Particularly in the heating of semiconductor wafers, which takes place for a short time in so-called RTP (Rapid Thermal Processing) equipment, it is difficult to accurately determine the temperature of a wafer due to ambient influen- ces and transparency of the wafer.

Earlier patent applications of applicant in this technical field are the Netherlands patent application 89.00003 and corresponding European and American applications, in addition to the as yet unpublished Netherlands patent application 90.01200.

For an exact temperature measurement it is necessary to know the correct correlation between emitted radiation and temperature. Significant problems here are the following: - the radiation emitted by an object is always smaller than the radiation emitted by a "black" object according to Boltzmann's Law. For actual objects the emissivity e _int has a value between 0 and 1;

- due to reflections (and transmissions) in the en- vironment an emissivity measured in practice is always grea¬ ter than the above stated e _int ;

- if an object is simultaneously heated, the thermal radiation of a heat source affects the measurement;

The present invention provides a method for measuring the temperature of an object that is heated by one or more radiation sources, wherein radiation generated by the object is received in at least one radiation pick-up and wherein the radiation sources are changed at least partially in intensity at a predetermined cyclic rate of change and wherein on the basis of the change in the radiation value measured by the radiation pick-up the degree of compensation

SUBSTITUTESHEET

for the reflectivity and/or emissivity of the object is determined.

The present invention further provides a device for measuring the temperature of an object comprising: - one or more radiation sources for heating the ob¬ ject;

- a radiation pick-up for receiving the radiation generated by the object;

- modulation means for changing the intensity of the radiation sources at a predetermined cyclic rate of change; and

- compensation means for determining the reflectivity and/or emissivity of the object on the basis of the radiation value measured by the radiation pick-up. Finally, the present invention provides a method for heating an object wherein the compensation steps of the above method and device are applied.

Further features, details and advantages of the pre¬ sent invention will be elucidated in the light of a descrip- tion of a preferred embodiment thereof with reference to the annexed drawing, in which: fig. 1 shows a schematic view in section of a prefer¬ red embodiment of the present invention; fig. 2 shows a view over the line II-II in fig. 1; fig. 3 and 4 show graphs elucidating the preferred embodiment of the present invention. fig. 5 shows a further graph of measurements according to the present invention.

An object W, for instance a wafer of Si material which may or may not be provided with insulating portions, is placed in a schematically designated RTP device 1 (fig. 1, 2) for heating by halogen lamps 2, 3 arranged respectively in an upper part 4 and a lower part 5. In addition a radiation pick-up 6 is provided with a lens 7 oriented through a schematically designated opening 8 between the halogen lamps 3 and towards the wafer . Using the relatively strong lens 7 a large aperture Ω is obtained so that, as indicated with broken lines in fig. 1, rays of

SUBSTITUTESHEET

halogen lamps 3 reflected against wafer W as well as radiation from the halogen lamp 2 passing through the wafer W can be received in a sufficiently large solid angle.

When the halogen lamp intensity I is varied in time t as shown schematically in fig. 3, wherein the average power supplied to the lamps amounts to 9 kw, while the intensity is varied at a frequency of 4 Hz and the minimum intensity amounts to roughly 50% of the maximum, such fluctuations are also detected by the radiation pick-up or pyrometer 6. This can be seen in fig. 4 in which a curve C] measured by a thermocouple indicates the temperature T as a function of time t, when the power is applied to the lamps 2 of fig. 1 as shown in fig. 3. The curve C ₂ shows the signal 6 received by the pyrometer 6, wherein the pyrometer is sensitive to radiation around a wavelength of 1.7 μm. It can be seen clearly that after approximately 20 seconds the fluctuations in the signal C ₂ have entirely disappeared, which means that at a temperature of about 600°C of the wafer W (see curve C]) the wafer has become impermeable to the infrared radiation generated by the halogen lamp 2, this corresponding with theoretically established values therefor. It will be apparent that on the basis of the magnitude of the fluctuations in the signal of the pyrometer C ₂ the transmissivity of the object W can be determined at any temperature.

The reflectivity of the object W can be determined in the same way using variations in the intensity generated by the lamps 3.

When during heating of the object with halogen lamps 2 and/or 3 from the top and bottom respectively the intensity is subject to cyclic variation, the output signal of the radiation pick-up or pyrometer 6 can be compensated for transmissivity and reflectivity of the wafer W-using correlation techniques and a reliable temperature measurement of the wafer can be obtained irrespective of the material thereof, the roughness etc.

If the halogen lamps 2 and 3 respectively are varied or modulated with mutually differing frequencies,

SUBSTITUTESHEET

compensation can be made separately in the output signal of the pyrometer 6 for either reflectivity or emissivity with per se known correlation techniques.

Side walls around the lamps 2 and 3 preferably take a reflecting form so that the most uniform possible radiation source is "seen" by the pyrometer. The rear wall of the upper part 4 of the device 1 is preferably provided with a non-reflecting or black layer such as a filter or organic coating layer. In order to compensate for the discrete character of the individual halogen lamps a window-shaped filter is pre¬ ferably placed in front of the pyrometer 6, whereby a more uniform distribution of the radiation intensity of the lamps 2 over the aperture Ω is obtained. In fig. 5 it is shown that the curve C ₃ measured according to the method of the present invention corresponds the temperature C ₄ of the wafer as measured by a thermocouple. Further C ₅ and C ₆ show the signal of a pyrometer and the emissivity resp.

SUBSTITUTESHEET