Electricity: electrical systems and devices – Electric charge generating or conducting means – Use of forces of electric charge or field
Reexamination Certificate
2000-05-17
2001-11-20
Jackson, Stephen W. (Department: 2836)
Electricity: electrical systems and devices
Electric charge generating or conducting means
Use of forces of electric charge or field
C361S235000
Reexamination Certificate
active
06320737
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a method of holding a wafer on an electrostatic chuck, a method of removing a wafer from an electrostatic chuck and an electrostatic chucking device which are used properly for etching systems, CVD systems, sputtering systems, etc. used widely for thin film forming and its patterning in fine processes represented by those for manufacturing semiconductor and other electronic devices.
2. Description of the Related Art
Conventionally, a semiconductor manufacturing system such as etching system, CVD system, sputtering system, etc. has been provided with an electrostatic chuck for fixing a wafer at a specified position so that the wafer can be processed in the manufacturing system. Such electrostatic chuck comprises a dielectric body formed by an insulator, and an electrode formed by a conductor for causing dielectric polarization in the dielectric body. The electrode is connected to a high voltage DC power supply. When a DC voltage is impressed to the electrode by this high voltage DC power supply, the dielectric body is dielectrically polarized, with which the dielectric body exhibits an attracting force. In other words, this electrostatic chuck can attract and hold the wafer on its dielectric body by the attracting force provided by impressing the DC voltage.
When removing the wafer from the electrostatic chuck after a desired processing, a voltage with reverse polarity is impressed to the electrostatic chuck so as to discharge the electric charge accumulated on the electrostatic chuck. Or the wafer is exposed to plasma to discharge the electric charge accumulated on the wafer.
When various plasma processings are carried out using such an electrostatic chuck, the temperature of the electrostatic chuck rises usually due to generated plasma. Furthermore, as in the case of an etching process, where a series of processings are carried out in a plurality of steps, the temperature of the wafer must be changed significantly between steps, and accordingly the temperature of the electrostatic chuck must also be changed significantly sometimes.
If the temperature of the electrostatic chuck is thus changed significantly during a processing, however, the following problem arises.
As a material for the dielectric body of the electrostatic chuck polyimide or ceramics is generally used, but polyimide is not suitable for use in high temperature. Thus, ceramics is usually used in processings at high temperatures such as plasma processing. As for ceramics, its specific resistance becomes low when the processing temperature is high as shown in FIG.
1
. When the processing temperature goes low, its specific resistance increases. The specific resistance changes such way according to the processing temperature, and accordingly the attracting force of the electrostatic chuck also changes according to the processing temperature. When the processing temperature goes high, therefore, the attracting force becomes strong and when the processing temperature goes low, the attracting force becomes weak as shown in FIG.
2
.
Consequently, when the temperature of the electrostatic chuck changes to which a fixed voltage is impressed constantly, the attracting force of the electrostatic chuck, that is, the wafer holding force of the electrostatic chuck also changes. If the wafer holding force is reduced at this time, problems such as wafer displacement may occur, and accordingly the processing may be failed. When the wafer holding force increases, the wafer becomes unremovable from the electrostatic chuck sometimes when it must be removed.
OBJECT AND SUMMARY OF THE INVENTION
Under such the circumstances, it is an object of this invention to provide a method for holding wafer on the electrostatic chuck, a method for removing wafer from the electrostatic chuck and an electrostatic chucking device that can prevent the problems associated with wafer holding or wafer removed caused by temperature changes of the electrostatic chuck in processes accompanied by temperature changes.
As a result of earnest studies to achieve the above object, the inventor has reached to an idea that the electrostatic chuck can provide a constant attracting force regardless of processing temperatures if the impressed voltage to the electrostatic chuck is changed with the change in its temperature as shown in FIG.
3
. Furthermore, the inventor has also reached an idea that the wafer can be removed from the electrostatic chuck without failure regardless of processing temperatures if, when a voltage of reverse polarity is impressed to the electrostatic chuck or the wafer is exposed to plasma so as to discharge the electric charge on the electrostatic chuck or the wafer, the value of the impressed voltage of reversed polarity, the voltage impression time, and the plasma exposure time are controlled according to the temperature of the electrostatic chuck. According to such ideas, the inventor has advanced the studies to complete this invention.
In other words, a method of holding a wafer on an electrostatic chuck according to the first aspect of this invention solves the problem by comprising the steps of:
setting the wafer on the electrostatic chuck;
impressing a DC voltage on the electrostatic chuck to provide the electrostatic chuck with an attracting force;
detecting a temperature of the electrostatic chuck; and
controlling the attracting force constant by changing a value of the DC voltage according to the temperature of the electrostatic chuck having been detected;
The problem can be also solved by an electrostatic chucking device which carries out the above method by comprising:
an electrostatic chuck attracting and holding a wafer thereon;
a temperature detecting unit for detecting a temperature of the electrostatic Chuck;
a power supply connected to the electrostatic chuck, which impresses a DC voltage on the electrostatic chuck to provide the electrostatic chuck with an attracting force; and
a controller for controlling the attracting force constant by changing a value of the DC voltage according to the temperature of the electrostatic chuck having been detected.
In the above method and the electrostatic chucking device, the value of the DC voltage can be controlled so that it is lowered from a preset value when the temperature of the electrostatic chuck is detected to become higher than a preset temperature and is raised from the preset value when the temperature of the electrostatic chuck is detected to become lower than the preset temperature.
Thus, according to the above method and the electrostatic chucking device, the attracting force of the electrostatic chuck for attracting and holding the wafer can be kept constant regardless of temperature changes of the electrostatic chuck.
The problem can be also solved by a method of removing a wafer from an electrostatic chuck according to the second aspect of this invention wherein the wafer is attracted and held by impressing a DC voltage on the electrostatic chuck and is removed by impressing a reverse voltage with polarity reverse to that of the DC voltage on the electrostatic chuck, and the method comprises the steps of:
detecting a temperature of the electrostatic chuck;
defining a value of the reverse voltage according to the temperature of the electrostatic chuck having been detected;
reversing polarity of the DC voltage impressed on the electrostatic chuck;
impressing the reverse voltage on the electrostatic chuck with the value of the reverse voltage having been defined; and
removing the wafer from the electrostatic chuck.
The problem can be also solved by an electrostatic chucking device which carries out the above method according to the second aspect of this invention by comprising:
an electrostatic chuck attracting and holding a wafer thereon;
a temperature detecting unit for detecting a temperature of the electrostatic chuck;
a power supply connected to the electrostatic chuck, the power supply impressing a DC voltage on the electrostatic chuck to provide the electrostatic chuck with an attra
Hirano Shinsuke
Jozaki Tomohide
Jackson Stephen W.
Sonnenschein Nath & Rosenthal
Sony Corporation
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