Coating apparatus – Gas or vapor deposition – With treating means
Reexamination Certificate
1998-11-02
2001-12-04
Bueker, Richard (Department: 1763)
Coating apparatus
Gas or vapor deposition
With treating means
C118S715000, C118S724000, C118S728000, C118S730000, C136S232000
Reexamination Certificate
active
06325858
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to apparatus for the high temperature processing of substrates and, more particularly to chemical vapor deposition (CVD) of materials on semiconductor wafers in a CVD reactor.
BACKGROUND OF THE INVENTION
Generally, in CVD reactors, the material being deposited not only deposits on the wafer, as is desired, but some material, not necessarily the same as that on the wafer, is also deposited on the reactor chamber walls and other parts within the reactor, notably the wafer support and a ring positioned around the wafer support in many reactors. Periodically, in order to maintain a repeatable process, the chamber has to be cleaned. Such chamber cleaning typically occurs by heating the wafer support, chamber walls and other parts to a suitably high temperature and admitting a flow of a halogen containing gas, for example Hcl.
Reactors for epitaxial deposition commonly employ a susceptor and a surrounding ring which helps to control the temperature of the susceptor. These components are usually made from graphite and coated with silicon carbide (SiC). Eventually, the Hcl etch will penetrate the SiC coating which will cause rapid deterioration of the properties of the deposited films. Hence, they must be replaced. One type of well-known reactor employs thermocouples adjacent the ring for sensing the temperature of the rings surrounding the susceptor, which in turn is an indirect measure of the temperature of the susceptor and a wafer positioned on it. These thermocouples are usually sheathed with quartz. Frequent thermal cycling of the quartz to temperatures in excess of 1000° C. causes devitrification of the quartz sheath and failure of the thermocouples, thus requiring replacement.
Commonly, the chamber is formed of quartz. A problem in high temperature chemical vapor deposition operations is that reactant gases may coat the interior of quartz chamber walls. Coatings on the chamber walls can have a number of undesirable aspects including the flaking of particles off the walls and the need for more frequent cleaning of the chamber. Some of the material depositing on the quartz chamber walls may not be etched away when the chamber is cleaned. If sufficient deposits gather, the quartz chamber locally loses its transparency and will heat rapidly by radiation from the lamps conventionally positioned adjacent the exterior of an upper chamber wall and adjacent the exterior of a lower chamber wall. This eventually requires the need to wet clean or even to replace the quartz chamber.
If the chamber walls become too hot, the reactant gases can deposit on the walls in similar fashion to depositing on a wafer. Quartz is the material of choice for chamber walls because quartz is to a large extent transparent to the heat energy provided by the lamps. As the wafer, the susceptor and the surrounding compensation ring are heated by this radiant energy, they reradiate energy back towards the chamber walls. Some of this reradiated energy has a wave length at which a significant portion of the energy is absorbed by the quartz chamber walls. Consequently, to maintain the temperature of the walls below that at which deposition on the walls will occur, it is customary to flow air or other coolant across the lamps and adjacent chamber walls. This cooling, however, can cause some sections of the chamber walls to be maintained at temperatures at which reactant gases can condense on those cooler areas. Other chamber components, such as a spider used to support the susceptor and a stand used to support the ring, are also commonly made of quartz and are therefore subject to the same problems of devitrification and exposure to processing gases.
The need to replace susceptors, rings, thermocouples, chambers and various other chamber components naturally results in down-time for the reactor and significant costs for replacement components. In addition, there is significant time and expense in returning the reactor to the condition to provide the desired film properties on the wafers being coated.
It is an object of this invention to significantly extend the life of the components within the CVD chamber. It is a further object of this invention to decrease the amount of deposits on the chamber walls and some components in the CVD chamber to extend their life. It is also an object to increase the cleaning efficiency of the cleaning agent. Related to the last two objects, it is a further object of this invention to reduce down time and hence increase throughput.
SUMMARY OF THE INVENTION
In accordance with the invention, there is provided a chemical vapor deposition reactor for the processing of semiconductor wafers wherein the life of the chamber and of all the internal components is extended and matched to the life of the process chamber by proper choice of infrared absorbing and nonabsorbing parts/materials. In one arrangement, the chamber is in the form of a horizontally oriented quartz tube divided into an upper region and a lower region by a front divider plate, a susceptor surrounded by a temperature compensation or slip ring, and a rear divider plate. In the upper region, the flow of reactants is introduced to cause the growth of silicon or other material on a wafer positioned on the susceptor. In the lower region of the reactor, a purge gas is introduced to keep the reactive gases from diffusing or flowing into the bottom part of the reactor.
To minimize the deposition of unused reactant gases on the chamber walls downstream from the susceptor, surfaces are positioned in the gas stream to cause some of the unused reactants to deposit on them rather than on the adjacent chamber walls. The surfaces are made of infrared light absorbing material that can withstand high temperatures, such as silicon carbide. In one arrangement, the surfaces are on a plate that extends generally parallel to the gas flow and is spaced between the rear chamber divider plate and the upper wall of the chamber so that both the upper and lower surfaces of this so-called getter plate are exposed to the unused reaction gases. Also, the plate reradiates energy in a broader spectrum including wave lengths more readily absorbed by the quartz walls. Positioning the plate close to the upper chamber wall maximizes that effect. By properly controlling the temperature, this arrangement minimizes the deposition or condensation on the cooler, adjacent quartz chamber wall, and improves the cleaning of the wall too, thereby extending the life of the chamber.
Another technique for minimizing deposition on quartz chamber walls in this manner is to position a shield or heat absorber adjacent the chamber of walls that tend to be to cool or otherwise tend to receive the most deposition or condensation. This can vary for differing chamber configurations. For example, in some chambers, walls surrounding a susceptor may benefit from the use of such shields. In addition to lengthening the life of the chamber, such shields can minimize particle problems due to the flaking of deposition coating. Further, doping of subsequent wafers as a result of leftover dopant in the deposit on the chamber is also minimized. Blockage of the radiant heat through the chamber walls surrounding the susceptor restricts cooling on the edges of the chamber.
Mounted adjacent the susceptor are one or more thermocouples having an external sheath more durable than quartz, such as silicon carbide. Silicon carbide does not devitrify or wear out upon high temperature cycling and, thus, the life of the thermocouple sheath is greatly extended over that of previously used quartz sheaths. Because silicon carbide might react unfavorably with the thermocouple, a thin quartz or other nonreacting material sleeve is positioned over the thermocouple junction within the silicon carbide sheath.
Silicon carbide shields are provided throughout the chamber to protect quartz reactor components from devitrification. In one embodiment, a silicon carbide cap is provided over a quartz sheath covering a central thermocouple, thereby protecting the quartz from the
Barrett Eric
Goodman Matt
Halpin Mike
Jacobs Loren
Meyer Michael J.
ASM America Inc.
Bueker Richard
Knobbe Martens Olson & Bear LLP
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