Electric heating – Heating devices – Combined with container – enclosure – or support for material...
Reexamination Certificate
2002-09-30
2004-07-27
Fuqua, Shawntina (Department: 3742)
Electric heating
Heating devices
Combined with container, enclosure, or support for material...
C219S405000, C219S411000, C392S416000, C118S724000, C118S725000, C432S229000, C432S230000
Reexamination Certificate
active
06768084
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to semiconductor thermal processing systems, and more specifically to a system and method for rapid thermal processing using a linearly-moving heating assembly with a radially-tunable thermal radiation profile.
BACKGROUND OF THE INVENTION
High temperature processing of semiconductor (e.g., silicon) wafers is important for manufacturing modern microelectronics devices. Such processes, including silicide formation, implant anneal, oxidation, nitridation, diffusion drive-in, chemical vapor deposition (CVD) and atomic layer deposition (ALD), may be performed at high temperatures and in proper ambient gases or vacuum using conventional thermal processing techniques. Furthermore, many modern microelectronics circuits require feature sizes smaller than one micron and junction depths less than a few hundred angstroms. In order to limit both the lateral and downward diffusion of dopants, as well as to provide a greater degree of control during processing, it is desirable to minimize the duration of high temperature processing as well as vary the gaseous composition around the semiconductor wafers.
One approach for minimizing processing time utilizes a single-wafer rapid thermal processor (RTP). Single-wafer rapid thermal processing of semiconductor wafers provides a powerful and versatile technique for fabrication of ultra-large-scale-integrated (ULSI) electronic devices. Conventional systems and methods of wafer thermal processing may suffer from various shortcomings, however, as will be described hereafter.
One conventional RTP system combines low thermal mass photon-assisted rapid thermal heating with an inert or reactive gaseous ambient for semiconductor wafer processing. Such a single-wafer RTP system utilizes high intensity lamps, optical temperature sensors and sophisticated control algorithms to heat a semiconductor wafer at a high temperature ramp rate, thereby reducing problems associated with high thermal budget to device fabrication. In lamp-based processing, the wafer is generally heated to temperatures of between 450° C. to 1400° C. and may furthermore be rapidly cooled after processing. Problems may be encountered, however, with the use of high intensity lamps as a heat source, particularly for larger diameter wafers. Specifically, it may be difficult to maintain a uniform temperature across a wafer due to individual lamp spacing, as well as other factors.
Typically, not only do temperature differences arise during heating and cooling transients in lamp-based RTP systems, but non-uniformities may also persist during processing. As illustrated in prior art
FIG. 1A
, a conventional lamp-based RTP lamp assembly
10
is shown, wherein the lamp assembly comprises a plurality of individual incandescent lamps
20
. The plurality of lamps
20
are distributed across a surface
15
of the lamp assembly
10
, leaving physical spaces
30
between each individual lamp.
FIG. 1B
illustrates a partial cross-section of the lamp assembly
10
, illustrating several individual lamps
20
. Each lamp
20
comprises a filament
40
, such as tungsten, whereby electrical current passing through the filament resistively heats the filament, thus emitting thermal radiation
50
outward from the lamp. However, a filament
40
only takes a very small portion of physical space in a lamp
20
. The spaces
30
between lamps
20
as well as the largely empty spaces inside lamps
20
, however, contribute to the non-uniformity of the received thermal radiation over the substrate
60
. To obtain uniform heating, lamp based systems typically utilize some combination of optical guides, lenses, and/or reflectors (not shown), as well as wafer rotation, to more evenly distribute thermal radiation onto the substrate
60
. Despite these measures, it may be necessary in some systems to actively switch individual lamps or groups of lamps on and off rapidly to control the wafer temperature and minimize the effects of the non-uniform thermal radiation from the lamps. Furthermore, additional problems may be encountered in lamp-based systems due to aging and degradation of lamps and other components. As a result, it may be difficult to maintain repeatable performance, and a frequent replacement of parts and system cleaning may be necessary. Similar problems also exist in linear-lamp based rapid thermal processing systems.
Furthermore, since effective cooling of lamps is essential to increase the life time of lamps, the interior walls of a typical lamp-based RTP system are usually much colder than the wafer under processing and are not uniform in temperature. Therefore, heat transfer between the wafer and the interior walls via conduction and convection has detrimental effects to the uniform heating of the wafer under processing. Furthermore, ambient gases and gas-surface reaction products may deposit and condense onto the cold chamber walls of lamp-based RTP systems, blocking thermal radiation from lamps to the wafer and interfering with pyrometric temperature measurement.
A more advanced hot-wall rapid thermal processing (RTP) furnace (e.g., U.S. Pat. No. 4,857,689 and No. 6,183,127) can yield superior results over the lamp-based RTP systems in terms of temperature uniformity, process reproducibility and cost while still possessing comparable performance in terms of thermal budget and process throughput. In such hot-wall RTP systems, a stable monotonic temperature and thermal radiation gradient is maintained along the axis of the RTP furnace by constantly heating the upper section of the process chamber and actively cooling the lower section of the process chamber. This steady-state temperature profile is also axially symmetric, with a radial component optimized to ensure the uniform heating of a wafer.
The temperature of a wafer under processing is controlled by varying the position of the wafer along the temperature gradient. Since a thermal steady-state is maintained throughout the entire furnace, and between the furnace and the gas ambient, wafer heating is dominated by the thermal equilibration between the wafer and its furnace environment. Ambient gases flow through the hot wall chamber to interact with the wafer under processing. A hot-wall RTP furnace has a much larger total thermal radiation area than the total filament area of a lamp-based RTP system. A shortcoming associated with the hot-wall RTP systems is the relatively large internal volume of the process chamber, particularly when fast ambient gas switching is required during rapid thermal processing. However, fast ambient gas switching has been successfully realized by placing a wafer inside a small volume quartz reactor that linearly moves along the temperature gradient inside the process chamber.
Yet another rapid thermal processing system utilizes a heated block, or receptor, for thermally processing a wafer within a single chamber. The receptor resides in the chamber, and is heated by one or more resistive heaters. The wafer is inserted into the chamber and is placed on pins protruding through the receptor, and is subsequently lowered via the pins onto the receptor, such that heat transfer occurs from the receptor to the wafer via conduction, convection and radiation. The use of a receptor within a single chamber, however, may introduce various problems. For instance, in rapid thermal chemical vapor deposition (RTCVD) and low-pressure chemical vapor deposition (LPCVD) applications, the receptor can be coated by the material being deposited on the wafer (e.g., doped or undoped polysilicon, silicon dioxide, silicon nitride, etc.). The unwanted depositions on the receptor can result in particulate generation, cross contamination, process uniformity drifts, as well as problems associated with temperature measurement and process control.
Therefore, for at least the above mentioned reasons, an improved rapid thermal processing system and method is needed to alleviate many of the problems associated with the prior art.
SUMMARY OF THE INVENTION
The following presents a simplified summary of
Hebb Jeff P.
Liu Yong
Axcelis Technologies Inc.
Eschweiler & Associates LLC
Fuqua Shawntina
LandOfFree
Advanced rapid thermal processing (RTP) using a... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Advanced rapid thermal processing (RTP) using a..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Advanced rapid thermal processing (RTP) using a... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3213802