Thermal measuring and testing – Temperature measurement – Nonelectrical – nonmagnetic – or nonmechanical temperature...
Patent
1995-07-26
1997-04-29
Bennett, G. Bradley
Thermal measuring and testing
Temperature measurement
Nonelectrical, nonmagnetic, or nonmechanical temperature...
374120, 374126, G01K 1100
Patent
active
056241909
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to the technical field of measuring the surface temperature of an object, in particular a portion of a semiconductor, by using non-penetrating optical techniques.
In the preferred technical field of the invention, namely that of fabricating semiconductor materials, use is made of surface treatments such as depositing films, etching, annealing, or growing films epitaxially, that require accurate knowledge of the temperature of the substrate for control purposes.
PRIOR ART
In the prior art, it is known that this objective can be achieved by using a thermocouple to measure the temperature of a semiconductor. The major drawback of that technique is associated with the difficulty of establishing good thermal contact between the thermocouple and the semiconductor material. In addition, thermocouples present the drawback of possessing response times that are slow, thus leading to the temperature values that are obtained being mean values and making it impossible to detect temperature changes that are limited in time.
Another known temperature-measuring method relates to optical or infrared pyrometry. That technique consists in directing a light beam of given wavelength onto the semiconductor material and in measuring the optical energy emitted by the semiconductor material. Given the emittance of the material, it is possible to deduce the temperature of the radiation-emitting body from the energy as measured. Optical pyrometry provides the major advantage of allowing the temperature of a substrate to be measured without requiring direct or physical contact with the semiconductor material. However, it can be seen that optical pyrometry can give different results as a function of the emittance that is used. In addition, it is necessary to avoid interference from parasitic light radiation, such as that coming from heating lamps. Finally, that method is not very accurate at low temperatures.
European patent application 0 483 394 also proposes an optical method of determining the temperature of a surface. That technique consists firstly in measuring the change in polarization of a light beam when reflected on a surface, and secondly in measuring the degree of polarization. The change of polarization is related to the reflection coefficient of the reflecting layer. Such a technique makes it possible to measure the thermodynamic temperature of an object in accurate manner by correcting the measurements for certain interfering effects, in particular the effects of roughness and of background noise due to thermal emission from other heated parts, such as the reactor walls. Nevertheless, that method suffers from drawbacks. The first drawback relates to the difficulty of taking account of the presence, if any, of a surface layer when using a measurement performed at a single wavelength. Temperature variations may be accompanied by variations in layer thickness which give rise to error in the measured temperature: Another drawback of that technique lies in the difficulty of implementing it, in particular because it makes use of apparatus that is complex and completely novel.
BRIEF SUMMARY OF THE INVENTION
The object of the invention is to escape from the drawbacks mentioned above by proposing a method for accurately measuring the surface temperature of an object, such as a semiconductor, by using an ellipsometric measurement technique that takes account of the growth of a layer of material on the surface of the object.
To achieve this object, the method of the invention consists in:
performing ellipsometric measurements on the object in order to determine, on the basis of measured parameters, firstly at least one first photon energy for an electromagnetic beam at which measurements are substantially independent of temperature, and secondly at least one second photon energy for an electromagnetic beam at which measurements are dependent on temperature;
creating and directing towards the object, an incident electromagnetic beam including at least the first and second
REFERENCES:
patent: 4332833 (1982-06-01), Aspnes et al.
patent: 4498765 (1985-02-01), Herve 374126
Journal of the Optical Society of America, vol. 8, No. 2, Feb. 1991, New York, NY, USA, "Isoellipsometric-parameter curves for layers on silicon".
Hu Yao-Zhi
Irene Eugene
Joseph Jacques
Bennett G. Bradley
Ecole Centrale de Lyon
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