Multipoint temperature monitoring apparatus for semiconductor wa

Details Multipoint temperature monitoring apparatus for semiconductor wa Multipoint temperature monitoring apparatus for semiconductor wa

1996-02-29

1998-10-20

Gutierrez, Diego F. F.

Thermal measuring and testing

Temperature measurement

In spaced noncontact relationship to specimen

374130, 374128, 374133, 374131, 374 1, 392416, 118724, G01J 508, G01J 502, G01J 528, G01J 562, G01J 506

Patent

active

058236813

DESCRIPTION:

BRIEF SUMMARY
FIELD AND BACKGROUND OF THE INVENTION

The present invention relates to methods and systems for monitoring the temperature of semiconductor wafers during processing.
The measurement of the temperature of a semiconductor wafer using remote, or non-contact, means during processing is technologically important. Conventional pyrometry, which is the mainstay temperature measurement technique for such applications suffers from significant limitations which have been overcome with varying degrees of success by a number of innovations in recent years. These limitations include the following.
First, the emissivity of the semiconductor wafer, i.e., the wafer emission relative to the emission of a perfect blackbody at the same temperature, is generally not known and is dependent on wavelength, temperature and surface conditions, such as morphology and the presence of layers & other structure.
Second, the semiconductor wafer is often transparent to radiation in the wavelength band in which the pyrometer operates, which precludes the use of conventional pyrometry. In some cases the wafer goes from transparent to opaque during the process as a result of the deposition of metallic or other materials.
Third, in typical processing environments various hot objects act as sources of background radiation and contribute to the signal detected by the pyrometer, thereby introducing errors in the temperature measurement.
Finally, semiconductor wafer processing is frequently carried out simultaneously in a number of different process chambers within a single cluster tool. It would therefore be advantageous to be able to simultaneously measure temperatures in different locations using a single cost effective system.
Considerable prior art is available describing different techniques and apparatus designed to overcome some of the above limitations.
Many techniques have been proposed in which the emissivity of a remote body is determined by measurement of reflectivity and by use of Kirchoff's law. For example, Brisk et al. (U.S. Pat. No. 4,647,774, incorporated by reference), uses a collimated laser beam which is bounced off a remote target. Yomoto et al. (U.S. Pat. No. 4,890,245, incorporated by reference), Nulnan et al. (U.S. Pat. No. 4,919,542, incorporated by reference) and Moslehi et al. (U.S. Pat. No. 5,156,461, incorporated by reference), all suggest similar concepts specifically for the measurement of semiconductor wafer temperatures.
However, in all cases it is implicit that collimated, rather than convergent, radiation is used to perform the reflection measurements from the wafer surface. While the use of collimated radiation has the advantage of allowing remote optical access it may result in erroneous reflectivity measurements and hence inaccurate emissivity estimates from surfaces which are not optically smooth in the wavelength band of interest.
Moslehi et al. have proposed a technique to overcome this shortcoming which entails the use of laser scatterometry to measure the wafer "scattering parameter" at one wavelength. Laser scatterometry is utilized to extract the scattering parameter at a different wavelength from that of the optical pyrometer. The emissivity may then be computed by combining this scattering parameter with the specular reflectivity measured in the pyrometer wavelength band. However, this technique requires considerable hardware and various empirically derived relations. Furthermore, Moslehi et al. have proposed a technique with a view toward application in rapid thermal processing and have therefore chosen in their detailed description a pyrometer wavelength band in the mid infrared (5.4 microns).
Yomoto and Moslehi et al. also suggest measurement of transmissivity T in conjunction with reflectivity R for the case of transparent wafers, and suggest the use of the more general form of Kirchoff's Law, .epsilon.=1-R-T, where T is transmission, R is reflectivity and .epsilon. is emissivity. However, even this procedure will yield erroneous values of T and possibly of R, and consequently erroneous emissiv

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