Electric heating – Heating devices – Combined with container – enclosure – or support for material...
Reexamination Certificate
2002-09-17
2004-05-25
Fuqua, Shawntina (Department: 3742)
Electric heating
Heating devices
Combined with container, enclosure, or support for material...
C219S443100, C219S446100, C219S468100, C219S542000, C219S543000, C118S620000, C118S621000, C118S725000, C118S730000, C361S233000, C361S234000
Reexamination Certificate
active
06740853
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a multi-purpose wafer holder for holding a wafer (or other substrate) during processing in a plasma system. More specifically, the holder includes at least one stacked layer to provide clamping, conduction, heating and/or cooling. Examples of layers include an electrostatic chuck, a multi-zone He gas delivery system, a multi-zone resistance heater, and a multi-zone cooling system.
2. Description of the Background
It is known within the semiconductor processing field to use resistance heaters to heat a semiconductor wafer that is in the presence of a processing gas. Heating alters the characteristics of the reaction process occurring on the semiconductor wafer. For example, such resistance heaters have been used within quasi-hot wall, or warm wall, reactors where the resistance heater serves as the support for the silicon wafer and simultaneously heats the wafer to carry out a predetermined processing step. Often, a processing gas of a predetermined purity and/or pressure is circulated over the heated silicon wafer to modify the surface characteristics of the silicon wafer. Chemical vapor deposition is one environment in which such resistance heaters are used to process semiconductor wafers.
Such resistance heaters have typically employed heating elements of (1) a nickel-chromium alloy (nichrome) or (2) an aluminum-iron alloy, which are electrically resistive and which generate heat when an electrical current is applied through the elements. Examples of commercially available materials commonly used to fabricate resistive heating elements employed in ovens are Kanthal, Nikrothal and Alkrothal, which are registered trademark names for metal alloys produced by Kanthal Corporation of Bethel, Conn. The Kanthal family includes ferritic alloys (FeCrAl) and the Nikrothal family includes austenitic alloys (NiCr, NiCrFe).
However, resistance heater elements have not, in the past, been exposed to the processing gas that is circulated over the silicon wafer within the reactor. Moreover, large heater elements with large thermal masses have been required to provide a barrier of material between the wafer and the heater elements when heating in known plasma systems. Known electrically resistive materials, such as some of the Kanthal alloys, require an oxygenated environment for long element life. The presence of oxygen causes an aluminum oxide to form upon the surface of a Kanthal alloy heater element which inhibits evaporation of the heater element. An acceptable level of oxygen is 5% of 760 torr with no other gases which react to the alloy surface. Alternatively, environments with less oxygen can cause the oxide layer to become porous and allows iron oxide to migrate along grain boundaries, causing contamination of the system.
Traditionally, the heater elements of wafer processing systems also have had thermal masses that are significantly greater than the wafer or substrate that they have heated. In known systems, heater elements weighing tens of pounds have been used to heat wafers weighing only two ounces. As a result of the large thermal mass, the heater has a pronounced lateral profile which heats a wafer much more in the center region than compared to the edge region of the wafer. In order to compensate for the thermal profile, complicated devices having on the order of 30 parts were used in known systems to adjust the applied heat. A large thermal mass also leads to a high thermal inertia—an effect where the heater element continues to apply heat to the wafer (or other substrate) after the wafer has already achieved its desired temperature. Also, in known systems, radial or lateral heat transfer has been higher than in the substrate being processed, making it harder to isolate changes in temperature in the wafer.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a wafer holder that is fabricated as a stack of at least one element, each element performing at least one wafer processing function.
It is a further object of the present invention to provide an improved wafer chuck using electrostatic clamping to provide a more uniform thermal conduction of a wafer than a non-electrostatically clamped wafer.
It is yet another object of the present invention to measure the effective clamping of a wafer to the electrostatic chuck by measuring the capacitance of (1) the wafer and (2) two adjacent electrodes housed inside the chuck that provide the clamping.
It is an additional object of the present invention to provide an He gas delivery system (known as a Helium back side) for increasing conduction to a wafer.
It is a further object of the present invention to provide a multi-zone He gas delivery system for increasing conduction in one region of a wafer more than in another region of the wafer by providing different pressures in the different zones.
It is another object of the present invention to provide a resistance heater for heating a semiconductor wafer within a wafer processing reactor wherein the processing gas circulated about the wafer is isolated from the resistance heater element.
It is another object of the present invention to provide a resistance heater which utilizes materials such as Kanthal alloys, Hastaloy, platinum, and molybdenum.
It is yet another object of the present invention to provide an oxygenated environment for those high resistance heater elements which would otherwise degrade in a low oxygen environment.
It is still another object of the present invention to provide such a resistance heater having multiple heating zones for better control of temperature uniformity.
It is a further object of the present invention to provide a resistance heater where the gas environment surrounding the heater element differs from and is completely isolated from the gas environment within the semiconductor wafer reactor.
It is another object of the present invention to measure the heat transfer characteristic of a substrate to be heated and to provide a resistance heater which is designed to apply additional heat to areas which have higher heat loss.
It is a further object of the present invention to provide a resistance heater configured to provide uniform heating across a non-circular element to be heated.
It is an additional object of the present invention to provide a resistance heater with a thermal mass closely equivalent to the thermal mass of the wafer to be heated.
It is an object of the present invention to provide a cooling system to reduce the temperature of a substrate before, during or after a plasma process.
It is an additional object of the present invention to provide a multi-zone cooling system that cools a wafer before, during or after a plasma processing step according to a heat loss pattern of the wafer.
It is another object of the present invention to provide a combined stack of more than one of the above elements (i.e., more than one of a multi-zone electrostatic chuck, a multi-zone He gas delivery system, a multi-zone resistance heater, and a multi-zone cooling system).
Briefly described, and in accordance with a first embodiment, the present invention relates to a stack of elements onto which a substrate (e.g., a wafer or an LCD panel) can be placed during a series of one or more plasma or thermal processing steps. The types of elements in the stack include, but are not limited to: an electrostatic clamp (either single- or multi-zone), a He gas delivery system (either single- or multi-zone), a resistance heater (either single- or multi-zone), and/or a cooling system (either single- or multi-zone). At least one of the elements is selected based on the processing step(s) to be performed. Each element is hermetically sealed from each other element and from the processing environment. Accordingly, one embodiment of the present invention acts as more than one of: an electrostatic chuck with electrostatic clamping, a resistance heater, and a cooling system.
According to one embodiment of the present invention, an electrostatic
Johnson Wayne L.
Strang Eric J.
Fuqua Shawntina
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Tokyo Electron Limited
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