Electricity: electrical systems and devices – Electric charge generating or conducting means – Use of forces of electric charge or field
Reexamination Certificate
1996-07-19
2001-01-16
Sherry, Michael J. (Department: 2836)
Electricity: electrical systems and devices
Electric charge generating or conducting means
Use of forces of electric charge or field
C279S128000
Reexamination Certificate
active
06175485
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to the fabrication of integrated circuits. More particularly, the invention provides an electrostatic chuck having an improved dielectric coating and a method for fabricating the improved dielectric coating.
Electrostatic chucks are devices which have gained wide usage in the semiconductor industry for clamping semiconductor wafers during manufacturing processes, such as high-density plasma reactions. Electrostatic chucks employ an electrostatic force between oppositely charged surfaces to secure the wafer to the chuck. Fabrication of electrostatic chucks typically involves machining a process-compatible metal, such as aluminum or anodized aluminum, into a suitable support pedestal and grit-blasting the top surface of the pedestal. A layer of dielectric material, such as ceramic, is then typically applied to the upper surface of the pedestal and ground to a smooth, planar upper surface for supporting the wafer. During processing, a voltage is applied between the wafer and the metal pedestal, generating an opposing charge on either side of the dielectric layer. This opposing charge creates an attractive, substantially uniform, coulomb force therebetween that secures the wafer to the dielectric layer.
One important consideration in the manufacture of electrostatic chucks is the electrical properties of the layer of dielectric material, such as its dielectric strength and dielectric constant. For example, the clamping force of an electrostatic chuck, i.e., the force with which the wafer is held in place on the chuck, generally increases with the square of the applied voltage to the chuck (for a given dielectric layer thickness). In typical processes, a relatively large voltage is applied across the electrostatic chuck to clamp the semiconductor wafer to the chuck during processing. This large clamping voltage is usually required because cooling gas is delivered between the semiconductor wafer and the chuck to decrease the temperature of the wafer. This cooling gas impinges on the back side of the wafer and lifts the wafer away from the chuck. Increasing the dielectric strength of the dielectric layer increases the capability of the dielectric layer to withstand higher applied voltages without causing dielectric breakdown across the layer and subsequent failure of the electrostatic chuck.
Another important consideration in the manufacturing of electrostatic chucks is the porosity of the dielectric layer. A porous dielectric layer is less resistant to bombardment from plasma during processing and, therefore, may wear down relatively quickly, increasing the downtime and decreasing the throughput of the wafer manufacturing process. Porosity also has an adverse effect on the electrical characteristics of the dielectric layer, i.e., the layer's electrical stability and dielectric strength. In addition, a porous dielectric layer tends to absorb moisture and/or gases from the chamber into the open pores of the dielectric layer. Moisture and gas build-up within these pores further degrades the electrical characteristics of the dielectric layer.
Dielectric layers are typically formed by plasma spraying a ceramic powder, such as aluminum oxide, onto the upper surface of a metallic pedestal. In the plasma spray process, an electric arc is established between a pair of spaced electrodes, and gas is directed in contact with one of the electrodes so that the gas contains an electric arc. The powder used to produce the coating is mixed with the arc-containing gas and the mixture is constricted through a nozzle and deposited on the pedestal to form the dielectric layer. Although the plasma spraying process produces adequate dielectric layers, it would be desirable to improve the electrical properties of these dielectric layers to thereby improve the performance and increase the lifetime of electrostatic chucks.
In addition, it would be desirable to improve the yield produced during the manufacturing of electrostatic chucks (i.e., the ratio of the amount of serviceable electrostatic chucks to the total amount of chucks produced). One factor that reduces the yield of chucks produced by the plasma spray process is metallic contamination during processing. Metal particles are occasionally removed from the electrodes during plasma spraying and mixed into the powder that forms the dielectric layer. Metal particles on the surface of the dielectric layer may damage the semiconductor wafer during processing. In addition, the metal particles may provide a conductive path that allows voltage to arc through the dielectric layer. For these reasons, electrostatic chucks having a critical amount of metal contaminants in the dielectric layer are typically considered unserviceable, which reduces the overall yield and increases the cost of manufacturing the electrostatic chucks.
SUMMARY OF THE INVENTION
The present invention provides an electrostatic chuck having an electrically insulating layer, such as a dielectric layer, with improved electrical properties and increased resistance to plasma and chemical corrosion. The invention also provides a method for fabricating the electrically insulating layer and applying the layer to a pedestal to form a portion of an electrostatic chuck.
The electrostatic chuck of the present invention comprises an electrically conductive pedestal and an electrically insulating layer applied to the upper surface of the pedestal. The electrically insulating layer is usually a dielectric layer formed from a ceramic material, such as aluminum oxide. The electrically insulating layer has a porosity that is at least less than 4 percent of its total volume. Usually, the porosity of the insulating layer is less than 2 percent and preferably less than 1% of its total volume. This low porosity enhances the layer's resistance to plasma bombardment and chemical corrosion and improves the electrical properties of the layer, such as the dielectric strength and the dielectric constant of the layer. In addition, the low porosity decreases the adsorption of moisture and other gases into the dielectric layer, which further enhances the electrical properties of the chuck.
The dielectric layer of the present invention has improved electrical properties over many existing dielectric layers for electrostatic chucks. Usually, the dielectric layer will have a strength greater than 300 V/mil and preferably greater than 400 V/mil in a substantially dry state. This high dielectric strength minimizes arc breakdown across the dielectric layer and subsequent failure of the electrostatic chuck during processing, thereby allowing the operator to apply larger clamping forces to the wafer. The dielectric layer of the present invention also has a stable dielectric constant of about 8.5 to 11, after a relatively short drying time, which reduces the downtime of the electrostatic chuck. In addition, the upper surface of the dielectric layer has an average surface roughness, R
a
, of about 1-2 R
a
after suitably grinding. The smooth upper surface decreases particle contamination on the back side of semiconductor wafers that are placed on or near the upper surface of the dielectric layer.
Another advantage of the present invention is that the dielectric layer has a substantially low percentage of contaminants. Usually, the dielectric layer will have less than 400 ppm contaminants and preferably less than 200 ppm contaminants. Contaminants, particularly metallic contaminants, degrade the performance of the electrostatic chuck, because they may provide a conductive path that allows voltage to arc through the dielectric layer. In addition, the metallic contaminants may be transferred to the back side of the semiconductor wafers during processing, which damages or destroys the wafers.
The dielectric layer of the present invention is fabricated and applied to an electrically conducting pedestal with a detonation gun process. This process includes combining a coating material, preferably in the form of a powder, with a fuel gas mixture in a conventional or spec
Krishnaraj Padmanabhan
Lingampalli Ramkishan Rao
Lue Brian
Wu Shun Jackson
Applied Materials Inc.
Sherry Michael J.
Townsend & Townsend & Crew
LandOfFree
Electrostatic chuck and method for fabricating the same does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Electrostatic chuck and method for fabricating the same, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Electrostatic chuck and method for fabricating the same will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2462694