Electric resistance heating devices – Heating devices – Radiant heater
Reexamination Certificate
1999-03-22
2001-10-09
Walberg, Teresa (Department: 3742)
Electric resistance heating devices
Heating devices
Radiant heater
C219S390000, C219S405000, C118S724000, C118S725000
Reexamination Certificate
active
06301434
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The field of the present invention relates in general to semiconductor processing. More particularly, the field of the invention relates to a system and method for chemical vapor deposition (CVD) and thermal processing, such as epitaxial deposition.
2. Background
A variety of semiconductor processes require uniform thermal processing at high temperatures. Examples of such processes include rapid thermal anneal (RTA) and CVD. In many systems, high intensity lamps (usually tungsten-halogen lamps or arc lamps) are used to selectively heat a wafer within a cold wall furnace. Since the lamps have very low thermal mass, the wafer can be heated rapidly. Rapid wafer cooling is also easily achieved since the heat source may be turned off instantly without requiring a slow temperature ramp down. Lamp heating of the wafer minimizes the thermal mass effects of the process chamber and allows rapid real time control over the wafer temperature.
However, it is often difficult to control the temperature of the semiconductor substrate using only low thermal mass lamp heating. Temperature gradients during processing can lead to defects such as crystallographic slip and non-uniform deposition of materials onto the semiconductor substrate. Some reactors use a large thermal mass silicon carbide coated graphite susceptor to maintain temperature uniformity of the substrate during processing. The substrate is placed on the susceptor which acts as a thermal ballast to even out non-uniformities across the back side of the substrate. The substrate has a high thermal conductivity, absorbs radiant energy from the lamps, and conducts it laterally to maintain temperature uniformity. The susceptor is typically wider than the substrate which allows it to compensate for radiative heat loss at the edge of the substrate.
A large thermal mass susceptor, however, retains significant thermal energy and makes it difficult to rapidly adjust the temperature of the substrate. In addition, in CVD processes, material is often deposited on the susceptor as well as the substrate. As a result, the susceptors must be cleaned and replaced from time to time. In addition, in the event of damage to the susceptor surface, pin holes may form which expose the underlying graphite and contaminate substrates placed on the susceptor.
During CVD processes, such as epitaxial deposition, undesired deposits may form on the hot susceptor as well as on other components in the reactor chamber. The chamber walls are typically cooled to inhibit deposits. Nonetheless, deposits may accumulate over time and cleaning is often necessary. Typically, an HCL gas is used to etch the unwanted deposits from non-quartz surfaces during cleaning, but the etch is not always effective for deposits on quartz. Quartz components often must be removed from the reactor for cleaning. In addition, wear from processing and cleaning can cause components and materials in the chamber to flake or spall which may interfere with the quality of some processes.
What is desired is an improved apparatus and method for CVD and/or rapid thermal processing of a semiconductor substrate. Preferably, such a system and method would provide uniform substrate processing temperature without using a large thermal mass graphite susceptor. What is also desired is an improved apparatus and method for CVD processes, such as epitaxial deposition. Preferably, such a system and method would have reduced contamination, reduced deposition on chamber walls and components and reduced wear of components, while providing simplified cleaning.
SUMMARY OF THE INVENTION
One aspect of the present invention provides a CVD reactor which is configured to reduce contamination, inhibit undesired deposits and simplify cleaning. A lamp system or other radiant heat source radiates energy into the processing chamber through a quartz window to heat a semiconductor substrate. A transmissive dual gas injection manifold is provided between the window and the semiconductor substrate. A reactant gas is dispersed through the manifold over the substrate for deposition. A purge gas is dispersed through the top of the manifold toward the window to prevent deposits from forming on the window. The purge gas then flows radially over the edges of the manifold and down the periphery of the chambers near the walls. The purge gas essentially forms a curtain which inhibits undesired deposits.
Another aspect of the present invention provides opaque liners to cover the cool chamber walls. The liners may be formed from opaque quartz. The liners absorb and reflect radiant energy during both processing and cleaning. Since the liners are warm, deposits are relatively easy to etch off during cleaning. The liners prevent stubborn deposits from forming on cold chamber walls (or cold clear quartz liners as in some conventional systems). Opaque quartz skirts may also be used to enclose the bottom portion of the chamber below the semiconductor substrate to prevent deposits on the back side of the substrate or substrate support mechanisms. Purge gas may also be provided to the region behind the substrate.
Another aspect of the present invention provides for an active ring heater and/or relatively hot thermally conductive material adjacent to the peripheral region of the substrate. The heater and/or thermal insulation compensates for edge losses and helps maintain temperature uniformity of the substrate and also depletes reactive gases near the walls and liners. The depletion of reactive gases helps prevent undesired deposits on the liners and in the region of the chamber below the substrate.
Another aspect of the present invention provides a substrate lift/rotation mechanism using support posts at the periphery of the substrate and/or substrate support and relatively flat rings or plates spaced from the substrate to lift and/or rotate the posts. The mechanism has a relatively flat thermal profile and does not disturb the thermal processing uniformity of the substrate. Rotation of the substrate during processing is used to enhance uniformity.
Another aspect of the present invention provides a thin thermally conductive substrate support which can be rapidly heated and cooled. A radiative cavity may be formed behind the substrate and/or support to provide thermal insulation and even out non-uniformities through radiative distribution of energy in the cavity to maintain equilibrium. A ring heater may also be used to heat the substrate support and/or radiative cavity to enhance uniformity.
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Johnsgard Kristian E.
Johnsgard Mark W.
McDiarmid James
Parks Steven E.
Fuqua Shawntina
Mattson Technology Inc.
Murphy Michael J.
Walberg Teresa
Wilson Sonsini Goodrich & Rosati
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