Thermal measuring and testing – Thermal calibration system
Patent
1993-10-28
1996-09-10
Gutierrez, Diego F. F.
Thermal measuring and testing
Thermal calibration system
356 43, 374 2, G01K 1500
Patent
active
055539394
DESCRIPTION:
BRIEF SUMMARY
The present invention concerns a method and device for calibrating an optical pyrometer, and associated reference wafers. One of the applications of the present invention relates in particular to the calibration of pyrometers associated with ovens for the rapid heat treatment of semiconductor wafers of silicon, germanium, gallium arsenide, etc.
BACKGROUND AND OBJECTS OF THE INVENTION
It is usual, particularly in the aforesaid application, to measure the temperature prevailing inside an oven by means of an optical pyrometer. Such an instrument enables the temperature of a body (wafers to be treated) to be determined by analysing the radiation emitted by the latter without any physical contact with the body itself.
However, pyrometers are subject to loss of adjustment and/or drift particularly as a function of the number of measurements made. Up till now, in order to recalibrate such a pyrometer, a reference thermocouple was fixed to the upper face of a wafer placed in an oven and the pyrometer was recalibrated so that the readings given by the thermocouple and those given by the pyrometer coincide.
Such a calibration method has many drawbacks, the most significant of which is that it requires the installation of a thermocouple in the oven, with its electrical connections to the means for processing the signals. In the majority of applications, it is essential for the objects treated (the wafers) to be treated without any contamination and therefore without any handling. However, introducing the thermocouple into the treatment oven and passing the electrical connections through are contamination factors. Moreover, the thermocouple wires must be soldered to the wafer by means of soldering carried out with a material different from that of the wafer. Because of this, the temperature reading given by the thermocouple has an error inherent in the nature and form of the soldering. This error, which is difficult to predict, cannot be corrected in a reproducible manner.
The objective of the present invention is to mitigate all these drawbacks by providing a method and device for calibrating an optical pyrometer which do not require the introduction of any foreign bodies into the oven and allow in situ calibration of the pyrometer.
BRIEF DESCRIPTION OF THE INVENTION
To this end, the method according to the invention for calibrating an optical pyrometer consists of: one of its faces, referred to as the active face, the reference region having electromagnetic wave reflection discontinuity at a known temperature, region, reference region, means of the optical pyrometer to be calibrated, electromagnetic wave is observed, moment, value, temperature value coincide.
Thus, by transmitting an electromagnetic wave, and particularly a laser wave, towards the reference region of the wafer, a radiation reflected by this reference region is created. Measuring and recording the intensity of this reflected radiation makes it possible to monitor the change in the reflection coefficient of the reference region during the period of the rise in temperature of the oven. At the same time, the pyrometer to be calibrated measures the temperature of the reference region. Determining the moment when a reflection discontinuity appears makes it possible to register the value of the temperature measured by the pyrometer at this moment. By comparing this temperature value measured and the known temperature value corresponding to the discontinuity observed, the correction to be made to the pyrometer to be calibrated is determined.
In this way a calibration is carried out, in situ, of the optical pyrometer associated with a given oven, without the introduction of any foreign body into the oven.
In a preferred method of implementing the method, a wafer is used on which the reference region consists of an active material having reflection discontinuity when it changes from the solid state to the liquid state. Preferably the known temperature is the melting point of this active material.
Preferably and in order to refine the measurement of the
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Dilhac Jean-Marie
Ganibal Christian
Rousset Bernard
Commonaute Economique Europeenne (CEE)
Dutton, Jr. Harold H.
Gutierrez Diego F. F.
Jamison W. Charles L.
Liebman Diane F.
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