Coating apparatus – Control means responsive to a randomly occurring sensed... – Temperature responsive
Reexamination Certificate
2001-08-17
2002-12-10
Lund, Jeffrie R. (Department: 1763)
Coating apparatus
Control means responsive to a randomly occurring sensed...
Temperature responsive
C118S725000, C118S696000, C156S345240, C392S407000, C392S411000, C392S416000, C392S418000, C219S390000, C219S395000, C219S411000, C219S412000, C219S413000
Reexamination Certificate
active
06491757
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to supports for wafers in semiconductor processing chambers and, more particularly, to a system for supporting a wafer above a susceptor within a chemical vapor deposition chamber.
BACKGROUND OF THE INVENTION
High-temperature ovens, or reactors, are used to process semiconductor wafers from which integrated circuits are made for the electronics industry. A circular wafer or substrate, typically made of silicon, is placed on a wafer support called a susceptor. Both the wafer and susceptor are enclosed in a quartz chamber and heated to high temperatures, such as 600° C. (112° F.) or higher, frequently by a plurality of radiant lamps placed around the quartz chamber. A reactant gas is passed over the heated wafer, causing the chemical vapor deposition (CVD) of a thin layer of the reactant material on the wafer. Through subsequent processes in other equipment, these layers are made into integrated circuits, with a single layer producing from tens to thousands of integrated circuits, depending on the size of the wafer and the complexity of the circuits.
If the deposited layer has the same crystallographic structure as the underlying silicon wafer, it is called an epitaxial layer. This is also sometimes called a monocrystalline layer because it has only one crystal structure.
Various CVD process parameters must be carefully controlled to ensure the high quality of the resulting semiconductor. One such critical parameter is the temperature of the wafer during the processing. The deposition gas reacts at particular temperatures and deposits on the wafer. If the temperature varies greatly across the surface of the wafer, uneven deposition of the reactant gas occurs.
In certain batch processors (i.e., CVD reactors which process more than one wafer at a time) wafers are placed on a relatively large-mass susceptor made of graphite or other heat-absorbing material to help the temperature of the wafers remain uniform. In this context, a “large-mass” susceptor is one which has a large thermal mass relative to the wafer. Mass is equal to the density times volume. The thermal mass is equal to mass times specific heat capacitance.
One example of a large-mass susceptor is shown in U.S. Pat. No. 4,496,609 issued to McNeilly, which discloses a CVD process wherein the wafers are placed directly on a relatively large-mass, slab-like susceptor and maintained in intimate contact to permit a transfer of heat therebetween. The graphite susceptor supposedly acts as a thermal “flywheel” which transfers heat to the wafer to maintain its temperature uniform and relatively constant. The goal is to reduce transient temperature variations around the wafer that would occur without the “flywheel” effect of the susceptor.
In recent years, single-wafer processing of larger diameter wafers has grown for a variety of reasons including its greater precision as opposed to processing batches of wafers at the same time. Although single-wafer processing by itself provides advantages over batch processing, control of process parameters and throughput remains critical. In systems in which the wafer is supported in intimate contact with a large-mass, slab-like susceptor, the necessity of maintaining uniform susceptor temperature during heat-up and cool-down cycles limited the rate at which the temperature could be changed. For example, in order to maintain temperature uniformity across the susceptor, the power input to the edges of the susceptor had to be significantly greater than the power input to the center due to the edge effects.
Another significant problem faced when attempting to obtain high-quality CVD films is particulate contamination. One troublesome source of particulates in the CVD of metals and other conductors is the film that forms on the back side of the wafer under certain conditions. For example, if the wafer back side is unprotected or inadequately protected during deposition, a partial coating of the CVD material forms thereon. This partial coating tends to peel and flake easily for some types of materials, introducing particulates into the chamber during deposition and subsequent handling steps. One example of protecting the back side of a wafer during processing is given in U.S. Pat. No. 5,238,499 to van de Ven, et al. In this patent an inert gas is introduced through a circular groove in the peripheral region of a support platen. In U.S. Pat. No. 5,356,476 to Foster, et al., a semiconductor wafer processing apparatus is shown, including a plurality of ducts for introducing helium or hydrogen around the perimeter of a wafer to prevent flow of reactant gases downwardly into a gap between the perimeter of the wafer and a wafer support lip. The aforementioned devices, however, share the feature of rather large wafer support platens, characterized by the aforementioned detrimental high thermal mass.
Presently, there is a need for an improved wafer support system while ensuring temperature uniformity across the wafer surface.
SUMMARY OF THE INVENTION
The present invention embodies a susceptor which supports a wafer spaced therefrom and effectively decouples conductive heat transfer between the two elements. The wafer is supported on one or more spacers in a recess preferably in an upper surface of the susceptor, the top plane of the wafers preferably being approximately level with an outer ledge of the susceptor. In one arrangement, spacer pins are utilized, and in another a single spacer ring is used. The susceptor preferably includes a plurality of interior passages opening into the recess at a plurality of small sweep gas holes. A sweep gas flows through the susceptor and out the holes and protects the back side of the wafer from deposition gas and particulate contamination. The sweep gas is heated as it flows through the susceptor so as not to cause localized cooling of the wafer and possible areas of slip.
In one embodiment, the susceptor is formed by top and bottom mating sections and the internal passages are formed by grooves in one of the juxtaposed surfaces of the two sections. Desirably, a multi-armed member supports and rotates the susceptor, the member preferably being substantially transparent to radiant energy. The arms of the support member are preferably hollow and deliver sweep gas to the lower surface of the susceptor at apertures in communication with the internal passages. Some of the sweep gas may be diverted to exit the susceptor proximate the spacer pins to provide sweep gas protection therearound at all times.
In another aspect of the invention the spacer ring mentioned is located to be positioned beneath the periphery of the wafer and serves to reduce the size of the sweep gas outlet from beneath the wafer and to block deposition gas from flowing to the wafer backside. The ring is configured to support the wafer in one arrangement. Preferably, the ring and the susceptor are configured to form sweep gas outlet passages. As another embodiment, the ring is spaced slightly from the wafer to provide a thin annular outlet for the sweep gas, and the wafer is supported by pins.
In one aspect, the invention provides a susceptor to be positioned in a high temperature processing chamber for supporting a wafer to be processed. The susceptor includes a thin, substantially disc shaped lower section and a thin, substantially disc shaped upper section having a lower surface in engagement with an upper surface of said lower section. One of the sections has an outer diameter larger than that of the other section, the larger section having a recess in which the other section is positioned. One or more gas channels are defined by the engaging surfaces of the sections. The susceptor includes one or more gas inlets in the lower section opening to its lower surface and the channels. One or more gas outlets in the upper section open to the upper surface of the upper section in an area beneath that in which a wafer to be processed is to be positioned. The mating recess is preferably formed in a lower surface of the upper section. In one form, the chan
Foster Derrick W.
Glenn Hartmann
Goodman Matthew
Halpin Michael W.
Hawkins Mark R.
ASM America Inc.
Knobbe Martens Olson & Bear LLP
Lund Jeffrie R.
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