claim 18, wherein the regulating means is a pressure regulator.

20. The system of claim 18, wherein the regulating means shuts off the variable quantity to the driving means when the predetermined variable quantity is detected.