Etching a substrate: processes – Gas phase etching of substrate – Application of energy to the gaseous etchant or to the...
Reexamination Certificate
1998-09-30
2004-09-14
Gulakowski, Randy (Department: 1746)
Etching a substrate: processes
Gas phase etching of substrate
Application of energy to the gaseous etchant or to the...
C307S130000, C361S230000, C361S234000, C361S236000
Reexamination Certificate
active
06790375
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to vacuum plasma processors including a chuck for holding workpieces in place during processing and, more particularly, to a method of and apparatus for facilitating dechucking wherein the force applied by the chuck to hold the workpiece in place during processing is effectively monitored and controlled.
Another aspect of the invention relates to such processors wherein a voltage applied to an electrostatic chuck is controlled in response to current flowing between the chuck and a source of the voltage in response to current flowing through the chuck when a previously processed workpiece was removed from the chuck.
BACKGROUND ART
Vacuum plasma processors include a vacuum chamber containing a workpiece holder, i.e., chuck, for carrying a workpiece having an exposed surface which is plasma processed, i.e., a surface which a plasma etches and/or on which a plasma deposits materials. The etching and depositing are achieved inter alia by ions in a low impedance plasma in the chamber resulting from introducing one or more suitable gases into the chamber and the application of an r.f. field to the gas.
The workpiece temperature is controlled by applying an inert heat transfer gas, such as helium, to the back face of the workpiece. The heat transfer gas improves thermal contact between the workpiece and the chuck which is cooled by water. Typically, the workpieces are relatively thin substrate plates made of electrical conducting materials (i.e., metals), semiconductors or dielectric glass sheets. The workpiece must be clamped to the chuck to hold the workpiece in place against the pressure of the heat transfer gas pushing on the workpiece back face.
Removing certain workpieces from electrostatic chucks is a problem, particularly for semiconductor workpieces, as well as low and intermediate resistivity dielectric workpieces, (i.e., dielectric workpieces with resistivities less than about 1×10
15
&OHgr;m). Birang et al., U.S. Pat. No. 5,459,632, which appears to have the same disclosure as Birang et al., U.S. Pat. No. 5,612,850, discloses a semiconductor wafer dechucking method wherein a dechucking voltage applied to a monopolar chuck electrode has the same polarity as the polarity of the voltage used to maintain the workpiece in a chucked position. The dechucking voltage has a magnitude different from the chucking voltage to minimize the electrostatic attractive force between the chuck and workpiece. An “optimum” value for the dechucking voltage is determined empirically or by monitoring the amplitude of a current pulse produced as the workpiece is initially mounted on the chuck.
Monitoring the amplitude of the current pulse which flows through the workpiece and the electrostatic chuck when the workpiece is first applied to the chuck is not applicable to processing of glass, dielectric workpieces. This is because no current flows between the electrostatic chuck and the dielectric workpiece when the workpiece is initially placed on the chuck. For glass panels, there is no current pulse when a new panel is first lowered onto the electrostatic chuck. This is because any residual sticking charge on the previously processed dielectric workpiece left with that dielectric workpiece when it was removed from the electrostatic chuck.
As pointed out in Birang et al., U.S. Pat. No. 5,491,603, the method disclosed in the other two Birang et al. patents requires sophisticated measurements of a very short duration electrical pulse. To avoid such sophisticated measuring procedures, the '603 patent discloses a somewhat complex method of calculating the “optimum” voltage by applying an electrostatic potential to the chuck, then introducing a gas between the wafer and chuck and then reducing the electrostatic potential of the chuck while observing a rate of gas leakage from between the wafer and chuck. The optimum dechucking voltage is recorded in a memory as the value of electrostatic potential that occurs when the leakage rate exceeds a predetermined threshold. The calculated optimum voltage is apparently applied to the chuck as or after the plasma is turned off; after the plasma is turned off the wafer is lifted from the chuck. There is no disclosure in the '603 patent of controlling the chucking voltage applied to the chuck during wafer processing in response to the flow rate of gas applied to the workpiece via the chuck during processing. The '603 patent also has no disclosure of maintaining the force applied by the chuck to the wafer substantially constant during wafer processing by a plasma.
Watanabe et al., U.S. Pat. No. 5,117,121 discloses a method of releasing a semiconductor wafer from a bipolar electrostatic chuck. To clamp the semiconductor wafer workpiece to the bipolar chuck, a first DC voltage having a predetermined amplitude and polarity is applied between two chuck electrodes. After clamping by the first DC voltage and before the workpiece is removed from the chuck, a second DC voltage, having a polarity opposite to the polarity of the first voltage, is applied to the chuck electrodes to eliminate a residual attractive force which the chuck is applying to the semiconductor workpiece. The second voltage has an amplitude which is one-and-a-half to two times higher than the amplitude of the voltage of the first polarity. The second voltage is continuously applied to the bipolar electrodes for a time period inversely proportional to the amplitude of the second voltage. Apparently, the amplitudes of the first and second voltages are empirically determined. In any event, the amplitudes of the first and second voltages are not determined in response to measurements made during workpiece processing.
It is, accordingly, an object of the present invention to provide a new and improved method of and apparatus for electrostatically chucking and dechucking workpieces in a vacuum plasma processor.
An additional object of the invention is to provide a new and improved method of and apparatus for effectively measuring and controlling the forces applied to a workpiece by an electrostatic chuck during workpiece processing to facilitate removal of the workpiece from the electrostatic chuck when processing is completed and thereby increase wafer throughput.
Another object is to provide a new and improved method of and apparatus for controlling a reverse polarity voltage applied by an electrostatic chuck to a workpiece upon completion of workpiece processing to facilitate removal of the workpiece from the electrostatic chuck when processing is completed and thereby increase wafer throughput.
SUMMARY OF THE INVENTION
According to one aspect of the invention, dechucking a workpiece from a chuck of a vacuum processor is facilitated by effectively monitoring a chucking force applied to the workpiece by the chuck while the workpiece is being processed and controlling the chucking force applied to the workpiece during workpiece processing in response to the monitored force.
Preferably, the chuck is an electrostatic chuck and the chucking force is controlled by controlling the voltage applied to an electrode of the chuck. The force is preferably monitored by flowing a fluid through the chuck to the workpiece. The fluid has a tendency to move the workpiece relative to the chuck. The force applied by the chuck to the workpiece includes the combination of forces exerted by the fluid on the workpiece and the electrostatic chucking force the chuck applies to the workpiece. The forces are effectively monitored by monitoring the flow rate of the fluid acting on the workpiece. In the preferred embodiment, the fluid is a heat transfer fluid for the workpiece.
The electrostatic chuck and the workpiece are such that the electrostatic force has a tendency to increase as time progresses if the voltage is constant. This tendency is preferably overcome by decreasing the chucking voltage in such a manner as to cause the electrostatic force to remain substantially constant during workpiece processing.
Because the present invention monitors and c
Holland John P.
Howald Arthur M.
Gulakowski Randy
Lam Research Corporation
Lowe Hauptman & Gilman & Berner LLP
Winter Gentle E
LandOfFree
Dechucking method and apparatus for workpieces in vacuum... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Dechucking method and apparatus for workpieces in vacuum..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Dechucking method and apparatus for workpieces in vacuum... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3215683