Electric heating – Heating devices – Combined with container – enclosure – or support for material...
Reexamination Certificate
1999-04-20
2001-11-06
Walberg, Teresa (Department: 3742)
Electric heating
Heating devices
Combined with container, enclosure, or support for material...
C219S390000, C118S724000, C118S729000, C392S416000
Reexamination Certificate
active
06313443
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to apparatus for thermal processing of materials, and specifically for processing semiconducting wafers at variable temperatures.
BACKGROUND OF THE INVENTION
Thermal processing of semiconducting wafers, such as silicon wafers, to produce semiconductor devices is well known in the art. The processing typically comprises maintaining a wafer at a different, known temperatures for predetermined times. During the processing, it is necessary to know the temperature of the wafer to a high accuracy in order to achieve repeatable results. Pyrometers, which measure temperature based on infrared emission and reflection from the wafer, are commonly used to monitor the temperature. Accurate pyrometric temperature measurement is dependent, however, on knowing the emissivity of the wafer, which varies with prior processing steps, temperature, and process steps performed while the measurement is being made.
Rapid Thermal Processing (RTP) is a state-of-the-art process used to manufacture semiconductor devices, wherein a wafer, or a region of a wafer, is cycled rapidly through a series of predetermined temperatures. Often rapid thermal processing is combined with chemical vapor deposition (RTCVD). Both processes rely on accurate, real-time determinations of the temperature of the region being processed. A review of RTP entitled
Rapid Thermal Processing Science and Technology
(ISBN 0-12-247690-5), Academic Press, California (1993), is herein incorporated by reference. Chapter 9 of the review indicates that processing efficiency is critically dependent on accurate temperature measurement of wafers during the processing.
In “Advances in Temperature Measurement and Control for RTP,” by Peuse et al., 5
th International Conference on Advanced Thermal Processing of Semiconductors—RTP
1997, which is incorporated herein by reference, the authors describe processing of semiconductor wafers using an RTP system known as the Centura system, produced by Applied Materials Inc., of Santa Clara, Calif. The system relies on placing the wafer in a highly reflective enclosure, so as to eliminate as nearly as possible the effects of variations in emissivity of the wafer, whereby the total enclosure closely approximates a black body. (The theory of pyrometric temperature determination by analysis of radiation from an object requires that an emissivity or an effective emissivity of the object be known; a black body has an emissivity of unity.) U.S. Pat. No. 5,490,728, to Schietinger et al., which is incorporated herein by reference, describes a non-contact pyrometric technique for measuring characteristics, including temperature, of a substrate. The technique estimates the emissivity of a wafer by comparing the amplitude of ripple flux in radiation reflected from the wafer with an incoming ripple flux amplitude due to an AC-powered heating lamp.
U.S. Pat. No. 5,255,286, to Moslehi et al., which is incorporated herein by reference, describes a method of optical pyrometry based on irradiating a semiconductor wafer with monochromatic coherent radiation at a wavelength of the order of 5 &mgr;m. Intensities of reflected coherent radiation and emitted incoherent radiation from the wafer are used to determine a value of the emissivity and of the temperature of the wafer.
In “Optical Pyrometry in RTP/RTCVD Systems: A New Approach,” by Glazman et al., 6
th International Conference on Advanced Thermal Processing of Semiconductors—RTP'
98, which is incorporated herein by reference, the authors describe a technique for measurement of the temperature of a semiconducting wafer using optical pyrometry. The technique uses an active multi-spectral system to dynamically measure the true emissivity of the wafer. The measured emissivity is utilized together with measurements of radiation emitted by the wafer in order to evaluate the temperature of the wafer.
SUMMARY OF THE INVENTION
It is an object of some aspects of the present invention to provide methods and apparatus for improved thermal processing of materials.
It is a further object of some aspects of the present invention to provide methods and apparatus for improved temperature measurement of materials.
It is a further object of some aspects of the present invention to provide methods and apparatus for improved thermal processing of moving regions of materials.
In preferred embodiments of the present invention, an object to be thermally processed, typically a semiconducting wafer, is placed in a chamber wherein the object is heated to above the ambient temperature. The wafer is held within the chamber by a wafer support assembly, a section of which, generally opposite the wafer, is preferably cooled to a temperature substantially below that of the wafer. The wafer support assembly is constructed so that the assembly and a surface of the wafer together form a substantially closed cavity, so as to exclude therefrom radiation from sources other than the wafer surface.
The temperature of a region of the surface of the wafer is measured by collecting radiation from the region in a distal end of a radiation guide, preferably comprising a fiberoptic. The radiation guide preferably passes through and is thermally coupled to the cooled section of the assembly. The guide is shielded from radiation, other than radiation from the region, by the structure of the closed cavity. The radiation guide is radiatively coupled at its proximal end to a pyrometer, which determines the temperature of the region responsive to the collected thermal radiation. The shielding of the radiation guide from extraneous radiation and the reduction of thermal radiation entering the guide by virtue of cooling of the support structure substantially improve the accuracy of the temperature measurement of the particular region of the wafer at which the fiberoptic is directed. The ability to process the wafer at accurately known temperatures significantly improves the efficiency and speed of thermal processing, compared to methods and systems at present known in the art. Furthermore, thermally coupling the radiation guide to the cooled section of the assembly cools the distal portion of the guide, and thereby prolongs the life of the guide.
Preferably, the pyrometer measures the temperature of the region of the wafer based on a known emissivity of the region. Alternatively, the pyrometer is able to measure the temperature independently of prior knowledge of an emissivity of the region, as is described in the above-referenced patents and publications, for example, or as is otherwise known in the art. It is not necessary that the region be in thermal equilibrium with the chamber.
In some preferred embodiments of the present invention, the wafer undergoing thermal processing is mounted substantially horizontally inside a vacuum-tight chamber. The chamber comprises inlet and outlet tubing which are used to evacuate the chamber and to enable the ingress of gases used for the processing. Preferably, the wafer support assembly whereon the wafer is mounted is rotatable about a vertical axis, and rotates the wafer in the chamber in order to improve processing uniformity across the wafer. The chamber further comprises heaters, most preferably incandescent lamps positioned above the wafer, which are used to heat the wafer. The radiation guide, substantially transparent to radiation emitted from the heated wafer, is fixedly mounted generally along the axis of the wafer support assembly so as to rotate with the assembly and the wafer. An upper (distal) end of the rotating guide is positioned close to, but not touching, a region of the wafer whose temperature is to be measured, in order to collect thermal radiation from the region.
A lower (proximal) end of the rotating guide is optically coupled to a distal end of a fixed radiation guide, which is preferably aligned axially with the rotating guide. Most preferably, the diameter of the fixed guide is substantially equal to the diameter of the rotating guide, so that there is minimal loss when radiation transfers
Harnik Arie
Iskevitch Eliezer
Schwarzfuchs Elie
Fuqua Shawntina
Nixon & Vanderhye P.C.
Steag CVD Systems, Ltd.
Walberg Teresa
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