Heating element with a diamond sealing material

Details Heating element with a diamond sealing material Heating element with a diamond sealing material

1999-05-14

2001-02-20

Pelham, Joseph (Department: 3742)

Electric heating

Heating devices

Combined with container, enclosure, or support for material...

C219S390000, C118S725000, C118S728000

Reexamination Certificate

active

06191390

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates generally to a heating element, and more particularly to a heating element disposed in a support plate for heating a substrate in a processing chamber.
A susceptor is a mechanical part that holds a substrate in a processing chamber for a fabrication step, such as chemical vapor deposition (CVD). The susceptor includes a substrate support plate mounted on a stem, along with a lift assembly for raising and lowering the substrate within the processing chamber. The substrate support plate is heated to facilitate the fabrication process. Typically, a heating element is disposed within the support plate. The heating element maybe a tube assembly which includes a heating filament surrounded by an outer sheath. The space between the heating filament and the outer sheath may be filled by a sealing material.
Heat density refers to the amount of heat which is generated by a heating element over a given length of the element. Power density is a related concept which refers to the amount of power (in watts) which is dissipated over a given length of the element. Heating elements having high heat and power densities are preferable in substrate fabrication processes to minimize the area of the support plate occupied by the heating element, while still enabling adequate heating of a substrate.
To achieve high heat and power density performance for the heating element, the sealing material should efficiently transfer heat from the filament to the outer sheath; that is, the sealing material should be thermally conductive. However, the sealing material should also be electrically insulative to prevent a short circuit between the heating filament and outer sheath. The outer sheath of the heating element may be constructed of a metal such incoloy, which is an alloy primarily composed of iron, nickel and chromium manufactured by The International Nickel Co., Inc. The sealing material may be magnesium oxide (MgO) or boron nitride (BN).
The susceptor plate undergoes heating and cooling each time a substrate is processed in the chamber. This repeated heating and cooling subjects the sealing material to considerable thermal stresses. The shock of repeated thermal stresses may reduce the thermal conductivity or increase the electrical conductivity of the sealing material. If the thermal conductivity of the sealing material decreases, heat will accumulate in the filament. As a result, the filament may burnout or the susceptor may be not adequately heated. If the electrical conductivity of the sealing material increases, then there may be a short circuit between the filament and the outer sheath. Thus, the sealing material should be resistant to thermal shock so that the heating element has a long lifetime.
SUMMARY OF THE INVENTION
In general, in one aspect, the invention is directed to a heating element. The heating element has a heating filament, a sheath surrounding the heating filament, and a sealing material disposed inside the sheath to conduct heat from the filament to the sheath. The sealing material contains a diamond powder.
Implementations of the invention may include the following. The sealing material may also include a filler material, such as magnesium oxide or boron nitride. The diamond powder may have a particle size of about five to fifty microns or fifteen to thirty microns. The diamond powder may have a particle size selected to provide the sealing material with a thermal conductivity of several hundred watts per meter per degree Kelvin and an electrical resistivity of about 10
16
. The diamond powder may have a particle size selected to provide the sealing material with a thermal conductivity and an electrical resistivity greater than those of a ceramic material. The sheath may be electrically conductive.
In general, in another aspect, the invention is directed to a substrate support structure for use in a processing chamber. The substrate support structure includes a plate having a top surface for supporting a substrate, and a heating element in the plate. The sealing material in the heating element contains a diamond powder.
Among the advantages of the invention are the following. A substrate support plate is provided with a heating element having a long lifetime. The heating element includes a sealing material which is which is thermally conductive, electrically insulative, resistant to thermal shock, and chemically inert. The heating element assures proper heat dissipation for high heat and power density applications. The particle size of the diamond powder may be selected to provide desired thermal and electrical properties.
Additional advantages of the invention will be set forth in the description which follows and in part will be obvious from the description, or may be learned by practice of the invention. The advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the claims.


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