Electricity: electrical systems and devices – Electric charge generating or conducting means – Use of forces of electric charge or field
Reexamination Certificate
2001-08-10
2004-11-02
Sircus, Brian (Department: 2836)
Electricity: electrical systems and devices
Electric charge generating or conducting means
Use of forces of electric charge or field
Reexamination Certificate
active
06813134
ABSTRACT:
FIELD OF THE INVENTION AND RELATED ART STATEMENT
The present invention relates to an electrostatic chucking device which attracts and holds a sample such as a wafer or the like using an electrostatic force in various devices used in a semiconductor fabrication process, for example, and a method for manufacturing such electrostatic chucking devices.
In a semiconductor manufacturing process, a sample such as a wafer or the like is required to be processed in vacuum in an etching device, a plasma CVD device, an ion implantation device, an ashing device, an electric beam lithography, an X ray lithography or the like, for example. Here, an electrostatic chucking device is used as means for holding the wafer or the like.
This electrostatic chucking device is, in general, constituted by laminating an electrostatic chucking sheet having a laminar structure which is comprised of a first insulation layer, an electrode layer and a second insulation layer on a metal substrate. A wafer is placed on the second insulation layer of the electrostatic chucking sheet and a high voltage is applied between the wafer and the electrode layer. By making use of an electrostatic attractive force (Coulomb force) which is generated between the wafer and the electrode, the wafer is attracted to and held on a stage. A polyimide film or a ceramic thin plate which exhibits an excellent heat resistance is used as a first insulation layer, a metal vapor-deposited film or a plated film is used as an electrode layer, and polyimide film is used as the second insulation layer. Further, adhesive layers are respectively formed between the metal substrate and the first insulation layer, between the first insulation layer and the electrode layer, and between the electrode layer and the second insulation layer.
In such an electrostatic chucking device, it is necessary to maintain a wafer surface temperature at a low temperature by efficiently dissipating heat energy generated in the inside of the wafer in use. Accordingly, various means have been proposed to cope with this task.
For example, Japanese Patent Publication 87177/1993 proposes a technique which enhances the thermal conductivity of the whole electrostatic chucking device by making a thickness of an electrostatic chucking sheet (first insulation layer, electrode layer and second insulation layer) which is laminated on a metal substrate as thin as possible or by dispersing thermal conductive fillers as thin in one or two adhesive layers which are inserted for adhesion between the metal substrate, the first insulation layer, the electrode layer and the second insulation layer.
Further, Japanese Laid-open Patent Publication 209,256/1998 and Japanese Laid-open Patent Publication 209,257/1998 respectively have proposed an electrostatic chucking device in which a first insulation layer is comprised of an insulation plate made of ceramic, wherein a thermal conductivity is enhanced by making the layer thickness of respective adhesive layers thinner and when an insulation film which constitutes a second insulation layer laminated on a ceramic insulation plate is fatigued, the insulation film can be easily exchanged.
Further, Japanese Laid-open Patent Publication 297,805/1999 has proposed an electrostatic chucking device which can prevent the worsening of the flatness of a wafer attraction surface or the peeling-off of an adhesive layer from a ceramic insulation plate for a long period by using an adhesive containing rubber components and phenol anti-oxidizing agent as a layer which adheres a metal substrate and a first insulation layer which is laminated on the metal substrate and is made of a ceramic insulation plate.
However, in these conventional electrostatic chucking devices, in case the electrostatic chucking device is mounted on a plasma etching device, for example, when its use time exceeds 300 to 600 hours, an electrostatic chucking sheet which is mounted on a metal substrate is usually gradually peeled off from a periphery thereof. Accordingly, the electrostatic chucking sheet loses its flatness and it becomes difficult to bring a wafer into uniform contact with a surface of the electrostatic chucking sheet. This generates the difference in the cooling efficiency depending on portions of the wafer so that it gives rise to the irregularities with respect to the temperature distribution. Particularly, the failure in cooling in an outer peripheral portion of the wafer has a possibility to cause a serious defect such as a seizure of resistor due to overheating.
Further, when the phenomenon that the outer peripheral portion of the electrostatic chucking sheet is peeled off further progresses, the outer peripheral portion is rolled up from a substrate so that a warping force of the electrostatic chucking sheet exceeds an attraction force of the electrostatic chucking device to attract the wafer. Accordingly, a gap is generated between an attraction surface and the wafer even in the state that the wafer is attracted so that He gas which is supplied between the attraction surface and a rear surface of the wafer as a heat transmission medium leaks through this gap. As a result, it is difficult for the electrostatic chucking device to achieve or maintain a given gas pressure so that the wafer cooling ability of the He gas becomes insufficient whereby normal etching processing cannot be performed or a whole device may become inoperable when it is interlocked resulting in the ending of the lifetime of the electrostatic chucking device.
In view of the above, inventors of the present invention have extensively studied a mechanism which generates the problem on the peeling-off of the outer peripheral portion of the electrostatic chucking sheet. As the result of the studies, the inventors have made a following finding. That is, when an epoxy-based adhesive, a rubber-based adhesive, a modified polyester-based adhesive or the like is used as material of the adhesive layers formed for adhesion between the metal substrate, the first insulation layer, the electrode layer and the second insulation layer, or when an adhesive which contains one or two kinds of copolymers selected from a group consisting of a butadiene-acrylonitrile copolymer, an olefin-based copolymer and a polyphenyl ether copolymer and a hindered phenol-based anti-oxidizing agent is used as such adhesive layers, the adhesive layers are subjected to a severe corrosion from the outer peripheral portions thereof due to plasma particles at the time of performing the plasma etching and hence, only the adhesive layers are gradually burnt out so that the electrostatic chucking sheet is peeled off from the outer peripheral portion. The inventors also have found that this problem is particularly noticeable with respect to the adhesive layer formed for adhesion between the metal substrate and the first insulation layer.
In the electrostatic chucking device which is constituted of the metal substrate, the first insulation layer, the electrode layer, the second insulation layer and the adhesive layers, the heat resistance of the adhesive layers is lower than that of the other constituent members and hence, an upper limit of the use temperature of the electrostatic chucking device is determined based on the heat resistance of the adhesive layers.
Accordingly, as the adhesive layers, the use of an adhesive which exhibits the excellent heat resistance such as a polyimide-based adhesive, a modified polyamide-based adhesive or a polyamide-imide-based adhesive can be considered.
However, the hardening temperature of such a heat resistant adhesive usually exceeds 300° C. Accordingly, when an aluminum alloy which is subjected to an alumite treatment is used as the metal substrate of the electrostatic chucking device, due to the difference of thermal expansion coefficient between the aluminum alloy and an alumite film (the thermal expansion coefficient of the aluminum alloy being usually approximately three times greater than the thermal expansion coefficient of the alumite film), cracks occur in the alumite film because of heating
Miyashita Kinya
Tatsumi Yoshiaki
Arent & Fox PLLC
Creative Technology Corporation
Kitov Zeev
Sircus Brian
LandOfFree
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